Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 092357

Area Forecast Discussion
National Weather Service Des Moines IA
657 PM CDT Wed Aug 9 2017

.SHORT TERM.../Tonight through Thursday/
Issued at 341 PM CDT Wed Aug 9 2017

An area of showers over northern Iowa are mainly driven by warm
air advection around 700mb this afternoon. This has been a
persistent, slow area of rainfall today with Estherville
receiving nearly three quarters of an inch. Lighting with these
showers has been with limited to non-existent. This area of rain will
continue to slowly slide off to the east this afternoon, but
should begin to dissipate this evening. Behind this area of rain,
some clearing may allow for additional showers and thunderstorms
to form late this afternoon and evening. However, instability will
be modest at best with bulk shear generally between 25 to 30
knots so most storms should stay below severe limits. Otherwise
tonight, clouds should be widespread much of the night with lows
in the 60s except far northern Iowa with upper 50s.

The next weather feature to impact our weather locally is viewed
in 20z water vapor imagery with a compact shortwave spinning into
western North Dakota. As this moves southeastward tonight and
into the Great Lakes tomorrow, may see additional showers and
isolated storms try to develop. While instability will be a bit
better tomorrow, shear appears to be lower than this afternoon. In
addition, low levels are rather dry. This all means that any rain
chances will not be widespread with amounts on the low side. The
most favored area for any rain would be southern Iowa.

.LONG TERM.../Thursday night through Wednesday/
Issued at 341 PM CDT Wed Aug 9 2017

In the wake of the shortwave departing into the Great Lakes, cold
air advection with winds from the northwest will usher back in
slightly cooler and drier air to the state. Any lingering showers
will be across far southern Iowa and be clear of the state by
Friday sunrise. As high pressure builds over the northern Plains,
it will provide for a dry day with ample sunshine with
temperatures at least a few degrees below normal.

Into the weekend, a stretched, broad PV anomaly will begin to
have an effect on our weather as it starts to drop out of Canada
into the northern Rockies. This will bring an increase of cloud
cover on Saturday with chances for showers and storms returning
late Saturday into Sunday. However, easterly flow and drier mid-
levels may limit the rainfall potential.

Continued low-end precipitation chances will persist through early
next week along with below normal temperatures with northwest flow
aloft. In coordination with neighboring offices, did remove rain
chances Monday afternoon and night leaning toward the 12z runs of
the GFS/ECMWF, which have the area dry. Meanwhile, the 12z CMC
had precipitation due to high pressure being closer to the
forecast area compared to the GFS/ECMWF.


.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 657 PM CDT Wed Aug 9 2017

Isolated showers will continue to be a threat overnight ahead of
an approaching cold front. However, with relatively dry low
levels, conditions will be mainly VFR for the duration of the
forecast. Most ceilings will remain in the mid to high levels with
little restriction to visibilities other than from the isolated
showers. Winds will be south to southwest overnight becoming
westerly on Thursday.





SHORT TERM...Ansorge
LONG TERM...Ansorge
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