Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 230822
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
322 AM CDT Wed Aug 23 2017

.SHORT TERM.../Today through Tonight/
Issued at 322 AM CDT Wed Aug 23 2017

Large area of high pressure situated across NE/KS to translate
eastward across IA and southeastward into MO/IL tonight. Northwest
flow pattern in place aloft, with a shortwave trough to drop
southeastward through MN/IA tonight. Theta-e advection to increase
with WAA as well, which should result in increasing cloudiness
through the night. As the moisture increases by late tonight could
see some light showers develop/spread across far northeastern
portions of the forecast area toward sunrise. Slightly better
chances just beyond into Thursday morning. Cooler temperatures
remain in place today, however with WAA kicking in should see temps
climb slightly above readings from Tuesday. Winds should be lighter
today, and shift around to the southeast tonight.

.LONG TERM.../Thursday through Tuesday/
Issued at 322 AM CDT Wed Aug 23 2017

The long term forecast remains quiet, with steady temperatures and
some light rain chances but nothing of significant impact. On
Thursday a large mid/upper level trough will be moving away to our
east over the Great Lakes region, while a modest deep layer ridge
builds over the Rockies and High Plains. This will be a classic
"dirty ridge" with subtle shortwave impulses and vorticity maxima
embedded within it, and will slowly progress eastward in the later
part of the week around Friday and Saturday. This will result in
low POPs being carried through much of this period, especially
across our northern counties where subsidence associated with the
broad ridge will be weaker. However, instability and moisture will
be very limited so all that is forecast are a few light showers
and possibly a thunderstorm or two.

Around Saturday night a pattern change will begin to take place,
with two features of interest. The first will be the remnants of
tropical cyclone Harvey, currently over the Bay of Campeche, which
all prognostic models re-intensify and bring up along the Texas
coast over the weekend. The second will be a broad mid/upper level
trough digging across central Canada. This trough will slide
eastward until it encounters a weakness to the south, over our
region, as a result of the aforementioned impulses embedded within
the weak ridge preceding it. The Canadian trough will then dig
down into the Midwest, exploiting this weakness, and becoming
established over the Minnesota/Iowa/Wisconsin area by around
Sunday night. This will bring somewhat more widespread rain
chances to our forecast area around Sunday and Monday, however,
again only scattered light showers are anticipated with possibly a
few thunderstorms, and no severe weather. Beyond this the primary
question will be how the Upper Midwest trough interacts with
whatever tropical cyclone had been previously stalled in southeast
Texas, whether it digs this cyclone out and ejects it
northeastward, or whether it leaves it behind near the western
Gulf coast, and what this will mean for our steering flow over
Iowa next week.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1203 AM CDT Wed Aug 23 2017

There is high confidence in VFR conditions through the period with
little in the way of clouds. Winds should generally be light and
variable, outside of a subtle W to NW increase during peak mixing
of the day.

&&

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

&&

$$

SHORT TERM...Beerends
LONG TERM...Lee
AVIATION...Small


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