U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 191624 
Storm Prediction Center ac 191623 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1123 am CDT Tue Sep 19 2017 

Valid 191630z - 201200z 

..there is an enhanced risk of severe thunderstorms from the 
eastern Dakotas into western Minnesota... 

..there is a slight risk of severe thunderstorms from the northern 
plains into the upper Mississippi Valley... 

..there is a marginal risk of severe thunderstorms surrounding the 
slight risk area... 

..there is a marginal risk of severe thunderstorms from West Texas 
into southwest Oklahoma... 

Severe storms with a threat for a few tornadoes, numerous large hail 
and damaging wind events, a few of which should be significant, are 
expected across parts of the eastern Dakotas into western Minnesota 
from about 4 PM to 4 am CDT. 


Satellite and rap analysis data indicate several impulses moving 
through a broad synoptic upper trough that is situated over the 
northwestern states. A lead shortwave trough is currently moving 
northeast through eastern Montana into western ND, and an upstream 
impulse will affect this region this afternoon. 

..central and eastern Dakotas into Minnesota... 

Late this morning a cold front extends from a weak surface low 
through the western Dakotas into eastern Wyoming preceded by a 
pre-frontal trough. A warm front stretches from central Minnesota through 
southern and western ND. Low to mid 60s f boundary layer dewpoints 
will advect through pre-frontal warm sector beneath plume of steep 
lapse rates, sampled by 12z raobs, contributing to a corridor of 
moderate instability with 1500-2500 j/kg MLCAPE. However, strong 
convective inhibition associated with the elevated mixed layer and 
widespread multi-layer clouds should delay more robust thunderstorm 
development until late afternoon. Mid-level convection embedded 
within multi-layer cloud plume will continue spreading through the 
warm sector with limited solar insolation. This and strong 
convective inhibition suggest most of the robust thunderstorm 
development will probably remain confined to the zone of stronger 
forcing along eastward-advancing cold front during the late 
afternoon. The low-level jet will strengthen within the exit region 
of an approaching mid-upper jet resulting in strong (45-55 kt) 
effective bulk shear supportive of organized severe storms. Mixed 
modes with both supercells and linear bowing segments are expected 
early in the storms evolution, with a gradual trend toward upscale 
linear growth during the evening. Tornadoes, very large hail and 
damaging wind are all possible. Overall tornado threat will depend 
to some degree on Mode evolution and appears to be greatest in 
corridor from northeast South Dakota into southeast North Dakota. 
Later this evening into overnight storms will continue into the 
upper Mississippi Valley with damaging wind becoming the primary 

..West Texas to southwest OK... 

The dryline will be the focus for isolated to scattered storm 
development late afternoon to early evening. Steep 700-500 mb lapse 
rates of 7-8 c/km will support moderate buoyancy with MLCAPE 
reaching 1500-2500 j/kg. While mid-level winds will be modest, 
veering of the wind profile with height should yield 25-30 kt 
effective shear, supporting a few transient supercell and multicell 
clusters. Isolated occurrences of large hail and damaging winds are 
possible before storms wane after sunset. 

.Dial/Broyles.. 09/19/2017 


Mesoscale Discussion

acus11 kwns 172244 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 172244 

Mesoscale discussion 1654 
National Weather Service Storm Prediction Center Norman OK 
0544 PM CDT sun Sep 17 2017 

Areas affected...east New Mexico...southeast Colorado...and the 
Texas and Oklahoma panhandles 

Concerning...Severe Thunderstorm Watch 486... 

Valid 172244z - 180015z 

The severe weather threat for Severe Thunderstorm Watch 486 

Summary...isolated to widely scattered storms capable of producing 
downburst winds and large hail will persist through at least 01z 
over the southern High Plains. However, a gradual weakening trend 
should commence with onset of nocturnal cooling. 

Discussion...storms continue spreading off the higher terrain of Colorado 
and nm and are also developing along southwestern extension of a 
front as well as in association with numerous outflow boundary 
interactions over the Texas Panhandle. Latest objective analysis shows 
the atmosphere to be moderately unstable in this region with 1500 
j/kg MLCAPE and 7-7.5 c/km mid-level lapse rates. Moreover, easterly 
low-level winds north of the front beneath modest southwesterly 
winds aloft is resulting in sufficient (35-40 kt) effective bulk 
shear for a few storms to develop mid-level updraft rotation. The 
stronger storms will continue to pose a severe risk next couple 
hours followed by an overall weakening trend as the boundary layer 
begins to stabilize. 

.Dial.. 09/17/2017 

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


Latitude...Lon 38570361 38000247 35810095 34200042 33330115 32480305 
32770428 35480487 37970485 38570361