U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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Storm Prediction Center ac 230736 


Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0236 am CDT sun Sep 23 2018 


Valid 251200z - 261200z 


..there is a slight risk of severe thunderstorms from parts of 
eastern Missouri northeastward to the Lake Erie vicinity... 


... 
Severe risk -- mainly in the form of damaging winds -- is forecast 
to evolve Tuesday from the Ozarks vicinity northeastward to the 
lower Great Lakes. 


... 
A long-wave upper trough is progged to reside over central noam at 
the start of the period, with a shorter-wavelength trough embedded 
therein to advance slowly eastward with time. 


In conjunction with short-wave progression aloft, a seasonably 
strong surface cold front -- initially expected to lie from the 
upper Great Lakes southwestward to the southern rockies -- will 
likewise advance eastward/southeastward, and should extend from 
roughly the Lake Erie vicinity southwestward in an arcing manner 
across the mid-south, and then to central Texas. 


Elsewhere, upper-level ridging will flank the large area of cyclonic 
flow, while corresponding surface high pressure prevails both east 
and west of the advancing surface front. 


..the Ozarks vicinity northeastward to the lower Great Lakes... 
As a surface cold front sweeps across the upper Great Lakes/Midwest 
region during the day Tuesday, modest pre-frontal boundary-layer 
heating/destabilization is expected. Robust large-scale ascent -- 
focused near the surface front -- should allow development of a 
frontal or pre-frontal convective band, which will likely grow 
upscale into an at least loosely continuous squall line through late 
afternoon/early evening. With moderately strong west-southwest flow 
aloft supporting both locally organized updrafts and fast storm 
motion, locally damaging winds will likely affect a broad portion of 
the Midwest vicinity as the system advances quickly eastward. 


With the strongest flow over northern fringes of the outlook area, 
some risk for damaging winds appears evident despite more limited 
availability of cape with northward extent. Later, as instability 
diminishes diurnally across the entire risk area, severe threat 
should gradually decrease through the overnight hours. 


.Goss.. 09/23/2018 


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