Knoxville, Iowa Weather Forecast Discussion

527
FXUS63 KDMX 090340
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
1040 PM CDT Mon Sep 8 2025
...Updated for the 06z Aviation Discussion...
.KEY MESSAGES...
- Scattered showers and thunderstorms return to the area
  tonight through Tuesday.
- Warmer weather will build in later this week, with daily high
  temperatures well into the 80s from Wednesday onward and
  nearing 90 by Friday. Rain chances return again later next
  weekend.
&&
.DISCUSSION...
Issued at 304 PM CDT Mon Sep 8 2025
Upper-level pattern shows a weak upper-level trough in eastern NE/KS
early this afternoon that was associated with early day showers and
cloud cover in eastern NE that have largely struggled to move into
Iowa given dry air still in place. This weak trough will continue to
slowly push eastward tonight through Tuesday before upper-level
ridging returns Wednesday, persisting through at least the end of
the work week. In the short term, this trough continues to be
associated with scattered showers and a few storms from late tonight
through Tuesday though QPF remains overall limited. Coverage and
timing continue to remain in question as well with CAMs all over the
place and global models trending towards later with more limited
coverage west/southwest tonight into early Tuesday and then again
north Tuesday afternoon. The main reason for this continues to be
the dry air as discussed in the last several updates/discussions
which remains robust in soundings initially but then remains to a
lesser extent above and below the mid-levels that do eventually
saturate. The end result is slowed down PoPs tonight followed by
wider coverage than is likely needed for shower/storm chances
tonight into Tuesday. Expect some trimming to continue to occur
in subsequent updates with some locations staying dry, some
seeing only a few sprinkles, and some maybe receiving a bit more
robust shower or thunderstorm that could have some gusty winds
as well given the dry air already mentioned. The main
instability axis remains to the west tonight and although does
start to slide eastward into Tuesday afternoon, remains on the
more minimal side, most values under 1000 J/kg of MUCAPE. Shear
also remains quite weak, generally less than 20-25 knots of bulk
shear from tonight through tomorrow night which together with
instability keeps severe storms out of the forecast, though as
noted above, a stronger storm could have a stronger wind gust.
On the note of winds, breezy winds this afternoon thanks to an
increasing pressure gradient and good mixing will actually
remain a bit more elevated tonight and not decrease as much as
typical in the evening as the pressure gradient remains tighter
through the day Tuesday. The other feature of note is wildfire
smoke being brought in from the northwest in the upper levels
keeping skies hazy for locations that do start to clear out from
the overarching cloud cover moving in tonight lingering into
tomorrow with the shower/storm chances.
Drier conditions are then forecast Wednesday through the end of the
week as the aforementioned ridge moves in. The dry forecast
will be paired with increasingly warmer temperatures as the
thermal ridge moves eastward but current NBM temperatures are
actually the extreme high end outlier in the forecast
distribution and may be overdone. There is confidence it will
certainly be warmer heading into late week/weekend with
temperatures in the 80s to near 90, but temperatures well into
the 90s as seen in the extended forecast on Saturday are an
outlier at this point and may need some further adjustments over
the next few days.
&&
.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1040 PM CDT Mon Sep 8 2025
High level clouds have been slowly increasing across the state
with a swath of stratus clouds with low end VFR bases pushing
up over western Iowa. While TAFs show prevailing VFR conditions,
it is possible those low level clouds move near FOD and less so
MCW and drop into MVFR after sunrise Tuesday. Scattered showers
and storms are still expected, but timing continues to slow
down with their arrival near or after 12z. With limited spatial
coverage and overall chances low, continue to forgo any
inclusion at this time. Next rain or storm chance would be
Tuesday night over northern Iowa, but again chances are largely
below 30% and will continue to assess possible inclusion in
future updates. Breezy winds from the south at 8-12 knots will
prevail overnight through much of the day Tuesday before
diminishing Tuesday evening.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...05
AVIATION...Ansorge

NWS DMX Office Area Forecast Discussion