Area Forecast Discussion
Issued by NWS Des Moines, IA

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915
FXUS63 KDMX 161807
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1207 PM CST Mon Jan 16 2017

.UPDATE...
Issued at 1205 PM CST Mon Jan 16 2017

No changes to headlines at the moment, but they will be re-
evaluated heading into the afternoon package. There has been some
minor improvement as the surface wet bulb line has nudged
northward to Highway 30 but with additional at least intermittent
rains anticipated into the afternoon the net ice accums should
stay fairly steady state, especially on elevated and untreated
surfaces.

&&

.SHORT TERM.../Today through Tonight/
Issued at 424 AM CST Mon Jan 16 2017

The freezing rain/ice storm event is well underway with
widespread ice totals of 0.10 to 0.20 inches being reported. Many
reports of surfaces treated Sunday evening have now iced over and
it is now extremely icy across much of the forecast area. The
first wave of precipitation currently extends from central into
northeast Iowa and has consisted of nearly all freezing rain.
There is a lull in the precipitation over southern Iowa though
pockets of freezing rain and freezing drizzle area in place there.
A second precipitation shield is lifting northeast through
western Missouri and Kansas ahead of the main upper level system
which is back in Oklahoma. This precipitation will arrive mid
morning through mid afternoon then will pivot over northern Iowa
before moving southeast this evening before ending.

The precipitation type and icing efficiency today remains the
primary forecast challenge. MOS guidance temperatures remain too
warm today with saturated conditions keeping temperatures within 2
degrees of dew points. In addition an increasing easterly wind
will funnel dry air from the high pressure to the east leading
to evaporative cooling, counteracting the latent heat release and
keeping temperatures in check while precipitation falls.
Temperatures should push above freezing south of Interstate 80 by
this afternoon and possibly a bit farther north. Temperatures of
33- 34 degrees though may not completely stop freezing on roads
and walkways due to the very cold ground temperatures. Drier air
aloft will end ice introduction over southern Iowa for a time but
drizzle/freezing drizzle will remain likely. Have bumped the one
quarter inch ice accumulation line to near the Highway 3 corridor
thus will be expanding the Ice Storm Warning to include
Waterloo/Waverly/Hampton areas.

Have kept isolated thunderstorm mention over the far southeast
with convective instability and modest MUCAPEs reaching the area
immediately ahead of the surface low.

.LONG TERM.../Tuesday through Sunday/
Issued at 424 AM CST Mon Jan 16 2017

The main forecast concern was focused on the unseasonably warm
temperatures late this week and into the weekend. Leaned toward a
blend of the GFS/ECMWF throughout the forecast package.

Wednesday through Sunday...Surface high pressure will move into the
state tomorrow once the current system exits the region during the
morning hours Wednesday. Some lingering pops across the northeast
through 15z Wednesday, but otherwise conditions look to be dry
until early Friday. A nice warm and sunny day, at least for mid-
January, in store for Thursday with the weak ridge overhead. A
weak 500mb trough will move across the Southern Plains into the
Missouri Valley late Thursday night into Friday. This system
remains moisture starved as well as minimal forcing present. Thus,
have low confidence with any significant precipitation Friday.

Saturday is shaping up to be the warmest day over the extended
period. Decent southerly flow and mixing develop throughout the day
with the only caveat being a thin stratus layer persisting across
the state. Regardless, the WAA looks strong enough to hoist
maximum temperatures well into the 40s and even lower 50s.

Sunday night into Monday...upper level trough digs deeper into the
central CONUS during this time and develops a surface low pressure
that looks to provide some rain/snow chances to the state. The
GFS/ECMWF remain in decent agreement with the timing and location of
the surface low track and have highest pops going from 00-12z Monday
across central iowa.

&&

.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1200 PM CST Mon Jan 16 2017

Widespread IFR/LIFR conditions continue across central IA
including a large area of rain and freezing rain moving south to
north. The precipitation will decrease and become more
intermittent into tonight but stratus and fog will persist as the
parent surface low moves from KS at 18z into IL after 06z. The
stratus and fog will persist in broad cyclonic flow behind the
system however keeping at least IFR conditions in place through
the valid period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Ice Storm Warning until midnight CST tonight for IAZ023>028-
033>039-044>050-057>060.

Ice Storm Warning until 6 PM CST this evening for IAZ061-062-
070>074-081>084-092>095.

Winter Weather Advisory until midnight CST tonight for
IAZ004>007-015>017.

Winter Weather Advisory until 6 PM CST this evening for IAZ075-
085-086-096-097.

&&

$$

UPDATE...Small
SHORT TERM...Donavon
LONG TERM...Podrazik
AVIATION...Small



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