487
FXUS63 KDMX 161940
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
240 PM CDT Thu May 16 2024

.KEY MESSAGES...

- Warm Friday and Saturday with highs in the 80s.

- Isolated storms possible Saturday.

- Several periods with storm chances from late Sunday through
  Tuesday night and again by late in the week.

&&

.DISCUSSION...
Issued at 237 PM CDT Thu May 16 2024

A few showers and isolated thunderstorms have developed across far
southeast Iowa this afternoon along a weak frontal boundary that was
ushering in drier air to the state. The drier air is resulting in
the erosion of this mornings cumulus filed over central and north
central parts of the state. This trend will continue as the as the
boundary moves off the to the east. The precipitation over the far
southeast will depart as well. High pressure ridge will move quickly
across central Iowa this evening with the wind turning southerly
already by midnight or shortly after. Friday will be warmer and dry
with high temperatures in the low to mid 80s for most areas.

The Gulf moisture will likely remain cutoff from Iowa through
Saturday night with high pressure ridge cutting the flow off. The
thermal ridge will move across Iowa on Saturday leading to another
bump in temperatures with widespread highs in the 80s expected. A
boundary will move into the region Saturday afternoon and evening
while the parent short wave moves from Montana and into North
Dakota. While it is possible that a few storms fire along the
boundary, the lack of moisture available due to the Gulf flow shut
off and it is possible the surface boundary undercuts the thermal
ridge aloft, which would lead to capping. Those factors in addition
to the lack of good forcing should keep any precipitation isolated
to scattered at best. Another area of high pressure will quickly
follow and settle over Iowa Saturday night and into Sunday morning.
During this time, a strong upper level system will be dropping
southeast into the Pacific Northwest which will tilt the upper flow
to southwesterly. The switch to southwest flow will help allow the
Gulf moisture to stream back northward. In addition, a strong short
wave fragment originating from a close low off the southwest
California coast, will eject out in the southwest flow and arrive
into Iowa later Sunday.

Timing of the short wave and also the arrival of the Gulf moisture
will be the primary factors on thunderstorm timing for Sunday/Sunday
night. Most likely scenario at this time is thunderstorms developing
over western Iowa Sunday afternoon, then moving eastward Sunday
night. Another strong short wave will be following this system by
Monday afternoon or night with additional thunderstorm chances and
those chances will persist until the main upper level energy to the
west lifts out and clears the region, likely sometime Tuesday night.
In addition to a few chances for severe weather during this time
period, the heavy rainfall threat may return with a few periods with
PWATS topping 1.50 inches along with several rounds of storms
possible. A break in the weather should arrive by Wednesday and
persist into at least early Thursday. Another potent upper low will
be over the Pacific northwest early Thursday. This system will bring
more weather to the state once it ejects out towards the region
sometime towards the end of next week. With streams running above
normal flows currently, will have to monitor the river flood
potential as repeated rounds may bring renewed flooding.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1232 PM CDT Thu May 16 2024

Cumulus has developed across much of the area. While there still
could be a localized brief MVFR cig, the cigs are rising with
daytime mixing leading to cloud bases above 3 kft. In addition
to the rising cigs, the clouds will begin to diminish in areal
coverage by mid afternoon, except the far northeast. West wind
today will become light tonight and transition to southerly by
Friday morning.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon