Area Forecast Discussion
Issued by NWS Des Moines, IA

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074
FXUS63 KDMX 061738
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1138 AM CST Tue Dec 6 2016

.SHORT TERM.../Today through Tonight/
Issued at 331 AM CST Tue Dec 6 2016

Frontal boundary has nearly cleared the forecast area early this
morning with brisk northwest winds picking up on the backside.
However, the push of colder air is just arriving in western Iowa and
this cold advection will intensify through the morning as the brisk
winds persist.  The narrow band of precipitation associated with the
front will continue to produce light rain and light snow across
portions of central Iowa, mainly east of the I35 corridor through
daybreak, although as strong subsidence and drier air work into the
state, any precipitation will end quickly by mid morning in the far
eastern portions of the CWA.  Highs in the east may occur this
morning prior to the arrival of the stronger cold advection with
nearly steady temperatures farther west as the cold advection will
already be underway.  Winds will be strong from the west northwest
today aided by subsidence and some sunshine helping with mixing.
Anticipate winds to be just sub-advisory in the favored windy areas
of the north and west with gusts of 40-45 mph in these locations.
Relatively clear and cooler conditions tonight with a brisk wind
persisting, although not nearly strong as the daytime velocities.

.LONG TERM.../Wednesday through Monday/
Issued at 331 AM CST Tue Dec 6 2016

Fairly decent agreement with the long-range models through the mid-
term, with some differences noted toward the end of the period.
Mainly with timing/placement of systems. Broad upper level trough
still in place across the region Wednesday and begins to move east
into Thursday with more of an anticyclonic northwesterly upper level
flow pattern in place, with weak ridging in place across the western
US. An upper level trough then builds into the western US for the
end of the week into the weekend with shortwave energy streaming
eastward through the state. Much of the moisture/energy remains to
the north of the CWA, but still some light snow will be possible
across the northern CWA. A developing area of low pressure will
slide through the region mainly Saturday into Saturday night, with
the GFS/EC in disagreement on the strength/placement of this system.
GFS deepens the low more than the EC, and digs it further south
which would result in a more organized storm system to move through
the state with central IA on the colder side of the low. EC keeps
the wave more open and progressive, and is a bit further north
keeping much of the state in the warmer air and with lighter
precipitation. Will continue to pops during that timeframe and
monitor for more certainty in the next few days.

As for temperatures through the period, still have the colder air in
place to begin the period, with a reinforcing shot of colder air
into Thursday. This push of cold air could result in some light
flurries further north. Stronger flow aloft and caa will keep winds
blustery through Thursday. H85 temps drop to around -15C by 00Z
Friday, which will result in highs only in the teens to around 20
Thursday and overnight lows around 10 above. Wind chills will likely
fall into the single digits below zero both Tuesday and Wednesday
night. Temperatures then moderate aloft into the weekend with highs
climbing back toward the seasonal averages. Another cold snap looks
to come just beyond the current forecast period toward the middle of
next week.

&&

.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1138 AM CST Tue Dec 6 2016

VFR conditions will prevail most sites through the period. KMCW
will have intermittent MVFR cigs this afternoon that may linger in
to this evening. Breezy west wind will continue this afternoon
with the gusts diminishing overnight before increasing again
Wednesday morning. Mid level clouds will increase overnight but
remain AOA 10 kft.

&&

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

$$

SHORT TERM...Cogil
LONG TERM...Beerends
AVIATION...Donavon



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