370
FXUS63 KDMX 280355
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1055 PM CDT Wed Aug 27 2025

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

.KEY MESSAGES...

- Scattered showers and storms possible across the far north
  this afternoon (40%). The severe weather threat is low.

- Low chance showers across central Iowa late Thursday afternoon
  (<25%).

- Weekend rain possible in the west, but continues to trend
  slower.

&&

.DISCUSSION...
Issued at 202 PM CDT Wed Aug 27 2025

OAX`s 12z sounding showed just how shallow the theta-e advection is
today, with southwest flow contained between 900 and 700mb. 1-2km of
saturation is all we have to work with this afternoon, not enough
moisture to take advantage of the deep-layer shear in Iowa. A PV
anomaly seen best on GOES water vapor imagery serves as a source of
synoptic-scale lift, with a boundary remaining in southern MN. A
rumble of thunder will be possible in northwest Iowa as MUCAPE
values over 1000 J/kg in southern MN aren`t far away. Rainfall
amounts will be at most a tenth of an inch and small hail will be
possible in any robust updraft. A boundary today near the Canadian
border will sink States-side tonight, eventually weakening and
stalling out over Iowa tomorrow. Less cloud cover means we`ll mix
out better, with the chances of some light convective showers
remaining in play, especially at peak heating in the afternoon.
South of this boundary, temperatures will be in the low 80s.

For Friday, a shortwave seen this morning over parts of Washington
and Idaho will be on approach, just a slow approach thanks to the
Great Lakes high. Dry air will delay the low-level moisture
transport, decreasing intensity and coverage of rain. This is
seen best by the dry soundings with winds from the east in the
low- levels. The simulation from the NAM makes the most sense on
Friday with the bulk of showery activity occurring on the
moisture discontinuity axis between the two air masses. Trends
in 12z guidance today follows the expectation of the
stubbornness of high pressure blocking: the onset of better
precipitation is stalled. Western Iowa will have the best chance
of rain (<40%) both Saturday and Sunday. Central Iowa has about
a 20% chance each day.

The high will loosen its grip on the region early next week, giving
Iowa some low-end rain chances from the passing low pressure (<25%
chance each day). A closed low over the PNW will eject a series of
shortwaves on the northwest flow west of the high. This is why much
of next week is full of rain chances, as it remains to be seen where
in the region the waves will impact the most. What can be said is
the reinforcement of wind with a northerly component will lock highs
in the 70s for the next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1052 PM CDT Wed Aug 27 2025

VFR conditions prevail early this morning with any remnant cloud
cover from earlier rainfall quickly drifting eastward. Winds
remain light and generally out of the south southwest, then
switch to more north and easterly as a boundary drops southward.
A few showers/isolated thunder is possible along this boundary
tomorrow afternoon and evening, but any impacts would be
extremely isolated. Therefore, no mention in TAFs at this time.

&&

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

&&

$$

DISCUSSION...Jimenez
AVIATION...Dodson