State Precipitation & Temperature Update for Arizona

Conditions through August 2009

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 09/24/2009. The data are preliminary.

Precipitation Percentiles by Watershed (through August 2009)

Temperature Percentiles by Climate Division (through August 2009)

SHORT TERM CONDITIONS: 1-6 MONTHS

August precipitation was well below average in all watersheds except the lower Gila and the Virgin. Thirteen watersheds had precipitation below the 21^st percentile, and eight were below the 11^th percentile. August temperatures were above average in all climate divisions, but the northwest division, which includes the Virgin watershed, was the nearest to average at the 67^th percentile. The three-month period of June through August was much drier than average across most watersheds, with the driest summer conditions in the Little Colorado and San Simon watersheds, and the wettest conditions in the Lower Gila watershed. The Upper Gila and San Pedro watersheds had wet conditions early in the monsoon, but dried out in late July and August, leaving them between the 25^th and 40^th percentiles. Temperatures for the three-month period were above the 83^rd percentile in 4 climate divisions, and above the 91^st percentile for the division that includes Maricopa and Pinal counties. The three northern climate divisions were below the 74^th percentile. Although this is warmer than average, it is relatively cool compared to recent 3-month periods. The six-month period continues to be the worst of the short-term periods, with below average precipitation in all watersheds. Only one watershed, the lower Gila, is above the 24^th percentile for precipitation. Eleven watersheds had precipitation below the 13^th percentile, and the Santa Cruz is below the 3^rd percentile. Temperatures over the last six months were again above average statewide, with northern and central Arizona between the 71^st and 84^th percentiles, and southern Arizona above the 89^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	47.37	CD1	67.83
Upper Colorado	7.69	CD2	77.39
Little Colorado	5.13	CD3	84.78
Verde	7.69	CD4	92.17
Bill Williams	10.26	CD5	84.78
Agua Fria	10.26	CD6	90.43
Lower Gila	56.41	CD7	96.52
Salt	5.13
Lower Colorado	15.38
Upper Gila	15.38
Santa Cruz	10.26
San Pedro	15.38
Willcox Playa	10.26
San Simon	17.95
White Water Draw	20.51

AUGUST 2009: 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	16.22	CD1	73.25
Upper Colorado	15.38	CD2	60.87
Little Colorado	2.56	CD3	69.57
Verde	5.13	CD4	84.35
Bill Williams	12.82	CD5	77.83
Agua Fria	5.13	CD6	91.30
Lower Gila	71.79	CD7	83.91
Salt	7.69
Lower Colorado	12.82
Upper Gila	25.64
Santa Cruz	10.26
San Pedro	38.46
Willcox Playa	17.95
San Simon	2.56
White Water Draw	10.53

JUNE 2008 - AUGUST 2009 (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	8.11	CD1	71.93
Upper Colorado	15.38	CD2	76.52
Little Colorado	10.26	CD3	83.48
Verde	5.13	CD4	82.61
Bill Williams	5.13	CD5	80.87
Agua Fria	5.13	CD6	94.78
Lower Gila	35.90	CD7	89.57
Salt	7.69
Lower Colorado	7.69
Upper Gila	12.82
Santa Cruz	2.56
San Pedro	10.26
Willcox Playa	23.08
San Simon	5.13
White Water Draw	18.42

MARCH 2008 – AUGUST 2009 (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 was slightly below average in five watersheds and well below average in the other ten watersheds. Seven watersheds were below the 11^th percentile. The driest watersheds were in the southeast corner, plus the Virgin watershed in the northwest. During the past 12 months, temperatures have been above the 74^thpercentile in all areas of the state. Maricopa and Pinal Counties have been above the 98^th percentile.

The 24 month period remains the wettest long-term period; but only two watersheds, the Salt and lower Gila, had above average precipitation, while eight watersheds were below the 25^th percentile. Temperatures were above the 83^rd percentile everywhere except Mohave County in the northwest, which is at the 70^th percentile. The Pinal-Maricopa County climate division, is still the warmest, above the 97^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	5.56	CD1	75.44
Upper Colorado	28.95	CD2	82.46
Little Colorado	23.68	CD3	85.96
Verde	15.79	CD4	74.12
Bill Williams	26.32	CD5	89.47
Agua Fria	23.68	CD6	98.25
Lower Gila	34.21	CD7	92.98
Salt	39.47
Lower Colorado	36.84
Upper Gila	10.53
Santa Cruz	5.26
San Pedro	7.89
Willcox Playa	10.81
San Simon	7.89
White Water Draw	10.53

SEPTEMBER 2008 – AUGUST 2009 (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	2.86	CD1	69.91
Upper Colorado	43.24	CD2	84.07
Little Colorado	24.32	CD3	83.19
Verde	21.62	CD4	75.22
Bill Williams	24.32	CD5	89.38
Agua Fria	21.62	CD6	97.35
Lower Gila	67.57	CD7	88.50
Salt	64.86
Lower Colorado	37.84
Upper Gila	35.14
Santa Cruz	18.92
San Pedro	29.73
Willcox Playa	18.92
San Simon	45.95
White Water Draw	18.92

SEPTEMBER 2007 – AUGUST 2009 (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 drier than the 24-month period in most watersheds. The driest areas are in southeast and west central Arizona. The Lower Gila is still the only watershed that has received above average precipitation, at the 67^th percentile. Twelve watersheds are at or below the 36^th percentile. Temperatures over the three-year period remain well above average, with only the northwest climate division below the 73^rd percentile, and the Pinal-Maricopa County division is the warmest at the 98^th percentile.

The 48-month period remains the driest long-term period, with only the lower Gila watershed near average at the 43^rd percentile. Fourteen watersheds are below the 32^nd percentile, seven watersheds are below the 12^th percentile, and four are at or below the 3^rd percentile. The four-year temperatures continue to be the highest on record in the southern two climate divisions, and above the 89^th percentile in four other climate divisions. Only Mohave County is below the 77^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	2.94	CD1	73.21
Upper Colorado	41.67	CD2	84.82
Little Colorado	30.56	CD3	86.61
Verde	22.22	CD4	79.91
Bill Williams	16.67	CD5	88.39
Agua Fria	13.89	CD6	98.21
Lower Gila	66.67	CD7	91.07
Salt	52.78
Lower Colorado	30.56
Upper Gila	36.11
Santa Cruz	8.33
San Pedro	22.22
Willcox Playa	25.00
San Simon	27.78
White Water Draw	33.33

SEPTEMBER 2006 – AUGUST 2009 (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	3.03	CD1	76.58
Upper Colorado	20.00	CD2	89.19
Little Colorado	11.43	CD3	90.09
Verde	5.71	CD4	90.99
Bill Williams	2.86	CD5	90.99
Agua Fria	2.86	CD6	100.00
Lower Gila	42.86	CD7	100.00
Salt	25.71
Lower Colorado	17.14
Upper Gila	20.00
Santa Cruz	2.86
San Pedro	20.00
Willcox Playa	25.71
San Simon	8.57
White Water Draw	31.43

SEPTEMBER 2005 – AUGUST 2009 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

September 2009 Arizona Drought Update based on precipitation data through August 2009)

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

SUMMARY

The 3-month period of June through August was much drier than average across most watersheds, with the driest summer conditions in the Little Colorado and San Simon watersheds, and the wettest conditions in the Lower Gila watershed. The Upper Gila and San Pedro watersheds had wet conditions early in the monsoon, but dried out in late July and August, leaving them between the 25^th and 40^th percentiles. Temperatures for the three-month period were above the 83^rd percentile in 4 climate divisions, and above the 91^st percentile for the division that includes Maricopa and Pinal counties. The three northern climate divisions were below the 74^th percentile. Although this is warmer than average, it is relatively cool compared to recent 3-month periods.

The 6-month period continues to be the worst of the short-term periods, with below average precipitation in all watersheds. Only one watershed, the lower Gila, is above the 24^th percentile for precipitation. Eleven watersheds had precipitation below the 13^th percentile, and the Santa Cruz is below the 3^rd percentile. Temperatures over the last six months were again above average statewide, with northern and central Arizona between the 71^st and 84^th percentiles, and southern Arizona above the 89^th percentile.