Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 131743

Area Forecast Discussion
National Weather Service Des Moines IA
1143 AM CST Tue Feb 13 2018

.SHORT TERM.../Today through Tonight/
Issued at 344 AM CST Tue Feb 13 2018

Large area of high pressure across much of the Great Lakes and
west into Wisconsin will continue to move east today with return
flow and warm advection occurring into Iowa. Mid-level warm
advection is ongoing across Iowa currently with radar echoes
occurring, however with very dry air in place, little to no
precipitation is reaching the ground. Warmer air will continue to
lift north today, however the deeper snow pack will mitigate some
of the impact across the state. The current snow line resides just
south into northern Missouri. High temperatures today will
primarily range from mid to upper 20s north to the mid to upper
30s south. Low dew points in the 20s will limit melting today due
to evaporative cooling effects. The lack of melting should limit
the fog potential overnight.

.LONG TERM.../Wednesday through Monday/
Issued at 344 AM CST Tue Feb 13 2018

The inversion aloft will intensify and lower tonight into Wednesday.
There is a wide disparity between MOS guidance values and raw
output values due to the strong inversion aloft. Given the current
snow pack, expect it will be very difficult to mix too far
through the inversion and would keep temperatures much cooler than
MOS values. Have lowered the forecast with upper 30s north to low
to mid 40s south.

The lower level moisture and higher dew points will arrive late
Wednesday afternoon far south with dew points of 32 reaching
central Iowa into the overnight. These dew points will accelerate
melting and will also increase the fog potential Wednesday night
into early Thursday with dew point values warmer the the snow
surface arriving. Enough saturation over the far southeast may
yield a stratus deck and potential for drizzle and/or light rain
Thursday morning. A short wave and associated cold front will pass
through Thursday night. The system will be lacking moisture and do
not expect much if any precipitation. Gusty northwest winds will
develop in the wake of the cold front. Much colder temperatures
for Friday with highs in teens to mid 20s. Return flow will arrive
by Saturday and will again bring warmer temperatures to the state.
The next system arrives Sunday night into Monday and will bring
the next threat for precipitation to the state. At this time, snow
would be the predominant precipitation type. Much too early to
forecast amounts


.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1143 AM CST Tue Feb 13 2018

Main concern will be fog potential overnight. Models have various
solutions with SREF probs vsby less 1 mile nearing 65-75% across
much of the forecast area. Other hires solutions show mainly north
affected. Concerns remain about lack of snow cover just south of
the area and slow increase in dewpoints overnight. Have included
MVFR br over northern sites from 08z onward for now...with the
possibility of more prominent area of fog by morning where
melting and any moisture will have longer residence time over
snowpack. Models also indicate stratus deck moving north out of MO
toward 18z over far south. Uncertainties remain for both features
attm. Otherwise winds under 12kts aft 00z. /rev




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