Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 122044

Area Forecast Discussion
National Weather Service Des Moines IA
344 PM CDT Tue Sep 12 2017

.SHORT TERM.../Tonight through Wednesday/
Issued at 341 PM CDT Tue Sep 12 2017

Tonight into Wednesday...The main focus of the forecast was on
temperatures.   Large surface high pressure remains in control of
the weather pattern with the remnants of the Irma lurking southeast
of the state. Some high clouds from Irma have made its ways into
southern portions of the Iowa, but are not making a huge impact on
temperatures this afternoon. However, these high clouds may stick
around for much of the evening as the remnants of Irma slowly
migrate northeast into the mid-Atlantic. Still, these clouds are
thin and broken enough not to be too concerned for an influence on
temperatures tonight. The other minor concern is fog across the
northeast towards sunrise Wednesday.  No mention attm with the
amount of dry air and large dewpoint depressions, but certainly
cannot rule out some very low fog.

.LONG TERM.../Wednesday night through Tuesday/
Issued at 341 PM CDT Tue Sep 12 2017

Remnants of Irma will continue to lift into the Ohio Valley then off
to the Northeast.  Any precip from this will be confined to far
southeast Missouri, Illinois and Indiana.  High clouds is all Iowa
will see from this system.  Otherwise we will be in in weak ridging
aloft with a surface high drifting east through Wednesday night.
Over the West, a trough will evolve which will enhance the ridge
over the Midwest.  The result of this will be warmer temps and
increasing moisture from late Wednesday through Friday.  We will see
temps approach 90 across the South Thursday and Friday. A couple of
shortwaves will move across the flow and try to break down the ridge
and between this upper level disturbance and increasing instability
with periodic waves of theta-e advection, we will see a chance for
showers and an isolated thunderstorm or two from late day
Thursday/Thursday night into Friday mainly west and north.

There should be a break in precip chances Friday but Friday night
through Sunday the upper trough over the west will advance across
the Rockies and pivot across the Northern Plains.  A surface low
will mature over the Plains and advance across the region Saturday
through early Sunday.  this will drive a cold front across Iowa
during the day Saturday which will extend from the Great Lakes,
across Illinois and somewhere across southern Iowa or Northern
Missouri by mid day Sunday.  Showers and thunderstorms are expected
along the front though it appears that the better forcing will occur
behind the front so coverage will be more scattered than widespread
Saturday becoming a little more widespread Saturday night.  Shear
will be sufficient for a few storms to be severe though given the
questionable forcing will hold off on determining specific threats
just yet. The rest of Sunday into Monday will be dry as a surface
high builds into the region.

The next shot of precip may come as early as Monday night but more
likely Tuesday.  Model differences were enough that confidence was
low enough to go with model blends at this point.


.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1221 PM CDT Tue Sep 12 2017

VFR conditions will prevail throughout the entire TAF period. Low
potential for widespread fog development Wednesday morning and
left out mention attm, but certainly cannot completely rule out
some brief MVFR visibility b/t 09-13z Wednesday.




SHORT TERM...Podrazik
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