Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 111741
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1141 AM CST Mon Dec 11 2017

.UPDATE...
Issued at 1001 AM CST Mon Dec 11 2017

Updated to include Decatur and Clarke Counties in the wind
advisory. Stronger winds aloft and soundings suggest winds may
advance farther east this afternoon. Will monitor for additional
updates through day.  /rev

&&

.SHORT TERM.../Today through Tonight/
Issued at 332 AM CST Mon Dec 11 2017

The forecast concern is focused on the clipper system anticipated
to bring blustery winds later this morning and into the afternoon
hours. The biggest change to the forecast was increased winds
several knots across the western half of the forecast area as the
strong PV anomaly punches into the state by around 15z this
morning. Should see some stout initial gusts exceeding 40 knots
across the west and can expect the blustery winds to persist into
the afternoon hours with the strong mixing developing. Winds atop
the mix layer range from 35-45 knots. Utilized the ARW but the
latest NAM, RAP, and HRRR are in fairly good agreement with the
winds coming in stronger than previously anticipated. With the
increase in winds and wind gusts today, issued a wind advisory for
western portions of the forecast area. Cannot rule out some gusts
to 45 mph at locations east of this advisory area, but seems to
be a limited time frame if they do occur. The other concern was
precipitation chances but this system lacks any significant depth
of moisture as the strong PV anomaly pushes south across Iowa
today. Have mainly rain mentioned today with no ice introduction
into the column and surface temperatures warming to above freezing
by the time the mainly forcing moves through the area.

.LONG TERM.../Tuesday through Sunday/
Issued at 332 AM CST Mon Dec 11 2017

Large amplified trof over the eastern United States will persist for
the rest of the week as several short waves drop into the backside
of the trof.  The first of these will arrive on Wednesday with a
cold front diving through the state during the day.  Winds will pick
up in the wake of the front with cold advection and tight pressure
gradient aiding the strong winds.  In addition, near surface mixing
will also help in momentum transfer of the stronger winds aloft.
Strongest forcing will remain to the northeast of the state with
precipitation likely staying in Minnesota and Wisconsin.  Thermal
ridging ahead of the front will be across the state to start the day
with unseasonably mild temperatures, especially in the south before
the cold air arrives by later in the day.  The colder air will
remain across the state on Thursday with a weak reinforcing
shortwave passing through the state later in the day.

The upper pattern tries to become a bit more zonal toward next
weekend as the eastern trof become much less amplified.  This should
allow warmer air into the state by next weekend with temperatures
above normal.  However, there remains a decent amount of uncertainty
with models having a difficult time resolving the numerous
shortwaves in the flow both spatially and temporally into the
weekend.

&&

.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1140 AM CST Mon Dec 11 2017

Main challenges continue wind and lowered CIGS. Cold front heading
southeast now with northwest winds gusting to near 45kts at times
along with sustained 25 to 27 kts over much of area. Shortwave
dropping southeast will finally begin to diminish toward 12z as
gradient winds relax and adiabatic mixing diminishes. Aft 00z
winds should be lower in the range of 15 to 22 kts with gusts to
30 to 35 kts at times. For the short term through 22z east
sites...VCSH with lingering light precipitation possible at
KOTM/KALO but elsewhere other than passing flurry/drizzle no
impacts to visibility expected. CIGs to remain MVFR through much
of evening with some improvement west aft 03z and east/southeast
between 05/07z as shortwave moves east./rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM CST this evening for IAZ004-005-015-023-
024-033>035-044>047-057>059-070>072-081>083-092>094.

&&

$$

UPDATE...REV
SHORT TERM...Podrazik
LONG TERM...Cogil
AVIATION...REV


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