Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 130538
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1138 PM CST Fri Jan 12 2018

.SHORT TERM.../Tonight through Saturday/
Issued at 339 PM CST Fri Jan 12 2018

Weak short wave energy will drop south through South Dakota and
Nebraska tonight with some modest vertical ascent within the mid
level moisture field. Surface flow originating from the large Arctic
high pressure moving south from the Dakotas will keep profiles quite
dry below 850 mb. A few flurries are possible west of Interstate 35
but not much else precipitation wise. Afternoon temperatures remain
quite cold and generally in the 3 to 12 above range. Main challenges
for tonight will be increasing clouds from the west northwest then
timing of clearing over the north. The clouds will provide some
insulation and will keep temperatures from falling as much as in the
clearing regions. The northern one third to one half of Iowa should
be clearing by late tonight into Saturday morning to allow
temperatures to fall into the 5 to 15 below range and combined with
northernly winds of 5 to 10 mph, will drop wind chill values into
the 20 to 30 below range. Will be issuing a wind chill advisory for
these regions and generally encompasses areas along and north of
Highway 30.

The Arctic high pressure will pass across Iowa on Saturday and will
continue the clearing skies and cold temperatures. High temperatures
will be near to slightly warmer than today.

.LONG TERM.../Saturday night through Friday/
Issued at 339 PM CST Fri Jan 12 2018

The short wave that will bring light snow to portions of the Midwest
Saturday night into early Sunday is tracking more to the southwest
and will be minimal impact to the area outside light snow potential
over the far southwest. Any accumulations will be an inch or less. A
more significant short wave and Arctic boundary will arrive late
Sunday into Sunday night. The majority of the kinematic forcing
associated with the upper short wave will move across Minnesota and
Wisconsin, however, a portion of the energy will move through
central and northeast Iowa. In addition the exit region of the upper
level jet will be focused across Iowa and will create additional
vertical ascent. A deep dendritic layer will develop with this
system from the surface to near 13 kft and will promote dendritic
growth. The moisture profiles are a bit unorganized and the
separation between this system and another moving through western
Nebraska and Kansas may cause a precipitation split over central and
southwest Iowa. As of now, snowfall amounts of 1 to 2 inches are
possible especially over the northeast forecast area and lesser
amounts elsewhere. The wind cold become a factor as well with wind
gusts of 35 mph or greater will be possible as the Arctic air
arrives.

The arrival of the Arctic air and expected winds will bring
extremely cold wind chill values to the area by Sunday night through
Tuesday morning. Wind chill values of 20 to 35 below will be common
by Monday morning with little improvement through the day. Wind
chill values may approach 40 below over northern Iowa by Monday
night into Tuesday morning. Wind chill headlines are anticipated
through this period. Little to no significant weather is forecast
through the remainder of the extended. The cold upper trough across
the region will break around Wednesday followed by a transition to
more zonal to southwest flow by Friday and should bring high
temperatures back into the 30s and 40s to end the period.

&&

.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1137 PM CST Fri Jan 12 2018

Widespread VFR ceilings will persist overnight, mainly across the
southwest half of Iowa with gradual clearing on Saturday morning.
Visibilities will be unrestricted for the duration of the forecast
with north to northwest winds through Saturday. Winds will become
variable on Saturday evening as warm advection begins later
Saturday night.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until 10 AM CST Saturday for IAZ004>007-
015>017-023>028-033>039-047>050.

&&

$$

SHORT TERM...Donavon
LONG TERM...Donavon
AVIATION...Cogil



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