FXUS63 KDMX 290450

Area Forecast Discussion
National Weather Service Des Moines IA
1150 PM CDT Sat May 28 2022

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

.DISCUSSION.../Tonight through Saturday/
Issued at 244 PM CDT Sat May 28 2022

Key Messages:

- Progressively breezier each day through Monday
- Storm chances NW Sunday night and NW/Central Monday night


A few showers and thunderstorms moved across the northern half of
the state this morning through midday as a boundary moved across the
state associate with the surface low just north of the area. By
early afternoon these exited the area, leaving behind sunny skies.
Winds have been rather breezy today as well with deep mixing
allowing for gust over 30 mph at times across the area. Additional
thunderstorms are possible late tonight into early Sunday as another
weak surface low moves towards the area. Confidence in much
convective activity in Iowa if fairly low as the current
trajectory in the GFS/EC synoptic models and in most CAMs pushes
activity off to our north. As we move forward through the holiday
weekend each day will see an incremental increase in wind strength
and thunderstorm strength.

Good moisture transport and broad lift will allow for increased
cloudiness on Sunday with a stray shower not out of the question. It
will be another breezy day with tightening pressure gradient and
winds at the top of the mixed layer generally in the 30-40 kt range.
While we won`t fully realize this, some gusts over 30 kts are
certainly possible tomorrow of similar or slightly greater strength
than seen today. Additional storms are expected late in the evening
thanks to a surface low quickly spun up by lee cyclogenesis ahead of
the approaching longwave trough axis. The storms will be a little
more robust compared to tonight, though the location within the
CAMs is similar with storms expected to clip northwest Iowa.
Instability is more than sufficient at 2-3000+ J/kg for convective
storms to become robust and shear of 40+ kts will help storms
organize. As the previous discussion mentioned, shear orientation
will be an important player in determining convective mode into
NW Iowa.

Monday will be a similar story, third verse. Once again gradient
winds will be enhanced by deeper mixing, though gusts over 40 kts
may be possible as the gradient tightens up and winds at the top
of the mixed layer peak. This could put parts of the area near
wind advisory criteria and will need monitoring. There remain
significant model evolution differences with the Euro favoring a
deep cutoff low that would blow convection mainly north of the
area vs. the more open wave progression of the GFS. Instability
increases to the 3000+ J/kg range with deep layer shear again in
the 40-50 kt range. Hodographs show good curvature and low level
helicity is 200-300+ m2/s2, favoring rotating updrafts to support
large hail and a tornado threat, in addition to the damaging wind
threat. There is also a signal for an axis for high QPF,
especially in the GFS, across NW parts of the area. Ensemble
members are not quite as robust and the deterministic, however
with deep warm cloud depths and high PWATs, efficient rain
producers are expected. As this is the driest part of our area,
hydro issues should not pose much of a problem, despite isolated
pockets of heavy rain.

A trailing cold front will drop temperatures much of the upcoming
week with highs around 70 on Wednesday and 70s lingering thorugh the
end of the week. Models solutions diverge, however it does appear
that there may be another chance for rain mid week and late in
the week.


.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1149 PM CDT Sat May 28 2022

VFR conditions are forecast through the TAF period. There is a
small chance of brief SHRA/TSRA at FOD/MCW early Sunday AM, but
probability/impact too low for TAF mention. Otherwise, the story
will be strong southerly winds on Tuesday, with periods of LLWS
40-50+ KT through early Sunday AM and again Sunday night/Monday






NWS DMX Office Area Forecast Discussion