988
FXUS63 KDMX 191142
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
642 AM CDT Sat Apr 19 2025

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Widespread 90+ percent chance of measurable rainfall Sunday
  and Sunday evening. At least moderate rainfall amounts likely
  (60+%).

- Active pattern continues next week with several periods of
  precipitation possible

- Cool Sunday with the precipitation, but turning warmer with
  above normal temps Tue through the end of next week

&&

.DISCUSSION...
Issued at 400 AM CDT Sat Apr 19 2025

Dry conditions and seasonal temperatures can be expected today,
however a noted MS Valley short wave on Easter will bring
widespread rainfall to Iowa and increased potential for severe
weather and flooding for states to the south. The pattern will
remain active next week as well with quasi-zonal flow bringing
systems through every few days and temperatures at or just above
normal. The feature of note this morning is a somewhat phased
long wave trough from AZ into the northern Plains with primary
PV anomalies in its based and across the Dakotas. This trough
will separate this weekend however with the Dakotas PV anomaly
passing to our north with little fanfare, and out attention
looking toward the progression of the short wave ejecting out of
the trough base. A considerable moisture fetch in the strong
southwest flow aloft and varied layers of frontogenesis continue
to fuel convection along the sharp, deep baroclinic zone from
the Plains into the Mid MS Valley today. The AZ PV anomaly will
eject into the Plains early tomorrow however lifting the
aforementioned baroclinic zone and its associated theta-e
advection and frontogenesis into IA Sunday. This will spread
widespread rains south to north across the state with strong,
phased kinematic and thermodynamic forcing, and then deformation
and some evidence of a trowal lingering precipitation into the
night north.

Guidance does depict differences on the NW-SE placement of the
max precip axis and extension of the warm/instability sector,
with the NMMB core NAM and NamNest more aggressive in that
regard versus other models. Most of the other deterministic,
ensemble, and GEFS based AI/ML guidance favor the farther east
surface low progression mainly relegating any severe weather
potential just to our south and east. However, even though it
seems to be an outlier at the moment, the Nam/NamNest solutions
would increase our surface based severe weather and tornado
potential with coincident elevated 0-3km CAPEs and 0-1km SRH
values in far southeast sections, and while they are FV3 based
on possibly overdone, the last few hours of the 00z HREF also
note a few updraft helicity tracks approaching our far southeast
counties, which would be possible considering the strength of
the effective shear (50+ knots at times). Thus model trends
driving the tight gradient in the small section of SPC Day 2
outlook southeast is something to monitor regarding severe
weather into tomorrow.

Confidence is higher in widespread appreciable rains. 00z GEFS
and EPS peak 24hr 1" rainfall probabilities Sunday into Sunday
night are 60+% for both ensembles across much of the forecast
area, and as high as 80% in the EPS. Current soil conditions and
river capacity point toward any river flooding potential being
still minimal for the time being as RFC contingency forecasts
suggest within bank rises, even if 95% percentile ensemble QPF
comes to fruition. The HEFS 10 day GEFS based 10% exceedance
probabilities also suggest within bank rises at nearly all
forecast points. Most of those are in the greater Cedar River
basin (including Shell Rock and Winnebago), and that would
include precip beyond the weekend to do that. With plenty of
clouds and precip anticipated Sunday and Sunday night, have also
shrunk the diurnal temp range somewhat by lowering/raising NBM
highs/lows respectively.

This compact short wave should be lifting into the Great Lakes
by late Monday giving Iowa a brief break from precipitation
chances. However the pattern will remain active in the quasi-
zonal flow with several systems bringing an extended period of
precipitation chances into the forecast from late Monday night
through the end of the current forecast period (Friday). This is
more due to timing uncertainties that rain chances every day
however. This lower amplitude flow will also keep mild, above
normal temps in the forecast with highs 70F+ in manly locations
Tue-Thu.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 641 AM CDT Sat Apr 19 2025

Confidence is fairly high that VFR conditions will persist
through the period with mainly high cloudiness. Winds should
change little today remaining from the northwest, and then
decrease somewhat and becoming east-northeast by tonight.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Small