State Precipitation & Temperature Update for Arizona

Conditions through August 2010

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 100^th 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 100^th 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. Current update is 9/27/2010. The data are preliminary.

Precipitation Percentiles by Watershed (through August 2010)

Temperature Percentiles by Climate Division (through August 2010)

SHORT TERM CONDITIONS: 1-6 MONTHS

August precipitation was quite variable across the state. Four watersheds were drier than average, the Virgin and Verde were between the 28^th and 33^rd percentiles, while the Santa Cruz and San Simon watersheds were much drier, between the 15^th and 18^th percentiles. Two watersheds, the Bill Williams and Salt, were near normal, while the other nine watersheds were all wetter than average, above the 62^nd percentile. Temperatures were much warmer than average in August. All counties were above the 67^th percentile, and all the southern counties were above the 89^th percentile. The three-month period, from June through August, was also very wet, due to the wet conditions in both July and August. However, the rainfall was not uniform across the watersheds. San Simon watershed along the southern border was the driest, below the 3^rd percentile. The Virgin, Bill Williams, and Santa Cruz were the other three watersheds with below average precipitation. Two watersheds had near normal precipitation and nine were above the 65^th percentile for precipitation. Temperatures in the three-month period were also quite warm, with all counties above the 75^th percentile. The six-month period precipitation, from March through August, has become the driest short-term interval, with five watersheds below the 25^th percentile. Four watersheds are near average, and six are wetter than average, above the 67^th percentile. All counties had temperatures near or slightly above average, with the coolest at the 55^th percentile, and the warmest at the 68^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	28.21	CD1	76.72
Upper Colorado	77.50	CD2	67.67
Little Colorado	67.50	CD3	81.03
Verde	32.50	CD4	84.48
Bill Williams	52.50	CD5	90.52
Agua Fria	62.50	CD6	89.66
Lower Gila	67.50	CD7	91.38
Salt	55.00
Lower Colorado	65.00
Upper Gila	77.50
Santa Cruz	17.50
San Pedro	77.50
Willcox Playa	75.00
San Simon	15.00
White Water Draw	60.00

AUGUST 2010: 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	15.79	CD1	83.48
Upper Colorado	67.50	CD2	78.02
Little Colorado	90.00	CD3	76.29
Verde	55.00	CD4	75.00
Bill Williams	27.50	CD5	87.07
Agua Fria	55.00	CD6	91.38
Lower Gila	82.50	CD7	87.93
Salt	85.00
Lower Colorado	77.50
Upper Gila	72.50
Santa Cruz	30.00
San Pedro	75.00
Willcox Playa	65.00
San Simon	2.50
White Water Draw	66.67

JUNE 2009 - AUGUST 2010 (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	18.42	CD1	67.83
Upper Colorado	75.00	CD2	55.17
Little Colorado	75.00	CD3	56.90
Verde	25.00	CD4	58.19
Bill Williams	15.00	CD5	56.90
Agua Fria	50.00	CD6	63.79
Lower Gila	72.50	CD7	57.33
Salt	57.50
Lower Colorado	72.50
Upper Gila	67.50
Santa Cruz	20.00
San Pedro	67.50
Willcox Playa	55.00
San Simon	12.50
White Water Draw	56.41

MARCH 2009 – AUGUST 2010 (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 12-month period precipitation is the wettest statewide, with all watersheds above the 43^rd percentile. Three watersheds are near average, and twelve are wetter than average, above the 61^st percentile. Temperatures were near average in seven counties, with Mohave, La Paz, Yuma, Maricopa and Pinal counties warmer than average and the northeastern counties slightly cooler than average.

The 24-month period is the driest long-term interval with ten watersheds drier than average. All ten are below the 37^th percentile, and six are below the 22^nd percentile. The two wettest watersheds are the lower Colorado and lower Gila, at the 61^st percentile. The other three, the upper Colorado, Salt, and San Pedro, are near average. Temperatures for the 24-month period were warmer than average in all counties, with the warmest conditions in Maricopa and Pinal counties, above the 94^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	48.65	CD1	67.83
Upper Colorado	76.92	CD2	32.17
Little Colorado	61.54	CD3	53.91
Verde	48.72	CD4	56.52
Bill Williams	43.59	CD5	69.57
Agua Fria	64.10	CD6	80.87
Lower Gila	74.36	CD7	59.13
Salt	69.23
Lower Colorado	74.36
Upper Gila	64.10
Santa Cruz	61.54
San Pedro	71.79
Willcox Playa	65.79
San Simon	53.85
White Water Draw	61.54

SEPTEMBER 2009 – AUGUST 2010 (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	16.67	CD1	70.18
Upper Colorado	50.00	CD2	64.04
Little Colorado	34.21	CD3	79.39
Verde	18.42	CD4	64.91
Bill Williams	21.05	CD5	82.46
Agua Fria	36.84	CD6	94.74
Lower Gila	60.53	CD7	80.70
Salt	47.37
Lower Colorado	60.53
Upper Gila	36.84
Santa Cruz	15.79
San Pedro	44.74
Willcox Playa	31.58
San Simon	13.16
White Water Draw	21.05

SEPTEMBER 2008 – AUGUST 2010 (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 period is mixed, with three watersheds wetter than average, lower Gila, Salt, and upper Gila, and seven drier than average. The driest are the Virgin and Santa Cruz, both below the 25^th percentile. Five watersheds are near average. Temperatures have remained above average in all counties, with the southern half of the state above the 78^th percentile for temperature. Maricopa and Pinal County continue to be above the 96^th percentile.

The 48-month period has only one watershed with above average precipitation (lower Gila at the 75^th percentile), but it also has seven watersheds with below average precipitation. Five of the dry watersheds are below the 20^th percentile, and the Virgin River is below the 6^th percentile. The four-year period continues to be the warmest interval, with all climate divisions above the 72^nd percentile, and five climate divisions above the 79^th percentile. Maricopa and Pinal Counties remain above the 98^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	11.43	CD1	69.91
Upper Colorado	56.76	CD2	71.68
Little Colorado	35.14	CD3	78.76
Verde	32.43	CD4	67.26
Bill Williams	32.43	CD5	84.96
Agua Fria	40.54	CD6	96.46
Lower Gila	81.08	CD7	81.42
Salt	67.57
Lower Colorado	51.35
Upper Gila	62.16
Santa Cruz	24.32
San Pedro	56.76
Willcox Playa	37.84
San Simon	48.65
White Water Draw	35.14

SEPTEMBER 2007 – AUGUST 2010 (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	5.88	CD1	73.45
Upper Colorado	52.78	CD2	79.46
Little Colorado	36.11	CD3	83.04
Verde	19.44	CD4	72.32
Bill Williams	19.44	CD5	86.61
Agua Fria	19.44	CD6	98.21
Lower Gila	75.00	CD7	84.38
Salt	52.78
Lower Colorado	41.67
Upper Gila	44.44
Santa Cruz	19.44
San Pedro	44.44
Willcox Playa	41.67
San Simon	27.78
White Water Draw	47.22

SEPTEMBER 2006 – AUGUST 2010 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

September 2010 Arizona Drought Update (based on precipitation data through August 2010)

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 precipitation was quite variable across the state. Four watersheds were drier than average, the Virgin and Verde were between the 28^th and 33^rd percentiles, while the Santa Cruz and San Simon watersheds were much drier, between the 15^th and 18^th percentiles. Two watersheds, the Bill Williams and Salt, were near normal, while the other nine watersheds were all wetter than average, above the 62^nd percentile. Temperatures were much warmer than average in August. All counties were above the 67^th percentile, and all the southern counties were above the 89^th percentile.

The 3-month period, from June through August, was also very wet, due to the wet conditions in both July and August. However, the rainfall was not uniform across the watersheds. San Simon watershed along the southern border was the driest, below the 3^rd percentile. The Virgin, Bill Williams, and Santa Cruz were the other three watersheds with below average precipitation. Two watersheds had near normal precipitation and nine were above the 65^th percentile for precipitation. Temperatures in the three-month period were also quite warm, with all counties above the 75^th percentile.

The 6-month period precipitation, from March through August, has become the driest short-term interval, with five watersheds below the 25^th percentile. Four watersheds are near average, and six are wetter than average, above the 67^th percentile. All counties had temperatures near or slightly above average, with the coolest at the 55^th percentile, and the warmest at the 68^th percentile.

The 12-month period precipitation is the wettest statewide, with all watersheds above the 43^rd percentile. Three watersheds are near average, and twelve are wetter than average, above the 61^st percentile. Temperatures were near average in seven counties, with Mohave, La Paz, Yuma, Maricopa and Pinal counties warmer than average and the northeastern counties slightly cooler than average.

The 24-month period is the driest long-term interval with ten watersheds drier than average. All ten are below the 37^th percentile, and six are below the 22^nd percentile. The two wettest watersheds are the lower Colorado and lower Gila, at the 61^st percentile. The other three, the upper Colorado, Salt, and San Pedro, are near average. Temperatures for the 24-month period were warmer than average in all counties, with the warmest conditions in Maricopa and Pinal counties, above the 94^th percentile.

The 36-month period is mixed, with three watersheds wetter than average, lower Gila, Salt, and upper Gila, and seven drier than average. The driest are the Virgin and Santa Cruz, both below the 25^th percentile. Five watersheds are near average. Temperatures have remained above average in all counties, with the southern half of the state above the 78^th percentile for temperature. Maricopa and Pinal County continue to be above the 96^th percentile.

The 48-month period has only one watershed with above average precipitation (lower Gila at the 75^th percentile), but it also has seven watersheds with below average precipitation. Five of the dry watersheds are below the 20^th percentile, and the Virgin River is below the 6^th percentile. The four-year period continues to be the warmest interval, with all climate divisions above the 72^nd percentile, and five climate divisions above the 79^th percentile. Maricopa and Pinal Counties remain above the 98^th percentile.