Des Moines, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

826
FXUS63 KDMX 141145
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
645 AM CDT Mon Apr 14 2025

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

.KEY MESSAGES...

- Elevated sustained winds today, especially in the north this
  morning and later this evening. Winds will generally remain
  under 30mph.

- Showers and storms likely (>60%) this afternoon and evening.
  Higher wind gusts upwards of 50mph possible with storms,
  although a severe gust cannot be ruled out.

- Severe storms possible (15% chance of severe) on Thursday.
  Hail is possible with other threats still in question, at this
  time.

&&

.DISCUSSION...
Issued at 404 AM CDT Mon Apr 14 2025

Objective analysis last night showed the axis of a shortwave trough
in Minnesota with wind maximums in the trough base on the approach
for today. The surface reflection of the front is well off to the
southeast with CAA peaking through the early morning. This is how
wind gusts remained overnight. An upper-level jet will deepen a
backside feature as it dives over the state this afternoon,
maximizing pressure gradients to around 30 ubar/km again late
this afternoon. A second boundary will be collocated. While the
temperature gradient being advected in won`t be strong, the
dryness of the low-level airmass remains so. Even the NAM, which
traditionally hangs on to PBL moisture longer, mixes us above
800mb by this afternoon. Even into the cloud layer, lapse rates
are dry adiabatic, with superadiabatic lapse rates appearing at
the surface. There are some question marks regarding peak
synoptic winds today as PBL winds average around 30kts, meaning
not a lot of acceleration for gusts will take place; however,
these winds being not far from the surface could help drive the
sustained winds higher and into Advisory-level. Confidence
wasn`t high enough to issue an Advisory overnight due to the
lull in CAA and subsidence in between the synoptic features
today, as well as the cloud cover potentially inhibiting some of
the momentum transfer to the surface. Trends will be monitored
with the passage of the next front later today.

The focus on winds will be more with the convection moving across
the area this afternoon. Have introduced likelies (>60%) across the
north this afternoon and evening, although it should be noted that
QPF will be low from high-based storms. MUCAPE values are
approaching 200 J/kg and is driven mostly by the aforementioned
steep lapse rates; this is enough to produce scattered storms. The
inverted-v soundings are leading to DCAPE values are actually coming
in higher, close to 300 J/kg. This paired with low-level theta-e
differences between -2 and -5K imply cold pool acceleration due to
dry air entrainment, translating to wind gust potential. Models such
as the HRRR and RRFS support this outcome as they have 50kt gusts
collocated with simulated storms. Confidence in any one storm having
severe winds is around 10%, but at least anticipate strong gusts
upwards of 50 mph to accompany showers and storms.

The backside northwest flow continues to influence the weather on
Tuesday, mostly in the form of lessening breezes and cooler
temperatures around 60 degrees. The pattern shifts back to southerly
for Wednesday, but this time with more moisture at play. An MCS in
northern MO will kick things off Wednesday evening and precipitation
will spread into Iowa as the LLJ is pulled northward with the
deepening low pressure to our west. A seasonably strong EML will
encroach behind the advection wing showers and storms, introducing
an unstable airmass for activity later in the day Thursday where
convection will fire along the northern gradient. Supporting this is
a wave ejecting off a parent upper low in the Four Corners region.
Deep layer shear over 50kts is abundant across the state, but some
questions remain in how much capping could inhibit surface-based
potential. At the very least, the potential is there for severe
hail. The shortwave is picked up by the upper low to our north,
giving the system a more west-to-east trajectory by late Thursday.
The trailing cold front will setup close to the state late Friday,
bringing some chance for more convection at least across the
southeast. The parent trough then comes more into play at the end of
the weekend as it makes its way into the region. The Euro`s faster
open wave solution appears to be an outlier compared to the rest of
the ensemble suites, which favor a slower and deeper solution. That
system will be worth watching for severe weather potential somewhere
in the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 640 AM CDT Mon Apr 14 2025

MVFR to blanket northern sites for a brief window this morning,
but lift to MVFR before 18z. Main changes is adjustments to
PROB30 groups this afternoon with a gust group introduced to
account for increased wind gusts with showers and storms. Have
removed thunder from KDSM as confidence is lower in storms
reaching site.

&&

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

&&

$$

DISCUSSION...Jimenez
AVIATION...Jimenez