455
FXUS63 KDMX 060502
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1202 AM CDT Mon May 6 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

-Warmer Monday as southeast winds increase with near advisory
 winds across the northwest.

-Strong to severe thunderstorms Monday evening into early
 Tuesday. Damaging wind and perhaps few tornadoes are the
 primary hazards. Pockets of locally heavy rain also possible.

-Another round of showers and a few storms on Wednesday with
 localized heavy rain possible, mainly north.

&&

.DISCUSSION...
Issued at 245 PM CDT Sun May 5 2024

A rather fine afternoon across Iowa with filtered sunshine along
with light winds as surface ridge slides east across the state.
Upper low south of the state has some showers approaching southeast
Iowa but this is expected to remain south of the forecast area the
rest of this afternoon into the evening.  Otherwise, quiet
conditions persist into tonight as warm advection intensifies ahead
of a strong shortwave passing through the Rockies.  This continues
into Monday with deep southerly flow and moisture returning through
the day. Surface pressure gradient tightens considerably with rapid
lee side cyclogenesis and southeast winds intensify through the
day. This is likely to produce near advisory winds in the
northwest by later in the afternoon into the evening. Will not
issue an advisory at this time but continue to monitor for
potential headline.

The moisture return is expected to be in a fairly narrow corridor in
advance of the surface boundary with the instability axis reflecting
this in a relatively narrow width across Iowa by early Monday
evening. The highest instability is in the south and west up to
around 1500 J/KG along with strong bulk shear in excess of 40kts.
CAMS are all fairly consistent with the development of a linear
system in eastern Nebraska during the afternoon with a QLCS passing
into Iowa during the evening hours.  Instability initially should be
sufficient for stable evolution of the system. However as the system
progresses eastward, the cold pool is likely to eventually win out
as the instability wanes.  This makes the west and south the best
threat for severe wind gusts and a few tornadoes as SRH values of
200+ m2/s2 will exists ahead of the line.  Eventually, the cold pool
will overtake the updrafts with the line weakening farther east.
Rainfall is also expected to be quick hitting and relatively heavy
as PWATs increase to 1-1.5" ahead of the line.  While not expected
widespread flash flood issues, the heavy rain may lead to renewed
river flooding on a few of the basins within central Iowa.

Subsidence passes over the state for much of Tuesday with relatively
low chances of showers although some showers in the north are
possible along a residual boundary.  A better chance for additional
showers and a few storms arrives on Wednesday as another shortwave
approaches the state.  An inverted trof acts as a focus for the
activity which increases by the afternoon.  Both GFS and ECMWF
indicate the northern half of Iowa for decent QPF which would only
add to any runoff and potential to also induce additional rises or
potential flooding on area rivers.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1158 PM CDT Sun May 5 2024

MVFR stratus to move into sites from the southwest, impacting
KFOD, KDSM, and KOTM. Cloud bases will rise to VFR, but remain
BKN through the afternoon hours. Gusty southeast winds will have
gusts up to 30kts after 18z, increasing after 00z ahead of
showers and thunderstorms. Cigs are expected to sink to MVFR and
IFR with these storms. Have added thunder mention to KFOD and
KDSM to reflect initial arrival time.

&&

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

&&

$$

DISCUSSION...Cogil
AVIATION...Jimenez