Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/18/22
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1004 PM CDT Mon Oct 17 2022
.UPDATE...
Issued at 1004 PM CDT Mon Oct 17 2022
Cancelled the Winter Weather Advisory for Porter and Jasper
counties in northwest Indiana overnight, as best focus for any
travel impacts from accumulating lake effect snow looks to remain
east of the forecast area. Otherwise, forecast is generally on
track with light snow showers and flurries generally decreasing in
coverage late this evening west and southwest of Lake Michigan.
Regional radar coverage since mid-afternoon has depicted the
primary lake convergent axis along the eastern shore of Lake
Michigan, with associated heavier lake effect precipitation
focused mainly across far southwest lower Michigan and north
central Indiana. High-res CAM guidance indicates this trend will
continue over the next several hours, with the probability of
travel impacts associated with any accumulating snow over Porter
and Jasper counties continuing to diminish. Based on this, and
being past the evening heavier travel period, have elected to
cancel the winter weather advisory for those counties. Less
organized rain/snow showers will likely affect northwest Indiana
into the overnight hours, though with no significant accumulations
expected.
Elsewhere, scattered snow showers which were associated with an
earlier mid-level short wave have diminished/dissipated across
northern IL and parts of the IL/IN state line region. A few
flurries may linger at times into the overnight hours. Blustery
northwest winds will persist with gusts of 25 to 30 mph at times,
and up to 40 mph along the immediate Indiana lakeshore. With
strong northerly winds persisting, have made no changes to current
Lakeshore Flood Advisory which continues through Tuesday.
Updated products available.
Ratzer
&&
.SHORT TERM...
Issued at 330 PM CDT Mon Oct 17 2022
Through Tuesday...
The primary forecast messages through Tuesday are:
* Continued well below normal temperatures in blustery conditions,
with gusts up to 30 to 35 mph, and near the Indiana lake shore
of 45 to 50 mph
* Flurries with spotty snow showers through this evening, with
focus turning to downstream areas in northwest Indiana of Lake
Michigan by mid-evening; still high uncertainty whether there
will be snow accumulation of impact and the potential for that
has diminished since early this morning -- if trend continues
the Winter Weather Advisory will be cancelled early
* Minor lakeshore flooding along the northwest Indiana shore
through Tuesday; possible some minor lakeshore flooding or at
least spray on parts of the Cook County shore
The substantial long wave trough across eastern North America is
well defined today, with a broad but very well-defined closed
circulation center over the Great Lakes. The 500 mb temperatures
with this center are around -35C, which are at record cold for
October using GRB sounding climatology. Numerous vorticity maxima
within this upper trough have provided isolated pockets of ascent
and deeper saturation for showers, which have been primarily snow
showers in our forecast area. Some of these have produced brief
"snow globe" behavior with ~1 SM visibility underneath them,
including even in the far western forecast area (near Rock Falls
and Rochelle). The next wave for northern Illinois is less-defined
and a little more sheared than its predecessor, and this will
swing southward from Wisconsin by early to mid evening. This is
forecast to increase snow shower chances, including for Chicago.
Due to limited saturation depth above -10C per aircraft soundings,
and overall limited low-level focus to drive stronger shower
updrafts, the quality of the snow with any of these showers should
not be great in northern Illinois. Also the quick forward
progression should be enough to limit any accumulations. Flurries
and snow showers should taper from northwest to southeast across
northern Illinois during the later evening.
For northwest Indiana (downstream of the lake), disorganized lake
effect snow showers look to be the primary mode, apart from a
window of time mid-evening into early overnight when a more
concentrated, mesoscale-influenced focus could set up. This
potential though is lessening as convergence is presently along
the Michigan shore per observations -- that`s quite possibly too
far east for a focus in our CWA. This is forecast by CAMs to
wobble some, including slightly westward, with growing instability
of lake-induced CAPE > 800 to as much as ~1,500 J/kg along the
Porter County shore (modifying forecast soundings for lake temps
and current dew points over the water). The next mid-level wave
over northern lower Michigan does look to sharpen the convergence
over eastern Lake Michigan through the evening, but whether or not
a well-defined wave such as multiple earlier runs of the HRRR
showed, is uncertain. If so, it would support brief periods of
heavier snow showers. But if trends continue as such for another
few hours, the evening shift likely will be able to cancel this
impact-based Advisory early.
As for winds and waves...the surface low depth is down to 997 mb
over Lake Huron and will continue to gradually deepen through
tonight before holding steady on Tuesday, and all at the same time
with little movement. The locked-in cyclonic flow pattern will
support continued cold air advection mixing and a pressure
gradient that will keep gustiness tonight through Tuesday. Over
the lake, there have been marine platform observations of 45 to 50
mph (50 at St. Joseph, Michigan), so the going Wind Advisory for
lakeside Indiana areas looks good. Did extend it some during the
day tomorrow and may need to go through the entire afternoon. The
building waves from these winds have already been up to 9.5 feet
at Michigan City, IN, and per wave model guidance utilizing
forecast winds, these should get solidly be into the 10 to 15 ft
area, especially for Porter County, tonight and Tuesday.
Otherwise, clouds should show some thinning in western parts of
the CWA late this evening, though how quickly is of low
confidence. The thicker the clouds, the more the temperatures may
hold up. Still expecting most of northern Illinois apart from
downtown Chicago to drop to freezing or below. Do note that we at
NWS Chicago have collaboratively ended our growing season
products as of today, so no more Frost/Freeze headlines will be
issued this autumn.
Tuesday`s precipitation focus will be Porter County, Indiana and
eastward, with lake effect showers or flurries of a disorganized
nature probable to continue. These should be light enough for
little to no snow accumulation due to a lack of strong
convergence and associated deeper updrafts. Inland, stratocumulus
clouds are expected, and cannot rule out sprinkles with these.
MTF
&&
.LONG TERM...
Issued at 330 PM CDT Mon Oct 17 2022
Tuesday night through Sunday...
Main weather features of interest are:
- Upper Low and associated trof continue to spin across eastern
Canada, holding the colder temperatures in place through mid-week.
- Low ejects out of the area during second half of week, bringing a
return to warmer temperatures to end the week through the weekend.
- Zonal flow arrives Friday, ridging into the weekend, when
temperatures are forecast to climb back to the 60s and 70s.
- Next chance for precip arrives to end the weekend, as another Low
pressure system and trof takes hold over the northern Plains and
upper Midwest.
Precip chances will be coming to an end Tuesday night across
northwestern Indiana as the sfc Low lifts slowly ENE through the
eastern Great Lakes into Canada. Temperatures moderate into mid-
week, as a weak zonal flow system sets up. As the upper Low ejects
out of the Great Lakes Thursday, southwesterly winds return across
the central Plains into the Midwest to end the work week. A ridge of
High pressure dominates the weather pattern Friday through much of
the weekend, where southerly winds bring another rise in
temperatures back to the 60s and low 70s. Ahead of the next weather
producing system, southerly winds ramp up Sunday with models
bringing 20-30mph gusts. Another Low pressure system tracks through
the northern Plains late Sunday into Monday, swinging a trailing
frontal boundary through the area...bringing the next chance of
rainfall to the region.
SB
&&
.CLIMATE...
Last updated at 315 PM CDT Mon Oct 17 2022
Here are the current records in place for today and Tuesday. Note
Chicago (O`Hare) has reached at least 41 so today will not be a
record.
October 17 October 18
Record Cold Record Low Record Cold Record Low
Maximum Maximum
Chicago 40 (1880) 26 (1948) 38 (1930) 20 (1948)
Rockford 44 (2002) 24 (1992) 41 (1972) 19 (1952)
&&
.AVIATION...
For the 00Z TAFs...
Forecast concerns for the terminals...
*Gusty northwest winds persisting through Tuesday evening
*Occasional MVFR clouds this evening through Tuesday morning
*Chance for lake effect showers at GYY this evening
A deep upper-level trough continues to reside over the Great Lakes
region which is helping to maintain the gusty northwest winds
currently being observed across the area. Winds are expected to
ease a tad late this evening, but gusts will still remain in the
upper 20 to around 30 kt range through Tuesday evening. As the
trough begins to move east Tuesday evening gusts are expected to
ease to around 20 kts overnight Tuesday night into Wednesday.
In addition to the winds, there will also be a chance for a few
flurries across northeastern Illinois this evening with more
robust lake effect showers in northwest Indiana. Aircraft and
forecast soundings have continued to show that the snow growth
region has struggled to saturate which has limited more robust
snow showers developing as previously forecast. However, there has
been just enough moisture in the snow growth region to promote
occasional flurries as noted in recent radar and observational
trends therefore I have maintained the VCSH mention at the
Illinois sites to account for this potential. These flurries are
expected to come to an end this late this evening as drier air
filters in aloft. More robust lake effect showers have continued
to be observed across northwestern Indiana and the open waters of
Lake Michigan where soundings have shown much better saturation in
the snow growth region. While most sites along the immediate lake
shore have reported more of a rain-snow mix the thinking is that
most areas should transition over to all snow as surface
temperatures cool this evening. For that reason I have continued
the TEMPO for -SHSN at GYY to account for this potential through
late evening.
Lastly, there is also the possibility for occasional MVFR ceilings
through Tuesday morning especially in areas that experience any
showers. Otherwise VFR conditions are expected to prevail through
the TAF period with ceilings gradually scattering out Tuesday
evening.
Yack
&&
.MARINE...
Issued at 649 AM CDT Mon Oct 17 2022
Northwest gales are expected through Tuesday. The strongest gales
to 40 knots (briefly to 45 knots in the Indiana nearshore) are
expected this evening as a trough shifts across Lake Michigan.
Winds will only slowly diminish through the day Tuesday, with some
gale gusts to 35 knots remaining possible into Tuesday evening.
Kluber
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Lakeshore Flood Advisory...INZ001 until 10 PM Tuesday.
Wind Advisory...INZ001-INZ002 until 1 PM Tuesday.
Lakeshore Flood Advisory...INZ002 until 4 AM Wednesday.
LM...Gale Warning...nearshore waters until 10 PM Tuesday.
&&
$$
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