421
FXUS63 KDMX 270933
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
333 AM CST Mon Jan 27 2025

.KEY MESSAGES...

- Warm and breezy today and Tuesday, and warm again Thursday.
  Near record or record highs possible northeast Tuesday and
  Thursday.

- Elevated fire weather conditions today

- Dry through Thursday, then precipitation chances return late
  in the week

&&

.DISCUSSION...
Issued at 333 AM CST Mon Jan 27 2025

Our recent dry, breezy, and warm northwest aloft flow pattern
will persist into the middle of the work week, but that will
change later this week with precipitation chances increasing to
end the work week. Skies were clear to start the day with
soundings showing plenty of dry air through the troposphere. A
lobe of kinematic and mainly thermodynamic forcing was rotating
into the northern Plains and Great Lakes through the base of the
large Hudson Bay upper low however, with these effects brushing
IA later today mainly with increasing mid and high layer
cloudiness. While the 00z HRW ARW is fairly aggressive breaking
out precip into northern IA by late afternoon and influencing
the HREF somewhat, this seems to be an overzealous outlier with
nearly all the other guidance dry. While mid levels may near
saturation, soundings suggest 2km and below should be equally
dry keeping any precip virga. Temperature wise, it should be
another decent downslope warm up day. Guidance has been under-
performing in the these situation recently, so have nudged highs
to the high end of the guidance suite both today and tomorrow.
Highs should be well into the 40s today, and touch or exceed 50
in spots tomorrow. Near record highs are possible northeast
Tuesday, aided by the atypical lack of snow cover. These dry low
levels will also promote sufficient mixing to tap stronger
winds at 500m or so, resulting in wind gusts north of 30-40 mph
today and tomorrow. This regime will also lower dewpoints and
result in elevated fire weather conditions discussed below.

A short wave on the nose of a jet segment dropping into the
southeast Canadian upper low will support this warmth Tuesday,
but also follow with a weak cool front and trailing surface high
pressure with only minor cooling Wednesday. By Thursday our
attention will turn to the current southern CA upper low as it
passes through AZ and NM Wednesday and eventually reaches the
southern Plains Thursday night. This pattern shift will flip low
level winds to southerly again Thursday, and with rising H5
heights bringing in even warmer air. Widespread highs in the
50s are anticipated Thursday, with record highs possible again
northeast where records are more tempered due to what would
typically be snow cover.

Although there are differences with respect to timing and how
soon the system weakens/opens up, the deterministic and ensemble
guidance suite is now in much better agreement with the system
passing to our south late this week. While there will be some
thermodynamic components and theta-e advection at onset, the
main forcing mechanism for us appears to be kinematic and
deformation zone driven with noted H5/H3 QG forcing, this should
result in the most substantial precipitation event we have seen
for awhile over southern IA. Although timing is uncertain, this
looks to appears sometime Thursday night through Friday night
with the GFS/GEFS suite slower, and companion EC guidance a bit
faster and opening up sooner. While any particular 6 hr window
of measurable precipitation chances through this window are 50%
or less due uncertain system timing, precipitation chances with
system passage as a whole are higher. EPS and GEFS 24 hr
probabilities of at least a tenth of an inch of precip are 70+%
with the system. While most of the system looks to be a cold
rain, there is still some minor snow potential south along the
MO border closer to the upper low with EPS and GEFS 24 hr
probabilities of 1" 30% or less.

Once this system passes later in the week, our pattern will turn
to progressive zonal flow aloft. This will bring yet another
round of warmer temps to end the weekend, and possibly some
light rain or light snow north as a short wave crosses the
northern Plains. However any precipitation that occurs looks to
be minor and transient, if it occurs.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1122 PM CST Sun Jan 26 2025

VFR conditions prevail through the period. Gusty westerly winds
will develop through the day today, with gusts of 25 to 30+ kts
at times. Stronger gusts up to 35 kts are possible in northern
Iowa, especially KMCW. Still anticipating a few hours of LLWS
in the morning at KFOD, KMCW, and KALO. Have also added a few
hours of LLWS to KDSM before mixing occurs and surface gusts
pick up later this morning. More LLWS may also develop for a
few hours at KDSM and KOTM as the inversion sets up this
evening, but have kept out of TAFs at this time given the short
duration and it being toward the end of the TAF period.

&&

.FIRE WEATHER...
Issued at 333 AM CST Mon Jan 27 2025

Although we are out of season, a special Fire Weather Planning
Forecast will be issued today. With near record warming north,
wind gusts to 35 mph or more north, and relative humidities
below 30% by afternoon, this will elevate fire weather
conditions, especially with most fuels dry from the lack of
recent precipitation and atypically low snowfall and snow cover.
High temperatures mainly in the 40s should temper the concern,
but Red Flag conditions will be approached with GFDI values in
the Very High category by afternoon.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Dodson
FIRE WEATHER...Small

NWS DMX Office Area Forecast Discussion