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SPC May 9, 2024 2000 UTC Day 1 Convective Outlook

1 year 4 months ago

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0248 PM CDT Thu May 09 2024 Valid 092000Z - 101200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TEXAS EAST ACROSS PARTS OF THE CENTRAL GULF COAST STATES AND SOUTHERN GEORGIA... ...SUMMARY... Very large hail with multiple supercells appears probable across parts of north and central Texas into the ArkLaTex vicinity this afternoon and evening. A broader corridor of severe hail and damaging-wind potential will extend from east Texas into the lower Mississippi Valley and Southeast. ...Southeast... The main changes with the 20z update were to remove most severe probabilities from much of SC/NC. Convection has mostly moved offshore and redevelopment is not expected. Furthermore, instability will remain very weak across much of NC and any storms that may form into the evening/overnight should remain fairly weak. Probabilities were not changed much over AL/GA from the previous outlook given expected MCS moving into these areas overnight and posing a risk for damaging wind gusts. ...OK/TX to Lower MS Valley... The Marginal risk (level 1 of 5) was extended northward into central OK where ongoing thunderstorms will pose some risk for marginally severe hail this afternoon/evening with eastward extent into AR. The Enhanced risk (level 3 of 5) has been nudged a small amount south across southeast TX and LA based on latest short term guidance and CAMs trends. Damaging gusts and hail will be the main concern as thunderstorms congeal over north/central TX into an eastward progressing MCS during the evening/overnight. ..Leitman.. 05/09/2024 .PREV DISCUSSION... /ISSUED 1146 AM CDT Thu May 09 2024/ ...Synopsis... Water-vapor imagery late this morning shows a mid-level trough over the western Great Lakes/Upper MS Valley and a mid- to upper-level low situated over eastern UT. A broad belt of strong westerly 500-mb flow will extend from the Desert Southwest eastward across the southern Great Plains and to the Mid-Atlantic and Southeast U.S. coast. Satellite imagery also depicts an embedded disturbance quickly moving east across AL into western GA late this morning. Another upstream disturbance is currently moving east-northeast across northern Mexico into the Rio Grande Valley/Edwards Plateau late this morning. In the low levels, a surface low over the OH Valley is largely displaced from the area of greatest severe thunderstorm concern today, which is located from TX east to the GA/SC vicinity. A myriad of ongoing thunderstorm bands and convective outflow over the Southeast will serve as corridors for additional and continued thunderstorm activity through at least the early to mid afternoon. Farther west, a dryline and west-east oriented frontal zone over north TX east to the ArkLaMiss will also act to focus severe thunderstorm development later today and tonight. ...North, central and east TX... Scattered thunderstorms are forecast to develop this afternoon and evening ahead of the aforementioned mid-level disturbance across central and eventually into eastern portions of TX. Storm development will likely initially favor near and north of a frontal zone draped across north TX with dryline storms later this afternoon. The Fort Worth and Del Rio, TX raobs sampled 8-9 deg C/km 700-500 mb lapse rates. Very large CAPE via a very moist boundary layer will likely favor explosive updraft growth as storms quickly become supercellular. Low-level shear will likely be subdued due to lack of a strong low-level mass response, thereby acting to limit overall tornado potential. Nonetheless, a few supercells within an environment characterized by very large buoyancy and moist low levels will potentially yield some tornado risk via local storm-scale processes such as mergers and boundary interactions. Large to giant hail --potentially 3+ inches in diameter -- as well as locally severe gusts and perhaps a tornado or two will be the primary threats. The wind threat could evolve upscale and start forward-propagating eastward into LA wherever early cells can aggregate into clusters. QLCS tornadoes are also possible with any MCS. ...Southeast... Bands of strong to severe thunderstorms ongoing during the midday will likely continue to propagate east-southeast across eastern AL into GA and SC. A very moist/unstable airmass evident in the 12z Birmingham and Atlanta raobs (1800 and 1300 J/kg MLCAPE) will continue to gradually destabilize, despite considerable cloud coverage across AL/GA. Fewer clouds across south-central GA into the coastal plain of SC will continue to heat more rapidly downstream of the ongoing storms and yield an environment favorable for a continued damaging-wind risk through the mid to late afternoon. For short-term convective details and environmental analysis, please refer to MCD #728 and forthcoming MCDs over the region. Farther west, from western AL westward into LA this afternoon, weak large-scale subsidence in wake of the AL/GA impulse will probably act to limit storm coverage during the day. Isolated severe storms are possible as the airmass continues to destabilize and potentially yield an isolated hail/wind threat. Later this evening into the overnight, a cluster of thunderstorms is forecast to evolve over the Arklatex and move east across LA into MS and eventually MS/AL/FL Panhandle. Severe gusts (60-85 mph) and the risk for a few tornadoes will probably accompany this activity as it moves east during the evening and overnight. ...Mid/upper Ohio Valley to Tidewater... Isolated to widely scattered thunderstorms are possible this afternoon across portions of the OH Valley, with damaging gusts and marginally severe hail possible. Some heating coupled with lower 60s surface dewpoints will contribute to MLCAPE ranging from 500-1500 J/kg. Though upper flow will be strong, nearly unidirectional profiles and lack of greater midlevel winds should keep effective-shear magnitudes in the 30-40 kt range over much of the area. Farther east/southeast, cool/stable air north of a damming/preceding frontal zone across VA and the Delmarva should limit the northern end of severe potential. Destabilization and available moisture will be substantially limited today in the nominal warm sector, between the damming front and a great deal of MCS/outflow activity to the south over the Carolinas/GA. Therefore, while thunderstorms are possible this afternoon and deep shear may be adequate for a few organized cells, severe potential appears isolated. Read more