Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 171204

Area Forecast Discussion
National Weather Service Des Moines IA
704 AM CDT Sat Mar 17 2018

...Update for Winter Headlines and 12z Aviation Discussion...

Issued at 703 AM CDT Sat Mar 17 2018

Wintry precipitation continues early this morning mainly focused
between Hwy 30 and I-80 along and east of the Des Moines metro.
This precipitation is still expected to come to an end from
northwest to southeast this morning. Iowa DOT road conditions
show limited if any impacts to roads over far north central Iowa
and have allowed the Winter Weather Advisory to expire in this
area. Elsewhere, will extend the advisory for lingering wintry
precipitation and road impacts until 10am. Road temperatures are
forecast to rise well above freezing by this time so impacts
should be lessening by mid- =morning. Rest of the forecast
remains on track at this time.


.SHORT TERM.../Today through Tonight/
Issued at 340 AM CDT Sat Mar 17 2018

GOES-East imagery shows the cyclonic spin over north central
Missouri as low pressure passes south of the state tonight.
Nighttime Microphysics imagery shows deeper ice clouds over central
and southern Iowa, which correlates well with where KDMX WSR-88D is
showing the precipitation early this morning. At 2:30am, a wintry
mix consisting of all forms (rain, ice pellets, and big ol` wet
flakes) was falling outside our office. Iowa DOT reports roads in
central Iowa between and including Hwy 20 and I-80 as partially or
completely slush or snow covered. As the early morning progresses,
ice introduction continues to be gradually lost and strong omega and
Q-vector convergence wanes over central and southern Iowa quickly
wanes between now and around 12z. This will end much of the steadier
precipitation toward daybreak. However, precipitation will continue
as cross sections and soundings show plenty of low level moisture
with weak omega lingering into mid-morning. This will foster more
freezing drizzle or drizzle versus snow. Drier air will work in over
northern Iowa ending the precipitation there first shortly after
sunrise before ending across all of central Iowa by midday as the
low pressure moves into the Ohio Valley.

While the precipitation will come to an end by midday today, the low
clouds will persist, especially over the southwestern half of the
state. Parts of northeast Iowa may have a good amount of sunshine as
high pressure drops in from the Dakotas. These thick clouds make the
high temperature forecast a bit lower confidence than typical.
Leaned toward the cooler side of guidance over the southwestern part
of the forecast area and the warmer side of guidance over the
northeast. This netted highs from the upper 30s to middle 40s. With
the low clouds lingering overnight, kept temperatures up a bit over
southern areas with lows ranging from the middle 20s to low 30s.

.LONG TERM.../Sunday through Friday/
Issued at 340 AM CDT Sat Mar 17 2018

Upper ridging to be in place initially Sunday with an area of high
pressure sliding off to the east with return flow setting up as an
upper wave digs through the central Rockies and out into the western
high Plains. This system is expected to slide eastward across
southern KS/OK and through southern MO into Monday before pushing
into the KY/TN region Monday night. Another upper wave will dig
south/southeastward through the northern Plains into NE Monday and
move through IA into Tuesday. The first southern system may brush
the far west/southwest/south central bringing a chance for some
light rain mainly into Monday. Winds also may pick up and become
gusty into Monday with a tightened pressure gradient in place. The
second system is expected to bring a better chance for precipitation
to much of the area into by late Monday night into early Tuesday.
Colder air will move in with the second system allowing any precip
to start mixing with snow or change to all snow into Tuesday
morning. Currently not a lot of snow expected with this system with
mainly a dusting to just under an inch possible with the highest
amounts expected in the northwest.  The second wave also shears
apart some as it drops through the state so expect precip chances to
wane through the day Tuesday with dry conditions resuming Tuesday

Upper ridging then builds out west by mid-week with northwesterly
flow aloft Wednesday into Thursday. GFS tries to show a weak wave
moving through the state, but the EC is not as bullish so could see
an increase in clouds with mainly dry conditions for Wednesday into
Thursday. By Thursday night WAA kicks in with moisture advection as
well all ahead of a large, broad upper level trough digging into the
western/west central US. An elongated area of low pressure stretches
from north to south across the Plains states with impulses of energy
aloft ejecting out of the main upper trough. This will result in
additional precipitation chances by Thursday night through Friday
night and possibly beyond the period into Saturday. The surface low
is expected to push track across southern Iowa by late Friday night.
Could see some periods of a rain/snow mix, especially in the north
but soundings across the south indicating better chance of rain for
much of the event.


.AVIATION.../For the 12Z TAFS through 12Z Sunday morning/
Issued at 703 AM CDT Sat Mar 17 2018

Wintry precipitation will end over central Iowa by mid-morning at
all terminals. Low clouds will persist through the period at FOD,
DSM, and OTM with IFR or MVFR restrictions expected. Model
guidance is trying to develop fog after midnight tonight over the
terminals, but favored the low ceilings at this time. Farther
north, conditions are already VFR this morning at MCW and MVFR
ceilings at ALO will improve to VFR around midday today. Winds
will remain light through the period.


Winter Weather Advisory until 7 AM CDT this morning for IAZ004-



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