Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/01/20
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
937 PM CST Mon Nov 30 2020
.UPDATE...
934 PM CST
We have had reports of a glaze of ice in portions of Porter county
Indiana. Investigation of forecast and AMDAR soundings suggests
that we are losing some of the deeper moisture that is allowing
supercooled water to dominate in the clouds across Lake Michigan,
and this is resulting in freezing drizzle or freezing rain to mix
in with the snow.
Fortunately forcing is easing some and precipitation should
lighten up with time, though freezing drizzle may continue through
the night and even into the morning commute. Therefore, we have
updated the winter weather advisory to reflect that the higher
impacts will be from ice than snow. Travelers in northwest Indiana
should use caution this evening and overnight.
KMD
&&
.SHORT TERM...
237 PM CST
Through Tuesday night...
Main update for this afternoon is that we decided to drop the winter
weather advisory for Lake and Jasper counties but keep it going for
Porter. Even most of Porter has been seeing very little activity so
far today as the dominant lake effect snow band remains parked to
the east over La Porte and Starke counties. Confidence is not high
that Porter even sees much this evening or overnight, but if the
band shifts west or if it breaks down and allows for development of
less organized multi-band snow showers across the area, a quick
couple of inches would not be out of the question. Areas of Lake
and Jasper also could still see some light accumulations, but based
on trends so far today, this is looking less likely to cause
problems widespread enough to justify keeping the advisory tonight.
Tuesday morning, as winds continue backing toward the northwest,
only the far northeast corner of Porter County would be favored for
any additional snowfall, and this would be very light. Most
locations on the Illinois side and close to the Indiana stateline
actually should be clear by morning ahead of a ridge building in
from the west. The tradeoff is overnight lows in the upper teens to
lower 20s, compared to upper 20s in areas with continued cloud cover
and snow chances early tomorrow.
By Tuesday afternoon sunny skies should spread across the area, and
despite continued northwest flow we should manage to climb into the
mid to upper 30s in most locations, though winds gusting to around
20 mph will make it feel about 10 degrees cooler. Tuesday night
with lighter winds and clear skies, overnight lows again drop into
the low to mid 20s, close to normal for early December.
Lenning
&&
.LONG TERM...
237 PM CST
Wednesday through Monday...
The local area will be between the departing low to the east and
another upper low digging into the southern high plains. The
western part of this trough will cutoff over the Four Corners
while the eastern portion continues eastward and is absorbed by
the northern stream trough centered over eastern Canada. The
southeast part of the forecast area will be on the fringe of the
trough as it weakens as it passes Thursday and Thursday night. The
signal continues to be dry as this occurs so will stay with that
idea for now. Once the trough clears, the area will be influenced
by a brief period of upper ridging into Friday night before
another northern stream trough digs southward into the upper Great
Lakes Saturday and into the upper Ohio Valley into Sunday. Not too
much in the way of deeper moisture is forecast locally, with the
core of the system staying to the east at this point but will need
to keep an eye precip potential as the weekend gets closer. Highs
will be fairly steady from midweek onward with readings in the
low to mid 40s. Overnight lows will be in the 20s. Another brief
round of colder air will spread in for Monday bringing the
potential for highs in the 30s should it come to pass.
MDB
&&
.AVIATION...
For the 00Z TAFs...
A lake-enhanced stratus deck from ~3000 to 5000 feet in which
severe icing is occurring (three reports of such in the past 20
minutes) will persist through much of the night at DPA/ORD/MDW/GYY
and points eastward. Overnight, cloud-layer winds will gradually
turn ever so slightly northwesterly allowing for improvement from
west to east, though the stratus will remain over Lake Michigan
for much of the remainder of the TAF period. For now, have
maintained the 1000Z "end time" of the deck at ORD/MDW, and 18Z at
GYY. Surface winds will remain northwesterly through the TAF
period as well, though with a gradual decrease in wind speeds from
this point forward as the low-level pressure gradient relaxes
(though gusts in the 20-25 kt range will remain possible through
the overnight hours).
Occasional spits of flurries will continue at all terminals
through about midnight except at GYY where light snow showers will
be possible through about daybreak Tuesday. Further improvement
in clouds is expected as Tuesday wears on, with SKC possible by
the end of the TAF period.
Borchardt
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Lakeshore Flood Advisory...ILZ103-ILZ104 until 6 AM Tuesday.
IN...Lakeshore Flood Warning...INZ001-INZ002 until noon Tuesday.
Winter Weather Advisory...INZ002 until 6 AM Tuesday.
LM...Gale Warning...nearshore waters until
midnight Tuesday.
&&
$$
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