Des Moines, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

154
FXUS63 KDMX 111120
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
620 AM CDT Wed Jun 11 2025

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

.KEY MESSAGES...

- Quiet today and tonight

- Thunderstorm chances return tomorrow, mainly in northern Iowa
  with isolated storms possible farther south. Wind, hail, and
  locally heavy rainfall are the main concerns.

- Additional shower and thunderstorm chances into Thursday and
  Friday, with more limited severe weather chances.

&&

.UPDATE...
Issued at 207 AM CDT Wed Jun 11 2025

The short-term forecast through tonight has not changed
appreciably since the yesterday afternoon discussion, but the
Thursday daytime period has come into somewhat better focus.
Around sunrise Thursday convection should be ongoing near/just
north of the IA/MN border as discussed below, while another slug
of moisture coincident with a weak 500 mb low drifts north
northeastward across Missouri. A surface high pressure ridge
will squeeze in between these two systems right across most of
Iowa, and should provide a relatively dry and warm day for much
of our service area, excepting the far north. Accordingly, have
bumped temperatures up by a few degrees and lowered sky cover a
bit. Also kept the southern half of the area dry through the
morning, but maintained low (20-30%) POPs there the afternoon as
some CAMs are depicting isolated convection coincident with
peak heating and the approach of the weak Missouri low scraping
by our southeastern corner. Shear fields continue to look
fairly weak for the most part on Thursday, but more storms
developing near the eastern South Dakota/Nebraska border will
drift into our northwestern counties late Thursday night and
could pose a marginal wind threat given the degree of
instability present. This is well covered by the SPC Day 2
outlook.

&&

.DISCUSSION...
Issued at 249 PM CDT Tue Jun 10 2025

The upper level pattern becomes more zonal overnight tonight into
Tuesday as the ridge to our west breaks down ahead of multiple
shortwaves/troughing developing to the north and west. At the same
time, a closed upper low will develop over the southern CONUS. Warm,
moist air streaming north ahead of the closed low to the south will
meet the troughing to the north, generating a warm/stationary front
draped from west to east and roughly between Highway 20 and
Highway 18. This front will be the focal point for showers and
thunderstorms as mid- and upper- level forcing passes along the
boundary through Wednesday afternoon and evening.

There will be no lack of moisture transport on Wednesday as the gulf
moisture from the south phases with a fairly healthy pacific
moisture stream, pushing PWAT values to around 1.5-1.6", with
locally higher values nearing 2". Normal PWAT values for this time
of the year are right around 1", so not significantly higher than
normal but around 125% to 150% of normal, suggesting efficient
rainfall is possible. In addition to the moisture, temperatures will
warm into the upper 80s to low 90s tomorrow, leading to a very
unstable airmass along and south of the boundary. MUCAPE values of
2500 to 3000 J/kg will be common, and model soundings suggest this
being primarily surface based south of the boundary through the
afternoon. Any displaced parcels will allow for rigorous updrafts
capable of producing hail and heavy rainfall. Similarly, the warm
temperatures with dewpoints in the 60s to near 70 suggest a well
mixed boundary layer in the afternoon tomorrow. Soundings show the
typical inverted-v sounding with downdraft CAPE values over 1000
J/kg. These suggest the potential for strong downdraft winds as
heavy rain falls and evaporates, as well as efficient cold pool
production which could lead to additional wind concerns as they
propagate outward.

While the thermodynamic portfolio is robust tomorrow, relatively
weak flow will keep 0-6 km shear values below 30 kts in the warm
sector, preventing balance between the cold pool and environment and
limiting widespread organized convection. The environment will still
be conducive for severe hail and strong winds as updrafts initially
go up, but the lack of shear will limit the longevity of severe
storms and the residence time needed for larger hail stone
production. Wind shear does improve along and north of the boundary,
making this area slightly more favorable for more organized
convection, especially if storms can tap into the vorticity along
the surface boundary. The mean wind will be oriented along the
boundary, although storms may tend to drift more southeasterly as
additional updraft development occurs along outflow from the initial
convection.

The severe weather chances will be most likely in the late afternoon
and evening, with diminishing likelihood for severe impacts
overnight, especially with a meager low level jet. There will still
be a steady stream of moisture through the area with showers and
storms continuing along and north of the Iowa/Minnesota border
overnight. This should give some relief from heavy rainfall along
the surface front in northern Iowa, but will want to watch how the
front evolves and how far south it progresses in the evening, as
this could bring overnight precipitation chances further south as
well, which would further exacerbate any heavy rain impacts. For
more information on potential impacts due to heavy rain, see
the hydro discussion below.

While Wednesday evening certainly has the best chances for severe
weather, shower and thunderstorm chances persist into Thursday and
Friday as the upper low continues to pull moisture up from the
south and another lobe of forcing passes through the zonal flow
to our north. The warm front will drift back north with the
second wave, taking the better wind fields with it and leaving
an unstable but weakly forced environment in it`s wake. This
will lead to more isolated severe weather chances in northwest
Iowa, with more widespread showers and sub-severe storms.
Recent guidance now has the better rainfall amounts rooted to
the better forcing to our north in Minnesota, with more marginal
amounts overhead. That said, Thursdays storms will be somewhat
dependent on how things evolve on Wednesday, so will want to
keep an eye on model and observational trends through tomorrow,
as a southerly trend could cause more heavy rainfall to fall in
the same places they occur on Wednesday.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 620 AM CDT Wed Jun 11 2025

VFR conditions are forecast this morning and early afternoon.
Thunderstorms will then develop after around 21Z and into
tonight, with the northern terminals (MCW/FOD/ALO) most likely
to be impacted. Will include targeted TEMPO/PROB30 groups for
TSRA at those terminals. In the last 6-10 hours of the 12Z TAFs
confidence in SHRA/TSRA timing and placement decreases so have
left the TAF dry except at MCW where probability of lingering
rain is higher. Even aside from SHRA/TSRA, low clouds should
develop early Thursday morning and may result in prevailing MVFR
ceilings.

&&

.HYDROLOGY...
Issued at 249 PM CDT Tue Jun 10 2025

Heavy rainfall over the next few days may lead to flooding concerns
including flash flooding, urban flooding and river flooding.
Location, intensity, duration and amount of QPF will be key in the
ultimate flood risk. With the initial active weather setup
potentially affecting subsequent active weather setups, there is more
uncertainty than normal regarding overall QPF.

Latest model/NBM QPF and National Water Model (NWM) output suggests
the most likely scenario would be some isolated flash flooding /
scattered ponding of water especially in urban areas in conjunction
with the initial active weather late Wednesday into Wednesday night
across roughly the northern half of the CWA especially north of U.S.
Highway 20. Location and evolution of subsequent active weather and
QPF is more uncertain, however present thinking is that the rainfall
would lead to additional isolated flash flooding / scattered ponding
especially in urban areas early Thursday morning onward. In terms of
river flooding, scattered significant within-bank rises are
expected. Some locations are expected to approach or exceed the the
bankfull to action stage range. Isolated minor river flooding is
possible as well. The timing of the river responses would be mainly
from Thursday afternoon onward into the weekend.

Since the above information is based on conditions and QPF as of the
forecast discussion time, any deviations in QPF going forward may
affect the anticipated flooding as well. This event will bear
watching especially from a hydrologic perspective over the next few
days.

&&


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

&&

$$

UPDATE...Lee
DISCUSSION...Dodson
AVIATION...Lee
Hydrology...Zogg