FXUS63 KDMX 191138

Area Forecast Discussion
National Weather Service Des Moines IA
538 AM CST Tue Jan 19 2021

...Updated for 12z Aviation...

.DISCUSSION.../Today through Monday/
Issued at 341 AM CST Tue Jan 19 2021

An area of light snow/flurries/freezing drizzle is moving across
central Iowa this morning associated with a fairly weak shortwave
through. Though light, this could cause some slippery conditions
for the morning commute before is quickly exits the area shortly
after daybreak. Lift within the shortwave is very subtle, however
given sufficient moisture fields in model soundings and low
dewpoint depressions in surface observations this kind of
environment would not take much of a nudge to produce light
precipitation. A slightly more "robust" shortwave across the
northern plains early is evidenced on satellite and radar early
this morning. This secondary wave will drop across the area late
this morning into the afternoon bringing additional light snow
chances across the north/northeast. Accumulations will again be
fairly light, but a dusting to around a half inch is possible.
Subsidence is a bit stronger behind this secondary shortwave which
will impact a couple things this afternoon. First, loss of ice
introduction in the afternoon could result in a brief period of
light freezing drizzle as the system exits the area. And second,
subsidence will help to increase winds this afternoon with
soundings indicating 25-35+ mph gusts. The increasing winds this
afternoon could cause some minor blowing snow issues, especially
with a semi fresh snowpack after the weekend snow.

Warm air advection increases across the area Wednesday with upper
level ridging and a shortwave moving well to the north placing the
area within the warm sector. Initial southwest winds are fairly dry
before winds shift fully west later in the day Wednesday within
downslope flow and bring in better dewpoints. As such, there is some
concern that the snowpack could have a greater influence on highs
and prevent temperatures from getting quite as warm. Timing of that
wind shift will play role in just how warm the area can get on
Wednesday. By Thursday a cold front pushes across the area,
increasing cold air advection across the area. High pressure settles
across the area Friday, resulting in the coldest day of the week.

Meanwhile, a trough digging across the western US will begin to
phase with the northern stream as it moves in the central US. The
system is fairly messy as it moves across the CWA as models do not
completely phase the northern and southern streams until east of the
area. as such, there is still considerable uncertainty with this
system, especially in regards to precipitation type. Models
struggle with depth of the warm nose aloft and loss of ice
introduction later in the event which would significantly impacts
any accumulations. A wintry mix is likely further south with
better chances for only snow further north and into Minnesota, but
this will remain sensitive to any shift in timing and track.


.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 538 AM CST Tue Jan 19 2021

MVFR to IFR cigs blanket much of the area with considerable
improvement over western Iowa as early morning wintry weather
exits the area. Most sites will see a brief improvement in flight
conditions mid to late morning before a second round moves into
the state with a return to MVFR/IFR conditions. -SN is possible at
KFOD/KMCW/KALO this afternoon, possibly reaching KDSM though the
southern extent is less certain. All sites will see winds increase
this afternoon and evening, gusting 20-25+ kts at times. Winds
diminish and cigs improve by this evening.





NWS DMX Office Area Forecast Discussion