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ACUS01 KWNS 071954

SWODY1

SPC AC 071953



Day 1 Convective Outlook  

NWS Storm Prediction Center Norman OK

0253 PM CDT Sun Apr 07 2024



Valid 072000Z - 081200Z



...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE

MID-MISSISSIPPI VALLEY...



...SUMMARY...

Widely scattered strong/isolated severe thunderstorms remain

possible late this afternoon and evening in the lower/mid

Mississippi Valley.



...20Z Update...

The only change made in the 20Z Day 1 Outlook update was to expand 2

percent tornado probabilities westward into far southeast SD, where

adequate insolation has boosted 0-3 km CAPE to 50-100 J/kg ahead of

a vertical-vorticity rich surface boundary (per 19Z mesoanalysis). 



Otherwise, the previous forecast remains on track, with no major

changes or additions made. Please see the previous forecast below

for more details.



..Squitieri.. 04/07/2024



.PREV DISCUSSION... /ISSUED 1129 AM CDT Sun Apr 07 2024/



...Mid/lower Mississippi Valley area...

While dewpoints remain in the 30s and 40s across the SLGT risk area

late this morning, low-level moisture advection is ongoing ahead of

the advancing cold front, with low to mid 60s dewpoints now observed

across central and southern portions of Arkansas.



As the front advances eastward, and the more favorable low-level

theta-e airmass continues advecting northward, filtered heating will

support modest destabilization, with afternoon mixed-layer CAPE

values rising into the 500 to 1000 J/kg range.



Stronger ascent will remain just north of the SLGT risk area, as a

lobe of vorticity rotating through cyclonic southwesterly flow aloft

on the southeastern side of closed upper low over Nebraska crosses

Illinois/Indiana this afternoon.  Still, scattered convective

development is expected to begin by mid to late afternoon across the

Mid Mississippi Valley, and southward into the Delta region, in

focused low-level ascent near the cold front.  While modest CAPE

will likely limit severe potential, the deep-layer wind field

(veering and increasing favorably with height across the pre-frontal

warm sector) will likely augment a few of the stronger updrafts,

suggesting that a few storms will become capable of producing hail

and/or damaging winds.  A tornado or two will also be possible, with

hodographs indicating favorable helicity with any right-moving

supercell.



Severe potential should peak through late afternoon, and then

gradually diminish this evening as the boundary layer cools, and the

cold front weakens with time.



...Parts of central/southeastern Iowa and vicinity...

As the weakening/vertically stacked low shifts northeastward out of

Nebraska and across northwestern Iowa this afternoon, continued

daytime heating of a marginally moist (40s dewpoints) boundary

layer, residing beneath rather steep mid-level lapse rates will

continue to facilitate weak destabilization.  Thunderstorms have

developed late this morning across portions of northern and central

Illinois, and across north-central Iowa and into adjacent southern

Minnesota.  By mid afternoon, new convective development is expected

along the occluded front currently moving northeastward across the

Nebraska/Iowa border/Mid-Missouri Valley at this time, as it shifts

into central and southeastern Iowa.  While the evolving, low-topped

storms should remain largely sub-severe, a strong to severe wind

gust or two, and even a brief tornado, will be possible, through

late afternoon/early evening.



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