Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 101123

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

...Updated Aviation Discussion...

.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 12Z TAFS through 12Z Monday morning/
Issued at 519 AM CST Sun Dec 10 2017

Generally VFR conditions are expected throughout the TAF period.
However, some MVFR stratus may skirt across MCW and ALO later
today with the cold front passing through. However, low confidence
in mentioning due to the potential of staying just northeast of
these two locations and that if it does reach MCW/ALO, appears to
be short duration. The latest HRRR/RAP suggest the stratus
impacting MCW b/t 18-21z but the other hires models remain above





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