U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 220541 
Storm Prediction Center ac 220540 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1240 am CDT Fri Sep 22 2017 

Valid 221200z - 231200z 

..there is a slight risk of severe thunderstorms across portions of 
northeast North Dakota and northern Minnesota... 

..there is a marginal risk of severe thunderstorms surrounding the 
slight risk...and extending south-southwestward to eastern New 
Mexico/far West Texas... 

Scattered thunderstorms are expected to pose a severe risk across 
northeast North Dakota into northern Minnesota, mainly during 
afternoon and into the evening. Isolated severe risk is possible 
southward into the central and southern High Plains during the 
afternoon and into the evening. 

Highly amplified upper flow is forecast across the U.S. Today, with 
little progression expected as a Stout Ridge remains over the 
central and eastern states and a trough encompasses the west. 

At the surface, a weak low initially over the South Dakota vicinity 
is forecast to move north-northeastward with time along a baroclinic 
zone, crossing Minnesota and moving into western Ontario late in the 
period. Meanwhile, the trailing cold front in the wake of the low 
is expected to make slow southward progress across the Central 

..parts of northeast North Dakota into northern Minnesota... 
Weak short-wave troughing within the otherwise weakly anticyclonic 
flow field aloft is forecast to cross the Dakotas during the 
afternoon, in conjunction with surface-low progression into the 
western Minnesota vicinity. Elevated storms are expected to develop 
during the afternoon north of the low, spreading east across 
northeast North Dakota/northern Minnesota and adjacent southern 
Manitoba/western Ontario. With diurnal/surface-based development in 
the warm sector not expected due to capping, main severe risk will 
be large hail with stronger/elevated storms. 

A few additional storms -- elevated above a diurnally cooling 
boundary layer -- may evolve across the Minnesota vicinity during 
the evening, to the cool side of the cold front moving slowly 
southeast in the wake of surface low passage. Some risk for hail 
would also exist in this scenario, possibly continuing into the 
overnight hours. 

..mid-Missouri Valley area south-southwest to the southern High 
isolated afternoon convection is expected to develop across portions 
of the central and particularly the southern High Plains, as heating 
supports ample afternoon destabilization. This region will likely 
remain on the far eastern fringe of stronger/weakly cyclonic flow 
aloft, with shear thus likely to become sufficient for weakly 
organized updrafts. Risk for large hail and locally damaging gusts 
with a couple of the strongest cells will likely exist during the 
afternoon, diminishing diurnally into the evening hours. 

Farther north into the mid-Missouri Valley, the eventual/slow 
southward advance of the cold front in the wake of surface low 
passage may support development of a few storms during the afternoon 
-- with somewhat more widespread evening development of elevated 
storms possible near/to the cool side of the front. While locally 
gusty winds may occur locally during the afternoon, hail with a few 
more robust/elevated storms will likely become the main risk during 
the evening/overnight. 

.Goss/Gleason.. 09/22/2017 


Mesoscale Discussion

acus11 kwns 220911 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 220910 

Mesoscale discussion 1664 
National Weather Service Storm Prediction Center Norman OK 
0410 am CDT Fri Sep 22 2017 

Areas affected...parts of central into northeastern Minnesota 

Concerning...severe potential...watch unlikely 

Valid 220910z - 221145z 

Probability of watch issuance...20 percent 

Summary...strong storms with gusty winds or marginally severe hail 
are expected to persist across parts of central Minnesota into 
northwest Wisconsin this morning, but the severe threat appears too 
localized for a watch. 

Discussion...scattered storms continue to develop over the area in a 
region of Theta-E advection associated with a 40-50 kt southwesterly 
low-level jet and warm front. The air mass feeding into these storms 
is very moist and unstable, but shear in the cloud-bearing layer is 
very marginal for a sustained severe threat. 

Though most cells have tended to be pulse in nature, one larger 
cluster over central Minnesota may be able to produce some cold pool of 
consequence if it continues to grow in size. The low-level jet will 
tend to veer with time, shunting the lift from warm advection 
farther northeast. Any additional cells may contain a marginal hail 
threat for a short period of time, with wind threat conditional on 
clusters maintaining themselves long enough to produce a cold 

.Jewell/grams.. 09/22/2017 

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


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