SPC MD 1968


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Mesoscale Discussion 1968
NWS Storm Prediction Center Norman OK
0346 PM CDT Thu Sep 12 2019

Areas affected...Southeastern Minnesota...northeastern
Iowa...west-central Wisconsin

Concerning...Severe Thunderstorm Watch 648...

Valid 122046Z - 122245Z

The severe weather threat for Severe Thunderstorm Watch 648

SUMMARY...The threat for all severe hazards will continue in WW 648
for at least a few hours. Discrete storms ahead of the ongoing
linear segment pose the greatest tornado threat as they interact
with the warm front. Threat will transition to mainly damaging winds
as the linear segment overtakes discrete activity with time. A
downstream Severe Thunderstorm Watch is possible later this evening.

DISCUSSION...While a cluster of storms has congealed along the MN/IA
border, discrete activity has continued to increase ahead of this
linear segment with a storm in Howard County, IA showing increasing
low-level rotation per KARX radar velocity data. Given the effective
SRH of 200-300 m2/s2 along the warm front, any discrete activity
will be capable of producing a tornado. The tornado threat will
likely be limited spatially as the linear segment is likely to
overtake the discrete storms out ahead of it within the next few
hours. Furthermore, RAP forecast soundings show storms are likely
marginally surface based as cloud cover has limited low-level
destabilization. As such, the threat for damaging wind gusts will be
on the increase this evening with storm mode transitioning to linear
with time. Storms may form along the cold front in western portions
of WW 648; however, a mainly linear mode and ongoing upstream
activity should limit their severity.

Areas downstream of Tornado Watch 648 will likely be considered for
a Severe Thunderstorm Watch later this evening conditional on the
intensity of the line segment forecast to move east along the
northward lifting warm front.

..Wendt.. 09/12/2019

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   44109377 44599294 44839126 44398971 44068945 43508955
            42778993 42579008 42509015 42529059 42599203 43119335
            43699377 44109377 

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