Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250944
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
344 AM CST Sun Feb 25 2018

.SHORT TERM.../Today through Tonight/
Issued at 343 AM CST Sun Feb 25 2018

System that impacted the state Saturday is currently spinning over
near Lake Superior with the sfc low in the same vicinity. Sfc
pressure gradient remains tight across the forecast area with
westerly to southwesterly winds in place. Stratus shield starting to
erode with drier air moving into the state, and expect it to
continue to clear through sunrise with mostly sunny skies expected
through the day. An area of high pressure to build northward into
the state today, but weak cyclonic flow aloft with a weak shortwave
may result in partly cloudy skies toward this evening. Otherwise
little moisture to work with, so no precipitation expected. Overall
not a huge push of cold air behind the exiting system, so
temperatures today be mild with 30s across the north and into the
low to mid 40s south with near neutral temperature advection. Winds
will diminish a bit toward sunrise from the windy conditions
currently, with even spotty advisory criteria currently. However
winds will remain a bit gusty through the day, with the sfc pres
gradient relaxing toward late today into tonight and winds
diminishing by this evening.

.LONG TERM.../Monday through Saturday/
Issued at 343 AM CST Sun Feb 25 2018

Monday through Tuesday...Upper level ridging will develop over the
region bringing a period of dry conditions and warming temperatures.
Highs up north will be the slowest to respond due to snow cover.
Highs in these areas will likely not top 40 degrees.  However across
southern portions of the forecast area temperatures will jump into
the 50s with a few 60s possible on Tuesday. This will be helped
along by a brisk southerly wind as well.

Wednesday through Thursday...Models vary greatly with the Euro
continuing to flip flop on details.  The GFS has been consistent in
depicting a deep upper trough that closes off into an upper low with
a nearly stacked surface low over southeast Iowa.  The Euro flips
between a closed upper low and an open wave pushing across.  The
latest iteration is back to an upper open wave.  Either way we are
looking at precip during this period but with the GFS...it would be
considerably more precip and likely in the form of snow across the
north...a lot of snow across the north.  Turning to soundings, it is
clear that the airmass over the state will saturate quickly and to a
substantial depth.  This calls into question the highs for Wednesday
and Thursday.  Dewpoints on Wednesday will be in the upper 20s
northwest to the mid 40s southeast.  If we are indeed saturated, one
would expect temps to be closer to these dewpoints than the upper
50s and low 60s that MOS guidance is putting out.  Thursday will be
colder but guidance is still too warm.  I knocked temps back on
Tuesday about a category in the southeast and a few degrees north.
On Thursday, temps were again cooled but only by a couple degrees.

Soundings also suggest that other than a brief period of freezing
rain or sleet west central to northwest late Wednesday...ptype will
be all rain.  Late Wednesday night we do changeover to snow from
northwest into central Iowa as colder air pushes in with some
transition zone where again some freezing rain may occur.  The snow
will continue north Thursday but southern portions will likely
remain warm enough for rain.  The bulk of any snowfall falls in the
day4 to day 5 period and that is a bit too far out to figure how
much snow might occur...especially given the model uncertainty. Very
messy forecast beginning late tonight through Thursday night.
Soundings do show a rather deep mixed layer with winds near the top
of the mixed layer between between 35 and 40kts.  Winds will likely
be strong across the south especially on Wednesday night and
Thursday.  If this were to translate a little further north...where
snow is expected, we could be looking at a decent winter storm. This
system will continue to be evaluated for potential headlines in the
coming days.

Thursday night through Saturday...Once that Wednesday/Thursday
system passes east, upper ridging rebuilds across the region and dry
and warmer conditions move back into the forecast.  Highs will
range from the mid 30s north to near 50 south.

&&

.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1137 PM CST Sat Feb 24 2018

Area of MVFR cigs still passing across much of Iowa though will
continue move east overnight with conditions becoming VFR and will
then last through Sunday. Breezy west winds overnight will
diminish a bit on Sunday.

&&

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

$$

SHORT TERM...Beerends
LONG TERM...FAB
AVIATION...Donavon


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