253
FXUS63 KDMX 191114
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
514 AM CST Sun Jan 19 2025

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Dangerously cold conditions through Tuesday morning with wind chills
  of -20F to -30F at times, especially over the northern half
  of the state.

- Temperatures warm back to closer to seasonal norms Wednesday
  into Thursday along with chances (around 20%) for light
  snowfall.

&&

.DISCUSSION...
Issued at 242 AM CST Sun Jan 19 2025

Our Arctic cold snap is well underway as a 1040+mb sfc high
anchored over the northern high Plains and beneath an expansive
deep trough aloft continues to push bitter cold air into the
region. Wind chills tonight have fallen to -10F to -30F over
the forecast area. Only marginal recovery through the daylight
hours today with highs in the single digits above zero and
steady northwest winds keeping wind chills comfortably below
zero. Issued the next in our series of Cold Weather Advisories
for tonight into Mon AM for the northern 2/3 of the forecast
area where wind chills of -20F or colder are highly likely once
again. Air temps bottom out Monday night as the surface high
nudges eastward and winds relax a bit, allowing for more
efficient radiational cooling within a bitter cold airmass
characterized by highly anomalous 850mb temps of -26C to -32C.
Statistical guidance from the GFS and NAM suggest lows as cold
as -20F are possible in portions of northern Iowa. NBM and
GEFS/ECENS are not quite as aggressive with <10% probs of lows
reaching -20F, but have still been steadily trending slightly
colder. Another round of cold weather headlines will need to be
considered with future forecast updates.

Models have been trending a bit slower to erode the cold airmass
Tue with another day stuck in the single digits and teens. A
return to southerly sfc flow and waa take over Tue night into
Wed and quickly brings temps back closer to seasonal norms.
Attention at this point turns to increasing potential for light
wintry precipitation Wed into Thu as successive weak shortwaves
traverse through the persistent mean northwest flow aloft.
Confidence in the precip scenario is hindered by skepticism on
the quality and timing of moisture return back into the region
in the wake of the exceptionally dry Arctic airmass. Both the
GEFS and ECENS have increasing probs (40-60%) for measurable
precip, but very low probs (<10%) for snow accums exceeding 1".
May be looking at a high PoP/low QPF scenario of light snow
and/or flurries which is typically poorly captured by the global
models and NBM output at this time range.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 512 AM CST Sun Jan 19 2025

VFR conditions prevail over the vast majority of the area early this
morning. A few translucent low cloud streaks are evident on
satellite, producing tempo MVFR cigs and even very fine snow flakes
at times. These streaks are very narrow and should dissipate by mid-
morning, so opted to only include them as a tempo group at KDSM and
KFOD. Beyond that point VFR conditions should prevail at all
terminals through the remainder of the TAF period. Gusty northwest
winds relax below 10 kts after 00z this evening.&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Cold Weather Advisory until noon CST today for IAZ004>007-
015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097.
Cold Weather Advisory from 3 AM to 11 AM CST Monday for
IAZ004>007-015>017-023>028-033>039-044>050-057>059-070-071.

&&

$$

DISCUSSION...Martin
AVIATION...Martin