Norwalk, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

570
FXUS63 KDMX 300745
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
245 AM CDT Mon Jun 30 2025

.KEY MESSAGES...

- Patchy fog over northern Iowa this morning

- 20% chance of showers and storms later this morning into this
afternoon with isolated sub-severe gusty winds possible.

- Cooler airmass today and Tuesday followed by warmer conditions
Wednesday into the Fourth of July weekend. Storm chances returning
by late Wednesday into early Thursday and perhaps later Friday into
Saturday.

&&

.UPDATE...
Issued at 245 AM CDT Mon Jun 30 2025

While the surface cold front is moving southeastward and is
nearly through our service area early this morning per shift in
wind direction, drier air is lagging behind with dewpoints still
well into the 60s behind the front. With dewpoint depressions a
few degrees at most, there has been very patchy fog development
over northeastern Iowa into north central Iowa per surface
observations and somewhat of a signal in the Nighttime
Microphysics RGB of GOES- East. This fog is expected to continue
and expand and to some degree become thicker/lower visibility
through sunrise over these areas before dissipating by 9am. It
is not fully out of the question that a dense fog advisory may
be needed in our far northeastern service area around
Waterloo/Cedar Falls. However, current chance of this occurring
is no higher than 40% so will continue to monitor. Otherwise,
watching a line of weak showers moving into northwestern Iowa
that is expected to move into north central Iowa in the next
hour or so. Additional convection over Nebraska is being handled
best by the RAP and HRRR, which shows this largely staying
southwest of our forecast area if not the state.

As we head into the daytime hours, a shortwave trough that is
presently over North Dakota will swing into Iowa later this morning
through this afternoon. While there should be a fair amount of cloud
cover, instability still increases to around or over 1000 J/kg as
low level lapse rates steepen to 7 to perhaps 8 C/km with mid-level
lapse rates around 6 C/km. This forcing and environment should allow
for showers and storms to develop, though they are not expected to
be widespread and most locations will not see rainfall. Forecast
soundings show some degree of sub-cloud layer dry air and this dry
air being entrained into downdrafts may produce isolated sub-severe
gusty winds. Most CAMs do not exceed 30 knots, but a few runs such
as the 0z NAMNest and 0z ARW cores show 30-35 knot gust potential.
This activity will diminish late this afternoon into this evening
with dry conditions expected through Wednesday. Highs today will be
lower by several degrees in the low and middle 80s in the cold air
advection regime, but 850mb temperatures begin to recover by Tuesday
with highs ticking up a few degrees into the middle 80s and more so
on Wednesday.

&&

.DISCUSSION...
Issued at 240 PM CDT Sun Jun 29 2025

Morning Mesoscale Convective System (MCS) and residual blow-off
clouds has put quite the damper on temperatures today - about 5
degrees cooler than was expected at this time yesterday. Lack
of insolation and resultant cooler temperatures has
significantly reduced storm prospects and severe potential
across the CWA this afternoon/evening; a trend that was
captured well in 1630z SWODY1 Slight-Marginal shift. All of the
12z CAMs captured this well, with only the 12z HRRR and FV3
convecting along a relatively diffuse "cold" frontal which is
progd to be located roughly from Waterloo to Lamoni by mid-
later afternoon. If storms are able to materialize along this
boundary, northeast portions of the CWA would be best
positioned for best thunderstorm organization given proximity
to the mid-level shortwave trough. The best updrafts of which
would be capable of producing primarily damaging wind (DCAPEs of
1000 j/kg) and brief heavy rain. So - have made wholesale
forecast changes to reduce rainfall chances across the board for
this afternoon and evening - generally into the 20-50% range.
Of course, this will mitigate flooding threat as well, so no
longer anticipate a widespread flooding concern. Storms will
depart quickly this evening, giving way to drying thru much of
the overnight.

MCS Fest is set to continue once again later tonight as the next
one moves out of Nebraska and into the Midwest. 12z output has a
bit more consensus compared to last night`s tracking it mainly
into SW Iowa and MO. It doesn`t look to get into the region
until sunrise Monday; and have adjusted precipitation chances
accordingly. As for Monday, did maintain low storm chances as
the mid-level thermal trough moves overhead, steepening mid-
level lapse rates, and likely allowing for at least isolated
convection. Although expect most areas will stay dry for
Monday.

A drier air mass works in for Tuesday. Medium range guidance
differ on timing and magnitude of thunderstorm chances into the
holiday weekend, so confidence decreases after Wednesday.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1152 PM CDT Sun Jun 29 2025

VFR conditions ongoing across much of the area. A few locations
have started to see patchy fog develop which may continue
through the overnight especially in the northeast, towards
KALO/KMCW. Confidence in timing and impacts is not high, but
started with some patchy fog mentions, though adjustments may be
needed should fog become more dense. For later Monday
morning/early afternoon, although confidence has diminished in
shower/storm chances with time and associated impacts, for
consistency left prob 30 groups at KDSM and KOTM. Will continue
to evaluate trends and adjust or add mentions to other sites if
needed/confidence increases in shower/storm timing and impacts.
Light and variable winds expected through the overnight before
winds settle out of the northwest and increase during the
daytime Monday to around 10-15 knots, with a few higher gusts.

&&

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

&&

$$

UPDATE...Ansorge
DISCUSSION...Hahn
AVIATION...05