Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 150455

Area Forecast Discussion
National Weather Service Des Moines IA
1155 PM CDT Wed Mar 14 2018

.SHORT TERM.../Tonight through Thursday/
Issued at 335 PM CDT Wed Mar 14 2018

Gusty southwest winds have pushed temperatures into the lower 60s
over the central and southern portion of the forecast area, while
40s to upper 50s were found over the north. Expecting the winds to
decouple with the sunset tonight as well as a wind shift behind a
very weak cold front this evening. Slightly cooler tomorrow, but
still above normal over the south and near normal in the north.

.LONG TERM.../Thursday night through Wednesday/
Issued at 335 PM CDT Wed Mar 14 2018

The main focus of the extended period was on the system to roll
across the state Friday into Friday night. In short, a brief
period of wintry mix Friday morning with the onset of
precipitation across the southwest and then Friday night over
northern Iowa looking to see some light snow accumulations. As far
as travel impacts, low confidence in any significant concerns
with the short duration of the wintry mix Friday morning and the
majority of the accumulating snow will likely be on
grassy/elevated surfaces.

Models are in fairly good agreement with the synoptic pattern
through Saturday but there are some moderate differences wrt to
the temperature profile and precipitation type/timing. First,
Friday morning there still remains a short period of a wintry mix
across the southwest to central portion of the forecast area.
There is ice introduction, but a large warm layer (+3C to +4C)
between 850-700mb will be enough to melt any snow falling through
this layer. Surface temperatures quickly rise above freezing
between 12-16z Friday, but during this time there looks to be a
wintry mix of sleet/freezing rain as the band moves northeast.

By Friday afternoon and evening, the GFS is certainly more bullish
with the accumulating snow over northern Iowa as it suggests a
decent frontogenetical band quickly advecting northward ahead of
the surface low. Plenty of UVM within the dendritic layer, but
the main question is temperatures near the surface. Since the GFS
is slightly stronger with the lift Friday afternoon/evening, the
temperature profiles remain below freezing and allow for a bit
more snow. NAM is drier, or at least slightly slower to completely
saturate the column per MCW to FRM soundings by around 00z
Saturday. Confident enough to nudge up the snow amounts, albeit
still around an inch across northern Iowa. Winds during the
falling snow late Friday afternoon into the evening may cause some
visibility restrictions. Winds atop the mixed layer range from 30
to 40 knots over much of the forecast area Friday afternoon and
evening and can certainly expect gusts to 30 mph during the
aforementioned time frame. System will quickly pull east of the
forecast area and cut back on pops past 12z Saturday to just the
far east-central portion. As the low pushes eastward early
Saturday morning, ice introduction is gradually lost from north to
central portion and thus another brief period of a wintry mix is
possible b/t 06-12z Saturday.

Sunday into Thursday...ECMWF and GFS have similar timing and
track location of the next surface low Monday into Tuesday. It
places the forecast area within the cold air regime of the low
and potentially providing some snow accumulation by late monday
afternoon and into the evening. Moisture throughout the column
doesn`t seem to be an issue and the majority of the column remains
below freezing. Therefore, the precipitation type remains either
snow or rain attm.


.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1155 PM CDT Wed Mar 14 2018

VFR conditions are expected through the valid forecast period. Winds
will switch to a northeasterly direction and increase to 10-15kts by
this afternoon.





SHORT TERM...Podrazik
LONG TERM...Podrazik
AVIATION...FAB is the U.S. government's official web portal to all federal, state and local government web resources and services.