National Weather Service Raw Text Product

Displaying AFOS PIL: AFDDMX Received: 2018-01-12 05:34 UTC


037 
FXUS63 KDMX 120534
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1134 PM CST Thu Jan 11 2018

.SHORT TERM.../Tonight through Friday/
Issued at 309 PM CST Thu Jan 11 2018

GOES-16 water vapor imagery shows the dry slot over far eastern Iowa 
pushing into Wisconsin this afternoon. The main deformation zone 
precipitation is over north central Iowa and quickly moving to the 
northeast. Another area of precipitation over the southeast forecast 
area aided by 850-700mb frontogenesis was also moving to the 
northeast. The dry slot cut off the ice introduction layer leading 
to some freezing drizzle. However, this was offset by the arctic air 
surging in at the low levels with saturation in the dendritic layer 
keeping light snow more common as far as precipitation type. KDMX 
radar also has shown late this morning into early this afternoon 
thin snow bands oriented northwest to southeast generally parallel 
to the wind direction. These bands have been able to form likely due 
to a bit of instability per cross sections of equivalent potential 
temperature. Winds from the northwest averaging 20 to 30 mph with 
higher gusts have prevailed this afternoon as well causing blowing 
snow per surface observations and Iowa DOT plow cams. With 
precipitation winding down, will drop the Winter Storm Warning. 
However, will keep a Winter Weather Advisory going for the forecast 
area through 6pm for areas of blowing snow, hazardous travel 
conditions, and/or lingering light snow over the east.

As this system continues to move away from the area, snowfall will 
end around sunset and skies will clear tonight. Winds will become 
not as strong, but remain breezy overnight. With the arctic airmass 
settling in, temperatures will drop into the single digits below 
zero except for the southeast forecast area. For northern Iowa, wind 
chills will drop below -20F and will issue a Wind Chill Advisory 
starting this evening through mid-morning Friday. While Friday will 
dawn mostly sunny, clouds will increase as a shortwave trough dives 
through the Rockies onto the central Plains. Models have continued 
the trend of this trough losing its forcing as it nears Iowa and 
therefore will keep the forecast dry during the day Friday. 
Temperatures will rise only into the single digits above zero over 
northern Iowa with low and middle teens over southern Iowa.

.LONG TERM.../Friday night through Thursday/
Issued at 309 PM CST Thu Jan 11 2018

A couple systems to impact Iowa over the weekend and persistent cold 
are the highlights for the forecast period. A strong upper level 
system will transverse east across the Southern Plains on Friday 
then lift northeast then will lift northeast into the Ohio Valley 
Friday night. As this occurs, another system will be diving 
southeast into the Upper Midwest. The system impacting has been 
trending weaker and main impacts will be very light snow. The 
combined systems mentioned previously will though upper trough 
across the Mississippi Valley and bring cold advection to Iowa. A 
strong short wave will move into the mid Missouri Valley Saturday 
night into Sunday morning. This system will feature a 2 to 4 hour 
period with a deep dendritic layer and descent forcing for light to 
moderate snow and could have the potential for 1 to 2 inches mainly 
west of Interstate 35.  

The strongest system will arrive late Sunday into Sunday night ahead 
of potentially the coldest air of this winter season. Another area 
of light snow will develop by late Sunday afternoon and overnight 
and will bring the potential 1-3 inches possible mainly over the 
northeast forecast area. Wind gusts of 30 to 40 mph may accompany 
the system as the Arctic air spills south into Iowa. These winds 
may cause some blowing snow but also will drop wind chills into 
the 20 to 30 below range by Monday morning along and north of 
Highway 30. The wind combined with high temperatures near zero 
over north central Iowa will keep wind chills near 20 below zero 
much of the day. The coldest night will be Monday night with 
overnight low falling into the 5 to 15 below range and winds of 10
to 20 mph persisting. This will cause wind chill values to 
approach 40 below zero for some areas of northern Iowa by Tuesday 
morning. 

The cold weather will continue Tuesday then modestly warmer on 
Wednesday before the upper level pattern breaks and becomes more 
zonal towards Thursday.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1134 PM CST Thu Jan 11 2018

Scattered MVFR ceilings are in place across the eastern half of IA
at 06z. While recent radar and satellite trends suggest these may
have now become false ceilings to due mixing and ice aloft, have
error on the side of caution and continued these for a few more
hours. Otherwise there is fairly high confidence in VFR conditions
through the remainder of the valid period with clear skies into
Fri until mid clouds increase late in the day.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until 10 AM CST Friday for IAZ004>007-
015>017-023>028-033>038.

&&

$$

SHORT TERM...Ansorge
LONG TERM...Donavon
AVIATION...Small