Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/09/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 538 PM CST Tue Feb 8 2022

.SHORT TERM...
Issued at 100 PM CST Tue Feb 8 2022

Through Wednesday night...

Mostly sunny skies and a relative dry airmass characterized by
surface dew points in the lower 20s has allowed for temperatures to
warm nicely this afternoon with readings ranging from the mid to
upper 30s in snow-free areas to around the freezing mark elsewhere.
A stout low-level inversion remains in place with recent AMDAR
soundings depicting a roughly 20F temperature rise from about 500
to 1500 feet. The inversion continues to prevent a 35-45kt southwesterly
low-level jet from fully mixing downward, though occasional gusts
in the 20 to 25 mph continue across the area. All things
considered, it`s a nice day out there!

Upper-level clouds will increase this evening ahead of a sharp upper-
level shortwave and associated surface cold front currently
stretching from eastern Minnesota to central Iowa. While the clouds
shouldn`t be as thick as last night, radiational cooling will be
stunted somewhat with overnight lows expected to fall into the upper
20s. The cold front will sweep across our area toward daybreak,
though precipitation potential appears fairly low owing to a dry low-
level airmass. For example, cloud bases along the front in Iowa
right now are greater than 10kft which is typically too high for
even a flurry to survive the trip to the ground. Behind the front,
increasing mixing aided by CAA will lead to breezy west winds during
especially north of I-80 where the snowpack isn`t as deep. Highs
tomorrow should top off in the low to mid 30s.

As a secondary shortwave anchored by 700mb temperatures of -16C
currently located in northern North Dakota pinwheels southeastward
into the Lower Great Lakes Wednesday evening, low-level lapse
rates will steepen leading to an expansion of low-level stratus.
Snow showers appear poised to develop in scattered fashion in
response to DCVA and cooling mid-level temperatures toward
sunset. As is often the case with compact waves in cyclonic flow
aloft, the greatest snow shower coverage will hinge on exactly
where the wave tracks. For now, areawide 20 to 30% PoPs appear
areawide. Snow accumulations beyond a localized dusting appear
low owing to marginal surface temperatures. Snow showers should
taper to flurries toward midnight as low temperatures drop toward
the lower 20s.

Borchardt

&&

.LONG TERM...
Issued at 309 PM CST Tue Feb 8 2022

Thursday through Tuesday...

A positive PNA type upper level pattern featuring enhanced
northwesterly flow aloft across the central CONUS is expected to
persist into this weekend. The pattern looks to drive at least two
additional quick moving clipper type storm systems across the
Great Lakes through Monday. Each of these clipper systems are likely
to result in a couple windows for precipitation in our area, and
will bring reinforcing shots of cold Canadian air to the region.
Thereafter, model and ensemble guidance continue to suggest that
the larger scale pattern may transition back into a more active
negative PNA type pattern (upper level pattern with enhanced
southwesterly flow aloft over the central US) for next week.

Thursday is expected to be a chilly day (highs in the 20s) as we
get clipped by a colder airmass shifting into the area in the wake
of Wednesdays clipper. However, another strong clipper system
(central pressure around 990 mb) is expected to rapidly shift
southeastward into the Upper Great Lakes by early Friday morning.
Strong pressure falls in advance of this system will result in a
increase in south-southwesterly winds (30 to 35 mph gusts) across
the area late Thursday night. Surface temperatures will thus
likely bottom out early Thursday evening, then begin to rise
overnight, with readings likely peaking around 40 degrees Friday
afternoon.

The primary track of the surface low will remain well north of
the area into Friday. This is not typically a track that favors
much snow accumulation for the area. However, there appears to be
good support amongst the forecast guidance that we will see a
period of accumulating snow late Thursday night into Friday
morning. The most notable aspect that supports this idea is the
deep and strong isentropic upglide forecast across the area
beneath the favorable exit region of an upper level jet streak
digging into the Upper Midwest. Good forced ascent in this regime
would support a rapidly moistening column with ample low to mid
level moisture. The threat of accumulating snow may only persist
for a few hours, through mid morning Friday, but with the snow
potentially falling at a high rate in the morning, we could see
accumulating snow impacting the Friday morning commute across
northern IL and northwestern IN. I continued the trend of
increasing POPs and snow amounts during this period.

The snow may end, or begin to mix or change to light rain Friday
afternoon as drier mid-level air works into the area and surface
temperatures warm through the 30s, so travel conditions should
improve with time during the day. A strong cold front will then
sweep eastward across the area Friday evening, with gusty
northwest winds (35+ mph) developing in its wake. This will help
usher in a much colder airmass Friday night and Saturday. Surface
winds should ease through the day Saturday as a cold Canadian
surface high builds into the area, but high temperatures will
only been in the upper teens to low 20s. Aside from the
possibility for some lake effect snow into parts of Porter county
IN and points east, most areas should remain precipitation free on
Saturday. Winds look to remain light across the area Saturday
night, and if cloud cover remains low, we could see temperatures
fall below zero in some of the favored areas.

Temperatures should moderate a bit, back into the low to mid 20s,
on Sunday as another clipper system approaches the area.
Depending upon the exact track this system takes, we could
experience yet another quick round of accumulating snow sometime
late Sunday or Sunday night. A brief cold shot then moves into the
area on Monday, but a larger scale pattern change early next week
should allow temperatures to warm back to around freezing for
highs by Tuesday.

KJB

&&

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

Aviation Forecast Concerns:

* Brief period of LLWS conditions for Chicago terminals early this
  evening.

* Blustery west-southwest/west winds Wednesday afternoon/evening.

* MVFR ceilings and a potential for flurries/light snow showers
  late Wednesday afternoon and evening.

Surface low pressure will move slowly across the northern Great
Lakes region through the period. A pair of cold fronts will push
across the forecast area in association with this low, the first a
relatively weak one this evening, then a second stronger one with
an accompanying mid-level disturbance later Wednesday. The first
front will bring a wind shift from southwest to west-southwest
overnight and a period of VFR ceilings in the 100-150 level. Low
level moisture will gradually increase early Wednesday ahead of
the second front, which is expected to result in development of
MVFR ceilings by late morning/midday. Winds will also gradually
increase, with gusts from 250-260 degrees near 20 kts expected by
midday and eventually increasing into the 25 or a bit higher range
by late Wednesday afternoon and evening. Westerly winds will
likely continue to gust at 25 kts or so into Wednesday night.

With the increasing low level moisture and approach of the
aforementioned mid-level disturbance, chances of at least some
spotty light precipitation will increase by mid-late afternoon
across the area. While a few spits of rain/sprinkles can`t be
ruled out early, mainly flurries or light snow showers are
expected as the column cools and moisture becomes deep enough to
support precipitation. Steepening low level lapse rates and cloud
tops reaching into the preferred snow-growth region may support
20-30 percent coverage of isolated snow showers with MVFR or
high-end IFR visibilities, and perhaps a dusting of accumulation
in some spots.

Ratzer

&&

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

$$

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