Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 121745

Area Forecast Discussion
National Weather Service Des Moines IA
1145 AM CST Fri Jan 12 2018

Issued at 450 AM CST Fri Jan 12 2018

Decided to add counties along the US 30 corridor to the wind chill
advisory given some additional drop in temperature over the next
few hours...and persistent winds bring wind chills in this region
down to 20 to 25 below at times. Remainder of area in advisory
will continue as well. /rev


.SHORT TERM.../Today through Tonight/
Issued at 324 AM CST Fri Jan 12 2018

Confidence: High

Main concern will be the cold.  High pressure heading south today
with strong cold air advection continuing to push into the region
early today. Gradient winds remain quite brisk at 08z with 15 to 20
mph sustained winds and gusts to near 30 mph at times.  This has
been keeping wind chills from 20 to 30 below over the north half of
the region...generally along and north of US 30.  Temperatures will
remain quite cold by sunrise with winds dropping off a bit. Will
monitor the US 30 corridor for possible extension of wind chill
advisory. As well...a slow recovery is expected through the late
morning with winds remaining about 12 to 15 mph.  For the remainder
of the afternoon some sunshine early today will allow afternoon
highs to recover to the single digits north to the teens south.
Already the next upstream system is spreading mid-level clouds into
central South Dakota and western Nebraska.  This will overspread the
region by late afternoon with cloud cover remaining in the region at
least through 09z tonight south of I 80 while the north again clears
out by 12z Saturday.  The weak lee side wave responsible for the
cloud cover will spread some light snow across Nebraska today and
this evening. Meanwhile only leftover moisture and very weak mid
level lift will reach far western sections of the forecast area by
this evening. There may be a few flurries in the far west this
evening. The Northern Plains high will once again reassert itself
tonight and clear out the northern half of the region by 12z. Along
with that H850 temperatures will drop back to near -19 by 12z to -
15C south. This along with northwest sfc gradient winds of near 10
kts will once again push wind chill values down to the -20 to -30 F
range from US 20 north to the border. It`s likely that headlines for
wind chills will again be needed for Northern Iowa tonight as the
combination of cold lows...wind create similar conditions to early

.LONG TERM.../Saturday through Thursday/
Issued at 324 AM CST Fri Jan 12 2018

In the long term concerns still revolve around the cold through
the middle of next week. Temperatures will be coldest Monday and
Tuesday. Headlines are still a strong probability Monday night as
winds remain brisk through the overnight hours with temperatures
of 15 below across northern portions of the forecast area. We are
looking at wind chills of greater than 30 below in this time
frame. Finally by mid-week the upper trough that is responsible
for dumping the arctic air into the region shifts east and allows
an upper ridge to build by late week. Beyond the long term, a
trough appears to want to set up somewhere across the west placing
a zonal to southwest flow across Iowa. If this happens, we will be
back above freezing.

As for precip chances in the long term, the best chance remains to
be Sunday into Sunday night as a deep trough drops down out of
Canada and into the Upper Midwest. Models have been consistent
with timing and features. Forcing looks pretty strong and it is
this feature combined with another arctic high that will bring
our next shot of bitterly cold air to Iowa Monday/Tuesday. QPF
appears a little overdone but given the amount of forcing, the
consistency of the models and the higher snow ratios expected
across the north central to northeast Iowa...we could see a couple
inches of new snow out of this. Still in question is how far
southwest to bring the higher PoPs with this system. For now, I
stayed with consensus though I did increase the PoPs to likely
across the northeast quarter to third of the forecast area. Other
than this system Sunday, the long term does look pretty dry,
though with as cold as it will be we can`t rule out flurries
should there be any subtle passing disturbance.


.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 1145 AM CST Fri Jan 12 2018

VFR conditions are expected through the forecast period. Mostly
clear skies to begin the period followed by some mid level clouds
in the 6-9 kft range later this afternoon through Saturday
morning. Breezy northerly winds will persist.




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