U.S. Severe Weather Forecast (Convective Outlook)

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000 
acus01 kwns 200557 
swody1 
Storm Prediction Center ac 200555 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1255 am CDT Fri Sep 20 2019 


Valid 201200z - 211200z 


..there is a slight risk of severe thunderstorms across parts of 
the northern plains into parts of the Central High plains... 


... 
Scattered severe storms associated with wind damage, isolated large 
hail and a couple tornadoes are possible today across the northern 
plains, with marginally severe storms possible in parts of the 
central and southern High Plains. 


..northern plains... 
An upper-level low will move northeastward into the northern rockies 
today as an associated trough moves across the intermountain west. 
Ahead of the system, south-southwesterly mid-level flow will be 
located across much of the central and northern plains. 
Strengthening low-level flow ahead of the system will help to 
reinforce a moist airmass from the Dakotas eastward across 
Minnesota. A cold front will advance eastward into the western 
Dakotas today where thunderstorm development may take place along 
the front early this afternoon. Thunderstorms are expected to 
increase in coverage as the front moves eastward across the central 
Dakotas late this afternoon. Additional thunderstorms may develop in 
the Post-frontal airmass in southeast Montana and northeast Wyoming. 
As convective coverage maximizes in the evening, linear mesoscale convective system 
development will be possible from far northwest Minnesota 
southwestward into south-central North Dakota and west-central South 
Dakota. 


Concerning the severe weather potential, surface dewpoints by 
afternoon should range from the mid 60s f in the central Dakotas to 
the lower 70s in central Minnesota. In response, moderate to strong 
instability is forecast to develop by late afternoon with MLCAPE 
values reaching 3000 to 4000 j/kg in some locations ahead of the 
front. Forecast soundings along the western edge of the strongest 
instability show moderate deep-layer shear profiles with 0-6 km 
shear in the 30 to 40 kt range. This should support an organized 
severe threat from late afternoon throughout the evening. Although 
supercells with isolated large hail will be possible with storms 
that remain discrete, the more dominant Mode is expected to be 
linear as an mesoscale convective system forms along and ahead of the front. Wind damage 
will be possible along the leading edge of the squall-line. An 
isolated tornado threat may also occur with any supercell that can 
develop or with rotating cells embedded in the line. The squall-line 
is forecast to move across northwestern Minnesota, eastern North 
Dakota and central South Dakota during the evening and continue 
moving slowly eastward through the overnight period. 


..southern and Central High plains... 
Southwest mid-level flow will be in place today across the southern 
and Central Plains. At the surface, a Lee trough will deepen across 
eastern Colorado and eastern New Mexico. To the east of the trough, 
surface dewpoints should range form the mid 60s f in western Kansas 
to the lower 70s in the southeastern Texas Panhandle. In response to 
the moist airmass, a north-to-south corridor of moderate instability 
is expected to develop by early afternoon. Model forecasts suggest 
that thunderstorm development will be most likely on the southern 
end of the strongest instability from the southern Texas Panhandle 
into parts of West Texas where low-level convergence should be 
enhanced. NAM forecast soundings at Amarillo and Lubbock by late 
afternoon show MLCAPE peaking around 1500 j/kg. In addition, 0-6 km 
shear values are forecast to be in the 35 to 45 kt range. This 
environment suggests that isolated severe storms with hail and 
strong gusty winds will be possible. The amount of instability is 
expected to be too marginal for a more substantial severe threat. 


.Broyles/karstens.. 09/20/2019 


$$ 

Mesoscale Discussion


000 
acus11 kwns 192238 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 192238 
nez000-ksz000-192345- 


Mesoscale discussion 1986 
National Weather Service Storm Prediction Center Norman OK 
0538 PM CDT Thu Sep 19 2019 


Areas affected...south-central Nebraska and into northwest Kansas 


Concerning...severe potential...watch unlikely 


Valid 192238z - 192345z 


Probability of watch issuance...20 percent 


Summary...local severe risk is evident across portions of 
southwestern and into south-central Nebraska, where isolated 
updrafts have quickly developed. Risk should remain limited in area 
and duration. 


Discussion...latest visible satellite loop shows a couple of intense 
updrafts which have developed near a subtle/westward-moving Gravity 
wave, that currently arcs from southwest Nebraska southeastward into 
central Kansas, and then eastward into central Missouri. The 
thermodynamic environment within which the convection is developing 
is quite favorable for robust/tall updrafts, given very steep lapse 
rates aloft and a warm/moist boundary layer combining to yield 3000 
to 4000 j/kg mixed-layer cape, per recent objective analysis. 


With that said, deep-layer shear is relatively weak, despite 
low-level veering, owing to weak westerly winds at mid levels. The 
relative lack of kinematic contribution to updraft intensity 
therefore suggests only multicell organization for the most part, 
with risk for hail and/or wind likely to remain local/isolated. In 
addition, the threat should remain fairly limited in overall 
duration, with storms likely to diminish after dark as the boundary 
layer cools/stabilizes. Until then, hail up to Golf Ball size, and 
wind gusts up to or slightly exceeding severe criteria will be 
possible. 


.Goss/Edwards.. 09/19/2019 


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


Attention...WFO...Gid...lbf...gld... 


Latitude...Lon 41619871 40219862 39549931 39900073 41320143 41650095 
41809987 41619871