549
FXUS63 KDMX 230441
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1041 PM CST Sat Feb 22 2025

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Warming Trend Continues with slight chance (20%) rain north
  Monday
- Midweek system with light rain chances 40 to 50%
- Cooler by weekend but uncertainty on how much given some
  model spread

&&

.DISCUSSION...
Issued at 145 PM CST Sat Feb 22 2025

.Short Term /Tonight through Sunday Night/...

Confidence: High

Main challenge next few days will be temperatures. With snow cover
across our area and areas west/southwest, warming will be somewhat
capped over some areas due to the melting expected as we continue to
warm. With todays highs nearing/breaching the freezing mark, snow
will likely melt and compact into the overnight. Increasing clouds
this afternoon/clouds tonight will help keep mins in the upper teens
to lower 20s with southwest flow over the area.  Sunday, we will
continue to warm as H925/H850 temperatures moderate through the
period.  Soundings suggest that mixing will be rather limited due to
shallow boundary layer depth. Combined with preexisting snow cover,
there will be preferred areas of warming the next few days. Those
with greater snow cover will warm more slowly while the south and
far northwest likely see highs a bit warmer. Sunday the clouds/warm
air advection will lift east of the state and allow all of the
region to see sunshine through the day. Highs will reach the lower
40s northwest, upper 30s to 40 in the snow band from west central to
northeast areas and in the mid 40s in the far south. Sunday night we
will cool to around the freezing mark over many locations. The
melting snow tomorrow will likely moisten the boundary layer and
potentially we may see frost develop on area roads Monday morning.
This would be more true of road/surfaces that have not been treated
with salt in the past week. Those that have or still have salt
lingering may just become wet as humidity levels near the surface
get above 85 to 90%. This will be monitored by the next several
shifts; particularly the overnight shift Sunday night.

.Long Term /Monday through Saturday/...

Confidence: Medium to High

We continue with a few weak systems moving over the region next week
Monday through Friday.  The bulk of the energy is entering the flow
over the Pacific Northwest and the attendant moisture will be
somewhat limited compared to our usual moisture source from the
Gulf. The first system just brushes the far north Monday
afternoon/evening. Both model suites mean ensemble precipitation
over the north amounts to a few hundredths where any rain falls into
Monday evening. We will continue to see some influence from the snow
cover on high temperatures Monday, though less than Sunday.  Highs
Monday will rise to around 50 far northwest and in the lower 50s in
areas generally along and south of I80. The west central to
northeast will warm to the mid to upper 40s.  Both model suites
indicate a weak boundary passing south of the state Monday evening
with a cooler airmass passing over the state Tuesday. This is
currently not reflected in our guidance. There remain some timing
differences with the approach of the midweek system with the GFS
suite slower than the Euro. Though H850/H925 temperatures will be on
the increase by late afternoon Tuesday, this may not be enough to
push our current forecast to the values we are forecasting and we
may have to make a few degree downward adjustment moving forward.
With the main sfc/aloft low again north of Iowa Tuesday/Tuesday
night, we will see most of the forcing take place nearer the low.
With respect to available moisture, this system again originates in
the Pacific Northwest and will have not have much moisture, though
more than the previous. The best area of warm air advection/lift
will be over northern/eastern areas Wednesday evening into early
Wednesday morning and most of the precipitation will be done by 12z
Wednesday. A few days back it looked like some of the cold air would
arrive prior to the lows exit, but all solutions now point to a
liquid event. Following the midweek system, weak cold air advection
again arrives for Wednesday with a general weak rise/fall in airmass
temperatures as another northern stream wave passes over MN/WI
Friday into Saturday. There are some differences with the
hemispheric H500 pattern by weeks end with the EC digging a
piece of energy into the Great Lakes by Saturday while the GFS
keeps nearly all of the energy locked within the gyre. Thus the
extent of any cool down is currently a bit uncertain going into
next weekend. The current 12z EC is beginning to mirror the GFS
more than the 00z run. Average guidance suggests a middle of
the road approach with upper 30s/40s forecast while in reality
the spread is about 5 to 10 degrees across the board.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1041 PM CST Sat Feb 22 2025

VFR conditions are expected through the TAF period and beyond. A
few patches of fog may form later tonight near sunrise Sunday,
but the probability of impact at any terminal is far too low
(~10%) to include in the outgoing TAFs.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...REV
AVIATION...Lee