• Temperatures Observed This Morning
• A 60° Change in One Week:  Rare or Not?
• Quantifying this Early Season Cold
• A Chilly Pair of Days, Along with Low Wind Chills

Temperatures Observed this Morning

Text Listing of Minimum Temperatures  

A 60° Change in One Week:  Rare or Not?

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
636 AM CST SUN NOV 24 2013 /736 AM EST SUN NOV 24 2013/

...A 60 DEGREE CHANGE IN ONE WEEK: RARE OR NOT?...

LAST WEEK STARTED WITH NEAR 70 DEGREE TEMPERATURES ON SUNDAY
NOVEMBER 17TH. THAT UNSEASONABLE WARMTH WAS ONE OF MANY ELEMENTS
IN PLACE THAT BROUGHT A RECORD NOVEMBER TORNADO OUTBREAK TO
ILLINOIS ON THAT DAY. SUCCESSIVE COLD FRONTS THROUGH THE NEXT
SEVEN DAYS AFTERWARD BROUGHT TEMPERATURES PROGRESSIVELY
DOWNWARD...WITH SINGLE DIGITS IN PLACES THIS SUNDAY MORNING
NOVEMBER 24TH. THE CHANGE IN JUST A ONE WEEK PERIOD OF TIME
CERTAINLY FELT SIGNIFICANT...BUT WAS IT REALLY ATYPICAL FOR THIS
AREA? WELL...YES AND NO.

.CHICAGO...

CHICAGO SAW A HIGH OF 69 DEGREES ON NOVEMBER 17TH WHILE THIS
SUNDAY MORNING HAD A LOW OF 12 DEGREES. THIS NEARLY 60 DEGREE
CHANGE MAY SEEM DRASTIC...BUT THE CITY ACTUALLY AVERAGES A 60
DEGREE SPAN OF TEMPERATURES DURING A WEEK`S PERIOD A LITTLE UNDER
ONCE A YEAR (106 TIMES IN 142 YEARS). IN FACT...2013 ALREADY HAD
BROUGHT SUCH A SHARP CHANGE WHEN THE MERCURY WENT FROM 63 DEGREES
ON JANUARY 29TH TO 0 DEGREES ON FEBRUARY 1ST.

WHAT MAKES THIS CHANGE UNIQUE IS THAT IT OCCURRED IN AUTUMN. THERE
HAVE ONLY BEEN FIVE TIMES IN 142 YEARS IN CHICAGO THAT A
TEMPERATURE CHANGE OF 60 DEGREES IN ONE WEEK`S SPAN OCCURRED IN
METEOROLOGICAL AUTUMN (SEPTEMBER-NOVEMBER)...AND THIS MOST RECENT
WEEK FELL JUST SHY OF THAT. THE LAST TIME IT HAD OCCURRED WAS 1976
WHEN THE TEMPERATURE WENT FROM 61 DEGREES ON THE 26TH TO 0 DEGREES
ON THE 29TH. THE OTHER FOUR TIMES WERE IN 1930 (64 DEGREE
CHANGE)...1911 (62 DEGREE CHANGE)...1901 (62 DEGREE CHANGE)...AND
1898 (64 DEGREE CHANGE). ALL OF THESE WERE IN NOVEMBER.

WHY ARE SUCH TEMPERATURE CHANGES IN A WEEK`S PERIOD MORE RARE IN
AUTUMN? WELL IT LIKELY HAS TO DO WITH A FEW FACTORS. LOOKING BACK
AT WHEN THE MOST COMMON TIME OF THE YEAR IS TO HAVE THESE SHARP 60
DEGREE CHANGES IN A WEEK IS BY FAR AND AWAY LATE WINTER INTO EARLY
SPRING. FOR ONE...THAT TIME OF THE YEAR TENDS TO HAVE SNOW COVER
MORE REGULARLY THAN AUTUMN. SNOW COVER CAN EASILY MODIFY AN AIR
MASS AND LEAD TO PRONOUNCED COOLING OF THE AIR AND THUS ALLOW FOR
A GREATER CONTRAST. ALSO...WARM AIR RETURN AS PRONOUNCED AS
NOVEMBER 17TH IS VERY RARE DURING THIS SHORT DAYLIGHT TIME OF
YEAR. LATE WINTER INTO EARLY SPRING HAS NOTICEABLY LONGER DAYLIGHT
AND HEATING...AND THUS CAN BRING EVEN MORE STRIKING WARM SURGES
AHEAD OF WEATHER SYSTEMS. FINALLY...LAKE MICHIGAN IS MUCH MILDER
THIS TIME OF YEAR THAN IN SPRING...AND MAY INFLUENCE TEMPERATURES
FROM CHANGING AS DRASTICALLY AS THEY MIGHT WITH A SHARPLY COOLING
LAKE INFLUENCE THAT IS SEEN REGULARLY IN LATE WINTER AND SPRING.

.ROCKFORD...

ROCKFORD ALSO SAW A HIGH OF 69 DEGREES ON NOVEMBER 17TH WHILE THIS
SUNDAY MORNING BROUGHT A LOW OF 9 DEGREES. ROCKFORD AVERAGES SUCH
60 DEGREE TEMPERATURE CHANGES IN A SINGLE WEEK SPAN MORE THAN
ONCE A YEAR (152 TIMES IN 106 YEARS). THE LIKELY REASONS THIS IS
MORE FREQUENT THAN IN CHICAGO IS THAT IT IS FURTHER AWAY FROM THE
INFLUENCES OF LAKE MICHIGAN AND THE LARGER URBAN HEAT
ISLAND...BOTH OF WHICH CAN RESTRICT EXTREME TEMPERATURE CHANGES.
ROCKFORD HAS ALREADY SEEN SUCH A SHARP CHANGE IN 2013 WHEN THE
MERCURY WENT FROM 62 DEGREES ON JANUARY 29TH DOWN TO -4 DEGREES ON
FEBRUARY 1ST.

AN AUTUMN CHANGE OF 60 DEGREES IN JUST ONE WEEK IS NOT ANYWHERE
NEAR AS RARE AS CHICAGO...AS THIS WAS THE 21ST TIME IT HAD
OCCURRED IN THE PAST 106 YEARS. IT HAD BEEN AWHILE THOUGH SINCE
THE LAST TIME...WHICH OCCURRED IN OCTOBER OF 1992 WHEN THE
TEMPERATURE HAD BOTTOMED OUT AT 18 ON THE 19TH AND REBOUNDED TO 78
DEGREES ON THE 22ND.

SO WHILE MOST FELT THE NOTICEABLE TEMPERATURE DIFFERENCE IN JUST
ONE WEEK...THIS IS CERTAINLY NOT UNHEARD OF ESPECIALLY IN OUTLYING
LOCATIONS FROM CHICAGO. BUT FOR THE WINDY CITY DURING THE AUTUMN
SEASON...THIS PAST WEEK`S NEAR 60 DEGREE RIDE IS FAIRLY RARE.

$$

MTF 

Quantifying This Early Season Cold

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
300 PM CST SAT NOV 23 2013 /400 PM EST SAT NOV 23 2013/

...THE COLDEST EARLY SEASON NIGHT IN OVER 20 YEARS POSSIBLE TONIGHT...

SHOULD THE FORECAST LOW TEMPERATURES FOR ROCKFORD AND CHICAGO-
OHARE VERIFY TONIGHT...THE LOW TEMPERATURES ON SUNDAY NOVEMBER
24TH WILL BE THE COLDEST THIS EARLY IN THE SEASON IN OVER 20
YEARS FOR BOTH LOCATIONS.

THE FORECAST LOW FOR ROCKFORD IS 7 DEGREES. YOU HAVE TO GO ALL THE
WAY BACK TO NOVEMBER 7TH 1991 FOR A TEMPERATURE THIS LOW IN THE
FIRST 24 DAYS OF THE MONTH. THE PREVIOUS OCCURRENCE OF A LOW
TEMPERATURE COLDER THAN 10 DEGREES THIS EARLY IN THE SEASON WAS
NOVEMBER 24TH 1997...WHICH BOTTOMED OUT AT 9 DEGREES.

IN CHICAGO...THE FORECAST LOW IS 11 DEGREES. THE LAST TIME CHICAGO
SAW A TEMPERATURE THIS COLD THIS EARLY IN THE SEASON WAS ON
NOVEMBER 4TH 1991. A LOW TEMPERATURE COLDER THAN 15 DEGREES THIS
EARLY IN THE SEASON LAST OCCURRED BACK ON NOVEMBER 22ND
2000...WHEN THE MERCURY DIPPED TO 14 DEGREES.

$$

RC

A Chilly Pair of Days & Low Wind Chills

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
623 AM CST FRI NOV 22 2013 /723 AM EST FRI NOV 22 2013/

...IMPRESSIVE EARLY SEASON COLD SNAP ON THE WAY THIS WEEKEND..

BASED ON CURRENT FORECASTS...ROCKFORD AND CHICAGO COULD BE ON
TRACK TO HAVE THE COLDEST TWO DAY PERIOD FOR SO EARLY IN THE
SEASON SINCE BACK ON NOVEMBER 21ST AND 22ND 2000.

FORECASTS FOR THIS WEEKEND CALL FOR HIGHS IN THE MID 20S TO
AROUND 30 AND LOWS IN THE MID TEENS TO LOWER 20S IN
CHICAGO...WITH READINGS LIKELY TO BE JUST A COUPLE DEGREES COLDER
IN ROCKFORD.

BACK ON NOV 21ST AND 22ND 2000 ROCKFORD HAD HIGH TEMPERATURES OF
30 AND 26 RESPECTIVELY WITH LOW TEMPERATURES BOTH DAYS OF 11
DEGREES. IN CHICAGO...THE HIGH TEMPERATURES WERE 24 AND 30 WITH
LOW TEMPERATURES OF 14 DEGREES BOTH DAYS. SO WHILE IT IS NOT
UNPRECEDENTED TO SEE TEMPERATURES SO UNSEASONABLY COLD THIS
EARLY...IT IS FAR FROM COMMON.

IN ADDITION...THIS UPCOMING COLD SNAP LOOKS TO HAVE IMPRESSIVELY
LOW WIND CHILLS FOR NOVEMBER. CURRENT FORECASTS HAVE WIND CHILL
VALUES AT OR BELOW 5F...WITH EVEN THE POSSIBILITY OF REACHING
ZERO SATURDAY NIGHT INTO EARLY SUNDAY MORNING. THESE CURRENT
FORECAST WIND CHILLS ARE THE COLDEST PRIOR TO DECEMBER SINCE
NOVEMBER 26 2010 (3) AT ROCKFORD...AND SINCE NOVEMBER 24 2005 (-2)
AT CHICAGO. ROCKFORD HAS NOT REACHED A ZERO OR LOWER WIND CHILL
THIS EARLY IN THE SEASON SINCE NOVEMBER 24 2005.

$$

RC/ENI/MTF