245
FXUS63 KDMX 100415
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1115 PM CDT Wed Jul 9 2025

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- First round of storms arrives late tonight into Thursday
  morning. Heavy rain is the primary concern. Localized amounts
  exceeding 3 inches possible (40% confidence).

- Severe weather enters the picture tomorrow with wind being the
  primary threat. A tornado or two cannot be ruled out.

- Heaviest rainfall expected Thursday night with more severe
  weather potential returning Friday afternoon.

&&

.DISCUSSION...
Issued at 249 PM CDT Wed Jul 9 2025

The peak of the H850 ridge was centered over central into southern
Iowa this morning with a moisture plume of 12C+ over Nebraska. The
main moisture transport axis is noticeable from the festering
convection in eastern Nebraska. A secondary moisture axis, albeit
high-based and shallow, will be the catalyst for a few scattered
showers and storms this afternoon. Updrafts will be narrow and short-
lived along this boundary. Highs will top out just below 90 degrees,
warmest across the south.

The main sequence of an extended string of active weather begins in
the west tonight as the aforementioned moisture plume is advected in
along the LLJ. The orientation of the LLJ won`t change much at all
until a front arrives late Friday night. We`ll be set up for heavy
rainfall. PWATs around the 2 inch mark along with warm cloud depths
exceeding 3500m make for efficient rainfall production and less
ice introduction. The LLJ will nearly match the vector of the
mean wind, orienting Corfidi vectors to the south, albeit low in
magnitude. This means that any MCS that forms will naturally
propagate southward and into the instability axis, helping to
maintain its intensity. Storm motions will be slow, leading to
localized high rainfall amounts. Overall, the N-S QPF swath in
most guidance makes sense spatially with amounts exceeding an
inch in this max region commonplace. Given the rainfall
benefactors mentioned above, can`t rule out localized amounts
reaching or exceeding 3 inches. Strong cold pools from the
moisture content will allow for gusty winds with the main MCS
clusters, but with this threat sparse and fleeting due to weak
effective shear (<20 kts) at this point in time. An EML will
begin to build in along the southwest flow and will focus the
moisture away from the low-levels and steepen lapse rates during
the day. Meanwhile, a PV anomaly from northern CA will flatten
the upper- level ridge, opening Iowa to a series of synoptic
shortwaves from the Intermountain West. Mesoscale features will
also be in play due to any remnant outflow/debris from overnight
activity. Much of the 12z CAM guidance produces an MCV in
central Iowa which would be a local enhancement to lift--and
available vorticity for tornadogenesis. While these smaller
scale features will not be accurately known until presently
analyzed, they boost the potential for continued precipitation
through Thursday. Both on the CAPE gradient and potentially at
peak heating above the EML where moisture is preserved. Gusty
winds will again be possible with storms in the afternoon, but
the primary hazard will again be heavy rain.

The primary shortwave arrives Thursday night along with another push
of 2 inch PWATs and favorable warm cloud depths. The
orientation of LLJ again lurks over western and central Iowa,
this time with a stronger moisture transport magnitude. This
time period will contain some of the heaviest rainfall of the
week, aided even more by a stalled warm front somewhere across
the state. Another widespread 1-2"+ and locally higher amounts
will be along this front. The triple point then approaches the
weakly- capped environment on Friday. Deep-layer shear
parameters along the warm front favor severe weather, although
some of the model output could be bloated by simulated cold
pools. Surace-based parameters at the mercy of mesoscale debris
in the warm sector. Trends will be monitored. The cold front
will then be dragged across the state Friday night into early
Saturday, bringing more rain, this time appearing more
progressive due to it being a cold front. More synoptic energy
arrives by Sunday, but the moisture content at this time appears
questionable.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1109 PM CDT Wed Jul 9 2025

VFR conditions with light winds still prevail early this
overnight period, though clouds are continuing to increase west
to east with with storms moving towards the Missouri River.
These storms will continue to push eastward through the
overnight period reaching KFOD first, by around 09Z and then
other sites thereafter, but confidence is higher in northern
sites (KMCW) and KALO, though thunder more questionable by the
time storms reach KALO. Similarly, some questions remain in
southward extent, but KDSM likely to see at least rain if not
storms too, with KOTM generally more on the southern edge. Have
updated to prevailing or tempo groups based on latest guidance
but adjustments may still be needed as storms move into the
area. Heavy rain may decrease visibilities more than currently
indicated while stronger storms, especially west near KFOD,
could have some gusty winds. Additional shower/storms are
possible Thursday afternoon into evening with greater confidence
late Thursday night into Friday morning, but confidence in
timing/impacts too low to include explicit mentions at this
time.


&&

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

&&

$$

DISCUSSION...Jimenez
AVIATION...05