2001 DENVER, COLORADO (DEN)



Denver enjoys the invigorating climate that prevails over much of the central Rocky Mountain region, without the extremely cold mornings of the high elevations during winter, or the hot afternoons of summer at lower altitudes. Extremely warm or cold weather in Denver is usually of short duration.

Situated a long distance from any moisture source, and separated from the Pacific Ocean by several high mountain barriers, Denver enjoys low relative humidity, light precipitation, and abundant sunshine.

Air masses from four different sources influence Denver weather. These include arctic air from Canada and Alaska, warm, moist air from the Gulf of Mexico, warm, dry air from Mexico and the southwestern deserts, and Pacific air modified by its passage over mountains to the west.

In winter, the high altitude and mountains to the west combine to moderate temperatures in Denver. Invasions of cold air from the north, intensified by the high altitude, can be abrupt and severe. However, many of the cold air masses that spread southward out of Canada never reach the altitude of Denver, but move off over the lower plains to the east. Surges of air from the west are moderated in their descent down the east face of the Rockies, and reach Denver in the form of chinook winds that often raise temperatures into the 60s, even in midwinter.

In spring, polar air often collides with warm, moist air from the Gulf of Mexico and these collisions result in frequent, rapid and drastic weather changes. Spring is the cloudiest, windiest, and wettest season in the city. Much of the precipitation falls as snow, especially in March and early April. Stormy periods are interspersed with stretches of mild, sunny weather that quickly melt previous snow cover.

Summer precipitation falls mainly from scattered thunderstorms during the afternoon and evening. Mornings are usually clear and sunny, with clouds forming during early afternoon to cut off the sunshine at what would otherwise be the hottest part of the day. Severe thunderstorms, with large hail and heavy rain occasionally occur in the city, but these conditions are more common on the plains to the east.

Autumn is the most pleasant season. Few thunderstorms occur and invasions of cold air are infrequent. As a result, there is more sunshine and less severe weather than at any other time of the year.

Based on the 1951–1980 period, the average first occurrence of 32 degrees Fahrenheit in the fall is October 8 and the average last occurrence in the spring is May 3.

NORMALS, MEANS, AND EXTREMES

DENVER, CO (DEN)

LATITUDE:    LONGITUDE:     ELEVATION (FT):    TIME ZONE:    WBAN: 03017

39 49′ 58″ N  104 39′ 27″ W  GRND: 5379  BARO: 5382  MOUNTAIN (UTC + 7)

2001 Denver, Colorado (DEN)

ELEMENT POR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR
TEMPERATURE F NORMAL DAILY MAXIMUM 30 42.5 46.3 52.2 61.4 70.7 81.2 88.1 85.6 76.6 66.3 52.0 43.9 63.9
MEAN DAILY MAXIMUM 6 43.4 47.1 53.9 58.9 70.0 80.7 88.6 86.6 77.7 64.7 52.3 43.2 63.9
HIGHEST DAILY MAXIMUM 6 72 69 79 84 93 98 101 99 97 87 78 72 101
YEAR OF OCCURRENCE 1997 1999 1997 1996 1996 2001 2001 1995 1995 1997 1999 1998 JUL 2001
MEAN OF EXTREME MAXS. 6 65.7 65.5 74.5 78.0 86.9 93.7 99.0 95.6 92.4 83.4 71.7 62.7 80.8
NORMAL DAILY MINIMUM 30 13.8 18.3 23.7 32.0 41.2 50.1 56.0 54.2 45.1 34.2 23.4 15.3 33.9
MEAN DAILY MINIMUM 6 17.9 20.9 25.6 32.1 42.7 51.2 59.6 58.4 49.3 36.3 25.7 18.5 36.5
LOWEST DAILY MINIMUM 6 -14 -16 -2 6 23 34 44 42 25 3 -3 -19 -19
YEAR OF OCCURRENCE 1997 1996 1996 1997 2000 1998 1997 1995 1996 1997 1997 1998 DEC 1998
MEAN OF EXTREME MINS. 6 -2.4 2.7 7.7 16.8 30.0 39.9 50.7 49.6 32.3 20.1 4.9 0.3 21.1
NORMAL DRY BULB 30 28.2 32.3 38.0 46.8 55.9 65.6 72.1 69.8 61.0 50.2 37.6 29.6 48.9
MEAN DRY BULB 6 30.7 34.0 39.7 45.4 56.5 66.0 74.1 72.5 63.5 50.5 39.0 30.9 50.2
MEAN WET BULB 6 25.1 27.6 27.6 31.9 40.2 46.0 59.3 58.9 51.0 40.4 31.5 25.4 38.7
MEAN DEW POINT 6 15.1 16.3 21.1 27.2 38.8 44.3 49.5 50.2 41.1 28.9 21.1 15.5 30.8
NORMAL NO. DAYS WITH:
MAXIMUM 90
MAXIMUM 32
MINIMUM 32
MINIMUM 0
H/C NORMAL HEATING DEG. DAYS 30 1141 916 837 546 288 84 0 11 162 459 822 1097 6363
NORMAL COOLING DEG. DAYS 30 0 0 0 0 6 102 224 160 42 0 0 0 534
RH NORMAL (PERCENT)
HOUR 05 LST
HOUR 11 LST
HOUR 17 LST
HOUR 23 LST
S PERCENT POSSIBLE SUNSHINE
W/O MEAN NO. DAYS WITH:
HEAVY FOG (VISBY 1/4 MI) 6 2.3 3.0 3.5 2.8 2.2 1.2 1.7 1.5 1.5 2.2 1.9 1.2 25.0
THUNDERSTORMS 6 0.0 0.2 0.8 2.4 7.3 10.8 14.5 11.4 5.6 0.7 0.0 0.0 53.7
CLOUDINESS MEAN:
SUNRISE-SUNSET (OKTAS) 1 5.0 5.3 7.2 5.6 2.5 2.5 2.5
MIDNIGHT-MIDNIGHT (OKTAS) 1 5.3 7.2 6.4 3.0 2.0
MEAN NO. DAYS WITH:
CLEAR 1 3.0 10.0 9.0 6.0 10.0 12.0 2.0 7.0 6.0 9.0 13.0
PARTLY CLOUDY 1 4.0 2.0 6.0 4.0 5.5 9.0 2.0 9.0 6.0 1.0
CLOUDY 1 3.0 6.0 10.0 13.0 5.5 5.0 1.0 3.0 5.0 2.0 2.0
PR MEAN STATION PRESSURE (IN) 6 24.53 24.56 24.56 24.54 24.56 24.61 24.69 24.70 24.66 24.61 24.60 24.57 24.60
MEAN SEA-LEVEL PRES. (IN) 6 29.99 29.99 29.93 29.88 29.84 29.83 29.88 29.92 29.94 29.95 30.01 30.04 29.93
WINDS MEAN SPEED (MPH) 6 9.4 9.7 10.3 11.3 10.5 10.4 9.7 9.4 9.3 9.8 9.3 9.9 9.9
PREVAIL. DIR (TENS OF DEGS) 5 20 21 21 01 21 16 21 21 22 21 22 21 21
MAXIMUM 2-MINUTE:
SPEED (MPH) 6 41 46 53 53 49 49 54 49 39 46 45 47 54
DIR. (TENS OF DEGS) 28 26 28 33 36 30 13 28 02 29 27 30 13
YEAR OF OCCURRENCE 1996 2000 1995 2001 2001 1999 1999 2001 2001 2001 2000 1997 JUL 1999
MAXIMUM 5-SECOND:
SPEED (MPH) 6 48 54 56 60 58 63 64 61 49 54 54 53 64
DIR. (TENS OF DEGS) 29 26 32 33 01 29 13 29 02 29 28 29 13
YEAR OF OCCURRENCE 1996 2000 1997 2001 2001 1999 1999 2001 2001 2001 2000 2000 JUL 1999
PRECIPITATION NORMAL (IN) 30 0.50 0.54 1.26 1.68 2.62 2.05 1.99 1.65 1.34 0.99 0.89 0.60 16.11
MAXIMUM MONTHLY (IN) 6 0.78 0.64 1.96 5.86 4.67 3.07 5.92 3.52 2.34 1.87 0.72 0.50 5.92
YEAR OF OCCURRENCE 2001 2001 2000 1999 1995 1995 1998 1997 1996 1997 2001 1997 JUL 1998
MINIMUM MONTHLY (IN) 6 0.05 0.09 0.19 0.33 1.57 0.73 1.01 0.56 0.73 0.08 0.31 0.06 0.05
YEAR OF OCCURRENCE 1998 1996 1999 1996 1997 1998 1996 1996 1998 2001 1995 1995 JAN 1998
MAXIMUM IN 24 HOURS (IN) 6 0.51 0.30 0.63 2.06 2.00 1.15 3.06 1.46 1.22 1.12 0.47 0.19 3.06
YEAR OF OCCURRENCE 2001 2001 1996 1999 2000 1999 1997 2000 1996 1997 1999 1997 JUL 1997
NORMAL NO. DAYS WITH:
PRECIPITATION 0.01
PRECIPITATION 1.00
SNOWFALL NORMAL (IN)
MAXIMUM MONTHLY (IN)
YEAR OF OCCURRENCE
MAXIMUM IN 24 HOURS (IN)
YEAR OF OCCURRENCE
MAXIMUM SNOW DEPTH (IN)
YEAR OF OCCURRENCE
NORMAL NO. DAYS WITH:
SNOWFALL 1.0

2001 Denver, Colorado (DEN)

PRECIPITATION (inches) 2001 DENVER, CO (DEN)
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
1995 0.28 2.44 4.67 3.07 2.31 1.04 2.28 0.72 0.31 0.06
1996 0.29 0.09 0.77 0.33 2.40 1.77 1.01 0.56 2.34 0.39 0.38 0.06 10.39
1997 0.26 0.54 0.26 1.30 1.57 2.57 5.60 3.52 0.97 1.87 0.61 0.50 19.57
1998 0.05 0.23 0.86 2.47 1.73 0.73 5.92 1.19 0.73 1.20 0.40 0.42 15.93
1999 0.38 0.15 0.19 5.86 2.37 2.52 3.84 3.37 1.20 0.31 0.47 0.29 20.95
2000 0.24 0.23 1.96 0.71 3.09 0.79 1.42 3.06 1.52 0.52 0.61 0.27 14.42
2001 0.78 0.64 1.10 1.20 3.80 1.53 4.76 0.71 1.00 0.08 0.72 0.14 16.46
POR=6 YRS 0.34 0.32 0.82 2.16 2.69 1.76 3.87 2.12 1.30 0.85 0.52 0.29 17.04

2001 Denver, Colorado (DEN)

AVERAGE TEMPERATURE (F) 2001 DENVER, (DEN)
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
1995 39.3 42.9 50.0 62.2 70.9 75.3 61.7 48.5 41.8 33.0
1996 27.0 33.9 36.0 48.0 58.1 68.2 73.4 71.6 60.8 50.9 37.2 33.0 49.8
1997 27.9 30.0 42.1 40.5 56.6 67.8 73.1 69.7 64.3 49.7 34.8 27.9 48.7
1998 32.7 33.9 36.9 44.8 59.1 63.0 74.3 71.7 68.0 50.2 42.1 28.9 50.5
1999 33.7 38.6 43.7 42.6 54.8 64.2 73.9 71.2 59.2 52.5 47.3 33.8 51.3
2000 33.0 39.2 40.4 49.8 59.2 67.0 76.7 74.5 63.6 50.5 28.9 28.3 50.9
2001 30.0 28.3 39.8 49.6 57.1 69.4 76.7 73.5 66.8 51.5 40.9 31.7 51.3
POR=6 YRS 30.7 34.0 40.1 45.5 56.9 66.1 74.5 72.3 63.9 50.8 38.9 30.7 50.4

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 Denver, Colorado (DEN)

HEATING DEGREE DAYS (base 65 F) 2001 DENVER, CO (DEN)
YEAR JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN TOTAL
1994-95 788 655 457 132
1995-96 26 2 188 505 686 981 1166 894 893 230 29 0 5600
1996-97 0 4 192 444 824 985 1142 975 704 728 264 35 6297
1997-98 2 11 92 475 895 1142 996 865 865 597 186 137 6263
1998-99 1 1 46 453 680 1113 962 731 654 666 311 85 5703
1999-00 1 3 194 383 528 962 984 744 754 446 215 61 5275
2000-01 0 5 149 447 1074 1131 1079 1021 775 455 256 46 6438
2001- 0 4 65 416 717 1026

2001 Denver, Colorado (DEN)

COOLING DEGREE DAYS (base 65 F) 2001 DENVER, CO (DEN)
YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
1995 0 0 0 55 212 327 98 0 0 0
1996 0 0 0 3 26 133 269 215 71 13 0 0 730
1997 0 0 0 0 11 126 260 160 77 8 0 0 642
1998 0 0 0 0 13 88 296 215 143 0 0 0 755
1999 0 0 0 0 2 69 283 203 30 2 0 0 589
2000 0 0 0 0 43 127 368 305 115 5 0 0 963
2001 0 0 0 0 18 184 373 274 125 5 0 0 979

2001 Denver, Colorado (DEN)

SNOWFALL (inches) 2001 DENVER, CO (DEN)
YEAR JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN TOTAL
POR=



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