985 
FXUS63 KDMX 072329
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
629 PM CDT Tue Sep 7 2021

.DISCUSSION.../Tonight through Tuesday/
Issued at 200 PM CDT Tue Sep 7 2021

Upper shortwave tracking through the Great Lakes has shoved a cool
front through the forecast area today. CAA and a compressed
pressure gradient behind the front have created breezy northwest 
winds, gusting above 30 mph at times in some locations. Storms 
have fired along and just ahead of the frontal boundary as it 
tracks into northern Illinois and southeast Iowa, but so far warm 
and dry mid- levels have inhibited convective development in our 
area. Hi- res models suggest additional convection may fire to the
west as the atmosphere becomes more unstable through peak heating
hours. The front should have just cleared our far southeast 
counties by that point and thus the forecast is dry. Winds relax a
bit tonight as the boundary layer cools and decouples, then pick 
back up again tomorrow as another wave of CAA moves through and 
the diurnal mixing taps into 15-25 kt flow just off the surface. 
Temperatures tomorrow will be a bit cooler with highs in the 70s. 
Favorable conditions for strong radiational cooling Wednesday 
night with clear skies and light winds. Temperatures were lowered 
a bit from NBM guidance which brings much of the north and west 
into the mid to upper 40s.

Forecast remains dry through Friday as deep northerly flow on the
eastern periphery of a western conus ridge pushes the frontal 
boundary well south toward the Gulf region, leaving our local 
atmosphere starved for appreciable moisture. The pattern becomes a
bit more active as the ridge axis begins to veer east and
undergoes deamplification from a series of shortwave troughs.
Forecast is trending warmer and breezy for Saturday as warm
southerly flow returns in response to an approaching upper wave.
GFS and ensemble guidance suggests some highs in the 90s will be
possible, however the forecast was not adjusted from NBM output
due to the potential for some mid/hi cloud cover. Euro is more
progressive and brings a surface front through on Saturday, while
the GFS is lagging more toward Saturday night into Sunday. The 
front will need to be watched for possible precip chances, 
although deep moisture return will be difficult due to a surface 
ridge axis parked along the TX/LA coasts. Still a signal for some 
precip in the GEFS/ECENS output, so an introduction of slight 
PoPs by the NBM is appropriate for now. A more favorable window 
for precipitation looks possible early next week as the boundary 
returns north as a warm front. Passing upper waves may activate 
the boundary and have more moisture to work with. 

&&

.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 629 PM CDT Tue Sep 7 2021

VFR conditions are forecast for the next 24 hours and beyond. The
TAFs are split out only for diurnal variation in northwesterly
winds, diminishing in the next hour or two then increasing and
becoming gusty again during the day on Wednesday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

DISCUSSION...Martin
AVIATION...Lee