U.S. Severe Weather Forecast (Convective Outlook)

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000 
acus01 kwns 251626 
swody1 
Storm Prediction Center ac 251625 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1125 am CDT Tue Sep 25 2018 


Valid 251630z - 261200z 


..there is a slight risk of severe thunderstorms this afternoon 
through tonight for the middle MS valley to lower Michigan and 
northwestern Ohio... 


... 
Scattered damaging gusts and isolated large hail will be possible 
this afternoon and evening from eastern Iowa to northern Illinois 
and southern Wisconsin, and at least isolated damaging gusts will be 
possible into the overnight hours across lower Michigan. A couple 
of tornadoes will be possible this afternoon from northeastern 
Indiana into northwestern Ohio. 


... 
A weak surface cyclone in south central Iowa as of late morning will 
move northeastward toward southwestern qc and gradually deepen by 
the end of the period, in advance of a shortwave trough progressing 
from the northern plains to the Great Lakes. An associated surface 
cold front (now from central WI/Iowa to central ks) will move 
southeastward to North Texas and the lower Great Lakes by 26/12z. A 
broad swath of 68-72 f boundary-layer dewpoints has spread 
northeastward in advance of the cold front, though midlevel lapse 
rates greater than 7 c/km are confined to a small area of the 
Central Plains, with lesser lapse rates to the east. Ongoing 
clusters of storms from central in southward are related to a 
remnant tropical moisture plume with diffuse embedded speed maxima. 
Larger cloud breaks and stronger surface heating is expected west 
through northwest of the ongoing in storms today. 


..eastern in to northwestern Ohio this afternoon/evening... 
The ongoing storms across in will spread northeastward today as weak 
embedded mcvs interact with the moist environment across the Ohio 
Valley. Storm Mode will likely remain somewhat messy clusters, and 
surface heating will be slowed by persistent clouds. Still, the 
stronger low-level shear this afternoon should be focused from 
eastern in across western Ohio with weak surface-based buoyancy, and a 
couple of tornadoes will be possible. 


..eastern Iowa/northern Illinois/southern WI this afternoon/evening... 
The threat for isolated strong/severe storms should evolve from the 
ongoing convection approaching central Iowa. These storms have been 
elevated through the morning, but will gradually phase with the 
surface low/cold front and warm sector from eastern Iowa to northern 
Illinois/southern WI this afternoon. Surface heating in advance of the 
cold front, combined with the frontal circulation and forcing for 
ascent preceding the midlevel trough moving eastward from NE/SD, 
should support some increase in storm intensity this afternoon. 
Though low-level shear is not expected to be particularly strong 
(the stronger low-level southwesterly flow is confined to the Ohio 
Valley moisture plume), MLCAPE near 1000 j/kg and effective bulk 
shear near 50 kt will favor an organized band of storms (with bowing 
segments and embedded supercells) capable of producing damaging 
winds and isolated large hail. 


..northern in to lower Michigan this evening through tonight... 
In the wake of today's ongoing convection across in/OH, additional 
storm development will be possible this evening into tonight. The 
remnants of the afternoon/evening storms in WI/Illinois could reach 
western lower Michigan by early tonight, with additional storm development 
possible from in into southeastern lower Michigan. A modest increase in 
low-level flow/shear is possible this evening across lower mi, 
though forecast hodographs do not look particularly favorable for 
tornadic supercells. 


.Thompson/nauslar.. 09/25/2018 


$$ 

Mesoscale Discussion


000 
acus11 kwns 251428 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 251427 
iaz000-251630- 


Mesoscale discussion 1497 
National Weather Service Storm Prediction Center Norman OK 
0927 am CDT Tue Sep 25 2018 


Areas affected...central/southern Iowa. 


Concerning...severe potential...watch unlikely 


Valid 251427z - 251630z 


Probability of watch issuance...20 percent 


Summary...thunderstorm coverage and intensity is expected to 
gradually increase over the next few hours. A few damaging wind 
gusts and/or instances of severe hail are possible. 


Discussion...recent regional radar imagery shows a fast-moving 
linear segment progressing into far west-central Iowa. This line 
segment appears to be associated with the leading edge of the better 
forcing for ascent attendant to the shortwave trough moving through 
the Central Plains. Cold front progressing through the region is 
moving a bit slower than this line segment, which now appears to be 
co-located with the frontal zone. The downstream airmass is 
currently characterized by widespread cloudiness and meager 
instability. Even so, continued heating amidst the moderately moist 
airmass should help destabilization over the next few hours. 
Resultant moderately unstable airmass coupled with strong forcing 
for ascent and enhanced low- to mid-level flow should allow for 
increased thunderstorm coverage and intensity. A few of these storms 
could become severe, with the primary threat of damaging wind gusts. 
Some hail is also possible. Severe coverage is expected to be too 
low during the next few hours to merit a watch, but trends will be 
monitored closely. 


.Mosier/Thompson.. 09/25/2018 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...dmx...oax... 


Latitude...Lon 41849536 42109489 42339388 42519241 41389246 40879339 
40649547 41339583 41849536