EXPLAINER: January 2009 Archives

January 2009 enters the record books as the city's 10th coldest. Its average temperature
of 15.9 degrees ties 1994 as Chicago's coldest January in 16 years. Saturday's high of
38 degrees was the month's peak reading, making it the first January since 1985 and only
the ninth since 1871 with so low a maximum temperature.
Thawing will continue Sunday, but colder air will return to the region Monday and
Tuesday on strong north winds, the western flank of a large storm system expected to charge up
the East Coast. That storm is expected to bring heavy snow to portions of the Northeast,
but the Chicago area could be the recipient of several inches of lake-effect snow as the
cold air sweeps south down the full length of Lake Michigan.
MAJOR THAW EXPECTED BY WEEK'S END
Milder weather appears headed for Chicago by the end of the week as a westerly flow of
Pacific air approaches. By Saturday highs could surge into the 40s here for the first time
since Dec. 30, bringing a chance of rain to the city.
--By Steve Kahn, WGN Weather Center Meteorologist

Chicago's coldest January in 24 years ends at midnight Saturday. With its passing,
two-thirds of the 2008-09 meteorological winter season is behind us. Its abnormally cold
temperatures have been compared for weeks to those of winter 2000-01. But by late Friday,
Chicago's average temperature since Dec. 1 slipped to 19.3 degrees. It's a decline which now
makes this winter the coldest of the past quarter century -- since 1983-84.
Friday's high struggled to 14 degrees -- one of this winter's seven coldest. The
reading was 17 degrees below normal. Clear skies and exceptionally dry air Friday sent west
suburban temperatures plummeting below zero. But this morning's warm frontal passage is to
boost highs to 31 degrees Saturday afternoon and to 35 degrees Sunday -- the mildest in 28
days.
TAMPA'S SUNDAY GAME-TIME TEMPERATURES NOT SO SUPER
Just three days ago readings peaked in the lower 80s, but in the wake of a cold front
that brought 2 inches of rain Friday night, the area's heaviest since October, Tampa's
temperatures have crashed. Readings will hover around 60 degrees at Sunday's kickoff and fall
into the 50s during the game.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

It's been the coldest January in 24 years, and the resurgence of arctic air Friday
slashes high temperatures 14 degrees from Thursday's high and delivers subzero wind- chills.
Of the month's first 29 days, 21 have been below normal -- 72 percent of them. The month's
frigid average temperature of just 15.8 degrees -- well below last year's 24.2 degrees
-- is 8.5 degrees below average and secures January a "10th coldest ranking" among the 138
Januarys on record here.
Milder air makes its move on Chicago this weekend but its encounter with the area's
snowpack will limit temperature increases. Though temperatures are to flirt with or slightly
exceed 32 degrees, it appears a virtual certainty this month will close as the first
January not to have produced an official high of 38 degrees since 1985.
An inch or more of snow has been on the ground at Midway Airport for 25 concecutive
days. The snow's impact on weekend temperatures will be profound. Projected temperature
profiles late Satur- day suggest readings will be in the low 40s in a layer 4,000 to 7,000
feet above ground -- yet only 31 degrees at the surface.
In Florida, only a week after windchill advisories, high temperatures Thursday included
Miami's 84 and Orlando's 85.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

More than 60 percent of the Lower 48 was covered with snow late Wednesday, greatest of
the past five winters. The behemoth of a winter storm which buried the Mid-Atlantic and
New England Wednesday after a deadly trek distributing ice and snow across 34 states,
contributed mightily to the nation's snowy state. The 2.4 inches -- much of it lake-effect
-- which fell at O'Hare, advanced the season's snow tally to 44 inches -- 19.1 inches
more than a year ago. It was the city's 31st measurable snow -- the third greatest to date
in 124 years. Areas downstate were reeling after more than a foot of snow accumulated.
Sumner -- on the Illinois/Indiana border near Vincennes -- was hit by 12.5 inches as was
Indianapolis where the storm was the worst in 13 years. 16 inches was reported at Grand
Valley, Penn. and more than two feet of snow was expected in New England's mountains.
Our area's heavy snowpack facilitates at least two reinforcing surges of arctic air over
the coming week -- the first to arrive Thursday night, gripping the area into Saturday
morning -- and the second to hit Sunday night and Monday. "Mild" air will make its move on
the area this weekend with rising temperatures and gusty winds Saturday night
propelling readings above freezing Sunday.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Snow at the north end of a huge winter storm lingers into morning over sections of the
Chicago area. It's fallen here at a fraction the rate of the heavy snows that began in
Downstate Illinois and Indiana early Tuesday. The half foot reported late Tuesday near St.
Louis increased to more than 8 inches to the east in Ohio -- and the snow was still
coming down hard and working east toward the Mid-Atlantic and New England States where more
than a foot is predicted by Thursday.
Snowfall overnight in portions of the Chicago area has been enhanced by some moisture
off Lake Michigan. A 150-mile long but only 10- to 20-mile wide band of snow had formed
late Tuesday over Lake Michigan. Radar indicated the so-called moisture plume of snow was
producing enhanced snowfall within a corridor from south of Ludington, Mich., to the
Chicago shoreline. The feature was produced by converging low-level winds which were
concentrating lake moisture. With computer models predicting the plume likely to remain intact into
Wednesday morning, the potential for a few spells of heavier snowfall may linger near
Lake Michigan until the feature shifts east and diminishes later in the morning.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

The southern Midwest -- including Downstate Illinois and Indiana from St. Louis to Terre
Haute and Indianapolis and south -- bears the brunt of the season's latest winter storm.
But the Chicago area isn't likely to escape the system's impact completely. Flurries
may flutter earthward near Lake Michigan at times Tuesday as light winds just above the
surface shift northeast. It's not a perfect lake snow setup -- but history shows
An upper disturbance's arrival late Tuesday is to provide the primary impetus for light
snow formation later Tuesday and Tuesday night. Projected cloud temperatures suggest the
snowflakes this system spawns will be especially fluffy, posessing nearly twice the
volume of typical snowflakes. Snowfall estimates through Tuesday night include a dusting to 1
inch in northern counties near the Wisconsin line and totals ranging from 1-2 inches for
the city and surrounding suburbs. As much as 1-3 inches may fall in southern counties and
perhaps even a few spots near Lake Michigan. By comparison, 8 inches or more may occur
in the hardest hit areas of southern Indiana with potentially serious icing either side of
the Ohio River.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Winter storm watches have been issued from Oklahoma to West Virginia beginning late
tonight and extending into Wednesday.
The Chicago area may receive 1 to 3 inches of snow, with the greater amounts far south
trending to just a trace far north.
Low pressure is expected to move east-northeast Tuesday out of Oklahoma through Arkansas
and Kentucky; on Wednesday it's poised to track over West Virginia and affect the
Northeast.
If the storm follows the path indicated, a wide band of icing could cover portions of
Missouri, Arkansas and Kentucky. Heavy, wet snow will fall north of the low, with southern
portions of Illinois, Indiana and Ohio in line for 5 to 10 inches. A band of 3- to 5-inch
snowfall would fall north of the heavier snow through central portions of those states,
with lesser totals across northern portions, including the Chicago area.
--By Paul Dailey, WGN Weather Center Meteorologist

Upper level jet stream winds will flow nearly west to east over the Ohio Valley much of
the week ahead. This will allow the southern flank of cold Canadian-source high pressure
to maintain a foothold over Chicago. Through Tuesday, high temperatures will average
nearly 13 degrees below normal, then a moderation the latter half of the week will bring the
overall 7-day high average through next Saturday to about 7 degrees below normal.
Chicago will be situated on the northernmost side of low pressure systems passing far to
the south early in the week, giving cloudiness and periodic light snow or flurries.
Brief clearing should occur on the backside of low pressure on Wednesday, then a cold front
will drop temperatures and give another round of flurries Thursday and Friday. If computer
models prove correct, a brief one-day surge of warmer air could occur next Saturday,
just in front of another cold front next Sunday.
FLORIDA WARMS UP AFTER COLD SPELL
After low temperatures dropped into the low 20s across the north, and the mid-30s in
central portions of Florida this past week (some 15 to 20 degrees below normal) readings are
expected to edge up closer to normal levels this week.
--By Paul Dailey, WGN Weather Center Meteorologist

The arctic spigot is wide open as the 8th weekend of meteorological winter dawns. The
latest blast of cold air isn't as extreme as the chill that sent Chicago temperatures below
zero for nearly 48 straight hours just over a week ago. However, it's likely to produce
the coldest weekend temperatures here in 54 weeks with much of Saturday in single digits
and nighttime lows near zero. The cold air's been so pervasive this month that January's
average temperature is running 5 degrees below normal.
The chill isn't limited to the Midwest. Floridians have shivered in recent days. Key
West's Friday morning low was 47 degrees -- a reading that shattered the old record for the
date by 5 degrees.
In Marquette, Mich., snowfall has been so frequent, the seasonal tally is at 156 inches.
Waves of heavy snow sweep the central Rockies the next four days. Totals in excess of 4
feet are possible in the mountains of Colorado, Wyoming and Utah.
NEARLY 3 WEEKS SINCE BARE GROUND
Snow first covered the ground here on Dec. 1. Since then, 40 of the past 55 days have
boasted a snow cover of 1 inch or more at Midway Airport. Chicagoans haven't seen bare
ground since Jan. 5.
--By Paul Dailey, WGN Weather Center Meteorologist

Barometer readings in the Yukon, where Chicago's weekend weather has taken form, have
soared to levels rare -- even by arctic standards. Cold air masses are so dense, it's not
unusual for pressure readings within them to surge. The atmospheric pressure at the core
of this air mass -- strengthened by a frigid cross-polar injection of bitterly cold
Siberian air the past few days -- is predicted to reach 31.40 inches (1063 mb) over northwest
Canada early Friday -- a reading far higher than Chicago's record barometer reading of
30.98 inches (1049 mb). Air masses supporting such lofty central pressures rarely sit
still -- and this one is no exception. It's frigid southern flank invaded Montana and the
Dakotas late Thursday with 40 m.p.h. wind gusts and 24 hour temperature drops of 30+
degrees. The high's move into the Chicago area is to be marked by strengthening winds Friday
that will blow haze and any morning fog out of the area, but also to send temperatures
crashing to single digits Friday night. Though not quite as cold or as windy as the
barbarically chilly air which gripped the area just over a week ago, the Yukon high threatens to
produce Chicago's chilliest weekend temperatures in 54 weeks and more snow in the
Indiana/Michigan snowbelt.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Temperatures surge above freezing for the first time in 18 days Thursday afternoon. The
timing couldn't be better. This is the day each year that Chicago's normal temperatures
begin their slow seasonal climb. A month from today, normal highs will be 7 degrees milder
and the period of daylight 75 minutes longer. Weather records reveal most years have
recorded nearly half of winter's coldest readings by this date. Still, that leaves plenty of
wintry weather to go. Almost half of a typical season's snowfall occurs beyond Jan. 22
-- something verified by the fairly active pattern expected later this weekend and next
week. Not only might snow occur Sunday, more snow is possible midweek and again late next
week.
The air mass responsible for Thursday's "warm-up" smashed records in the Plains and in
the West on Wednesday. The mercury soared to 71 degrees at Denver, 80 degrees in Phoenix
and 70 in Las Vegas.
The snow cover here cuts deeply into that warmth, forcing the mildest temperatures
several thousand feet aloft. But mid- to upper 30s are a good bet this afternoon.
The next bitter blast of arctic air roars into Chicago on Friday night, promising to
make the eighth weekend of meteorological winter among the season's coldest.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Snow fell measurably a 29th day Tuesday. It didn't amount to much at Midway and O'Hare
-- the snowfall was a lake-effect event, which meant the heaviest accumulations occurred
in lakeside areas of Cook County south into portions of Will County and east into the
Indiana lake-snow belt. The area near Porter, Ind., was socked with 9.3 inches of the fluffy
lake snow while 8 inches fell at Whiting.
The comparatively paltry 0.1 inch totals reported at the city's airports were enough to
establish one more onerous winter benchmark: becoming the first season since snow
observations began in 1884-85 with as many days of measurable snow on the books (29) through
Jan. 20. The seasonal snow tally at O'Hare is now 41.6 inches, dwarfing last season's
19.6-inch tally by 22 inches!
It's not cold everywhere. The 64-degree high Tuesday at Rapid City, S.D., set a record
there, while it was 67 degrees in Denver and 80 degrees in Phoenix.
THURSDAY'S MILD SURGE LIKELY THE WARMEST IN MORE THAN 2 WEEKS
If not for the area's extensive snowpack, Thursday's highs would surge into the low 50s
-- but the mid-30 to 40-degree readings predicted will be the warmest since Jan. 4.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

It won't last long -- but a brief break in Chicago's subfreezing temperatures predicted
Thursday may well produce Chicago's mildest reading in more than three weeks. Our
forecast of 38 degrees Thursday would be January's mildest to date. Up to now, the highest
monthly reading has been 37 degrees on Jan. 4.
The 7-inch snow cover at Midway and 8 at O'Hare -- always a factor forecasters take
seriously when predicting "warm ups" this time of year -- will take a toll on the mild air
coming this way. The incoming air mass could produce 50+-degree highs in a non-snow
Winter 2008-09 is now the coldest in 8 years and is nearly 8 degrees colder than last
year. January's chill has been even more impressive, lagging the same period a year ago by
12 degrees and coming in as the coldest in a decade. The winter season ranks 15th
coldest in 139 years and has forced Chicagoans to increase home heating an estimated 21 percent
over last winter.
Cold air resurges this weekend, and a storm system sweeping toward the heartland early
next week could be a snow producer and will have to be monitored.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

A strong north-south jet stream aloft continues to pour chilling air out of the Arctic
into the eastern half of the United States. This upper flow will shift east enough to
allow an intrusion of warmer air into the Midwest.
The southern extent of the snow cover extends from the Iowa-Missouri border through
Central Illinois into southern Indiana and then east to the Atlantic Coast. Sunlight
reflected off the white 32-degree surface works against any temperature increase. Thus, the warm
southwest flow into the Chicago area midweek will be over an expansive snowpack which
will inhibit its influence. Nevertheless, readings will reach well into the 30s on Wednesday
and Thursday. A cold front will sweep through the area Thursday night, and Chicago's
temperatures will plummet to zero by the weekend.
EVEN FLORIDA NOT EXEMPT FROM COLD
The chilling cold should push all the way into southern Florida midweek, with lows
Wednesday and Thursday mornings in the 20s across northern portions and the 30s in the central
and even southern portions of the peninsula.
--By Paul Dailey, WGN Weather Center Meteorologist

Low pressure passed well to the north of Chicago on Saturday, minimizing the fine light
snow that fell over northeast Illinois. The low center tracked further north than Friday
forecasts anticipated, and as a result the heaviest accumulating snowfall occurred along
the low center track through northern Wisconsin into central Lower Michigan. Three to
five inches of snow fell over northeastern Wisconsin and then the low intensified as it
passed over Lake Michigan into central Lower Michigan. Winter storm advisories and warnings
were in effect over Lower Michigan until early Sunday morning. As of 8 p.m. Saturday
evening, snowfalls of 4 to 6 inches were common, with 13 inches reported in Antrim County in
northern Lower Michigan and Ludington on Lake Michigan in west-central Lower Michigan.
BRIEF 'WARM-UP' MIDWEEK
Strong northerly flow from the surface up to jet stream levels will keep temperatures
below normal over northeast Illinois into Tuesday. A slight weakening of this northerly
flow will then allow a temporary intrusion of warmer air midweek, with the warm-up peaking
just ahead of a cold front Thursday. High temps Wednesday/Thursday could be 4 to 8
degrees above normal.
--By Paul Dailey, WGN Weather Center Meteorologist

Blasts of arctic air as extreme as this week's depart with all the speed of molasses in
January. The sheer density of these brutally cold air masses dictates that the
comparatively low density "mild" air replacing them must initially ride up and over the chilly air
before being mixed to the surface by gusty winds like those which greet Chicagoans
Saturday morning.
Friday morning's low of 18 degrees below zero at O'Hare was the city's coldest in 13
years. Lows of minus 18 or lower have occurred here only 30 times over the past 139
years.
Suburban lows were truly eye-catching! Sugar Grove bottomed out at minus 31. On only two
other days has a Rockford low been colder. Records there date back to 1893. A reading of
36 below in west suburban Ogle County's Rochelle was chilly enough to equal the state's
all-time low -- but the reading was on a thermometer whose calibration isn't monitored
closely enough to meet the criteria for inclusion as an official record.
Except for 20 minutes just after 11:30 a.m. Friday when the official temperature at
O'Hare crept above zero to 1 degree, the span of zero or lower temperatures reached 45
consecutive hours late Friday evening.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

It was colder Thursday afternoon in Chicago than at the North Pole -- 6 below zero here
versus 8 degrees. The day's unlimited sun had no impact on temperatures. Daytime readings
didn't rise. Minute ice crystals -- often incorrectly characterized as "steam" -- rose
from Lake Michigan. Temperatures as cold as Thursday's are extraordinarily rare here. The
day's high of 1 below at O'Hare occurred at midnight Wednesday. Of the 50,404 high
temperatures on record in 139 years of official weather observations, only 44 of them have
registered 1 below or lower.
The cold spell will ease -- but primarily Friday night as winds increase. Velocities may
grow strong enough to promote blowing snow -- especially in open areas -- late Friday
night through Saturday morning with 30 m.p.h. gusts possible.
Chicago's suburbs have experienced the area's coldest readings. Morning lows Thursday
hit 24 below at west suburban Sugar Grove and Illinois' coldest reading -- 29 below --
occurred 80 miles west/southwest of Chicago's Loop in Ashton.
'PINEAPPLE EXPRESS' WARMS ALASKA
Interior Alaska -- bitterly cold days ago -- has had local 105-degree temperature
increases to the 50s -- breaking records.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Thursday is the midpoint of meteorological winter -- a point which should offer
winter-weary Chicagoans at least some solace. The 18 inches of snow which had by late Wednesday
accumulated over a record-tying 9 consecutive days of measurable snow -- only 11.3 inches
falls in an entire January -- has provided the warmth-suppressing snowpack over which
the frigid air has invaded. Snow is extraordinarily reflective, preventing sunlight from
warming the air above.

The current air mass swept into Alaska and the Yukon from Siberia more than three weeks
ago then stalled. But, a band of warm southerly winds, extending from Hawaii into the
49th state, have dislodged the chill and sent it spilling into the Lower 48. Temperatures
within the southbound air mass plunged to 47 degrees below zero Wednesday morning in
Embarrass and 45 below in Sea Gull Lake -- both in Minnesota. It's the reason Chicagoans face
winter's coldest readings, which threaten to include a nearly 40-consecutive hour spell of
subzero readings through midday Friday. It's not the city's longest subzero streak.
That occurred over 100 hours in December 1983. Uninterrupted subzero readings haven't
occurred here over a full calendar day here since Feb. 3, 1996.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Winter 2008-09 -- the coldest in 8 years -- is to turn brutally cold the remainder of
the work week once snow exits Wednesday. Temperatures drop below zero Wednesday night and
may remain there through Friday morning, producing what could be a 58 consecutive-hour
stretch of subzero temperatures over many parts of the area. Only in the Loop and near Lake
Michigan may the mercury struggle to zero (or just above) for a brief period Thursday --
though that's not guaranteed.
A full calendar day hasn't failed to break above zero officially in Chicago since Feb.
3, 1996, when the high was 5 degrees below zero and the low was minus 19.
The snow Wednesday -- the 26th day with measurable snow this season -- is the product of
the latest Alberta Clipper. With the system's storm center tracking to the city's south,
winds just above the surface may take on an easterly component -- blowing off the lake
-- for several hours Wednesday afternoon, producing lake snow showers in addition to the
system's 1-4 inch snowfall.
21st COLDEST WINTER OF PAST 139 YEARS
The 22.4 average temperature since Dec. 1 is 7 degrees colder than the same period a
year ago.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

The powerful winds sweeping the area as Tuesday dawns have sent some of 2 to 5 inches of
fluffy overnight snow airborne. Blowing and drifting snow is to cut into visibilities
through mid-morning -- especially in open areas where occasional white-out conditions
threaten. But it's the arctic chill these winds deliver which is to become Tuesday's major
weather story while igniting lake-effect snows in sections of the Indiana snowbelt. The
chill is the first and least formidable of this week's two arctic blasts. The intense cold
that follows Wednesday night and Thursday appears especially brutal and may produce
calendar day highs that fail to break above zero for the first time since 1996. Snow with a
more intense Alberta Clipper enhanced by lake moisture Tuesday night and Wednesday
threatens another significant snowfall.
FULL SEASON OF SNOW HAS ALREADY FALLEN -- 60 PERCENT OF SNOW HERE TYPICALLY FALLS AFTER JAN.13
Though it is not even mid-January, the city has already surpassed the 124 year long-term
seasonal snow average of 36.6 inches with 37.9 inches on the books. Typically 60 percent
of the season's snow is yet to fall, so the city could be looking at its second straight
60 inch-plus snow season.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Still digging out from the weekend storm that brought up to a foot of snow to the city,
the Chicago area is bracing for three more shots of snow along with one of the coldest
arctic blasts in more than a decade.
With a polar express jet stream locked in place, a parade of storms is slated to roll
through the city this week bringing snow and severe cold.
Winter 2008-09 to date is already one of the snowiest on record, and that lofty total
should climb substantially by the end of the week. Chicago is poised to eclipse the 38-inch
total that normally falls during an entire snow season as early as Monday night.
High temperatures may fail to break zero Thursday, something not experienced here
since Feb. 2-3, 1996.
PARTS OF EUROPE ALSO REELING FROM WINTRY WOES
Severe winter weather has also been plaguing Europe in recent days. At least 12 people
have died in the cold that saw readings plunge to nearly 20 below zero in Poland and
Germany. Snow has snarled travel, and many schools have been forced to close. In southern
France, Marseilles recorded its heaviest snowfall in 20 years.
--By Steve Kahn, WGN Weather Center Meteorologist

More than a foot of snow blasted the northern portion of the Chicago area Friday and
Saturday. Officially the city reported 12 inches at O'Hare, making this the
largest snowfall here since 12 inches fell on Jan. 30-31, 2002. Snowfall totals tapered to
the south, with Midway tallying 7.9 inches. While the cleanup from this storm has just
begun, forecasters are already tracking several more snow systems. Some snow showers may
develop Sunday afternoon, but two fast-moving "clipper-type" systems promise more
accumulating snow Monday night and Wednesday.
THURSDAY COULD BRING THE CITY ITS COLDEST DAY IN NEARLY 13 YEARS
The real weather story will be the intense cold that invades the area later this week.
Temperatures will plunge in the wake of Wednesday's storm, falling well below zero by
Thursday morning. With arctic air gripping the area, Thursday's highs are expected to remain
below zero -- something that has not happened here since February 1996. Gusty northwest
winds will accompany the bitterly cold weather, sending windchills to dangerous levels of
30 degrees below zero -- or lower.
--By Steve Kahn, WGN Weather Center Meteorologist

Chicagoans dodged a bullet Friday evening. Snows, which had slashed visibilities to a
quarter mile for several hours of the morning rush -- depositing as much as 3 to 5 inches
across the northwest and north suburbs and 1 to 3 inches in the city -- paused much of
the afternoon, sparing the critical evening commute period. But by late Friday,
intensifying snowfall had visibilities in free fall, covering roads with snow as the second major
wave of snowfall in the latest storm hit. A burgeoning corridor of heavy snow extended from
Iowa across northern Illinois, featuring visibilities as low as a quarter mile --
indicating heavy snowfall.
LENGTHY FRIDAY/SATURDAY STORM
THE BIGGEST SNOW-PRODUCER YET
The final snow totals in this storm are expected to breeze by the 4.8-inch O'Hare
Airport tally recorded Dec. 16, which had been Chicago's heaviest snow this season.
Snowfall this season has been historic. The 26.5 inches on the books late Friday ranks
as the heaviest tally at this point in a snow season since 2000-01 -- and the only total
as heavy by Jan. 10 since 1980.
Another potentially significant snow could reach the area Tuesday night.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

This winter's 21st measurable snow is to be spread across 32 hours -- twice the length
of the city's most substantial previous snow this season -- and it arrives in at least two
distinct periods. Snow accumulates 1 to 3 inches in the first, enough to complicate
Friday morning's rush hour. But there are indications the snow band will shift north of the
city offering a break in snowfall, or at least a reduction to more occasional snowfall
this afternoon. But, the second wave of snowfall -- and this system's most substantial --
sweeps in later this evening and tonight and is likely to last into Saturday morning. At
that point northeast winds will have replaced Friday's southeast flow and the potential for
lake-enhanced snow showers (snow showers feeding off lake moisture) may take over into
early Saturday afternoon.
Our snowfall forecast -- 4 to 9 inches north of Interstate Highway 80, trending heavier
to the north and near the lake, and 1-3 inches with amounts trending lighter southa -- is
based on projections of 0.49 inches of water from the system which is to fluff into
about 6 inches of snow. The addition of 1-3 inches of lake snow finishes the tally.
HUGE NORTH/SOUTH TEMP SPREAD OF 85+ DEGREES IS FUELING STORM
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Measurable snow fell Wednesday for the 19th time, totaling 2 inches at O'Hare
International Airport since Tuesday and pushing the city's official tally past the 2 foot mark
(24.5 inches). The 2008-09 season is one of only five in the past 124 years in which
measurable snow (0.1-inch or more) has fallen that frequently. Over the term of official snow
records dating back to 1884, an average of 10 measurable snows has visited the area by Jan.
8 with a seasonal snow tally to date closer to 12 inches -- half as much as has fallen to
date this season. Nearly 66 percent of the city's seasonal snow typically falls beyond
this date.
While sun emerges from the clouds Thursday, an approaching weather system is to
encourage warm air to surge up and over the cold air mass predicted to remain in place into
Thursday night. That sets up another burst of snowfall Friday morning.

BLUSTERY STORM FRIDAY NIGHT INTO SATURDAY MAY TAP LAKE MOISTURE
More ominous is a Colorado low expected to track across Downstate Illinois and Indiana
Friday night and Saturday. Moisture will be available to this windy system -- including
some moisture off Lake Michigan.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

January's first accumulating snow hit Tuesday, totaling 1 inch at O'Hare Airport and 0.5
inches at Midway. More is due Wednesday. An upper disturbance due to reach the area
during the afternoon could build passing morning flurries into heavier snow showers -- any
one of which may produce a dusting to as much as 1 inch. Though a fraction of what can
happen this time of the year, these totals are enough to produce black ice -- hard to spot
slippery spots -- on area roads; caution is advised.
The winter storm behind the area's bursts of snowfalls is actually treating the Chicago
area comparatively kindly. Not so lucky are sections of 23 states to the east and south,
where thundery downpours are initiating flooding in the system's warm section, ice
accumulating in the mountains of Pennsylvania and significant snows likely to cripple sections
of northern New England and Canada's St. Lawrence Valley.
RARE JANUARY TORNADOES HIT IN 65-DEGREE WARMTH A YEAR AGO
Unseasonable warmth produced a rare mid-winter severe weather outbreak a year ago,
including tornadoes in Poplar Grove and Harvard in Illinois and Pell Lake and Paddock Lake in
Wisconsin.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

A period of light snow targets the Chicago area late Tuesday and Tuesday night,
threatening the first modest accumulations here in over a week. The ground's been free
of a 1-inch or greater snow cover for 11 days despite a seasonal snow total to date of
22.5 inches—an amount that is 176 percent of the "normal" tally and above last year’s
18.7 inches to date. At least an inch of snow has been on the ground 22 days this
cold season—ahead of average of 14 days through Jan. 6 over the past 15 years but
behind last years 26 days. The figure falls far short of the 41 days with 1 inch or more
of snow on the ground by this date in the record 1978-79 snow season. The brunt of
Tuesday’s storm will pass to the south and east of Chicago, with 15 states under some
form of winter weather advisory.

SEASONAL SNOW TOPS 120 INCHES ACROSS UPPER MICHIGAN--AND MORE COMING
Low pressure systems will produce almost continuous snowfall the later half of the
week. Several inches of new snow will add to already enormous seasonal tallies.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Chicagoans will experience a "normal" January day today -- if there is such a thing.
High temperatures rise into the upper 20s, and that's pretty close to the climatological
expectation of 30 degrees on this date.
With seasonably cold air already in place, the next storm system is to be a
snow-producer for Chicago, but a dicey forecast situation is shaping up. The approaching low pressure
system will have tapped moisture from the Gulf of Mexico and therefore has the potential
to generate copious snow totals along and just to the northwest of the path of its low
pressure center. That path is expected to extend from Louisiana to Ohio and then northeast
into New England. Best estimate is that the Chicago area will see snow but remain
northwest of the belt of greatest snow accumulations (across central Illinois and northern
Indiana) late Tuesday into Wednesday morning.
LATE-WEEK SNOW AND ARCTIC BLAST
Another accumulating snow is possible Friday, followed by a powerful surge of air of
arctic origin. That means the weekend's nighttime temperatures are likely to be near or a
few degrees below zero. Chicago logs 10 subzero lows in an average winter.
--By Richard Koeneman, WGN Weather Center Meteorologist

It may seem counterintuitive to Chicagoans but, in its annual orbit of the sun, the
Earth actually passes closer to the sun during winter and swings farther from it during the
summer. It is a misconception that winter is cold because of the greater distance from the
sun this time of the year.
Astronomers refer to the point of the Earth's closest passage to the sun as perihelion,
and it occurs at 9 a.m. Monday when the Earth-sun distance shrinks to 91.3 million miles.
That's about 3.1 million miles closer to the sun than at aphelion (the point when the
Earth is farthest from the sun, in early July). On average, the Earth-sun distance is 93.0
million miles.
Chicago's winter temperatures average about 45 degrees lower than in summer, and
seasonal temperatures are little affected by the Earth's varying distance from the sun. Winter
is cold because the Northern Hemisphere tilts away from the sun at that time of the year.
TUESDAY-WEDNESDAY STORM
The next winter storm arrives at Chicago with snow, potentially heavy, beginning Tuesday
afternoon. Accumulations of at least a few inches are likely before snow diminishes to
flurries late Wednesday.
--By Richard Koeneman, WGN Weather Center Meteorologist

Low pressure is forecast to track over Chicago this weekend. Temperatures will rise
slowly, reaching the lower 30s later this afternoon at about the same time rain spreads in
from the southwest. Some areas, especially north of the city, may experience a period of
freezing rain at the start, becoming all rain later in the evening.
Widespread freezing rain will occur farther to the north, with heavy snow expected
across northern Minnesota, Wisconsin and upper Michigan.
Rain will diminish and briefly change to snow flurries before ending early Sunday.
HEAVY SNOW AND COLD MIDWEEK
An upper-air disturbance will usher snow-producing low pressure through the Midwest
midweek with snow beginning later Tuesday in the Chicago area and continuing through
Wednesday before ending Thursday. Accumulations are likely with this storm, but the latest
forecasts place the heaviest snow well to the south and east of Chicago.
A strong northwest flow at the jet-stream level will steer arctic cold high pressure
into the northern Plains and Midwest Wednesday, and then persist over Chicago the remainder
of the week.
--By Paul Dailey, WGN Weather Center Meteorologist

The last significant weather event to hit the Chicago area was the heavy rain of Dec.
27. Since then, the city has logged six consecutive days (including today) of relatively
tranquil weather.
Experience has taught Chicagoans that interludes of placid winter weather of that
duration are likely to end with a splash -- or a snow shovel. That's true of the situation at
hand. Two distinct storm systems have Chicago in their sights.
Gathering cloudiness on Saturday heralds the arrival of the first system -- a rather
mild event that brings light rain, possibly beginning as a period of freezing rain, by
Saturday evening.
BIG SNOW AHEAD?
The second system is the one to watch. It's to be the more energetic of the two, and
much colder as well.
Approaching from the south-southwest and dripping with moisture from the Gulf of Mexico,
it has the potential to put several inches of snow across the Chicago area Tuesday
afternoon into midday Wednesday, then frigid arctic air arrives in its wake. That cold air
will be accompanied by strong northwest winds and subzero windchill temperatures.
--By Richard Koeneman, WGN Weather Center Meteorologist