532
FXUS63 KDMX 132340
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
640 PM CDT Tue Aug 13 2024

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

.KEY MESSAGES...

- Back-to-back rounds of thunderstorms overnight tonight into
  Wednesday morning and again late Wednesday into Thursday
  morning. Heavy rain and a few strong to severe storms are
  possible.

- Warmer and quieter forecast into the weekend.

&&

.DISCUSSION...
Issued at 231 PM CDT Tue Aug 13 2024

Lingering patchy fog and drizzle early this morning has started to
diminish into this afternoon. Despite the increasing sunshine,
warming has been delayed today and trimmed a couple degrees off of
the forecast highs for today. The rest of the evening will generally
be quiet as our attention turns to two upcoming rounds of convection.

The first arrives in the overnight hours to southwest Iowa as storms
develop on the nose of the LLJ across Nebraska. Storms will continue
to lift into central Iowa through the morning hours, weakening as
the LLJ fades out. Instability is better further south into the warm
sector, along with better shear, but a stronger storm or two is
possible with this leading wing of convection. Heavy rain will also
be a possibility with these storms in southwest Iowa when convection
is more robust as PWATs of 2+" remain possible.

Weak, spotty showers maybe linger through the day as ahead of the
main shortwave that will pass across the area late Wednesday evening
and into Thursday morning. This wave is more robust with 1500+ J/kg
MLCAPE, however shear is offset which is expected to limit the storm
organization. CAMs corroborate and depict a rather messy storm mode
and evolution overnight. Sounding hodographs continue to display
large looping profiles, however storms will not arrive into
southwest Iowa until 03z or after and expect the nocturnal inversion
will prevent storms from realizing much of the lower level SRH
available. HREF similarly shows a decrease in helicity track as
storms move across Iowa through the overnight hours. As such,
the tornado threat, while not zero, is quite low. The primary
severe hazards with the overnight storms will be strong winds a
perhaps some hail. At the same time, heavy rain will be in play
once again as moisture transport is maximized into the area
with PWATs once again over 2". HREF indicates pockets of 2-3+"
of rain are possible into the early Thursday morning hours which
may result in a few areas with ponding of water or isolated
flash flood problems, especially in parts of southwest Iowa that
receive heavy rain both tonight/Wed AM and again overnight into
Thu AM.

As the trough pushes east warmer and drier air moves into the area,
making way for a warmer and mostly quiet weekend. Temperatures
are expected to rebound back into the low to mid 80s. For now
the forecast is quiet, but there is a weak signal for
precipitation perhaps on Sunday. At this time frame confidence
is low and details will be better determined in the coming days.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 624 PM CDT Tue Aug 13 2024

Ceilings have all but lifted this evening, with just a few to
scattered clouds below 3kft remaining. Therefore, expecting VFR
conditions to prevail into the night. Lower clouds and
precipitation approach the area tomorrow morning, bringing MVFR
to potentially IFR conditions at times. A few isolated storms
may also be possible in the morning, especially further east,
but have left out of TAFs due to low confidence in lightning
impacts. As rain/clouds progress east, they will begin to
dissipate. Therefore, have lower confidence in impacts at sites
further east, such as KALO and KOTM.

Gusty winds also pick up out of the southeast at all sites
tomorrow, with gusts near or exceeding 25 kts possible in the
afternoon. There may be a brief period of VFR conditions through
the afternoon, especially south, but additional shower and
thunderstorm chances then begin to develop late afternoon into
the evening.

&&

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

&&

$$

DISCUSSION...Hagenhoff
AVIATION...Dodson