National Weather Service Raw Text Product

452 
FXUS63 KDMX 301741
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1241 PM CDT Mon Jun 30 2025

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

.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. Small hail would also be possible. 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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1237 PM CDT Mon Jun 30 2025

Have not added in precip mentions within the next 6 hours for
sites as confidence remains low in precipitation. Some widely
scattered showers are still possible in the north and east 
before 00z with gusty winds possible. Highest confidence in 
precipitation at KOTM, but given present convection mostly 
southeast of the site, have sided with the idea that most of the
precipitation will continue to focus away from the terminal.

&&

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

&&

$$

UPDATE...Ansorge
DISCUSSION...Hahn
AVIATION...Jimenez