Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 121813

Area Forecast Discussion
National Weather Service Des Moines IA
1213 PM CST Mon Feb 12 2018

.SHORT TERM.../Today through Tonight/
Issued at 400 AM CST Mon Feb 12 2018

Bottom Line Up Front...
Wind Chill values in the -15 to -20 or so degree range this
morning roughly along and north of Highway 20, otherwise a quiet
short term fcst period.

Tonight and Today...
A 1045mb sfc high will start the morning in North Dakota,
propagating southeastward through the Upper Midwest, making it to
the Great Lakes Region by 12z Tue. Concurrently, an upper jet will
streak through Iowa from SW to NE, aiding in a decent cirrostratus
field setting up for this afternoon. This should obviously inhibit
some insolation... so while 850mb temps are slightly warmer today
than they were yesterday, the net impact should be slightly cooler
temps today than yesterday.

As the aforementioned high makes it east of the region tonight,
strong WAA will begin to infiltrate Iowa... likely leading to steady
to slightly increasing temps overnight. The past couple of days,
primarily the GFS, has tried to squeeze out some light snow/flurries
over NW Iowa as a PV anomaly races through that portion of the
state. There is weak, but sufficient, 500mb-300mb Q-vector
convergence ahead of this feature to support mid-upper level
ascent. However, with the WAA, the modestly saturated DGZ will be
around 4km, with the low level cloud base in the lowest 1 km...
too much of a difference for seeder-feeder generation. The dry air
appears to be too much to overcome, so have left precip out.

.LONG TERM.../Tuesday through Sunday/
Issued at 400 AM CST Mon Feb 12 2018

Bottom Line Up Front...
Fog likely Wednesday via melted snow. Notable change in fcst from
24 hours ago to add both precip across much of Iowa for Thursday,
and strong winds Thursday afternoon through Thursday night.

Wednesday... WAA advection continues in earnest across Iowa
Wednesday. 850mb temps make it to +7C to +10C by Wednesday
afternoon. Forecast soundings continue good run-to-run consistency
in featuring a stout inversion across most of Iowa. With sfc
dewpoints over 32 being advected over Iowa, high likelihood of
melting snow Wednesday. Inversion will likely trap moisture from
melting snow, setting much of now snow-covered Iowa up for a high
fog potential Wednesday afternoon into Thursday morning. Have not
added in fcst at this time, but confidence should be high enough
during the next forecast update or two to add fog for Wednesday PM
and Thursday AM. Dense fog most certainly cannot be ruled out at
this time.

Thursday into Friday...
Long-range models starting to come into agreement with most
recent 00z package. 09z Mon water vapor imagery shows a broad
upper low near the Four Corners region. Long-range models carry
this low southward and then rapidly to the northeast over the
Rockies. In the 00z Mon runs, a more well- defined sfc reflection
has been developed. 00z Mon solutions place this sfc low near
Kansas City by 12z Thu, with an attendant warm front branching
into the southeastern tier of counties in the DMX CWA. Models have
been trending slower and stronger with this low... so track still
undetermined. Meanwhile, a 1040mb high is progged to come off the
Rockies behind this system. There is a boatload of dry-air
entrainment and large-scale subsidence being advected down with
this high, so precip chances will quickly become nil. Of note is
the strong wind potential. Pressure gradient much tighter than 24
hours ago, now making into the 3mb/80 km range. Coupled with 3-hr
pressure rises of +3 to +5mb coming down, 25 to 35 mph winds look
very plausible... Will monitor for potential strengthening.

Next Weekend...
The models continue to have poor resolution for this upcoming
weekend`s weather. There seems to be a general trend to place Iowa
in return SW flow, but beyond that, lack of run-to- run
consistency makes it useless to try to dial in on any mesoscale


.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1212 PM CST Mon Feb 12 2018

Few concerns for the next 24 hours. VFR conditions are expected
with mid to high level clouds. Light winds until 15z Tuesday when
winds will mix to 15 to 17kts at KFOD/KMCW. Winds remain light
east northeast to southeast through 12z then south. /rev




SHORT TERM...Kotenberg
LONG TERM...Kotenberg
AVIATION...REV is the U.S. government's official web portal to all federal, state and local government web resources and services.