U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 191807 
Storm Prediction Center ac 191805 

Day 1 convective outlook resent 2 
National Weather Service Storm Prediction Center Norman OK 
0105 PM CDT Fri Jul 19 2019 

Valid 191630z - 201200z 

..there is a moderate risk of severe thunderstorms across 
east-central Minnesota and northern Wisconsin... 

Corrected for moderate risk line/retransmission 

A regional outbreak of severe thunderstorms with the possibility of 
strong tornadoes and widespread significant wind damage is expected 
from central Minnesota across northern Wisconsin during the mid/late 
afternoon into tonight. 

..upper Midwest/Great Lakes... 
A regional outbreak of severe thunderstorms is expected later this 
afternoon into tonight. That said, some specific uncertainties 
remain with the timing details/exact sub-regional corridor of peak 
severe-weather risk given capping/warm temperatures aloft and 
uncertainty with the decay of the cloud shield from the earlier mesoscale convective system 
across South Dakota. 

A very strong summertime belt of westerlies exists across the 
northern tier of the conus, with 50-100 kt westerlies noted between 
500/250 mb in 12z upper-air data spanning Montana to the 
Dakotas/Minnesota. Where storms develop/increase later today, this 
very strong belt of winds aloft will be influential in storm 
organization including supercells and potential evolution of a 
fast-moving mesoscale convective system (possible if not likely derecho) later 

Consult mesoscale discussion 1523 regarding midday details across 
western Minnesota. Additional surface-based thunderstorm development 
may emanate from the ascent/differential heating related to the mesoscale convective system 
remnants, focusing downstream surface-based severe potential across 
central Minnesota. An extremely unstable air mass (mlcape >4000 
j/kg) will continue to become established from southeast southeast 
South Dakota through central/southern Wisconsin as the elevated 
mixed-layer overspreads surface dew points rising into the mid to 
upper 70s. A surface cyclone over central south Dakotas should track 
towards the Twin Cities through early evening. Strong low-level 
convergence near/northeast of this cyclone along the warm front 
should sustain surface-based storm development across central into 
east-central Minnesota. 

Intense supercells are likely to develop rapidly, with an attendant 
threat for all severe hazards including the possibility of a strong 
tornado or two amid 50-60 kt effective shear and 0-3 km srh >300 
m2/s2. The very warm/moist thermodynamic profiles will also support 
generation of strong cold pools which should eventually yield a 
bowing, forward-propagating mesoscale convective system across northern Wisconsin into parts 
of northern lower and Upper Michigan. Strength of the vertical shear 
suggests the potential for intense bowing segments capable of 
yielding a derecho with significant/widespread severe wind gusts. 

..lower Great Lakes/northeast states... 
Have upgraded parts of the region for thunderstorm-wind related 
potential this afternoon into evening. This will be related to the 
possible east-southeastward persistence of a complex of storms 
across Ontario and additional scattered development that is expected 
in the Lee of the lower Great Lakes. The ambient air mass will be 
moderately to strongly unstable but the region will generally be 
south of the stronger westerlies aloft. The overall expectation is 
for predominantly multicellular, outflow-dominant storms capable of 
isolated damaging wind gusts this afternoon and evening. 

..South Dakota tonight... 
Another round of 700-mb warm/moist advection will occur tonight 
within a tight baroclinic zone well north of a surface front arcing 
across Nebraska into northeast Wyoming. Large elevated buoyancy and 
strong effective shear will support a risk for isolated large hail. 
While storms will generally tend to be elevated, there may be some 
wind damage potential if upscale quasi-linear growth occurs late 
tonight as storms progress east-southeastward across South Dakota. 

.Guyer/Wendt.. 07/19/2019 


Mesoscale Discussion

acus11 kwns 191854 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 191853 

Mesoscale discussion 1526 
National Weather Service Storm Prediction Center Norman OK 
0153 PM CDT Fri Jul 19 2019 

Areas affected...much of central Minnesota 

Concerning...severe potential...Tornado Watch likely 

Valid 191853z - 192130z 

Probability of watch issuance...95 percent 

Summary...storms are expected to form over west-central Minnesota 
around 20-21z, with supercells possible initially. Tornadoes and 
large hail are likely. A damaging wind threat is expected later 
today as storms merge into an mesoscale convective system. 

Discussion...the combination of satellite imagery and surface 
observations show an east-west oriented outflow boundary across 
southern Minnesota, with low pressure over east-central South Dakota into southwest 
Minnesota. A very warm, moist, and unstable air mass exists along and south 
of the boundary where temperatures continue to rise above 90 f. 
While temperatures north of the boundary are relatively cooler, 
rapid recovery will occur due to southwest flow just above the 
surface combined with mixing. Substantial pressure falls are 
occurring over the cooler air, mainly due to warm advection just off 
the surface. 

Deep, moist convergence is currently centered over west-central Minnesota, 
and this is where several models suggest initiation will occur. This 
seems reasonable, especially once warmer temperatures > 90 f arrive. 

Backed surface winds are contributing to 0-1 srh values in excess of 
300 m2/s2, with relatively low LCLs near the boundary, and extreme 
instability. This will certainly support supercells and tornadoes, 
assuming discrete cells. As such, a Tornado Watch will be needed 
soon. Eventually, storms will merge into an mesoscale convective system with a damaging wind 

.Jewell/guyer.. 07/19/2019 

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


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