713
FXUS63 KDMX 171721
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1221 PM CDT Tue Jun 17 2025

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

.KEY MESSAGES...

- Periods with thunderstorms, some strong will continue
  throughout today and into 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 248 AM CDT Tue Jun 17 2025

Convection across southern Iowa has diminished early this morning
while an MCS continues to move east across Kansas and Nebraska.
Remnants of this are expected to move into Iowa later on this
morning as it continues to diminish in strength. By this
afternoon diurnal heating is expected to drive redevelopment
along remnant outflow boundaries from this in central to
southern Iowa, while further development in northern Iowa will
be aided by upper level support from the shortwave moving across
this area. The low track driving today`s most robust convection
has shifted south quite a bit compared to yesterday`s CAM runs.
The instability gradient is shifted south with values into Iowa
around 1000-1500 J/kg and shear around 20kts with better shear
also shifted south. If this tracking holds through the day,
severe chances into Iowa will be limited with little in the way
of support for more organized storms. If things shift further
north, more robust storms and the tornado threat would reach
back into southern Iowa, but that is not the case at this time.
Of course, CAMs have struggled significantly with this pattern
the past several day, so confidence in the convective evolution
today is not high.

By Wednesday the low off to the south will lift north and east with
Iowa on the north side, receiving widespread stratiform rain as
it finally exits the area. Between today and Wednesday, expect
a widespread 1" of rain across a lot of Iowa with pockets of
2-3+" likely. Current river forecasts bring a number of
locations to action or just exceeding minor flood stage in
northern to central Iowa. Shifts in precipitation will impact
how the water is routed into basins and these forecasts will
continue to be fine tuned.

Another quick moving wave will pass across the area late
Thursday into Friday, but much of the forecast late this week
and through the weekend is dry. Temperatures soar through the
end of the week and weekend while humidity sticks around - it`ll
be hot and muggy. Friday through Sunday look to be the warmest
days with the heat index of "feels like" temperatures exceeding
100 degrees in many locations for the first time this summer.
Temperatures come down into next week with storm chance
returning.

&&

.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 WEDNESDAY/...
Issued at 1221 PM CDT Tue Jun 17 2025

Scattered showers and thunderstorms are forecast at intervals
through the 18Z TAF period. Confidence in timing and coverage is
unusually low, but in general the most likely time frames will
be late this afternoon and evening, and overnight into Wednesday
morning. Have included PROB30 groups at all terminals in the
former period, and VCSH in the latter period, but expect
refinement via subsequent TAF issuances and amendments today and
tonight. Aside from SHRA/TSRA, VFR conditions will prevail
through this evening, but then lowering cloud bases overnight
should result in prevailing MVFR ceilings by Wednesday morning,
with pockets of IFR possible but more unlikely. Within
SHRA/TSRA, visibility will be highly variable and ceilings may
be lower at times as well.

&&

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

&&

$$

UPDATE...Hagenhoff
DISCUSSION...Donavon
AVIATION...Lee