655
FXUS63 KDVN 182032
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
Issued by National Weather Service Des Moines IA
232 PM CST Tue Nov 18 2025

.KEY MESSAGES...

- Once lingering light showers clear out of northwestern
  Illinois this afternoon, the forecast is dry but cloudy and
  cool through Wednesday with highs in the mid-40s to lower
  50s.

- Thursday and Friday will see highs generally in the 50s, and
  even some lower 60s on Thursday. Some clouds and rain chances
  may persist during this time, mainly in our southern counties
  toward the MO/IA/IL tri-state area.

- The weekend forecast for Saturday through Sunday is dry and
  quiet, with daily highs mainly in the 50s.

&&

.DISCUSSION /TONIGHT THROUGH TUESDAY/...
Issued at 232 PM CST Tue Nov 18 2025

A gradually weakening low pressure system has been moving
eastward across the area today, providing a few sprinkles and
light showers while thunderstorms moved by to our southeast,
over central Illinois. A large area of low clouds surrounding
the low has spread across most of Iowa and Illinois and held
temperatures in the 40s for all but our southern fringe of
counties around the tri-state area. As the low moves quickly
away to the east tonight, it will be replaced by a broad deep-
layer ridge, resulting in very light winds at the surface. This
will keep the clouds in place, mitigating radiational cooling
potential and resulting in Wednesday morning low temperatures
only a handful of degrees below this afternoon`s readings in
most areas.

The ridging will dampen out late Wednesday as zonal 500 MB flow
sets in overhead, in advance of a deep trough/low digging into
the far southwestern U.S. The low clouds blanketing the region
Wednesday morning will thus be slow to move or erode during the
day, and forecast high temperatures are only a few degrees over
today`s levels with another generally cool and grey day
forecast, though without the light rain we saw today. By
Thursday the southwest U.S. 500 MB trough will begin swinging up
toward the Four Corners region, while in the northern stream an
energetic wave sinks from south central Canada down into the
northern Great Lakes. The surface trough trailing from this
northern wave will move through Minnesota during the day but
will be washing out as it approaches, well south of the parent
system, while in advance of the trough a col region will result
in light southwest surface winds in our area during the day. Slightly
warmer and more humid air moving in aloft, as well as gradual
airmass modification, should allow for temperatures to climb
higher by Thursday afternoon especially if some clearing can
occur. Consequently, forecast highs are warmer in the mid-50s
to lower 60s across the service area. This scenario also signals
a return of low rain chances to our southern counties as
moisture advection kicks in above the surface, however, these
chances are limited by a lack of forcing for vertical ascent, as
well as the relatively shallow nature of any saturated layer in
the column and have thus maintained only 20-30% rain chances
mainly south of Highway 34/Interstate 74.

From Thursday night through the weekend forecast confidence
decreases due to the evolving 500 MB pattern and interactions
between several low pressure centers/troughs. By Thursday
evening the Canada/Great Lakes low will be moving slowly
eastward toward upper New England, while a new 500 MB low will
come ashore over central California. The previously discussed
500 MB trough swinging from the Four Corners region east
northeastward toward the central U.S. will fizzle out between
these two larger systems, becoming stretched into a broad zone
of 500 MB vorticity somewhere over the Midwestern states at the
end of this week. At the surface, this will manifest as a broad
baroclinic zone stretching roughly west to east, with modest
southerly flow to its south and with a large surface high
pressure area and light northerly flow dominating areas to its
north. In the broad interceding zone, a prolonged period of rain
and some thunderstorms will occur as the 500 MB system
stretching overhead produced prolonged forcing and lift. That
being said, the majority of longer-range model solutions place
this swath of rainfall just to our south, from Kansas and
Missouri over to southern Illinois and into the Ohio River
valley. For now will maintain some mention of rain chances
across most of our forecast area Friday into Friday night,
however, have begun to focus them toward the south and expect
this trend will continue in future updates as we begin to remove
rain chances from north to south and ultimately maintain them
only in our southern counties. Of course, this will depend on
future forecast model trends not reversing the trend of the last
24 hours or so, but given the apparent geometry of the large
surface high and baroclinic zone, climatology supports this as
a reasonable expectation.

Once the weakening, stretching 500 MB system over the central
U.S. fades out in the early part of the weekend, the forecast is
then dry and quiet from Saturday into early next week as a more
benign synoptic pattern sets in. Eventually, the aforementioned
California gyre will kick eastward into the central U.S. and
bring some return of precipitation chances around next Tuesday
or Wednesday, but at this range the details of any such
evolution remain unclear.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1118 AM CST Tue Nov 18 2025

Low stratus clouds are blanketing much of the area today and
will spread gradually southward and thicken over the remainder
of the area tonight. This will result in prevailing IFR or
lower conditions at DBQ, CID, and MLI for most or all of the
18Z TAF period, with ceilings generally around FL007-010 at MLI
and lowering toward the north to FL003-006 at DBQ where BR will
also reduce visibility at times. Farther south, at BRL, the
ceilings will be somewhat higher initially around FL025-035
before deteriorating as the lower stratus moves in, and
eventually becoming IFR later tonight into Wednesday morning.

&&

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

&&

$$

SHORT TERM...
LONG TERM...NWS
AVIATION...NWS