SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 PM CDT Thu Jun 13 2024
Valid 132000Z - 141200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN SOUTHERN
IA...NORTHERN MO...AND NORTHERN/CENTRAL IL...
...SUMMARY...
Severe thunderstorms are expected late this afternoon and early
evening across parts of southern Iowa into northern Missouri and
northern/central Illinois. Very large hail, destructive wind gusts,
and a couple of tornadoes all appear possible. A broader corridor of
severe hail/wind potential will extend from portions of the
southern/central High Plains to the Great Lakes.
...20Z Update...
Overall prior forecast appears reasonably on-track. Only minor
changes were made based on latest observational trends. This was
largely to the west/north side of ongoing convection/frontal
placement from MI to IA and in south FL. For additional short-term
forecast information, please see MCD 1248 regarding the
south-central High Plains and MCD 1249 for the Mid-MS to Lower MO
Valleys.
..Grams.. 06/13/2024
.PREV DISCUSSION... /ISSUED 1128 AM CDT Thu Jun 13 2024/
...Great Lakes...
A mid-level shortwave trough with associated westerly
mid/upper-level jet will move eastward across the Upper Midwest and
Great Lakes today. An attendant surface cold front will likewise
sweep eastward across these regions through this evening, with the
primary surface cyclone forecast to remain in Canada. Partly cloudy
skies this morning should give way to better opportunity for diurnal
heating this afternoon. Increasing low-level convergence along the
front, along with ascent associated with shortwave trough/mid-level
jet, should encourage convective development along/near the front by
mid afternoon across parts of Lower MI into northern IL/IN and
vicinity. Sufficient instability and deep-layer shear are forecast
to support robust thunderstorms with a threat for scattered damaging
winds and severe hail. The magnitude of the severe threat will be
dependent on how much instability can develop, with differences
remaining in high-resolution guidance regarding both how much
convection develops, and how intense it will become. Regardless,
some severe threat remains apparent, and the Marginal/Slight Risks
have been maintained across this region with minimal changes for
this update.
...Mid Mississippi Valley...
A surface cold front is progged to sag more slowly
south-southeastward across the mid MS Valley today, with better
forcing aloft generally remaining to the north across the Upper
Midwest and Great Lakes. A rather moist low-level airmass, with
surface dewpoints generally in the upper 60s to low 70s, will remain
along/south of this boundary across the mid MS Valley. Robust
daytime heating of this airmass, along with steep mid-level lapse
rates, will promote moderate to strong instability (MLCAPE 2500-3500
J/kg) by mid/late afternoon from southeast NE/northeast KS into
southern IA/northern MO and vicinity. Warm mid-level temperatures
noted on area 12Z soundings (700 mb temperatures of 13+ C) will
likely inhibit robust convective development for much of the day,
until surface temperatures reach at least the low 90s and finally
erode lingering MLCIN.
Explosive thunderstorm development is likely by 20-22Z along/near
the front, as strong instability combines with enhanced deep-layer
shear to support an threat for multiple intense supercells. Very
large hail of at least 2-3 inches in diameter, and perhaps a couple
tornadoes, will be a threat with these initially discrete
supercells. With mid-level westerly flow largely parallel to the
surface boundary, a quick transition/upscale growth into one or more
bowing clusters seems likely by early evening. This activity should
tend to have a greater threat for severe/damaging winds, including
the potential for some significant gusts of 75-80 mph. The severe
wind/hail threat should continue in a relatively narrow corridor
this evening across the mid MS Valley, before increasing MLCIN and
nocturnal cooling gradually reduce the overall severe risk tonight.
...Kansas into the Southern/Central High Plains...
A hot and deeply mixed airmass is anticipated along/near the front
across KS into the southern/central High Plains. This region will
generally be displaced to the south of stronger forcing aloft, and
warm mid-level temperatures may inhibit convection for much of the
day. Still, most guidance suggests isolated to scattered
thunderstorms will develop with a very well mixed boundary layer and
steepened low/mid-level lapse rates. Severe/damaging downdraft winds
appear to be the main threat with this activity, although some hail
may also occur with any marginal supercell structures that can form.
Based on latest guidance trends, the Slight Risk has been expanded
westward to include more of western KS and eastern CO. Isolated
significant severe wind gusts (75+ mph) may occur with any loosely
organized clusters across KS. But, weaker deep-layer shear compared
with locations farther east suggests the overall severe threat will
probably remain fairly isolated.
...South Florida...
A loosely organized band of convection is ongoing across parts of
south FL. While mid-level lapse rates are expected to remain poor,
sufficient instability and deep-layer shear may support occasional
strong/gusty winds with the more robust activity this afternoon and
early evening. A brief tornado or two may also occur given modestly
enhanced low-level flow.
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