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794
FXUS63 KDMX 230801
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
301 AM CDT Mon Sep 23 2024

.KEY MESSAGES...

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- Showers returning southeast today (25 to 40% chance)
- Tuesday slight rain chances with no impacts
- Lower confidence complex late week pattern with continued rather
  seasonal with showers possible (35 to 50% chance)
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&&

.DISCUSSION...
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Issued at 301 AM CDT Mon Sep 23 2024

Confidence: Medium to High

Weak ridge of high pressure managed to sneak into the region late
Sunday afternoon and provide for some clearing over the north and a
bit of sunshine late afternoon in the south. Subjective surface
analysis shows lee side trough forming over the High Plains while an
H500 trough evident on water vapor imagery is moving into southeast
Nebraska at 05z. This will eventually tap some of the moisture over
the mid Mississippi River Valley, resulting in some showers in
increasing PVA over the southeast as the trough swings east this
afternoon and evening. The region will see a variety of sky
conditions today with the north likely seeing a bit more sunshine
than the south during the afternoon. Areas between I80 and US30 will
see a sun cloud mix today. With that, highs will range from the
lower 70s north to the upper 60s in the far south. This evening
clouds will linger in the far southeast while most of the region
clears out through 06z. The next upstream wave over southern Canada
will dig south into Iowa by Tuesday morning with increasing clouds
and shower chances returning over the northwest; gradually spreading
south southeast into the afternoon hours. Slight rain chance to
chance rain (15 to 30%) will cover the southwest third of the
forecast area for Tuesday afternoon. Though CAPE is rather limited,
there may be enough to hear a rumble of thunder over the far
southeast Tuesday afternoon. The main ramifications of the digging
trough over Canada will be to phase with the southern stream H500
trough, creating a more extensive trough from the Great Lakes
southwest to the Southern Plains by late Tuesday evening. With the
chances for showers tomorrow, highs will be milder over the east and
far west in the lower 70s. Most areas will just top out over 70 for
the day.

.Long Term /Tuesday Night through Sunday/...

Confidence: Medium

As the trough swings southeast, any showers will come to an end by
late afternoon with partly cloudy skies continuing into the evening
hours. Most of the area will see decent radiational cooling Tuesday
night which will bring overnight mins back down to the mid to upper
40s north and in the lower 50s south. There remains a fair amount of
difference in the medium range models once again with the 00z
packages. The EC is again slower with any eastward progression of
the eventual H500 closed low over northern AR while the GFS initially
begins to trek it east, then retrogresses the upper level closed
low west southwestward into Friday evening. With the expectation
of more significant tropical development in the Gulf by later
Thursday into Friday, tracking into the eastern Gulf near Florida,
the models continue to advertise the tropical and extra tropical
systems phasing and eventually fully phasing into a rather
unusual upper level system over the mid to southern Mississippi
River Valley by later Friday and into the weekend. Though the
timing and placement of the large gyre remains rather uncertain,
it appears to impact our area with showers and some thunderstorms,
beginning as early as Friday to beginning as late as Saturday
afternoon. As might be expected, the blended approach we utilize
in our extended stretches the timing from late Thursday all the
way to Sunday night. This is not likely the best representation
and we will need to revisit the timing again for most of this
upcoming week. Given the tropical nature of the system, a large
portion of the southeast into the Central US will see rainfall
in excess of 3 to 5 inches. Specifically in our area, the risk
of any significant rain will remain lower with a mean ensemble
forecast by both the EPS and GEFs of about a half to 1.5 inches.
Farther south from central/southern MO to the southeast states,
a prolonged and more impactful rainfall and flooding event may
unfold later this week and into the weekend. Prior the arrival
of the unusual fall event this week, highs Wednesday and Friday
will likely be the warmest with mid to upper 70s from central to
northern areas; lower 70s south. Following that from Saturday
through Sunday will be more range bound in the lower to mid 70s
with shower chances for much of the period, provided the system
wobbles back north and west far enough to impact the region for
several days. Stay tuned for more forecast refinements as we
move through the week.
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.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1217 AM CDT Mon Sep 23 2024

Few impacts this period. H500 mb trough to track across Iowa
through period with return of moisture southeast leading to
lowering cigs and potential for some light showers aft
20z at OTM which will continue through 06z. Remainder of the
region will remain with high clouds while the southeast/south
will be BKN/OVC030 to 110 aft 18z through 06z. Small chance OTM
may see brief period of MVFR aft 00z as the band of showers
moves through. Winds light and variable through the period and
under 6kts. /rev

&&

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

&&

$$

DISCUSSION...REV
AVIATION...REV