National Weather Service Raw Text Product

Displaying AFOS PIL: AFDDMX Received: 2018-01-12 11:36 UTC


487 
FXUS63 KDMX 121136
AFDDMX

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

.UPDATE...
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 
today.

.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 12Z TAFS through 12Z Saturday morning/
Issued at 536 AM CST Fri Jan 12 2018

Few concerns this period. Wind remain a minor issue this morning
with sustained northwest winds near 15kts at KMCW,KALO,KDSM,KOTM
but will lessen aft 20z - 23z today. Mid level cloud deck to the
west will advance east and will enter the area between 22-00z.
Otherwise VFR conditions will continue with winds under 10 kts aft
06z Sat. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until 10 AM CST this morning for IAZ004>007-
015>017-023>028-033>039-045>050.

&&

$$

UPDATE...REV
SHORT TERM...REV
LONG TERM...FAB
AVIATION...REV