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ACUS02 KWNS 151728

SWODY2

SPC AC 151727



Day 2 Convective Outlook  

NWS Storm Prediction Center Norman OK

1227 PM CDT Mon Apr 15 2024



Valid 161200Z - 171200Z



...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHEAST

IOWA...NORTHERN MISSOURI...AND WEST-CENTRAL ILLINOIS...



...SUMMARY...

Scattered severe thunderstorms are likely from Tuesday morning into

the evening across a portion of the central states from the Corn

Belt to the Ozark Plateau. The most concentrated area of significant

severe hail and tornado potential is forecast over southern Iowa

into northern Missouri and west-central Illinois. A more isolated

severe threat is anticipated across portions of the Mid-Atlantic

states.



...Synopsis...

A robust upper-level low is evident in mid-morning water-vapor

imagery over the Four Corners region. At the surface, pressure falls

are ongoing as a lee cyclone begins to consolidate across the High

Plains. Over the next 24-48 hours, this surface low is forecast to

migrate east towards the MS River Valley, likely reaching northern

IA by late afternoon/early evening as it begins to occlude.

Thunderstorms will be focused within a preceding warm advection

plume, along a leading outflow boundary associated with

early-morning convection, and along a trailing cold front. The most

intense convection is expected in the vicinity of the surface low

along the northern fringe of the warm sector where strong synoptic

ascent will overspread a buoyant air mass with favorable low-level

wind shear; however, several mesoscale details that will likely

determine the overall magnitude of the severe event will be

dependent on the intensity/coverage of early-morning convection,

which introduces uncertainty into the forecast. 



...Corn Belt/Lower MO and Mid-MS Valleys...

Latest guidance continues to show reasonably good agreement in the

potential for ongoing showers and thunderstorms across eastern NE/KS

at 12 UTC Tuesday morning. This activity should intensify through

the morning across northern MO/central IA amid diurnal heating of a

moist, and weakly capped warm sector. While somewhat modest

mid-level lapse rates (6-7 C/km) will limit MLCAPE to around 1000

J/kg, strong veering flow in the lowest 2 km and 60-70 knot flow

aloft may support early supercell development with an attendant

tornado/wind threat. Low-level helicity will likely be maximized

along the surface warm/occluding front across portions of western IL

into IA, and recent CAMs continue to show a strong UH signal across

this region. 



However, this potential will likely be modulated by two factors. The

first is the degree of cloud cover/stratiform precipitation on the

northern fringe of the warm sector - especially across MO/IA/IL,

which may limit the degree of low-level destabilization. The second

is storm coverage, which remains very uncertain given high spread in

recent CAMs' depiction of convective evolution over the next 24

hours. Greater thunderstorm coverage than currently anticipated at

12 UTC may complicate convective mode later in the day, and the

strong synoptic ascent in the vicinity of the surface low, coupled

with weak capping, may favor higher convective coverage. If this

occurs, northerly storm motions along the primary boundary may favor

storm interactions/consolidation into one or more clusters/lines

that may favor a severe wind risk over tornado/hail. Regardless, the

overall synoptic regime and forecast environment support maintaining

the current risk probabilities. The strong effective bulk shear

values (60-70 knots) and effective SRH near 250 m2/s2 suggest that

significant hail and/or significant tornadoes are possible if a

predominantly discrete mode can be realized. Some solutions hint at

re-development late afternoon along the cold front across northern

MO/southern IA, but confidence in this scenario is low given the

high dependence on rapid destabilization after preceding convection.





...OH Valley into the Mid-Atlantic...

Isolated to scattered thunderstorms are expected to develop by late

morning within a warm advection regime over the OH River Valley.

While buoyancy will be somewhat meager (500-1000 J/kg MLCAPE),

elongated deep-layer hodographs may support storm longevity as they

meander southeast into the Appalachians/Mid-Atlantic region. Surface

temperatures warming into the low to mid 80s will steepen low-level

lapse rates to near 8 C/km, which may support a few damaging gusts

with the stronger cells.



..Moore.. 04/15/2024



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