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ACUS01 KWNS 161244

SWODY1

SPC AC 161242



Day 1 Convective Outlook  

NWS Storm Prediction Center Norman OK

0742 AM CDT Tue Apr 16 2024



Valid 161300Z - 171200Z



...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF

IOWA...NORTHERN MISSOURI...AND NORTHWESTERN ILLINOIS...



...SUMMARY...

Scattered severe thunderstorms appear likely today, centered mostly

over northern Missouri, Iowa, and northwestern Illinois. Large hail,

damaging winds, and tornadoes should occur in this corridor. More

isolated activity could develop as far south as the Ozarks of

northern Arkansas.



...Synopsis...

An upper trough/low over the central Plains this morning will

continue to eject east-northeastward across the mid MO Valley and

Upper Midwest through tonight. A 70-90 kt mid-level jet will

overspread parts of the Midwest through the day, contributing to

substantial deep-layer shear and thunderstorm organization. At the

surface, a 990 mb low over central NE will likewise develop

east-northeastward through the day in tandem with the upper wave. A

warm front should lift northward across parts of the Midwest, with

generally low to mid 60s surface dewpoints present across the warm

sector as far south as the Ozarks. A composite Pacific cold

front/dryline will move quickly eastward from the southern/central

Plains into the mid Ms Valley by this evening. This boundary should

stall across the southern Plains, and may begin to lift northward

late tonight.



...Midwest/Mid Mississippi Valley...

A large area of showers and thunderstorms is ongoing this morning

from parts of eastern KS/NE/SD into IA. Much of this activity across

the central Plains is being driven by large-scale ascent associated

with the ejecting upper trough/low, along with strong warm/moist

advection with a 40-50 kt southerly low-level jet. As this

convection continues to spread eastward this morning in tandem with

the migrating low-level jet axis, it will probably become more

elevated, especially as it moves into northern MO and IA and a less

unstable airmass to the north of the warm front. Still, an isolated

severe threat may persist in the short term with these

thunderstorms. The effect of this early-day convection on robust

destabilization in its wake along/ahead of the cold front remains a

concern and potentially limiting factor for additional severe

thunderstorm development this afternoon. Even so, most guidance,

including multiple recent runs of the RAP, shows a narrow corridor

of weak to moderate instability developing along/south of the warm

front in IA, and ahead of the cold front sweeping eastward across

MO/IA. This re-destabilization should be aided by a pocket of steep

mid-level lapse rates and cold temperatures aloft on the southeast

side of the upper trough/low.



Assuming that low to mid 60s surface dewpoints and modest daytime

heating can aid in this instability actually materializing, then a

risk for supercells should exist over parts of IA, northern MO, and

northwestern IL. Both low-level and deep-layer shear appear strong

enough for supercells. Steep lapse rates will aid in hail

production, with some chance for 2+ inch diameter stones with the

more robust cores. Tornadoes will also be a concern, as the enhanced

boundary-layer flow and enlarged/curved hodographs associated with a

the low-level jet will aid in updraft rotation. The best tornado

potential will probably be focused along/near the warm front in IA,

where the greatest low-level shear is forecast. Here, a strong

tornado appears possible. Isolated to scattered damaging winds may

also occur.



Farther south into the Ozarks and Mid-South, the potential for

severe thunderstorms appears more conditional. Various NAM/RAP

forecast soundings exhibit generally poor lapse rates, with at least

weak inhibition through much of the period. Given these regions

displacement from the upper trough/low to the north, it remains

unclear how robust updrafts will be in a more marginal low/mid-level

lapse rate environment. Still, have maintained the Slight Risk into

parts of the lower MS Valley, but convection may struggle to

intensify this afternoon/evening.



..Gleason/Grams.. 04/16/2024



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