Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 141759
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1159 AM CST Sun Jan 14 2018

.UPDATE...
Issued at 1159 AM CST Sun Jan 14 2018

Have updated today into tonight with latest radar trends showing
the area of snow remaining across the far south/southeast and some
scattered flurries across the north. Also increased winds a bit
late tonight behind the front. Still expecting decent area of snow
to move through the forecast area by late afternoon into this
evening. Should see a few hour period with reduced visibilities
through the evening, and may have some lowered visibilities
continue late tonight with blowing snow as winds increase out of
the northwest.

&&

.SHORT TERM.../Today through Tonight/
Issued at 327 AM CST Sun Jan 14 2018

Confidence: Medium to High

Short wave tracking southeast into Iowa/Nebraska now spreading light
snow across the southwest and eventually working east today with
warming temperatures through the afternoon hours as a weak warm
front accompanies the light snowfall.  Winds will remain light
through the daytime event today so few if any impacts are expected.
Snowfall totals across the south likely to be under an inch with
this warm air advection/mechanically driven snowfall. Stronger wave
showing up in Goes 16 mid-level water vapor imagery spread across
Saskatchewan/Western Manitoba.  The low is expected to quickly dig
nearly due south and deepen a sfc wave into northern/east Central
Iowa by 06z tonight.  Along with that a closed H850 low will track
from near International Falls at 00z Monday southeast to near La
Crosse by 12z Monday. A band of snow will accompany the low and
passage of a strong Arctic cold front which will enter northwest
Iowa by 00z and quickly track southeast through the remainder of the
forecast area by 06z. Light snow should enter the northwest between
20-21z and spread quickly southeast through the evening hours. The
models differ a bit on placement of the sfc low location by 06z but
both the GFS/Euro and Hires models have been consistent in
precipitation amounts of about .06 to .09 with this event from north
central through the east central counties...slightly lighter amounts
back to the west. With snow ratios of 20 to 23:1 this will likely
drop between 1 to 2 inches of snow northeast.  Once the cold front
arrives...winds will be on the increase between 06 and 12z when
sustained winds will reach 15 to 25 mph with gusts to 30 to 35 mph
at times over the northeast overnight.  At this juncture will be
holding off on any headlines for the event. The winds will lag the
main snowfall by a couple of hours...reducing the risk of visibility
impacts.  WPC sref ensemble vsby probabilities suggest that there is
only a 10-20% chance of any low visibilities during the event.
However...after the winds pick up still expect to see some blowing
snow so have added patchy blowing snow over the northeast half.
Fracturing is likely to occur resulting in some settling...but
certainly between 06 and 12z snow will probably blow over roads and
early morning commuters Monday may need a heads up on road
conditions if this occurs.  The other big story will be the cold
weather.  After coordination between offices and internally between
short/long term...have decided to issue a Wind Chill Advisory to US
30 from 09z tonight through 18z Tuesday.  More details about the
rest of the area/period can be found in the next section of the AFD.
Temperatures tonight will quickly fall into the single digits below
zero north after midnight and fall to the single digits south and 5
to 10 below by 12z north.  Wind chills will be near -20 from US 30
north to the border by 12z and remain near that mark the entire day.

.LONG TERM.../Monday through Saturday/
Issued at 327 AM CST Sun Jan 14 2018

Summary...Arctic air intrusion will have been well under way by the
start of the forecast period, bringing about temperatures that will
not eclipse single digits until Wednesday afternoon. With breezy NW
winds, dangerous wind chills, especially Mon night into Tue morning,
will tag along as well. Relief comes to end the week as temps rise
above freezing.

Monday through Wednesday Morning...Cold front should be through the
state by 12z Monday, leaving behind strong CAA and 20-25 mph NW
winds and gusts approaching 35 mph.  Blowing snow concerns, at least
the degree of, are a bit questionable considering that only around
an inch may have fallen previously, the heavier amounts relegated
further NE closer to Wisconsin, and the greatest probability will
likely reside prior to 12z. Regardless, have kept blowing snow
mentions, perhaps over zealously, in through Monday given the
sustained strong winds. Overall, the bigger concern through this
window will be the sustained cold and wind chills. Highs Mon/Tue
will only be in the single digits above zero, along with lows
Tue/Wed morning ranging from around -5 to -15 degrees. While not
as outright cold as previous arctic outbreaks this season, winds
will be up throughout its time here, dropping wind chills into the
-25 to near -40 degree range from Mon morning through Tue
morning. Wind chill headlines are a certainty. An advisory
currently resides from Highway 30 north from early Mon morning
thorugh Tue morning, and will almost certainly see an expansion
southward and upgrade to warning over its existing area for Mon
evening into Tue.

Wednesday Afternoon through Saturday...Relief in the way of warmer
temperatures comes to the region as the upper level trough quickly
slides eastward and zonal flow to weak ridging prevails. Primarily
southerly surface flow will raise temps into the teens Wed and
eventually into the mid 30s to low 40s by Fri and Sat. While quiet
on the discernible weather front, models show increasingly divergent
solutions as early as Thur evening. Biggest potential impact to the
forecast lies just outside of this package, Sunday, where GFS paints
potentially significant winter weather as an upper level closed low
passes while the Euro depicts a quieter and slower open trough
passage.

&&

.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 11590 AM CST Sun Jan 14 2018

Very light snow with MVFR to low VFR CIGS in place this afternoon.
Gusty southerly winds at times. This evening another wave of snow
to move through with VSBYS dropping to around 1 mile at times
with the snow. Winds to shift around to the northwest tonight, and
increase to become strong and gusty. Some BLSN possible
especially in the north. Right now have highlighted with low
VFR/MVFR VSBYS.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory from 3 AM Monday to noon CST Tuesday for
IAZ004>007-015>017-023>028-033>039-044>050.

&&

$$

UPDATE...Beerends
SHORT TERM...REV
LONG TERM...Curtis
AVIATION...Beerends


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