212
FXUS63 KDMX 261951
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
251 PM CDT Sat Apr 26 2025

.KEY MESSAGES...

- Although somewhat conditional, a Moderate Risk (4/5) of severe
  weather is in place for central and northeast Iowa Monday and
  Monday night with an Enhanced Risk (3/5) elsewhere.

- Active weather persists into at least midweek even outside
  this severe weather potential with intermittent chances for
  showers and storms until drier weather by the end of next week

- Warmer and more humid Monday, otherwise seasonal temperatures
  through the period

&&

.DISCUSSION...
Issued at 251 PM CDT Sat Apr 26 2025

It should be a pleasant evening tonight with upper level
ridging overhead, but all eyes will turn to the approaching
Rockies closed upper low as short wave ejects from its base late
Sunday and reaches the MO Valley Monday. Higher based
warm/moist advection was already occurring through the Plains
with weak elevated convection on the leading edge over
northeastern NE. This should continue advancing north and east
tonight, and although the primary theta-e advection push should
remain to our north, there should be sufficient thermodynamic
support this far south for showers to transit northern IA
tonight into Sunday morning. Little if any thunder is
anticipated with minimal instability in place as of yet.

After a break by later Sunday, one last surge of warm/moist
advection aloft is expected to generate another round of
elevated convection, mainly north, and get us more fully into
the warm sector Monday. A few strong to severe storms with hail
are possible as four figure MUCAPEs rooted around 1.5km return
and effective shear reaches +/- 40kts. This convection is
expected to linger into Monday morning to some degree, with
questions on how this affects severe weather trends into the
afternoon and evening.

The instability and shear parameter space will become
noteworthy by Monday afternoon with highs in the 80s and
dewpoints in the 60s. Both the GFS and EC deterministic runs
note 2000-2,500 J/kg MLCAPEs but with varied degrees of CINH,
and strong 50 kt 0-6km deep shear. With this parameter space in
place, the SPC Day 3 outlook notes widespread Enhanced (3/5)
and Moderate Risk (4/5) areas across the forecast area with
similar corroborating depictions in various GEFS and EPS based
AI/ML output. The signal in the deterministic and far ranges of high
res models is less aggressive however. Recent FV3 based cSHield
and RRFS CAM output depicts the stronger 2-5km updraft helicity
coverage to our north with NCAR MPAS based CAM ensemble output
showing a similar signal. This suggests either a lack of a
sufficient forcing mechanism this far south, and/or CINH
struggles to be overcome. This lingering precip potential and
associated low level moisture, and resultant low level mixing,
are still in question with uncertainties on how long or if the
elevated mixed layer/inversion signature in soundings devolves
into better mixing and MLCINH erosion. Mass convergence along
the dry line isnt noteworthy, and with the triple point and
associated synoptic scale lift retreating northward across MN
this would be a concern. If something does trigger along the
dryline, GFS soundings note some tornadic potential with 50-100
J/kg 0-3km CAPEs and sufficient but not alarming 500m
streamwise vorticity and percentage of total vorticity. This
varied parameter salad all suggests a conditional threat with
somewhat reduced confidence, and an insufficient signal to alter
the outlook and expectations for the time being. In simpler
terms, if robust convection develops all modes of severe weather
(large hail, damaging wind, tornadoes) are all possible, hence
the high end outlook, but where this develops (north/south
extent) remains in question. Confidence should increase by this
time tomorrow when more CAM guidance encompasses the event.

Any convection that develops should exit to the east overnight with
both temperatures and humidities dropping back to more seasonal
levels, and at least a minor break from much in the way of
precipitation through at least Tuesday. What`s left of our
early week long wave trough in the southern stream, and a bit
more robust northern stream wave, will weakly phase in the
central CONUS midweek reintroducing a period with chances for
showers and a few storms until Thursday night or Friday when
drier, less active northwest flow takes hold followed by upper
ridging into the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1249 PM CDT Sat Apr 26 2025

VFR conditions with nothing beyond increasing mid clouds can be
expected this evening. Although likely remaining VFR, ceilings
do lower somewhat as the potential for showers increases north
overnight and into Saturday morning. Eventually low level
moisture increases sufficiently that at least MVFR ceilings may
develop central and west by late Sunday morning.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Small