Aggregator

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1026 AM CST Mon Nov 20 2023 Valid 201630Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EAST TEXAS INTO LOUISIANA AND MISSISSIPPI... ...SUMMARY... Tornadoes (some strong), damaging thunderstorm winds, and isolated large hail are expected from this afternoon across east Texas and parts of Louisiana, through tonight across the Delta region into portions of Mississippi and Alabama. ...East Texas into the Lower Mississippi Valley and Central Gulf Coast... A positively tilted upper trough over the southern/central Plains will progress slowly eastward through the period across the lower and mid MS Valley, while transitioning to a closed mid/upper-level low. At the surface, a weak low centered over southern/central OK this morning is forecast to develop across northeast TX and towards the ArkLaMiss by this evening. An associated warm front will continue to lift/mix northward through tonight across east TX into the lower MS Valley. A cold front attendant to the surface low will also sweep eastward over these regions through the period. Low-level moisture return is ongoing in earnest this morning across east TX into the lower MS Valley, with at least low 60s surface dewpoints becoming prevalent across the warm sector along and south of the diffuse warm front. Most guidance suggests that mid to perhaps upper 60s surface dewpoints will become more common by late this afternoon from far east TX into parts of southern/central LA/MS. Large-scale ascent associated with the mid/upper-level trough and increasing low-level warm advection associated with a gradually strengthening southerly low-level jet will both aid in the development of surface-based convection by early afternoon. Initial development will likely emanate from bands of elevated low-level warm-advection driven showers/thunderstorms ongoing across central into east TX. Rather strong deep-layer shear of 50-60+ kt will easily support supercells with this initial activity. Around 500-1250 J/kg of MLCAPE should also be present with continued diurnal heating of the moistening low-level airmass, which will support surface-based thunderstorms as this convection spreads into LA this afternoon and early evening. Large hail may be a concern with any supercell that can be sustained. But, the tornado potential is expected to gradually increase this afternoon and evening from parts of far east TX into northern/central LA and southern/central MS as a southerly low-level jet strengthens to around 35-40 kt. Favorable low-level shear and the best chance for several tornadoes will likely be maximized along/near the warm front this evening and tonight, with ample curvature noted in the 0-1 km layer from various NAM/RAP forecast hodographs. No changes have been made to the Enhanced Risk, which still seems to capture the best corridor of strong tornado potential and scattered to possibly numerous damaging wind gusts. Cell mergers and some upscale growth seems likely this evening and overnight across the lower MS Valley. Line-embedded low-level circulations should still pose a threat for QLCS tornadoes as one or more clusters/lines advances eastward across MS and western AL late tonight through early Tuesday morning in a weakly unstable but strongly sheared environment. ..Gleason/Bentley.. 11/20/2023 Read more

MD 2272 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF NORTH TX...SOUTHEAST OK...AND SOUTHWEST AR
Mesoscale Discussion 2272 NWS Storm Prediction Center Norman OK 0711 AM CST Mon Nov 20 2023 Areas affected...portions of north TX...southeast OK...and southwest AR Concerning...Severe potential...Watch unlikely Valid 201311Z - 201515Z Probability of Watch Issuance...20 percent SUMMARY...Isolated hail around a half inch to near one inch in diameter is possible the next few hours. DISCUSSION...A deepening field of altocumulus is evident in IR imagery this morning across north TX. Based on 12z FWD RAOB, these clouds are likely rooted around 600 mb. This indicates increasing ascent associated with the approaching upper trough is spreading east, and aiding in modest growth over the past hour. Regional 12z RAOBs still indicate quite a bit of low-level inhibition, with layers of dry air above shallow boundary-layer moisture. Moistening and heating through mid to late morning will continue to improve the thermodynamic environment, while large-scale ascent erodes capping. In the short term, steepening midlevel lapse rates and favorable vertical shear may support transient strong cells capable of marginally severe hail through around 16z. A severe thunderstorm watch is not expected at this time, as initial convection is expected to only slowly increase in intensity the next few hours, but trends will be monitored closely. ..Leitman/Edwards.. 11/20/2023 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LZK...SHV...TSA...FWD...OUN... LAT...LON 34179250 33729279 32029513 31449665 31579733 31939779 32289768 34649587 35089512 35169438 34989351 34409263 34179250 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Mon Nov 20 2023 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF EAST TEXAS ACROSS CENTRAL/NORTHERN LOUISIANA TO CENTRAL/SOUTHERN MISSISSIPPI... ...SUMMARY... Tornadoes (some strong), damaging thunderstorm winds and isolated large hail are expected from this afternoon across east Texas and parts of Louisiana, into tonight across the Delta region into portions of Mississippi and Alabama. ...Synopsis... The mid/upper-level pattern will be dominated by extensive, progressive synoptic troughing, shifting eastward across the central CONUS. A broad, complex cyclone, with multiple circulation centers and vorticity maxima, is apparent in moisture-channel imagery from SD through the central Plains and parts of the lower Missouri Valley, to the southern High Plains and parts of OK. Part of a northern-stream shortwave trough over western Canada is expected to dig southeastward to the northern Plains through the period. As that occurs, a 500-mb low should consolidate across central/eastern KS today, shifting across northern MO toward northern IL by the end of the period. A high-amplitude, positively tilted trough will extend southwestward from that low, reaching the Ozarks, north-central to southwest TX, and Chihuahua/Sonora by 12Z tomorrow. A surface low was analyzed at 11Z near CHK, with cold front across southwestern OK to the TX South Plains and east-central NM. In response to the mid/upper-level processes, the low should move/ redevelop southeastward over the Arklatex by 00Z, then swing northeastward to near EVV by 12Z. At 00Z, the cold front should extend southwestward over east TX and deep south TX. The warm front's baroclinicity should diffuse somewhat diurnally and shift rapidly northeastward across LA and portions of MS today. The warm front should reach parts of western/southern AL overnight before being overtaken from north-south by the cold front or (more likely, by then) pre-cold-frontal belt of convection. ...East TX/Arklatex to central Gulf Coast States... Multiple rounds of thunderstorms are possible through tonight along and especially ahead of the cold front, shifting northeastward and eastward across the outlooked areas. Convection may develop earliest -- in the next few hours -- in/near an expanding field of midlevel UVV and related altocumuli now apparent in satellite imagery over north-central/northeast TX. The 12Z FWD sounding indicates these clouds were rooted near 600 mb, though they have deepened since, and that a weak EML-capping regime persists. Any sustained thunderstorms developing in this area will pose a large- hail threat initially, but what becomes surface-based may pose wind and perhaps tornado concern later today as the boundary layer beneath destabilizes. This convection should expand/shifts east- northeastward toward the Arklatex vicinity. The core concentration of severe threat -- including the potential for several tornadoes, some strong (EF2+) -- should be from parts of east TX across central LA to central/southern MS this afternoon into late evening. In step with the warm front, 60s F surface dewpoints are expected to shift east-northeastward. Though tempered some by low-cloud cover, diabatic heating (along with theta-e advection) should destabilize the warm sector diurnally. This will remove MLCINH, favoring potential for gradual development ahead of the main band of lift over east TX, as well as supporting strong-severe thunderstorms in the band. In turn, that renders the possibility of supercells with long warm-sector residence times in 500-1200 J/kg MLCAPE, 55-65 kt effective-shear magnitudes, 200-400 J/kg effective SRH, and 100-250 J/kg of 1/2-km SRH,. Highest SRH and largest hodographs should be in the evening, near an LLJ. However, considerable uncertainty remains as to number/coverage of storms that can remain restively discrete while in that environment. If confidence increases in associated longer-tracked tornado potential, based on 12Z guidance and daylight mesoanalysis trends, an upgrade may be needed in a succeeding outlook. Overnight, a line of strong-severe thunderstorms should continue advancing eastward over the remainder of MS and into parts of AL, gradually moving into progressively weaker (but still at least marginally favorable) surface-based buoyancy by 12Z. The eastern extent still is uncertain, given a common bias in models (including most convection-allowing guidance as well as synoptic progs) to underforecast nocturnal squall-line speed in this area of the country. Therefore actual severe potential by 12Z probably has a much sharper east edge than we can depict now, due to those timing uncertainties. Embedded mesovortices, moving into favorable SRH and high RH, but weak low-level lapse rates, will locally maximize the damaging-wind threat and at least brief tornado potential tonight. ..Edwards/Leitman.. 11/20/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Mon Nov 20 2023 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF EAST TEXAS ACROSS CENTRAL/NORTHERN LOUISIANA TO CENTRAL/SOUTHERN MISSISSIPPI... ...SUMMARY... Tornadoes (some strong), damaging thunderstorm winds and isolated large hail are expected from this afternoon across east Texas and parts of Louisiana, into tonight across the Delta region into portions of Mississippi and Alabama. ...Synopsis... The mid/upper-level pattern will be dominated by extensive, progressive synoptic troughing, shifting eastward across the central CONUS. A broad, complex cyclone, with multiple circulation centers and vorticity maxima, is apparent in moisture-channel imagery from SD through the central Plains and parts of the lower Missouri Valley, to the southern High Plains and parts of OK. Part of a northern-stream shortwave trough over western Canada is expected to dig southeastward to the northern Plains through the period. As that occurs, a 500-mb low should consolidate across central/eastern KS today, shifting across northern MO toward northern IL by the end of the period. A high-amplitude, positively tilted trough will extend southwestward from that low, reaching the Ozarks, north-central to southwest TX, and Chihuahua/Sonora by 12Z tomorrow. A surface low was analyzed at 11Z near CHK, with cold front across southwestern OK to the TX South Plains and east-central NM. In response to the mid/upper-level processes, the low should move/ redevelop southeastward over the Arklatex by 00Z, then swing northeastward to near EVV by 12Z. At 00Z, the cold front should extend southwestward over east TX and deep south TX. The warm front's baroclinicity should diffuse somewhat diurnally and shift rapidly northeastward across LA and portions of MS today. The warm front should reach parts of western/southern AL overnight before being overtaken from north-south by the cold front or (more likely, by then) pre-cold-frontal belt of convection. ...East TX/Arklatex to central Gulf Coast States... Multiple rounds of thunderstorms are possible through tonight along and especially ahead of the cold front, shifting northeastward and eastward across the outlooked areas. Convection may develop earliest -- in the next few hours -- in/near an expanding field of midlevel UVV and related altocumuli now apparent in satellite imagery over north-central/northeast TX. The 12Z FWD sounding indicates these clouds were rooted near 600 mb, though they have deepened since, and that a weak EML-capping regime persists. Any sustained thunderstorms developing in this area will pose a large- hail threat initially, but what becomes surface-based may pose wind and perhaps tornado concern later today as the boundary layer beneath destabilizes. This convection should expand/shifts east- northeastward toward the Arklatex vicinity. The core concentration of severe threat -- including the potential for several tornadoes, some strong (EF2+) -- should be from parts of east TX across central LA to central/southern MS this afternoon into late evening. In step with the warm front, 60s F surface dewpoints are expected to shift east-northeastward. Though tempered some by low-cloud cover, diabatic heating (along with theta-e advection) should destabilize the warm sector diurnally. This will remove MLCINH, favoring potential for gradual development ahead of the main band of lift over east TX, as well as supporting strong-severe thunderstorms in the band. In turn, that renders the possibility of supercells with long warm-sector residence times in 500-1200 J/kg MLCAPE, 55-65 kt effective-shear magnitudes, 200-400 J/kg effective SRH, and 100-250 J/kg of 1/2-km SRH,. Highest SRH and largest hodographs should be in the evening, near an LLJ. However, considerable uncertainty remains as to number/coverage of storms that can remain restively discrete while in that environment. If confidence increases in associated longer-tracked tornado potential, based on 12Z guidance and daylight mesoanalysis trends, an upgrade may be needed in a succeeding outlook. Overnight, a line of strong-severe thunderstorms should continue advancing eastward over the remainder of MS and into parts of AL, gradually moving into progressively weaker (but still at least marginally favorable) surface-based buoyancy by 12Z. The eastern extent still is uncertain, given a common bias in models (including most convection-allowing guidance as well as synoptic progs) to underforecast nocturnal squall-line speed in this area of the country. Therefore actual severe potential by 12Z probably has a much sharper east edge than we can depict now, due to those timing uncertainties. Embedded mesovortices, moving into favorable SRH and high RH, but weak low-level lapse rates, will locally maximize the damaging-wind threat and at least brief tornado potential tonight. ..Edwards/Leitman.. 11/20/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Mon Nov 20 2023 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF EAST TEXAS ACROSS CENTRAL/NORTHERN LOUISIANA TO CENTRAL/SOUTHERN MISSISSIPPI... ...SUMMARY... Tornadoes (some strong), damaging thunderstorm winds and isolated large hail are expected from this afternoon across east Texas and parts of Louisiana, into tonight across the Delta region into portions of Mississippi and Alabama. ...Synopsis... The mid/upper-level pattern will be dominated by extensive, progressive synoptic troughing, shifting eastward across the central CONUS. A broad, complex cyclone, with multiple circulation centers and vorticity maxima, is apparent in moisture-channel imagery from SD through the central Plains and parts of the lower Missouri Valley, to the southern High Plains and parts of OK. Part of a northern-stream shortwave trough over western Canada is expected to dig southeastward to the northern Plains through the period. As that occurs, a 500-mb low should consolidate across central/eastern KS today, shifting across northern MO toward northern IL by the end of the period. A high-amplitude, positively tilted trough will extend southwestward from that low, reaching the Ozarks, north-central to southwest TX, and Chihuahua/Sonora by 12Z tomorrow. A surface low was analyzed at 11Z near CHK, with cold front across southwestern OK to the TX South Plains and east-central NM. In response to the mid/upper-level processes, the low should move/ redevelop southeastward over the Arklatex by 00Z, then swing northeastward to near EVV by 12Z. At 00Z, the cold front should extend southwestward over east TX and deep south TX. The warm front's baroclinicity should diffuse somewhat diurnally and shift rapidly northeastward across LA and portions of MS today. The warm front should reach parts of western/southern AL overnight before being overtaken from north-south by the cold front or (more likely, by then) pre-cold-frontal belt of convection. ...East TX/Arklatex to central Gulf Coast States... Multiple rounds of thunderstorms are possible through tonight along and especially ahead of the cold front, shifting northeastward and eastward across the outlooked areas. Convection may develop earliest -- in the next few hours -- in/near an expanding field of midlevel UVV and related altocumuli now apparent in satellite imagery over north-central/northeast TX. The 12Z FWD sounding indicates these clouds were rooted near 600 mb, though they have deepened since, and that a weak EML-capping regime persists. Any sustained thunderstorms developing in this area will pose a large- hail threat initially, but what becomes surface-based may pose wind and perhaps tornado concern later today as the boundary layer beneath destabilizes. This convection should expand/shifts east- northeastward toward the Arklatex vicinity. The core concentration of severe threat -- including the potential for several tornadoes, some strong (EF2+) -- should be from parts of east TX across central LA to central/southern MS this afternoon into late evening. In step with the warm front, 60s F surface dewpoints are expected to shift east-northeastward. Though tempered some by low-cloud cover, diabatic heating (along with theta-e advection) should destabilize the warm sector diurnally. This will remove MLCINH, favoring potential for gradual development ahead of the main band of lift over east TX, as well as supporting strong-severe thunderstorms in the band. In turn, that renders the possibility of supercells with long warm-sector residence times in 500-1200 J/kg MLCAPE, 55-65 kt effective-shear magnitudes, 200-400 J/kg effective SRH, and 100-250 J/kg of 1/2-km SRH,. Highest SRH and largest hodographs should be in the evening, near an LLJ. However, considerable uncertainty remains as to number/coverage of storms that can remain restively discrete while in that environment. If confidence increases in associated longer-tracked tornado potential, based on 12Z guidance and daylight mesoanalysis trends, an upgrade may be needed in a succeeding outlook. Overnight, a line of strong-severe thunderstorms should continue advancing eastward over the remainder of MS and into parts of AL, gradually moving into progressively weaker (but still at least marginally favorable) surface-based buoyancy by 12Z. The eastern extent still is uncertain, given a common bias in models (including most convection-allowing guidance as well as synoptic progs) to underforecast nocturnal squall-line speed in this area of the country. Therefore actual severe potential by 12Z probably has a much sharper east edge than we can depict now, due to those timing uncertainties. Embedded mesovortices, moving into favorable SRH and high RH, but weak low-level lapse rates, will locally maximize the damaging-wind threat and at least brief tornado potential tonight. ..Edwards/Leitman.. 11/20/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Mon Nov 20 2023 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF EAST TEXAS ACROSS CENTRAL/NORTHERN LOUISIANA TO CENTRAL/SOUTHERN MISSISSIPPI... ...SUMMARY... Tornadoes (some strong), damaging thunderstorm winds and isolated large hail are expected from this afternoon across east Texas and parts of Louisiana, into tonight across the Delta region into portions of Mississippi and Alabama. ...Synopsis... The mid/upper-level pattern will be dominated by extensive, progressive synoptic troughing, shifting eastward across the central CONUS. A broad, complex cyclone, with multiple circulation centers and vorticity maxima, is apparent in moisture-channel imagery from SD through the central Plains and parts of the lower Missouri Valley, to the southern High Plains and parts of OK. Part of a northern-stream shortwave trough over western Canada is expected to dig southeastward to the northern Plains through the period. As that occurs, a 500-mb low should consolidate across central/eastern KS today, shifting across northern MO toward northern IL by the end of the period. A high-amplitude, positively tilted trough will extend southwestward from that low, reaching the Ozarks, north-central to southwest TX, and Chihuahua/Sonora by 12Z tomorrow. A surface low was analyzed at 11Z near CHK, with cold front across southwestern OK to the TX South Plains and east-central NM. In response to the mid/upper-level processes, the low should move/ redevelop southeastward over the Arklatex by 00Z, then swing northeastward to near EVV by 12Z. At 00Z, the cold front should extend southwestward over east TX and deep south TX. The warm front's baroclinicity should diffuse somewhat diurnally and shift rapidly northeastward across LA and portions of MS today. The warm front should reach parts of western/southern AL overnight before being overtaken from north-south by the cold front or (more likely, by then) pre-cold-frontal belt of convection. ...East TX/Arklatex to central Gulf Coast States... Multiple rounds of thunderstorms are possible through tonight along and especially ahead of the cold front, shifting northeastward and eastward across the outlooked areas. Convection may develop earliest -- in the next few hours -- in/near an expanding field of midlevel UVV and related altocumuli now apparent in satellite imagery over north-central/northeast TX. The 12Z FWD sounding indicates these clouds were rooted near 600 mb, though they have deepened since, and that a weak EML-capping regime persists. Any sustained thunderstorms developing in this area will pose a large- hail threat initially, but what becomes surface-based may pose wind and perhaps tornado concern later today as the boundary layer beneath destabilizes. This convection should expand/shifts east- northeastward toward the Arklatex vicinity. The core concentration of severe threat -- including the potential for several tornadoes, some strong (EF2+) -- should be from parts of east TX across central LA to central/southern MS this afternoon into late evening. In step with the warm front, 60s F surface dewpoints are expected to shift east-northeastward. Though tempered some by low-cloud cover, diabatic heating (along with theta-e advection) should destabilize the warm sector diurnally. This will remove MLCINH, favoring potential for gradual development ahead of the main band of lift over east TX, as well as supporting strong-severe thunderstorms in the band. In turn, that renders the possibility of supercells with long warm-sector residence times in 500-1200 J/kg MLCAPE, 55-65 kt effective-shear magnitudes, 200-400 J/kg effective SRH, and 100-250 J/kg of 1/2-km SRH,. Highest SRH and largest hodographs should be in the evening, near an LLJ. However, considerable uncertainty remains as to number/coverage of storms that can remain restively discrete while in that environment. If confidence increases in associated longer-tracked tornado potential, based on 12Z guidance and daylight mesoanalysis trends, an upgrade may be needed in a succeeding outlook. Overnight, a line of strong-severe thunderstorms should continue advancing eastward over the remainder of MS and into parts of AL, gradually moving into progressively weaker (but still at least marginally favorable) surface-based buoyancy by 12Z. The eastern extent still is uncertain, given a common bias in models (including most convection-allowing guidance as well as synoptic progs) to underforecast nocturnal squall-line speed in this area of the country. Therefore actual severe potential by 12Z probably has a much sharper east edge than we can depict now, due to those timing uncertainties. Embedded mesovortices, moving into favorable SRH and high RH, but weak low-level lapse rates, will locally maximize the damaging-wind threat and at least brief tornado potential tonight. ..Edwards/Leitman.. 11/20/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Mon Nov 20 2023 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF EAST TEXAS ACROSS CENTRAL/NORTHERN LOUISIANA TO CENTRAL/SOUTHERN MISSISSIPPI... ...SUMMARY... Tornadoes (some strong), damaging thunderstorm winds and isolated large hail are expected from this afternoon across east Texas and parts of Louisiana, into tonight across the Delta region into portions of Mississippi and Alabama. ...Synopsis... The mid/upper-level pattern will be dominated by extensive, progressive synoptic troughing, shifting eastward across the central CONUS. A broad, complex cyclone, with multiple circulation centers and vorticity maxima, is apparent in moisture-channel imagery from SD through the central Plains and parts of the lower Missouri Valley, to the southern High Plains and parts of OK. Part of a northern-stream shortwave trough over western Canada is expected to dig southeastward to the northern Plains through the period. As that occurs, a 500-mb low should consolidate across central/eastern KS today, shifting across northern MO toward northern IL by the end of the period. A high-amplitude, positively tilted trough will extend southwestward from that low, reaching the Ozarks, north-central to southwest TX, and Chihuahua/Sonora by 12Z tomorrow. A surface low was analyzed at 11Z near CHK, with cold front across southwestern OK to the TX South Plains and east-central NM. In response to the mid/upper-level processes, the low should move/ redevelop southeastward over the Arklatex by 00Z, then swing northeastward to near EVV by 12Z. At 00Z, the cold front should extend southwestward over east TX and deep south TX. The warm front's baroclinicity should diffuse somewhat diurnally and shift rapidly northeastward across LA and portions of MS today. The warm front should reach parts of western/southern AL overnight before being overtaken from north-south by the cold front or (more likely, by then) pre-cold-frontal belt of convection. ...East TX/Arklatex to central Gulf Coast States... Multiple rounds of thunderstorms are possible through tonight along and especially ahead of the cold front, shifting northeastward and eastward across the outlooked areas. Convection may develop earliest -- in the next few hours -- in/near an expanding field of midlevel UVV and related altocumuli now apparent in satellite imagery over north-central/northeast TX. The 12Z FWD sounding indicates these clouds were rooted near 600 mb, though they have deepened since, and that a weak EML-capping regime persists. Any sustained thunderstorms developing in this area will pose a large- hail threat initially, but what becomes surface-based may pose wind and perhaps tornado concern later today as the boundary layer beneath destabilizes. This convection should expand/shifts east- northeastward toward the Arklatex vicinity. The core concentration of severe threat -- including the potential for several tornadoes, some strong (EF2+) -- should be from parts of east TX across central LA to central/southern MS this afternoon into late evening. In step with the warm front, 60s F surface dewpoints are expected to shift east-northeastward. Though tempered some by low-cloud cover, diabatic heating (along with theta-e advection) should destabilize the warm sector diurnally. This will remove MLCINH, favoring potential for gradual development ahead of the main band of lift over east TX, as well as supporting strong-severe thunderstorms in the band. In turn, that renders the possibility of supercells with long warm-sector residence times in 500-1200 J/kg MLCAPE, 55-65 kt effective-shear magnitudes, 200-400 J/kg effective SRH, and 100-250 J/kg of 1/2-km SRH,. Highest SRH and largest hodographs should be in the evening, near an LLJ. However, considerable uncertainty remains as to number/coverage of storms that can remain restively discrete while in that environment. If confidence increases in associated longer-tracked tornado potential, based on 12Z guidance and daylight mesoanalysis trends, an upgrade may be needed in a succeeding outlook. Overnight, a line of strong-severe thunderstorms should continue advancing eastward over the remainder of MS and into parts of AL, gradually moving into progressively weaker (but still at least marginally favorable) surface-based buoyancy by 12Z. The eastern extent still is uncertain, given a common bias in models (including most convection-allowing guidance as well as synoptic progs) to underforecast nocturnal squall-line speed in this area of the country. Therefore actual severe potential by 12Z probably has a much sharper east edge than we can depict now, due to those timing uncertainties. Embedded mesovortices, moving into favorable SRH and high RH, but weak low-level lapse rates, will locally maximize the damaging-wind threat and at least brief tornado potential tonight. ..Edwards/Leitman.. 11/20/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Mon Nov 20 2023 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF EAST TEXAS ACROSS CENTRAL/NORTHERN LOUISIANA TO CENTRAL/SOUTHERN MISSISSIPPI... ...SUMMARY... Tornadoes (some strong), damaging thunderstorm winds and isolated large hail are expected from this afternoon across east Texas and parts of Louisiana, into tonight across the Delta region into portions of Mississippi and Alabama. ...Synopsis... The mid/upper-level pattern will be dominated by extensive, progressive synoptic troughing, shifting eastward across the central CONUS. A broad, complex cyclone, with multiple circulation centers and vorticity maxima, is apparent in moisture-channel imagery from SD through the central Plains and parts of the lower Missouri Valley, to the southern High Plains and parts of OK. Part of a northern-stream shortwave trough over western Canada is expected to dig southeastward to the northern Plains through the period. As that occurs, a 500-mb low should consolidate across central/eastern KS today, shifting across northern MO toward northern IL by the end of the period. A high-amplitude, positively tilted trough will extend southwestward from that low, reaching the Ozarks, north-central to southwest TX, and Chihuahua/Sonora by 12Z tomorrow. A surface low was analyzed at 11Z near CHK, with cold front across southwestern OK to the TX South Plains and east-central NM. In response to the mid/upper-level processes, the low should move/ redevelop southeastward over the Arklatex by 00Z, then swing northeastward to near EVV by 12Z. At 00Z, the cold front should extend southwestward over east TX and deep south TX. The warm front's baroclinicity should diffuse somewhat diurnally and shift rapidly northeastward across LA and portions of MS today. The warm front should reach parts of western/southern AL overnight before being overtaken from north-south by the cold front or (more likely, by then) pre-cold-frontal belt of convection. ...East TX/Arklatex to central Gulf Coast States... Multiple rounds of thunderstorms are possible through tonight along and especially ahead of the cold front, shifting northeastward and eastward across the outlooked areas. Convection may develop earliest -- in the next few hours -- in/near an expanding field of midlevel UVV and related altocumuli now apparent in satellite imagery over north-central/northeast TX. The 12Z FWD sounding indicates these clouds were rooted near 600 mb, though they have deepened since, and that a weak EML-capping regime persists. Any sustained thunderstorms developing in this area will pose a large- hail threat initially, but what becomes surface-based may pose wind and perhaps tornado concern later today as the boundary layer beneath destabilizes. This convection should expand/shifts east- northeastward toward the Arklatex vicinity. The core concentration of severe threat -- including the potential for several tornadoes, some strong (EF2+) -- should be from parts of east TX across central LA to central/southern MS this afternoon into late evening. In step with the warm front, 60s F surface dewpoints are expected to shift east-northeastward. Though tempered some by low-cloud cover, diabatic heating (along with theta-e advection) should destabilize the warm sector diurnally. This will remove MLCINH, favoring potential for gradual development ahead of the main band of lift over east TX, as well as supporting strong-severe thunderstorms in the band. In turn, that renders the possibility of supercells with long warm-sector residence times in 500-1200 J/kg MLCAPE, 55-65 kt effective-shear magnitudes, 200-400 J/kg effective SRH, and 100-250 J/kg of 1/2-km SRH,. Highest SRH and largest hodographs should be in the evening, near an LLJ. However, considerable uncertainty remains as to number/coverage of storms that can remain restively discrete while in that environment. If confidence increases in associated longer-tracked tornado potential, based on 12Z guidance and daylight mesoanalysis trends, an upgrade may be needed in a succeeding outlook. Overnight, a line of strong-severe thunderstorms should continue advancing eastward over the remainder of MS and into parts of AL, gradually moving into progressively weaker (but still at least marginally favorable) surface-based buoyancy by 12Z. The eastern extent still is uncertain, given a common bias in models (including most convection-allowing guidance as well as synoptic progs) to underforecast nocturnal squall-line speed in this area of the country. Therefore actual severe potential by 12Z probably has a much sharper east edge than we can depict now, due to those timing uncertainties. Embedded mesovortices, moving into favorable SRH and high RH, but weak low-level lapse rates, will locally maximize the damaging-wind threat and at least brief tornado potential tonight. ..Edwards/Leitman.. 11/20/2023 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0301 AM CST Mon Nov 20 2023 Valid 231200Z - 281200Z ...DISCUSSION... While there is notable spread amongst extended-range guidance regarding synoptic-scale details, there is general agreement that a substantial large-scale upper-level trough will cover most of the CONUS through next weekend. Periodic frontal passages will suppress low-level moisture return and result in generally cool and stable conditions for most areas. There remains some potential for a frontal wave to develop over the Gulf of Mexico on D5/Friday, as a cutoff mid/upper-level low over Mexico finally ejects northeastward. Most guidance has trended toward a more suppressed solution with this scenario, though some potential remains for a frontal wave to move over Florida, accompanied by a moist and favorably sheared warm sector. Aside from this relatively low-probability scenario, the severe-thunderstorm threat appears very limited into early next week. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0301 AM CST Mon Nov 20 2023 Valid 231200Z - 281200Z ...DISCUSSION... While there is notable spread amongst extended-range guidance regarding synoptic-scale details, there is general agreement that a substantial large-scale upper-level trough will cover most of the CONUS through next weekend. Periodic frontal passages will suppress low-level moisture return and result in generally cool and stable conditions for most areas. There remains some potential for a frontal wave to develop over the Gulf of Mexico on D5/Friday, as a cutoff mid/upper-level low over Mexico finally ejects northeastward. Most guidance has trended toward a more suppressed solution with this scenario, though some potential remains for a frontal wave to move over Florida, accompanied by a moist and favorably sheared warm sector. Aside from this relatively low-probability scenario, the severe-thunderstorm threat appears very limited into early next week. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0301 AM CST Mon Nov 20 2023 Valid 231200Z - 281200Z ...DISCUSSION... While there is notable spread amongst extended-range guidance regarding synoptic-scale details, there is general agreement that a substantial large-scale upper-level trough will cover most of the CONUS through next weekend. Periodic frontal passages will suppress low-level moisture return and result in generally cool and stable conditions for most areas. There remains some potential for a frontal wave to develop over the Gulf of Mexico on D5/Friday, as a cutoff mid/upper-level low over Mexico finally ejects northeastward. Most guidance has trended toward a more suppressed solution with this scenario, though some potential remains for a frontal wave to move over Florida, accompanied by a moist and favorably sheared warm sector. Aside from this relatively low-probability scenario, the severe-thunderstorm threat appears very limited into early next week. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0301 AM CST Mon Nov 20 2023 Valid 231200Z - 281200Z ...DISCUSSION... While there is notable spread amongst extended-range guidance regarding synoptic-scale details, there is general agreement that a substantial large-scale upper-level trough will cover most of the CONUS through next weekend. Periodic frontal passages will suppress low-level moisture return and result in generally cool and stable conditions for most areas. There remains some potential for a frontal wave to develop over the Gulf of Mexico on D5/Friday, as a cutoff mid/upper-level low over Mexico finally ejects northeastward. Most guidance has trended toward a more suppressed solution with this scenario, though some potential remains for a frontal wave to move over Florida, accompanied by a moist and favorably sheared warm sector. Aside from this relatively low-probability scenario, the severe-thunderstorm threat appears very limited into early next week. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0301 AM CST Mon Nov 20 2023 Valid 231200Z - 281200Z ...DISCUSSION... While there is notable spread amongst extended-range guidance regarding synoptic-scale details, there is general agreement that a substantial large-scale upper-level trough will cover most of the CONUS through next weekend. Periodic frontal passages will suppress low-level moisture return and result in generally cool and stable conditions for most areas. There remains some potential for a frontal wave to develop over the Gulf of Mexico on D5/Friday, as a cutoff mid/upper-level low over Mexico finally ejects northeastward. Most guidance has trended toward a more suppressed solution with this scenario, though some potential remains for a frontal wave to move over Florida, accompanied by a moist and favorably sheared warm sector. Aside from this relatively low-probability scenario, the severe-thunderstorm threat appears very limited into early next week. Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0211 AM CST Mon Nov 20 2023 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are currently not expected on Wednesday. ...Synopsis... Guidance varies with respect to upper-level pattern evolution on Wednesday, with recent GFS runs and the 20/00Z ECMWF depicting a relatively amplified shortwave trough moving eastward from the TN Valley toward the Carolinas, while other guidance depicts a broader positively tilted trough moving offshore earlier in the forecast period. Despite these differences, most guidance agrees that a cold front will be near or just offshore of coastal NC at the start of the period Wednesday morning, with the trailing portion of the front expected to move across the FL Peninsula through the day. ...Eastern NC and the Outer Banks... While some severe threat could evolve late in the D2/Tuesday period across eastern NC into the Outer Banks, most guidance suggests the effective warm sector will be very near the coast or offshore by the start of the D3/Wednesday period. As a result, severe probabilities were not included with this outlook. However, if the front is slower than currently anticipated, then some threat for isolated damaging wind and/or a brief tornado could briefly persist after 12Z Wednesday morning, within a weakly unstable but moist and strongly sheared environment. ..Dean.. 11/20/2023 Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0211 AM CST Mon Nov 20 2023 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are currently not expected on Wednesday. ...Synopsis... Guidance varies with respect to upper-level pattern evolution on Wednesday, with recent GFS runs and the 20/00Z ECMWF depicting a relatively amplified shortwave trough moving eastward from the TN Valley toward the Carolinas, while other guidance depicts a broader positively tilted trough moving offshore earlier in the forecast period. Despite these differences, most guidance agrees that a cold front will be near or just offshore of coastal NC at the start of the period Wednesday morning, with the trailing portion of the front expected to move across the FL Peninsula through the day. ...Eastern NC and the Outer Banks... While some severe threat could evolve late in the D2/Tuesday period across eastern NC into the Outer Banks, most guidance suggests the effective warm sector will be very near the coast or offshore by the start of the D3/Wednesday period. As a result, severe probabilities were not included with this outlook. However, if the front is slower than currently anticipated, then some threat for isolated damaging wind and/or a brief tornado could briefly persist after 12Z Wednesday morning, within a weakly unstable but moist and strongly sheared environment. ..Dean.. 11/20/2023 Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0211 AM CST Mon Nov 20 2023 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are currently not expected on Wednesday. ...Synopsis... Guidance varies with respect to upper-level pattern evolution on Wednesday, with recent GFS runs and the 20/00Z ECMWF depicting a relatively amplified shortwave trough moving eastward from the TN Valley toward the Carolinas, while other guidance depicts a broader positively tilted trough moving offshore earlier in the forecast period. Despite these differences, most guidance agrees that a cold front will be near or just offshore of coastal NC at the start of the period Wednesday morning, with the trailing portion of the front expected to move across the FL Peninsula through the day. ...Eastern NC and the Outer Banks... While some severe threat could evolve late in the D2/Tuesday period across eastern NC into the Outer Banks, most guidance suggests the effective warm sector will be very near the coast or offshore by the start of the D3/Wednesday period. As a result, severe probabilities were not included with this outlook. However, if the front is slower than currently anticipated, then some threat for isolated damaging wind and/or a brief tornado could briefly persist after 12Z Wednesday morning, within a weakly unstable but moist and strongly sheared environment. ..Dean.. 11/20/2023 Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0211 AM CST Mon Nov 20 2023 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are currently not expected on Wednesday. ...Synopsis... Guidance varies with respect to upper-level pattern evolution on Wednesday, with recent GFS runs and the 20/00Z ECMWF depicting a relatively amplified shortwave trough moving eastward from the TN Valley toward the Carolinas, while other guidance depicts a broader positively tilted trough moving offshore earlier in the forecast period. Despite these differences, most guidance agrees that a cold front will be near or just offshore of coastal NC at the start of the period Wednesday morning, with the trailing portion of the front expected to move across the FL Peninsula through the day. ...Eastern NC and the Outer Banks... While some severe threat could evolve late in the D2/Tuesday period across eastern NC into the Outer Banks, most guidance suggests the effective warm sector will be very near the coast or offshore by the start of the D3/Wednesday period. As a result, severe probabilities were not included with this outlook. However, if the front is slower than currently anticipated, then some threat for isolated damaging wind and/or a brief tornado could briefly persist after 12Z Wednesday morning, within a weakly unstable but moist and strongly sheared environment. ..Dean.. 11/20/2023 Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0211 AM CST Mon Nov 20 2023 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are currently not expected on Wednesday. ...Synopsis... Guidance varies with respect to upper-level pattern evolution on Wednesday, with recent GFS runs and the 20/00Z ECMWF depicting a relatively amplified shortwave trough moving eastward from the TN Valley toward the Carolinas, while other guidance depicts a broader positively tilted trough moving offshore earlier in the forecast period. Despite these differences, most guidance agrees that a cold front will be near or just offshore of coastal NC at the start of the period Wednesday morning, with the trailing portion of the front expected to move across the FL Peninsula through the day. ...Eastern NC and the Outer Banks... While some severe threat could evolve late in the D2/Tuesday period across eastern NC into the Outer Banks, most guidance suggests the effective warm sector will be very near the coast or offshore by the start of the D3/Wednesday period. As a result, severe probabilities were not included with this outlook. However, if the front is slower than currently anticipated, then some threat for isolated damaging wind and/or a brief tornado could briefly persist after 12Z Wednesday morning, within a weakly unstable but moist and strongly sheared environment. ..Dean.. 11/20/2023 Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0211 AM CST Mon Nov 20 2023 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are currently not expected on Wednesday. ...Synopsis... Guidance varies with respect to upper-level pattern evolution on Wednesday, with recent GFS runs and the 20/00Z ECMWF depicting a relatively amplified shortwave trough moving eastward from the TN Valley toward the Carolinas, while other guidance depicts a broader positively tilted trough moving offshore earlier in the forecast period. Despite these differences, most guidance agrees that a cold front will be near or just offshore of coastal NC at the start of the period Wednesday morning, with the trailing portion of the front expected to move across the FL Peninsula through the day. ...Eastern NC and the Outer Banks... While some severe threat could evolve late in the D2/Tuesday period across eastern NC into the Outer Banks, most guidance suggests the effective warm sector will be very near the coast or offshore by the start of the D3/Wednesday period. As a result, severe probabilities were not included with this outlook. However, if the front is slower than currently anticipated, then some threat for isolated damaging wind and/or a brief tornado could briefly persist after 12Z Wednesday morning, within a weakly unstable but moist and strongly sheared environment. ..Dean.. 11/20/2023 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0202 AM CST Mon Nov 20 2023 Valid 211200Z - 221200Z ...NO CRITICAL AREAS... ...Synopsis... The mid-level pattern over the CONUS is forecast to continue amplifying as the upper low over the central US slides eastward. An attendant surface cyclone is projected to weaken as it moves northeastward across the TN Valley and into the eastern OH Valley by Tuesday evening. Widespread precipitation and cooler temperatures will overspread the eastern half of the US, limiting fire-weather concerns. To the west, eastern Pacific ridging will also intensify with strong high pressure developing within the Great Basin and the Intermountain West. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves onto the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. ..Lyons.. 11/20/2023 ...Please see www.spc.noaa.gov/fire for graphic product... Read more