802
FXUS63 KDMX 041127
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
627 AM CDT Thu Jun 4 2026

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Showers and storms over northern Iowa diminish this morning.

- Flash flooding possible tonight with highest risk south of
  Highway 30 and west of I-35. Isolated rain totals could
  exceed 5 inches in these areas. A few severe storms are also
  possible with hail and perhaps a tornado or two late this
  afternoon or evening.

- A lull in rain and storms Friday, but storms return late in
  the afternoon into the night. Renewed concerns for flash
  flooding and severe storms.

- After a break in storms and rainfall on Saturday, chances return
  to the state later Sunday into Monday.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 355 AM CDT Thu Jun 4 2026

Regional radar shows showers and thunderstorms over far
northern Iowa and points north on the edge of an 850mb dewpoint
gradient and tied to the low level jet. This activity is
expected to sputter and diminish to a large degree over northern
Iowa this morning; however, have maintained low PoPs around 20%
to cover any spotty activity that may try to gin up in the
dissipating low level jet and thermal lift. As we move into the
afternoon hours, dewpoints will push into the 60s across central
Iowa under a sky filled with clouds and some breaks of
sunshine. Upstream of Iowa, a shortwave trough, perhaps of MCV
origins, will be lifting towards western Iowa reaching there by
late this afternoon. By then, mixed layer (ML) CAPE values will
be approaching 1500 J/kg in southern Iowa and with the
shortwave`s forcing and thermal lift, will see an increase in
scattered storm coverage. There are both hydrologic/flash flood
and severe storm concerns as these develop in the afternoon into
tonight. A common theme of late has been the weak deep layer
shear at or less than 25 knots, which should limit storm
organization. Initial severe storm concern will be on hail that
should be limited in size by a water laden atmosphere. As we
move into the evening hours, the low level jet will point into
southern and eastern Iowa and ramp up with 850mb speeds
approaching 40 knots. This will increase the low level curvature
and area underneath the hodograph so that storm relative
helicity values (SRH) increase to near 100 m2/s2 in the 0-500m
and a bit above in the 0-1km layer. Not surprising, LCLs are low
in this environment and the 0-3km CAPE will be over 200 J/kg so
cannot rule out a tornado or two this evening over southwestern
quadrant of Iowa.

While the severe risk will wane by late evening, the flash flooding
concerns will be growing. Forecast soundings show precipitable water
values peaking around 1.8 inches, which is well above the 90th
percentile (1.4") and could exceed the daily max. In addition, there
are very deep warm cloud depths nearing 4000m leading to efficient,
warm cloud rain processes. While there is no apparent surface
boundary, the 850-300mb flow around 25 to 30 knots should favor
rainfall that could repeat over the same area. Rainfall amounts by
sunrise Friday could be 2 to 4 inches with bullseye higher amounts
approaching 6 inches over southern into portions of central Iowa
with lesser amounts in northern Iowa. NASA SPoRT soil percentiles
are largely unchanged from this time yesterday at the 30th
percentile or lower in the 0-10cm rapid response and 0-40cm
river response layers. However, there are localized pockets in
Adair, Greene, and Taylor Counties that could be more
susceptible to rainfall response due to recent rainfall over the
past 5 days or so. Further, rainfall rates may exceed
infiltration rates and this is even more true over urban areas
that have more impervious surfaces. The experimental WPC urban
rain rate dashboard for Des Moines has shown increasing
probabilities for 2"/3 hours over the last 24 hours and is now
up to 15-20%. A flood watch for flash flooding was coordinated
amongst Omaha and Kansas City for this growing flash flood risk
late this afternoon into tonight, which roughly lines up with a
portion of the day 1 slight risk of excessive rainfall from WPC.

Storms will be pushing east of I-35 in the first several hours of
daylight Friday morning. There is growing consensus amongst models
that after this pushes out Friday morning, there will be little in
the way of additional storms until late Friday afternoon if not
Friday evening. There are exceptions, like the RAP and GFS, but PoPs
for now have favored a lower percentage. There should be some degree
of cloud clearing with temperatures rising into the 80s and
dewpoints in the 60s. Beneath a low level capping inversion, strong
instability will grow with MLCAPEs up to around 4000 J/kg in parts
of the state by late in the afternoon, but once again deep layer
shear will be a limiting factor perhaps reaching 30 knots. Storms
may wait until evening to develop either along the weak convergence
of a west to east surface boundary over Iowa if not more likely, per
convective allowing models, Nebraska closer to the origin of the low
level jet and then move into Iowa later in the evening/night. Either
way, severe storms with large hail given the large CAPE profile and
steep mid-level lapse rates and damaging wind gusts given the dry
mid-level air with downdraft CAPE values nearing 1000 J/kg may be
possible in portions of Iowa in the evening. Of equal and perhaps
more concern, depending on how much and where rain falls
tonight/Thursday night, will be flash flooding into Friday night.
Precipitable water values and warm cloud depths will still be quite
favorable for heavy rainfall. In addition, the 850-300mb layer wind
is oriented closer to the orientation of the surface boundary, which
may lead to rainfall rounds anchoring to the boundary. Soils will be
primed in some areas by tonight/Thursday night`s rainfall and with
another 1 to 3 inches possible in parts of southern or central Iowa
Friday night, the flash flood threat will need careful monitoring
into the overnight hours.

River flooding potential continues to look unlikely with the 5 and
10 day experimental Hydrologic Ensemble Forecasting Service (HEFS)
showing a little more than a half dozen action stage forecasts.
However, HEFS is forced by the GEFS rainfall, which often tends to
undo the rainfall. When looking at a singular run of the GFS, there
may be a bit more of a signal for higher flowers. For example, the
3/0z and 3/18z runs of the 3 day GFS forced National Water Model
have shown lower annual exceedance probabilities, which relates
to higher, more impactful flows. While this has not been over
central Iowa and has moved around spatially from the Cedar
Rapids area to east of the Quad Cites, it does suggest there
could end up being higher flows somewhere in the region with
exact placement dependent on future rainfall magnitude and
location.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 257 PM CDT Wed Jun 3 2026

Showers and thunderstorms are expected to continue into
Saturday morning, mainly over southern Iowa in relation to where
the frontal boundary is progged to generally stall for the day.
While most areas look to be dry for much of the day, additional
showers and storms look to redevelop over parts of southern
Iowa in relation to the lingering aforementioned front by the
evening. Confidence however on exact placement is on the low end
at this time, as models such as the GFS push this boundary near
the IA/MO border into northern Missouri by Saturday evening.
Certainly some placement differences to keep an eye on over the
coming days. The pattern Sunday and beyond looks to remain on
the more active side as additional wave pass through the area,
along with slightly warmer temperatures overhead. More specific
details however on timing and location of showers and storms
will be better known in the coming days as models better capture
these features.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 628 AM CDT Thu Jun 4 2026

Showers early this morning are limited in area and generally
north of a FOD to ALO line. Thus, have removed PROB30 at FOD,
but will have to monitor in case a shower pops up farther south
and AMD. For MCW, have maintained a PROB30 for shower potential.
There will then be a break in precipitation until this afternoon
when storms develop and increase in coverage into tonight. For
all but OTM, this results in prolonged SHRA into tonight with
PROB30s for most likely window of storms. Further adjustment to
impacts is expected at 18 and 0z issuance. Ceilings will be
lowering tonight into MVFR and perhaps IFR, but have just
advertised MVFR to start at all but OTM.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 4 PM CDT this afternoon through Friday
morning for IAZ046>048-057>060-070>073-081>083-092>094.

&&

$$

SHORT TERM...Ansorge
LONG TERM...Bury
AVIATION...Ansorge