990
FXUS63 KDMX 120859
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
359 AM CDT Mon May 12 2025

.KEY MESSAGES...

- Warm, dry and breezy conditions expected through midweek,
  especially northwest. Highs approaching 90 degrees.

- Scattered thunderstorms possible in the southeast Tuesday
  afternoon (30% chance).

- 70% chance of thunderstorms in the north on Wednesday night
  into Thursday. The threat for severe weather will continue to
  be evaluated.

&&

.UPDATE...
Issued at 327 AM CDT Mon May 12 2025

The Southern Plains upper low is beginning to lift north through
the lower Mississippi River Valley today and will be moving more
northeast into the Ohio Valley on Tuesday. This movement is in
response to another strong upper level low that is moving from
the Pacific Northwest and into the intermountain west during
this period. All of this will allow more moisture to stream
north and into at least parts of southeast and eastern Iowa over
the next two days. With more moisture/clouds/dew points in
southeast Iowa, the trend early this week will remain with the
warmest high temperatures northeast and the coolest southeast.
Did remove the precipitation chances for this afternoon over the
far southeast with a delay in the deeper moisture. Did continue
to increase PoPs for the east central/southeast by Tuesday
afternoon as waves of theta-e advection and lowering static
stability arrive.

The main forecast focus this week is the increasing
thunderstorms chances and possibly severe weather potential as
the western upper low progresses east and steepening southwest
flow into Iowa occurs late Wednesday into Wed night and perhaps
lasting into Thursday. The Wednesday night activity likely will
be elevated along the theta-e advection push and storm coverage
will be dependent on the elevated mixed layer (EML) erosion for
even elevated convective initiation as the moisture to aid this
activation is below the EML. That EML may re-intensify going
into Thursday and any additional activity may rely on a passing
cold front and any moisture pooling and EML layer cooling for
initiation. A few strong storms are possible mainly north Wed
night with large hail potential. A greater threat for severe
weather may be early next week with a more favorable setup
arrives with another strong system moving into the region and
more favorable deeper moisture available.

&&

.DISCUSSION...
Issued at 228 PM CDT Sun May 11 2025

Upper level ridge was centered over Iowa today with the continued
rex block keeping moisture well away from the region. Making
moisture matters worse is the easterlies from the Great Lakes high.
Dew points already well underperformed compared to what was
forecasted at this time yesterday. Have leaned towards the low end
of guidance distribution. Increased dryness also means continued
gustiness with the winds due to efficient mixing, the fastest winds
being in northwest Iowa. This is also the region in closer proximity
to the unseasonably warm thermal ridge that is bringing record highs
to the Northern Plains. The mixture of hot, dry and windy conditions
prompt concerns for fire weather; it is dangerous to burn in
northwest Iowa despite the greenness of the fuels. Expect
sporadic gusts up to 25mph to remain possible until diurnal
decoupling happens with sunset. Highs in northwest Iowa will
make a run at 90 degrees for highs this afternoon.

A surface cyclone in the Northern Plains will continue to pull the
thermal ridge northward, bringing H850 temps at 25C+ all the
way into southern Canada. The Great Lakes High will keep the
worst of the heatwave to our north and northwest this week, but
Iowa will see above-average highs, nonetheless. The warmest
temperatures will be in the north and west. The blocking upper
low will break free starting tonight. This will allow for some
theta-e advection to encroach on the southeastern part of the
state, beginning with midlevel clouds, followed by a slim chance
of showers and storms Monday and Tuesday afternoon (<20% chance
Mon, ~30% chance Tues). Soundings have inverted-v profiles
beneath the cloud layer, with primarily convective processes
with 500 J/kg SBCAPE values being the source of lift. With
thunderstorms that develop, they will be scattered in coverage.
Gusty winds will accompany them, but the weak flow will offer
little in the way of shear, keeping these storms pulsey, in
nature.

The aforementioned upper-level low will make a slow trek towards the
Great Lakes region by midweek, its northerly flow over Iowa
preventing much in the way of moisture advection aloft. Its height
rises centered over the state narrows the window for moisture
advection in the low levels before the next system arrives for
Thursday. In regards to trends with that system, models are starting
to agree on the idea of the trough developing a closed low,
deepening as it crosses the Midwest late this week. Placement isn`t
quite there yet and neither is timing, but there is a slowing trend
since the more intense solution has become more favored, meaning
that Iowa may see convection moreso during the daytime Thursday.
Most ensemble guidance hints at a mature cyclone as it passes by
Iowa, hinted at by the dry slot approaching during the day
Thursday in most solutions. With this synoptic consensus in
mind, deep-layer shear will be oriented parallel to the cold
front, favoring a line of storms. This would bring damaging
winds into play. There are still questions as to how much
forcing over Iowa will be present to break the cap, as well as
how much moisture will be available. This far out, the MPAS
suite has a representative depiction of a bowing MCS moving
across Iowa, but given the poor moisture regime mentioned
earlier, the mid 60 dew points in the MPAS members is likely
overzealous, making their storm coverage suspect. The last
forecast note to watch for with this system will be the winds on
Friday, especially in the north, as the pressure gradient
tightens aloft.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1042 PM CDT Sun May 11 2025

No aviation impacts are anticipated through the TAF period.

&&

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

&&

$$

UPDATE...Donavon
DISCUSSION...Jimenez
AVIATION...Lee