U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 221952 
Storm Prediction Center ac 221950 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0250 PM CDT Thu Jun 22 2017 

Valid 222000z - 231200z 

..there is a slight risk of severe thunderstorms late this 
afternoon and evening across parts of the central Gulf Coast 

..there is a slight risk of severe thunderstorms across parts of 
the Central High plains...and within a corridor across the middle 
Missouri Valley through the southern Great Lakes region... 

..there is a marginal risk of severe thunderstorms surrounding the 
Gulf Coast slight risk area...into portions of the middle south... 

..there is a marginal risk of severe thunderstorms across areas 
surrounding the slight risk across the Central Plains and middle 
Missouri Valley into the Great Lakes region... 

Thunderstorm activity, potentially capable of producing localized 
damaging wind gusts and a couple of tornadoes, will persist across 
parts of the central Gulf states into the mid south late this 
afternoon and evening. Other widely scattered strong to severe 
storm development is possible in a corridor from the Central High 
plains through the mid Missouri Valley and southern portions of the 
Great Lakes region. 

..20z outlook update... 
The general idea of the preceding outlooks remains largely 
unchanged. However, adjustments have been made to the categorical 
and probabilistic lines to account for ongoing trends, and attempt 
to better define areas of severe weather potential for late this 
afternoon and evening. Higher (slight risk) severe probabilities 
east northeast of the Central High plains are generally focused 
within the narrow corridor of stronger boundary layer heating now 
taking place just ahead of the cold front from the Central 
Plains/mid Missouri Valley into the upper Great Lakes region, and 
along/south of a remnant outflow boundary across parts of the upper 
Midwest. This is mostly south of the strongest westerlies, but 
shear on the southern fringe of the westerlies, coupled with 
thermodynamic profiles characterized by relatively steep mid-level 
lapse rates and moderate cape, appears to provide an environment 
conducive to strong/severe storm development. For more specific 
details concerning ongoing or more imminent severe weather 
potential, please refer to the latest Storm Prediction Center mesoscale discussions. 

.Kerr.. 06/22/2017 

Previous discussion... /issued 1143 am CDT Thu Jun 22 2017/ 

..Gulf Coast states/lower MS valley into Tennessee Valley... 
Tropical Depression Cindy, centered over far west-central la as of 
mid/late morning, is expected to continue to drift slowly 
north-northeastward through the afternoon into tonight. Even while 
the system may begin to fill with a tendency for a weakening surface 
low, strong low/mid-level southerly winds on the eastern periphery 
of the system will continue to yield the possibility of low-topped 
supercells and at least some tornado risk over a relatively broad 
area of the region. A few weakly rotating cells have been noted this 
morning across the western Florida Panhandle as well as southeast la into 
southern MS, and this same scenario/supportive environment should 
somewhat expand north-northwestward through the afternoon and 
evening. The overall tornado risk, which appears relatively modest 
overall across a broad region, should diurnally peak this afternoon 
into early/mid-evening, although some tornado risk could continue 
into the overnight and early morning hours of Friday. 

..co/Wyoming Front Range and central/southern High Plains... 
Isolated high-based storms are expected to develop by late afternoon 
along the south/southeastward-moving front spanning portions of Kansas 
into southeast NE. Where storms develop, moderate amounts of 
cape/vertical shear will allow for semi-organized clusters of storms 
capable of isolated large hail aside from a locally damaging wind 
risk with outflow dominant convection. 

Other storms are likely to develop this afternoon within an evolving 
Post-frontal upslope flow regime, with initial development along and 
just east of the Colorado/southeast Wyoming Front Range. As an increasingly 
moist environment develops into the region and the boundary layer 
destabilizes, relatively long/straight hodographs will support the 
possibility of splitting supercells capable of large hail. 
Severe-caliber wind gusts will also possible given relatively 
deep/well-mixed sub-cloud layers. 

..upper Midwest/Great Lakes... 
Ahead of a southeastward-moving cold front, a fast-moving cluster of 
storms will continue eastward from southeast Minnesota into southern WI 
today to the north of an outflow boundary and weakening convection 
across eastern Iowa/far southern WI and far northern Illinois. Widespread 
cloudiness across WI to the north of the outflow boundary should 
largely curb surface-based severe potential, with storms otherwise 
likely to develop by mid/late afternoon along the 
southeastward-moving front across Iowa and possibly into far southeast 
Minnesota/southwest WI. While the strongest winds aloft will tend to lag 
(to the west/northwest) the cold front, sufficient vertical shear 
(30-40 kt) in the presence of moderate buoyancy (generally 1500-2500 
j/kg mlcape) will yield multicells and some supercells capable of 
large hail and damaging winds especially late this afternoon into 


Mesoscale Discussion

acus11 kwns 222008 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 222008 

Mesoscale discussion 1124 
National Weather Service Storm Prediction Center Norman OK 
0308 PM CDT Thu Jun 22 2017 

Areas affected...north Georgia 

Concerning...severe potential...watch unlikely 

Valid 222008z - 222145z 

Probability of watch issuance...20 percent 

Summary...mini-supercells with a threat of a brief tornado or two 
will continue this afternoon. Limited coverage and magnitude of the 
threat makes watch issuance unlikely. 

Discussion...mini-supercell development has recently taken place 
across north Georgia, just to the northwest of Atlanta. While 
low-level flow is not quite as strong as areas further west, a very 
moist boundary layer, modest instability, and favorably veering 
low-level wind profiles will continue to support the development of 
small rotating cells through the afternoon. The greatest threat will 
likely be near and just north of a diffuse surface boundary across 
north Georgia, where surface winds are backed to more of an 
east-southeasterly direction. A tornado or two will be possible as 
these small cells interact with the surface boundary. 

.Dean/guyer.. 06/22/2017 

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


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