667
FXUS63 KDMX 212337
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
537 PM CST Thu Nov 21 2024

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Gusty winds gradually diminish west to east through the
  night.

- Cool temperatures Friday, but warming trend into the weekend
  with mid 40s to upper 50s returning by Sunday. Dry conditions
  continue Friday-Sunday.

- Colder next week as high temperatures fall to the 30s.

&&

.DISCUSSION...
Issued at 245 PM CST Thu Nov 21 2024

Expansive cloud shield continues to spin around the low which has
moved into the Ohio Valley region, as noted on satellite early this
afternoon. In Iowa, stratus did not linger nearly as long as
anticipated nor as suggested by most guidance leading to clearing
skies and the return of sunshine for many across central Iowa. The
additional sunshine has resulted in slightly warmer temperatures
today in the 30s to mid 40s, which is likely a welcome change after
yesterday. However, the gusty winds remain with a tight pressure
gradient over the state of Iowa with gusts ranging from about 25-45
mph around 19Z (1 PM CST), the highest gusts in eastern areas.
Although a few sites have touched low end wind advisory criteria,
the windier conditions are to the east of the area where a wind
advisory remains into this evening (see NWS DVN discussion/products
for further details). Winds will gradually diminish tonight into the
overnight west to east as the surface low consolidates and a high
pressure begins to nudge into the region. This could create some
potential for patchy fog overnight/early Friday mainly west or
northwest into portions of northern Iowa where lingering low level
moisture combines with the light winds in proximity to the incoming
high. Uncertainty remains high in exact placement in time with
significant variability amongst models and questions remaining in if
fog can even form with the winds (although diminishing), back
building stratus, and some additional incoming higher level clouds.
All this being said, probabilities for visibilities less than 1 mile
are only 10-20% in portions of northern to western Iowa, per HREF
ensemble, and even less with the NBM. Thus, given low confidence and
overall likeliness, no fog mentions were added to the forecast but
will let next shift continue to evaluate trends and provide updates
if conditions become more favorable. Meanwhile, the
aforementioned back building stratus will bring the return of
clouds over much of the eastern 1/3rd to 1/2 of the area
(portions of central/east central into eastern Iowa), which will
help keep lows similar to a tad warmer than last night and in
the upper 20s to near 30s, while areas west drop towards the low
20s and maybe even some teens!

With the high pressure moving through Friday into early Saturday,
dry conditions are expected to continue to end the week and start
the weekend. A cooler Friday featuring highs only in the upper 30s
to mid 40s (though less wind!) will give way to warming temperatures
Saturday and even more so Sunday as flow returns to be out of the
southwest bringing warm air advection and highs in the 40s to 50s
Saturday, and maybe even a few readings near 60 south on Sunday (if
cloud cover doens`t spoil it). A weak wave will pass beneath the
weak upper ridge on Sunday but continues to remain out of phase with
the better parameter space and lacks moisture needed for
precipitation. End result at this point will be increasing cloud
cover Sunday, as previously alluded to, however, much cooler air
filters back into the area behind this wave into Monday. After our
pleasant weekend, high temperatures fall back into the 30s with lows
in the teens to 20s with these cooler temperatures persisting
through much of the next week. This may be your last weekend
with warmer temperatures to finish any fall outdoor projects!

As noted in the previous discussion, we do continue to watch
multiple waves tracking through the otherwise primarily zonal upper
flow next week that could introduce precipitation chances at times,
and could be in the form of frozen precipitation/snow given the
temperatures noted, should sufficient moisture exist. In saying
this, it is exceptionally challenging to focus in on specific
details at this time range and within a zonal flow regime given
the number of energy pulses that drift through the overarching
flow. The main takeaways at this point are to continue to
monitor the forecast for updates for any precipitation chances,
but to otherwise prepare for colder temperatures as we head into
Thanksgiving week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 537 PM CST Thu Nov 21 2024

MVFR conditions due to low stratus remain over the eastern
terminals this evening, with this low cloud cover expected to
become more widespread across all terminals into the late
evening and remain through at least late morning to early
afternoon Friday. Low ceilings will result in widespread MVFR
and at times IFR conditions through Friday morning. Clouds
gradually depart eastward into the afternoon and towards the
evening Friday, improving ceilings. A small signal remains to
the north and west for fog into Friday morning, though
uncertainty remains as winds still look to be a bit too high to
develop fog, so have left out and will continue to monitor.
Breezy NW winds gradually lighten up this evening, with values
generally up to 8-12 knots into Friday.

&&

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

&&

$$

DISCUSSION...KCM
AVIATION...Bury