Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 232019

National Weather Service Des Moines IA
319 PM CDT Sun Oct 23 2016

.SHORT TERM.../This evening through Monday/
Issued at 314 PM CDT Sun Oct 23 2016

Breezy northwest winds this afternoon will weaken into this evening
as mixing decreases and surface ridging across the northern Plains
builds into the state. The weakening pressure gradient will allow
winds to relax nicely overnight with a light north flow by daybreak.
While the airmass is relatively dry, some short term models are
indicating moistening conditions in low levels during the early
morning hours with some development of lower cloudiness in northern
IA.  Have trended toward more clouds in the north late, but still
quite uncertain as to the extend, if any of clouds prior to sunrise.
Temperatures will cool quickly in the dry airmass and should drop
all night with good radiational cooling as winds die off through the

.LONG TERM.../Monday night through Sunday/
Issued at 314 PM CDT Sun Oct 23 2016

At this point not much change to the going forecast with the
primary concern remaining in the Tuesday/Wednesday time frame. A
second similar but weaker system will impact the area next weekend
but model consensus remains all over the place.

For Tuesday the model consensus is a touch slower and a little
further south with the low and frontal boundary but by Tuesday
afternoon and night forcing dramatically increases over Iowa with a
ribbon of theta-e advection continuing to be forecast from Algona
into northwest IL. Soundings have deep saturation occurring by
that time and PWATS around an inch and a half. Heavy rain with
amounts on the order of an inch and a half to two inches possible.
Instability however is not impressive and mainly across southern
Iowa. For that reason I left the isolated thunder wording across
the north with more scattered to widespread wording south. The heaviest
rainfall amounts should still be along and north of where the
warm front sets up...which is still in some question.

The upper trough pushes across the state on Wednesday with rain
ending from west to east during the afternoon.  Thursday will be
cool but seasonally so.

For Friday an upper ridge builds west but models begin to diverge
here as the Euro noses the ridge into the upper Midwest while the
GFS drives another trough across the northern plains flattening the
pattern over the region.  Either way it will be the warmer day in
the long term.  I mention the model difference on Friday because it
will impact the weekend.  Both models develop a shortwave coming off
the Rockies but the GFS deepens the wave that passes Friday over the
Great Lakes and sharpens the ridge which slows the wave and brings
the weekend shortwave through us later and dives it further south.
Model blends are closer to the GFS solution but at this point it is
too far out and model consensus is too low to favor one solution
over another so precip trends were not altered.


.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1242 PM CDT Sun Oct 23 2016

Aviation weather continues to be quiet with dry airmass across the
state. A few low clouds may approach the northeast tonight and
will continue to monitor, however have gone with VFR conditions at
all TAF locations for duration of forecast. Surface winds will
gradually shift from northwest to northeast/east by end of period.




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