544
FXUS63 KDVN 311710
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1210 PM CDT Sun Aug 31 2025

.KEY MESSAGES...

- Seasonable temperatures and mostly dry weather continue
  through the first part of the week.

- A strong cold front Wednesday brings our best chance of light
  rain along with much cooler temperatures.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 300 AM CDT Sun Aug 31 2025

Mesoanalysis this morning shows surface high pressure over Michigan
which has continued to feed a cool, dry, easterly flow across
Illinois and Iowa. Further to our west, a mid level shortwave trough
remains stuck over Nebraska, trapped in part by ridging moving
south into Minnesota. This has produced persistent showers and
thunderstorms to our west including parts of eastern Iowa with
some mid and high level cloud cover extending into the western
portion of our forecast area as well. The widespread showers and
storms are likely to remain to our west again today, and with
lower dewpoints finally oozing in from the east we are less
likely to develop afternoon thunderstorms locally. Less than 20
percent of 00Z HREF guidance produce measurable rain in our
forecast area, and of those members that do it is for only a
small area. So with this forecast even our low PoP for today has
come down even further, with it likely that the entire area
remains dry today. Temperatures will again be a little cooler
than normal for late August, in the mid to upper 70s for highs.

Surface high pressure gradually moves ESE into New England and
the Mid Atlantic region tonight into Monday. This leads to
another quiet night tonight with temperatures in the 50s, or
perhaps the 60s where cloud cover hangs on. Winds gradually take
on more of a southeasterly component beginning on Monday and
daytime temperatures nudge up a degree or two as the influence
of the cooling high wanes. The trough to our west finally begins
to move southward, taking the more widespread showers and storms
along with it. While NBM continues to maintain some low PoP in
parts of our area Monday, it`s becoming increasingly likely that
we are missed by the rain from this trough as it moves more
south than east over the coming days. If clouds are more
extensive across our area, it would have the effect of holding
down high temperatures a few degrees. Tuesday will likely be the
warmest day of the week with even less influence from the high
to our east and less cloud cover as well.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 300 AM CDT Sun Aug 31 2025

As we`ve been discussing for several days now, the big changes
coming this week involve a trough dropping down from the north
and a strong cold front ushering in much colder weather.
Currently this trough is moving east across the Canadian Arctic,
while the surface high is chilling in Alaska and the Yukon
where current temperatures are in the 30s and 40s. As the trough
moves east, a portion of that trough will get kicked out and
head straight south this week, dragging that cool surface air
mass southward along with it. The trough dives south to a
position near Duluth, Minnesota on Wednesday where it deepens
for a day or so as its influence invades the central and eastern
US. Guidance has come into strong agreement on this opening
move, though there remains considerable variance on where the
center of the trough wobbles and how long the influence of the
broader trough lingers in our area. Our high confidence message
at this point is that we will see some widespread light rain in
the vicinity of the front on Wednesday with much cooler
temperatures for the end of the week potentially into the
weekend.

As discussed yesterday, long range ensemble guidance is pretty
consistent in producing light rain across our region along or
behind the front on Wednesday. Nearly 100 percent of 12Z ensemble
members produce rain in the 24 hour period around Wednesday,
and NBM PoP has begun to catch up as the timing of the front is
becoming more clear. PoP has increased considerably on Wednesday
while it has decreased Tuesday night and Wednesday night, a
sign of that increased confidence in timing. There won`t be a
lot of moisture to work with as the trough arrives, largely
feeding off moisture leftover from the persistent wetness over
Nebraska and eastern Iowa and lacking a Gulf connection. As a
result, we`re looking at primarily light rain with this, as less
than 50 percent of ensemble guidance produce 0.25 inch or more.
While there is the potential that we see just enough
instability for thunderstorms, the severe weather threat is low
due to a lack of greater moisture to fuel stronger instability.

As far as temperatures go, long range guidance seems to be
settling in on 850MB temperatures in the 0 to +5C range in the
core of the cold push on Thursday, remaining relatively stable
compared to the last 24 hours of model runs. Assuming full
mixing to 850MB, that would translate to surface temperatures in
the 50s to low 60s. NBM forecast highs in the low to mid 60s
look reasonable, if perhaps a bit on the warm side. Daytime
temperatures in the heart of the cold blast Thursday may be
considerably lower, especially as guidance may be
underestimating cloud cover within and around this deepening
trough. We will be within range of our daily record cool high
temperatures (see Climate section).

When it comes to low temperatures, we like to look at dewpoints
as a guide to how cool it can get under ideal cooling
conditions. While there remains some greater uncertainty on
dewpoints than on 850MB temperatures, the 40-45 degree range is
what`s favored right now. That suggests that under ideal cooling
conditions, low temperatures could reach down to that level or
perhaps a bit lower in the coolest spots. Near record lows, but
still likely warmer than what would pose a significant risk of
frost. That said, it may be quite hard for us to get ideal
cooling in this air mass especially without a surface high
nestling in overhead. It will be quite breezy behind the front,
and cold advection cloud cover would further limit ideal
surface cooling and keep the low levels better mixed overnight.
We`re more likely looking at a situation where cold advection
brings a relatively small diurnal range in temperatures Thursday
into early Friday, with temperatures holding in the 40s and
50s until the cold advection breaks and the sun begins to warm
things up.

For Friday and into the weekend there`s considerably more
uncertainty on temperatures and even precipitation. While the
going NBM forecast shows a rather quick warm up back into the
70s and a dry forecast, there`s a little more to that story. The
wobbling trough may drive additional cold fronts through the
region Friday into the weekend, and the embedded shortwave
troughs rounding the broader trough could bring additional
threats for showers. For example, the 00Z operational GFS and
ECMWF both bring one of those troughs through on Friday
accompanied by light rain and renewed cold advection. Of the
12Z ensemble guidance 20 to 40 percent of members continue to
produce light precipitation through Saturday in the continued
cyclonic flow. Eventually the trough will move northeast toward
James Bay, replaced by broad ridging extending out of the
western US. There`s considerable uncertainty on how quickly that
happens, though, primarily affecting the temperature forecast
next weekend. If the trough lingers longer, as indicated by the
00Z GFS which actually brings a third front through this
weekend, then we`ll hold on to the cool 60s through the weekend.
If instead the trough exits quickly and ridging resumes in its
wake, we will see a quicker warm up back into the 70s or even
the 80s next weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1208 PM CDT Sun Aug 31 2025

VFR conditions will prevail through the TAF period, with light
easterly winds between 5-10 KTs and a mix of clouds. Otherwise,
no sig wx is expected at this time.

&&

.CLIMATE...
Issued at 300 AM CDT Sun Aug 31 2025

With the upcoming cool air mass, some daily record lows and
record cool highs are in range of being tied or broken. The
current records for Thursday and Friday are shown below:

RECORD COOL HIGH TEMPERATURE:
              September 4      September 5
Moline        61 in 1874       61 in 1876
Dubuque       58 in 1994       61 in 1920

RECORD LOW TEMPERATURE:
              September 4      September 5
Moline        39 in 1974       42 in 1974
Dubuque       38 in 1974       44 in 1988 and others
Cedar Rapids  38 in 1974       42 in 1974
Burlington    40 in 1974       44 in 1962

&&

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

&&

$$

SHORT TERM...Gunkel
LONG TERM...Gunkel
AVIATION...Gunkel
CLIMATE...