Area Forecast Discussion
Issued by NWS Des Moines, IA

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473
FXUS63 KDMX 242125
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
325 PM CST Sat Feb 24 2018

.SHORT TERM.../Tonight through Sunday/
Issued at 324 PM CST Sat Feb 24 2018

Bulk of forcing is ongoing this afternoon with strong kinematics and
good isentropic lift.  Mid levels have remained relatively dry
except in far western and northern areas leading to widespread
drizzle across much of central and southern Iowa as temperatures
have climbed above freezing east of a line from Mason City through
Fort Dodge to Atlantic.  Will continue to see saturation deepen
ahead of approaching front with precipitation becoming heavier late
this afternoon into early evening along the front as it progresses
eastward across the forecast area.  Northern Iowa will see strictly
snow which may be heavy at times with convective elements
progressing northward into Minnesota.  Total amounts may not be as
high as previously thought but 2 to 4 seem reasonable.  Farther
south, drizzle and rain are expected to persist ahead of the front
with temperatures remaining above freezing.  However, there will be
some snow coincident or just behind the front as cold air advects
quickly in on the backside of the boundary.  If any convective
elements develop along the front, there may be a brief period of
heavy snow with them as well.  Otherwise, there is also some concern
where the winds are light this evening prior to frontal passage that
fog may quickly thicken.  While this will only be for a short time
prior to the front passing, it may become dense until the heavier
precipitation begins.  Overall snow amounts in central and southern
Iowa will be minimal.  The advisory will be maintained in all areas
but it remains very marginal on the southeast side where snow
amounts will be quite light.  The biggest concern will be the cold
air arriving on the backside of the front with strong west winds
helping water on roads to freeze somewhat quickly.  This may lead to
some icing concerns into the evening.

Otherwise, once the front passes, strong west winds and clearing
skies are forecast overnight as cooler air arrives.  Relatively
strong subsidence is then expected into Sunday with some sunshine as
westerly flow at the surface.

.LONG TERM.../Sunday night through Saturday/
Issued at 324 PM CST Sat Feb 24 2018

Summary...Quiet weather will dominate the next few days, along with
temperatures rising above freezing, even into the 50s across the
south. Wed/Thur could be impactful with guidance beginning to show
some semblance of agreement of a large wrapped up low sliding across
SE Iowa. Implications may range from heavy rainfall to blizzard-like
conditions across Iowa.  Quiet, relatively warm weather returns to
end the week/start next weekend.


Sunday through Wednesday Morning...By Sunday, upper level flow will
being to become predominantly zonal across CONUS as the upper level
system responsible for the freezing rain/snow Saturday departs into
the Great Lakes and eastern Canada. The zonal upper level flow and
surface return flow will be in place through mid-week, resulting in
temperatures gradually rising over the next few days, topping out
Wednesday in the 40s/50s.  A weak backdoor cold front will likely
keep northern Iowa from tapping into the 40s Tue/Wed, as high
pressure slowly slides across the Dakotas.

Wednesday Afternoon through Thursday...Easily the greatest potential
for impactful weather over the next 7 days. GFS has shown relative
consistency in developing a cutoff upper low and surface reflection
as an upper level trough ejects out of the SW US.  Euro has
predominantly held off on developing anything of that strength,
keeping it as an open wave, however that changed with the 12z run.
Euro now in fair agreement with the GFS, depicting a tightly wound
surface low approaching 986 mb. Should this come to fruition,
blizzard-like to blizzard conditions appear likely somewhere over
N/NW areas. Elsewhere further S, heavy rain to thunderstorms.  Given
Euro flip just in the last run, confidence too low to make any large
changes to the forecast.  Should consistency remain over the next
couple runs, a ramp up in messaging will likely be necessary, among
other things such as increasing winds, etc... A big hindrance to
precip type at the moment is high variability in the ensembles,
approaching 5 standard deviations in some cases, only adds to low
confidence in overall ability to make gainful changes to the
forecast at this time. Once again, easily the time frame to pay
attention to.

Friday through Saturday...Quiet weather returns with ridging
depicted across also synoptic guidance. Temperatures would appear
set to rise back into the 40s/low 50s by Saturday.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 115 PM CST Sat Feb 24 2018

Poor general aviation conditions this afternoon into the early
evening with widespread IFR/LIFR ceilings and visibilities. Areas
of fog, light rain, light freezing drizzle, sleet and snow are
expected across central into northern Iowa ahead of a front which
will pass through this evening. Strong west winds on the backside
of the this system will allow for rapid clearing with VFR
conditions becoming widespread after midnight across much of the
area. The west winds and VFR ceilings and visibilities will
persist into Sunday morning.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM CST this evening for IAZ033-
034-044>049-057>060-070>072-081-092.

Winter Weather Advisory until midnight CST tonight for
IAZ004>007-015>017-023>028-035>039.

&&

$$

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



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