U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 301942 
Storm Prediction Center ac 301940 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0240 PM CDT sun Aug 30 2015 

Valid 302000z - 311200z 

..there is a marginal risk of severe thunderstorms across parts of Montana... 

isolated severe storms with wind and hail may develop across parts 
of Montana this afternoon into mid-evening. 

With current forecast reasoning on track...no substantial changes to 
outlook areas appear required this forecast. 

.Goss.. 08/30/2015 

Previous discussion... /issued 1130 am CDT sun Aug 30 2015/ 

Morning satellite imagery depicts a lead shortwave trough moving 
through central Montana with a hard edge to the cloud deck suggesting 
strong subsidence behind the wave. Another shortwave trough -- 
embedded within the larger mean trough extending across much of western 
Canada and into the northwest Continental U.S. -- Is moving through western Washington with 
continued eastward progression into the northern rockies/northern High Plains 
anticipated. Farther east...broad upper trough extends across much of 
eastern Continental U.S. With several weak embedded vorticity maxima. A 
well-defined middle-level vorticity maximum currently moving northeastward into southeast Alabama/SW 
Georgia will continue northeastward across the Carolina Piedmont. 

15z surface analysis places the primary baroclinic zone in Montana from 
just east of ggw southwestward through bil and into western Wyoming...slightly ahead of 
the clearing line observed on visible satellite imagery. Weak 
frontal boundary also extends from SW Texas northeastward through the middle MO 
valley and into lower Michigan. 

..cntrl Montana... 
Clearing trend behind the main wave is expected to continue as the 
wave persists across central Montana...which would allow for at least 
modest heating in its wake. However...the presence of the upstream 
shortwave trough casts some doubt onto just how clear the skies get. 
Regardless...filtered sunshine coupled with downsloping southwesterly winds 
should result in good boundary layer mixing and...when coupled with 
steep middle-level lapse rates and modest moisture...some instability. 
Lift associated with the approaching shortwave trough will provide 
the impetus for thunderstorm development with guidance in good agreement 
that thunderstorm activity will begin around 21z and persist across central Montana 
through the remainder of the afternoon and evening. Strong southwesterly flow 
aloft /50-60 knots at 500 mb/ will result in strong shear profiles and 
long hodographs...supporting thunderstorm organization and at least some 
potential for high-based supercells capable of hail and gusty winds. 

... Carolinas... 
thunderstorm activity is expected across most of the area as the middle-level 
low interacts with a very moist environment. Cloudiness and 
generally moist profiles will keep instability low with a resulting 
low threat of severe. Shear will likely be enhanced somewhat from the 
central Florida Panhandle northeastward through the coastal Carolinas but most 
recent guidance as well as the recent convective burst just off the 
NE Florida coast suggest the warm sector will remain offshore...keeping 
the severe threat low. 

Mesoscale Discussion

acus11 kwns 282301 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 282301 

Mesoscale discussion 1754 
National Weather Service Storm Prediction Center Norman OK 
0601 PM CDT Friday Aug 28 2015 

Areas affected...boundary waters of northestern Minnesota 

Concerning...severe potential...watch unlikely 

Valid 282301z - 290100z 

Probability of watch issuance...20 percent 

Summary...isolated severe hail and damaging wind may accompany 
scattered storms developing southeast from Ontario through about 03z. 
Relatively limited spatiotemporal extent and overall amplitude of 
the threat should preclude a Severe Thunderstorm Watch issuance. 

Discussion...a right-moving supercell just north of Rainy Lake appears 
likely to have a severe hail core per recent mrms mesh data within 
increasing thunderstorm development across northwestern Ontario. This activity 
appears to be tied to a weak shortwave impulse evident in water 
vapor imagery crossing the border region that should also be 
supporting an increase in low-level warm air advection per afternoon model forecasts. 
The majority of cams appear a bit overeager with convective 
development thus far. But on the fringe of moderate middle-level wnwlys 
and probable steep middle-level lapse rates...it appears plausible that 
a couple transient supercells and/or a multicell cluster develops 
east-southeast across the boundary waters area through at least sunset. 
Weakening shear with southern extent and increasing mlcin will likely 
result in diminishing intensity towards late evening. 

.Grams/Darrow.. 08/28/2015 

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


Latitude...Lon 48759278 48249080 47769091 47419144 47349209 47469282 
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