SPC MD 419


MD 0419 Image

Mesoscale Discussion 0419
NWS Storm Prediction Center Norman OK
0242 PM CDT Mon Apr 22 2019

Areas affected...Portions of eastern IA...northwest
Illinois...southwest Wisconsin

Concerning...Severe potential...Watch unlikely 

Valid 221942Z - 222145Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated severe storms, capable of producing damaging wind
gusts and marginally severe hail, will be possible over the next
several hours. A WW is not anticipated at this time.

DISCUSSION...A 1012 mb surface low is slowly translating across
Iowa, in tandem with a 500-mb shortwave trough and associated
differential CVA, providing modest deep-layer ascent to portions of
the Upper-Mississippi Valley. Marginal destabilization has
transpired over the past few hours, with limited solar radiation
penetrating the upper-level cirrus deck and warming the boundary
layer. Modest heating is expected to continue, and with the
continued deep-layer ascent slowly increasing across the area, a
gradual increase in convection may be expected throughout the
afternoon hours. 

The vertical thermodynamic profile across the area is relatively
modest, with steep sfc-3km lapse rates at nearly 8 C/km, and 7 C/km
lapse rates above 3 km (based on the DVN 18Z observed sounding), but
with mediocre low-level moisture (dewpoints mainly below 60F, with a
near 20F T/Td spread). As a result, MLCAPE is expected to remain
around/below 1000 J/kg through the afternoon, amidst 30-45 knots of
effective bulk shear and weak low-level shear, supporting a marginal
severe threat. The relatively steep low-level lapse rates may
promote damaging wind gusts with the stronger downdrafts. Given the
modest lapse rates above 3 km, a few instances of marginally severe
hail may also occur. Still, the combination of marginal deep-layer
ascent, buoyancy, and vertical wind shear, suggests that the severe
threat will be isolated, with a severe WW issuance not expected.

..Squitieri.. 04/22/2019

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


LAT...LON   41308989 41709275 42299280 42869248 43479204 43649129
            43399056 43068988 42358944 41608924 41308989 

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