402
FXUS63 KDMX 280446
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1146 PM CDT Mon May 27 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Scattered showers and thunderstorms this afternoon with strong
  winds being the main impact.

- Additional scattered showers expected tomorrow, severe risk
  is low.

- Quiet through mid-week before shower and thunderstorm chances
  return late week into the weekend.

&&

.DISCUSSION...
Issued at 300 PM CDT Mon May 27 2024

>> Shower and Thunderstorm Chances This Afternoon/Evening

After the scattered showers and thunderstorms passed through the
area this morning, skies cleared briefly through mid-day. This
allowed for a few hours of sunshine to mix out the boundary layer
and steepen lapse rates, ultimately kicking off more scattered
showers and thunderstorms this afternoon. The dry low levels below
these storms have resulted in strong winds at the surface as rain
falls and evaporates through the layer, with some locations
reporting gusts near 50 mph. A few more prominent updrafts have also
produced some small hail, but with a relatively shallow 1000
J/kg of CAPE, and fairly high LCLs, storms will likely struggle
to produce any severe criteria hail. That being said, if any
larger hail is produced, it would likely be further south where
effective shear values are around 35 to 40 kts. In addition to
small hail and strong winds, the 100-200+ J/kg of 0-3 km CAPE
and modest amount of low level vorticity may help to produce a
few funnel clouds today but increasing LCLs this afternoon
should help mitigate any touchdowns. That being said, cant rule
out a very brief landspout before bases increase later this
afternoon, especially given the large amounts of stretching
present. Storms today will be during the peak heating period,
diminishing as the surface inversion sets in and as the wave
departs east.

>> Additional Precipitation Chances Tomorrow

A second wave will move through the overall northwest flow tomorrow
morning, bringing another chance for a few showers and thunderstorms
right on the coattails of todays wave. These chances will be over a
similar area to todays, mainly favoring the northern and eastern
portions of the state but with additional chances over southern Iowa
as well. Not anticipating much for severe risks with any storms on
Tuesday, with very low amounts of CAPE (less than 1000 J/kg)
limiting the chance for any stronger storms. These remain scattered
through the day as the wave passes, diminishing Tuesday evening.

>> Quiet Before Shower and Storm Chances Return Thursday and
Friday

Beyond the scattered showers Tuesday, the forecast looks mostly
quiet through the middle of the week with an upper level ridge and
surface high pressure building in overhead. As we get later into the
week, another 500 mb trough begins to dig in over the northwestern
US and will bring us our next chances for thunderstorms. The arrival
of the gulf moisture behind the surface high pressure looks to be
Thursday into Friday, with a minor timing discrepancy between the
GFS and ECMWF. The ECMWF has it arriving on Thursday morning, while
the GFS holds off any precipitation in the area until late Thursday
night to early Friday morning. Ensemble guidance splits these
solutions, favoring towards a Thursday morning to mid-day arrival.
This timing discrepancy, in conjunction with additional waves
passing through into the weekend, has resulted in a prolonged period
of forecasted precipitation starting Thursday morning and lasting
through the end of the 7 day period. This is likely a bit overdone
and will not be a consistent washout, but it does look to be an
active weekend with off and on shower and thunderstorm chances
possible into the beginning of next week.

Severe chances through this period will be better determined in the
coming days, but right now it looks like the better instability will
stay west of the area on Thursday and Friday, then increase overhead
on Saturday and Sunday. The Gulf stays pretty open through the
weekend as well, supplying us with a good amount of moisture
supportive of heavy rainfall. That all being said, this is all still
a ways out and we will have to see how the pattern continues to
evolve as it draws nearer.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1146 PM CDT Mon May 27 2024

Much of the period will feature VFR conditions, though latest
guidance suggests a period of sub-VFR conditions at ALO around
12z. Not a lot of confidence given the recent change and
ensemble support is less than 50% so have omitted for now. Have
introduced VCSH at MCW in the morning as there is general
agreement in showers moving southeast into north central Iowa in
the morning. This may need to be expanded to ALO and FOD in
future updates. Otherwise, SCT to BKN VFR ceilings will prevail
during the day Tuesday.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Ansorge