025
FXUS63 KDVN 292326
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
626 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- Near to slightly below normal temperatures are expected to
  continue through Tuesday, followed by a notable cool down.

- A cold front midweek brings a better chance of rain followed  by
  much cooler temperatures.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 127 PM CDT Fri Aug 29 2025

The backdoor cold front generally washed out overnight, but the weak
convergent axis is still noted along it in eastern Iowa into central
Illinois, and this remains a relevant feature within our
forecast. The axis, and with that, the narrow swath of building
cumulus and isolated showers, is positioned from near Macomb IL,
to Washington IA, to just west of Waterloo IA. CAMs generally
are supporting development of storms similar to yesterday along
this axis in the afternoon and evening. To the north, an area of
rain is found in Wisconsin, well north of the lingering
boundary. There could be a few showers forced by the southern
end of that activity this afternoon as well. All this mesoscale
activity will not likely amount to much today, given limited
instability, and weak forcing. The vast majority of our area
will be dry and pleasant through tonight. I did add a stripe of
patchy fog in western areas for the early morning hours
Saturday. Any fog formation will be shallow in nature, and
quickly burn off Saturday morning after sunrise.


Saturday, this situation looks to once again repeat, with a few
isolated showers/weak storms forming along the axis of weak
convergence in eastern Iowa, while the rest of the area sees another
pleasant day in the upper 70s to lower 80s. I`ve capped pops at 20%
for this axis, once again forecast to be near the aforementioned
position.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 127 PM CDT Fri Aug 29 2025

There are some big weather changes coming in the long term
forecast. Northern stream ridging moves into the Canadian
prairies this weekend, gradually pushing aside the persistent
troughing over the eastern Great Lakes and New England. But by
the time this ridge begins to nudge closer to our region, it
will already be being overtaken by a more robust trough dropping
quickly south out of the Canadian Arctic. This trough will be
ushering in much cooler air into the Upper Midwest for the
middle to later part of next week.

At the surface, high pressure over the western Great Lakes
gradually weakens and shifts east through early next week.
Temperatures remain near or slightly below normal for late
summer, mainly in the 70s for highs and 50s for lows. The focus
for daily showers and thunderstorms remains off to the west
where shortwave troughs embedded in the northwesterly jet
produce more frequent showers and storms over the Northern
Plains and into western Iowa. We can`t rule out a stray shower
mainly across our Iowa counties most days, but the chances
remain fairly low this far east with dry conditions generally
prevailing.

The best chance of rain this week comes with the arrival of the
trough and associated cold front Tuesday night into Wednesday.
Among the 00Z long range ensemble guidance, 40 to 60 percent of
members produce measurable rain with the passage of this
feature. Rain amounts won`t be excessive as there`s a lack of a
deep moisture connection ahead of the front and it does move
through fairly quickly.

The air mass taking aim at us behind next week`s front is
coming straight out of the Canadian Arctic, and it`s likely to
be at least a bit cooler than the last one we saw. There`s still
some variability in the guidance on how deep this trough is,
where its core tracks, and how long it lingers. So there is some
corresponding uncertainty in just how cool we get and for how
long. For daytime temperatures in this air mass we take a look
at 850MB temperatures to get a feel for what can be achieved in
fully mixed conditions. 850MB temperatures in the 2-6C range
suggest highs in the 60s with that variability also showing up
in the NBM interquartile range increasing to about 7 to 10
degrees late this week. On the cooler side of that range, some
areas may not get out of the 50s. As far as nighttime
temperatures, we look to dewpoints for a feel for what the air
mass is capable of if we can get a clear, calm night. Dewpoints
forecast in the low 40s suggest that if we do get a night of
strong cooling then temperatures could approach or perhaps
exceed those dewpoints in spots. However, it`s unclear at this
stage whether we`ll see the right conditions lining up for us to
get a full taste of this chill. With such a strong trough
there`s a good chance that winds behind the front remain strong
enough to prevent good nighttime cooling at least initially.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 622 PM CDT Fri Aug 29 2025

VFR conditions are expected through at least 09z.30. Scattered
showers and isolated storms to continue for the next 1-3 hours,
with some additional development possible along residual outflow
boundaries. Some brief MVFR vsbys and thunder may occur if a
storm goes over a terminal (CID/MLI) but confidence too low to
mention for now. Will continue to monitor and amend if needed
this evening. Activity to quickly weaken after sunset, with
some MVFR fog possible early Sunday at CID/DBQ. Some guidance
was suggesting even lower vsbys at DBQ, but with current model
performance decided to hold off on introducing anything lower at
this time. A similar setup is expected late Saturday morning
and afternoon with low VFR-base Cu developing and a few
isolated showers possible.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

$$

SHORT TERM...Ervin
LONG TERM...Ervin/NWS
AVIATION...Gross