372
FXUS63 KDMX 172323
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
623 PM CDT Thu Jul 17 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Dry and pleasant into Friday morning.

- Multiple rounds of showers/storms late Friday into this
  weekend with potential for heavy rain and severe weather at
  times. Details below.

- Warming temperatures into mid next week with return of 100+
  degree heat indices, especially south.

&&

.DISCUSSION...
Issued at 257 PM CDT Thu Jul 17 2025

Surface high pressure will continue to keep conditions dry and quiet
through the rest of the day into early Friday when the high drifts
eastward into the Great Lakes Region. Northerly mid-level flow has
kept pleasant temperatures into the area with readings early this
afternoon in the upper 60s to low 70s. Tonight will be another
cooler summer night with lows in the 50s to 60s. Enjoy it while you
can as active weather and warmer temperatures are incoming over the
next several days.

Behind the departing high pressure Friday, mid-level flow switches
to be out of the southwest starting to bring some warmer
temperatures back into the area, though highs are still pleasant for
mid-July and in the upper 70s to low 80s. After the drier conditions
and lower dew points today, moisture off the open Gulf will also be
on the increase Friday bringing the return of dew points in the 60s
to 70s making, especially southern areas, feel more humid again by
the afternoon.

Several shortwaves will move through the region at times from later
Friday through the weekend within the upper west to northwesterly
flow that will be in place well into next week. The first is a mid-
level low which will be tracking through the Dakotas into Minnesota
through the day with a trailing boundary that will move into
northwest Iowa overnight into Saturday morning. Prior to that, the
boundary that departed the area yesterday causing heavy rain to
occur in northern MO into the KC Metro will actually lift back
northward into the state through the afternoon and evening. Some
CAMs kick off some isolated showers or storms as this southern
boundary lifts northward given the warm, unstable airmass in place
in the warm sector, but the better instability through southwest
into portions of central Iowa remains offset from the better shear
through the end of peak heating Friday. Although many run to run and
model to model discrepancies remain, there is more consistency in
the CAMs with either clusters or a full line of storms moving into
the area from the north late Friday night into Saturday morning.
Some, like the 06/12Z HRRR, 00/12Z RRFS, and the 00/06Z NAMNest (but
not the 12z) all have versions of strong to even severe storms
diving southeast through the area during the mainly overnight hours
bringing a threat of strong to even damaging winds with it. In
saying this, confidence remains lower in exactly when and where
storms may occur and how any kind of potential MCS may progress out
of MN into Iowa. Unlike many of the past several days, bulk shear
remains more favorable, especially in northern Iowa, with at least
1000 J/kg of CAPE if not more (model dependent) lasting through the
night. Will need to continue to watch this overnight period closely
for strong to severe storms. Locally heavy rain may also be possible
with favorable warm cloud depths and pwats of 1.5-2", though overall
hydro threat remains lower with likely progressive storms, several
drier days preceding, continuing maturing crops, and QPF totals
largely below 1". Some isolated amounts of 2"+ are noted in the 24-
HR, localized probability matched mean HREF into 12Z Saturday,
location uncertainty remains higher with overall storm
timing/location uncertainty, so although not out of the question,
confidence is not high in these higher QPF values being realized
either. The SPC Day 2 Marginal (Level 1 out of 5) through much of
the area and WPC Day 2 Slight (Level 2 out of 4) in northern Iowa
cover the overall threats will for severe and hydro concerns
respectively.

Beyond the Friday night into Saturday time period, the continued
chances for showers and storms will remain as will the threat for
locally heavy rain and some strong to severe storms. However,
subsequent threats are all contingent on the previous day
overnight/early morning activity and how the atmosphere recovers
into peak heating and the mesoscale details of where either outflow
or boundaries exist spatially. Although afternoon to evening strong
to severe storms are certainly possible Saturday with strong
instability and bulk shear forecasted to be in place, storm
development is more uncertain, though southern Iowa would be the
most likely location at this point. Generally the best
rain/storm chances are in the overnight to early morning period
Saturday night and again Sunday night, but will need to continue
to evaluate the mesoscale details for increased confidence in
timing/location/severity of storms. NBM PoPs are well overdone
through the weekend accounting for the uncertainty in timing of
storm development but it won`t be raining/storming at every
moment of the weekend. For any with outdoor plans this weekend,
keep an eye on the weather and have a plan in place should a
warning be issued with subsequent Day 3 SPC Slight Risk (Level 2
out of 5 for severe weather Saturday into early Sunday) and Day
3 and 4 WPC Slight Risk (Level 2 out of 4 for excessive
rainfall Saturday into early Sunday and Sunday into early
Monday). Temperatures too will generally be on an increase into
next week. The weekend remains more uncertain with how storm
chances play out, but the heat looks to build into mid next week
where 100+ degree heat indices return to the forecast in
especially southern Iowa.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 623 PM CDT Thu Jul 17 2025

Low clouds based around FL025-040 will decrease in coverage this
evening with VFR conditions prevailing for much of tonight.
However, the low clouds will spread back into the area from the
southwest early Friday morning and may bring more MVFR ceilings
mainly to DSM/OTM by around 12Z. Confidence level in
occurrence/timing of such conditions is too low to include in
the 00Z TAFs, but will reassess for the 06Z issuance.

&&

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

&&

$$

DISCUSSION...05
AVIATION...Lee