Osceola, Iowa Weather Forecast Discussion

520
FXUS63 KDMX 232002
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
302 PM CDT Tue Sep 23 2025
.KEY MESSAGES...
- Showers, and an isolated thunderstorm, will continue across
  southern Iowa through early tonight. No severe weather is
  expected.
- Patchy fog possible again tonight, low /20% chance/ of dense fog.
- Dry and seasonal conditions return from Thursday through the
  upcoming weekend. Pleasant but warm highs in the 70s/low 80s
  with modest humidity.
&&
.DISCUSSION...
Issued at 258 PM CDT Tue Sep 23 2025
Upper air analysis and water vapor imagery this afternoon is
depicting several circulations over the upper Midwest, an upper low
over Lk Superior and second elongated area of low pressure from Iowa
wwd to the Rockies. The primary sfc low is located over OK, with a
baggy sfc trough extending newd across nrn Missouri into IL.
The latest short term guidance continues to depict modest QG upper
forcing /PVA/ along with a upper level deformation zone persisting
across nrn MO and srn IA through the evening and early overnight
hours. This combined with residual low level moisture /H8 dewpoints
of 8C to 10C/ and weak moisture convergence will result in a
continuation of showers and maybe an isolated thunderstorm,
mainly along and south of I-80. Mid-level lapse rates remain
generally poor /moist adiabatic/ so instability is minimal
/MUCAPE < 500 J/kg/ with feeble deep layer shear less than 20
kts. A consensus of the CAM output suggests precip activity will
continue through the evening hours before waning by midnight,
with partial clearing thereafter. If skies do clear, patchy fog
will again be possible per the typical autumn fog season. Low
confidence on fog coverage and vsby restrictions attm, due to
around 5 kts of sfc flow and uncertainty in the extent of
clearing.
Wednesday...
After any lingering fog, high pressure is expected to build into the
region from the west.  By this point, the upper low should have
shifted far enough east to place us in a mostly subsident upper
flow regime. The one caveat is that model soundings do show
moisture lingering in the PBL. Thus, as heating commences mid-
morning, we`ll likely see a decent amount of cumulus/stratocumulus.
A majority of the 23/12Z deterministic models show that the
cloud depths should be shallow enough to limit any
precipitation. However, its possible a few higher based very
light showers or sprinkles develop during the afternoon as noted
by SimZ in a few of usually robust CAMs. At this point, we`ll
leave any explicit mention of showers out of the forecast for
now. With a northerly low level flow, high temps on Wednesday
will stay in the 70s.
Extended Forecast...Thursday into the Weekend.
Surface and upper ridging will develop across the central CONUS by
late week.  Expect partly to mostly clear conditions will
temperatures nudging back upwards by Friday into weekend.  Expect
highs in the upper 70s to lower 80s on Thursday, with widespread 80s
on Friday into the weekend and early next week.  This would be about
5 to 10 degrees above seasonal averages. Dewpoint values should
remain modest in the 50s, so humidity won`t be a major issue.
&&
.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1224 PM CDT Tue Sep 23 2025
MVFR CIGs have persisted longer than expected across the north,
due to plentiful low level moisture. Expect these MVFR CIGs to
persist through ~20Z before rising and scattering out. Across
the central and south, showers are redeveloping, most numerous
to the south of DSM/OTM. However, kept a PROB30 going for now to
account for scattered coverage in the late afternoon and
evening. High pressure will attempt to build in overnight. If
skies clear, and winds decouple, fog will be possible again. For
this issuance, highlighted a few hours of MVFR VSBYs at FOD/MCW
for now. As drier air moves into the area, expecting VFR
conditions to return Wed afternoon.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Fowle
AVIATION...Fowle

NWS DMX Office Area Forecast Discussion