221
FXUS63 KDMX 042007
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
307 PM CDT Thu Jun 4 2026

.KEY MESSAGES...

- Scattered to numerous thunderstorms are expected this
  afternoon into tonight. Widespread severe weather is not
  expected but an isolated strong to severe storm is possible,
  including a small tornado threat.

- Flash flooding risk trending up tonight with highest risk
  extending from southwest Iowa into northeastern Iowa,
  including the Des Moines and Waterloo metro areas. Rainfall
  totals of 2 to 4 inches likely, locally 5 inches in isolated basins.

- A lull in rain and storms midday Friday, but storms return
  late Friday afternoon into Friday 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 300 PM CDT Thu Jun 4 2026

Late this afternoon into Tonight...

Combination of residual MCV and low amplitude upper shortwave
currently over NE/SD will lift northeastward across the upper
Mississippi Valley region through tonight.  Seasonally strong low
level moisture /sfc Tds in the 60s/ combined with diurnal heating
has led to modest MLCAPE of 1000-1500 J/kg across much of the DMX
CWA. As expected, scattered showers and thunderstorms have developed
as of 2pm CDT across portions of western and central Iowa.  The
severe threat this afternoon into tonight still looks to remain low.
Weak mid-level lapse rates /moist adiabatic/ and modest deep layer
shear /20-30kts/ should result in a messy multicell storm mode which
should limit hail production. Downburst wind potential is also low
with minimal values of DCAPE /less than 500 J/kg/ and low cloud
bases which will limit subcloud evaporation. There remains some
tornado risk this afternoon, mostly the landspout variety,
again due to the lower LCLs, moderate 0-3km CAPE, and some
semblance of weak boundary across the central sections of Iowa.
These landspouts would be most likely during the initial,
incipient updraft phase. Later this evening, as the LLJ
increases, slightly more elongated, looping hodographs do
develop, which would increase low level SRH should any storms
remain balanced. Thus, a low tornado risk will remain into the
evening hours.

Of greater concern this evening into the overnight is the heavy
rainfall and flash flood potential.  As noted, previously, there are
several factors favorable for heavy rainfall: 1) deep and anomalous
moisture with PWATs from 1.5 to 1.8 inches along with high freezing
levels of 12-14k feet; 2) relatively weak wind profiles which will
lead to slower storm motions; 3) storm motions parallel to the weak
low level boundary, leading to the possibility of training
storms; 4) strengthening low level jet after 00Z which will
enhanced moisture transport and convergence, and sustain
convection overnight. The one "missing" ingredient is the lack
of strong sfc boundary, but this could be augmented by storm
scale outflow. As such, expecting very efficient rainfall rates
of at least 1 to 2 inches per hour at times, which will likely
lead to pockets of 2 to 4 inches of rainfall, perhaps over 5
inches in isolated locations if more persistent training
develops. Based on recent output from the 12Z CAMs/HREF, and
the various AI tools, have expanded the Flash Flood Watch
northeastward across portions of east-central and northeastern
Iowa. Storm activity will likely continue through much of the
overnight before ending towards daybreak on Friday.

Friday into Friday Night...

Storms are expected to be largely south and east of the CWA by
Friday morning as the upper shortwave/MCW move into the Great Lakes
region.  In its wake, expecting a period of subsidence with a
general "lull" in the precipitation through at least midday
Friday. Soundings are showing the possibility of stratus hanging
around for a portion of the day as a stronger push of warmer
mid-level air /EML/ arrives. Assuming at least partial clearing,
temps should again warm into the mid 80s with sfc dewpoints
creeping higher into mid/upper 60s. This moisture along with
steeper mid level lapse rates will yield much stronger
instability Friday PM. Deep layer shear will also be more robust
with 0-6km shear from 30-40kts, supporting multicell and
possible supercell storm mode. Model soundings do show capping
to be a potential hindrance to storm development, so its
possible that we remain capped until evening, perhaps until
after 8pm or 9pm, until the arrival of the low level jet. The
Level 2, Slight Risk remains in place across much of Iowa, with
all modes of severe weather possible. Additionally, the location
of the east/west sfc boundary will play a key role, not only
with the severe potential, but also with another round of heavy
rainfall. Right now, the models are in poor agreement on the
location of boundary, so this will need to be fine tuned in
future shifts. A Level 2 Slight Risk for Excessive Rainfall
remains in place for tomorrow, and its possible the Flood Watch
may need to be extended or reissued with many of the same
factors for heavy rainfall mentioned above. Finally, depending
on the amount of rainfall over the 2 day period, river flooding
could also become an issue with at least within bank rises
likely, and possible minor flooding as suggested by the latest
HEFS output.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 300 PM CDT Thu Jun 4 2026

Additional rounds of 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. Another lull is expected on Saturday with
additional storms possible on Saturday night and again into
Sunday as another surge of moisture pushes nwd.

Confidence on convective details at this range remain low, and
the timing and location of showers and storms will be better
known in the coming days as models better capture these
features. Temperatures should remain at or above seasonal
averages.


&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1233 PM CDT Thu Jun 4 2026

Showers and thunderstorms will gradually become more numerous
this afternoon and into this evening and tonight. Terminals in
the north /FOD and MCW/ will be impacted as early as 18-20z with
a line of thunderstorms then expected to gradually sag swd into
central and eastern Iowa during the evening and overnight hours.
Expect occasional MVFR to IFR CIGs and VSBYs with the stronger
showers and thunderstorms, and have include TEMPOs and PROB30s
to account for these trends. Some storms could become strong,
with strong and variable winds possible. Into the overnight,
showers and scattered thunderstorms will continue and CIGs will
continue to drop with prevailing IFR conditions expected at
FOD/MCW/ALO through early Friday AM. Gradually improving
conditions will not occur until after 15z on Friday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday morning for IAZ026>028-036>039-
046>050-057>061-070>074-081>083-092>094.

&&

$$

SHORT TERM...Fowle
LONG TERM...Fowle
AVIATION...Fowle