966
FXUS63 KDMX 151132
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
632 AM CDT Sat Jun 15 2024

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

.KEY MESSAGES...

- Decaying MCS this morning.

- Severe storms possible later this afternoon and evening,
  mainly west of Interstate 35. A few tornadoes are possible.

- Heavy rainfall could occur in some areas late this afternoon
  and overnight.

- Very warm Sunday and Monday with heat index values of 95 to
  100 possible.

&&

.DISCUSSION...
Issued at 324 AM CDT Sat Jun 15 2024

An MCS is moving east across the eastern half of Nebraska this
morning with the main line nearly the Missouri river followed by
trailing stratiform. An MCV is evident on the northwest side of the
system with as it swirls and lifts northeast. An area of very high
based showers developed over northern Iowa and in a region of upper
level theta-e advection occurring at 600 mb or higher. Very dry air
below these showers has limited the amount of precipitation actually
reaching the ground but there have been a few locations measuring
0.01"-0.02" of rain. The MCS will continue to decay as it moves
east/northeast over the next several hours. There is some
uncertainty on how far east this system will get before it fully
decays but it should not get much past Interstate 35 as it outruns
the instability axis. Additional non-severe storms may fire behind
the decaying system this morning.

Temperatures today are also problematic as the convective debris
from this mornings MCS may linger for a while though some sunshine
should eventually emerge over western and southern parts of Iowa
sometime this afternoon. A strong short wave trough will arrive late
this afternoon and early this evening over western Iowa and ahead of
it deeper moisture return will be ongoing with dew points in the low
70s expected over far western Iowa. Assuming that destabilization
will be ongoing ahead of the trough arrival, convective initiation
should occur as the kinematic forcing arrives. The deep layer shear
values are not that impressive due to the weak flow in the mid-
levels by values in the 25 to 35 kt range could potentially lead to
a few supercells to develop. Low level shear and turning will be
more favorable with 0-1 km SRH profiles near 150 m/s2 with much of
that occurring in the 0-500m layer and with expected lowering LCLs
and increasing low level instability, ie 0-3 km CAPE, the parameters
are favorable for a few tornadoes into the early evening hours. The
potential for good streamwise vorticity ingestion is also expected.
Large hail will also be possible with strong updrafts favorable for
updraft acceleration and the 0-3 km theta-e differences of 25-30k
would support cold pools and a damaging wind threat. In addition, a
heavy rain threat may materialize, especially over northwest/north
central Iowa where repeated rounds of storms may occur through the
overnight numerous rounds of theta-e advection arrive as the low
level jet continues to point into the region. PWAT values in excess
of 1.50 inches and possibly near 2 inches will be in place providing
plenty of moisture available.

By Sunday, the warm front should be north into Minnesota, resulting
in mostly dry and very warm conditions with highs in the low to mid
90s. Did back these down a few degrees as the NBM remains near the
high end of guidance, which is not supported by the expected thermal
profiles with a relatively moist airmass in place. Did not drop
further as some deterministic solutions are trying to mix out the
high dew points in parts of central and southern Iowa. Heat index
values may touch 100 in some areas Sunday afternoon. The boundary is
expected to remain north trough early Tuesday but convective chances
are still problematic. The Corfidi vectors do suggest that an MCS
over Minnesota, could propagate south into northern Iowa. This seems
on the less probable end of the spectrum but will still monitor
trends. Highs on Monday may again be suffering from the NBM`s warm
bias with highs mainly in the 90s again but for now have left closer
tot the NBM and the NBM 50th blend. The boundary will drop back
south into the region by later Tuesday and into Wednesday. This will
bring another round of storms to the region. Will continue to
monitor the heavy rain threat throughout the period as a rich
moisture supply will remain. Severe chances will certainly be
possible once the boundary returns as well. A subtropical high over
the east central CONUS mid-week will ridge westward into the
southern CONUS. This will move the boundary back northward and bring
more warm weather for the end of the week.  Should the boundary
stall over the region, it could also mean more severe weather and
heavy rain potential.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 629 AM CDT Sat Jun 15 2024

Decaying MCS over western Iowa may reach KDSM/KFOD yet this
morning. A brief MVFR cig could occur at KFOD. Scattered storm
chances are possible most locations this morning then again
overnight with the possible exception of KOTM. Storms will be
most widespread overnight. Again, MVFR cigs could accompany
storms tonight. Breezy southeast winds today may be gusty at
times. The wind may become variable for a bit this morning from
outflow and outflow is possible with any storms during the
period.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon