063
FXUS63 KDMX 020404
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1104 PM CDT Sat Jun 1 2024

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

.KEY MESSAGES...

- Fog likely east overnight

- Several periods of convection expected Sun-Tue although
  confidence in details is low. Severe weather possible at times
  with damaging wind the primary concern.

- Mainly dry from midweek into the start of next weekend with
  seasonal temperatures

&&

.DISCUSSION...
Issued at 305 PM CDT Sat Jun 1 2024

Our weather pattern will be active later this weekend and into
early in the next work week as our progressive, low amplitude
flow persists and eventually evolves into a stronger MO Valley
upper trough late Tuesday. Although confidence in the details is
low due to varied model solutions, this will overall keep the
potential for thunderstorms of varied strength and severity in
the forecast off and on until the middle of next week when less
active northwest flow returns.

In the meantime, Iowa is in generally subsident flow behind the
mid level OH Valley short wave, and a lower level circulation
quite evident in visible satellite imagery across eastern MO.
There are still low chances for showers and a few storms central
and east early this evening however, with a few weak showers
already evident on radar. The airmass is generally uncapped with
little CINH, but some weak convergence has aided the spotty
showers east, with the latest GOES Cloud Phase Distinction
images also noting some enhancement farther west into central
IA. A few convection allowing models /CAMs/ do suggest very
isolated development, so have kept a token mention in these
areas until shortly after sunset. Effective shear is weak, so
there is little severe potential outside of a brief funnel cloud
with steep low level lapse rates generating 100+ J/kg 0-3km
MLCAPEs. Even if anything matures further, it should dissipate
with the loss of insolation leading to dry conditions through at
least the start of the early morning hours. There is little
upstream at the moment, but some CAMs suggest lingering Plains
peak heating convection could drift into western sections toward
daybreak and then dissipate with the loss of instability. Much
of the model guidance also continues to suggest some radiational
fog development east overnight, which matches pattern
recognition with light winds following lingering low level
moisture and cloudiness.

Confidence decreases later in the day tomorrow however, as is
often the case with warm season convection in these weakly
forced initiation mechanisms. ARW based HRRR and HRW ARW
solutions, as well GFS and EC parameterized solutions, suggest
peak heating development northwest with some low end severe
potential in fairly seasonal instability and shear parameter
space, while the NamNest, FV3, and other ARW NSSL WRF
solutions hold off until latest in the evening. Confidence
increases in that regard however with more uniform guidance
agreement, with an increasing potential for upstream peak
heating development maturing into a severe MCS with wind being
the primary threat. Although it would likely be elevated and
rooted around 0.5-1km per forecast soundings, 12Z HRRR across
western IA approaching daybreak depicts ESRH 500+ m2/s2 and
effective shear 50+ kts suggesting an organized MCS being
maintained with that and other CAMs noting quasi-linear
structure reinforcing the wind potential. This is also
corroborated by elevated NCAR HRRR neural network severe wind
probabilities. The complex should be weakening in time as it
crosses the MO River and moves east, but may still be capable
of damaging winds west, and even a few brief QLCS tornadoes
depending on its maturity.

Some convection may linger into day, as the forecast becomes
more nebulous with nondescript forcing, but broad but weak
moisture transport could maintain anything that lingers into the
night to some degree. Confidence increases again around Tuesday
when a maturing long wave trough brings a lobe of larger scale
synoptic lift coincident with its associated frontal passage.
This will bring one last higher chance for convection until the
pattern becomes less active later into the week and to start
the weekend with mainly dry continues in persistent northwest
flow aloft behind the Ontario/Great Lakes closed upper low. The
severe potential around Tuesday is undefined for the time being,
with GEFS based CSU machine learning solutions suggesting some
severe potential, while the deterministic GFS keeps MLCAPEs
<2000 J/kg and 0-6km shear <40kts.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 1104 PM CDT Sat Jun 1 2024

Fog is expected to develop over eastern Iowa tonight, and might
affect some of the eastern terminals, MCW/ALO/OTM, before or
around sunrise Sunday. However, confidence in dense fog is low
given these terminals will be on the western periphery of the
higher threat area, and high clouds will be moving in from the
west concurrently. For now have maintained 1SM BR groups at
those three terminals, but amendments may be needed overnight.
Aside from the possible fog, VFR conditions will prevail through
the TAF period, with isolated SHRA/TSRA possible mainly Sunday
afternoon and evening, then again just after the end of the 06Z
TAF period.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Lee