December and Winter Climate Data for Chicago and Rockford

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December and Winter Climate Data for Chicago and Rockford

Climate Statistics for Chicago and Rockford for the Month of December

DECEMBER TEMPERATURE DATA
AVG HIGH

AVG LOW

AVG TEMP

RECORD WARM/YEAR

RECORD COLD/YEAR

CHICAGO
34.8

20.7

27.7

43.4 in 1877

14.3 in 1983

ROCKFORD
33.2

17.7

25.4

35.5 in 1923

12.5 in 2000

DECEMBER PRECIPITATION DATA	AVG PRECIP	RECORD WETTEST/YEAR	RECORD DRIEST/YEAR
CHICAGO	2.25	8.56 INCHES in 1982	0.16 INCHES in 1896
ROCKFORD	1.98	5.04 INCHES in 1971	0.17 INCHES in 1907

DECEMBER SNOWFALL DATA
AVG SNOWFALL

RECORD SNOWIEST/YEAR

LEAST SNOW/YEAR

CHICAGO
8.5

33.3 INCHES in 1951

TRACE in 1889, 1912

ROCKFORD

11.3

30.1 INCHES in 2000

TRACE in 1905, 1908, 1910, 1939

WINTER TEMPERATURE DATA
AVG HIGH

AVG LOW

AVG TEMP

RECORD WARM/WINTER

RECORD COLD/WINTER

CHICAGO
33.6

20.7

26.4

37.2 in 1877-1878

18.3 in 1903-1904

ROCKFORD
32.2

16.3

24.2

32.0 in 1931-1932

14.1 in 1978-1979

WINTER PRECIPITATION DATA	AVG PRECIP	RECORD WETTEST AND DRIEST /WINTER
CHICAGO	5.77	13.79 INCHES in 1987 1.60 INCHES in 1930-1931
ROCKFORD	4.76	10.38 INCHES in 1945-1946 1.28 INCHES in 2002-2003

WINTER SNOWFALL DATA	AVG SNOWFALL	RECORD SNOWIEST AND LEAST SNOW/WINTER
CHICAGO	28.4	80.6 INCHES in 1978-1979 5.7 INCHES in 1930-1931
ROCKFORD	29.2	65.1 INCHES in 2007-2008 4.0 INCHES in 1927-1928

Chicago , IL 1873-2010 December Temperature Probabilities of Exceedance To use these probabilities, here's an example: In the 20th percentile, from Dec 1-Dec 10, there's only a 20% chance of experiencing a temperature at or above 47 degrees on any given day during that period. The middle 60%, from the 80th percentile (30 deg.) to the 20th percentile (47 deg.) marks what can be seen as the typical range of high temperatures that would be experienced from Dec 1-Dec 10. Thus, a high temperature above or below the 1981-2010 normal can often fit within this typical range. The same technique can be used for low temperatures. The "Warmest" and "Coolest" temperatures are the highest and lowest high and low temperatures observed in the historical record for each 10 day period of the month.
*Probability of Exceedance*	*High Temperature*			*Low Temperature*
	*Dec 1-10*	*Dec 11-20*	Dec 21-31	*Dec 1-10*	*Dec 11-20*	Dec 21-31
*Warmest*	71	67	69	58	57	51
*10%*	53	48	47	38	35	34
*20%*	47	43	42	34	32	31
*30%*	43	40	39	32	29	28
*40%*	40	37	36	29	26	25
*50%*	38	35	34	26	23	22
*60%*	35	33	32	23	20	18
*70%*	33	30	29	20	16	14
*80%*	30	25	25	16	10	9
*90%*	25	19	18	10	3	2
*Coldest*	2	-2	-11	-14	-14	-25

*Average*	*38.4*	*34.4*	*33.7*	*25.2*	*21.5*	*20.4*
*Standard Deviation*	*10.9*	*11.1*	*11.1*	*11.0*	*12.1*	*12.4*

Rockford *, IL 1905-2010*
*Probability of Exceedance*	*High Temperature*			*Low Temperature*
	*Dec 1-10*	*Dec 11-20*	Dec 21-31	*Dec 1-10*	*Dec 11-20*	Dec 21-31
*Warmest*	67	61	66		43	46
*10%*	51	44	43	34	32	31
*20%*	45	40	39	30	29	27
*30%*	41	37	36	27	25	24
*40%*	38	35	35	25	22	21
*50%*	36	33	33	22	18	17
*60%*	34	31	30	19	15	13
*70%*	31	28	27	15	10	8
*80%*	28	22	23	11	4	3
*90%*	22	16	16	5	-2	-3
*Coldest*	1	-2	-11	-20	-21	-24

*Average*	*36.3*	*31.8*	*31.4*	*20.8*	*16.7*	*15.6*
*Standard Deviation*	*10.9*	*10.9*	*10.8*	*11.6*	*12.8*	*13.0*

Official Outlooks from the Climate Prediction Center (CPC)

December Temperature Outlook	December Precipitation Outlook

Winter Temperature Outlook	Winter Precipitation Outlook

NWS Chicago's 2012-2013 Winter Outlook for Northern Illinois and Northwest Indiana

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