U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 180601 
Storm Prediction Center ac 180600 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0100 am CDT Thu Jul 18 2019 

Valid 181200z - 191200z 

..there is a slight risk of severe thunderstorms across the upper 

Areas of severe storms are possible across the upper Midwest on 

Upper ridging and weak flow aloft will remain in place across the 
central and southern Continental U.S. While enhanced westerly flow aloft 
extends from the Pacific northwest through the upper Great Lakes. A 
convectively induced shortwave will likely move across the upper 
Great Lakes early Thursday, moving into eastern Ontario by Thursday 
evening. A second shortwave trough (and associated speed max) is 
expected to move across the northern rockies Thursday evening. 

At the surface, broad area of low pressure currently in place across 
the central and northern plains expected to remain largely in place 
while Lee troughing across the High Plains deepens. Southern portion 
of a cold front associated with a low moving across the Canadian 
prairie provinces will move across the northern plains Thursday 

..upper Midwest...Upper Great Lakes... 
showers and thunderstorms will likely be ongoing across the region 
early Thursday morning. Most of these storms are expected to weaken 
as the low-level jet loses strengthen and they drift northeastward 
into a more stable air mass. The only exception is storms along the 
southern periphery of the anticipated storm cluster. In this area, 
the low-level jet will likely remain stronger longer, helping to 
maintain storm intensity as warm, moist, and unstable air is 
continually advected into the storms. The development of a 
forward-propagating convective line may occur, with the resulting 
line moving into northern Illinois and northern in. Confidence in the 
development of a convective line is currently too low to introduce 
more than 5% probabilities but higher probabilities may be needed in 
subsequent outlooks. 

During the late afternoon, scattered, predominately cellular 
thunderstorms are possible along and ahead of the cold front moving 
through the northern plains and into the upper Midwest. Despite 
dewpoints in the mid 60s, warm mid-level temperatures and only weak 
surface convergence suggest limited storm coverage. Long hodographs 
support rotating updrafts with any storms that do form. Primary 
severe threat will be strong wind gust but large hail and a tornado 
or two are also possible. 

Thunderstorms are also possible across southern Minnesota and 
central/southern WI Thursday evening. Residual outflow from 
antecedent storms combined with a strengthening low-level jet and 
the approaching front is expected to result in thunderstorm 
initiation. Dewpoints in this region are expected to be in the low 
to mid 70s with mid-level lapse rates likely around 7.5 deg c per 
km. As a result, extreme buoyancy will be in place with MLCAPE over 
4000 j/kg. Given the onset of nocturnal cooling, these storms may 
have a relatively brief window to remain surface-based. Even so, the 
strong instability coupled with modest vertical shear supports the 
potential for severe thunderstorms. Primary severe threat is 
damaging wind gusts but large hail and a tornado or two are also 

.Mosier/Bentley.. 07/18/2019 


Mesoscale Discussion

acus11 kwns 180407 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 180406 

Mesoscale discussion 1514 
National Weather Service Storm Prediction Center Norman OK 
1106 PM CDT Wed Jul 17 2019 

Areas affected...central South Dakota 

Concerning...Severe Thunderstorm Watch 521... 

Valid 180406z - 180500z 

The severe weather threat for Severe Thunderstorm Watch 521 

Summary...isolated damaging wind remains possible as storms move 
through central South Dakota next hour or two, but a longer term severe threat 
and need for a downstream ww remains uncertain at this time. 

Discussion...small cluster of storms over central South Dakota is moving east 
of ww 521. The atmosphere downstream is strongly unstable (2000-3000 
j/kg mlcape). However, temperatures have fallen into the low 70s f, 
and convective inhibition has undergone a substantial increase. 
Nevertheless, storms have consolidated a cold pool and an mesoscale convective vortex 
circulation is evident based on radar data. These mesoscale forcing 
mechanisms might be sufficient to sustain the storms another couple 
hours, but a longer-term severe threat remains uncertain given the 
increasingly hostile thermodynamic environment. 

.Dial.. 07/18/2019 

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


Latitude...Lon 44780020 45310030 45629938 45199888 44659887 44069957 
44220026 44780020