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596
FXUS63 KDMX 181937
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
237 PM CDT Sat May 18 2024

.KEY MESSAGES...

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- Progressive pattern to spark increasingly active thunderstorm
  pattern through the first half of next week.

- Storms may become strong to severe along with heavy rain
  throughout the active period, but especially on Tuesday.

- Temps to be overall seasonal, with Wednesday looking the
  coolest (65-70) through the period.
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&&

.DISCUSSION...
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Issued at 237 PM CDT Sat May 18 2024

Well-defined shortwave trough evident on satellite pix spinning
west of Winnipeg early this afternoon; with the attendant
surface front extending south thru Minnesota and just about 1/3
of Iowa. Air mass cools 10-15F in its wake, with upper 60s
approaching the MO River. Temps ahead of the front have climbed
into the mid-upper 80s; with dew points in the low 60s. Decent
cap in place per forecast soundings; which is supported by
limited cu at this point. Latest CAMs suggest that this
inhibition will erode sufficiently tapping into 1500+ j/kg
MLCAPE to get a few storms along front and generally south and
east of DSM between 21-01z. Lack of sufficient deep layer shear
will be limiting factor for convective organization. However,
with DCAPEs in excess of 1000 j/kg, winds would be the primary
thunderstorm hazard. Any storms that are able to develop will
fall apart quickly by sunset.

Front makes it into N MO for all of about 12 hours before
lifting back north Sunday morning. Along the northward moving
warm-front, isolated elevated convection will be moving thru
Sunday morning into early afternoon. While severe threat with
this activity appears minimal, it may briefly interrupt any
outdoor activities. This activity shifts east and weakens thru
the day. Meanwhile, thunderstorm round #2 will be in the process
of developing across the plains as the next shortwave
translates east, arriving into central Iowa Sunday evening.
Initially discrete across the plains, these thunderstorms will
congeal into a thunderstorm complex moving through Sunday night.
Although greatest severe potential is with initial storms, deep
layer shear remains 30-35 knots as thunderstorm complex moves
through, which may be enough for severe potential lingering
Sunday especially west of I-35. Sunday night will also be the
beginning of a multi-day excessive rain threat, with deep warm
cloud depths and PWATs of 1.5-2".

That shortwave departs early Monday. Any gap will be short-lived
as the atmosphere once again destabilizes during afternoon with
SBCAPEs progd to be 2000-2500 j/kg with deep layer shear again
of 30-40 knots. More heavy rain and severe storms will be
possible Monday afternoon & evening.

Greatest severe potential of the period comes on Tuesday
afternoon as the next shortwave deepens as it emerges from the
plains lifting thru Iowa and Minnesota during peak heating. As
such, instabilities will be maximized at 3000 j/kg of progd
SBCAPE along with deep layer shear in excess of 50 knots in
areas. This is captured well in SPCs day 4 outlook.

Temperatures will briefly cool on Wednesday, before rebounding
by week`s end, with more thunderstorm chances returning.
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&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1234 PM CDT Sat May 18 2024

Main change with this TAF issuance was the addition of VCTS at
KOTM 23-01Z associated with frontal passage. Otherwise, VFR
conditions anticipated at area terminals through the period.
Weak morning showers/storms tomorrow morning may linger across
across areas mainly south of I-80 Sunday morning...so did add an
early mention to KDMX after 17z.

&&

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

&&

$$

DISCUSSION...Hahn
AVIATION...Hahn