U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 211625 
Storm Prediction Center ac 211623 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1123 am CDT Sat Jul 21 2018 

Valid 211630z - 221200z 

..there is a slight risk of severe thunderstorms over parts of the 
southeast states...and over the northern High Plains... 

Strong to severe thunderstorms are expected across parts of the 
southeastern U.S. And the northern High Plains. 

..south Georgia into North Florida... 
A long-lived band of thunderstorms is tracking southward across 
southern Georgia. The air mass ahead of the storms is very 
moist/unstable with dewpoints in the upper 70s and temperatures 
warming into the 90s. Increasing northwesterly mid level winds and 
remnant mesoscale organization of convective band suggest the risk 
of damaging winds across the region through the afternoon. 

..north Georgia/western Carolinas... 
In the wake of morning convection, skies are mostly clear across 
northern Georgia into western NC and upstate SC. Rapid heating and 
dewpoints remaining in the lower 70s will yield strong afternoon 
cape values. A shortwave trough evident in water vapor imagery over 
western Kentucky/Tennessee will approach the region and lead to the development 
of scattered thunderstorms. Strong effective shear values and 
relatively steep mid-level lapse rates suggest the potential for 
rotating storms capable of large hail and damaging wind gusts. This 
activity may persist through the evening and track across eastern Georgia 
and much of SC. 

..northern High Plains... 
Scattered thunderstorms will develop this afternoon from the plains 
of eastern Montana southward into eastern WY/co. Forcing mechanisms are 
hard to identify this morning, and the region is under the upper 
ridge axis. Nevertheless, a consensus of 12z model solutions 
indicate a few of these storms will become intense with large hail 
and damaging winds possible. Storms should remain strong as they 
spread into the western Dakotas and western NE this evening. 

.Hart/nauslar.. 07/21/2018 


Mesoscale Discussion

acus11 kwns 211850 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 211850 

Mesoscale discussion 1121 
National Weather Service Storm Prediction Center Norman OK 
0150 PM CDT Sat Jul 21 2018 

Areas affected...eastern Wyoming...northeast Colorado...western 
Nebraska...and western South Dakota 

Concerning...severe potential...watch possible 

Valid 211850z - 212115z 

Probability of watch issuance...40 percent 

Summary...storms are beginning to develop over the higher terrain 
and along a surface boundary across southeast Wyoming into 
north-central Colorado. Severe hail/wind are possible this afternoon 
as these storms mature and move eastward. 

Discussion...storms should continue developing this afternoon across 
eastern Wyoming/northeast Colorado as strong daytime heating, 
enhanced surface convergence, and upslope flow act to destabilize 
lower-levels and break the cap. As storms move eastward, MLCAPE of 
500-2000+ j/kg should support deep convection although shear is 
relatively weak across the discussion area (effective bulk shear of 
20-35 knots). However, low-level shear is likely to increase with 
surface pressure falls helping to increase surface convergence and 
strengthen southeasterly flow. This may allow for stronger storms to 
develop and enhance the severe threat. Steep low-level lapse rates 
(9+ c/km) and high LCLs indicate the potential for severe wind and 
rap soundings and mesoanalysis show 1200+ j/kg of dcape further 
supporting this risk. Severe hail is also possible, especially 
farther to the east/north across the discussion area as cape/shear 

.Nauslar/Hart.. 07/21/2018 

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


Latitude...Lon 40220529 41440537 42610566 43280593 43900616 44190491 
44050373 43110275 42960271 42560261 41670254 40930250 
40560259 40260318 40090391 40040526 40220529