531
FXUS63 KDMX 111748
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1248 PM CDT Mon May 11 2026

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Temperatures will fall into the 30s across northern Iowa this
  morning, and near freezing in some areas. A Frost Advisory
  remains in effect generally north of Highway 20.

- Shower and thunderstorm chances return late Monday night into
  Tuesday. A few stronger storms could develop in southeastern
  Iowa on Tuesday afternoon, with gusty winds being the main
  concern.

- Breezy conditions are forecast on Tuesday, especially in
  northern Iowa during the afternoon where northwest winds of
  25-30 MPH with gusts to 40 MPH or more are likely.

- Warmer temperatures are expected through much of the week and
  into next weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 220 AM CDT Mon May 11 2026

A large surface high pressure area is draped across the region
early this morning, centered over Minnesota into Wisconsin but
certainly extending through Iowa as well. The result is very
light north to northeast breezes across our service area. An
area of mid-level clouds has persistently developed over about
the southern half of Iowa on the periphery of the ridge,
limiting radiational cooling in that area with temperatures
largely remaining in the 50s as of this writing. However, across
northern and eastern Iowa where skies are clear, temperatures
have already fallen into the 40s and will fall farther before
sunrise, especially in spots where winds go calm. Lows
generally in the 30s are still expected in those areas this
morning, and the Frost Advisory remains in effect for our
northern counties roughly north of Highway 20. The clouds in the
south will gradually clear out this morning, but even in those
areas that clear before sunrise temperatures will not be able
to fall as far as in the north.

During the day today the surface ridge will move off to our east
over the Great Lakes, allowing for a return of south
southeasterly low-level flow by late in the day. Concurrently, a
modest mid-level thermal ridge will move over the High Plains
and toward Iowa by this evening, combining with the low-level
wind change to support warmer temperatures with highs this
afternoon ranging from upper 60s in our northeastern counties to
near 80 in the southwest. Satellite imagery does show cirrus
clouds approaching from the northwest which may affect our area
today, however, indications are that these will be quite thin
and not significantly mitigate the combined warming effects of
the synoptic pattern and a seasonally high solar angle.

From late tonight into Tuesday night, our primary feature of
concern is the 500 MB trough that will be digging from far
southern Canada later today, down into North Dakota and
Minnesota tonight, then across Iowa and the Great Lakes region
Tuesday and Tuesday night. This system will push an attendant
surface trough southeastward through Iowa on Tuesday, which will
have several impacts on our sensible weather. Ahead of the
boundary, tonight, low-level winds will turn to south and
eventually south southwest and gradually increase overnight,
supporting much warmer nighttime temperatures. Whereas lows this
morning will range in the 30s north to 40s south, on Tuesday
morning they will range in the 50s northeast to near 60
southwest. Also, with the 500 MB trough approaching late tonight
broad forcing for ascent will spread overhead along its leading
flank, combining with the low-level warm air advection to
support scattered showers ahead of the surface boundary,
particularly in our northeastern areas. Chance PoPs (30%) are
maintained in those areas for the expectation of scattered light
showers after midnight and into the early morning hours
Tuesday.

The precipitation outlook during the day Tuesday becomes more
uncertain. Most upper-level support will translate eastward
away from our area during the day, however, the surface boundary
will be moving through in the late morning (north/central) to
late afternoon (southeast) hours, with diurnal destabilization
occurring ahead of it. Forecast soundings depict a stout
mixed/dry layer with a weak capping inversion above it, and with
limited surface convergence along the boundary or forcing
aloft, there may not be sufficient impetus for initiation for
most of the day. However, most CAMS include scattered light
echoes filtering through during the day, which likely indicate
light elevated showers based above the mixed layer. Whether any
such showers will be able to precipitate through that layer to
the surface remains to be seen. By the afternoon, in our
southeast, if the cap can be overcome and moisture is sufficient
then we may be able to generate a few thunderstorms in our
southeastern counties just before the boundary pushes through,
which would carry some threat of strong wind gusts given the
steep low-level lapse rates, but that is a conditional threat.
For now, have maintained 20-30% PoPs in our central and
southeastern counties during the day to account for this
scenario.

In addition to precipitation potential, the passage of the
surface trough on Tuesday will also bring strong winds to the
area, especially in northern Iowa where confidence is high in
blustery conditions by the afternoon. A deep well-mixed layer
with dry adiabatic lapse rates up to 700 MB and homogeneous
northwest winds of 25-30 KT or higher within that layer support
surface winds approaching 30 MPH, with gusts to 40 MPH or higher
at times and advisory criteria could be met. Relative humidity
will fall to around 20% in many areas and combined with the
strong winds this could support elevated fire weather concerns,
however, these are heavily mitigated by the greenness of most
surface fuels. Even so, Tuesday will not be a conducive day for
outdoor burning.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 248 PM CDT Sun May 10 2026

Temperatures cool slightly on Wednesday, albeit still in the 70s.
The broad upper level ridging then fills in behind the departing
shortwave, warming temperatures into the 80s through the second half
of the work week. As mentioned in yesterday`s long term discussion,
despite the brief ridge moving in, the pattern quickly becomes
agitated through the end of the week and into next weekend with
multiple shortwaves and increasing shower and thunderstorm
potential, the first of which looks to be on Thursday night into
Friday as a healthy gulf moisture stream returns to the state.
Additional chances continue into the weekend. This will likely put a
damper on the highs in the 90s that NBM guidance had been
forecasting for next weekend and today`s extended forecast now
reflects this a bit better. That said, with the southwesterly to
westerly flow pattern, temperatures should stay seasonably warm
in the 80s through the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1238 PM CDT Mon May 11 2026

VFR conditions prevail today, with calm or light and variable
winds through mid-day. This afternoon, south southeast winds
will increase and become breezy overnight, then become more
southwesterly by tomorrow. Winds around 15 kts are expected
tonight, increasing up to 20 kts tomorrow morning. Gusts may be
somewhat sporadic tonight, but could near or exceed 25 kts. LLWS
is also expected overnight at all sites. Scattered showers are
possible by Tuesday morning, primarily at KMCW and KALO. KFOD,
KDSM, and KOTM could also see light rain/sprinkles Tuesday
morning into mid-day, but chances are too low to include in TAFs
at this time.

&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Dodson
AVIATION...Dodson