U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 251246 
Storm Prediction Center ac 251245 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0745 am CDT Tue Sep 25 2018 

Valid 251300z - 261200z 

..there is a slight risk of severe thunderstorms parts of the 

Scattered severe storms with damaging winds as the primary hazard 
may develop in eastern Iowa and spread east across northern Illinois 
this afternoon, into Southern Lower Michigan and northern portions 
of Indiana and Ohio this evening. 

Primary changes this outlook are to focus slight risk across parts 
of the corn belt to southern Great Lakes and greater tornado 
probabilities centered on Southern Lower Michigan to Northwest Ohio. 

Scattered convection is ongoing from in/mi/OH southwest through 
southern Illinois within a warm conveyor belt. While some diurnal 
weakening is anticipated into the afternoon, boundary-layer heating 
of the open warm sector will be slowed and limited in this region. 
In addition, mid-level lapse rates will remain poor with minimal 
height falls through late afternoon. This should hinder daytime 
severe storm potential despite lower 70s boundary-layer dew points. 

The more probable severe storm scenario should emanate from eastern 
Iowa this afternoon. Initially elevated convection over eastern NE 
should reach central Iowa midday and likely develop east along the 
increasingly baroclinic cold front. A confined plume of middle 60s 
boundary-layer dew points and surface temperatures approaching the 
upper 70s to lower 80s should result in MLCAPE reaching 600-1200 
j/kg. While low-level winds will be modest and veered, strengthening 
deep-layer speed shear will be sufficient for an organized cluster 
with embedded mid-level rotating updrafts. Severe hail may occur 
initially, but damaging winds from strong gusts should become the 
primary hazard. 

As the cold front accelerates and mid-level height falls associated 
with the amplifying shortwave trough spread east, a renewed increase 
in warm-conveyor convection should occur this evening, centered on 
Southern Lower Michigan to Northern Ohio. Low-level winds will be veered but 
should be strengthening, and this may support adequate hodograph 
curvature for a tornado or two. An isolated damaging wind risk may 
persist tonight across parts of in/Ohio as the front further impinges 
on the rich low-level moisture plume. 

.Grams/Peters.. 09/25/2018 


Mesoscale Discussion

acus11 kwns 251428 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 251427 

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... 


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