Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/08/21

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 541 PM CST Thu Jan 7 2021

.SHORT TERM...
230 PM CST

Through Friday night...

The persistent cloudy weather with nuances in the forecast
continues today, with little overall change heading into the
weekend. Cloud heights continue to increase with a weakening and
lifting inversion this afternoon. However, saturated cloud
thickness has increased to about 2kft (4-6kft AGL) per recent
aircraft/pilot reports around the Chicago metro. With the added
diurnal influence, isolated patches of flurries have been observed
and will remain possible through sunset.

tonight: Across central Lake Michigan, a mid-lake convergent
boundary has developed today, likely driven by a thermal trough
over the lake and possibly some land breeze influence off Lower
Michigan. With mid-lake radar returns already present east of
Sheboygan to the Door Peninsula and most high-res guidance showing
minimal QPF with this boundary as it moves into northeast
Illinois by mid-evening, have added isolated snow showers into the
forecast for much of the night. This includes areas as far inland
as Livingston County for a few hour window after midnight. Min
temps at the top of the saturated cloud layer will be around -8 to
-9C (similar to present) through at least the early overnight
hours, which should be sufficient for ice nucleation in a more
turbulent marine PBL. Inversion heights will begin to lower
overnight and likely suppress most of the activity in what is
already a meager LES set-up.

Friday and Friday night: The lowering inversion will result in a
descending stratus deck with thermal profiles less supportive of
ice nucleation by daybreak. If ceilings lower enough (i.e. under
2kft), anthropogenic forcing may again initiate sporadic pockets
of ice nucleation and resultant flurries Friday afternoon into
Friday night. Stronger northeast flow as high as 20 kt at 1kft AGL
may mitigate this potential by more efficiently
dispersing/shearing steam plumes originating from a stationary
point source.

Kluber

&&

.LONG TERM...
235 PM CST

Saturday through Thursday...

Quiet weather is expected to continue this weekend and into early
next week with surface high pressure holding firm across the
Upper Midwest. A ragged split flow in the upper levels will keep
most of the systems well to our south. Mostly cloudy conditions
look to continue through the next several days as well. A few lake
effect flurries may linger into Saturday morning before
northeasterly flow off the lake becomes more northwesterly during
the day. Otherwise, mostly dry conditions can be expected through
Wednesday. A quick diving wave treks across the Great Lakes
Sunday night into Monday which may bring in enough dry air to help
break up some of the cloudiness on Monday.

Temperatures will be mostly seasonable with highs in the lower to
mid 30s this weekend. Cooler air will push into the area Sunday
night into Monday behind the departing wave which will keep highs
in the mid 20s to lower 30s. Temperatures then gradually increase
through midweek. Just beyond the forecast period the pattern
shifts as ridging builds across the western CONUS which will place
the Great Lakes in a more favorable position for more active and
colder weather under northwest flow.

Petr

&&

.AVIATION...
For the 00Z TAFs...

Overcast skies will prevail through the TAF period at all
terminals. In the wake of a mid-level inverted trough, inversion
heights will lower this evening leading to a corresponding
lowering of ceilings. By daybreak Friday, ceilings should drop
below 2000 feet with a non-zero chance they approach 1000 feet as
the morning progresses (note that SREF probabilities for ceilings
below 3000 feet exceed 80% by daybreak, but lessen toward 50% for
below 1000 feet). With in-cloud temperatures anywhere from 3 to
9 below zero C, icing will remain possible on any aircraft with
long residence times through the cloud deck. Light snow showers
(really fine snowflakes based on upstream reports near Milwaukee)
forced by lake- induced troughing and corresponding low- level
confluence of winds along the lakeshore will be the norm through
the overnight hours, warranting a mention of VCSH at
ORD/MDW/DPA/GYY. No drops in visibility are anticipated. While not
explicitly shown in the outgoing TAF package, flurries in the
vicinity of the Chicago terminals may continue beyond daybreak
Friday with a slight preference for higher coverage near GYY.
Winds will remain north/northeast through the TAF period.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

Visit us at weather.gov/chicago

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSChicago
www.twitter.com/NWSChicago
www.youtube.com/NWSChicago