By Meteorologist Tom Skilling
This winter's mild temperatures have been SO unusual, it's been possible to quantify the warmth in myriad ways. But, here's a measure of the degree warmth we've experienced this season which hasn't yet been explored.
Only once BEFORE since official Chicago weather records began in 1870, has a winter's lowest temperature to date been as mild or milder than this year's minimum of 5-degrees by now.
By this time a year ago, nighttime lows had even managed to sink below zero twice, reaching 6-below on Feb. 3 and 4-below on Jan. 21.
No such reading has occurred at the official observation sites in the city this season. Chicago's official low temperature has yet to sink to 0-degrees---let alone below the benchmark reading. The coldest readings to date has been 5 above on Jan. 19-20.
It's not at all common for Chicago to make it through a cold season without a sub-zero reading. The last time that happened here was in 1982-83. Only 12 such seasons are on the books since records began here in 1870.
It's too early to conclude we've escaped "zero-free" just yet. The latest an official 0-degree temperature has occurred in the city was March 22, 1888 when Chicago's official temperature slipped to 1-below!
Monday's 33-degree high the coldest daytime reading here in 8 days
A sun-obscuring stratus deck became trapped beneath a "temperature inversion" here Monday. Temperature inversions---which occur when warm air sits on top of a shallow cold air layer---are common in meteorology. They thwart vertical air movement---a phenomenon referred to as "mixing" by meteorologists. As a result, clouds become trapped over an area rather than "mixing out", a situation which defeated warming here in Chicago and led to the area's coldest high temperature of the month and of the past 8 days.
The impact of these clouds is clear when Monday's high temperatures north of Chicago in Wisconsin are examined. There, because of sunshine which resulted from clearing skies, temperatures surged into the 40s.
First and weakest of the coming week's two cold surges to ride Tuesday's "northeast" winds into the area; stronger cold surge later this week
Tuesday's northeast winds deliver the week's first cool surge out of Canada. The second and, by far, strongest of the two arrives later this week. That late-week air mass could prove downright chilly since it's to be the product of a surge of cold air riding steering winds aloft across the North Pole from the Eurasian continent (Europe and Russia).
That cold spell is to mark the first time a lobe of frigid air off the deadly European/Russian cold wave is to cross the North Pole and descend into eastern North America, affecting the Midwest. It's likely to bring Chicago one of its chilliest set of days to date.
The intensity of the incoming late week chill combined with a flow off Lake Michigan could set up snowy spells Friday and Friday night capable of producing some sticking snow. We'll keep you posted on that.
The 2011-12 season's paltry 13.9 inches of snow ranks 35th lowest of the past 127 years; it's just 28 percent last year's tally to date
Just how unusual is receiving only 13.9-inches of snow through Feb. 7? VERY UNUSUAL! Nearly four times as much had fallen by this time last winter---and the tally this season is just 61 percent normal!
For the record, approximately a third of Chicago's seasonal snow has historically fallen beyond this date---not an unsubstantial amount!
Comparably "snow-starved seasons" through this point in winter have seen February snowfall turn around in 3 of 10 years
This winter's Chicago area snowfall has been so limited, a number of our readers, including many who plow snow for a living and others who enjoy outdoor sports which require a cover of snow, have asked if we can quantify the chances for additional snowfall. In other words, have these "low-yielding" seasons turned around in the past---and, if so, how often.
To answer this, my colleague Richard Koeneman identified ten winters with comparably little snow by this date----then analyzed the snow which fell in those years from Feb. 7 forward. He found 3 of 10 comparably low "snow-yielding" seasons saw snowfall the remainder of February turnaround and fall at rate faster than the historical norm.
This winter's mild temperatures have been SO unusual, it's been possible to quantify the warmth in myriad ways. But, here's a measure of the degree warmth we've experienced this season which hasn't yet been explored.
Only once BEFORE since official Chicago weather records began in 1870, has a winter's lowest temperature to date been as mild or milder than this year's minimum of 5-degrees by now.
By this time a year ago, nighttime lows had even managed to sink below zero twice, reaching 6-below on Feb. 3 and 4-below on Jan. 21.
No such reading has occurred at the official observation sites in the city this season. Chicago's official low temperature has yet to sink to 0-degrees---let alone below the benchmark reading. The coldest readings to date has been 5 above on Jan. 19-20.
It's not at all common for Chicago to make it through a cold season without a sub-zero reading. The last time that happened here was in 1982-83. Only 12 such seasons are on the books since records began here in 1870.
It's too early to conclude we've escaped "zero-free" just yet. The latest an official 0-degree temperature has occurred in the city was March 22, 1888 when Chicago's official temperature slipped to 1-below!
Monday's 33-degree high the coldest daytime reading here in 8 days
A sun-obscuring stratus deck became trapped beneath a "temperature inversion" here Monday. Temperature inversions---which occur when warm air sits on top of a shallow cold air layer---are common in meteorology. They thwart vertical air movement---a phenomenon referred to as "mixing" by meteorologists. As a result, clouds become trapped over an area rather than "mixing out", a situation which defeated warming here in Chicago and led to the area's coldest high temperature of the month and of the past 8 days.
The impact of these clouds is clear when Monday's high temperatures north of Chicago in Wisconsin are examined. There, because of sunshine which resulted from clearing skies, temperatures surged into the 40s.
First and weakest of the coming week's two cold surges to ride Tuesday's "northeast" winds into the area; stronger cold surge later this week Tuesday's northeast winds deliver the week's first cool surge out of Canada. The second and, by far, strongest of the two arrives later this week. That late-week air mass could prove downright chilly since it's to be the product of a surge of cold air riding steering winds aloft across the North Pole from the Eurasian continent (Europe and Russia).
That cold spell is to mark the first time a lobe of frigid air off the deadly European/Russian cold wave is to cross the North Pole and descend into eastern North America, affecting the Midwest. It's likely to bring Chicago one of its chilliest set of days to date.
The intensity of the incoming late week chill combined with a flow off Lake Michigan could set up snowy spells Friday and Friday night capable of producing some sticking snow. We'll keep you posted on that.
The 2011-12 season's paltry 13.9 inches of snow ranks 35th lowest of the past 127 years; it's just 28 percent last year's tally to date
Just how unusual is receiving only 13.9-inches of snow through Feb. 7? VERY UNUSUAL! Nearly four times as much had fallen by this time last winter---and the tally this season is just 61 percent normal!
For the record, approximately a third of Chicago's seasonal snow has historically fallen beyond this date---not an unsubstantial amount!
Comparably "snow-starved seasons" through this point in winter have seen February snowfall turn around in 3 of 10 years
This winter's Chicago area snowfall has been so limited, a number of our readers, including many who plow snow for a living and others who enjoy outdoor sports which require a cover of snow, have asked if we can quantify the chances for additional snowfall. In other words, have these "low-yielding" seasons turned around in the past---and, if so, how often.
To answer this, my colleague Richard Koeneman identified ten winters with comparably little snow by this date----then analyzed the snow which fell in those years from Feb. 7 forward. He found 3 of 10 comparably low "snow-yielding" seasons saw snowfall the remainder of February turnaround and fall at rate faster than the historical norm.
