Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/09/22
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
533 PM CST Sat Jan 8 2022
.SHORT TERM...
Issued at 231 PM CST Sat Jan 8 2022
Through Sunday...
The going forecast message continues with no major changes this
afternoon. The Winter Weather Advisory was expanded to include the
Wisconsin stateline region, and the Advisory as a whole was
extended through midnight. Main messages:
* Patchy freezing drizzle will become more widespread and in some
locations more steady by 5 PM, with scattered freezing rain
showers along and south of the Kankakee River Valley.
* Light glaze developing on untreated surfaces and some treated
ones too given the cold ground conditions; the primary treated
surfaces will likely have less impacts, such as in the heart of
the Chicago metro, but the degree to which will depend on the
drizzle rates and treatment effectiveness
* Freezing drizzle/light freezing rain to continue to 8 PM to
midnight depending on location, with some fog also possible
later this evening mainly along and south of I-80
* Blustery and colder on Sunday with temperatures inching downward
through the day; wind chills of 5 below to 5 above from late
morning on
Radar and observations, including mPing reports, have shown an
expansion of freezing drizzle over northern Illinois since 130 PM.
Recent AMDAR soundings from MDW show the saturated depth about
3,000 ft thick, sufficient for drizzle. Would expect as cloud
bases lower (aided by virga at first), the drizzle coverage should
become fairly widespread by 5 PM on continued modest to strong
isentropic ascent within that saturated layer. The peak coverage
of rain/drizzle looks to be during the early evening hours for our
CWA, with 50-55 kt of moisture transport on the low-level jet
over the area. This could result in some true freezing rain
showers such as seen earlier in central Illinois.
Air temperatures through early evening in most places look to
remain below freezing, with the 32 isotherm near I-70 still as of
230 PM. The temperatures of the warmest part of the saturated
layer aloft on AMDAR data indicate around 1 to 1.5C, so not super
warm hydrometeors which can help with light icing as they reach
the surface. Pavement temperatures on a handful of available area
sensors have inched upward, with mid 20s in far northern Illinois
and around 30 in northwest Indiana. With sunset, would expect
pavement temperatures to dip a bit, even if climbing above
freezing the next couple hours. So the early evening, roughly 5 to
9 PM, seems when impacts of this event should be maximized. Also
the winds ease some, where as of 230 PM they almost seem breezy
enough to dry some of the surfaces readily given the lightness
and non-steadiness of the current drizzle.
The system driving this long fetch of low-level moisture
transport atop the Mississippi River Valley into the Great Lakes
will be speeding east across Ontario tonight and bringing a cold
front toward the area. Ahead of this front during the late evening,
two deterrents to freezing precipitation will come into the play:
1.) the warm sector will inch northward and 2.) drying/diminished
isentropic ascent will spread eastward. These will not be
everywhere though, and some freezing drizzle is still expected
north of the 32 isotherm where it is still moist enough. This
includes in parts of the Chicago metro. So felt the need to extend
the Advisory until midnight, but do think some areas will have the
threat diminished by 9 to 10 P.M., namely the far south. Areas of
fog could develop with the boundary layer saturation and dew
points pushing up close to freezing late in the evening into early
overnight. This is mainly for along and south of I-80.
The surface cold front will progress through the area in the pre-
dawn to daybreak hours, ending precipitation chances and bringing
clearing skies a few hours after passage. Northwest winds will
gust to 25 to 30 mph through much of the day bringing cold
advection and sending temperatures into the teens and lower 20s
for the late morning and afternoon.
MTF
&&
.LONG TERM...
Issued at 204 PM CST Sat Jan 8 2022
Sunday night through Saturday...
Primary forecast concern remains light snow potential late Sunday
night into Monday morning. Additional concerns are low temps
Monday evening and winds Tuesday night.
A fast but weak clipper system will move across the area late
Sunday night through mid morning Monday. There still remains some
uncertainty regarding the exact track but the timing is more or
less consistent, arriving around the Monday morning commute. Qpf
amounts may only be a few hundredths of an inch, but with snow
ratios possibly as high as 20 to 1, a quick half inch to one inch
of fluffy snow is possible. Though it may fall in a fairly narrow
axis. Blended pops remain very low and have bumped pops up into
the 40 percent range and if trends continue, pops will need to be
increased further with later forecasts.
High pressure will move across the area Monday night and after
high temps Monday only in the teens, temps will likely drop
quickly with sunset, into the low single digits and possibly well
below zero across the northwest cwa. However, confidence is low
for how low temps will fall. There is some weak warm air advection
through the night and this has been a limiting factor for low
temps many times. Opted to make no changes to blended guidance,
which is a few degrees warmer from the previous forecast.
As this high pressure shifts east Tuesday, models are in good
agreement with moderating temps with increasing southerly winds as
the gradient tightens ahead of another cold front. Temps on
Tuesday likely only back in the 20s but they may hold in the 20s
Tuesday night with southerly winds gusting into the 30-35 mph
range, especially in the evening. More of a cool front/wind shift
Wednesday morning as temps climb well into the 30s. Highs back in
the 30s Thursday as well.
Models are in fair agreement with a storm system moving southeast
across the Great Lakes region Friday/Friday night with a trailing
cold front moving across the area. ECMWF keeps the area generally
dry while the GFS develops precip along the front, lifting a
second wave from the central Plains further north and across the
local area. Blended chance pops seem fine from this distance,
though overall duration of any precipitation that may form could
be shorter in time. cms
&&
.AVIATION...
For the 00Z TAFs...
Aviation Forecast Concerns:
* Freezing drizzle through around 07Z/1 AM CST for ORD/MDW.
* IFR cigs/vsbys, with some potential for LIFR late this evening.
* Winds shift WNW behind cold front just after midnight. This
should end precipitation, bring vsbys to VFR and cigs to MVFR
and continue to improve through early Sunday morning.
* Gusty NW winds Sunday, with gusts near 30 kt possible Sunday
morning. Gusts will then gradually ease through the afternoon.
Surface low pressure was well north of the region across Ontario
early this evening, with a cold front trailing through MN and IA.
Ahead of the front, south low level winds had brought low clouds
and freezing drizzle to the region. IFR ceilings and visibilities
covered much of the area, and are likely to persist through the
evening hours as the terminals remain in the broad "warm" sector
of the low to our north. Some potential exists later this evening
for patchy LIFR conditions to develop as winds diminish ahead of
the approaching cold front. Within this area of low clouds,
freezing drizzle has been prevalent and is expected to persist
until the cold front brings drier low level conditions overnight.
Latest (23Z) surface obs indicate above-freezing temps have lifted
into central IL/IN, though many locations still reporting freezing
precip due to cold ground conditions. Even if temps reach or go
just slightly above the freezing mark, think that freezing drizzle
may still be an issue. GYY would likely have a slightly better
chance of getting above freezing than ORD/MDW and points
northwest. Moisture to the northwest is shallower, and freezing
drizzle intensity may decrease or even end at RFD by mid-evening.
The cold front looks to move through RFD around 06Z and the
Chicago terminals 07-08Z. This will produce a wind shift to the
west-northwest (from southwest), eventually becoming gusty and
shifting more northwest toward morning. Drier air behind the front
will bring an end to the DZ/FZDZ and will erode lower clouds with
an improvement to MVFR and eventually VFR by sunrise. Winds will
likely be gusting in the 25-30 kt range for a time Sunday morning
before very gradually easing through the day.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-
ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-
ILZ108 until midnight Sunday.
IN...Winter Weather Advisory...INZ001-INZ002-INZ010-INZ011-INZ019
until midnight Sunday.
LM...Small Craft Advisory...Winthrop Harbor to Gary IN until 9 PM
Sunday.
Small Craft Advisory...Gary to Michigan City IN until 3 AM
Monday.
&&
$$
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