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afddmx

Area forecast discussion
National Weather Service Des Moines Iowa
1029 PM CST Mon Nov 11 2019

Short term.../tonight through Tuesday night/
issued at 230 PM CST Mon Nov 11 2019

Confidence: high

Arctic high moving quickly southeast today and displacing the upper
level system as it pulls to the east. Sufficient boundary layer
speed shear is resulting in horizontal convective rolls and some
cellular convective elements this afternoon as clouds fill in
again over the region. Most of this activity will diminish between
21-00z and skies will clear out tonight. Winds will also diminish
with temperatures nose- diving overnight across the region. Near
record to record lows are on the way for tonight with several
sites expected to break records. High pressure will settle into
the area with the sfc ridge axis finally moving east of the area
after 12z. With little moisture aloft and the limited warming
today; will likely see sub- zero lows over the west and north by
morning. Even a few locations in the northeast likely to drop
below zero with the record snowfall we received last night and
today. As another upper level jet Max approaches the northern
plains Tuesday afternoon; a Lee side trough will develop south to
the plains. This will increase warm air advection later Tuesday
into Tuesday night with a recovery in temperatures and dry
conditions continuing. Lows tonight will dip to about 2 to 3 below
north while the south will see single digit overnight lows. Highs
Tuesday will range from the upper teens/lower 20s northeast to
the mid 20s west and south. Tomorrow night with warmer air
streaming in aloft, lows should be a bit milder yet again with
lows in the lower teens east to the upper teens/lower 20s west.

Long term.../Wednesday through Monday/
issued at 230 PM CST Mon Nov 11 2019

Confidence: medium to high

The next system approaches for Wednesday with saturation and light
snow expected to develop over the north from 12z to 18z Wednesday.
The period of peak forcing will be 18z to 00z Wednesday as the
shortwave moves quickly to the east. Temperatures will warm enough
south for a rain/snow mixture by afternoon while the north will
continue cold enough for all snow. Current operational model trends
suggest that this system will have less moisture to work with than
last nights. Both the Euro/GFS are in fairly good agreement on
amounts and placement of qpf; keeping the lions share of the
development along the trailing cold front as the upper level trough
swings east across Iowa Wednesday afternoon. With warmer
temperatures aloft this time; snow to water ratios will be much
lower and closer to a 10:1 ratio on average, for the event. This
should cap snowfall totals in the 1 to 2 inch range over the north
with lesser amounts in the south where lift and subsequent snow will
be less due to these factors and an initial mix prior to changeover.
Though the system that passed through earlier today easily exceeded
a few days prior expectations, this storm will not have the strong
frontogenetical forcing which was responsible for the rapid
accumulations we experienced last night/early today. Once the
system track east, a Canadian high will slides southeast over the
great lakes; keeping the coldest air over New England. We actually
will recover quite quickly into Thursday and Friday as h850
temperatures build back into a 0 to 5c range by Saturday. Another
generally moisture starved system will pass over the area Sunday
with a light rain/snow mix expected over our area. Though still
below normal, temperatures from Friday through Monday will begin a
slow climb back closer to normals; reaching the lower 40s northeast
Monday and in the upper 40s/lower 50s southwest. Lows will be cold
through Friday morning in the 10s/20s warming to the 20s/lower 30s
by next weekend.

&&

Aviation.../for the 06z tafs through 06z Tuesday night/
issued at 1029 PM CST Mon Nov 11 2019

Skies have cleared and are expected to remain clear through the
overnight hours with some high clouds towards late Tuesday and
Tuesday night. Northwesterly winds starting to diminish some as
the ridge axis moves toward central Iowa. They will continue to
diminish through early Tuesday and then shift around to the west
to southwest to south through the forecast period. Winds will then
increase again toward the end of the forecast period due to the
surface pressure gradient tightening ahead of the next weather
disturbance for Wednesday.

&&

Dmx watches/warnings/advisories...none.

&&

$$

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