582
FXUS63 KDMX 281753
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1253 PM CDT Sun Apr 28 2024

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- More showers and storms today. A few may be strong to severe,
  but the threat looks highly conditional at this time.

- Storm chances return Tuesday along with the potential for
  strong to severe storms. Forecast trending wetter through the
  middle of the week.

&&

.DISCUSSION...
Issued at 252 AM CDT Sun Apr 28 2024

Shower and storm chances persist again today as an upper low
slowly moves toward the northern Plains. While the primary
moisture/instability axis will remain well south, some moisture
is pulled back westward toward the low and will help support
scattered to widespread precip. Hires guidance suggests the
greatest coverage occurs this afternoon into the early evening
hours. Severe threat today looks highly conditional as
instability looks limited due to precip/cloud cover. Deeper
convection that develops this afternoon over eastern
KS/northern MO could dribble into southern Iowa and pose a
threat for hail and gusty winds before weakening. Still cannot
rule out potential for a few weak tornadoes, although again
instability is a significant limiting factor. Ambient vorticity
increases as upper and sfc lows both pass near or west of the
forecast area. Sfc pressure field generally weakens and winds
try to veer from se to sw through the day. It will likely take
appreciable clearing and the development of more robust low
level instability to generate enough stretching to support a
quick spin up. Will need to monitor trends through the day, but
at this time the threat looks low.

Conditions dry out Monday as deep layer subsidence increases behind
the departing upper low. Moisture wrapping around the backside of
the system will promote broken to overcast cloud cover especially
early in the day, and will help hold highs in the upper 50s north to
mid 60s south.

Forecast activity picks right back up through the middle to latter
portions of the week as a series of shortwaves follow an upper
jet streak traversing the central Rockies into the local region.
Moisture returns northward on Tuesday ahead of an approaching
surface front. Precip chances ramp up by mid to late day as
showers and storms develop within the vicinity of the front.
SBCAPE builds to near 1000-2000 J/kg and effective shear ~40-50
kts, which would be sufficient to support more organized strong
to severe storm activity. This idea is backed by the CSU ML
output that paints lower end severe probs over the cwa. Front
stalls out just south of the area and is lifted back northward
on Wednesday as models have trended more progressive with
successive waves. The baroclinic zone serves as the general
focus for additional rounds of showers and storms by late
Wednesday through Thursday. While widespread heavy rain does not
likely, there is a signal in the models for a potential axis of
heavier QPF amounts, likely associated with training deeper
convection. Precip potential becomes more uncertain as a deeper
upper low pulls out of the central Rockies late in the week.
Euro camp is more progressive and considerably drier by the end
of the week, whereas the more sluggish GFS/GEFS solutions would
favor more precip chances into Friday.

&&

.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...Martin
AVIATION...Curtis