977
FXUS63 KDMX 090353
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1053 PM CDT Fri Aug 8 2025

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Active period this weekend with heavy rain and severe weather
  potential.

- Flash Flood Watch for very heavy rain potential Saturday
  afternoon through Monday morning. The primary periods are
  Saturday night and Sunday night.

&&

.DISCUSSION...
Issued at 309 PM CDT Fri Aug 8 2025

A very active forecast remains for this weekend and into early next
week. Surface low pressure over Nebraska with a boundary extending
northward into northern Minnesota where another weak low pressure is
located. That boundary will settle into northwest Iowa overnight and
will eventually stall over Iowa as the upper level flow becomes
southwesterly, hanging up the parallel boundary below it.

Deciphering the potential for thunderstorms late tonight into
Saturday morning still isn`t straight forward as the elevated mixed
layer (EML) may hold much of the night but there are a couple signs
that convection may occur above the EML late tonight. The 700 mb
temperatures of 13-15C will certainly hold surface based convection
at bay but those temperatures do cool overnight. May get some weak
elevated convection with the low level jet and surges of theta-e
advection passing across the state. The EML will begin to erode late
tonight and the instability axis will move into the state and that
may lead to thunderstorm development late tonight into Saturday.
While locally heavy rain and a strong storm may occur with this
early activity, the overall threat is lower compared to other
periods this weekend. A greater potential for thunderstorm
development in vicinity of the boundary over central Iowa is
expected sometime from late Saturday afternoon and into the evening
hours. Again a few strong to severe storms will be possible but the
highest threat is the potential for heavy to very heavy rainfall
with storm motions nearly parallel to the boundary leading to the
potential for training of storms. Low and mid level moisture
advection will maximize Saturday night into central and south
central Iowa while warm cloud depths increase to near 15 kft.
Rainfall rates of 2 to 3 inches per hour may occur. Backbuilding of
storms is possible as well which would further the training
potential. For this reason, in collaboration with WPC, a moderate
risk for Excessive Rainfall has been issued for Saturday/Saturday
night in addition to Sunday/Sunday night. The Sunday period
inclusion is due to the potential for a repeat performance though
due to potential outflow influences, the boundary may settle a bit
more south than where the heavy rain axis sets up the previous
period. Will continue to monitor this period for severe weather
potential also, but again, the primary threat appears to by the
heavy rain potential and the greatest concern periods are during the
nocturnal hours.

Storm potential persists into early next week as the southwest flow
into Iowa will persist until the primary upper level short wave
arrives late Tuesday into Wednesday. The exact location of the
surface boundary is more uncertain as guidance is trending southward,
which makes sense given the aforementioned impacts on the boundary by
storms and outflow above.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1053 PM CDT Fri Aug 8 2025

VFR conditions are expected to remain this evening and for much
of the period. Still expecting to see the development of showers
and storms after 06z, mainly impacting the northern terminals
through 12z and gradually reaching KDSM and KOTM by mid to late
morning. Uncertainties remain on exact timing and coverage,
with only slight timing adjustments on the PROB30 mentions.
More widespread shower and storm activity is expected later in
the day but will depend on how the morning to afternoon
shower/storms play out, so will be closely monitoring
conditions throughout the next several hours. Winds otherwise
will become more variable given the boundary passage during the
day.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Saturday afternoon through Monday afternoon
for IAZ037>039-048>050-059>062-072>075-082>086-093>097.

&&

$$

DISCUSSION...Donavon
AVIATION...Bury