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000
FXUS63 KDMX 152041
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
341 PM CDT Mon Apr 15 2024

.KEY MESSAGES...

- Slight risk for severe weather southwest tonight with hail and
  wind being the primary threat. Storms lifespan will be short.

- Enhanced risk of severe weather across the east tomorrow with
  two rounds of storms. All modes of severe weather possible.
  Heavy rainfall expected with up to 4 inches of rain in the
  northeast.

- Cooling temperatures beyond with rain chances Thursday. Below
  freezing lows return at the end of this week.

&&

.DISCUSSION...
Issued at 334 PM CDT Mon Apr 15 2024

A closed upper level disturbance currently in the Desert Southwest
will eject into the Plains later today, negatively tilting and
deepening as it moves across Nebraska. At this point in the
system`s evolution, it will be stacked and remain at roughly the
same heights while impacting the state. The pressure gradient
will be tight across the state, have issued a Wind Advisory
across the north for environment winds.

A wide open Gulf will push moisture advection through the midlevel
dry slot and northward this evening and overnight as the LLJ picks
up. With near max percentile PWATs and multiple rounds, heavy
rainfall will occur. The HREF Probability Matched Mean has amounts
totaling over an inch for the entire area. Portions of northern
and northeast Iowa will see all three rounds of convection and
therefore the most rainfall. HREF paints localized areas of over
4 inches. This will be right over the region of the state with
the worst drought conditions and can take the rain, but
localized urban impacts are still possible.

Round One, overnight convection:

This round`s evolution will impact what will transpire in the
upcoming rounds. The LLJ will nose into western Iowa, generally over
the location of the surface warm front which will be draped over
southwest Iowa. While the dry slot will inhibit midlevel moisture,
isentropic upglide will build in low level moisture which will have
some thermodynamics at its disposal. The gradient of the main
instability axis will hug the Missouri river with MUCAPE exceeding
1000J outstretched along the warm front. Shear in the lowest
3km will increase through the nighttime hours, but nocturnal
profiles will not be supportive of anything surface based.
Isolated severe hail will be possible due to the instability
profile, but weaker shear profiles will limit the organization
and lifespan of storms. The low center will drift northeast
through the morning and pull the LLJ and morning convection
northward. Main uncertainty is coverage of storms overnight. The
greater the coverage, the less instability available for the
next round.

Round Two, morning/midday convection:

A front with a trailing dry line will surge into the state early
Tuesday morning and begin to occlude with the warm front in
northwest Iowa. The upper level jet will veer into northern MO,
keeping stronger 0-6km layer shear and divergence south. For central
Iowa, the low level shear is more concerning. 0-3km shear will be
approaching 50kts and will be out of the SSW. CAMs illustrate this
round being a QLCS. Examining hodographs, 0-1km SRH values are
approaching 300 m2/sec2 and 0-0.5km will be in the 200s. With LCLs
very low, tornadoes are certainly in play. The questionable factor
is the available instability for the line, especially at a capacity
for the line to be surface based. Not only will there have already
been a first round of rain and storms overnight, but stratiform
rain will run ahead of the QLCS in the shear dominant
environment, eating away at the available instability for the
line.

Round Three, afternoon/evening convection:

On the heels of the second wave of convection will be the dry line
and will feature the last round of potential thunderstorms. This
round will be conditional on recovery of the near storm
environment and afternoon guidance is keying in on on this
being a possibility despite the short spacing in between.
Historically, we have seen quick recoveries with little to no
clearing between rounds (eg. 1999, 2001). The orientation of the
stratiform rain from the earlier round aids in recovery of
instability, but the position of the left exit region over the
area may allow for updrafts to fester. In this round, favorable
deep layer shear is present near the IA-MO border, so storms
that get going can get organized and produce at least severe
winds and some hail. There is uncertainty in the tornado
potential with this round due to the questionable
characteristics of the low level profile. Hodographs in the low
levels lose arching characteristics, but can be more favorable
if winds back. The better severe weather potential will be in
the high shear environment in northern Missouri where less
convection has overrun the environment.

Long term:

The closed low will then phase into a broader area of troughing by
midweek. There will be another opportunity for precipitation on
Thursday as frontogenesis sets up across the state. Northwest flow
sets in through the rest of the week and pushes highs back into the
50s. Zonal midlevel flow will keep us dry through the rest of the
week. Cool temperatures will lead to below freezing conditions
for lows into the weekend and may warrant frost/freeze
headlines.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1241 PM CDT Mon Apr 15 2024

VFR conditions to continue through the daytime hours with gusty
winds out of the east. Winds will become southeasterly tonight
ahead of rain and thunderstorms. Added VCTS mention associated
with first round of thunderstorms overnight. A second round of
thunderstorms will develop near the end of the TAF period and
will add thunder mention as confidence increases. Some storms
could be strong and severe. MVFR cigs to arrive with storms with
pockets of IFR possible after 12z.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 7 PM CDT this evening for IAZ004-005-
015-023-024-033-034-044-045.
Wind Advisory from 7 AM to 7 PM CDT Tuesday for IAZ004>007-
015>017-024>028-036>039.

&&

$$

DISCUSSION...Jimenez
AVIATION...Jimenez