State Precipitation & Temperature Update for Arizona

Conditions through August 2011

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. The percentiles have shifted to reflect the percentile categories used in the National Drought Monitor. Current update is 10/12/2011. The data are preliminary.

Precipitation Percentiles by Watershed (through August 2011)

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Temperature Percentiles by Climate Division (through August 2011)

SHORT TERM CONDITIONS: 1-6 MONTHS

August was relatively dry for the monsoon season, particularly in the northwest and south central Arizona. Only a few storms moved west of the Mogollon Rim, and the precipitation was quite localized. August temperatures set records around the state, with the Pinal-Maricopa County climate division and the Yuma-La Paz climate division having the hottest month ever, and Gila County was at the 99^th percentile. The three month period remains the wettest short-term interval with four watersheds having near average precipitation, and six having slightly less than average. However, three watersheds were below the 5^th percentile. Temperatures in the three-month period were much warmer than average, mostly as a result of the August heat. The six-month period is generally the driest short-term period, but for the southeastern corner the 12-month period has been the driest interval. In the six-month period, four watersheds are below the 5^th percentile, and six more are below the 13^th percentile. No watersheds have received near average precipitation. Six month temperatures were near average in northern and western Arizona, and were much warmer than average in all the other counties, mostly as a result of the dry monsoon so far.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	7.50	CD1	93.16
Upper Colorado	9.76	CD2	97.44
Little Colorado	34.15	CD3	99.15
Verde	21.95	CD4	99.15
Bill Williams	9.76	CD5	100
Agua Fria	12.20	CD6	100
Lower Gila	26.83	CD7	98.29
Salt	26.83
Lower Colorado	21.95
Upper Gila	39.02
Santa Cruz	19.51
San Pedro	29.27
Willcox Playa	39.02
San Simon	21.95
White Water Draw	36.59

AUGUST 2011: 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	30.77	CD1	68.1
Upper Colorado	36.59	CD2	80.77
Little Colorado	48.78	CD3	89.74
Verde	21.95	CD4	98.29
Bill Williams	4.88	CD5	88.89
Agua Fria	12.20	CD6	91.45
Lower Gila	43.90	CD7	99.15
Salt	48.78
Lower Colorado	39.02
Upper Gila	34.15
Santa Cruz	2.44
San Pedro	56.10
Willcox Playa	34.15
San Simon	2.44
White Water Draw	35.00

JUNE 2011 - AUGUST 2011 (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	12.82	CD1	57.76
Upper Colorado	31.71	CD2	64.53
Little Colorado	24.39	CD3	82.91
Verde	12.20	CD4	95.73
Bill Williams	4.88	CD5	73.93
Agua Fria	4.88	CD6	85.47
Lower Gila	29.27	CD7	96.58
Salt	12.20
Lower Colorado	21.95
Upper Gila	7.32
Santa Cruz	2.44
San Pedro	21.95
Willcox Playa	9.76
San Simon	2.44
White Water Draw	10.00

MARCH 2011 – AUGUST 2011 (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 has only one watershed, the upper Colorado, with near average precipitation, but six at or below the 5^th percentile, and two more below the 13^th percentile. The six driest watersheds are in the southeast corner of the state, and while the dry winter is the major culprit, the summer rainfall has not been sufficient to recover yet. Temperatures were slightly warmer than average across the northern counties, and significantly warmer than average in the southern half of the state, where ten counties were at or above the 87^th percentile.

The 24-month period is still the wettest long-term period with the Upper Colorado at the 77^th percentile, and four other watersheds above the 41^st percentile. Only two watersheds are below the 10^th percentile. The long term intervals (24, 36, and 48-month) continue to be wetter than the short-term intervals, but with a second consecutive La Niña winter in the forecast, that may change by spring. Temperatures on the Colorado Plateau were near average, and Mohave, La Paz and Yuma counties were below the 70^th percentile. The other counties were all above the 76^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	31.58	CD1	59.48
Upper Colorado	55.00	CD2	62.07
Little Colorado	25.00	CD3	83.62
Verde	32.50	CD4	93.1
Bill Williams	20.00	CD5	79.31
Agua Fria	5.00	CD6	87.93
Lower Gila	15.00	CD7	93.1
Salt	22.50
Lower Colorado	30.00
Upper Gila	5.00
Santa Cruz	2.50
San Pedro	5.00
Willcox Playa	10.26
San Simon	5.00
White Water Draw	2.50

SEPTEMBER 2010 – AUGUST 2011 (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	35.14	CD1	60.87
Upper Colorado	76.92	CD2	49.57
Little Colorado	41.03	CD3	76.96
Verde	30.77	CD4	80
Bill Williams	20.51	CD5	70.43
Agua Fria	17.95	CD6	87.83
Lower Gila	48.72	CD7	85.65
Salt	43.59
Lower Colorado	56.41
Upper Gila	33.33
Santa Cruz	5.13
San Pedro	33.33
Willcox Playa	20.51
San Simon	10.26
White Water Draw	20.51

SEPTEMBER 2009 – AUGUST 2011 (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 still the driest long-term interval, with two watersheds below the 3^rd percentile, six more below the 14^th percentile, and three near average for precipitation. Temperatures for the three year period were warmer than average with the four northern counties below the 72^nd percentile. Maricopa and Pinal, plus the seven south and southeastern counties, were all above the 90th percentile.

The 48-month period has two watersheds (Upper Colorado and Lower Gila) wetter than average (above the 62^nd percentile) and two (Virgin and Santa Cruz) much drier than average (below the 9^th percentile). Ten of the other eleven are also quite dry, below the 33^rd percentile. Temperatures for the four year period were also warmer than average in all counties, with Maricopa and Pinal counties above the 96^th percentile. The seven southeastern counties are above the 90^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	16.67	CD1	67.54
Upper Colorado	52.63	CD2	71.49
Little Colorado	31.58	CD3	81.58
Verde	21.05	CD4	79.82
Bill Williams	13.16	CD5	83.33
Agua Fria	10.53	CD6	96.49
Lower Gila	42.11	CD7	90.35
Salt	36.84
Lower Colorado	47.37
Upper Gila	13.16
Santa Cruz	2.63
San Pedro	10.53
Willcox Playa	7.89
San Simon	2.63
White Water Draw	7.89

SEPTEMBER 2008 – AUGUST 2011 (36-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	8.57	CD1	67.54
Upper Colorado	62.16	CD2	71.49
Little Colorado	32.43	CD3	81.58
Verde	24.32	CD4	79.82
Bill Williams	18.92	CD5	83.33
Agua Fria	18.92	CD6	96.49
Lower Gila	67.57	CD7	90.35
Salt	51.35
Lower Colorado	32.43
Upper Gila	21.62
Santa Cruz	2.70
San Pedro	21.62
Willcox Playa	18.92
San Simon	18.92
White Water Draw	13.51

SEPTEMBER 2007 – AUGUST 2011 (48-month): percentiles of precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

September 2011 Arizona Drought Update (based on precipitation data through August 2011)

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 was relatively dry for the monsoon season, particularly in the northwest and south central Arizona. Only a few storms moved west of the Mogollon Rim, and the precipitation was quite localized. August temperatures set records around the state, with the Pinal-Maricopa County climate division and the Yuma-La Paz climate division having the hottest month ever, and Gila County was at the 99^th percentile.

The 3-month period remains the wettest short-term interval with four watersheds having near average precipitation, and six having slightly less than average. However, three watersheds were below the 5^th percentile. Temperatures in the three-month period were much warmer than average, mostly as a result of the August heat. The six-month period is generally the driest short-term period, but for the southeastern corner the 12-month period has been the driest interval.

The 6-month period is generally the driest short-term period, but for the southeastern corner the 12-month period has been the driest interval. In the six-month period, four watersheds are below the 5^th percentile, and six more are below the 13^th percentile. No watersheds have received near average precipitation. Six month temperatures were near average in northern and western Arizona, and were much warmer than average in all the other counties, mostly as a result of the dry monsoon so far.

The 12-month period has only one watershed, the upper Colorado, with near average precipitation, but six at or below the 5^th percentile, and two more below the 13^th percentile. The six driest watersheds are in the southeast corner of the state, and while the dry winter is the major culprit, the summer rainfall has not been sufficient to recover yet. Temperatures were slightly warmer than average across the northern counties, and significantly warmer than average in the southern half of the state, where ten counties were at or above the 87^th percentile.

The 24-month period is still the wettest long-term period with the Upper Colorado at the 77^th percentile, and four other watersheds above the 41^st percentile. Only two watersheds are below the 10^th percentile. The long term intervals (24, 36, and 48-month) continue to be wetter than the short-term intervals, but with a second consecutive La Niña winter in the forecast, that may change by spring. Temperatures on the Colorado Plateau were near average, and Mohave, La Paz and Yuma counties were below the 70^th percentile. The other counties were all above the 76^th percentile.

The 36-month period is still the driest long-term interval, with two watersheds below the 3^rd percentile, six more below the 14^th percentile, and three near average for precipitation. Temperatures for the three year period were warmer than average with the four northern counties below the 72^nd percentile. Maricopa and Pinal, plus the seven south and southeastern counties, were all above the 90th percentile.

The 48-month period has two watersheds (Upper Colorado and Lower Gila) wetter than average (above the 62^nd percentile) and two (Virgin and Santa Cruz) much drier than average (below the 9^th percentile). Ten of the other eleven are also quite dry, below the 33^rd percentile. Temperatures for the four year period were also warmer than average in all counties, with Maricopa and Pinal counties above the 96^th percentile. The seven southeastern counties are above the 90^th percentile.