912
FXUS63 KDMX 161948
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
248 PM CDT Mon Jun 16 2025

.KEY MESSAGES...

- Periods with thunderstorms, some strong will continue into
  Tuesday night and early Wednesday.

- Areas with heavy rainfall also likely through Wednesday with
  the focus shifting south into central and southern Iowa.

- Turning hot and humid late week and into the weekend.

&&

.UPDATE...
Issued at 255 AM CDT Mon Jun 16 2025

The most immediate hazard this morning is the potential for patchy
fog development across the area with an environment with plenty of
available moisture and very little wind. Patchy valley fog has
already been reported overnight and expect that this will continue,
with perhaps some expansion, through sunrise.

Our attention remains focused on severe and hydro hazards,
primarily today and Tuesday. Early this morning convection
continues to bubble along the stationary boundary that is still
draped across northern Iowa. As has been the case the past
several nights now, shear is very weak and the severe potential
remains low with any of the overnight activity. While a lull is
likely into the morning hours, an isolated thunderstorm at any
time through today cannot be ruled out. CAMs struggle, as they
have all weekend, in handling convection in this environment
with plenty of instability and very little organizing shear. The
main window for convection with come later today when a
shortwave drops out of South Dakota and across northern into
central Iowa. This should provide a little better focus for
convective development compared to the last several days, and
shear is incrementally better as well. With 0-6 km shear
approaching 30-35 kts and MLCAPE 2500-3500+ J/kg across northern
Iowa strong to severe storms are anticipated. Wind and hail are
the primary concerns, given steep lapse rates over 7 C/km and
DCAPE nearing 1000 J/kg. There is also a low end tornado threat
in northwest Iowa with shear sufficient for sustaining rotating
updrafts and 0-3 CAPE around 100- 150 J/kg. At the same time,
expect continued efficient rain producers with 1-2" of QPF
across mainly northern Iowa today. This falls across areas that
received 1-3" of rain late last week, increasing the chance for
ponding of water, river rises, and isolated chances for flash
flooding in urban areas.

Remnants of a decaying central plains MCW are expected to move into
Iowa overnight into the early Tuesday morning hours. This may impact
convection later in the day as a more robust (the most robust
in this series) is set to move across the area on Tuesday. The
instability gradient continues to bisect the state on Tuesday
and expect that convection will ride along that gradient. Shear
is also a bit better but could be a little displaced from the
better instability. An important component on Tuesday is that in
addition to the best shear in this series, the directional shear
component will increase potential for sustained rotating
updrafts to produce hail and a tornado threat. Of course the
details of Monday`s convection and the remnant MCS across the
area on Tuesday morning will influence how these details come
together. And in addition to the severe potential, another
widespread 2" of rain is anticipated across central Iowa with
pockets of 3+" likely. With the repeated days of heavy rain the
hydro concerns increase, particularly in areas that may receive
back to back hits. We`ll be keeping a careful eye on these areas
towards Tuesday and into Wednesday as cumulative effects are
finally realized. With convection continue overnight and into
Wednesday as the system finally pushes off to the east,
lingering hydro concerns are expected as water filters into
river basins.

&&

.DISCUSSION...
Issued at 243 PM CDT Mon Jun 16 2025

Storms are still ongoing over parts of the northeast county warning
area including near Waterloo. This convection has been moving slowly
east/southeast since earlier this morning as it fired along an
outflow boundary from overnight storms. A few of the storms have
been strong and near severe and they are beginning to have stronger
cold pools associated with them, as indicated by the the 20+ degree
drop in temperatures. Wind gusts have responded as well with a few
gusts of 40 to 55 mph now being recorded. These storms have also
produced rainfall amounts of 1-2 inches. A pseudo boundary has setup
also as a result of the storms with south/southwest wind and
temperatures in the mid 80s mainly south of Highway 20 to near
Waterloo to Fort Dodge then arcing northwest into Minnesota.

The convective allowing models (CAMs) have not performed well today
and outside the HiRes ARW, the remainder of the CAMs have combined
for a near zero batting average on this mornings convection and the
new convection firing over southeast South Dakota along the primary
cold front. The lack of consistency with the CAMs and the turned
over air north and the pseudo boundary a bit south, the confidence
on the evolution of storms going into this evening is lower than
normal. Once potential outcome is the storms over southeast South
Dakota become rooted and then travel southeast along the pseudo
boundary where and instability axis is situated and eventually move
into central Iowa this evening. Otherwise, it could be a waiting
game for the development of an MCS over Nebraska mid to late
evening, though that system should turn southeast. The main cold
front will move into Iowa tonight and stall somewhere over central
Iowa. That will eventually become the focus for storm development
overnight or through the day Tuesday. The triple point will move
into should move into south central Iowa late Tuesday into Tuesday
night which may bring the tornado threat into the state.

Heavy rain potential will remain through Wednesday. The strongest
moisture advection will remain just south of Iowa but PWATs in
excess of 2" will be over Iowa at times from late Tuesday into early
Wednesday. Warm cloud depths by Tuesday night will be approaching 13
kft so efficient warm rain processes and slow storm motions will
lead to areas with heavy rainfall. At this point, much of the heavy
rain has been over northern Iowa. That focus should shift south into
central and southern Iowa. Will continue to monitor the situation as
several streams are running above normal.

After the short wave passage on Wednesday, 500 mb heights will be on
the increase and a transition to a very warm and humid pattern will
occur. High temperatures in the 90s with dew points in the 70s at
times will be the warmest weather so far this year. Eventually the
upper flow will undergo another transition late weekend into early
next week with a large upper high developing to the east and and
upper low to the west and southwest upper flow into Iowa. One period
to watch is Thursday night as this transition occurs as an MCS could
develop over Minnesota and drop southeast into Iowa. Otherwise, the
next convective chances, barring the presence of a stout enhanced
mixed layer (EML), will be next week, which may be stormy at times
after a lull late week and into the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1240 PM CDT Mon Jun 16 2025

Storms over northern Iowa continue and will impact KALO early in
the period. Gusty winds are also possible with these storms.
Less certainty in storm timing and potential and any given site
so limited the storm mention in this forecast. Wind will be
erratic over northern Iowa also early this afternoon before
re-establishing from the south. A cold will enter central Iowa
overnight and stall on Tuesday. This boundary will likely become
the focus for renewed convection.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon