297
FXUS63 KDMX 271847
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
147 PM CDT Sat Apr 27 2024

.KEY MESSAGES...

* Threat for strong to severe storms today, primarily south of
  I-80 this afternoon and evening. Primary threats for
  large/damaging hail and damaging straight line winds. A
  tornado or two cannot be ruled out.

* Lingering hydrologic threat with potential for multiple rounds of
  storms over same areas of southern Iowa possibly yielding 3"+ of
  rainfall. Flood Watch has been issued.

* Another round of strong to severe storms possible Sunday.
  Primarily over southern/southeast Iowa, with hail and winds
  leading threats.

* Multiple opportunities for showers/storms next week as a
  handful of shortwaves progress through the large scale flow.

&&

.DISCUSSION...
Issued at 145 PM CDT Sat Apr 27 2024

A welcome quiet start to the day after the events of yesterday
afternoon and evening. Multiple survey teams from the office are out
in the field assessing damage and tornado paths.

For today, another round of strong to severe storms remains expected
over roughly the southern half of the area, namely in/around a
surface warm front draped across the state. Compared to yesterday,
trends have pushed the surface front, and by virtue the "juiciest"
air, southward a bit. Aside from that, much of the advertised
environment remains with moderate lapse rates and supportive
deep layer shear for organization. SBCAPE values remain
forecast into the 2000- 3000+ J/kg range with dew points into
the mid 60s near/south of the front. Low level wind fields
certainly are relaxed comparatively to yesterday, though
hodographs still have suggestions of a tornado or two possible
with good low level curvature and streamwiseness to go along
with supportive low level CAPE, even as streamwise vorticity
values are on the lower end/more marginal. That said, large hail
and damaging straight line winds are primary risks this
afternoon and evening as activity. Morning model and CAM runs
have come into much better agreement as to the anticipated
progression of convection this evening, favoring upscale growth
out of NE Kansas and depicting a bowing complex of storms riding
along the frontal boundary and instability gradients. This
would thusly suggest that damaging winds may ultimately be the
primary threat, with hail most likely early in the event with
any initial discrete/semi- discrete cells. As additional lift
overspreads the area, there remains the potential for additional
storms, but that scenario appears more likely into areas of
northern Missouri in/along outflow boundaries/southward shunted
boundary. Regardless, wherever that scenario sets up will have
an additional hydrologic/flash flooding threat. With that in
mind, have hoisted a Flood Watch across the southern two tiers
of the state.

Into Sunday, some uncertainty remains with activity this
afternoon/evening playing a role, but there does remain another
potential window for strong to severe storms across southern Iowa as
an upper wave and associated surface low track northeastward across
the area. Cannot rule out any mode of severe weather, with tornado
potential near the low as it tracks across NW Iowa, as well as hail
and winds with any strong or organized convection within warmer/more
unstable airmasses.

Initially quiet start to the week next week will be disrupted by
multiple shortwave troughs moving through the larger flow with
periodic opportunities for showers and storms beginning as early as
Tuesday afternoon and evening.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1235 PM CDT Sat Apr 27 2024

MVFR to VFR conditions will initially prevail across all sites
this afternoon before anticipated convection and approach of
next upper wave and surface low are expected to degrade
conditions back towards IFR. Best opportunity for TSRA/SHRA will
be in/around KDSM/KOTM around/after 21z, then expanding
northward to at least encroach all TAF sites with SHRA/VCSH
mentions. Ceilings should fall towards 1kft, but have held off
on the most pessimistic of guidance for this issuance.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Sunday morning for IAZ070-081>086-092>097.

&&

$$

DISCUSSION...Curtis
AVIATION...Curtis