395
FXUS63 KDMX 282012
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
312 PM CDT Sun Apr 28 2024

.KEY MESSAGES...

* Another opportunity for a few strong storms today, mainly W/SW,
  but threat scaled back overall

* Briefly quiet Monday, then additional threats for some strong
  to severe storms return to the area Tuesday and possibly again
  Wednesday.

&&

.DISCUSSION...
Issued at 308 PM CDT Sun Apr 28 2024

Largely been a cloudy and more dreary day across the area thus far
with mostly cloudy skies and periodic showers streaming across the
area.

While the overall severe threat remains on the lower end of
the spectrum, there are a couple of items of note that may yet yield
a stronger storm or two and/or a weak tornado or two. RAP/HRRR and
CAMs in general, have struggled to pin down existing shower/storm
activity back west as well as the stratus deck evolution across the
state today, with all holding onto stratus into mid to late
afternoon before more rapid erosion. By about 18z, about the
southern two-thirds of Iowa had already seen a good amount of
erosion of the stratus deck, resulting in some filtered sun through
a relatively thin mid-level cloud deck. This may help develop more
favorable conditions for a stronger storm or two, including
potential for marginally supportive to supportive low level CAPE for
a landspout or weak tornado or two as the upper/surface lows move
through. However, existing shower activity ahead of the more
vigorous convection near surface front muddy the waters once again.
While HRRR has struggled some, it has had a consistent trend in
upping SBCAPE values along/ahead of the surface front with recent
runs suggesting potential for around/above 1500 J/kg versus <1000
J/kg in morning runs. Similar trends have been seen in the SPC RAP
mesoscale analysis in 0-3km CAPE and associated NST parameter space.
Deeper layer shear largely remains messy, marginal, and
predominantly unidirectional, limiting organization, large hail,
and damaging wind threats. At this point, the suggested main
threat may be a few weak tornadoes/landspouts associated with
any more vigorous convection along the surface front and nearer
the core of the low this afternoon and evening before the
lowest levels stabilize. This would point to west-central into
northwest Iowa this afternoon into the evening.

Monday will be on the quieter and side as the upper and surface lows
pull off to the northeast and westerly winds prevail. A few low
level instability driven showers may be seen north.

Temperatures quickly rebound Tuesday with southerly flow increasing
ahead of a shortwave trough and developing surface low. Expect highs
to soar back towards the upper 70s and lower 80s. Moisture does not
quite rebound in a similar fashion, but consistent signal for
SB/MUCAPE values to approach 2000 J/kg in a corridor over eastern
Nebraska into western Iowa by the afternoon and evening. Wind
profiles will be supportive for some organized convection with fair
curvature and effective shear values in excess of 40kts within
various guidance. Hail and damaging winds appear to be the primary
threats at this time, though a tornado would remain possible with
storms near/along the surface cold front. Into Wednesday, additional
chances for showers and storms present themselves as a warm front
quickly lifts back northward ahead of upper level shortwave and
developing surface low across the Front Range. Guidance this
afternoon has trended northward with the warm frontal placement by
the evening/overnight, so details remain in flux for both
strong/severe potential and any heavy rain threat. Activity looks to
be most robust with increasing LLJ activity Wednesday night.

Temperatures ease through the remainder of the week too with
highs back into the lower 60s return by Friday. Also rounding
out the week, discrepancy remains among flagship deterministic
models and ensemble suites with Euro solutions still favoring a
much more rapid upper trough passage while GFS/GEFS remain
slower and would prolong shower/storm opportunities to end the
week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1250 PM CDT Sun Apr 28 2024

Messy TAF period ongoing with smattering of VFR through IFR
conditions, generally from south to north across the TAF sites.
While some improvement remains likely this afternoon in/around
KMCW/KALO, where IFR currently prevails, degradation returns to
all sites as a couple possible waves of showers/thunder move
through this evening into overnight and expected spread of
stratus field behind frontal passage and as the upper/surface
low slide northeastward. Most prolonged IFR conditions around
KFOD/KMCW, with more likely MVFR KDSM/KALO/KOTM during latter
half of the period. Winds will be shifting from current
southerly to easterly winds to westerly by/after 12z.

&&

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

&&

$$

DISCUSSION...Curtis
AVIATION...Curtis