536
FXUS63 KDMX 252118
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
418 PM CDT Wed Jun 25 2025

.KEY MESSAGES...

- Scattered thunderstorms are expected this afternoon into
  evening mainly over northern into portions of central Iowa.
  Heavy rainfall is likely. Severe weather is possible with
  damaging winds the main concern, though some hail is possible.
  A tornado is possible as well, especially in the northeast.

- Additional heavy rain threat with overnight showers/storms
  into Thursday morning, mainly west to northwest into portions
  of northern Iowa.

- One more round of widespread storm chances Thursday afternoon
  and evening. Severe storms are possible with strong wind gusts
  and heavy rainfall the main threats.

&&

.DISCUSSION...
Issued at 337 PM CDT Wed Jun 25 2025

After another active overnight period with heavy rain lingering well
into this morning, focus becomes on how mesoscale details will
evolve for the next round this afternoon into evening. Rain showers
continued well into midday over portions of northern Iowa with cloud
cover persisting as well, though some clearing has occurred early
this afternoon. Over central to southern Iowa, clearing occurred
early this morning with sunshine returning and instability values
this afternoon rising to 2000-3000+ J/kg of MLCAPE with temperatures
well into the 80s to low 90s and very humid conditions given dew
points in the 70s. Although temperatures in the far north are a
little lower with the cloud cover, the entire area is in the warm,
moist sector with the surface boundary in southern MN. Of concern is
our southeast surface flow this afternoon with largely flow out of
the southwest in the mid to upper levels allowing for the solution
presented on in the previous update to gradually develop with some
clockwise-curved hodographs, especially in portions of northeast
Iowa up towards the surface boundary in MN. The far north to
northeast is also where SRH values are highest through the afternoon
to early evening hours, all of this presenting a threat for some
tornadoes to develop. To the west, wind and heavy rain remain the
primary concern with the rest of the convection expected to develop
from Nebraska into portions of western and northern Iowa. More
organized storms may still be able to develop some small to
marginally large hail as well though wind shear remains the primary
limiting factor, as it has the last several days. Storms this
afternoon and evening are expected to move mainly east-northeast
with time and be a bit more progressive than previous days but the
hydro threat remains a concern, see the hydro discussion for further
details.

Additional shower/storm development is expected late tonight to the
west as the LLJ ramps up again. This will once again present a heavy
rain threat into Thursday morning, but CAMs continue to suggest some
bowing clusters at times so will continue to watch any additional
wind threat that develops late tonight into the early overnight.
This remains a lower probability, though still possible with some
lingering instability late and the best shear in the north where
storms are expected to track.

Pending somewhat how activity plays out tonight into Thursday
morning will set the stage for our next threat Thursday afternoon
into evening. A boundary is expected to gradually orient north to
south allowing storms to develop and move through much of the area
from west to east. Plenty of instability is expected to redevelop
into the afternoon, though shear remains more marginal, though
continually better than previous days. The main threats with these
developing afternoon storms will once again be wind and heavy rain,
though storm progression should be faster again than in previous
days. Storm organization will be a big factor in the extent of the
severe threat with timing actually moving up faster than in previous
days and pushing storms through earlier in the day. Will need to
continue to monitor into the morning to evaluate the mesoscale
details further but at least one more day of continued active
weather with both severe and hydro threats.

Conditions quiet down temporarily Thursday night into Friday before
additional chances for showers and storms return at times into the
weekend but more so late weekend into early next week. Additional
details to be provided in the coming days.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1252 PM CDT Wed Jun 25 2025

Lingering showers over northern Iowa early this afternoon with
new showers and storms starting to develop as well. Challenging
aviation forecast going forward with thunderstorm timing and
impacts given lingering uncertainty exactly when/where
showers/storms occur. Most favorable locations remain north -
KFOD or KMCW, though new development is occurring over southern
Iowa as well, near KOTM. Confidence in showers/storms reaching
ALO remains lower, but kept with previous Prob30 group.
Adjustments in timing/impacts likely as storms develop this
afternoon but localized visibility drops could occur as well as
gusty winds with any stronger showers/storms. Although VFR
conditions will largely prevail, MVFR CIGs expected at times
with some IFR possible north, especially through the overnight
as additional rounds of showers/storms move through.

&&

.HYDROLOGY...
Issued at 337 PM CDT Wed Jun 25 2025

Both flash flood and river flooding remain a concern through later
this week, with river flooding concerns persisting well into next
week.

There has been a persistent signal of heavy rainfall mainly through
Thursday night into Friday morning, however uncertainty in the exact
placement of highest rainfall amounts remain. The latest 25/00Z HREF
and NBMv5.0 continue to show the axis with the highest QPF amounts
transitioning to portions of northwest and north-central Iowa
starting this afternoon, specifically along and north of US 30.
Confidence is increasing on seeing widespread amounts of 2-4" in
this area, with higher end amounts (from the HREF PMM or NBM 95th
percentile data) showing pockets of 5-8", with max amounts of 10+"
still in play. As is typically the case in these scenarios,
mesoscale details (e.g., exact storm initiation locations and
placement of outflow boundaries) cannot be accurately predicted at
this time range, so the placement of the heaviest precip may need to
be refined. In saying this, a Flood Watch for Flash Flooding
was issued for portions of northern into northwest Iowa for
expected activity this afternoon into evening, and then again
overnight given more primed areas in that area after recent
rainfall this week and prior. This may need to be shifted
southward based on storm development, however. Additional areas
may be considered for Thursday.

The hydrologic response of the heavy rainfall will depend
heavily on the meteorological activity and resultant QPF. Flash
flooding will be a possibility anywhere in the CWA where
persistent heavy rainfall occurs, with the flash flooding
possibly being triggered by either the rainfall intensity or the
sheer volume of rainfall.

In terms of river flooding, we are using 48 hrs of QPF in our going
river forecasts instead of the normal duration of 24 hrs,
recognizing the longer term duration of the heavy rainfall. This
change to QPF duration pertains only to those streams in the
Mississippi River drainage portion of our CWA, or roughly across the
northeast 2/3rds of our CWA. The river forecasts, compared to
yesterday, are higher in some locations, lower in other locations,
and near the same at some locations. The main reasons for the
forecast changes are mainly shifting of the QPF location. Most
changes, however, have remained within the same flood category. It
should also be noted that for many locations where action stage is
forecast, those forecast crests are near flood stage.

The larger streams of most concern presently include the Iowa,
Cedar, Winnebago, Shell Rock and Raccoon Rivers. For some locations,
the elevated stages and river flooding is expected to continue well
into next week.

Given the timing in those forecasts (i.e., forecast to reach flood
stage generally 2, 3 or more days out from the present time), as
well as lower confidence since it so far out in time, we opted to
continue mentioning these threats in our Hazardous Weather Outlook
(HWO) instead of issuing river flood watches or warnings at this
time. We expect to begin transitioning to river flood watches and
warnings beginning either this evening or Thursday morning.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Thursday afternoon for IAZ004>007-015>017-
023-024-033-034-044.

&&

$$

DISCUSSION...05
AVIATION...05
HYDROLOGY...Zogg/05