Weather Update for Chicago Area Wednesday, November 8, 2017 Cold with a Chance of Snow Friday and Saturday.

billmoranshow

 National Weather Service

Wednesday

A high pressure ridge continues to camp out in most of the midwest, bringing clear skies but bitter cold nights. Today Wednesday will be sunny with the highs in the mid 40s and winds will be calm 5-10 mph. Wednesday night temperatures start to go further south, dipping into the lower 30s. Time to get out the down comforters! Thursday a surface low pressure will being to enter the upper great lakes bringing cold north air. Daytime temperature to reach mid 40s, partly sunny with surface winds picking 15-20 mph with gust up to 30 mph as low pressure moves into the are. Thursday night will be bone chilling, hide under the comforter, stoke up the fire, snuggle with someone… or a your dog if their is no one to snuggle with, cold. Just be sure to brush your dog’s teeth before snuggling because of the breath thing. No one wants that. Then again some humans..same breath thing…so ask whoever you snuggle with to brush their teeth... Thursday nighttime temperatures will dip to 16 with a nasty wind out of the north at 20 mph gusting up to 30 mph. Friday and Saturday cold with highs in the mid 30s to low 40s, cloudy with 30% chance of….wait for it…flipping snow!  Sorry about that, but what do you want me to do about it? Stay warm!
Today
Sunny. Highs in the mid 40s. Northwest winds 5 to 10 mph in the morning shifting to the southwest in the afternoon.
Tonight
Clear in the evening then becoming partly cloudy. Lows in the lower 30s. Southwest winds 10 to 15 mph.
Thursday
Partly sunny in the morning then clearing. Blustery. Highs around 40. Then temperatures falling into the lower 30s by evening. Northwest winds 15 to 25 mph with gusts up to 30 mph.
Thursday Night
Clear in the evening then becoming partly cloudy. Lows 15 to 19 in the suburbs…but in the lower 20s downtown. North winds 10 to 15 mph. Gusts up to 30 mph in the evening.
Friday
Partly sunny. A 30 percent chance of snow showers in the morning. Highs in the lower 30s. Northeast winds 5 to 10 mph in the morning becoming east in the afternoon.
Friday Night
Partly cloudy. Lows in the mid 20s.
Veterans Day
Mostly cloudy. Highs in the upper 30s.
Saturday Night
Mostly cloudy. Light rain likely in the evening, then light rain and light snow likely after midnight. Lows in the lower 30s. Chance of precipitation 60 percent.
Sunday
Mostly cloudy. Light rain and light snow likely in the morning, then a chance of light rain in the afternoon. Highs in the lower 40s. Chance of precipitation 60 percent.
Sunday Night Through Tuesday
Partly cloudy. Lows in the mid 30s. Highs in the 40s.
 Detailed Weather Discussion from the NWS Chicago Office

Through tonight...

Surface high pressure ridge stretches from the Central Plains to
the southern Great Lakes region early this morning, with clear
skies and nearly calm winds resulting in chilly low 20` to low
30`s temps over most of the forecast area. The surface ridge axis
will drift south across the cwa through this evening, continuing
to provide clear skies and eventually light southwest winds. Low
level model thermal progs support high temps from the mid-40`s
north to the upper 40`s south, which appears reasonable given
plenty of sunshine.

Strong short wave associated with 120+ kt upper level speed max
is progged to dig southeast from the Canadian Rockies later today,
resulting in amplification of an upper trough across the Upper
Midwest and western Lakes region tonight. This will result in
development and deepening of surface low pressure over the
northern Lakes by early Thursday, and the approach of a strong
cold front. Through tonight, this will manifest as an increase in
mid-high clouds tonight ahead of the short wave and surface front,
with southwest winds ahead of the front producing steady or
slightly rising temps late tonight with lows around 30/low 30s
occurring during the evening in most areas. Precip should remain
north of the forecast area, with dry low level air in place here
and stronger forcing cross WI/MI closer to the track of the
digging vort max.

.LONG TERM...
330 AM CST

Thursday through Tuesday...

The main concern is the potent early season cold shot that will
pour into the area on Thursday and result in the coldest
night/early morning of the season thus far to start Friday,
followed by highs only in the 30s on Friday. The cold air mass
over the still mild lake waters will likely result in lake effect
snow showers moving into portions of the area late Thursday night
and then pivoting westward Friday morning before ending.

The Arctic front will quickly sweep across the area during the
morning. Have maintained a dry forecast for the frontal passage,
but would like to note that high-res 3km NAMnest simulated
reflectivity does indicate potential for spotty shower activity.
The air mass will be quite dry, but with short-wave forcing from
stout trough digging into the Great Lakes accompanying the cold
front, may add precip mention before sending zones for areas
mainly north of I-80 or pass concerns to day shift. If pockets of
saturation occur to allow precip to reach the surface, it would
likely be in the form of snow given below freezing wet bulb temps
and the whole column except for lowest levels below freezing.

Low-level cold advection will ramp up in earnest during the
afternoon behind the front driven by northwest winds gusting up to
25-30 mph. Thus after mid-day early afternoon highs in the mid 30s
to around 40 north of I-80 and lower to mid 40s south of I-80,
temperatures will sharply fall during the afternoon. 850 mb
temperatures will fall to as low as -15 to -17 Celsius by the late
evening across far northern Illinois, which is very impressive
cold this early in the season (colder than daily max for November
10th for DVN RAOB).

Strong Arctic high pressure of 1037-38 mb will move into the
western Great Lakes during the night, enabling north winds to
drop off away from Lake Michigan. Combined with extremely low dew
points in the single digits, anticipated radiational cooling
effect with low level cold advection added in should support low-
mid teens outside of Chicago (MAV/MET guidance is even a bit
colder than this in spots) along and north of I-80 and upper
teens to lower 20s south, with perhaps mid 20s along immediate
Indiana shore. While north winds will be fairly light inland, they
will be enough (5-10 mph) to drive minimum wind chill values into
the lower to mid single digits above zero in parts of northern
Illinois outside of the city. This is something to definitely keep
in mind when getting the kids ready for school early Friday.

The extremely cold air mass over a lake with water temperatures
still in the lower 50s will set the stage for the development of
lake effect snow showers Thursday night. As low level flow turns
north and then north-northeast late in the night into early
Friday, an at least loosely organized band will pivot into
northwest Indiana. Inversion heights/equilibrium levels will be
less than ideal at less than 7kft along with very dry air in upper
parts of the DGZ, but the thermodynamics will be quite impressive
with 850 mb to lake delta Ts of 20-25 Celsius and lake induced
instability of up to 500 j/kg.

Therefore, am becoming increasingly confident that the lake effect
snow showers will affect parts of the area near the lake, with the
cold temperatures also potentially supporting minor accumulations.
The uncertainties with the setup include possible mesolow
development and the question of how quickly the band pivots west
and then dissipates over northeast Illinois later in the morning
with flow turning from northeast to east-southeast. Outside of
the lake effect snow potential, despite the cold air mass starting
to lose its grip aloft, very cold highs in the lower to mid 30s
are forecast for Friday, compared to low 50s that are normal for
November 10th.

After another chilly but not nearly as cold night Friday night
with high pressure starting to depart, the models continue to
struggle with handling the pattern over the weekend. Guidance has
trended toward the idea of the ECMWF and its ensembles of the
first northern stream wave and surface low shearing
out/dissipating on Saturday, which means Saturday is now likely to
be dry. A short-wave trough arriving on the northern California
coast Friday evening will eject east and could be the impetus for
precipitation Saturday night through Sunday. Confidence is low on
the evolution of this wave, including with precipitation types
(though rain is currently favored by Sunday afternoon), but the
main message is that Saturday is now appearing to be the better
day of the weekend. A relaxation in the cold pattern is probable
next work week per ensembles.
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