Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 220541
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1141 PM CST Tue Feb 21 2017

.SHORT TERM.../Tonight through Wednesday/
Issued at 401 PM CST Tue Feb 21 2017

21z Tue sfc analysis has a sizable sfc high located over the TX/OK
panhandle. Meanwhile an extremely weak shortwave is cruising
across northern MN. This has placed Iowa firmly in SW flow. 850MB
temps started today roughly in the +9C to +12C range across Iowa.
With WAA coming in overnight, 850mb temps look to start tomorrow
in the +12C to +15C range. Dry air and large-scale subsidence is
dominant, so expecting little in the way of cloud cover and a
persistent forecast overall... just several degrees warmer than
today. Record to near-record highs appear likely again for
Wednesday.

.LONG TERM.../Wednesday night through Tuesday/
Issued at 401 PM CST Tue Feb 21 2017

Main focus is on winter storm potential Thursday into Saturday.

Confidence: Low-Medium

21Z Tue water vapor imagery picking up a huge upper trough just
offshore in the Pacific Ocean. Well-advertised system to track
onshore during the next couple of days, making it to the midwest by
Friday. Run-to-run consistency high in terms of the synoptic setup
of an associated sfc low and attendant cold front ejecting off the
base of the trough and propagating through the Midwest towards
Iowa and the Great Lakes. Model discrepancies have been
significant enough to negatively impact confidence in terms of
pinning down a specific track for the system. Over the past few
days, the ECMWF has been much more steady with pushing the sfc low
through southeastern Iowa. The GFS has had much more variability
with the track of the low. The 12z Tue GFS was unique in that it
pushed the low further north...The 12Z Tue ECMWF held with its
track over SE Iowa...The 12z NAM was a fast outlier...a typical
bias of the NAM in this time- range. So have gone with somewhat of
a non-NAM consensus blend with a heavy lean towards the 12z Tue
ECMWF. Not worth getting into specifics at this point, as a 20
mile shift of the low could yield huge differences in terms of
locations that receive more snow versus more rain and vice versa.

Regardless of track, confidence high in strong winds associated with
this system...especially on the northwesterly side as tight pressure
gradient slides across Iowa. Fcst soundings indicate winds atop
the mixed layer approaching 35 to 40 kts... so big impacts
possible in locations where snow occurs. Strong winds may linger
into Saturday...meaning blowing and drifting snow may be possible
Saturday morning, even though precipitation has ended.

In the extended, models not displaying much run-to-run
consistency. Long- range models have been trying to hint at
multiple weak, fast- moving short-waves coming through between
Monday and Wednesday. Given the nature of these clipper-type
systems, confidence will likely remain low in timing and location
for a few more days.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1141 PM CST Tue Feb 21 2017

Potential for LLWS early with strong inversion in place around
1500 ft agl. Otherwise generally VFR through the period though
localized fog may occur far north near KMCW and southeast in
vicinity of KOTM. Breezy southwest to west winds on Wednesday will
diminish shortly after sunset.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Thursday evening through Friday
afternoon for IAZ004-005-015-023.

&&

$$

SHORT TERM...Kotenberg
LONG TERM...Kotenberg
AVIATION...Donavon


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