Area Forecast Discussion
Issued by NWS Des Moines, IA

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320
FXUS63 KDMX 091133
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
533 AM CST Fri Dec 9 2016

.SHORT TERM.../Today through Tonight/
Issued at 331 AM CST Fri Dec 9 2016

Stratus clouds and flurries stubbornly persist across about the
northeast half of the forecast area early this morning. However,
some erosion is noted in satellite imagery further northeast and the
radar returns of flurries are gradually shrinking. In addition, a
storm system developing along the lee of the Rockies this morning is
compressing a surface ridge draped across eastern Nebraska, and as
it builds eastward today this should help to push the remaining
stratus out of our area by late morning. Have maintained low POPs
until around 8 am in this scenario, but in any event, no real snow
accumulation is expected. Later today, a weak mid-level impulse will
move over northern Iowa and may squeeze out some light snow showers,
even in the absence of convincing moisture. Will carry chance POPs
for a bit in the evening up toward the Minnesota border, but again,
little to no accumulation is anticipated. Aside from these
flurry/light snow chances, it will be quiet and cold again today
with highs again in the mid teens to mid 20s.

.LONG TERM.../Saturday through Thursday/
Issued at 331 AM CST Fri Dec 9 2016

Little in the way of changes for the main features through the
mid/long range. Focus still on the chances of snow this weekend and
then temperatures into next week. Large area of surface high
pressure to push east through Friday night, with a developing area
of low pressure over the central high plains in westerly upper level
flow pattern. Southerly flow and theta-e advection increasing
through the day Saturday, with onset of precipitation likely to be
toward the later morning hours as lower levels remain drier with
deeper saturation of the column not expected until 15-18Z west, and
18-21Z east. Main snow track still expected across the northern CWA,
with a period of snow for central/southern IA still possible in
strong waa/moisture advection. Overall expect a long duration of
light snow across the northern/northeastern third of the CWA leading
to moderate to heavy accumulations through Sunday night. State
remains under broad synoptic lift pattern until stronger shortwave
trough digs into the northern plains Sunday sending the first in a
series of cold fronts through the CWA. Therefore have continued
higher pops across the CWA into Sunday/Sunday night, with decent
lift/saturation expected across the entire CWA. Expect around an
inch of snow through Sunday night far south, 1 to 4 across the
central CWA along and south of a line from Sac City to Grinnell, and
then 4 to 7 inches over the 48 hour period across the north and
east. Even through heaviest snow totals pushing 6 inches, winter
watch headlines not considered at this point given the snow is
expected to occur over a long time period greater than 24 hours.
Other winter headlines such as advisories likely to be issued within
the next 24 hours.

Expect a break in the precip for Monday, before the first arctic air
moves in. Expect another round of light snow with the frontal
passage Monday night. Main dynamics move off to the north and east,
so mainly just light snow anticipated. Arctic air will then remain
entrenched across the CWA for much of next week. Some weak energy
moving through the west to northwesterly flow pattern aloft may
bring some light snow Tuesday into Wednesday, but overall nothing
looking widespread with more of a dry, very cold pattern expected
for now. Pushed guidance temps down a bit Tuesday through Wednesday
especially overnight lows across the north as snow cover from this
weekend`s systems should help send temps even colder than guidance
grids suggesting.

&&

.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 533 AM CST Fri Dec 9 2016

MVFR ceilings will continue intermittently at MCW/ALO/OTM for the
next couple hours, perhaps with some brief flurries, but satellite
imagery indicates the cloud field continues to erode and is
expected to break up by mid-morning with VFR conditions
thereafter. Tonight low clouds will redevelop, perhaps with some
light snow up toward MCW, but ceilings are expected to largely
remain VFR. Some MVFR ceilings may be possible again overnight,
but this will be reassessed for later TAF issuances.

&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Beerends
AVIATION...Lee



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