988
FXUS63 KDMX 261803
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
103 PM CDT Thu Jun 26 2025

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Showers and thunderstorms persist into the morning hours
  today, mainly over west central into northern Iowa. Heavy
  rainfall and localized ponding/flash flooding remain the main
  threat with this activity.

- Thunderstorms develop over western and northwestern Iowa
  through mid-day, tracking east southeastward through the state
  into the afternoon and evening. Severe weather is possible
  today, with damaging winds and tornadoes being the main
  concern, especially over northern and northeastern Iowa.

- Thunderstorm activity moves out after midnight. Warm
  temperatures build in over the weekend with additional rain
  and thunderstorm chances through the second half of the
  weekend.

&&

.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 FRIDAY/...
Issued at 1258 PM CDT Thu Jun 26 2025

Thunderstorms developed over central and western Iowa early
this afternoon ahead of strengthening low pressure centered over
eastern Nebraska. Expect the individual thunderstorms to move
generally north-northeastward as the line advances east through
this evening. Hail and gusty winds are possible at the terminals
as storms pass. Look for IFR ceilings after storms depart
tonight through late morning Friday.

&&

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

The main takeaways...one final round of heavy rainfall and possible
flash flooding is expected today before at least a short break in
precipitation on Friday. However, as water is routed through the
basins and river systems, river flooding concerns persist well into
next week.

This morning...showers and storms will impact portions of west-
central and north-central Iowa, mainly driven by moisture
convergence associated with the nocturnal LLJ.  Rainfall amounts of
1-3" are possible with this activity, so will keep the Flood Watch
in place through 18z as scheduled.

After a short lull, a broken line of storms will re-develop along a
cold front and move from west to east across much of the CWA today.
As in past days, robust moisture content, high freezing levels, and
ample instability will again lead to efficient rain rates. However,
this line of storms should be progressive, moving eastward around 30
mph. Many of the global models and CAMs are indicating widespread 1-
2" rainfall amounts, but the progressive nature of the storms should
prevent rainfall amounts from getting out of hand. The 26/00Z HREF
24hr PMM valid from 12z Thu to 12z Fri shows this nicely, with only
very sporadic amounts over 3" indicated. However, with the recent
rainfall and areas of saturated ground, these amounts of precip
could still cause issues so at least pockets of flash flooding is
still possible, especially if any training of storms occurs.

In terms of river flooding, we continue to use 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. As confidence grows, we expect to begin transitioning to river
flood watches and warnings perhaps with the river forecasts issued
later this morning.

&&

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

&&

$$

DISCUSSION...05
AVIATION...WFO Duluth
HYDROLOGY...05/Zogg