2001 CHICAGO, O'HARE INTERNATIONAL AIRPORT, ILLINOIS (ORD)



Chicago is located along the southwest shore of Lake Michigan and occupies a plain which, for the most part, is only some tens of feet above the lake. Lake Michigan averages 579 feet above sea level. Natural water drainage over most of the city would be into Lake Michigan, and from areas west of the city is into the Mississippi River System. But actual drainage over most of the city is artificially channeled also into the Mississippi system. Topography does not significantly affect air flow in or near the city except that lesser frictional drag over Lake Michigan causes winds to be frequently stronger along the lakeshore, and often permits air masses moving from the north to reach shore areas an hour or more before affecting western parts of the city.

Chicago is in a region of frequently changeable weather. The climate is predominately continental, ranging from relatively warm in summer to relatively cold in winter. However, the continentality is partially modified by Lake Michigan, and to a lesser extent by other Great Lakes. In late autumn and winter, air masses that are initially very cold often reach the city only after being tempered by passage over one or more of the lakes. Similarly, in late spring and summer, air masses reaching the city from the north, northeast, or east are cooler because of movement over the Great Lakes. Very low winter temperatures most often occur in air that flows southward to the west of Lake Superior before reaching the Chicago area. In summer the higher temperatures are with south or southwest flow and are therefore not influenced by the lakes, the only modifying effect being a local lake breeze. Strong south or southwest flow may overcome the lake breeze and cause high temperatures to extend over the entire city.

During the warm season, when the lake is cold relative to land, there is frequently a lake breeze that reduces daytime temperature near the shore, sometimes by 10 degrees or more below temperatures farther inland. When the breeze off the lake is light this effect usually reaches inland only a mile or two, but with stronger on–shore winds the whole city is cooled. On the other hand, temperatures at night are warmer near the lake so that 24–hour averages on the whole are only slightly different in various parts of the city and suburbs.

At the O'Hare International Airport temperatures of 96 degrees or higher occur in about half the summers, while about half the winters have a minimum as low as −15 degrees. The average occurrence of the first temperature as low as 32 degrees in the fall is mid–October and the average occurrence of the last temperature as low as 32 degrees in the spring is late April.

Precipitation falls mostly from air that has passed over the Gulf of Mexico. But in winter there is sometimes snowfall, light inland but locally heavy near the lakeshore, with Lake Michigan as the principal moisture source. The heavy lakeshore snow occurs when initially colder air moves from the north with a long trajectory over Lake Michigan and impinges on the Chicago lakeshore. In this situation the air mass is warmed and its moisture content increased up to a height of several thousand feet. Snowfall is produced by upward currents that become stronger, because of frictional effects, when the air moves from the lake onto land. This type of snowfall therefore tends to be heavier and to extend farther inland in south–shore areas of the city and in Indiana suburbs, where the angle between wind–flow and shoreline is greatest. The effect of Lake Michigan, both on winter temperatures and lake–produced snowfall, is enhanced by non–freezing of much of the lake during the winter, even though areas and harbors are often ice–choked.

Summer thunderstorms are often locally heavy and variable, parts of the city may receive substantial rainfall and other parts none. Longer periods of continuous precipitation are mostly in autumn, winter, and spring. About one–half the precipitation in winter, and about 10 percent of the yearly total precipitation, falls as snow. Snowfall from month to month and year to year is greatly variable. There is a 50 percent likelihood that the first and last l–inch snowfall of a season will occur by December 5 and March 20, respectively.

Channeling of winds between tall buildings often causes locally stronger gusts in the central business area. However, the nickname, windy city, is a misnomer as the average wind speed is not greater than in many other parts of the U.S.

NORMALS, MEANS, AND EXTREMES

CHICAGO, IL (ORD)

LATITUDE:    LONGITUDE:     ELEVATION (FT):    TIME ZONE:    WBAN: 94846

41 59′ 10″ N  87 54′ 51″ W  GRND: 655  BARO: 658  CENTRAL (UTC + 6)

2001 Chicago, O'Hare International Airport, Illinois (ORD)

ELEMENT POR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR
TEMPERATURE F NORMAL DAILY MAXIMUM 30 29.0 33.5 45.8 58.6 70.1 79.6 83.7 81.8 74.8 63.3 48.4 34.0 58.5
MEAN DAILY MAXIMUM 43 29.5 34.3 45.4 58.4 70.1 79.5 83.6 81.9 74.7 63.0 48.0 34.7 58.6
HIGHEST DAILY MAXIMUM 43 65 72 88 91 93 104 104 101 99 91 78 71 104
YEAR OF OCCURRENCE 1989 2000 1986 1980 1977 1988 1995 1991 1985 1963 1978 1982 JUL 1995
MEAN OF EXTREME MAXS. 43 49.5 54.5 72.0 80.5 87.5 93.0 95.0 92.9 89.9 81.7 68.1 55.9 76.7
NORMAL DAILY MINIMUM 30 12.9 17.2 28.5 38.6 47.7 57.5 62.6 61.6 53.9 42.2 31.6 19.1 39.5
MEAN DAILY MINIMUM 43 14.0 18.7 28.0 38.6 48.2 57.4 62.9 62.1 53.9 42.4 31.8 20.1 39.8
LOWEST DAILY MINIMUM 43 -27 -19 -8 7 24 36 40 41 28 17 1 -25 -27
YEAR OF OCCURRENCE 1985 1996 1962 1982 1966 1972 1965 1965 1974 1981 1976 1983 JAN 1985
MEAN OF EXTREME MINS. 43 -9.0 -2.9 10.0 23.1 34.1 43.5 50.2 50.8 38.6 27.2 15.3 -1.9 23.2
NORMAL DRY BULB 30 21.0 25.4 37.2 48.6 58.9 68.6 73.2 71.7 64.4 52.8 40.0 26.6 49.0
MEAN DRY BULB 43 21.7 26.5 36.8 48.4 59.2 68.5 73.2 71.9 64.3 52.8 39.7 27.4 49.2
MEAN WET BULB 18 22.5 26.2 34.0 43.0 53.3 62.1 66.7 65.9 58.3 47.7 34.8 26.6 45.1
MEAN DEW POINT 18 17.8 21.0 27.9 36.2 47.2 57.0 62.3 61.9 53.5 42.3 30.0 21.8 39.9
NORMAL NO. DAYS WITH:
MAXIMUM 90 30 0.0 0.0 0.0 * 0.8 3.8 6.7 4.2 1.5 0.1 0.0 0.0 17.1
MAXIMUM 32 30 17.6 12.7 3.9 0.1 0.0 0.0 0.0 0.0 0.0 0.0 1.7 11.9 47.9
MINIMUM 32 30 28.7 25.0 21.0 7.8 0.9 0.0 0.0 0.0 0.2 5.3 16.5 26.7 132.1
MINIMUM 0 30 7.0 3.2 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.9 13.3
H/C NORMAL HEATING DEG. DAYS 30 1364 1109 862 492 235 35 5 19 84 391 750 1190 6536
NORMAL COOLING DEG. DAYS 30 0 0 0 0 46 143 259 226 66 12 0 0 752
RH NORMAL (PERCENT) 30 72 72 70 65 64 66 68 71 71 69 72 76 70
HOUR 00 LST 30 75 76 76 72 73 75 79 81 81 76 77 78 77
HOUR 06 LST 30 76 77 79 77 77 78 82 85 85 81 80 80 80
HOUR 12 LST 30 67 65 61 55 53 55 57 57 57 55 64 70 60
HOUR 18 LST 30 71 69 64 57 54 55 58 61 63 64 70 74 63
S PERCENT POSSIBLE SUNSHINE 16 44 49 51 50 58 67 66 62 59 55 38 43 54
W/O MEAN NO. DAYS WITH:
HEAVY FOG (VISBY 1/4 MI) 44 1.7 1.8 2.2 0.9 1.2 0.6 0.5 0.7 0.4 0.8 1.3 1.9 14.0
THUNDERSTORMS 44 0.3 0.5 2.0 4.0 5.1 6.6 5.9 6.0 4.2 1.7 1.1 0.6 38.0
CLOUDINESS MEAN:
SUNRISE-SUNSET (OKTAS) 38 5.5 5.4 5.8 5.5 5.0 4.7 4.4 4.4 4.5 4.7 5.7 5.6 5.1
MIDNIGHT-MIDNIGHT (OKTAS) 32 5.3 5.0 5.1 5.0 4.5 4.3 4.0 4.0 4.2 4.3 5.4 5.5 4.7
MEAN NO. DAYS WITH:
CLEAR 39 6.8 6.0 4.9 6.0 7.2 7.3 8.0 8.6 8.5 8.6 5.2 5.7 82.8
PARTLY CLOUDY 39 6.2 6.5 8.5 7.6 9.9 11.5 12.1 11.2 9.5 8.5 6.2 5.9 103.6
CLOUDY 39 18.0 15.7 17.6 16.4 13.9 11.2 10.1 10.4 11.2 13.3 17.7 18.5 174.0
PR MEAN STATION PRESSURE (IN) 29 29.30 29.30 29.30 29.20 29.20 29.20 29.30 29.30 29.30 29.31 29.31 29.31 29.28
MEAN SEA-LEVEL PRES. (IN) 18 30.10 30.10 30.06 29.96 29.97 30.01 30.00 30.04 30.06 30.08 30.06 30.11 30.05
WINDS MEAN SPEED (MPH) 38 11.6 11.4 11.9 12.0 10.5 9.4 8.6 8.4 9.0 10.2 11.1 11.0 10.4
PREVAIL. DIR (TENS OF DEGS) 33 27 29 29 04 04 21 23 23 18 19 21 27 21
MAXIMUM 2-MINUTE:
SPEED (MPH) 5 37 38 41 43 37 39 37 41 37 43 41 32 43
DIR. (TENS OF DEGS) 09 26 02 26 28 30 01 24 28 07 23 33 07
YEAR OF OCCURRENCE 1999 2001 1998 1997 1998 1998 1997 2000 1997 1997 1998 2000 OCT 1997
MAXIMUM 5-SECOND:
SPEED (MPH) 5 47 56 47 56 54 48 61 59 48 52 57 41 61
DIR. (TENS OF DEGS) 09 24 02 25 27 30 20 25 21 07 24 27 20
YEAR OF OCCURRENCE 1999 1999 1998 1997 1998 1998 1999 2000 2001 1997 1998 2001 JUL 1999
PRECIPITATION NORMAL (IN) 30 1.53 1.36 2.69 3.64 3.32 3.78 3.66 4.22 3.82 2.41 2.92 2.47 35.82
MAXIMUM MONTHLY (IN) 43 4.47 5.56 5.91 7.69 7.14 9.96 8.33 17.10 11.44 8.54 8.22 8.56 17.10
YEAR OF OCCURRENCE 1999 1997 1976 1983 1970 1993 1982 1987 1961 2001 1985 1982 AUG 1987
MINIMUM MONTHLY (IN) 43 0.10 0.12 0.63 0.97 0.30 0.95 1.18 0.51 0.02 0.16 0.44 0.23 0.02
YEAR OF OCCURRENCE 1981 1969 1981 1971 1992 1991 1977 1969 1979 1964 1999 1962 SEP 1979
MAXIMUM IN 24 HOURS (IN) 43 2.00 3.78 2.39 2.78 3.45 3.79 2.90 9.35 3.00 4.62 2.99 4.53 9.35
YEAR OF OCCURRENCE 1960 1997 1985 1983 1981 1994 1993 1987 1978 1969 1990 1982 AUG 1987
NORMAL NO. DAYS WITH:
PRECIPITATION 0.01 30 11.1 9.4 12.4 12.6 10.9 10.1 9.8 9.5 9.5 9.2 10.9 11.6 127.0
PRECIPITATION 1.00 30 0.2 0.1 0.4 0.7 0.5 0.9 1.0 1.2 1.1 0.3 0.5 0.5 7.4
SNOWFALL NORMAL (IN) 30 10.7 8.4 6.5 1.8 0.1 0.0 0.0 0.0 0.0 0.5 1.9 8.8 38.7
MAXIMUM MONTHLY (IN) 42 34.3 26.2 24.7 11.1 1.6 T T T T 6.6 10.4 35.3 35.3
YEAR OF OCCURRENCE 1979 1994 1965 1975 1966 1992 1995 1989 1967 1967 1959 1978 DEC 1978
MAXIMUM IN 24 HOURS (IN) 42 18.6 11.1 10.6 10.9 1.6 T T T T 6.6 5.8 11.0 18.6
YEAR OF OCCURRENCE 1999 2000 1970 1975 1966 1992 1995 1989 1967 1967 1975 1969 JAN 1999
MAXIMUM SNOW DEPTH (IN) 41 28 27 20 11 1 0 0 0 0 3 6 17 28
YEAR OF OCCURRENCE 1979 1967 1965 1975 1966 1989 1975 2000 JAN 1979
NORMAL NO. DAYS WITH:
SNOWFALL 1.0 30 3.3 2.7 2.0 0.4 0.* 0.0 0.0 0.0 0.0 0.2 0.6 2.6 11.8

2001 Chicago, O'Hare International Airport, Illinois (ORD)

PRECIPITATION (inches) 2001 CHICAGO, O'HARE INTERNATIONAL AIRPORT, IL (ORD)
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
1972 1.01 0.73 3.45 4.77 3.02 3.55 4.97 6.97 8.14 2.92 3.05 2.89 45.47
1973 1.24 1.38 3.91 4.99 3.69 2.87 5.27 0.67 6.01 2.86 1.50 3.71 38.10
1974 3.29 2.11 2.40 4.27 5.09 4.69 2.96 2.60 1.47 1.88 2.47 2.12 35.35
1975 3.69 2.48 2.02 5.50 3.02 5.07 2.19 7.37 0.80 1.90 2.53 3.05 39.62
1976 0.85 1.87 5.91 4.05 4.03 2.93 1.44 1.29 1.49 1.41 0.65 0.64 26.56
1977 0.55 0.71 3.67 2.62 1.88 5.12 1.18 5.39 6.07 1.36 2.05 1.96 32.56
1978 1.48 0.43 1.16 3.94 2.80 6.36 4.61 1.96 6.88 1.08 2.24 4.41 37.35
1979 2.81 1.02 4.49 4.92 2.58 4.63 2.19 7.57 0.02 1.49 2.80 2.58 37.10
1980 1.04 1.24 1.96 3.41 3.22 3.42 3.56 8.54 5.65 2.09 1.10 3.43 38.66
1981 0.10 2.35 0.63 6.14 5.85 4.46 4.50 6.60 3.25 1.80 2.46 1.05 39.19
1982 2.90 0.41 4.15 2.78 2.08 1.56 8.33 3.93 1.15 1.88 6.95 8.56 44.68
1983 0.66 2.06 3.56 7.69 6.26 4.11 4.25 2.08 5.41 4.41 5.87 2.99 49.35
1984 1.15 1.39 3.00 4.11 4.49 2.02 3.19 2.10 3.84 3.15 2.64 2.92 34.00
1985 1.48 3.46 4.73 1.48 2.79 1.97 3.75 3.90 1.82 4.98 8.22 1.49 40.07
1986 0.39 2.58 1.49 1.85 3.11 3.49 4.30 1.15 7.12 3.75 1.41 1.09 31.73
1987 1.67 0.99 1.59 2.34 2.21 2.19 4.19 17.10 0.94 1.59 2.77 3.77 41.35
1988 1.88 1.29 2.15 2.08 1.19 1.05 2.74 3.29 3.79 5.05 6.45 2.40 33.36
1989 0.82 0.77 1.67 1.37 1.59 2.01 5.89 7.31 3.91 1.49 2.16 0.46 29.45
1990 1.97 2.25 3.09 1.79 6.85 4.50 2.25 7.75 1.03 4.10 5.60 1.94 43.12
1991 1.41 0.62 3.54 4.00 5.20 0.95 1.32 2.81 2.51 7.36 3.59 1.71 35.02
1992 0.87 1.39 2.67 2.21 0.30 1.35 3.77 3.56 4.31 1.79 5.41 2.49 30.12
1993 3.83 0.82 4.52 4.57 1.83 9.96 4.45 5.74 4.47 2.19 1.52 1.00 44.90
1994 1.77 2.56 1.09 2.20 0.58 6.09 1.62 4.05 1.04 3.23 3.75 1.61 29.59
1995 3.21 0.41 1.43 5.79 4.47 1.40 3.17 3.49 1.04 4.20 3.68 0.59 32.88
1996 1.58 0.71 0.95 2.59 6.95 4.80 3.95 1.45 2.73 2.32 1.48 1.21 30.72
1997 1.38 5.56 1.57 1.76 2.69 3.81 3.04 4.50 1.69 2.75 1.46 1.50 31.71
1998 2.67 1.70 4.29 3.56 3.02 2.90 1.75 6.88 2.34 5.22 2.00 1.20 37.53
1999 4.47 1.64 1.73 7.51 4.46 4.95 3.73 2.30 3.27 1.07 0.44 2.68 38.25
2000 1.35 1.97 1.18 5.15 4.02 4.32 3.58 2.26 3.59 1.12 2.71 2.11 33.36
2001 1.12 2.57 1.30 2.82 3.34 2.61 2.96 12.25 6.05 8.54 1.22 0.99 45.77
POR=43 YRS 1.75 1.53 2.55 3.66 3.32 3.79 3.55 4.23 3.48 2.73 2.71 2.12 35.42

2001 Chicago, O'Hare International Airport, Illinois (ORD)

AVERAGE TEMPERATURE (F) 2001 CHICAGO, O'HARE INTERNATIONAL AIRPORT, IL (
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
1972 19.6 23.6 34.0 44.8 61.0 65.7 73.6 73.8 63.5 49.3 37.7 23.9 47.5
1973 28.2 28.7 44.0 48.1 54.8 71.1 74.7 74.6 66.0 57.9 41.9 28.1 51.5
1974 24.8 27.4 38.6 52.3 56.8 65.5 73.6 70.0 60.5 52.8 40.6 30.2 49.4
1975 27.3 26.2 34.1 43.3 62.3 70.5 75.5 76.3 61.4 55.8 47.2 31.5 51.0
1976 19.9 35.2 42.8 52.3 55.9 70.1 74.0 70.8 62.7 48.3 32.4 19.4 48.7
1977 10.7 26.9 44.9 55.0 67.2 69.3 77.5 71.9 66.0 51.5 40.0 24.2 50.4
1978 15.7 16.8 31.9 47.5 58.3 67.6 72.0 72.4 68.8 51.4 40.8 25.8 47.4
1979 12.5 16.2 36.4 45.5 59.3 69.2 72.0 71.0 66.1 53.3 40.6 33.7 48.0
1980 23.4 21.5 32.6 46.5 59.7 65.3 75.7 75.7 66.0 48.4 39.9 28.0 48.6
1981 22.6 28.0 37.6 51.8 55.3 69.8 72.5 71.2 61.7 49.1 40.8 24.9 48.8
1982 12.2 21.5 35.1 44.5 64.3 62.1 74.1 68.8 62.1 53.2 39.1 36.0 47.8
1983 26.3 30.5 37.4 43.4 53.2 69.7 76.7 77.3 64.6 52.8 41.1 14.3 48.9
1984 17.1 33.9 29.5 45.8 55.5 70.3 70.3 72.8 61.1 54.7 37.9 31.0 48.3
1985 14.4 20.4 39.4 52.6 60.2 63.6 71.4 69.2 65.4 52.5 37.8 17.0 47.0
1986 22.8 24.0 40.4 51.5 59.5 66.3 74.9 68.5 66.8 53.7 36.0 30.6 49.6
1987 25.9 33.9 40.8 50.6 63.4 72.4 76.7 71.9 65.1 47.3 43.9 32.2 52.0
1988 19.8 22.7 38.1 48.2 61.0 71.7 76.8 76.8 65.9 46.1 41.7 27.7 49.7
1989 32.4 19.6 36.6 46.8 57.8 67.5 73.9 71.4 62.0 54.0 37.7 17.4 48.1
1990 33.9 31.3 41.3 49.9 56.2 69.6 71.7 71.9 65.9 51.6 44.7 28.6 51.4
1991 20.8 31.0 40.4 52.0 65.6 71.9 75.5 73.6 63.7 53.2 35.2 30.3 51.1
1992 28.1 33.3 37.5 46.1 56.9 64.9 69.3 67.0 62.7 50.4 38.3 28.6 48.6
1993 26.2 24.4 34.2 45.0 59.7 66.4 74.3 73.3 59.2 49.5 38.7 29.8 48.4
1994 15.9 22.1 38.5 51.1 58.2 70.2 73.4 68.7 66.8 54.7 44.4 34.8 49.9
1995 24.0 26.5 40.2 46.0 58.8 72.3 77.6 79.0 62.5 53.7 32.8 26.3 50.0
1996 23.4 26.0 30.8 45.2 55.0 68.0 69.9 72.3 63.5 51.9 33.4 27.7 47.3
1997 19.3 29.0 37.9 45.2 53.8 68.3 73.2 69.5 64.2 53.2 36.4 31.5 48.5
1998 29.6 38.7 39.0 49.8 64.8 69.3 74.5 73.5 67.7 55.5 44.8 34.7 53.5
1999 22.6 34.0 35.6 49.6 61.7 70.4 78.4 70.3 63.4 52.9 45.1 29.9 51.2
2000 25.3 34.1 44.2 47.2 62.0 67.3 71.1 72.4 64.7 56.1 37.0 16.0 49.8
2001 24.6 26.1 34.2 52.5 60.0 67.4 74.6 73.2 61.9 52.1 48.2 33.4 50.7
POR=43 YRS 21.7 26.5 36.8 48.5 59.4 68.5 73.2 71.8 64.3 52.8 39.7 27.3 49.2

REFERENCE NOTES:

PAGE 1:

THE TEMPERATURE GRAPH SHOWS NORMAL MAXIMUM AND NORMAL MINIMUM DAILY TEMPERATURES (SOLID CURVES) AND THE ACTUAL DAILY HIGH AND LOW TEMPERATURES (VERTICAL BARS).

PAGE 2 AND 3:

H/C INDICATES HEATING AND COOLING DEGREE DAYS.

RH INDICATES RELATIVE HUMIDITY

W/O INDICATES WEATHER AND OBSTRUCTIONS

S INDICATES SUNSHINE.

PR INDICATES PRESSURE.

CLOUDINESS ON PAGE 3 IS THE SUM OF THE CEILOMETER AND SATELLITE DATA NOT TO EXCEED EIGHT EIGHTHS (OKTAS).

GENERAL:

T INDICATES TRACE PRECIPITATION, AN AMOUNT GREATER THAN ZERO BUT LESS THAN THE LOWEST REPORTABLE VALUE.

+ INDICATES THE VALUE ALSO OCCURS ON EARLIER DATES.

BLANK ENTRIES DENOTE MISSING OR UNREPORTED DATA.

NORMALS ARE 30–YEAR AVERAGES (1961–1990).

ASOS INDICATES AUTOMATED SURFACE OBSERVING SYSTEM.

PM INDICATES THE LAST DAY OF THE PREVIOUS MONTH.

POR (PERIOD OF RECORD) BEGINS WITH THE JANUARY DATA MONTH AND IS THE NUMBER OF YEARS USED TO COMPUTE THE MEAN. INDIVIDUAL MONTHS WITHIN THE POR MAY BE MISSING.

WHEN THE POR FOR A NORMAL IS LESS THAN 30 YEARS, THE NORMAL IS PROVISIONAL AND IS BASED ON THE NUMBER OF YEARS INDICATED.

0.* OR * INDICATES THE VALUE OR MEAN–DAYS–WITH IS BETWEEN 0.00 AND 0.05.

CLOUDINESS FOR ASOS STATIONS DIFFERS FROM THE NON–ASOS OBSERVATION TAKEN BY A HUMAN OBSERVER. ASOS STATION CLOUDINESS IS BASED ON TIME–AVERAGED CEILOMETER DATA FOR CLOUDS AT OR BELOW 12,000 FEET AND ON SATELLITE DATA FOR CLOUDS ABOVE 12,000 FEET.

THE NUMBER OF DAYS WITH CLEAR, PARTLY CLOUDY, AND CLOUDY CONDITIONS FOR ASOS STATIONS IS THE SUM OF THE CEILOMETER AND SATELLITE DATA FOR THE SUNRISE TO SUNSET PERIOD.

GENERAL CONTINUED:

CLEAR INDICATES 0–2 OKTAS, PARTLY CLOUDY INDICATES 3–6 OKTAS, AND CLOUDY INDICATES 7 OR 8 OKTAS. WHEN AT LEAST ONE OF THE ELEMENTS (CEILOMETER OR SATELLITE) IS MISSING, THE DAILY CLOUDINESS IS NOT COMPUTED.

WIND DIRECTION IS RECORDED IN TENS OF DEGREES (2 DIGITS) CLOCKWISE FROM TRUE NORTH. "00" INDICATES CALM. "36" INDICATES TRUE NORTH.

RESULTANT WIND IS THE VECTOR AVERAGE OF THE SPEED AND DIRECTION.

AVERAGE TEMPERATURE IS THE SUM OF THE MEAN DAILY MAXIMUM AND MINIMUM TEMPERATURE DIVIDED BY 2.

SNOWFALL DATA COMPRISE ALL FORMS OF FROZEN PRECIPITATION, INCLUDING HAIL.

A HEATING (COOLING) DEGREE DAY IS THE DIFFERENCE BETWEEN THE AVERAGE DAILY TEMPERATURE AND 65 F.

DRY BULB IS THE TEMPERATURE OF THE AMBIENT AIR.

DEW POINT IS THE TEMPERATURE TO WHICH THE AIR MUST BE COOLED TO ACHIEVE 100 PERCENT RELATIVE HUMIDITY.

WET BULB IS THE TEMPERATURE THE AIR WOULD HAVE IF THE MOISTURE CONTENT WAS INCREASED TO 100 PERCENT RELATIVE HUMIDITY.

ON JULY 1, 1996, THE NATIONAL WEATHER SERVICE BEGAN USING THE "METAR" OBSERVATION CODE THAT WAS ALREADY EMPLOYED BY MOST OTHER NATIONS OF THE WORLD. THE MOST NOTICEABLE DIFFERENCE IN THIS ANNUAL PUBLICATION WILL BE THE CHANGE IN UNITS FROM TENTHS TO EIGHTS (OKTAS) FOR REPORTING THE AMOUNT OF SKY COVER.

2001 Chicago, O'Hare International Airport, Illinois (ORD)

HEATING DEGREE DAYS (base 65 F) 2001 CHICAGO, O'HARE INTERNATIONAL AIRPORT, IL (OR
YEAR JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN TOTAL
1972-73 15 10 109 481 811 1269 1135 1012 645 503 311 0 6301
1973-74 0 0 72 244 687 1139 1240 1046 812 383 266 63 5952
1974-75 0 1 176 384 724 1072 1160 1078 951 643 152 30 6371
1975-76 1 0 147 303 531 1033 1392 859 681 411 285 17 5660
1976-77 0 9 119 522 973 1408 1679 1060 616 332 115 41 6874
1977-78 0 8 42 413 741 1254 1521 1346 1020 518 264 46 7173
1978-79 1 4 59 418 718 1206 1622 1360 879 580 233 30 7110
1979-80 16 19 62 382 722 967 1281 1254 995 558 198 83 6537
1980-81 0 3 71 511 746 1140 1308 1031 846 397 313 6 6372
1981-82 8 6 135 489 719 1236 1632 1213 922 608 93 118 7179
1982-83 7 37 152 372 772 891 1194 961 847 643 364 38 6278
1983-84 16 0 125 383 714 1568 1479 894 1095 575 300 18 7167
1984-85 19 1 189 320 807 1046 1563 1245 787 418 183 103 6681
1985-86 0 6 141 380 813 1480 1302 1142 765 417 202 74 6722
1986-87 3 29 64 343 863 1060 1205 866 742 432 162 14 5783
1987-88 4 19 74 541 629 1011 1396 1221 828 503 176 40 6442
1988-89 0 9 63 583 693 1149 1003 1265 882 540 261 43 6491
1989-90 0 5 131 344 813 1471 956 938 733 491 271 33 6186
1990-91 10 5 103 425 605 1120 1365 945 756 393 142 13 5882
1991-92 0 0 163 367 887 1066 1137 913 847 560 284 77 6301
1992-93 9 37 136 449 795 1122 1196 1133 948 595 184 69 6673
1993-94 0 3 185 479 784 1084 1516 1197 817 433 253 51 6802
1994-95 1 23 63 322 611 932 1262 1074 760 561 199 25 5833
1995-96 1 0 150 349 958 1193 1284 1124 1054 589 343 58 7103
1996-97 9 0 119 399 940 1148 1410 1003 832 587 344 53 6844
1997-98 9 4 77 406 852 1030 1091 732 813 449 87 69 5619
1998-99 0 0 35 289 598 933 1309 860 903 456 149 34 5566
1999-00 1 4 110 368 591 1081 1224 892 640 528 148 57 5644
2000-01 6 3 112 286 833 1512 1248 1085 948 374 205 88 6700
2001- 5 0 128 394 496 973

2001 Chicago, O'Hare International Airport, Illinois (ORD)

COOLING DEGREE DAYS (base 65 F) 2001 CHICAGO, O'HARE INTERNATIONAL AIRPORT
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
1972 0 0 0 0 64 106 289 289 72 0 0 0 820
1973 0 0 0 5 3 189 308 301 108 32 0 0 946
1974 0 0 0 10 21 83 274 162 48 12 0 0 610
1975 0 0 0 0 76 203 332 358 46 24 1 0 1040
1976 0 0 0 36 6 178 286 196 56 8 0 0 766
1977 0 0 0 39 191 178 395 229 76 0 0 0 1108
1978 0 0 0 0 60 132 227 243 181 2 0 0 845
1979 0 0 0 2 61 164 241 213 99 26 0 0 806
1980 0 0 0 10 43 101 338 342 107 2 0 0 943
1981 0 0 0 9 20 157 248 204 44 0 0 0 682
1982 0 0 0 0 79 38 295 161 69 14 0 0 656
1983 0 0 1 0 4 189 385 388 122 10 0 0 1099
1984 0 0 0 5 11 184 190 254 77 8 0 0 729
1985 0 0 0 53 42 71 204 142 158 0 0 0 670
1986 0 0 7 17 37 118 318 145 123 3 0 0 768
1987 0 0 0 6 116 241 377 238 83 0 1 0 1062
1988 0 0 0 5 59 247 373 383 96 1 0 0 1164
1989 0 0 2 0 44 121 282 207 48 11 0 0 715
1990 0 0 7 43 8 179 226 224 137 11 1 0 836
1991 0 0 0 11 167 226 334 273 132 10 0 0 1153
1992 0 0 0 1 40 79 152 106 75 4 0 0 457
1993 0 0 0 0 28 118 294 266 19 5 0 0 730
1994 0 0 0 23 47 212 268 143 126 10 0 0 829
1995 0 0 0 0 13 254 398 445 81 8 0 0 1199
1996 0 0 0 0 41 154 166 235 79 2 0 0 677
1997 0 0 0 0 4 158 265 154 59 44 0 0 684
1998 0 0 13 0 88 205 301 267 123 5 0 0 1002
1999 0 0 0 0 52 201 422 176 70 2 2 0 925
2000 0 0 3 0 63 131 199 240 112 18 0 0 766
2001 0 0 0 7 58 168 309 262 44 1 0 0 849

2001 Chicago, O'Hare International Airport, Illinois (ORD)

SNOWFALL (inches) 2001 CHICAGO, O'HARE INTERNATIONAL AIRPORT, IL (ORD)
YEAR JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN TOTAL
1972-73 0.0 0.0 0.0 0.1 0.9 11.2 0.5 9.3 3.4 0.2 T 0.0 25.6
1973-74 0.0 0.0 0.0 0.0 T 18.8 7.4 9.6 1.4 T 0.0 0.0 37.2
1974-75 0.0 0.0 0.0 0.0 1.0 9.4 3.5 8.2 4.5 11.1 0.0 0.0 37.7
1975-76 0.0 0.0 0.0 0.0 6.4 6.8 10.0 1.6 1.9 0.8 T 0.0 27.5
1976-77 0.0 0.0 0.0 1.6 0.5 6.5 7.2 4.0 4.9 T 0.0 0.0 24.7
1977-78 0.0 0.0 0.0 0.0 5.2 12.7 21.9 7.9 4.5 0.2 0.0 0.0 52.4
1978-79 0.0 0.0 0.0 0.0 5.2 35.3 34.3 6.8 2.0 0.1 0.0 0.0 83.7
1979-80 0.0 0.0 0.0 0.0 4.0 0.9 6.2 14.7 11.6 4.2 0.0 0.0 41.6
1980-81 0.0 0.0 0.0 T 5.1 9.7 2.0 15.9 2.3 0.0 0.0 0.0 35.0
1981-82 0.0 0.0 0.0 T 3.6 4.9 21.1 4.8 14.3 10.6 0.0 0.0 59.3
1982-83 0.0 0.0 0.0 0.0 0.4 2.1 5.0 8.9 9.0 1.2 0.0 0.0 26.6
1983-84 0.0 0.0 0.0 0.0 1.0 16.5 17.2 1.9 9.7 2.7 0.0 0.0 49.0
1984-85 0.0 0.0 0.0 0.0 T 6.6 18.9 13.3 0.3 T 0.0 0.0 39.1
1985-86 0.0 0.0 0.0 0.0 1.1 5.2 6.9 10.9 4.1 0.8 0.0 0.0 29.0
1986-87 0.0 0.0 0.0 T 3.8 0.4 17.3 T 4.7 T 0.0 0.0 26.2
1987-88 0.0 0.0 0.0 0.1 1.0 18.7 5.4 15.5 1.9 T 0.0 0.0 42.6
1988-89 0.0 0.0 0.0 T 0.9 5.0 0.4 15.1 2.0 0.6 0.5 0.0 24.5
1989-90 0.0 T 0.0 6.3 3.9 5.4 3.2 13.6 1.3 0.1 T 0.0 33.8
1990-91 0.0 0.0 0.0 T T 3.2 11.1 3.3 5.9 T 0.0 0.0 23.5
1991-92 0.0 0.0 0.0 T 1.2 7.6 5.6 1.3 11.6 1.1 0.0 T 28.4
1992-93 T 0.0 0.0 0.3 0.2 5.7 15.2 8.0 13.8 3.7 0.0 0.0 46.9
1993-94 0.0 0.0 0.0 T 0.2 1.2 14.2 26.2 T T 0.0 0.0 41.8
1994-95 0.0 0.0 0.0 0.0 T 7.0 13.1 0.4 3.5 0.1 0.0 0.0 24.1
1995-96 T 0.0 0.0 T 3.9 9.9 5.9 0.3 3.9 T T 0.0 23.9
1996-97 0.0 0.0
1997-98 11.0 T 8.2 0.0 0.0 T
1998-99 0.0 0.0 0.0 0.0 0.2 1.0 29.6 1.9 18.2 0.0 0.0 0.0 50.9
1999-00 0.0 0.0 0.0 0.0 0.0 3.5 13.6 11.6 T 1.6 0.0 T 30.3
2000-01 0.0 0.0 0.0 T 0.1 30.9 1.5 2.2 4.2 0.3 T T 39.2
2001- T 0.0 0.0 T 0.0 1.6
POR=41 YRS T T T 0.4 1.9 8.4 10.8 7.8 6.5 1.6 0.1 T 37.5



User Contributions:

Jaylin
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Jan 19, 2012 @ 5:05 am
Keep these airtcles coming as they've opened many new doors for me.

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