432
FXUS63 KDMX 022023
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
323 PM CDT Thu May 2 2024

.KEY MESSAGES...
- Southeastern Iowa showers and storms ending tonight
- Scattered storms roll into Iowa late Friday night/Saturday morning
- Thunderstorms arriving later Monday into Monday night with severe
risk possible

&&

.DISCUSSION...
Issued at 323 PM CDT Thu May 2 2024

The main upper low over southern Saskatchewan will spin slowly
eastward and then northeastward toward Hudson Bay from today
through the beginning of the weekend. This upper low has swung a
shortwave through its base with a surface low over central Iowa
and a cold front near I-35 in southern Iowa. Rain and storms
have prevailed over parts of our southern and more so our
southeastern forecast area this morning into early this
afternoon. Automated personal rain gauges have recorded 1 to 3
inches with isolated amounts just now topping 3 inches so far
today from parts of Wayne to Monroe to Mahaska Counties, which
lines up well with MRMS QPE. Calls to emergency managers after
lunch time reveals numerous road closures - mainly gravel, but
even at least one paved road - with a few vehicles driving into
flooded areas. Thus, issued a flash flood warning for those
areas until early this evening. Rainfall let up briefly over the
warned area, but additional rainfall is transitioning up into
our southeastern Iowa forecast area and this will not allow
flooded areas to see appreciable improvement until the rain ends
later this evening. While rain rates are not expected to be
extreme, light to moderate rainfall falling on already saturated
soil may lead to low end water issues. Opted for the flash
flood watch over the (areal) flood watch given our already issue
flash flood warning. Additional totals of 1 to 2 inches are
possible in localized areas before the front pushes all the rain
out later this evening.

Tonight, as winds relax, the sky clears, and with the recent
rainfall, patchy fog may develop in at least favored low lying
locations. Any fog will dissipate early in the morning and it will
be a fine Friday with highs around 70 degrees in central Iowa.
Friday night will see another lobe of vorticity round the base of
the upper low. MUCAPEs look to be under 500 J/kg, but mid-level
lapse rates and deep layer shear could be favorable for a few
elevated stronger storms with hail and perhaps a few strong wind
gusts being the main threats late Friday night into Saturday
morning. After this departs, a weak ridge will pass over Saturday
night into Sunday and a southern stream shortwave trough and its
associated rain will pass largely south of the state with some token
chances in southern Iowa.

Attention then turns to a stronger shortwave trough and surface low
moving over the central and northern Rockies, respectively, early
next week. This low will occlude as it moves into the western
Dakotas, but will draw moisture northward back over the state with
dewpoints likely topping 60 degrees in at least southern Iowa.
Stronger kinematics will yield higher deep layer shear and
instability over 1000 J/kg and steep mid-level lapse rates will also
pool ahead of a cold front moving eastward into the state. This will
likely yield some strong to perhaps severe storms and while the SPC
day 5 outlook is just southwest of our area, the 00z runs of the
Colorado State`s machine learning random forest outlook and the CIPS
Experimental Analog-Based Severe Probability Guidance both highlight
a large sections of Iowa with 5-10% probabilities of severe with a
15% over the southwestern third to half of the state. These storms
will push across the state overnight into early Tuesday, though some
models have a slower timing of the front, which could lead to a
lingering strong storm risk over parts of our eastern area Tuesday
afternoon. Thereafter, the shortwave trough will meander and shear
out while our flow stays westerly or southwesterly aloft. This could
bring some shower potential later in the week as this occurs and the
shearing shortwave sinks closer to Iowa, but stronger storms do not
look favored as the instability and higher dewpoints will be shunted
to the south. Temperatures, however, will remain above normal
ranging from the upper 60s to low 70s north to the middle and upper
70s south.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1222 PM CDT Thu May 2 2024

Showers and thunderstorms continue from south central into east
central Iowa including at OTM early this afternoon. Thunder or
vicinity thunder has been focused through the afternoon hours at
OTM trimming any mention late this afternoon into this evening
as this activity moves out. Confidence was there to do such, but
will monitor in case we need to extend that mention. Farther
north and west, light showers or drizzle has been developing
from near DSM to west of ALO. Not sure how this will exactly
play out, but have included those mentions at both terminals
this afternoon. Otherwise, ceilings will in general improve into
tonight. Between 8 and 13z, there is medium to high confidence
in fog forming, but low confidence in location. For now, have
only included BR mention at ALO since there seems to be some
consensus there. Future forecasts will continue to evaluate.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight CDT tonight for IAZ074-075-084>086-
094>097.

&&

$$

DISCUSSION...Ansorge
AVIATION...Ansorge