586
FXUS63 KDVN 250923
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
323 AM CST Mon Nov 25 2024

.KEY MESSAGES...

- Low chance for some minor accumulating snow for portions of
  the area late Tuesday night into early Wednesday.

- Potential remains, but lower, for another storm system with a
  chance for rain or snow Wednesday and Wednesday night.
  Confidence is low in the track/strength of the system and
  subsequent snow potential and if any impactful weather will
  be seen. Continue to monitor the forecast!

- An arctic blast will lead to bitterly cold temperatures late
  this week into the start of December.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 314 AM CST Mon Nov 25 2024

Surface low pressure over west central Illinois will continue
to shift east this morning ahead of an approaching upper level
shortwave trough. Winds will shift to the northwest and become
brisk/windy today with a moderate pressure gradient and
steepening low level lapse rates in strengthening cold
advection. NBM 90th percentile gusts, which indicate a
reasonable high end gust potential, generally fall in the range
of 30 to 35 mph. There will also be a fleeting chance of
precipitation by mid morning through mid/late afternoon, mainly
north of I-80 attendant to a sweeping band of mid level Fgen
ahead of the shortwave trough. Thermally forecast soundings are
still warm enough in the lowest 2 km (brunt of the cold air
lagging) to favor predominantly rain, but soundings suggest it
could cool sufficiently to where a rain/snow mix or brief change
to snow can`t be ruled out along the Hwy 20 corridor (mainly in
NE Iowa) before ending. Further south of I-80 forcing is weaker
and would imply mainly just sprinkles if anything. Subsidence
quickly building behind the departing wave will lead to a
clearing trend from west to east this afternoon into early
evening. Temperatures today will likely exhibit a slow fall into
the 30s by evening under the gradual deepening cold air.
However, areas that manage to see sunshine this afternoon may
see temperatures level off or possibly rebound a few degrees.
These temperatures and brisk winds will have it feeling more
like the 20s in most areas by late afternoon, so it will feel
markedly colder accentuated by the above normal warmth of Sunday.

Tonight, the first of a few surges of cold air will grip the
region. High pressure building toward the region will bring
continued clearing early evening followed by diminishing winds.
This will set the stage for the coldest night of the season
thus far, with lows in the upper teens to mid 20s. Just enough
wind will exist to make it feel even colder and well down in
the teens to possibly a few single digits by daybreak Tuesday,
so kids will want to be prepared and bundled up for the bus stop!

Tuesday, will start off sunny but do anticipate increasing high
level cloudiness in the afternoon ahead of our next storm system.
Highs look to be near to a little below normal and range from the
upper 30s to near 45. Winds look to be much lighter and generally
around 5-15 mph.

Tuesday night we`ll continue to see the clouds thicken. The signal
for an Fgen band of snow developing late has diminished some, but
it`s still being hinted at. As a result, have reintroduced some
very low PoPs between Hwy 30 and Hwy 34 for late Tuesday night
that extends into Wednesday morning while expanding to include
more of the area expect far NE Iowa. Any accumulations look to be
minor with little in the way of impacts.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 314 AM CST Mon Nov 25 2024

Still monitoring Wednesday into Thanksgiving day for the potential
of wintry weather, but we also continue to see some large
discrepancies on the track/strength of this system. The deterministic
GFS and GEM and a preponderance of their ensemble membership (GEFS
and GEPS) still favor a weaker and much further south track as
they favor keeping the northern and southern stream unphased. If
this were to verify it would be a swing and a miss for any
precipitation for the local area. Meanwhile, the ECMWF and
preponderance of the ENS ensemble membership favor more phasing of
the northern and southern stream energy leading to a stronger system
and a further north track. This would lead to precipitation
extending further north and swiping areas especially along and south
of I-80. This scenario would also lead to warmer low levels and
subsequently creates marginal conditions for snow accumulation that
would be tied largely to rate. Overall, despite the fairly low
confidence forecast it would appear as though the probability for
impactful accumulating snow even with the stronger/further north
solution is low given the marginal BL temperatures. Nonetheless,
it`s still a good idea to stay tuned for updates or changes, especially
if planning travel for the Thanksgiving holiday.

What continues to remain high confidence in polar air encompassing the
region late week into early next week, as a blocking ridge develops
in the Pacific NW leading to a downstream deep upper trough from the
Great Lakes into the Mid Atlantic. This would favor a wintry regime
with reinforcing shots of bitterly cold air and well below normal
temperatures, along with the potential for shots of snow with clipper
systems. We`re looking at easily the coldest air of the season so
far with NAEFS and ECMWF ensembles clustering around 10th climatological
percentile on low level temperatures. NBM 25th to 75th percentile
supports highs mainly in the 20s and lows in the single digits and
teens, more typical of January! Adding in the wind and we`re talking
chills in the single digits above and below zero at night. Shiver me
timbers!

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1140 PM CST Sun Nov 24 2024

VFR conditions will begin the TAF period. However, as low pressure
pulls away from the area between 09z-15z winds will shift to
the NW and become gusty at 15-30 kt. This will advect in stratus
with predominantly MVFR CIGs 1-2kft agl. A brief bout of snow
showers and transitory IFR conditions is possible 14z-19z mainly
north of the Hwy 30 corridor, potentially impacting DBQ. I have
added a PROB30 mention to cover this potential. Otherwise,
anticipate low clouds to decrease from west to east and a return
to VFR by mid afternoon into early evening as subsidence builds
in. W/NW winds will gradually diminish to around 10 kt after sunset.

&&

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

&&

$$

SHORT TERM...McClure
LONG TERM...McClure
AVIATION...McClure