Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/15/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 824 PM CST Mon Feb 14 2022

.UPDATE...
Issued at 824 PM CST Mon Feb 14 2022

Had made some updates to near-term forecast earlier in the
evening to account for lingering low cloud cover over primarily
northeast IL. These low clouds will likely continue to drift
slowly east- northeast through late evening, trapped beneath
subsidence inversion noted at around 875 mb per recent aircraft
descent soundings from ORD and MDW. Have even recently received
reports of some flurries in the vicinity of ORD, possibly
generated/assisted by aircraft exhaust within the saturated layer
with temps around -12/13C favorable for dendrite formation. These
are highly localized and are not expected to be impactful or
accumulate. With persistent cloud cover this evening over
northeast IL have also adjusted hourly temp trend to maintain
slightly milder readings beneath the overcast.

Otherwise, mostly clear to partly cloudy conditions over the
remainder of the forecast area this evening, though high clouds
will increase from the west overnight as warm advection increases
aloft. Temps will vary with the cloud cover, potentially dipping
into single digits in a few spots but largely in the teens across
much of the area overnight.

Updated digital/text forecast products already available.

Ratzer

&&

.SHORT TERM...
Issued at 218 PM CST Mon Feb 14 2022

Through Tuesday night...

Currently, a 1032 mb surface high pressure system is located along
the ND/MN borders northwest of a surface pressure col approaching
the Lower Great Lakes. Broken mid-level clouds continue to clear
from northwest to southeast, only to be replaced by shallow diurnal
stratocumulus clouds. Temperatures are in the low to mid 20s and
winds are light.

Tonight, our area will be along the southern periphery of the
aforementioned surface high pressure system allowing for winds to
relax. Lows tonight should stall somewhere in the teens thanks to
increasing upper-level cloud cover from the Dakotas, though lower
readings in the upper single digits are certainly fair game should
cloud cover end up less than currently advertised. By daybreak
Tuesday, the high pressure system will be more or less entering
southern Ontario leading to a increasingly packed pressure
gradient and WAA regime in the western Great Lakes. Accordingly,
Tuesday will feature increasing clouds and breezy southeast winds.
Daytime temperatures will gradually warm into the mid-30s by
early afternoon, though it`ll feel chillier with the wind.

The upper-level pattern will undergo a fairly energetic transition
Tuesday night as a bowling-ball trough currently along the Pacific
coast curves around the base of the Rocky Mountains affording the
development of an impressively strong low-level jet across the
Mississippi River Valley. Winds at 2000 feet are progged to increase
to 60-70kt after sunset which, in spite of a WAA regime resistant to
downward motion, will lead to gusty southerly surface winds (25 to
35 mph). With the Gulf of Mexico wide open, the persistent southerly
flow will will pump warm and moist air into the Great Lakes allowing
temperatures to warm into the lower 40s by midnight Wednesday
(though it won`t feel so toasty with the gusty southerly winds).
Precipitation chances will increase thereafter, as described in
the Long Term Discussion below.

Borchardt

&&

.LONG TERM...
Issued at 340 PM CST Mon Feb 14 2022

Wednesday through Monday...

Plenty to unpack for the midweek forecast as a multi-faceted
event, potentially significant in some aspects, will impact the
area Wednesday night into Thursday. Forecast certainty is on the
higher side for the first half of this event, and then diminishes
through the latter half. Key messages are:

* Widespread rainfall, at times heavy, on Wednesday night into
  Thursday that will likely result in some ponding and possibly
  greater hydrologic issues

* High confidence in a transition to a mix and eventually snow
  happening from north to south across the area overnight
  Wednesday and Thursday morning into early afternoon

* Likelihood of some snowfall accumulation on Thursday, but how
  much of the area and where the heaviest rates occur remains with
  higher uncertainty that is usual for 2.5 to 3 days out (i.e. the
  spectrum of possible outcomes here is large!)

* Travel impacts to the Thursday morning commute are likely, and
  there may be travel impacts, possibly significant if tandem
  heavy falling snow and strong winds, through the entirety of the
  daytime for some of the area

The main synoptic players for this time period have remained
unchanged in the forecast analysis. By Wednesday morning, the
northern stream low of sub-1000 mb will be scooting eastward
across Ontario with a strong low-level jet over our region.
Increasing isentropic ascent within this over our region will
eventually lead to rain expanding during the afternoon. Despite
the stratus, temperatures should continue to inch up through the
mid and upper 40s with probably some lower 50s in parts of the
area Wednesday afternoon.

Wednesday night continues to look like the main rainfall time for
much of the CWA. A pronounced coupled upper jet structure with
the split stream is over the forecast area and will result in a
50-55 kt low-level jet. This will be aided by the southern stream
closed low in the New Mexico area Wednesday evening beginning to
translate east-northeast. The peak moisture transport/
replenishment and moisture convergence is during Wednesday night,
with precipitable waters of 0.7-1 inch from north to south, which
is in the top 5th percentile for this time of year. Warm cloud
processes are noteworthy for February for efficient rainfall, and
some embedded thunderstorms are possible south. One possible
"failure mode", at least in terms of receiving a large footprint
of >1.5" of rain, would be disruption to moisture transport by a
large footprint of convection to the south-southwest. Because of
the strength of the upper forcing, do not think this will be a
huge issue, and just may result in the heavy rain axis focusing
more south of I-80 in time through Wednesday night. Have leaned
that way with WPC and have 1.5-2.5 inches south of I-80 with
highest totals far south. Because of the antecedent frost depth,
at least minor flooding potential will be a concern. Also with ice
in the river basins and flooding from any break-up ice jam
potential too, an ESF will again be re-issued here.

The low-level baroclinic zone/cold front will be shifting
southeastward through the area Wednesday night and Thursday
morning as strong high pressure of 1035 mb across the Northern
Plains expands southeastward. This will be undercutting the
moisture transport allowing for a mixed phase transition with
warm, melted hydrometeors falling into a colder layer. This layer
will initially be near-surface and favor a period of freezing rain
shifting southeast. Eventually as the southern stream wave
approaches, deepening low pressure Thursday morning near/over
southern Missouri will favor more of a northeasterly low-level
wind. The deepening low-level cold layer could favor sleet and
also for a longer period than is typical to see sleet. Specifics
on precipitation type in this expected mixed phase is a challenge,
as well as the timing of transition to snow. In the camp of
northwest model solutions, there is a lengthier period of
freezing rain and/or sleet across the southeast half of the
forecast area much of Thursday morning. That could cause more ice
accumulation to >0.2 of an inch and more impacts as winds
increase.

Two model "camps" remain with this Thursday portion of the
forecast, with the GFS and its ensemble, the NAM, as well as a
handful of ECMWF ensemble members, to the northwest. This results
in a more appreciable snowfall over our northwest 2/3 of forecast
area, including all the metro, and icing to the south. The GEM
and to a slightly lesser degree the ECMWF remain progressive and
have consistently been so, with appreciable snowfall limited more
so to our southeast forecast area, and little to none in the
northwest. It remains difficult to favor one camp over the other,
and there is still very much a window for a middle solution, with
the 18Z NAM trended a bit more towards (deep low, but a bit
further southeast). The magnitude and speed of the low pressure
will be key too, as that will drive just how strong the winds are.

No matter the solution, enough cold air will be filtering in to
provide a transition to snow and at a rate for accumulating, wet
snow for part of our area Thursday morning. Model soundings from
the snow profile areas show copious moisture for an all snow
event (precipitable waters 0.4-0.7 and mixing ratios in the lift
layers of >5 g/kg). So it could easily be "pouring snow" where
this is occurring, and thus if there are particularly strong
winds (gusts >35 mph) such as shown the deeper model solutions,
this could be a period of dangerous travel. On the slower, deeper
solutions, snow would not end for most areas until later day or
early evening Thursday, with some potential for lingering lighter
lake effect into northwest Indiana Thursday night.

With the still dichotomy of solutions, it`s difficult to
communicate forecast snowfall amounts with this system, let alone
with many of our systems three days out. An area of 6+ inches of
snow could easily materialize with the rate potential, but where
and how wide of an area are all largely dependent on what the
track and speed of the low are. Just as plausible of a solution is
less than an inch of snow. Unfortunately, that level of
uncertainty is equal across the CWA at this time. Hopefully with
the southern stream system getting onshore tonight, it can
possibly help narrow in the solution corridor more.

Little changes made beyond. Looks breezy Friday night, and
possibly again on Sunday, but both with systems passing to our
north and do not look to provide precipitation for here.

MTF

&&

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

Primary aviation forecast concerns:
 * MVFR stratus this evening, possibly persisting overnight
 * Increasing SE winds through the day with sporadic gustiness in
   the afternoon
 * Strong low-level jet (LLJ) develops overnight Tuesday resulting
   in low-level wind shear (LLWS) concerns

An area of MVFR stratus was able to hold on this evening and has
been inching east into the Chicago area terminals over the past
hour. Confidence in how long cigs remain at or just below 3000ft
is on the lower side. For now expect this to persist through
midnight tonight, but it is possible it lingers beyond that.

Meanwhile winds will continue to ease,becoming light and variable
to near calm overnight. After sunrise, winds favor a southeast
direction and increase in speed through the day in the 12-16kt
range. There is also the potential for sporadic gustiness in the
afternoon and early evening. Winds begin to turn southerly toward
the end of the 30-hr TAF period.

By Tuesday evening the LLJ begins ramping up beginning a long
duration period of LLWS concerns for all area terminals. Current
TAFs have this up to 55kt but suspect this speed will trend higher
once more overnight hours are included in the TAF period. Surface
wind speeds also increase accordingly along with the potential
for gusts in the 25-30 kt range.

Petr

&&

.MARINE...
Issued at 218 PM CST Mon Feb 14 2022

As a trough deepens in the southern United States Tuesday night, a
strong 60 to 70 kt southwesterly low-level jet will develop into
the western Great Lakes leading to a prolonged period of gale
force winds within the Lake Michigan nearshore waters. The cold
waters of Lake Michigan will likely lead to a stout stable layer
through which the LLJ may struggle to penetrate, though any
elevated surface such as pilot houses of ships or the tops of
lighthouses will likely endure southwesterly gale force winds in
excess of at least 35 kt through much of Wednesday. Based on the
southwesterly wind trajectory, the largest waves will be directed
away from the Illinois and Indiana nearshore waters. After
collaboration with NWS Milwaukee, have issued a long-duration Gale
Watch from sunset Tuesday to sunset Wednesday.

A second period of gale-force winds, potentially to 45 kt, and
waves greater than 12 feet may materialize during daylight hours
Thursday as a surface low pressure system lifts into the Ohio
River Valley. These winds will be from the north-northeast.
Depending on the exact strength and track of the low, a few storm
force wind gusts to 50 kt and waves greater than 15 feet cannot be
ruled out. At this point, confidence in the 2nd period of gale
force winds is not high enough to warrant inclusion into the Gale
Watch though adjustments may be needed in later forecast packages.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Watch...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...6 PM
     Tuesday to 6 PM Wednesday.

&&

$$

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