State Precipitation & Temperature Update for Arizona

Conditions through August 2006

Precipitation is monitored for the state of Arizona across the 15 major watersheds (see map left). From the stations within each watershed, mean values of precipitation for the watershed as a whole are computed. These mean values are ranked against the monthly mean values for the period of 1971-present. The rankings are then divided by the number of years of data and multiplied by 100% to create percentiles.

 

Here, precipitation percentile values for the most recent month, along with previous 3-, 6-, 12-, 24-, 36-, and 48-month total are shown for each watershed. Low percentile values (brown shading) indicate dry conditions while high values (green shading) indicate wet conditions. For example, a precipitation total that falls at the 100th percentile means that it is the highest precipitation total for the 1971-present period.

 

Temperature is monitored for the state of Arizona across seven climate divisions (see map left). From the stations within each climate division, mean values of temperature for the climate division as a whole are computed. These mean values are ranked against the monthly mean values for the period of 1895-present. The rankings are then divided by the number of years of data and multiplied by 100% to create percentiles.

 

Here, temperature percentile values for the most recent month, along with previous 3-, 6-, 12-, 24-, 36-, and 48-month averages are shown for each climate division. Low percentile values (blue shading) indicate cool conditions while high values (orange/red shading) indicate hot conditions. For example, a temperature that falls at the 100th percentile means that it is the highest average temperature for the 1895-present period.

 

The maps of the seven periods for precipitation and temperature are shown below, with tables of the percentile values and descriptive text following the maps.

 

 

Precipitation Percentiles by Watershed (through August 2006)

 

Temperature Percentiles by Climate Division (through August 2006)


SHORT TERM CONDITIONS: 1-6 MONTHS

The month of August was characterized by average or above average precipitation across the entire state, except the Santa Cruz basin in the south, and the Bill Williams, Upper Colorado, and Virgin River watersheds in northeast Arizona. Willcox Playa and Santa Cruz had extremely high rainfall in several short bursts, enough to cause extensive flooding along the Santa Cruz river at the beginning of the month. The Salt River watershed, where August rainfall was above the 75th percentile, had enough run-off to raise the level of Roosevelt Lake. The increase in run-off was likely due to the effects of large burn areas in the basin. August was much cooler than June or July in most areas of the state, due to the higher humidities that lasted all month. Only the northeast plateau and the southwest desert had temperatures above the 75th percentile. The southeast and northwest had average temperatures below normal. For the 3 summer month period, only the Virgin and Bill Willliams watersheds had below normal rainfall. The western half of the state had summer rainfall near or above the 60th percentile while the eastern watersheds had rainfall above the 75th percentile. The cooler August temperatures brought almost all areas of the state below the 95th percentile for the summer temperatures, although most of the state remained above the 85th percentile. The exception was the southwest desert which remained at the 99th percentile for temperature. The shift in the 6 month period, dropping the dry February and adding the wet August, is apparent in the 6 month precipitation. All watersheds, except Bill Williams, had near or above average precipitation levels, with the southeast and east central watersheds moving above the 75th percentile. Last month, all watersheds except the San Pedro and Santa Cruz were below the 50th percentile. Now, only the Santa Cruz, Upper Colorado, Virgin, and Bill Williams are below the 50th percentile for precipitation. The shift from February to August dropped the northeast plateau below the 85th percentile and raised the northwest area above the 85th percentile. The entire southern half of the state remains above the 85th percentile for temperature.

 

Watershed

Precipitation Percentile

Climate Division

Temperature Percentile

Virgin

24.29

CD1

75.89%

Upper Colorado

41.67

CD2

38.39%

Little Colorado

72.22

CD3

54.46%

Verde

50.00

CD4

38.39%

Bill Williams

36.11

CD5

77.68%

Agua Fria

77.78

CD6

68.75%

Lower Gila

50.00

CD7

26.79%

Salt

77.78

 

Lower Colorado

50.00

 

Upper Gila

83.33

 

Santa Cruz

38.89

 

San Pedro

50.00

 

Willcox Playa

94.44

 

San Simon

50.00

 

White Water Draw

91.67

 

AUGUST 2006: percentiles of precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

 

Watershed

Precipitation Percentile

Climate Division

Temperature Percentile

Virgin

29.41

CD1

84.82%

Upper Colorado

58.33

CD2

91.07%

Little Colorado

80.56

CD3

90.18%

Verde

75.00

CD4

91.96%

Bill Williams

38.89

CD5

99.11%

Agua Fria

75.00

CD6

93.75%

Lower Gila

58.33

CD7

87.50%

Salt

86.11

 

Lower Colorado

72.22

 

Upper Gila

86.11

 

Santa Cruz

88.89

 

San Pedro

97.22

 

Willcox Playa

91.67

 

San Simon

69.44

 

White Water Draw

80.00

 

JUNE 2006 - AUGUST 2006 (3-month): percentiles of precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

 

 

Watershed

Precipitation Percentile

Climate Division

Temperature Percentile

Virgin

52.94

CD1

77.68%

Upper Colorado

41.67

CD2

86.61%

Little Colorado

75.00

CD3

83.93%

Verde

63.89

CD4

85.71%

Bill Williams

25.00

CD5

85.71%

Agua Fria

52.78

CD6

86.61%

Lower Gila

66.67

CD7

91.07%

Salt

83.33

 

Lower Colorado

55.56

 

Upper Gila

80.56

 

Santa Cruz

75.00

 

San Pedro

94.44

 

Willcox Playa

80.56

 

San Simon

61.11

 

White Water Draw

77.14

 

MARCH 2005 AUGUST 2006 (6-month): percentiles of precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

 

 

INTERMEDIATE TERM CONDITIONS: 12-24 MONTHS

The intermediate time periods of 1- and 2-years continue to show the importance of the historical context of drought. Most of the watersheds remain below the 15th percentile for 12 month precipitation, while the Virgin basin dropped below the 40th percentile and the Lower Colorado River basin dropped below the 25th percentile. The addition of a wet August has not lessened the longer term drought picture. The corresponding temperatures for the 1-year period have been extremely high, above the 85th percentile everywhere except the northeast corner of the state, which is above the 75th percentile.

 

In contrast, the 2-year period shows very little evidence of dryness across the western and west central portions of the state, with precipitation totals above normal. However, the Little Colorado and the southeastern watersheds show precipitation totals below the 35th percentile, with the driest watersheds being the San Pedro and Willcox Playa. This 2-year period still includes the extremely wet winter of 2005 with the extremely dry winter of 2006. Except for climate divisions 1 and 5 along the lower Colorado River, temperatures for the 2-year period were all at or above the 80th percentile.

 


Watershed

Precipitation Percentile

Climate Division

Temperature Percentile

Virgin

33.33

CD1

78.38%

Upper Colorado

14.29

CD2

91.89%

Little Colorado

14.29

CD3

88.29%

Verde

11.43

CD4

94.59%

Bill Williams

5.71

CD5

87.39%

Agua Fria

5.71

CD6

95.50%

Lower Gila

11.43

CD7

97.30%

Salt

8.57

 

Lower Colorado

20.00

 

Upper Gila

8.57

 

Santa Cruz

8.57

 

San Pedro

37.14

 

Willcox Playa

23.53

 

San Simon

5.71

 

White Water Draw

31.43

 

AUGUST 2005 AUGUST 2006 (12-month): percentiles of precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

 

Watershed

Precipitation Percentile

Climate Division

Temperature Percentile

Virgin

96.88

CD1

70.91%

Upper Colorado

88.24

CD2

90.91%

Little Colorado

41.18

CD3

87.27%

Verde

76.47

CD4

93.64%

Bill Williams

73.53

CD5

80.00%

Agua Fria

70.59

CD6

90.00%

Lower Gila

67.65

CD7

99.09%

Salt

52.94

 

Lower Colorado

91.18

 

Upper Gila

35.29

 

Santa Cruz

17.65

 

San Pedro

32.35

 

Willcox Playa

35.29

 

San Simon

26.47

 

White Water Draw

50.00

 

AUGUST 2004 AUGUST 2006 (24-month): percentiles of precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

 

 

LONG TERM CONDITIONS: 36-48 MONTHS

The 36 month precipitation rankings have changed very little in the central and southern watersheds from the August update, but the northern third of the state has dropped from being above the 75th percentile to being between the 60th and 75th percentiles. The southern half of the state is still below the 50th percentile, while the southeastern watersheds remains below the 25th percentile. The entire state is still above the 75th percentile for temperature, with the southeast and south central portions of the state above the 95th percentile for temperature.

 

The length of the drought is still apparent from the longer 4-year period. The northern and western watersheds have had near or above normal precipitation during the 4-year period, while the eastern and southeastern watersheds are still well below the 25th percentile. Along with the dryness has been excessive heat, particularly in the southeast. This is essentially unchanged after the wet August in the southeast watersheds. The temperatures over the 4 year period have still been above the 95th percentile in the southeast and south central climate divisions, and above the 75th percentile elsewhere in the state.

 

 


Watershed

Precipitation Percentile

Climate Division

Temperature Percentile

Virgin

87.10

CD1

77.06%

Upper Colorado

66.67

CD2

92.66%

Little Colorado

30.30

CD3

90.83%

Verde

54.55

CD4

96.33%

Bill Williams

48.48

CD5

88.07%

Agua Fria

45.45

CD6

95.41%

Lower Gila

60.61

CD7

99.08%

Salt

39.39

 

Lower Colorado

75.76

 

Upper Gila

21.21

 

Santa Cruz

12.12

 

San Pedro

24.24

 

Willcox Playa

27.27

 

San Simon

24.24

 

White Water Draw

42.42

 

AUGUST 2003 AUGUST 2006 (36-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

 

Watershed

Precipitation Percentile

Climate Division

Temperature Percentile

Virgin

-99.99

CD1

78.70%

Upper Colorado

65.62

CD2

90.74%

Little Colorado

28.12

CD3

95.37%

Verde

56.25

CD4

97.22%

Bill Williams

46.88

CD5

91.67%

Agua Fria

50.00

CD6

95.37%

Lower Gila

56.25

CD7

100.00%

Salt

28.12

 

Lower Colorado

75.00

 

Upper Gila

18.75

 

Santa Cruz

15.62

 

San Pedro

15.62

 

Willcox Playa

9.38

 

San Simon

21.88

 

White Water Draw

21.88

 

AUGUST 2002 AUGUST 2006 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

 

August 2006 Arizona Drought Update based on Precipitation (data through August 2006)

The following summary describes the heat and dryness across the state for the 1-, 3-, 6-, 12-, 24-, 36-, and 48-month periods.

 

SUMMARY

August brought above average monsoon rainfall for much of the state, particularly the southeast, where a few extreme rainfall events caused widespread flooding on the Santa Cruz River. The high run-off in the Salt River basin caused the level in Roosevelt Lake to rise during August. Although the 1 month rainfall does not end the drought, it improves the rangeland conditions and provides short term relief. The rainfall and associated humidity also brought significantly cooler temperatures to the southeast and northwest parts of the state. The northeast and southwest continued to have temperatures well above average in August.

 

The 3 summer months had precipitation totals near or above average for all basins except Bill Williams and the Virgin River in the northwest. Temperatures were above the 85th percentile everywhere except the northeast plateau. In the 6-month period the Bill Williams basin had precipitation below the 25th percentile, while all other areas of the state were near or above normal. Temperatures across the state continued to be well above average for the 6-month period.

 

Most of the watersheds remain below the 15th percentile for 12 month precipitation, while the Virgin basin dropped below the 40th percentile and the Lower Colorado River basin dropped below the 25th percentile. The corresponding temperatures for the 1-year period have been extremely high, above the 85th percentile everywhere except the northeast corner of the state, which is above the 75th percentile. The 12 month period includes the wetter than normal monsoon season and the much drier than normal winter season.

 

In contrast, the 2-year period, which combines the wet winter of 2005 and wet summer of 2006 with the dry winter of 2006 and dry summer of 2005, shows very little evidence of dryness across the western and west central portions of the state, with precipitation totals above normal. However, the Little Colorado and the southeastern watersheds show precipitation totals below the 35th percentile, with the driest watersheds being the San Pedro and Willcox Playa. Except for climate divisions 1 and 5 along the lower Colorado River, temperatures for the 2-year period were all at or above the 80th percentile.

 

For the 36 month period, the northern third of the state remains above average for precipitation, while the southern half of the state is still below average, and the southeastern watersheds remain well below the 3 year average. The entire state is still well above average for temperature, with the southeast and south central portions of the state above the 95th percentile.

 

The northern and western watersheds have had near or above normal precipitation during the 4-year period, while the eastern and southeastern watersheds are still well below the 25th percentile. Along with the dryness has been excessive heat, particularly in the southeast.