Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 100951
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
351 AM CST Sun Dec 10 2017

.SHORT TERM.../Today through Tonight/
Issued at 351 AM CST Sun Dec 10 2017

The main forecast concern today was focused on temperatures and
how warm they reach before the cold front located in northern
Minnesota drags south across Iowa later today. Warm front looks to
surge eastward this morning from eastern Nebraska/western Iowa
and provide some decent downslope effect over the forecast area.
For maximum temperatures today, leaned slightly warmer than
previous forecast, especially across the southwest half of the
CWA. Not a significant amount of cold air behind the cold front
expected to push through from 15z to 20z from north to south
today. Gusty northwest winds develop this afternoon before
decoupling by around 23z to 00z. Yet another shortwave tracks
across the Dakotas into Minnesota overnight tonight and skirts
into Wisconsin and possibly northeast Iowa. There is ice
introduction into the column past 06z tonight across the far
northeast but a significant dry layer between roughly 850mb to
700mb. Lift within the snow growth region isn`t strong, but the
column does try to completely saturate per MCW forecast sounding.
Certainly have low confidence with any snow accumulation, but
there is the potential for some snow reaching the surface and thus
kept mention of light snow going in the northeast overnight
tonight.

.LONG TERM.../Monday through Saturday/
Issued at 351 AM CST Sun Dec 10 2017

Little change in the extended forecast discussion as amplified
eastern trof remains across the eastern United States. However,
there is some hint at the flattening of the upper flow toward the
end of the period in the longer term model output. Will see a
surface boundary slide through the state at the beginning of the
period with strong cold advection by Monday afternoon. The strong
cold advection combined with the tight pressure gradient is
expected to lead to winds that are close to advisory criteria by
Monday afternoon. Winds at the top of the mixed layer are around
40kts suggesting surface wind gusts approaching 45 mph, especially
from I80 northward. In addition, lift associated with the upper
system passing through the state will likely produce some
flurries/sprinkles across the northern half of the forecast area
on Monday. A non-diurnal temperature curve is also needed as the
strong cold advection by afternoon leads to falling temperatures
after midday.

Next system approaches on Wednesday with a similar scenario to
Monday as the boundary moves through early in the day. However,
the cold advection will not be as strong nor will the winds. There
remains some threat of light rain/snow although the bulk of
forcing and deeper saturation will be to the north and east of the
state along with the heavier precipitation. The colder push will
last into Thursday before warm advection intensifies into Friday
and early next weekend. The aforementioned flattening of the upper
flow will begin to limit the amount of colder air arriving from
Canada by late in the period.

&&

.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1126 PM CST Sat Dec 9 2017

Mid and high level clouds are streaming over the state with the
highest concentration of these clouds over eastern Iowa. Bases are
down to FL100 and don`t expect them to lower to create any
restrictions overnight. A cold front will sweep through the state
Sunday morning causing winds to become a bit brisk as they switch
around and blow from the northwest. There remains questions on
whether stratus clouds with MVFR ceilings will move into northern
Iowa Sunday afternoon into Sunday evening. For now, just have high
MVFR ceilings for a few hours at KMCW where models have shown
consistency in this possibility.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Podrazik
LONG TERM...Cogil
AVIATION...Ansorge



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