470
FXUS63 KDMX 072043
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
343 PM CDT Tue May 7 2024

.KEY MESSAGES...

- Scattered showers & storms possible into the night

- Chances for showers and storms Wednesday into Thursday.
  Potential low overall, but severe weather still possible late
  Wednesday.

- Less active to end the week and into early next week with
  normal to above normal temperatures

&&

.DISCUSSION...
Issued at 343 PM CDT Tue May 7 2024

Isolated showers and storms have begun to develop in daytime
heating, a few with the lingering theta-e axis far east, and
others higher based in the drier air west associated with
approaching weaker mid level forcing, which will continue spotty
chances into the early morning hours Wednesday. Otherwise, the
sprawling parent upper level low will move little into tomorrow
and induce a weak surface reflection/inverted trough into
western Iowa during peak heating, which will also be aided by a
lobe of the aforementioned increase in mid level kinematic
forcing.

The storm environment is interesting and somewhat nebulous with
weak low level shear 1km and below, but strong deep 6-8km shear
and extremely elongated hodographs aloft along a sharp north to
south gradient (much higher south). While the 500-1500 J/kg
MLCAPEs are not alarming, steep low level lapse rates are a good
percentage of that (200+ J/kg 0-3km CAPE) with strong shallow
updraft stretching potential. This parameter space leads to
multiple hazardous weather concerns during the afternoon and
evening hours. Even though low level kinematics such as shear
and streamwise vorticity are weak, thermodynamically dominate
funnels/weak tornado potential is there along and ahead of the
inverted surface trough in what will likely be sub-1km LCLs.
This would be more favorable with discrete cells farther south
realizing the deeper shear and taking on the much slower Bunkers
RM motion (<20kts) versus a strong 30-40kt mean wind. Some
2-5km updraft helicity tracks are evident in the 12Z HREF as
well, supporting supercell potential coincident with the noted
thermodynamics, and there is also some signal in AI/Nadocast
guidance.

Weak low level shear under much stronger deep shear and
elongated hodographs would also be favorable for hail
production. Going into the early evening, the stronger mean wind
should subside as the upper low is finally on the move and
approaches leading to slower cell movement. Although the
moisture parameters are fairly season, this slow movement could
also lead to locally heavy rains with HREF PMM QPF suggesting
isolated 2-4 amounts are possible north. Looking into Thursday,
Low level focus and overall synoptic scale lift is weaker,
however moisture lingering in the trailing cyclonic flow will
lead to at least some chances for showers and a few storms
through the day. A strong Upper MS Valley short wave, whose
primary response will remain to our northeast, will start a
period of relatively inactive northwest flow aloft until the
pattern breaks down early next week with little model agreement
on how that will unfold.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1247 PM CDT Tue May 7 2024

Patchy MVFR ceilings may linger east for the next few hours, but
overall confidence is medium for VFR conditions through much of
the period. There may be a period of higher based convection
late afternoon and this evening, but otherwise nothing more than
FEW-BKN mid clouds can be anticipated through the period.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Small