Manning, Iowa Weather Forecast Discussion

146
FXUS63 KDMX 141124
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
624 AM CDT Sun Sep 14 2025
...Updated for the 12z Aviation Discussion...
.KEY MESSAGES...
- Very warm conditions continue over Iowa through Tuesday with
  highs in the upper 80s to low 90s in most places.
  Temperatures trend lower late week into next week.
- Isolated storm chances of 30% or less this afternoon into
  tonight. A few storms may produce strong wind gusts over
  western Iowa.
- While isolated storms may occur Monday and Tuesday afternoons, most
  widespread and highest chances of 50 to 70% are centered on
  Wednesday. Lingering intermittent showers and storms Thursday
  and Friday.
&&
.UPDATE...
Issued at 249 AM CDT Sun Sep 14 2025
GOES-East upper level water vapor imagery shows the trough
lifting over the central Rockies with a spin over central
Colorado early this morning. A broad swath of upper level
moisture is seen from Mexico up into Saskatchewan and Manitoba.
The high level clouds over Iowa as seen on Nighttime
Microphysics RGB imagery are on the eastern edge of this swath.
This will lead to filtered sunshine across the state today with
it more heavily filtered over western Iowa relative to eastern
Iowa. While the high temperature forecast from last night for
Saturday underperformed by 2.7 degrees on average at ASOS sites,
this filtered sunshine will have an impact on highs today.
Further, the center of thermal ridge will be shifting east of
central Iowa. Thus, temperatures were once again backed off just
slightly from the initial National Blend of Models with highs
near 90 degrees over northern and western Iowa with low 90s
elsewhere. As for storm chances this afternoon, guidance is
going back and forth on chances, especially east of I-35. HRRR
runs going back to Friday evening through midday Saturday were
showing isolated development over central and/or eastern Iowa in
the early to mid- afternoon hours with this corroborated by the
typically more convective prone FV3 and WRF-ARW. However,
Saturday evening`s and this morning`s early HRRR runs have
pulled these back. Forecast soundings look comparable to last
night showing quite a bit of dry air and leading to this
forecast cycle delaying and lowering PoPs this afternoon east of
I-35. That said, depending on your model choice, forecast
soundings show the cap is rather weak over north central Iowa so
may still be able to pop off a storm this afternoon.
As we move into this evening, the central Rockies trough will be
lifting through the Dakotas. This will give Iowa a glancing shot of
phased forcing via weak kinematics from a 45 knot 250mb jet and weak
thermodynamic low level thermal lift. These weak forcings will bring
a low chance of thunderstorms with a narrow window of possible
surface based storms until sunset after which storms will be
elevated. The CAPE and shear spaces are displaced spatially with the
low level jet of 35 knots over western Iowa and the higher
instability over eastern Iowa. If there were to be a stronger storm,
it would be over western Iowa where the deep layer shear is around
30 knots. Further, forecast soundings show high downdraft CAPE
values. If a storm can entrain the low level jet winds with
enhancement by evaporative cooling in the dry sub-cloud layer air,
gusty winds near severe criteria (58 mph) may result. Thus, the SPC
day 1 marginal that clips part of Crawford County seems appropriate.
Whatever storms remain Monday morning should wane quickly. Both
Monday and Tuesday will still be quite warm with highs a few degrees
either side of 90. And both afternoons may feature pop-up
thunderstorms during peak heating as forecast soundings show the cap
weak to non-existent and surface temperatures nearing if not
reaching the convective temperature. Higher and more widespread
chances for thunderstorms arrive Tuesday night through Wednesday as
a trough swings toward the region bringing a cold front with it.
Deep layer shear continues to look marginal at best so there is no
apparent severe weather risk at this time horizon. Following right
behind the trough will be a closed low that will keep intermittent
shower and storm chances in the forecast Thursday into Friday.
Conditions turn more seasonal if not a bit below normal late this
week into next weekend.
&&
.DISCUSSION...
Issued at 148 PM CDT Sat Sep 13 2025
12z upper air observations had 22C temperatures at 850mb at both TOP
and ICT. Models indicate the warmest batch of air is over Nebraska
at this time. 850mb temperatures over 20C are a high confidence
nudger toward highs in the 90s, especially in a dry (therefore
mixable) airmass such as the one seen today over the state.
Highs in the low to mid 90s will be commonplace today. The
longwave trough encapsulating the western CONUS has split maxima
of height falls today: one in the inner mountain west and the
other in the desert southwest. The desert feature is what will
be responsible for our showers and storms late tomorrow, but
before it gets here, it will continue to ignite convection in
the Southern and Central Great Plains, stunting the approach of
warmer temperatures than seen today. This is why the rest of the
forecast has lower highs compared to today, but still above
average nonetheless.
This feature will deepen and tilt negatively over the next 48 hours,
developing a closed low and stacking by the end of the day Sunday.
Its warm conveyor belt will pull the moisture axis into the Northern
Great Plains, but without the bulk of the instability axis. MUCAPE
values greater than 1500 J/kg will be found in portions of central
and eastern Iowa. Hi res guidance has trended towards showers and
storms taking advantage of this energy once convective temperature
is reached, owed to the transport of moisture found over the
Ozarks/Mid South this morning. Precipitation would be high-based as
the saturated parcels would launch around 700mb, per sounding
profiles. The threat for strong to severe storms is low (

NWS DMX Office Area Forecast Discussion