State Precipitation & Temperature Update for Arizona

Conditions through July 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 9/25/2010. The data are preliminary.

Precipitation Percentiles by Watershed (through July 2010)

Temperature Percentiles by Climate Division (through July 2010)

SHORT TERM CONDITIONS: 1-6 MONTHS

July precipitation was above or near average for all watersheds except the Bill Williams and San Simon basins. The Agua Fria and Virgin watershed were near average, and eleven others were above the 62^nd percentile. Four watersheds, the Little Colorado, lower Colorado, lower Gila and Salt watersheds were above the 87^th percentile for July. The Little Colorado was the wettest since 1971. Temperatures were extremely warm in July, with six climate divisions above the 85^th percentile. Only Gila County was below the 85^th percentile. Although many places experienced numerous thunderstorms, warm cloudy nights kept nighttime temperatures high, resulting in higher than average temperatures. The three-month period, from May through July, is the driest short-term period with seven watersheds at or below the 40^th percentile, three near average, and five above the 64^th percentile. The dryness was due to the drier than average conditions in May and June. The monsoon activity began quite late in most areas of the state. This period also had relatively mild temperatures with two climate divisions near average for temperature, and five climate divisions slightly warmer than normal, between the 62^nd and 72^nd percentiles. The six-month period precipitation, from February through July, remains the wettest short-term period, other than the single month of July. Only two watersheds, the Bill Williams and San Simon, had below average rainfall, while four received near average rainfall, and nine watersheds had above average rainfall during the past six months. This has helped to improve rangeland and forage, as well as fill stock ponds during the spring and summer. Only Mohave County had above average temperatures in the six month period. All other counties had average temperatures over the six month interval.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	41.03	CD1	93.10
Upper Colorado	65.00	CD2	85.78
Little Colorado	100.00	CD3	88.79
Verde	70.00	CD4	78.88
Bill Williams	20.00	CD5	93.97
Agua Fria	57.50	CD6	96.55
Lower Gila	87.50	CD7	90.52
Salt	95.00
Lower Colorado	92.50
Upper Gila	75.00
Santa Cruz	62.50
San Pedro	80.00
Willcox Playa	65.00
San Simon	25.00
White Water Draw	84.62

JULY 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	20.51	CD1	71.74
Upper Colorado	30.00	CD2	62.93
Little Colorado	92.50	CD3	56.90
Verde	40.00	CD4	50.00
Bill Williams	7.50	CD5	63.36
Agua Fria	35.00	CD6	70.26
Lower Gila	82.50	CD7	65.52
Salt	87.50
Lower Colorado	90.00
Upper Gila	52.50
Santa Cruz	40.00
San Pedro	55.00
Willcox Playa	47.50
San Simon	12.50
White Water Draw	64.10

MAY 2009 - JULY 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	64.10	CD1	66.96
Upper Colorado	62.50	CD2	44.83
Little Colorado	65.00	CD3	43.10
Verde	42.50	CD4	45.26
Bill Williams	20.00	CD5	52.59
Agua Fria	55.00	CD6	58.62
Lower Gila	77.50	CD7	43.10
Salt	62.50
Lower Colorado	75.00
Upper Gila	55.00
Santa Cruz	52.50
San Pedro	77.50
Willcox Playa	61.54
San Simon	35.00
White Water Draw	69.23

FEBRUARY 2009 – JULY 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 very close to normal in most watersheds. Ten watersheds were near the 50^th percentile, while only one was drier than average, Bill Williams, at the 38^th percentile. Four watersheds, including the San Pedro in southern Arizona, were above the 61^st percentile. Temperatures in most counties were only slightly warmer than average, but the Colorado Plateau was cooler than normal, at the 33^rd percentile. The warmest counties were Maricopa and Pinal at the 81^st percentile.

The 24-month period is quite dry, due to the dry conditions during the La Niña winter of 2008-2009. Four watersheds are below the 23^rd percentile, while seven more are between the 26^th and 37^th percentiles for precipitation. The upper Colorado and Salt are near average, and the lower Gila and lower Colorado are above the 63^rd percentile. Temperatures for the 24-month period were warmer than average everywhere except Gila County. Yavapai and all the southern counties were above the 78^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	55.56	CD1	68.70
Upper Colorado	61.54	CD2	33.04
Little Colorado	41.03	CD3	60.43
Verde	41.03	CD4	54.78
Bill Williams	38.46	CD5	60.87
Agua Fria	51.28	CD6	80.87
Lower Gila	74.36	CD7	61.30
Salt	58.97
Lower Colorado	71.79
Upper Gila	58.97
Santa Cruz	53.85
San Pedro	61.54
Willcox Playa	50.00
San Simon	53.85
White Water Draw	48.72

AUGUST 2009 – JULY 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	19.44	CD1	70.18
Upper Colorado	52.63	CD2	64.91
Little Colorado	28.95	CD3	80.70
Verde	26.32	CD4	56.14
Bill Williams	28.95	CD5	82.02
Agua Fria	34.21	CD6	96.49
Lower Gila	68.42	CD7	78.95
Salt	57.89
Lower Colorado	63.16
Upper Gila	36.84
Santa Cruz	23.68
San Pedro	36.84
Willcox Playa	21.05
San Simon	34.21
White Water Draw	18.42

AUGUST 2008 – JULY 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 remains the wettest long term interval, with seven watersheds below the 38^th percentile, and the driest, the Virgin River, below the 9^th percentile. Six watersheds are near average, and two, the lower Gila and Salt, are wetter than average, which is why the Salt-Verde reservoir system is still nearly full. Those watersheds have had two-three consecutive wet or normal years, while other parts of the state have not been as consistent. Temperatures for the 36-month period are similar to the 24-month period, but slightly warmer in Gila County and the northeastern counties.

The 48-month period also has seven watersheds drier than average, below the 39^th percentile, and four of those are at or below the 25^th percentile. Six are near average and only one, the lower Gila, is wetter than average. The four-year period continues to be the warmest interval, with only Mohave and Gila Counties below the 76^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	8.33	CD1	70.80
Upper Colorado	59.46	CD2	71.68
Little Colorado	45.95	CD3	79.20
Verde	29.73	CD4	63.72
Bill Williams	29.73	CD5	83.63
Agua Fria	32.43	CD6	96.46
Lower Gila	81.08	CD7	80.97
Salt	72.97
Lower Colorado	56.76
Upper Gila	59.46
Santa Cruz	35.14
San Pedro	45.95
Willcox Playa	32.43
San Simon	48.65
White Water Draw	37.84

AUGUST 2007 – JULY 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	2.94	CD1	73.45
Upper Colorado	50.00	CD2	77.68
Little Colorado	38.89	CD3	83.04
Verde	19.44	CD4	67.86
Bill Williams	16.67	CD5	84.82
Agua Fria	19.44	CD6	97.32
Lower Gila	72.22	CD7	83.93
Salt	58.33
Lower Colorado	41.67
Upper Gila	52.78
Santa Cruz	25.00
San Pedro	38.89
Willcox Playa	52.78
San Simon	30.56
White Water Draw	50.00

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

August 2010 Arizona Drought Update (based on precipitation data through July 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

July precipitation was above or near average for all watersheds except the Bill Williams and San Simon basins. The Agua Fria and Virgin watershed were near average, and eleven others were above the 62^nd percentile. Four watersheds, the Little Colorado, lower Colorado, lower Gila and Salt watersheds were above the 87^th percentile for July. The Little Colorado was the wettest since 1971. Temperatures were extremely warm in July, with six climate divisions above the 85^th percentile. Only Gila County was below the 85^th percentile. Although many places experienced numerous thunderstorms, warm cloudy nights kept nighttime temperatures high, resulting in higher than average temperatures.

The 3-month period, from May through July, is the driest short-term period with seven watersheds at or below the 40^th percentile, three near average, and five above the 64^th percentile. The dryness was due to the drier than average conditions in May and June. The monsoon activity began quite late in most areas of the state. This period also had relatively mild temperatures with two climate divisions near average for temperature, and five climate divisions slightly warmer than normal, between the 62^nd and 72^nd percentiles.

The 6-month period precipitation, from February through July, remains the wettest short-term period, other than the single month of July. Only two watersheds, the Bill Williams and San Simon, had below average rainfall, while four received near average rainfall, and nine watersheds had above average rainfall during the past six months. This has helped to improve rangeland and forage, as well as fill stock ponds during the spring and summer. Only Mohave County had above average temperatures in the six month period. All other counties had average temperatures over the six month interval.

The 12-month period precipitation is very close to normal in most watersheds. Ten watersheds were near the 50^th percentile, while only one was drier than average, Bill Williams, at the 38^th percentile. Four watersheds, including the San Pedro in southern Arizona, were above the 61^st percentile. Temperatures in most counties were only slightly warmer than average, but the Colorado Plateau was cooler than normal, at the 33^rd percentile. The warmest counties were Maricopa and Pinal at the 81^st percentile.

The 24-month period is quite dry, due to the dry conditions during the La Niña winter of 2008-2009. Four watersheds are below the 23^rd percentile, while seven more are between the 26^th and 37^th percentiles for precipitation. The upper Colorado and Salt are near average, and the lower Gila and lower Colorado are above the 63^rd percentile. Temperatures for the 24-month period were warmer than average everywhere except Gila County. Yavapai and all the southern counties were above the 78^th percentile.

The 36-month period remains the wettest long term interval, with seven watersheds below the 38^th percentile, and the driest, the Virgin River, below the 9^th percentile. Six watersheds are near average, and two, the lower Gila and Salt, are wetter than average, which is why the Salt-Verde reservoir system is still nearly full. Those watersheds have had two-three consecutive wet or normal years, while other parts of the state have not been as consistent. Temperatures for the 36-month period are similar to the 24-month period, but slightly warmer in Gila County and the northeastern counties.

The 48-month period also has seven watersheds drier than average, below the 39^th percentile, and four of those are at or below the 25^th percentile. Six are near average and only one, the lower Gila, is wetter than average. The four-year period continues to be the warmest interval, with only Mohave and Gila Counties below the 76^th percentile.