047
FXUS63 KDVN 221730
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1130 AM CST Fri Nov 22 2024

.KEY MESSAGES...

- Brief bout of above normal warmth on Sunday.

- The first of two rounds of cold air arrives Monday.

- Unsettled weather leading up to Thanksgiving with low
  confidence on forecast details.

- Turning much colder (70-80% chance) post-Thanksgiving, while
  potentially staying unsettled.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 307 AM CST Fri Nov 22 2024

Low pressure will continue to merge with a low off the New
England Coast today, leaving cyclonic flow lingering across
the region. Satellite/observational data shows a lot of lower
clouds/stratus upstream across the Upper Midwest into southern
Canada early this morning. The 00z RAOB from Minneapolis (MPX)
shows a large subsidence inversion trapping these lower clouds.
Mid level ridging/subsidence across the Plains into portions of
the Upper Midwest will build into the region tonight. In doing
so this subsidence should further strengthen a low level
inversion overhead, similar to what was observed at MPX last
night. Bottom line, confidence is high that we`ll see the cloud
cover stick around into tonight. We are likely to see a few
breaks, but overall more in the way of cloudiness is expected.
This should limit highs areawide to the upper 30s to mid 40s.
Some patches of drizzle will remain possible this morning across
portions of NW Illinois with the saturated low levels, as some
weak lift lingers with the passage of mid level shortwave
energy. A lingering pressure gradient will foster continued
gusty winds today tapering off by late afternoon through
evening, as ridging builds closer. NBM 90th percentile wind
gusts are in the range of 25 to 35 mph today giving an idea of
our max gust potential. So, breezy or brisk but not nearly as
windy as Thursday.

Later tonight into Saturday, as the flow turns neutral to
slightly anticyclonic with the ridge approaching I would
anticipate a decrease in the lower clouds. Typically this
time of year it`s tough to clear at night barring a strong
synoptic system, and so my feeling while some partial clearing
is possible especially far west/south, many of us will likely
hang onto the clouds and it may not be until during the day on
Saturday for the lower clouds to finally skedaddle. As a result
of favoring predominantly clouds tonight, I favored toward the
90th percentile of NBM lows giving a range of some upper 20s
where any partial clearing occurs (again would be favored far
west and south should it happen), to the lower to middle 30s
elsewhere. Saturday highs, with the idea of seeing a bit more
in the way of breaks or sunshine by afternoon, has highs
a skosh warmer from the mid 40s to around 50 with much lighter
wind.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 307 AM CST Fri Nov 22 2024

Late in the weekend into the start of the new work week, the
models generally depict a shortwave trough traversing the
northern tier of states within predominantly zonal flow aloft.
At the surface, we`ll see gusty southerly return flow develop
on Sunday ahead of a developing low pressure to our west.
This warm advection will help push highs into the 50s areawide,
with a few lower 60s possible south of I-80. Moisture is
mostly pacific in origin with limited/shallow low level
moisture with a veering LLJ and main IVT transport focused
into the Ohio Valley. Any precipitation Sunday night into
Monday would appear to be very light and possibly just drizzle
with the shallow low level saturation. We may have to watch
for our far northern service area on Monday to potentially get
brushed by wrap-around precipitation /light snow/ from a Great
Lakes low. This low will help dislodge a chunk of cold air and
settle in southward across the region Monday heading into
midweek, with temperatures dropping below normal with a period
of gustiness as the cold air arrives Monday into Monday night.

Forecast uncertainty increases greatly mid to late next week,
or around the Thanksgiving holiday due largely in part to
an active split jet stream. Cluster analysis show big differences
with the track and strength of a shortwave trough moving west
to east across the CONUS midweek, as one cluster is much more
pronounced with this southern stream wave as it ejects from
the Rockies toward the Ohio Valley while other clusters are
much weaker with one placing more energy in the northern stream.
Given the timing of around the Thanksgiving holiday we`ll
definitely be monitoring the forecast over the next few days
with this system, which is actually remnant energy from the
anomalously deep low situated off the Pacific Northwest coast
early this morning. This could bring some impactful weather
to portions of the region, so be sure to stay tuned!

While there is great uncertainty on precipitation chances and
timing/location mid to late next week, what is fairly certain
is an even colder airmass settling into the region around
Thanksgiving and through the following weekend, as the
deterministic and ensemble guidance support a chunk of arctic
air moving into the Midwest. This is due to an eventual N/NW
flow pattern resulting from a blocking ridge developing over the
North Pacific and Alaska, which could keep the much colder
conditions around through early December. For more on this
colder weather see the Climate section below.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1126 AM CST Fri Nov 22 2024

MVFR clouds are trapped under a layer of warmer air aloft.
Models prog the warmer layer aloft to persist through 12z/23
thus MVFR CIGS with areas of IFR CIGS will continue. After
12z/23 mixing of the low moist layer will commence allowing CIGS
to slowly rise through 18z/23 but still remain MVFR across
eastern Iowa and northern Illinois.

&&

.CLIMATE...
Issued at 307 AM CST Fri Nov 22 2024

A broad area of low pressure in the mid/upper levels of the
atmosphere is forecast to dominate much of the CONUS
starting around Thanksgiving and continuing through next
weekend. This will be accompanied by the most significant cold
air outbreak of the season thus far. The Climate Prediction
Center (CPC) 8 to 14 day (November 29 - December 5) temperature
outlook has the probabilities for below normal temperatures at
70-80 percent across the Midwest. For context, normal highs
during this timeframe are in the upper 30s and lower 40s, while
normal lows are in the lower to middle 20s.

The CPC 8-14 day precipitation outlook is for near to below
normal precipitation. Suffice it to say should any precipitation
occur it would likely be frozen. So, we`ll be monitoring this
forecast closely for the holiday and especially the post-
holiday weekend travel for any impactful weather.

&&

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

&&

$$

SHORT TERM...McClure
LONG TERM...McClure
AVIATION...08
CLIMATE...McClure