Area Forecast Discussion
Issued by NWS Des Moines, IA

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748
FXUS63 KDMX 172132
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
332 PM CST Wed Jan 17 2018

.SHORT TERM.../Tonight through Thursday/
Issued at 332 PM CST Wed Jan 17 2018

Fairly straight forward in the shorter term with dry atmosphere in
place across the Midwest. Therefore little in the way of clouds or
precipitation is expected through Thursday. Main issues are with
temperatures with building thermal ridge across the Plains and
into Iowa. Already have seen a vast improvement in temperatures
today with strong southwest surface flow aiding warm advection
through the state. This will persist overnight into Thursday with
the expanding warm air across the region. Despite the clear skies,
modest surface flow should help to buoy temperatures tonight with
readings only dropping into the teens in most locations. The
decent southwest flow and sunshine on Thursday should add another
10 to 15 degrees to highs which would likely have been more had
not the snow cover been in place.

.LONG TERM.../Thursday night through Wednesday/
Issued at 332 PM CST Wed Jan 17 2018

Longer term focus will be on the system expected to pass through
the region late this weekend into early next week. System is currently in
the eastern Pacific and is forecast to come onshore early Saturday
before beginning to strengthen over the intermountain west.
Cyclogenesis will occur along the Front Range of Colorado Saturday
into early Sunday before the low advects to the northeast on
Sunday into Monday. Timing differences are still apparent between
the Euro and GFS with the GFS remaining more progressive although
their actual tracks are quite similar.

In advance of the system, thermal ridging across the state on
Friday and good southwest surface flow will lead to temperatures
well above normal. Even Saturday will see above normal readings
although a bit more muted with increased cloud cover, weak and
meandering surface flow as a surface boundary settles into the
state. This boundary will begin to intensify on Saturday night
into Sunday with the ongoing cyclogenesis and increasing surface
flow. Soundings have an increases depth of near surface moisture
on Saturday night and likely to see drizzle/very light rain
develop late that night. Seems plausible that fog will may
become an issue with increasing dew points advecting over
relatively cool ground. This will persist into Sunday morning as
mid and upper levels stay relatively dry. However, deeper forcing
will arrive later Sunday into Sunday night with lift increasing
rapidly. The uncertainty here lies in the speed differences
between the models as opposed to placement. GFS would sweep the
surface low across the state by Monday morning with Euro just
entering the southwest. The slower evolution seems more plausible
given the historic more gradual progression of southwest US
systems, however will not totally discount the GFS. In either
case, much of central Iowa will remain liquid precipitation with
the warm sector into the southeast half of the forecast area.
There may be some thunder late Sunday afternoon into the evening
across the southeast given weak elevated instability. Otherwise,
the southeast will see the dry slot move overhead with the passage
of the surface low effectively cutting of precipitation until
potential wrap around later Monday.

Across the northwest, colder air will be deeper and snow is
favored precipitation type for most of this event near
Estherville. Some significant snowfall totals are not out of the
question in the far north to northwest where strong forcing
produces a good amount of QPF/Snow. In addition, northwest winds
should be quite robust producing blowing and drifting snow as
well. Headlines may be needed in a few more cycles should current
forecast output remain in place. Lingering precipitation is
expected later Monday into Monday evening with a broad area of
wrap around/deformation precipitation across much of central Iowa.
Temperatures will be much colder as well with strong cold
advection on the backside of the system.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1125 AM CST Wed Jan 17 2018

Widespread VFR conditions are expected for this forecast period
with generally good aviation weather. Visibilities will be
unrestricted with few ceilings. Surface winds will be strong from
the southwest and gusty during the daytime.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Cogil
LONG TERM...Cogil
AVIATION...Cogil



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