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000
FXUS63 KDMX 241138
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
638 AM CDT Wed Apr 24 2024

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Quiet today, with light winds and mostly sunny skies

- Active weather begins Thursday evening through Friday, with best
severe potential remaining Friday afternoon to evening

- After a quick break into the weekend, another system passing
through continues to suggest additional severe weather potential
late Saturday into Sunday

&&

.DISCUSSION...
Issued at 402 AM CDT Wed Apr 24 2024

A quiet start to the day as high pressure continues to make its way
down from the far Upper Midwest, which has led to winds turning
light and more variable across the state. Satellite imagery this
morning shows clear skies across the region, outside of some high
clouds scraping the southwestern portion of Iowa. Otherwise,
temperatures currently sitting in the upper 30s northwest and
through the 40s across the rest of the state are expected to
continue decreasing as efficient radiational cooling continues over
the next few hours. With lows expected to drop into the 30s north
and west, there could be some patchy frost that forms briefly,
before decreasing after sunrise. Outside of some high clouds
streaming across the west and south, skies are expected to be mostly
sunny, which will allow for temperatures to warm nicely through the
60s. Gradually shifting winds into the evening out of the southwest
is expected as the high pressure begins to depart the region.
Compared to this morning, overnight temperatures into Thursday will
be a bit warmer with values in the upper 30s through the 40s,
warmest west where increasing clouds are expected. This increase in
clouds is thanks to the gradual increase in moisture that is
expected throughout Thursday ahead of the first of two notable
systems expected to impact Iowa through the end of the work week.
This system will also be responsible for winds to increase out of
the southeast, becoming quite breezy as gusts between 25-30 mph are
generally expected across the forecast area. Ahead of the
approaching system previously mentioned, CAM guidance as well as
most model guidance is generally depicting a weak wave passing
through Kansas/Nebraska into Missouri, which along with forcing for
lift and moisture overhead looks to bring in some light shower
activity Thursday morning. For Iowa, this precipitation looks to
push mainly across the southwest half of the state, though minimal
rainfall amounts are expected.

Now, about the first system that was mentioned: A trough lifting out
of the Desert Southwest continues to depict lee-side cyclogenesis
into Thursday evening, with the surface low lifting northeast across
the Central Plains. A defined warm front in association with the low
pressure generally is expected to push into the region by Thursday
evening and continue lifting across the state through Friday
morning. Among model members, there are still some notable
differences in the coverage of precipitation, as the NAM and GFS
shows precipitation over much of the state before midnight,
while the Euro keeps much of the activity over southwestern Iowa
to start. Not surprising to have some differences at this time,
but would expect more consistency over the next few forecast
packages. As the initial precipitation pushes through, any
thunderstorm activity generally looks to be elevated in nature,
with CAPE values around or under 500J/kg, though effective shear
values are looking moderate around 40 kts. Overall, storms look
to remain below severe limits at this time, though some small
hail could occur at times. Otherwise, heavy rain is still
expected as the push of moisture out of the south reaches into
the state. Later on Friday, details become a bit more fuzzy as
the evolution of this overall system varies among models. In
terms of severe potential later on in the day, the NAM suggests
that drying into the afternoon hours would occur, before the
cold front enters western Iowa and tracks east across the state
into Friday evening. If decent clearing occurs ahead of the
frontal passage, surface based convection is suggested to
develop, with increased instability up to 1500-2000 J/kg,
effective shear of 30-40 knots and fairly steep lapse rates
supporting large hail potential. Looking further into model
soundings shows strong SRH values, along with favorable
curvature in the hodograph over Central Iowa that would support
the potential for a few tornadoes. On the other side of the
coin, model guidance such as the Euro/GFS are more pessimistic
on the severe potential as precipitation is suggested to remain
overhead throughout the day with no potential for clearing to
occur, limiting that potential for surface based potential late
in the day. Not much at this time to have high confidence on,
but with a few days ahead of this activity, can expect to get
more clear details in the coming days. Outside of the severe
potential, synoptic winds are expected to increase even further
as strong flow passes overhead, with gusts upwards of 40+ mph
gusts possible.

Into the weekend, precipitation coverage should generally decrease
Saturday, though some models still hold onto to lingering
precipitation largely across the north and east through the day.
Active weather however is not quite done yet, as another trough and
associated low pressure system is expected to lift into the region,
bringing additional chances for appreciable rain, and even possible
severe weather. Though details are more uncertain with this system,
generally speaking, the track of this system looks to make a more
direct passage as guidance depicts the center of the low tracking
over Iowa by Sunday. Before then, a defined cold front looks to
develop into Saturday night, which looks to include at least a
portion of southern/eastern Iowa. Overall parameter space per
sounding data shows moderate instability in the 1500-2000 J/kg,
effective shear around 30 kts and steep lapse rates supporting
a large hail risk, though a few tornadoes may also be possible.
Given the larger uncertainty in the placement of the cold front
however, will have to hold off on getting further into the weeds
given the extended timing ahead of this particular activity.
However, rainfall amounts look to be more appreciable as well
with totals by the end of the weekend upwards of 2-3+ inches
across the state, though slight changes are expected to occur in
amounts and coverage at this point.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 638 AM CDT Wed Apr 24 2024

VFR conditions are expected across the terminals throughout the
TAF period. Outside of some high clouds passing through at times
today, overall cloud cover is expected to increase after
00z-06z in the mid-levels. Wind will remain light, gradually
shifting southeast after 18z-21z.

&&

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

&&

$$

DISCUSSION...Bury
AVIATION...Bury