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ACUS01 KWNS 181632
SWODY1
SPC AC 181630

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Thu Jul 18 2019

Valid 181630Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE UPPER
MIDWEST...

...SUMMARY...
Isolated severe thunderstorms are expected across the Upper Midwest
mainly late this afternoon into tonight. Other strong storms with
gusty winds are possible across the Mid-Atlantic States this
afternoon and early evening.

...Minnesota/northern Iowa to Wisconsin...
Persistent bands of convection from northeast Iowa into southern
Wisconsin/northern Illinois this morning have continued to reinforce
an effective front and surface cold pool. This boundary will likely
be paramount in terms of a severe risk later today. This ongoing
precipitation should gradually wane in coverage/intensity this
afternoon, diminishing generally from west to east, as warm
advection diurnally abates.

Cold pool modification will occur with the boundary likely to shift
northward effectively as a warm front through the late afternoon and
evening. Although mid-level temperatures will generally be warming,
a conditional/isolated severe risk may exist as early as mid/late
afternoon near the roughly west/east-oriented boundary across
eastern South Dakota to southern Minnesota/northern Iowa, where
upwards of 3500-4500 J/kg MLCAPE may exist coincident with
supercell-supportive effective shear. That said, a more likely
scenario will be for storms, which may be slightly elevated, to
increase this evening across southern Minnesota and possibly far
northern Iowa into southern Wisconsin. Large hail will be possible,
particularly before possible MCS development occurs, with damaging
winds also a possibility in this scenario.

...Northern Indiana to Lower Michigan/northern Ohio...
An MCS continues to make an east-southeastward progression at midday
in the general vicinity of southern Lake Michigan. A considerable
cirrus canopy precedes this MCS and the MCS itself is not particular
organized at this time. Even so, the residual cold pool and MCV
could influence some increase in downstream thunderstorm development
across northern Indiana/southern Lake Michigan into northern Ohio.
While an overly organized severe risk is not currently anticipated,
some of these storms later this afternoon into evening could pose a
damaging wind risk.

...Western South Dakota/Black Hills vicinity...
Upper heights will weakly rise today while mid-level temperatures
will tend to warm. Even so, there is some concern that a relatively
moist boundary layer (60s F surface dewpoints), ample insolation,
and the orographic influence of the Black Hills could lead to very
isolated storm development late this afternoon. MLCAPE should
locally exceed 2000 J/kg and relatively long hodographs (45+ kt
effective shear) could support a supercell if a storm
develops/remains sustained. Low severe probabilities have been
introduced for a conditional-type severe risk.

...Mid-Atlantic States/Delmarva...
Ample insolation is evident early today particularly near/east of a
weak surface low and nearby surface trough, with surface-based
thunderstorms expected to develop/intensify through the
early/mid-afternoon hours. This should particularly be the case
across eastern portions of Maryland/Pennsylvania into New
Jersey/southern New York, southward into Virginia near/east of the
Blue Ridge. This region will be on the southern fringe of the
stronger westerlies, but steep low-level lapse rates and modest
westerly winds in the 1-3 km AGL layer will exist to pose a risk of
downbursts capable of locally damaging winds.

..Guyer/Nauslar.. 07/18/2019

$$


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