629
FXUS63 KDMX 241144
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
644 AM CDT Tue Sep 24 2024

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

.KEY MESSAGES...

- Today slight rain chances with no impacts
- Milder temperatures return Wednesday through Monday;
  especially northwest/north
- Lower confidence complex late week pattern with continued rather
  seasonal with showers possible (35 to 50% chance)
- Late week rainfall amounts greater than 1/2 inch mainly far
  southeast

&&

.DISCUSSION...
Issued at 232 AM CDT Tue Sep 24 2024

.Short Term /Today through Wednesday/...

Confidence: High

Forecast progressing as expected. Trough over the Northern Plains
already producing an area of light showers over western MN as well
as far northwest IA into northeast NE early this morning. Yesterday
afternoons southern stream wave departing, with a few lingering
showers now near Burlington.  Most of our area is currently between
systems, with clear skies and patchy fog expected through early
morning. Subjective H850 analysis shows moisture return has been
weak overall through the Central Plains, with dry conditions
aloft over Iowa, but there is a pocket of 5C dew points from the
Dakotas north to southern Manitoba. HIRES models and synoptic,
too, are in generally good agreement with the a trough/trailing
cool front associated with the long wave trough in the Northern
Plains to move east today across the region. This will bring
very light showers/sprinkles into central Iowa through 15z. In
the afternoon, some isolated showers/brief thunder will still be
possible in the south/southeast through around 00z. Chances
today will be (15-30%) with rainfall totals of a couple hundredths
expected. With clouds being the main temperature restraint
today, highs are likely to top out in the lower 70s most areas
with a few upper 60s in the southwest. Tonight will see clearing
with lows in a seasonal range of the upper 40s to lower 50s.
Tomorrow, high pressure will arrive with weak flow both at the
surface and aloft. This will result in a very pleasant day as
H850 temperatures recover to the lower to mid teens from east to
west by afternoon. Highs will warm to the mid to upper 70s over
the region.

.Long Term /Wednesday Night through Monday/...

Confidence: Medium

Confidence this period remains medium with still some timing issues
to iron out regarding the beginning time of the showers as well as
the ending time of the precipitation early next week.

The overall evolution of the rather complex, but anomalous pattern
we continue to anticipate affecting the central and eastern CONUS
through late week is still intact. There remains uncertainty in the
exact details, but there has been slightly better consensus between
the medium range models GFS/EC regarding the overall impact to our
area and Iowa in general. The exiting southern stream trough is
still expected to phase with the digging northern stream wave we are
experiencing today and this a closed low process will occur over
southeast MO or northern AR by late tonight/early Thursday. Looking
farther south into the Gulf, the expected TS or hurricane reaching
the western or northwest coast of FL by Thursday afternoon will
begin to phase with the closed off H500 low near Arkansas. As the
two systems phase further, a Fujiwara dance will commence with the
entire system swinging back west toward Iowa by Saturday. Remarkably
the GFS/EC suites are in rather similar agreement for now, with most
of the remainder of the week still dry in our area until Saturday
afternoon. For the remainder of the weekend into Monday, the H500
low just parks itself and will likely fill/weaken into early next
week. This will then keep clouds and perhaps some showers over the
southeast two thirds of our forecast area during that time. With our
area being on the north/back side of the upper level low through the
evolution, we will not see much in terms of moisture/rainfall
compared to the folks in the southeast/mid Atlantic and lower Ohio
River Valleys. Though the ensemble mean precipitation in both the
EPS/GEFs suites suggest up to 1/2 inch in the far southeast at most,
the current 00z deterministic suites have backed off to one to two
tenths of an inch. Contrast that to the deluge expected from
southern MO to the lower Ohio River Valley and areas south
and southeast which may end up with widespread 5 to 9 inch amounts.
Through the period we will see a variety of temperatures with
precipitation chances/cloud cover higher in the south and southeast.
This area will see lower highs Friday through Monday with lower to
mid 70s common. The north/northwest will be slightly warmer with
readings closer to the mid to upper 70s. Mins will be milder
southeast and cooler northwest for similar reasons. Looking out
beyond Monday, ridging high pressure should replace the old filling
H500 system. This will bring the region more sunshine and back to
pleasant conditions.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 644 AM CDT Tue Sep 24 2024

Patchy fog and IFR/MVFR stratus has developed ahead of a band of
showers west of I35 this morning. As the clouds increase aloft,
the fog will lift and cigs rise back to VFR over the east and
southeast aft 18z. Generally quiet remainder of period. /rev

&&

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

&&

$$

DISCUSSION...REV
AVIATION...REV