FXUS63 KDMX 180548

Area Forecast Discussion
National Weather Service Des Moines IA
1148 PM CST Sun Dec 17 2017

.SHORT TERM.../Tonight through Monday/
Issued at 331 PM CST Sun Dec 17 2017

System will depart to the east this evening with light flow across
the state initially.  The lingering low level moisture and light
winds should promote some fog development this evening and
anticipate at least some minor restrictions through midnight.
However, westerly flow will increase overnight with the passage of a
weak surface ridge.  This flow will be drier and aid in mixing
likely limiting fog potential as the night continues.  The low
status will also be pushed eastward by this increasing flow with
some clearing toward daybreak.  Overnight lows will be somewhat
tricky depending on the timing of clearing.  The longer the clouds
and fog linger, the better chance of temperatures remaining a bit

As for Monday, warm advection begins in earnest during the morning
and intensifies through the day.  The southwest surface flow will
increase and under mostly sunny skies, temperatures should respond
nicely by afternoon.  Anticipate readings to climb into the upper
40s to mid 50s given the good mixing through the day.

.LONG TERM.../Monday night through Sunday/
Issued at 331 PM CST Sun Dec 17 2017

Monday night through Wednesday night will be quiet with unseasonably
warm temperatures.  We are looking at lows in the 20s and 30s with
Tuesday in the 40s and 50s.  Wednesday will be a little cooler with
mid 30s northeast to near 50 southwest.  This will be the last of
the warm weather for the foreseeable future.

Thursday a deep trough digs into the desert southwest with a
resulting surface low developing in the western portions of the
Central Plains.  By Thursday evening the upper trough swings to the
lee side of the Rockies pushing the surface low and now inverted
trough with the surface low into central Iowa.  There will be a good
tap of moisture with this low but we will, at least initially be on
the warm side of this low so precip that develops Thursday will be
mainly rain south and east but northern Iowa should be cold enough
for snow.  Through the afternoon as the low progresses east and
colder air pours into the state, the rain will change to snow...and
based on soundings...rather quickly in the evening.  While the
amount of precip is in question as well as the switch over to
snow...it does look like some/most places will see measurable snow
by late Thursday night.

On Friday, models differ with the GFS suddenly hanging the low to
our east while the Euro and Canadian models push the low into the
Great Lakes.  This would put the deformation zone precip in
different locations.  The GFS would suggest a more widespread snow
statewide continuing into Friday while the other models keep much of
the state dry, except for far northern Iowa where additional snow
would be possible.  Too many variables to put a definitive number on
snowfall but it does look like most will see snow.

For later in the period...the Euro is more bullish digging yet
another trough into the west and spreading precip into the state
Saturday and Sunday, the GFS is similar but slower, moving precip in
the night of the 24th and 25th.  It is looking promising for a white
Christmas at this point.  In addition...the coldest air of the
season which has been bottled up in Canada looks like it will plunge
into the region beginning Friday night through the rest of the long
term period.

If we do get snow Thursday into Friday it will not likely completely
melt by the time the cold air arrives then add to that the snow
potential late in the weekend and on the 25th and we have the
makings for a white Christmas.  After seeing highs in the 50s early
this week, they will drop into the 20s and 30s by Friday and in the
teens and 20s by late in the weekend and next week. Overnight lows
from late weekend on will be in the single digits with teens only in
the far south.


.AVIATION.../For the 06Z TAFS through 06Z Monday night/
Issued at 1143 PM CST Sun Dec 17 2017

IFR and MVFR ceilings and visibilities continue in portions of
south central and east central Iowa. Surface winds will remain
weak and from the southwest through 12z. With light winds and a
moist boundary layer anticipating IFR and MVFR ceilings and
visibilities to remain overnight. After 12z, a surface trough in
western Iowa will traverse east across the state. Look for winds
to shift to strengthen resulting in increased mixing and a steady
improvement of ceilings and visibilities to VFR.





NWS DMX Office Area Forecast Discussion