Waukee, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

418
FXUS63 KDMX 251738
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1238 PM CDT Fri Jul 25 2025

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Early morning fog across southwest portions of Iowa.

- Showers and thunderstorms across southern Iowa overnight,
  expanding central and east through Saturday morning. Pockets
  of heavy rain possible, especially far southern Iowa.

- Turning hot Sunday into early next week. Heat index of 100-110
  expected.

&&

.UPDATE...
Issued at 303 AM CDT Fri Jul 25 2025

Primary focus with this update cycle has been on convective
trends for tonight into Saturday and the heat building later
this weekend. But first things first this morning, patchy and
occasionally dense fog has developed across southwest Iowa early
this morning thanks to plenty of available moisture and winds
that have gone calm overnight. Early visibility reductions were
brief and transient at most sites, but has become more
pervasive this morning, necessitating a fog advisory. This will
last through sunrise, with quick improvement expected by 7 am.

After the morning fog dissipates our attention turns to convective
trends for later this evening and overnight through Saturday
morning. The most notable change in the latest model guidance is
the continued southerly shift of the axis of heaviest
precipitation, which now appears to line up south of the Iowa
border. Even so, as a wave passes across the existing boundary
over northern Missouri expect showers and thunderstorms to lift
into the area. While showers and a few thunderstorms will
likely percolate south of the Iowa border through the afternoon,
expansion into southern Iowa become more likely into this
evening with this wave and as the LLJ kicks in overnight. The
LLJ orientation is further into Iowa Friday night compared to
the current early morning, increasing the likelihood for more
robust activity. Shear across the area is quite meager which
will mitigate much of the severe risk, however heavy rain
remains a concern far south. While the axis of heaviest rain has
shifted south in most recent model runs, the 00z HREF still
paints much of southern Iowa with 2-3+ inches of rain with
pockets of 6+ possible (though the potential for those higher
amounts, again, is shifting south into Missouri). We continue to
see PWATS of 2+" along with deep warm cloud layers and
continued moisture transport into the area, once again making
for what will likely be efficient rain producers. With much of
the tonight`s overnight rain staying out of Iowa, the area has
largely been spared from back to back nights of heavy rain which
will help ease some hydro concerns. Still, with windows for
high rain rates and heavier pockets of rain, some area could
still see hydro issues overnight tonight and into Saturday
morning.

As this system scoots east on Saturday high pressure builds
across the area and with it comes the heat. Temperatures return
to the 90s Sunday into Monday with dewpoints remaining quite
high thanks to linger moisture and peak corn sweat season. That
will combine to send the heat index (or what it "feels like")
into the 100- 110 range for a large portion of the area on
Sunday and Monday. Heat headlines are quite likely.

&&

.DISCUSSION...
Issued at 240 PM CDT Thu Jul 24 2025

Rainfall has all but subsided over the area early this afternoon,
although radar does indicate a few weak returns near the
Iowa/Missouri border. This area will be where additional
thunderstorm development is anticipated this afternoon and evening
as another weak wave orbits the broad upper ridging. This will bring
a stream of warm, moist south southwesterly flow upgliding over the
boundary in place over central to northern Missouri. As has been the
theme this year, these storms will exist in a moisture rich
environment, with an axis of 2.2 to 2.4 inch PWATs just to the south
of the state. This, in conjunction with mean storm motions roughly
parallel to the boundary, will bring prolonged heavy rainfall
starting late this afternoon into the evening. Model QPF shows
anywhere from 2 to 4 inches within the heaviest band and some
isolated pockets over 4 inches. placement of this heavier
rainfall axis will be primarily south of the state and into
Missouri, mainly impacting those in the far southern Iowa
counties along the Iowa/Missouri border. That said, models have
been less than reliable this year, so not ruling out a
regression to yesterday`s runs which had storms (and coincident
rainfall) slightly farther north into southern Iowa, especially
as the low level jet ramps up overnight. Fortunately, southern
Iowa didn`t see near the rainfall amounts from last nights
precipitation as those farther north, so this should help
mitigate hydrological impacts for at least tonight. Likewise,
the better instability axis also seems to be displaced to the
south with minimal deep layer shear in place. Therefore, the
overall severe threat appears low.

Any showers and thunderstorms still lingering tomorrow morning
should generally diminish as the LLJ diminishes into the morning
hours. However, another, slightly more prominent wave of energy will
lift northeastward into the state again tomorrow, pushing the
boundary farther north into the state. This will bring yet another
chance for both heavy rainfall and stronger storms into the forecast
area tomorrow afternoon through the overnight. From a moisture
perspective, the environment tomorrow night won`t be too
dissimilar from today/tonight, but may include a slightly
stronger moisture transport component. The key difference
between tonight and tomorrow lies with the 25 to 35 kt LLJ nosed
up into southern to south central Iowa, as opposed to a more
west to east orientation tonight. This will provide a steady
stream of moisture and forcing through the night, prolonging the
amount of time rain is falling, especially in far southern
Iowa. The main concern will be a cumulative effect of heavy rain
tonight which would be exacerbated by more heavy rainfall
tomorrow in areas where rain fell on both nights. Southern Iowa
would be the area most likely to see heavy rain both nights, but
is also the area with the driest soils relative to the rest of
the state. This should help raise the bar for flash flooding and
river flooding, but two nights of 2 to 4+ inch rainfall would
still likely create some issues, especially in areas that
achieve the higher end of that range on either night. Model
guidance is showing a signal for isolated pockets of 6 to 8
inches of total rainfall by Saturday morning, mostly over
northern Missouri and far southern Iowa.

Of similar concern, tomorrow`s rainfall will reach farther north
into the state than tonight`s, which poses a risk to areas that are
already experiencing elevated river levels from last night`s
rainfall in northern Iowa. As implied earlier, models have been
following a southerly trend, which is in the right direction to
avoid worsening conditions across the north, but still something to
keep an eye on. This is especially true in areas in central to north
central Iowa where water will be routing into and additional
rainfall is more of a possibility.

Finally, in addition to the heavy rainfall, not going to rule out
the potential for a few stronger storms on the nose of the low level
jet Friday night into Saturday. The storm prediction center
currently has the area in a general thunderstorm outlook with
minimal risk for severe weather, likely due to the lower CAPE values
and marginal deep layer shear. However, could certainly still see
some gusty winds overnight as any heavier cores collapse.

Friday night activity lingers into Saturday morning, then diminishes
through the day as an elevated mixed layer begins to leak in from
the west behind the wave. This will help to negate convection on
Saturday, although may see a few diurnally driven storms in the east
before those warmer 850 mb to 700 mb temperatures arrive aloft. This
elevated mixed layer (700 mb temperatures > 12C) remains overhead
Sunday into Monday, which will help to limit convective activity
through the end of the weekend and into early next week; bringing a
much needed break from the rain. Of course, this time of year you
trade one thing for another, as the warm temperatures aloft will
translate down to hot temperatures at the surface. Similarly, while
the atmosphere is capped off, our stream of surface moisture still
continues at the surface. This, in conjunction with moist soils and
corn evapotranspiration, will produce hot and humid conditions
Saturday and Sunday, pushing forecasted heat indices over 105F
areawide. Assuming this forecast remains on track tomorrow, heat
headlines will be needed for at least Sunday and Monday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1233 PM CDT Fri Jul 25 2025

A few features of note through this TAF period. Most immediate
concern is showers/isolated storms in southern Iowa near KOTM
and associated with MVFR ceilings. These are expected to linger
for at least few hours, but could potentially fester through the
evening as more widespread rain/storms spread over the state.
This will most likely impact KOTM, but KDSM and KALO will be on
the northern fringe of the best chances as well. Main impacts
from storms will be heavy rainfall and gusty winds.
Precipitation lingers into Saturday but should depart to the
east through late morning. In addition to the shower/storm
activity, ceilings will drop into MVFR to IFR tomorrow morning,
along with potential for patchy fog at all sites.

&&

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

&&

$$

UPDATE...Hagenhoff
DISCUSSION...Dodson
AVIATION...Dodson