Urbandale, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

615
FXUS63 KDMX 261141
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
641 AM CDT Thu Jun 26 2025

 ...Updated for the 12z 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.

&&

.UPDATE...
Issued at 403 AM CDT Thu Jun 26 2025

Once again, rain and thunderstorms linger over the forecast area
early this morning as the low level jet remains nosed up into
western Iowa. Coverage isn`t nearly as expanse this morning as the
previous, but radar does show a strip of slow moving storms in the
western portions of the forecast area and a larger area of
precipitation in northwest Iowa slowly meandering it`s way east.
This larger lobe of rainfall is expected to move through northern
Iowa and into southern Minnesota through the remainder of the
morning, but overall rainfall rates will be fairly low. Heavier
rainfall rates will be with storms farther south along and ahead the
instability gradient oriented roughly from west central into north
central. This remnant boundary/gradient too will lift north through
the evening as the low level jet advects warm, moist air back north.
Severe storms are not anticipated with this activity through the
morning, but there does remain some meager instability and shear in
the area, so will be monitoring for any sub-severe hail and wind
gusts. Therefore, heavy rainfall remains the primary concern through
the morning and have decided to keep the flood watch in place over
northern Iowa for any potential flash flooding concerns.

This boundary will continue northward through the day as an upper
level shortwave continues around the broad ridging in the
southeastern CONUS. At the surface, low pressure will follow the
wave, passing through northwestern Iowa today. Southeast of the wave
will be a moist, unstable airmass and a strengthening warm front
lifting northward into northern Iowa and eventually into southern
Minnesota. Trailing behind the wave to the west of the warm air mass
will be a roughly southwest to northeast oriented cool front
tracking east southeast through the day. This will put the triple
point over northwestern Iowa around mid-day and progressing east
northeastward into the afternoon and evening. Convergence along the
trailing cold front will be the genesis region for storms beginning
around 1 PM today. Individual storms will move east northeastward
but the overall activity will propagate east to southeastward with
the progression of the boundary and as thunderstorm outflow
propagates into the warm sector. Convection continues into the
evening hours, but will be fairly progressive and generally wrap up
around midnight.

Storms developing along the cold front will have access to a strong
thermodynamic environment in the warm sector with instability values
climbing to around 3000 to 3500+ J/kg (SBCAPE) or slightly lower
values around ~2500 to 3000 J/kg if take into account dry air
entrainment (ECAPE). The 70 dewpoints and generally moist vertical
profile will keep LCLs quite low (~400 to 500m), especially in
northern Iowa. Likewise, low level instability will be very high,
with model output suggesting 0-3 km CAPE values 250 to 300+ J/kg,
which will produce a favorable environment for vorticity stretching.
Despite this thermodynamic eye candy, the severe weather risks will
once again come down to the wind fields and how they evolve today.

Through the entire vertical profile, the flow remains unidirectional
aloft with only around 25 to 30 kts of deep layer shear. However,
near the surface, south to southeasterly winds will allow for
looping hodographs and 0 to 3 km shear values along the cold front
around 25 to 35 kts as well. Low level SRH values will also be
modest, with 0 to 1 km SRH values around 100 to 150 m2/s2 and
slightly higher around 150 to 200 m2/s2 in the 0-3 km layer. These
values raise some concern for tornadic activity today, both as
stretching occurs with any initial updrafts near the triple point
and warm front in northern Iowa but also with any QLCS-like features
that may develop and run northeastward parallel to the 0-3 km shear
vector. For this reason, the storm prediction center has upgraded
today`s outlook to include a slight risk for severe weather over
north central into northeastern Iowa, including a 5% tornado risk.
There will be failure modes for this which may come from a less
defined warm front and more southwesterly flow in the warm sector,
but low level shear and instability values like these, it deserves
watching closely. The kinematic environment worsens further south in
the state, which will help mitigate the tornado threat into central
and southern Iowa. Strong winds and heavy rainfall will still be a
concern with any initial convection that develops throughout the
state today, but as the line convects in southern Iowa, competing
outflows and multiple updrafts will lessen the potential for severe
weather on the southern edge of the activity. Storms will be
efficient rainers once again today, but the expectation is that
activity will be progressive enough to mitigate flooding concerns.
More on this in the updated hydrological discussion below.

Beyond today, hot temperatures build in through the weekend as well
as a few more precipitation chances mainly into Saturday and
Sunday.

&&

.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 /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 632 AM CDT Thu Jun 26 2025

Light showers and isolated thunder persist in northwest Iowa
early this morning, but only anticipating potential shower
impacts at KFOD, if at all. IFR to LIFR ceilings are being
reported with stratus in northern Iowa at KMCW and near KFOD,
which will likely linger through the morning. Fortunately,
the sun should help to lift these ceilings through the morning.

As we get into the mid-day to afternoon and evening hours,
strong storms will begin to develop along a southwest to
northeast oriented cold front moving west to east across the
area. Storms are expected at all sites, and have timed out the
most likely window for the line to move through in each sites
forecast. The total time that storms are occurring at any given
site will only be around 2 to 3 hours, but have included a
slightly longer period of thunder/showers to convey uncertainty
on arrival and departure times. Heavy rainfall and strong winds
are possible with these storms, as are a few tornadoes in the
northern and northeastern portions of the state.

Once the front moves through and storms pass, winds will flip
from a roughly southerly direction to a northerly direction
which will prevail through the remainder of the TAF period.
Likewise, low clouds will move in behind the storms with MVFR
to IFR ceilings likely and LIFR possible at times overnight.


&&

.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...
Flood Watch until 1 PM CDT this afternoon for IAZ004>007-
015>017-023-024-033-034-044.

&&

$$

UPDATE...Dodson
DISCUSSION...05
AVIATION...Dodson
HYDROLOGY...Fowle/Zogg