ESTIMATED RETURN PERIODS FOR SHORT-DURATION PRECIPITATION (Inches)
RETURN PERIOD (YEARS)

Rainfall Duration

1

2

5

10

25

50

100

5 Minutes

0.17

0.26

0.38

0.47

0.59

0.68

0.77

10 Minutes

0.27

0.40

0.59

0.72

0.91

1.06

1.20

15 Minutes

0.34

0.50

0.74

0.92

1.15

1.34

1.52

30 Minutes

0.47

0.70

1.03

1.27

1.60

1.86

2.10

1 Hour

0.60

0.88

1.30

1.61

2.02

2.35

2.66

2 Hours

0.65

0.94

1.39

1.72

2.15

2.49

2.82

3 Hours

0.69

1.01

1.48

1.82

2.27

2.62

2.97

6 Hours

0.81

1.16

1.70

2.07

2.57

2.96

3.35

12 Hours

0.91

1.30

1.90

2.30

2.84

3.26

3.69

24 Hours

1.02

1.44

2.10

2.53

3.12

3.57

4.04

Examples: This means that 0.74 inches of rain can be expected in 15 minutes once every 5 years.
This means that 0.60 inches of rain can be expected in 1 hour once every year.
This means that 2.57 inches of rain can be expected in 6 hours once every 25 years.


Source: ESTIMATED RETURN PERIODS FOR SHORT DURATION PRECIPITATION IN ARIZONA, Technical Memorandum WBTM WR-44, October 1969.

THUNDERSTORMS, HAIL, AND TORNADOES
ARIZONA MONSOON

The so-called "Arizona Monsoon" is a marginal summer type monsoon, not nearly as intense as those in other places of the globe. Some people insist that it should not be called "monsoon" but rather a period of summer thunderstorm activity. It is, however, a seasonal change in the wind direction from a westerly to a southerly wind during July, August, and early September.

It is not always a sustained period because there may be periods of hot, dry weather interspersed with the hot, humid days. The monsoon feature is most pronounced over the southern and central sections of the state and becomes more marginal over the northern part. The monsoon onset is often dramatic and occurs when the very hot, dry air is replaced by a surge of moist, tropical air. The source of the moisture is the Gulf of Mexico, the Gulf of California, and the Pacific Ocean off the west coast of Mexico.

The Monsoon moisture, combined with the intense solar heating, creates uncomfortable heat and humidity and produces an abundance of thunderstorms. These thunderstorms at times are very intense and may cause very heavy rain with flash flooding and destructive winds and blowing dust with visibility near zero.

For statistical purposes, a monsoon day has been defined as a day with average dew points of 55 degrees or higher. This figure represents a relatively high moisture value and is easily measured.

Monsoon Statistics: 1896-1995

Average Date of Monsoon Onset

July 7

Earliest Date of Onset

June 16 1925

Latest Date of Onset

July 25 1987

In Two Out of Three Years, Onset is between

July 1 & July 16

Average Date of First Break

August 16

Average Data of Ending

September 13

Monsoon Statistics: 1948-1995

Average Total Number of Monsoon Days

56 days

Greatest Number of Monsoon Days

99 in 1984; 86 in 1983

Least Number of Monsoon Days

27 in 1962; 28 in 1987

Greatest number of consecutive monsoon days was 72, from June 25 through September 4, 1984. This was also the greatest number of consecutive days with dew point of 60 degrees or higher.

Arizona Indian Proverb:"Rain will occur about a week after locusts begin to sing at night".

Monsoon Start & End Dates: 1948-1995

YEAR

BEGAN

ENDED

# OF MONSOON DAYS

TOTAL RAIN (JUL-AUG-SEP)

1948

Jul 17

Sep 1

40

1.04

1949

Jul 1

Sep 21

60

1.66

1950

Jul 4

Sep 8

40

2.25

1951

Jul 11

Sep 17

65

6.98

1952

Jul 3

Sep 24

66

2.93

1953

Jul 4

Aug 31

54

1.27

1954

Jun 23

Sep 13

76

1.35

1955

Jul 11

Sep 18

59

5.99

1956

Jul 10

Aug 27

37

1.40

1957

Jul 3

Aug 30

57

1.57

1958

Jun 19

Sep 13

68

3.28

1959

Jun 28

Sep 15

74

1.85

1960

Jul 21

Sep 16

54

1.19

1961

Jul 2

Sep 18

74

2.73

1962

Jun 27

Aug 22

27

0.71

1963

Jul 19

Sep 6

44

2.71

1964

Jul 7

Sep 15

60

3.69

1965

Jul 9

Sep 19

60

0.94

1966

Jun 27

Oct 8

65

4.26

1967

Jul 3

Sep 13

67

1.14

1968

Jul 3

Sep 3

43

2.29

1969

Jul 11

Sep 19

67

2.53

YEAR

BEGAN

ENDED

# OF MONSOON DAYS

TOTAL RAIN (JUL-AUG-SEP)

1970

Jul 17

Sep 13

51

4.35

1971

Jul 13

Sep 10

55

2.15

1972

Jul 13

Sep 10

43

2.20

1973

Jul 3

Aug 22

36

1.30

1974

Jul 14

Sep 28

47

3.06

1975

Jul 3

Sep 19

58

1.20

1976

Jul 9

Sep 28

47

3.29

1977

Jul 1

Oct 10

77

2.01

1978

Jul 9

Sep 9

49

3.23

1979

Jul 17

Aug 19

30

1.61

1980

Jul 19

Sep 7

39

0.75

1981

Jul 6

Sep 24

68

1.43

1982

Jul 6

Sept 26

71

2.52

1983

Jul 7

Oct 10

86

5.29

1984

Jun 25

Oct 5

99

9.38

1985

Jul 9

Sep 2

39

2.79

1986

Jun 29

Sep 3

56

2.93

1987

Jul 25

Sep 5

28

2.10

1988

Jul 7

Sep 2

47

1.50

1989

Jul 8

Sep 6

45

1.71

1990

Jun 29

Sep 25

77

4.86

1991

Jul 4

Sep 10

36

1.07

1992

Jul 6

Sep 22

60

4.28

1993

Jul 1

Sep 13

41

0.61

1994

Jul 17

Sep 13

54

2.01

1995

Jul 11

Sep 18

51

4.58

YEAR

BEGAN

ENDED

# OF MONSOON DAYS

TOTAL RAIN (JUL-AUG-SEP)

WETTEST AND DRIEST MONSOON: 1896-1995

 

YEAR

JULY

AUGUST

SEPTEMBER

TOTAL

DRIEST

1924

0.09

0.14

0.12

0.35

 

1914

0.21

0.30

Trace

0.51

 

1932

0.11

0.10

0.34

0.55

 

1993

Trace

0.55

0.06

0.61

 

1962

0.10

0.25

0.39

0.74

WETTEST

1984

5.15

0.87

3.36

9.38

 

1911

6.47

1.68

1.16

9.31

 

1946

2.56

2.01

2.88

7.45

 

1896

4.25

1.77

1.18

7.20

 

1951

1.30

5.33

0.35

6.98



AVERAGE NUMBER OF DAYS WITH THUNDERSTORMS AND AVERAGE NUMBER OF DAYS WITH HAIL BY MONTHS: 1896-1995

Month

THUNDERSTORMS

HAIL

January

0.3

0.1

February

0.7

0.2

March

0.9

0.2

April

0.9

0.1

May

1.1

0.1

June

1.2

*

July

6.6

*

August

7.9

*

September

3.5

0.1

October

1.2

0.1

November

0.6

*

December

0.4

0.1

Annual

25.4

1.0

*Less than .05



GREATEST NUMBER OF DAYS WITH THUNDERSTORMS AND GREATEST NUMBER OF DAYS WITH HAIL BY MONTHS AND YEAR OF OCCURRENCE: 1896-1995

Month

Thunderstorms

Hail

 

Number of storms

YEAR

Number

YEAR

January

3

1982

2

1945 1949

February

5

1931

2

1942

March

7

1905

2

1912 1941 1952 1973

April

12

1926

1

1908 1915 1926 1933 1940 1941 1942 1944 1951 1976 1988

May

8

1992

1

1907 1920 1926 1930 1973 1992

June

6

1972

1

1955 1965 1972

July

16

1908 1917 1984

1

1915 1940 1970 1984

August

20

1909

1

1905 1928 1942

September

13

1897

1

1903 1935 1950 1964 1984

October

4

1912 1928

2

1981

November

4

1959

1

1898 1905 1984

December

4

1940 1965

1

1921 1923 1926 1928 19 49 1964

Annual

48

1905

5

1926


FREQUENCY OF THUNDERSTORM OCCURRENCE IN PERCENT BY DAYS: 1896-1995

DAY

JUN

JUL

AUG

SEP

OCT

1

1

10

30

18

7

5

2

14

29

16

5

10

3

20

28

13

4

15

5

26

26

10

3

20

6

30

23

8

2

25

8

32

20

7

2

Arizona Indian Proverbs: "The clouds must look like many sheep before the rains will come." "When the clouds rise in terraces of white, soon will the country of the corn priests be pierced with arrows of rain."

LIGHTNING

It is estimated that some 1800 thunderstorms are in progress over the earth's surface at any given time and that lightning strikes the earth 100 times each second.

The average annual death toll for lightning is greater than for tornadoes or hurricanes. In 1984, 3 people were injured by lightning and 5 killed in Arizona. For the U.S., the figures were: 253 injuries and 67 fatalities. For the period 1959-1984, there were 71 injuries and 41 deaths in Arizona, and 6472 injuries and 2574 deaths nationally.

Lightning is a secondary effect of electrification within a thunderstorm cloud system. Updrafts of warm moist air rising into cold air can cause small cumulus clouds to grow into large cumulonimbus cloud systems and on into thunderstorms. The transition from a small cloud to a turbulent electrified giant can occur in as little as 30 minutes.

As a thunderstorm cumulonimbus develops, interactions of charged particles, external and internal electrical fields, and complex energy exchanges produce a large electrical field within the cloud. The distribution of electricity in a thunderstorm cloud is usually a concentration of positive charge in the frozen upper layers, and a large negative charge around a positive area in the lower portions of the cloud.

PROTECT YOURSELF

When a thunderstorm threatens, get inside a home or large building, or inside an all metal (not convertible) vehicle.

Inside a home, avoid using the telephone, except for emergencies.

If outside with no time to reach a safe building or an automobile, follow these rules:

Do not stand underneath a natural lightning rod such as a tall, isolated tree in an open area.

Avoid projecting above the surrounding landscape, as you would do if you were standing on a hilltop, in an open field, on the beach, or fishing from a small boat.

Get out of and away from open water.

Get away from tractors and other metal farm equipment.

Get off of and away from motorcycles, scooters, golf carts, and bicycles. Put down golf clubs.

Stay away from wire fences, clotheslines, metal pipes, rails, and other metallic paths which would carry lightning to you from some distance away.

Avoid standing in small isolated sheds or other small structures in open areas.

In a forest, seek shelter in a low area under a thick growth of small trees. In open areas, go to a low place such as a ravine or valley. Be alert for flash floods.

If you are hopelessly isolated in a level field or prairie and you feel your hair stand on end, drop to your knees and bend forward putting your hands on your knees. Do not lie flat on the ground.

(These are from the National Weather Service Lightning Safety).

DESCRIPTION OF KNOWN TORNADOES AND FUNNEL CLOUDS IN THE GREATER PHOENIX AREA: 1955-1990

June 13, 1955

Severe thunderstorms were widespread over much of the eastern two-thirds of the state throughout the day. About 10:00 a.m., several funnel clouds were observed underneath one main cloud north of the White Tank Mountains. Later the same day (about 4:30 p.m.) possible tornado damage occurred east of Queen Creek Village; damage estimated $8,000.

July 25, 1956

At about 4:00 p.m., a small tornado caused damage along a path about 200 feet long and 15 feet wide near 4421 North 14th Street. About $250 damage was caused.

October 23, 1956

At about 3:30 p.m., a tornado was observed near Lake Pleasant Reservoir. High winds and terrific roaring in the clouds accompanied the tornado.

March 7, 1958

At 10:17 a.m., a funnel cloud was sighted in Litchfield Park, but it did not touch the ground.

March 11, 1958

About 5 miles south of Phoenix, a possible tornado damaged a chick hatchery to the extent of about $2,000.

September 24, 1958

Between 10:05 and 10:35 a.m., a well-developed tornado skipped for 4 miles across open desert 8 miles northeast of Mesa.

July 19, 1961

Between 7:18 and 7:25 p.m., a funnel cloud was observed over Tempe. Funnel did not touch the ground.

July 22, 1961

A possible tornado destroyed two hangars and damaged a number of aircraft at Deer Valley Airport.

September 8, 1961

At 1:30 p.m. possible tornadoes caused damage to roofs extending from 7th Avenue and Southern across 7th Street and Broadway, to Camelback High School, to Scottsdale and to Paradise Valley.

March 11, 1965

At 10:37 a.m. a small funnel was observed about 20 miles east-northeast of Sky Harbor Airport. It did not touch the ground.

December 19, 1967

At 5;30 p.m. a small tornado moved through a Mesa subdivision from the southwest and unroofed several homes.

July 4, 1968

At 5:30 p.m., a small tornado destroyed a house, injuring two occupants, about 5 miles east of Mesa. Two other homes and a barn suffered considerable damage. The storm was moving toward the southwest when first sighted, then turned toward the northwest and followed a short skipping path before dissipating about 5 minutes after being sighted. $25,000 damage.

July 20, 1968

At 8:30 p.m., a small tornado damaged several homes in the eastern part of Phoenix near 52nd Street and Van Buren. The funnel moved toward the southwest, accompanied by a loud roaring noise but apparently remained on the ground for only a few blocks. Damages estimated at $10,000.

October 3, 1968

At 7:00 p.m., a storm struck the residential section of Glendale causing severe damage to two apartment buildings. Several parked automobiles were heavily damaged by falling concrete blocks. Flying glass injured several persons, hospitalized one. The tornado then followed a skipping path toward the west, causing additional damage to buildings and parked trailer-houses along the way.

February 22, 1969

At 1:45 p.m., a funnel cloud touched ground briefly in the open country near Deer Valley Airport. The funnel moved to the east. No damage.

July 19, 1970

At 7;25 p.m., a funnel cloud touched ground in the open desert country of Paradise Valley. The funnel moved toward the southwest but remained visible for only a few minutes. No damage.

September 5, 1970

At 4:00 p.m., a funnel cloud touched ground in Scottsdale about 1/2 mile west of Scottsdale Road moving east. It crossed Scottsdale Road at Fillmore Street and continued farther east for about 1 mile. Fences and trees were blown down and a number of roofs were damaged along the path. Length of path was 1-1/2 miles, width of path was 100 yards, about $10,000 damage to property.

August 30, 1971

At 5:45 p.m., a tornado touched ground for about 10 minutes in an unpopulated section of south Tempe. It then moved toward the northeast into a populated area and caused considerable property damage to homes, utilities, and trees. Several homes were completely demolished, and a number of others suffered extensive roof damage. Most of the injured were not hurt badly. Many were struck by flying glass. The tornado touched down briefly in west Mesa before dissipating. The storm was accompanied by heavy hail.

September 14, 1971

At about 7:15 p.m., three funnel clouds aloft were observed approaching and converging on the Treadway Ranch located near 83rd Avenue and Thomas Road. These funnels were about 50 feet wide at the bases and tapered larger to the cloud base. They touched down briefly over the corral area where there were 15 people and many prize horses. They ripped off the roof of one of the barns and did other damage to structures and equipment in the immediate area. Miraculously no people or animals were inured by the debris. Eyewitnesses stated that the first two funnels struck almost simultaneously followed by a dead calm before the third struck. A light shower attended their passage, and the tornadoes dissipated after striking the ranch. Damage was estimated at about $29,000.

October 18, 1971

At 1:40 p.m., a small tornado touched ground in the vicinity of 56th Street and Shea Boulevard in Paradise Valley. It moved east-northeast along the north side of Shea Boulevard and crossed Scottsdale Road, touching ground for about 15 minutes. The length of path was about 1/2 mile and the width of path was 50 yards. Two houses in its path suffered considerable damage and several others had roof damage. Total damage amounted to about $15,000. A second funnel cloud formed a short time later but did not touch the ground and lasted only for a few minutes.

June 13, 1972

At 7:33 p.m., a small tornado touched ground briefly near 40th Avenue and Southern avenue in southwest Phoenix. Two house-trailers were demolished, a utility pole blown down, and several trees uprooted. The length of path was about 1/4 mile. Estimated damage was about $40,000.

June 21, 1972

At 4:30 p.m., a small tornado caused about $15,000 property damage in Apache Junction, mostly to mobile homes.

June 21, 1972

At 5:05 p.m., two funnel clouds were observed together south of Tempe over open country then dissipated a few minutes after sighting. At 5:35 p.m., a funnel cloud was observed touching ground briefly over open country south of Tempe; a bluish white flash was observed at the base of the funnel.

June 21, 1972

At 6:30 p.m., extremely heavy wind damage to property along a 2-mile front was inflicted in the northern part of Paradise Valley. Inspection of the area by National Weather Service personnel after the storm, indicated that several tornado funnels, traveling together, were probably responsible for the destruction. One witness reported seeing two funnels close to one another at the height of the storm. There was also evidence that these funnel clouds touched ground in the vicinity of 36th Street and Camelback Road in Phoenix, then traveled northeastward into Paradise Valley. Also the pattern of damage in the area indicated that more than one vortex of high velocity winds passed through the area. Several hundred homes were either completely demolished or extensively damaged. Many homes that escaped complete destruction on the night of the 21st, were further damaged on the morning of the 22nd, when additional thunderstorms in the area caused heavy rains. The Arizona Statistical Division of Emergency Services made an estimate of the total property damage for the two-day period (June 21-22, 1972) of $10,800,000. Because of the relatively short-time internal between storms on the two days, it was impossible to estimate the tornado damage alone on the 21st.

August 12, 1972

At 8:00 p.m., a small tornado touched ground briefly in south Phoenix in an unpopulated area. No damage.

September 10, 1972

At 7:05 p.m., a tornado touched ground near the intersection of South Alma School Road and West Broadway in Mesa, moving in an east-southeasterly direction. It crossed Country Club Drive and turned northeast, dissipating near the intersection of South Mesa Drive and East Broadway. The tornado was attended by locally heavy rain and one-inch hail. Observers reported frequent cloud-to-cloud lightning near the storm and that some strokes were copper-green in color. One injury occurred when a seventeen month-old girl was cut by flying glass. Property damage was estimated at $1,000,000 by Maricopa County Emergency Services.

October 18, 1972

At 6:45 p.m., a tornado touched down about 1 mile east of Apache Junction. The storm was accompanied by marble-size hail and almost continuous lightning. Several mobile-homes were demolished by the wind. Most of the damage occurred near the intersection of Tomahawk Road and Scenic Road.

October 20, 1972

At 12:00 noon, a funnel cloud aloft was observed about 8 miles north-northeast of Phoenix. The funnel did not touch ground. No damage was reported.

May 31, 1973

At 4:45 p.m., the public reported a funnel cloud near 91st Avenue and McDowell Road, not touching ground. One-inch hail was reported in the same general area.

July 7, 1974

At 2:00 p.m., a funnel cloud a few miles south of Chandler was reported by the public. It formed in the southeast sector of the storm and dissipated as the rain began.

August 24, 1974

At 8:05 p.m., a small tornado, reported by the public, touched down near 193rd Avenue and West Earl Drive and destroyed a storage shed. It traveled from west to east.

May 4, 1976

At 2:15 p.m., a tornado was observed to be about 1 to 2 miles north of Falcon Field, east-northeast of Mesa. It tore up the desert as it moved in a westerly direction and then dissipated as it entered a citrus grove. The light dust filled column was very pronounced against the dark cloud background, and it tilted toward the east with height. There was also a very narrow, rope-like, column a short distance to the east of the main tornado, and it curved to the east with height. The tornado lasted about 12 minutes, and no property damage occurred.

May 4, 1976

At about 2:15 p.m. a tornado touched down about 5 miles southeast of Scottsdale Airport, as reported by the controllers in the Scottsdale Tower. The spinning dust filled column appeared to be about 40 feet in diameter, and there was much debris around the base of the column extending out for approximately 100 yards. The column was vertical up to about 800 feet and then curved to the northeast. It dissipated about 20 minutes after forming. There was no property damage.

May 4, 1976

At 3:03 p.m., a pilot reported a tornado over the Fountain Hills area. No damage was reported.

March 25, 1977

At 12:55 p.m., a pilot on the ground reported a tornado about 2 miles west-southwest of Luke Air Force Base, moved north, and lifted into the cloud at 1;00 p.m.

July 26, 1978

At 2:45 a.m., Maricopa Sheriff's Office reported a funnel cloud near Montezuma Peak. It was verified by radar with a hook echo at about 16 miles south-southwest of Sky Harbor International Airport.

December 30, 1978

At 1:56 p.m. to 2:03 p.m., a very elongated funnel cloud was observed to the north-northeast of Sky Harbor International Airport by National Weather Service personnel. At 4:30 p.m., a funnel cloud was observed by the public to be northeast of Scottsdale. At 4:55 p.m., a family of three funnel clouds was observed by a pilot to be in the Four Peaks area.

January 25, 1979

At 5:40 p.m., a funnel cloud was reported by the public and a pilot. It did not touch the ground, but associated strong winds destroyed one mobile home, damaged another, and tore down the rafters of a church under construction in Gilbert. At Sun Lakes, a large mobile home was overturned and heavily damaged. Numerous carports and roofs were also damaged.

February 1, 1979

At 2:15 p.m., to 2:20 p.m., a funnel cloud was observed to the east of Sky Harbor International Airport and moving to the east. It was observed by National Weather Service personnel on duty.

March 28, 1979

At about 6:30 p.m., a squall with severe thunderstorms passed through the Greater Phoenix Area. Localized severe damage was incurred along a line running from near Black Canyon Freeway and Thomas Road to beyond 32nd Street and Shea Boulevard. Many businesses and homes were either destroyed or heavily damaged. Only minor injuries were reported. Funnel clouds were observed. However, there was no confirmed sighting of a tornado. Scattered debris indicated no evidence of a tornado and damage was the result of a severe downburst. Total damage was estimated at about $5,000,000.

January 18, 1980

At about 5:30 p.m., funnel clouds were observed by persons in Fountain Hills. A thunderstorm with half-inch size hail, heavy rain, and vicious winds estimated at 100 m.p.h. damaged 50 residences in Fountain Hills and Scottsdale. In Fountain Hills, 4 were destroyed and 16 severely damaged. Study of the debris pattern showed a homogeneous direction, indicating a tornado was not involved. Only two persons received minor injuries. Total damage estimated at $1,000,000.

April 30, 1980

At 9:52 a.m., a very slender funnel cloud was sighted by Deer Valley Control Tower operators to be about 3 miles to the southwest. It extended down about 500 feet from the cloud base and then retracted in four minutes. Movement was to the east.

September 5, 1981

At about 7:20 p.m., a tornado touched down during a severe thunderstorm, for about one mile, in the far northern sections of Peoria and Glendale. It knocked down a section of a 69,000-volt power line, damaged several houses and mobile homes, and uprooted large trees. No injuries were reported.

August 8, 1983

At 5:18 p.m., during a severe thunderstorm, a small tornado touched down near 83rd Avenue and Osborn and destroyed a barn.

August 16, 1983

At about 5:10 p.m., a funnel cloud was sighted by the public over the western portion of Mesa.

August 16, 1983

At around 5:30 p.m., during a violent thunderstorm a small tornado moved from south to north about 1/2 mile west of the western edge of Sky Harbor International Airport and covered a distance of about 0.3 of a mile. It stopped a moving car and exploded the windows. It also knocked down about a dozen power line poles, one of which severely damaged several parked cars on the south side of Buckeye Road.

April 28, 1984

At 1:15 p.m., a pilot reported three funnel clouds three miles west of the Superstition Mountains.

August 9, 1984

At 8:00 p.m., a small tornado touched down just northeast of I17 and Bell Road and moved to the southwest and then veered to the northwest for a total distance of about one-half mile. Several houses were damaged.

August 9, 1984

At 8:00 p.m., Luke Air Force Base radar picked up an echo indicating either a tornado or a funnel cloud to the southeast. There was no visual contact and no evidence that it touched the ground.

August 15, 1984

At 2:45 p.m., a funnel cloud was reported by the public over the southeastern section of Mesa. It was visible for a few minutes.

September 18, 1985

At 3:40 p.m., a funnel cloud was reported by the public in the vicinity of El Mirage.

April 1, 1986

At about 7:50 a.m., over the extreme northern section of Phoenix, a series of small funnel clouds in rapid succession extended down a short distance and then drew back into the cloud base.

November 18, 1986

At about 5:00 p.m., a tornado hit near Apache Junction, ripped through two mobile-home parks, and damaged at least 60 homes. There were no injuries.

February 26, 1987

Between 3:15 and 4:30 p.m., funnel clouds were sighted at Williams AFB and Tempe.

May 10, 1987

at 4:40 p.m., a pilot reported a small funnel cloud 10 miles southwest of Williams AFB, just before a dust storm lowered the visibility to near zero.

May 20, 1987

At 4:05 p.m., a pilot reported a short-lived funnel cloud about 2 to 3 miles southeast of Falcon Field.

November 1, 1987

At 2:05 a.m., a pilot reported a small funnel cloud about 14 miles northwest of Phoenix. The observer on duty at Sky Harbor Airport noted several protuberances from a wall cloud to the west.

March 2, 1988

At 6:04 p.m., there were three reports of well-developed funnel clouds from portions of central and north-central Phoenix.

April 16, 1988

At 11:03 a.m., observers at Luke AFB watched several small, short-lived funnels form and dissipate over open land to the west and northwest. Movement was to the northeast.

January 4, 1989

At 11:00 a.m., a weak tornado was observed by National Weather Service personnel at Sky Harbor Airport. Movement was to the northeast. Some roof damage was done to businesses and a few homes near downtown Phoenix.

September 3, 1990

At 5:15 p.m., a small tornado touched down north of Union Hills Drive between 7th Street and 7th Avenue, on the far north side of Phoenix. It ended at 5:45 p.m., and did not cause any damage.

SUNSHINE, CLOUDINESS, AND FOG

AVERAGE AND HIGHEST AND LOWEST PERCENTAGE OF POSSIBLE SUNSHINE
BY MONTHS AND YEAR OF OCCURRENCE
1896-1995

Month

Average

Highest

Year

Lowest

Year

January

78

100

1924

54

1935

February

80

99

1924

47

1905

March

84

99

1988

60

1935

April

89

98

1954 1961 1989 1991

68

1926

May

93

99

1924 1927 1942 1983 1991

79

1992

June

94

100

1916 1917 1928 1939

78

1931

July

85

97

1961

67

1930

August

85

97

1956 1960

64

1935

September

89

99

1955 1956 1968 1973

76

1940

October

88

99

1973 1995

65

1972

November

83

98

1948 1956

62

1965 1982

December

77

98

1958

47

1914

Annual

85

94

1960 1989

75

1935

AVERAGE ANNUAL PERCENTAGE OF POSSIBLE SUNSHINE AT PHOENIX
AS COMPARED TO OTHER MAJOR U.S. CITIES

PHOENIX

85

Detroit

54

New York

59

Albuquerque

76

Great Falls

63

Oklahoma City

68

Atlanta

61

Houston

56

Philadelphia

57

Boston

60

Kansas City

63

Pittsburgh

49

Buffalo

52

Los Angeles

73

Saint Louis

58

Chicago

54

Memphis

65

Salt Lake City

66

Cleveland

51

Miami

73

San Francisco

66

Dallas

66

Minneapolis

58

Seattle

46

Denver

70

New Orleans

59

Washington

58

 

AVERAGE NUMBER OF CLEAR, PARTLY CLOUDY, CLOUDY AND HEAVY FOG DAYS BY MONTHS
1938-1995

 

CLEAR

PARTLY CLOUDY

CLOUDY

HEAVY FOG

January

13.9

7.0

10.1

0.5

February

12.5

6.7

9.0

0.1

March

14.4

8.1

8.5

0.1

April

17.2

7.3

5.6

0.0

May

20.8

6.8

3.5

0.0

June

23.1

4.7

2.2

0.0

July

16.6

10.3

4.2

0.0

August

17.6

9.6

3.8

0.0

September

21.6

5.4

3.0

0.0

October

20.3

6.2

4.4

*

November

17.7

6.2

6.1

0.2

December

15.3

6.3

9.4

0.5

Annual

211.0

84.6

69.7

1.5

*Less than .05

GREATEST NUMBER OF CONSECUTIVE DAYS WITH 100 PERCENT SUNSHINE EACH DAY 1896-1995

28 days

June 12-July 9

1928

27 days

June 4-June 30

1939

26 days

March 4-March 29

1988

GREATEST NUMBER OF CONSECUTIVE DAYS WITH 0 PERCENT SUNSHINE EACH DAY 1896-1995

3 days

November 22-24

1965

Arizona Indian Proverb: "If the sun appears dead, not bright and clear, in the spring, expect poor crops and very little rain".

WIND

AVERAGE SPEED, PREVAILING DIRECTION, AND PEAK GUST BY MONTHS
AND DAY AND YEAR OF OCCURRENCE

Average Speed (mph)

PREVAILING DIRECTION

PEAK GUST (MPH)

DIRECTION

DAY

YEAR

January

5.3

East

60

W

27

1983

February

5.9

East

54

W

19

1980

March

6.6

East

51 51

W W

1 25

1977 1989

April

6.9

East

49 49 49

SW S S

16 10 2

1976 1977 1981

May

7.0

East

59

SSE

20

1954

June

6.8

East

73

NE

5

1978

July

7.1

West

86

SE

7

1976

August

6.6

East

78

E

6

1978

September

6.3

East

75

SW

18

1950

October

5.8

East

61

W

1

1981

November

5.3

East

60

W

30

1982

December

5.1

East

68

W

4

1953

Annual

6.2

East

86

SE

July 7

1976

Arizona Indian Proverbs: "If the snow that falls during the winter is dry and is blown about by the wind, a dry summer will follow; very damp snow indicates rain in the spring".
"When smoke rises from the bottom lands and goes to the mountain, expect an early winter".

MEAN FREQUENCY OF OCCURRENCE OF PEAK WIND GUSTS BY MONTHS: 1970-1995

MPH

JAN

FEB

MAR

APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

20-24

4

4

6

8

12

11

11

10

8

5

3

4

25-29

2

2

3

4

4

4

5

4

4

2

2

1

30-34

1

1

2

2

3

2

2

2

2

1

1

1

35-39

*

*

1

1

2

1

3

3

1

1

1

*

40-44

*

*

1

1

1

1

1

1

1

*

*

*

45-49

*

*

*

*

*

*

1

1

1

*

*

*

50-over

*

*

*

0

*

*

*

1

*

*

*

*

*Less than 0.5

Example: In July, on the average, there were 11 days with peak wind gusts 20-24 mph, 5 days with peak wind gusts 25-29 mph, 2 days with peak wind gusts 30-34 mph, etc.

ESTIMATED RETURN PERIODS OF PEAK WIND GUSTS BY MONTHS
Based on Period of Record 1957-1995

RETURN PERIOD (YEARS)

10

25

50

100

200

500

January

44

52

59

67

76

90

February

48

58

66

75

86

102

March

47

53

57

63

68

76

April

47

51

55

58

62

68

May

49

55

61

67

74

84

June

53

61

68

75

84

96

July

63

73

81

90

99

114

August

63

71

79

86

95

108

September

50

55

60

65

70

78

October

50

61

70

80

92

110

November

48

59

68

78

90

109

December

39

44

48

52

57

64

Annual

71

80

88

97

106

120

Example: This means that in the month of July, a peak wind gust of 63 mph can be expected once every 10 years, a peak gust of 73 mph once every 25 years, a peak gust of 81 mph once every 50 years, etc.

PRESSURE
AVERAGE AND HIGHEST AND LOWEST STATION PRESSURE BY MONTHS
AND DAY AND YEAR OF OCCURRENCE
1896-1995

Station Elevation 1107 Feet
1896-1995

MONTH

AVERAGE

HIGHEST PRESSURE

DAY

YEAR

LOWEST PRESSURE

DAY

YEAR

January

28.89

29.42

24

1938

28.20

4

1913

February

28.86

29.34

1

1916

28.24

23

1948

March

28.78

29.26

12

1920

28.24

3

1983

April

28.72

29.23

4

1945

28.27

28

1898

May

28.66

29.05

2

1970

28.19

18

1902

June

28.63

28.95

2

1919

28.31

20

1947

July

28.68

28.97

20

1974

28.33

14

1900

August

28.89

28.96

28

1896

28.37

22

1903

September

28.69

29.00

29

1970

28.24

24

1915

October

28.76

29.17

29

1980

28.22

11

31

1928

1981

November

28.84

29.32

18

1969

28.24

30

1982

December

28.89

29.44

24

1898

28.16

13

1984

Annual

28.76

29.44

24

1898

28.16

13

1984

 

HIGHEST AND LOWEST SEA-LEVEL PRESSURE BY MONTHS
AND DAY AND YEAR OF OCCURRENCE

1896-1995

 

HIGHEST

DAY

YEAR

LOWEST

DAY

YEAR

January

30.62

24

1938

29.35

4

1913

February

30.55

1

1916

29.36

23

1948

March

30.45

12

1920

29.37

26

1984

April

30.42

4

1945

29.37

28

1898

May

30.19

2

1970

29.32

18

1902

June

30.11

2

1919

29.40

20

1947

July

30.11

20

1974

29.43

14

1900

August

30.09

28

1896

29.47

22

1903

September

30.15

29

1970

29.34

24

1915

October

30.34

31

1981

29.34

11

1928

November

30.50

18

1969

29.37

30

1982

December

30.62

24

1898

29.30

13

1984

Annual

30.62

24 DEC 24 JAN

1898 1938

29.30

13 DEC

1984

 

NORMAL 6-HOURLY PRESSURE CHANGES IN INCHES ENDING AT:

 

0500M (5 am)

1100M (11 am)

1700M (5 pm)

2300M (11 pm)

January

-0.01

+0.06

-0.10

+0.04

February

0.00

+0.06

-0.10

+0.05

March

+0.01

+0.05

-0.11

+0.04

April

+0.02

+0.05

-0.12

+0.05

May

+0.03

+0.04

-0.12

+0.05

June

+0.03

+0.04

-0.12

+0.03

July

+0.03

+0.04

-0.14

+0.07

August

+0.03

+0.04

-0.13

+0.07

September

+0.02

+0.05

-0.12

+0.05

October

+0.02

+0.04

-0.11

+0.05

November

0.00

+0.05

-0.10

+0.05

December

0.00

+0.05

-0.10

+0.05


Source: NORMAL PRESSURE AND TENDENCIES FOR THE UNITED STATES, 1931-1940, Weather Bureau Technical Paper
No. 1, 1943.

FLYING WEATHER

PERCENTAGE FREQUENCIES OF CEILING-VISIBILITY
Ceiling (Feet)

Visibility

0

100-200

300-400

500-900

1000-1900

2000-2900

3000-4900

5000-9500

Over 9500

Total

0-to-1/8

+

+

+

0

0

0

0

+

+

+

3/16-to-3/8

+

0

0

+

0

0

0

+

+

+

1/2-to-3/4

0

+

0

+

+

+

0

+

+

+

1-to-2.5

+

0

+

+

+

+

+

+

.1

.1

3-to-6

0

0

+

+

.1

+

.1

.1

.3

.7

7-to-15

0

0

0

+

.1

.1

.7

2.5

44.4

47.9

20-to-30

0

0

0

+

+

.1

.4

1.1

22.1

23.7

35-or-more

0

0

0

0

+

+

.2

.7

26.7

27.5

Total

+

+

+

.1

.2

.3

1.4

4.5

93.6

100

+Indicates more than 0 but less than .05 percent.

Source: SUMMARY OF HOURLY OBSERVATIONS -- PHOENIX, ARIZONA, 1951-1960, Climatology of the United States No. 82-2.

FREQUENCIES OF VISIBILITY-RESTRICTING PHENOMENA
IN TOTAL NUMBER OF DAYS BY MONTHS OVER THE TWENTY-SIX YEAR PERIOD
1965-1995

Visibility in Miles (Equal to or Less Than)

 

January

February

March

 

1/4

1

3

6

1/4

1

3

6

1/4

1

3

6

K,H

0

0

12

44

0

0

1

9

0

0

0

4

BD

0

2

4

6

0

2

4

11

1

5

8

23

F

12

15

19

26

1

1

2

5

3

4

4

6

R

0

6

21

44

0

0

14

37

0

2

20

44

 

 

April

May

June

 

1/4

1

3

6

1/4

1

3

6

1/4

1

3

6

K,H

0

0

0

0

0

0

0

1

0

0

0

0

BD

0

5

12

22

4

13

17

28

5

12

16

28

F

0

0

0

3

0

0

0

0

0

0

0

0

R

0

0

3

13

0

0

2

7

0

0

1

2

 

 

July

August

September

 

1/4

1

3

6

1/4

1

3

6

1/4

1

3

6

K,H

0

0

0

2

0

0

0

0

0

0

0

1

BD

12

44

82

112

18

44

77

99

8

20

29

38

F

0

0

0

0

0

0

0

0

0

0

0

1

R

0

5

13

26

1

6

16

29

1

6

12

22

 

 

October

November

December

 

1/4

1

3

6

1/4

1

3

6

1/4

1

3

6

K,H

0

0

0

4

0

3

7

35

0

0

12

63

BD

3

5

10

18

0

1

7

7

1

1

2

3

F

1

2

2

3

6

7

9

11

11

12

21

27

R

0

2

9

19

0

3

19

35

0

4

22

53

SYMBOL KEY K,H = Smoke and/or Haze
BD = blowing Dust
F = Fog (not accompanied by rain)
R = Rain (may be accompanied by fog)


Example: For the month of July, over the twenty-six year period, there was a total of 112 days when blowing dust reduced the visibility to 6 miles or less; on 82 of these days, it was reduced to 3 miles or less; on 44 of these days, it was reduced to 1 mile or less; on 12 of these days, it was reduce to 1/4 mile or less.

HOLIDAY WEATHER INFORMATION

HOLIDAY

Average Maximum Temp

Average Minimum Temp

Highest Maximum Temp

Year

Lowest Minimum

Year

Frequency of 0.01 inch or more of precipitation

New Year's (Jan 1)

65

40

81

1981

24

1919

11

Presidents Day (Feb 15-12)

71-72

45-46

88

1977 1981

26

1910 1964

16*

Easter Sunday (Mar 22-Apr 25)

77-87

50-58

105

1989

31

1897

9*

Memorial Day (May 22-31)

96-99

66-68

114

1910

48

1916 1917 1962 1965

2*

Independence Day (Jul 4)

106

78

118

1989

63

1912

7

Labor Day (Sep1-7)

102-100

77-75

116

1950

60

1921

15*

Halloween (Oct 31)

82

54

96

1988

36

1900

11

Arizona State Fair (Oct 25-Nov 15)

84-75

57-49

97

1934

28

1916

9*

Thanksgiving Day (Nov 22-28)

72-70

47-45

89

1950

27

1931

13*

Christmas Day (Dec25)

65

41

78

1980

26

1926

15

*These percentages relate to the probability of precipitation on any one day of the given period.

WEATHER EXTREMES

WEATHER EXTREMES FOR PHOENIX AS COMPARED TO THOSE FOR ARIZONA AND UNITED STATES


HIGHEST TEMPERATURE (Fahrenheit)

Phoenix

122

June 26, 1990

Arizona

128

Lake Havasu City (June 29,1994)

United States

134

Death Valley, California (July 10, 1913)


LOWEST TEMPERATURE (Fahrenheit)

Phoenix

16

January 7, 1913

Arizona

-40

Hawley Lake (January 7, 1971)

United States

-80 -70

Prospect Creek (25 SE Bettles), Alaska (January 23,1971) Rogers Pass, Montana (January 20, 1954)


GREATEST PRECIPITATION IN ONE HOUR (Inches)

Phoenix

1.72

August 18, 1966

Arizona

3.52

Tempe Citrus Experiment Station (September 14, 1969)

United States

12.00

Holt, Missouri (June 22, 1947) Kilauea Sugar Plantation Hawaii (January 24-25, 1956)


GREATEST PRECIPITATION IN TWENTY-FOUR HOURS (Inches)

Phoenix

4.98

July 1-2, 1911

Arizona

11.40

Workman Creek (30 NNW Globe) September 4-5, 1970

United States

43.00

Alvin, Texas July 25-26, 1979


GREATEST PRECIPITATION IN ONE CALENDAR MONTH (Inches)

Phoenix

6.47

July 1911

Arizona

16.95

Crown King August 1951

United States

107.00

Kukui, Hawaii March 1942

(Continental)

71.54

Helen Mine, California January 1909


GREATEST PRECIPITATION IN ONE CALENDAR YEAR (Inches)

Phoenix

19.73

1905

Arizona

58.92

Hawley Lake 1978

United States

704.83

Kukui, Hawaii 1982

Continental

332.29

MacLeod Harbor, Alaska 1976


LEAST PRECIPITATION IN ONE CALENDAR YEAR (Inches)

Phoenix

2.82

1956

Arizona

0.07

Davis Dam 1956

United States

0.00

Death Valley, California 1929 Bagdad, California 1913

 

Weather Extremes

GREATEST SNOWFALL IN TWENTY-FOUR HOURS (Inches)

Phoenix

1.0

January 20, 1933; January 20-21, 1937

Arizona

38.0

Heber Ranger Station December 14, 1967

United States

75.8

Silver Lake, Colorado April 14-15, 1921


GREATEST SNOWFALL IN ONE STORM (Inches)

Phoenix

1.0

January 20, 1933; January 20-21, 1937

Arizona

67.0

Heber Ranger Station December 13-16, 1967

United States

189.0

Mt. Shasta Ski Bowl, California February 13-19, 1959

 

 

175.4 Thompson Pass, Alaska December 26-31 1955


GREATEST SNOWFALL IN ONE CALENDAR MONTH (Inches)

Phoenix

1.0

January 1933; January 1937

Arizona

123.0

Sunrise Mountain March 1973

United States

390.0

Tamarack, California January 1911


GREATEST SNOWFALL IN ONE SEASON (Inches)

Phoenix

1.0

1932-1933; 1936-1937

Arizona

400.9

Sunrise Mountain 1972-1973

United States

1122.0

Rainier Paradise Ranger Station, Washington 1971-1972

 

974.5

Thompson Pass, Alaska 1952-1953


GREATEST DEPTH OF SNOW ON THE GROUND (Inches)

Phoenix

1

January 20, 1933; January 21, 1937

Arizona

91

Hawley Lake December 21, 1967

United States

451

Tamarack, California March 11, 1911


HIGHEST SEA-LEVEL PRESSURE (Inches)

Phoenix

30.62

December 24, 1898; January 24, 1938

Arizona

31.21

Grand Canyon December 22, 1967

United States

31.85

Northway, Alaska January 31, 1989


LOWEST SEA-LEVEL PRESSURE (Inches)

Phoenix

29.30

December 13, 1984

Arizona

29.15

Flagstaff February 7, 1937

United States

26.35

Matecumbe Key, Florida September 2, 1935


HIGHEST WIND VELOCITY, PEAK GUST (Miles Per Hour)

Phoenix

115

Dear Valley Airport: August 14,1996 (Wind speed possibly higher: wind instrument "pegged the meter" at 100 Knots, i.e., 115 MPH)

 

101

Luke AFB: August 29,1996

Arizona

115

Deer Valley Airport, Phoenix: August 14, 1996 (see note above)

 

101

Luke AFB, Phoenix: August 29, 1996

 

94

Davis-Monthan AFB, Tucson: July 8, 1996

United States

231

Mt. Washington, New Hampshire April 12, 1934