Area Forecast Discussion
Issued by NWS Des Moines, IA

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024
FXUS63 KDMX 261157
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
657 AM CDT Tue Sep 26 2017

.SHORT TERM.../Today through Tonight/
Issued at 355 AM CDT Tue Sep 26 2017

At the surface the cold front will be over far eastern Iowa at 12Z
and continue to move towards the Great Lakes through the day.  To
the west, high pressure will build into the region.  Aloft, the
upper low and associated trough will swing northeast.  Precip will
move into eastern portions of the forecast area by 18Z and be out of
the state by mid afternoon.  A weak vort max lifting across the
forecast area this morning along with some forcing will be enough
for some isolated storms especially south this morning but by mid to
late morning any threat of storms will be east of the forecast area.
There is a pretty broad area of low clouds over the Upper Midwest
and into the Plains so even though the rain ends, I am not looking
at much in the way of clearing until mid to late afternoon.

Cooler and drier air move in for tonight and for the first time in
awhile we will see temperatures tonight at or slightly below normal
with lows from the mid 40`s to the mid 50`s.

.LONG TERM.../Wednesday through Monday/
Issued at 355 AM CDT Tue Sep 26 2017

Area of high pressure will be in place across Iowa on Wednesday in
conjunction with the thermal trough moving through the area. Sunny
skies and cool conditions will prevail with high temperatures in
the 60s to near 70. Despite the area of high pressure, the wind
will be breezy by the afternoon with good mixing occurring to
around 850 mb. A vigorous short wave will drop southeast through
Minnesota on Thursday. Iowa will be mainly in the subsidence
region of the upper short wave therefore the threat for
precipitation will be quite low. Mixing will be deeper on Thursday
and nearing 700 mb. Therefore the diurnal breezy winds can be
expected again. The short wave dropping southeast and the upper
level ridge developing to the west will lead to northwest flow
aloft for Iowa by Friday. This will allow another surge of colder
air to drop south into the state Friday into the early portion of
Saturday. Friday nights temperatures will be cool with lows in the
40s and potential a few 30s across the north as winds drop off
with the arrival of high pressure.

Warm advection will arrive late Saturday and into Sunday as the
area of high pressure moves east and upper level ridging moves
east into the Midwest. High temperatures on Sunday will be well
into the 70s. Precipitation chances will arrive by early next
week though the typical seasonal transition issues are beginning
to show up in guidance. Timing and placement issues with several
highly amplified systems moving into the Pacific Northwest and the
strength of the subtropical high over the southeast CONUS are
creating less certainty by days 6-7. The overall pattern with lead
to southwest flow into Iowa and eventual moisture return. The
ECMWF being much more amplified with the subtropical high and a
bit farther west resulting in less Gulf moisture for the region.
The GFS is much more aggressive with moisture return just beyond
the extended.

&&

.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 657 AM CDT Tue Sep 26 2017

Cold front to continue to push east.  precip behind the front is
tied to an upper level system that will lift northeast today as
well.  winds will shift to the NW across all TAF locations by 18Z.
LIFR cigs will gradually lift to MVFR cigs by afternoon then become
VFR late in the day.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...FAB
LONG TERM...Donavon
AVIATION...FAB



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