U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 222000 
Storm Prediction Center ac 221959 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0159 PM CST Mon Jan 22 2018 

Valid 222000z - 231200z 

..there is a marginal risk of severe thunderstorms across parts of 
Alabama...southwest Georgia...and the Florida Panhandle... 

Isolated severe thunderstorms will remain possible across parts of 
Alabama, Georgia, and the Florida Panhandle through early evening. 

..Gulf Coast... 
Only change to severe probabilities is to remove areas behind a 
band/pockets of ongoing convection across Alabama and the western 
Florida Panhandle. Ahead of these cells, surface dew points in the 
upper 50s to lower 60s, combined with ample low-level and effective 
shear (based on regional vwp data), should be sufficient to maintain 
a potential for a few stronger wind gusts and perhaps a tornado. For 
more information, see mesoscale discussion 41. 

..Illinois to Ohio Valley... 
A few thunderstorms have formed across central Illinois this 
afternoon, aided by cooling mid-level temps ahead of a mature 
mid/upper cyclone. Enough surface heating has occurred to Foster 
sufficiently deep buoyancy for a few stronger cores. An isolated 
instance of marginally severe hail is not out of the question in the 
very near term, but decreasing instability through the afternoon 
will likely result in a downward trend in intensity with these 
cells. Farther southeast, shallow convection may form over parts of 
the Ohio Valley later this afternoon into the evening hours. While 
this convection may produce gusty winds due to downward momentum 
transport, their shallow/brief nature should preclude a severe 
threat worthy of probabilities. 

.Picca.. 01/22/2018 

Previous discussion... /issued 1022 am CST Mon Jan 22 2018/ 

..MS/Alabama area through late afternoon... 
A surface cyclone is near peak intensity this morning, and should 
continue to move east-northeastward today in association with a deep 
midlevel low immediately to its southwest. Other than some elevated 
convection in the zone of strong forcing for ascent north-northeast 
of the cyclone, a pre-frontal band of convection extends from 
central Kentucky to southern MS/southeastern la as of mid morning. This 
band of storms will intercept and limit the northward extend of the 
primary warm sector (with boundary layer dewpoints in the 60s and 
weak surface-based buoyancy) to the southern half of Alabama today. 
Deep-layer and low-level vertical shear will be sufficient for 
supercells and/or circulations embedded within line segments, and an 
associated threat for isolated damaging gusts and perhaps a tornado 
or two through late afternoon. Farther east and overnight, some 
destabilization and potential for organized storms will persist into 
the Carolinas, though the threat for damaging winds/tornadoes will 
be limited by the likely persistence of a near-surface stable layer. 

..IL/in to Kentucky/Tennessee late this afternoon/evening... 
Isolated low-topped thunderstorms will be possible later this 
afternoon/evening along the cold front (within the midlevel dry slot 
to the southeast of the surface cyclone) from northeastern Illinois across 
in. However, destabilization will be marginal at best, and the 
threat for severe storms will be limited by the modest buoyancy and 
relatively weak low-level shear where destabilization is more 
probable. Deep-layer vertical shear will be stronger with 
southeastward extent into parts of the Ohio Valley/KY/TN. Any 
destabilization in the wake of the morning pre-frontal 
rain/convection should be limited given the low sun angle and modest 
upstream moisture/lapse rates, which will likewise limit any 
potential for strong-severe storms late this afternoon into this 
evening along the cold front. 


Mesoscale Discussion

acus11 kwns 222116 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 222115 

Mesoscale discussion 0043 
National Weather Service Storm Prediction Center Norman OK 
0315 PM CST Mon Jan 22 2018 

Areas affected...portions of southeastern Minnesota...northern/central 
WI...and western Upper Michigan 

Concerning...heavy snow 

Valid 222115z - 230315z 

Summary...heavy snow, with rates around 1-2 inches per hour, will 
continue to develop northeastward this evening before slowly 
diminishing mainly after 03z. 

Discussion...area radar imagery shows a band of moderate to heavy 
snow extending from southeastern Minnesota into parts of western/central WI 
as of 21z. This deformation band is being supported by low/mid-level 
frontogenesis on the northern extent of a closed upper low over 
southern Iowa/northern MO. Snowfall rates of 1-2 inches per hour will 
likely continue within the core of this band as it develops slowly 
northeastward into northern WI and western Upper Michigan through the 
remainder of the afternoon and continuing into the evening hours. As 
the overall system becomes vertically stacked across Illinois and vicinity 
later this evening, the large-scale forcing and low/mid-level 
frontogenesis responsible for the heavy snow band will diminish. 
Accordingly, snowfall rates should slowly diminish below 1 inch per 
hour, mainly after 03z. 

.Gleason.. 01/22/2018 

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


Latitude...Lon 46439083 46808989 47058901 46968778 46588705 46298683 
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44749384 45309309 46439083