975
FXUS63 KDMX 251750
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1250 PM CDT Wed Sep 25 2024

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Milder temperatures return through Monday - especially
  northwest/north
- Slightly lower confidence late week pattern with continued
  rather seasonal temps & showers possible (lingering slight
  chance)
- Late week rainfall amounts trending much lower to dry over the
  region

&&

.DISCUSSION...
Issued at 250 AM CDT Wed Sep 25 2024

.Short Term /Today through Thursday/...

Confidence: High

System that affected Iowa Tuesday continues to depart to the east
and is currently over the eastern Great Lakes. Subjective H850
analysis shows we remain in weak northwest flow at 00z. A blocking
ridge of high pressure extends from the east coast  to the Gulf,
then back to the Western Plains and Rockies. The airmass has cooled
sufficiently this morning to again create some patchy fog in valley
areas over the region. Like Tuesday morning, it should burn off
quickly after sunrise. Today will be rather pleasant with high
pressure settling over the region this afternoon. A few fair weather
clouds are expected to develop mainly east of I35 today during the
afternoon hours. Otherwise, light winds and mild conditions are
anticipated as H850 temperatures recover to 10C east to near 13C
northwest. Tonight the ridge resides nearly overhead. With that
another night of decent radiational cooling will occur with a rather
shallow inversion setting up in the boundary layer. After highs
today in the upper 70s to around 80, tonight will see mins in the
mid to upper 40s north to the lower 50s south. Urban areas, like the
metro, will be warmer in the lower to mid 50s. Thursday will be
nearly a carbon copy of today. Though some fair weather clouds may
again develop in the afternoon, highs will warm to the upper 70s to
lower 80s over the area with light east southeast winds for the day.

.Long Term /Thursday Night through Tuesday/...

Confidence: Medium

The overall evolution of the closed H500 low and merger of the
eventual Hurricane Helene in the southeast will again be the
challenge of the late week forecast. Overall the position and
movement of the combined system is now trending farther east of
Iowa, suggesting that our area will be mainly or totally dry
compared to 2 to 3 days ago. Both the EC/GFS deterministic
solutions now keep all of our area dry through the weekend,
while the ensemble mean of both medium range models still
suggests a small potential of the upper low wobbling back toward
Iowa far enough, that some light showers may edge into the
region later Saturday and Sunday over the southeast. Rain
chances would be slight and any beneficial impact of rainfall
would be nil. Overall, a slight warming of the column will occur
between Friday into Monday as H850 temperatures warm from the
lower to mid teens to the mid teens. This will keep highs 5 to
10 degrees above normal for late September. Overnight mins will
be slightly above normal as well. By late in the weekend, a
system tracking through the Central Canadian Plains will drag a
cold front through Iowa Monday, followed by a rather cool
Canadian High Pressure system. This is expected to drop highs
back to the 50s to lower 60s by Tuesday, with lows late in the
period in the 30s to 40s. There remain some differences in the
EC vs GFS handling of next weeks cool off, but the signal for
a return to cooler, fall conditions is present in both solutions.
With the trends now for little weekend moisture, our area should
remain dry for much of the next 7 days.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1245 PM CDT Wed Sep 25 2024

VFR conditions ongoing and expected to continue through the TAF
period with just some daytime cumulus bringing few to sct CIGs to
most TAF sites this afternoon before clearing tonight. Winds
remain light, generally near to under 10 knots, out of the
north today but become light, under 5 knots, tonight, varying in
direction.


&&

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

&&

$$

DISCUSSION...REV
AVIATION...KCM