Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 222332

Area Forecast Discussion
National Weather Service Des Moines IA
632 PM CDT Sun Sep 22 2019

.DISCUSSION.../Tonight through Sunday/
Issued at 335 PM CDT Sun Sep 22 2019

The rain has moved off with the exception of patchy drizzle or some
sprinkles...which is expected to move off before this evening. High
pressure nosing in will bring cooler and drier air into the state
tonight through Monday.  Soundings show some residual low level
moisture far south/southeast for some fog potential but it will be
fighting the drier air moving in.  I did keep some patchy fog far
south with the heavy rainfall that occurred down there.  Not
expecting it to be an issue but lower lying areas may see lowered

On Tuesday, warmer air and more moisture pushes back into the state
ahead of the next system.  Aloft a trough will push across the
Northern Plains and Rockies during the day and deepen some across
the Upper Midwest from late afternoon through Tuesday night. At the
surface, a cold front will make it`s way across the state Tuesday
night.  Forecast soundings show increasing winds with height and by
Tuesday evening, a 90kt jet will be over northern Iowa. Moisture and
instability will be slowly increasing through the day. Through 18Z
the instability is still west of Iowa but by 21Z it`s nosing into
western/central Iowa and by 00Z we will see 2000 J/Kg of CAPE across
much of the area. Likewise, deep layer shear increases through the
day across us, maximizing in the evening.  At this point the models
seem to keep the best shear behind the front but despite the timing
of the front and the best shear being behind the front...the amount
of instability and shear present along the boundary will be enough
for thunderstorms to develop.  There will some severe storms Tuesday
evening given the setup.  Large hail and damaging wind look to be the
threats but SPC has an isolated tornado threat highlighted as well.

The upper trough swings east Wednesday morning ending the storm and
precip threat.  Cooler air will move in for Wednesday once again
with fall-like highs in the 60s and 70s for Wednesday and Thursday.

Thursday night through Friday, a similar situation to Tuesday night
sets up with another deep upper trough dropping through the Rockies,
increasing a southwest flow over the region bringing more moisture
and warmer temps back to Iowa.  Models develop two surface lows
dragging a warm front up across Iowa Thursday night...mainly late
then pushing a cold front through the state later Friday or Friday
night.  Once again, shear and instability increase along the
boundary but timing questions between the models remain.  Still
looks like our next best chance for showers and storms.  The pattern
is a bit of a broken record with ridging moving back for Saturday
and Sunday then Monday another trough develops west and shoots a
shortwave across the region Sunday night and Monday. So other than
brief cool downs with frontal passages the next week looks above
normal with temps and periodic chances for strong storms.


.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 632 PM CDT Sun Sep 22 2019

Few overall concerns this period other than lingering MVFR cigs
and band of -shra now moving through sites KMCW/KALO/KOTM as
secondary cool front drops south through 02z. Aft passage of
trough, winds become northwest and light/var aft 04z with light
winds expected remainder of period with VFR conditions. Weak
return warm air advection aft 18z Monday will produce patch of VFR
mid level cigs nearer KALO/KMCW through 06z with light WSW winds
returning. /rev




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