Dalby, Iowa Weather Forecast Discussion

938
FXUS63 KARX 151710
AFDARX
Area Forecast Discussion
National Weather Service La Crosse WI
1210 PM CDT Mon Sep 15 2025
.KEY MESSAGES...
- Heat and humidity linger through midweek, with a transition
  back to seasonable temperatures towards the end of the week.
- Confidence in widespread showers later this week is decreasing
  with the main rain axis shifting westward.
&&
.UPDATE...
Issued at 1038 AM CDT Mon Sep 15 2025
A line of showers and storms has developed across portions of
southeast MN and northeast IA from a resultant axis of 850mb
moisture transport along with some convergence in the low-
levels. The environment these elevated storms are in currently
observes a fairly robust capping inversion with around 1000-2000
J/kg of MUCAPE and only around 20-30 kts of effective shear. As
a result, not an overly impressive environment for any strong to
severe potential. Regardless, the general convective trend
expected over the coming hours would observe a slow weakening
trend as diurnal mixing will aid in drying out the low-levels.
However, the main forecast question later into the afternoon and
evening will be how any differential heating boundary left by
these storms may play a role in initiating further convection,
especially considering that model soundings in the recent
RAP/HRRR trend more surface based towards peak heating. The CAMs
generally favor holding off on any development until later this
evening and overnight as the nocturnal low-level jet marginally
increases, however given the unknowns of how any differential
heating may manifest have held with some small storm chances
(10-20%) through the afternoon.
&&
.DISCUSSION...
Issued at 245 AM CDT Mon Sep 15 2025
Summertime Warmth through Midweek
A blocking weather pattern lingers across the central CONUS
through much of the week, resulting in little change in our
summertime airmass over the next few days. Highs should continue
to top out in the 80s with dewpoints in the 60s and 70s through
Wednesday, with only a gradual cooling trend for Thursday
through Saturday as a mid to upper level cutoff low gradually
builds into the region from the west. Local modulations in these
forecast highs owing to storms are possible--mainly west of the
Mississippi River--but confidence in these storms is low (see
section below) and therefore it is tough to deviate from the
current NBM forecast highs. Temperatures should wander closer to
average by the upcoming weekend.
Low Probability Storm Risks for the Week
A multitude of low probably storms chances dot the forecast for
the upcoming week. This risk area is mainly west of the
Mississippi River with subsidence off the downstream ridge/high
pressure cell limiting the eastward progression of these storms.
For this morning, a ribbon of 335-K 700-mb theta-e air is
generating sprinkles across central Iowa early this morning.
This feature lifts NNE over the next 6-9 hours and could clip
southeastern MN before waning by mid-morning.
A passing upper tropospheric wave lifting NNE through the
Dakotas and western MN lowers heights just enough that surface-
based convection is a possibility this afternoon. HRRR/RAP
forecast profiles show 1500 J/kg of MLCAPE and somewhat
elongated hodographs that would be supportive of organized
convective structures. The missing piece is a forcing mechanism.
The upper trough axis will be lifting north of the region in
the afternoon and there is little in the way of a surface
boundary to latch onto. If anything, there is a signal for
weakly confluent flow at the surface that could be enough to
overcome the MLCIN. The widely varying (but rather dry)
solutions from the 00Z HREF members is telling of the low
predictability of this forecast. Have kept broad low (20%) PoPs
west of the Mississippi River to account for this remote storm
possibility. With ample moisture in play (PWATS around 90% of
climatology), any slower moving cell could produce efficient
rainfall rates.
Glancing ahead to the middle to latter part of the week, the
medium range solutions are depicting a stronger blocking pattern
that rebuilds somewhat for the end of the week over the Great
Lakes, refusing to give way to a cutoff low over the Northern
High Plains. This has resulted in a westward shift in the
precipitation probabilities that previously encompasses much of
the forecast area, relegating them to mainly west of the
Mississippi River. It doesn`t look like the low pushes into the
region until Friday or Saturday, which might be when we see more
widespread rainfall.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1210 PM CDT Mon Sep 15 2025
Showers and storms will be the primary aviation concern this
afternoon and into the overnight hours as ongoing showers and storms
continue to progress through the region. Additional showers and
storms may develop later this evening and into the overnight as
the nocturnal low-level jet strengthens slightly with exact
coverage of these showers and storms remaining uncertain. MVFR
to IFR visibility reductions will be possible with any
showers/storms through the overnight. Otherwise, VFR conditions
are generally expected with winds persisting from the southeast
at around 8-12 kts before falling to around 5 kts after sunset
this evening.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
UPDATE...Naylor
DISCUSSION...Skow
AVIATION...Naylor

NWS ARX Office Area Forecast Discussion