Area Forecast Discussion
Issued by NWS Des Moines, IA

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681
FXUS63 KDMX 021137
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
537 AM CST Fri Dec 2 2016

.SHORT TERM.../Today through Tonight/
Issued at 412 AM CST Fri Dec 2 2016

Weak cyclonic flow continues to subside as upper system moves up
the St. Lawrence River valley. Stratus will continue to hang
tough as ridge axis remains just west of the forecast area for
much of today. There may be a few more breaks in the overcast as
the shallow moist layer continues to shrink and some partial
sunshine is expected in the south and west today closest to the
ridge axis. Temperatures will climb toward the low 40s in the
south where the insolation will help by afternoon although low 30s
will persist in the north under the thicker stratus and close
proximity to the thermal trof. Ridge will slide across central
Iowa tonight with light winds and the continued shrinking of
status. Temperatures will also be cooler tonight as the light
winds and additional clearing should enhance radiational cooling
allowing readings to drop into the 20s overnight.

.LONG TERM.../Saturday through Thursday/
Issued at 412 AM CST Fri Dec 2 2016

Light snow accumulations for Saturday night and big drop in
temperatures by mid-week are still on track and were the main
focus during the extended period. Some continuity beginning to
show up between the ECMWF any GFS Tuesday into Thursday wrt to
snow potential, but both do agree on the abnormally cold
temperatures during this time. Leaned slightly closer to the GFS
as it has been the most consistent with its respective solution.

Saturday into Monday...upper level shortwave quickly ejects out of
the central Rockies Saturday and pushes into western Iowa by the
late afternoon hours Saturday. Soundings take a little time
becoming completely saturated up to around 500mb but with the
decent forcing moving across the state between 03-12z Sunday, this
should help saturate the surface layer to allow for snow to
develop overnight. Surface temperatures remain near freezing or
slightly warmer, but believe there is enough omega within the
dendritic layer to overcome the melting at the surface. Thus, the
central to southeast should see an inch or two of snow by sunrise
Sunday and potentially more if the precipitation stays all rain.
The time of day should also help accumulations as the best forcing
and deep moisture over the area are between 06-12z Sunday. Not
confident in the bullish NAM indicating advisory level snow
amounts in the southeast, per OTM bufkit sounding. However, this
location hasn`t seen much winter precipitation yet this season and
a headline might be needed for impacts. System quickly moves east
and have cut back on pops after 18z Sunday. Finally, at least the
western half of the state should see some sunshine Sunday
afternoon. Some weak downslope winds develop Sunday afternoon and
with the clearing skies, nudged up maximum temperatures across the
west.

Another warm day anticipate on Monday with surface high pressure
overhead. Trended drier Monday night over much of the forecast area
except the far northwest and southeast corners of the CWA.  The
northwest pops are due to an approaching cold and the southeast
are due to a strong upper low tracking across the Tennessee
Valley where this location may get clipped on the northwest side
of the low. However, the trends continue to shift this system
further southeast and likely to miss the forecast area altogether
Monday night.

Tuesday through Thursday...the only 6-hour confident dry period
forecast from 06z Tuesday to 12z Thursday is Wednesday 06-12z time
frame as much uncertainty remains with timing and location of next
system.  The GFS remains the faster solution and brings a strong
trough into the central CONUS and surface low to impact the state
during the day Wednesday into Wendesday night. The ECMWF is
further south and slower with track. Currently, the trend of the
extended models is to track the low south of the state and impact
the southern portions of the forecast area Wednesday into
Wednesday night.

High confidence in the unseasonably cold temperatures to filter into
the region Wednesday and persist through the end of the work week.
Lowered temperatures Wednesday into Thursday a 2-4 degrees as 850mb
temperatures drop to -15 to -20C and the 504-508dam (1000-500mb)
thickness line creeps into the state by Thursday. Also, stout
northwest winds by Thursday morning look to cause much of the
forecast area with sub-zero wind chill values.

&&

.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 537 AM CST Fri Dec 2 2016

Ceilings will very gradually increase in height during the
duration of the forecast. This will mean the VFR conditions will
expand from southwest toward the northeast with time although KMCW
and KALO may stay MVFR for duration of the forecast. As ceilings
increase, visibilities will remain unrestricted with west
northwest surface winds becoming light and somewhat variable
overnight as surface ridging slides into the state.

&&

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

&&

$$

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



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