State Precipitation & Temperature Update for Arizona

Conditions through September 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 10/21/2011. The data are preliminary.

Precipitation Percentiles by Watershed (through September 2011)

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Temperature Percentiles by Climate Division (through September 2011)

SHORT TERM CONDITIONS: 1-6 MONTHS

September was wetter than average in the northern and some of the southeastern watersheds. Only the Salt and lower Colorado watersheds were slightly drier than average. Six watersheds had near average precipitation. September temperatures were very hot, similar to the August temperatures. September was slightly cooler due to more thunderstorm activity. All counties were above the 87^th percentile. The three month period is still the wettest short-term interval (for drought purposes – we don’t use the 1 month interval), with three watersheds wetter than average, five watersheds near average, and four slightly drier than average. However, three watersheds were below the 18^th percentile. Temperatures in the three-month period were again much warmer than average, mostly as a result of the August heat. All the southern counties plus Yavapai County were above the 96^th percentile. The six-month period was very dry in the Bill Williams and Agua Fria watersheds, which were both below the 10^th percentile, along with San Simon down on the southern border. Eight watersheds were below the 25^th percentile and four more were near average. Six month temperatures were slightly warmer than average in northern Arizona, and much warmer than average in the southern half of the state.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	76.92	CD1	90.60
Upper Colorado	78.05	CD2	87.18
Little Colorado	73.17	CD3	90.60
Verde	58.54	CD4	88.89
Bill Williams	46.34	CD5	94.87
Agua Fria	48.78	CD6	95.73
Lower Gila	43.90	CD7	93.16
Salt	34.15
Lower Colorado	31.71
Upper Gila	41.46
Santa Cruz	87.80
San Pedro	68.29
Willcox Playa	80.49
San Simon	41.46
White Water Draw	63.41

SEPTEMBER 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	61.54	CD1	82.76
Upper Colorado	53.66	CD2	88.03
Little Colorado	60.98	CD3	96.58
Verde	39.02	CD4	97.44
Bill Williams	12.20	CD5	97.44
Agua Fria	17.07	CD6	98.29
Lower Gila	46.34	CD7	96.58
Salt	46.34
Lower Colorado	26.83
Upper Gila	41.46
Santa Cruz	34.15
San Pedro	70.73
Willcox Playa	46.34
San Simon	7.32
White Water Draw	40.00

JULY 2011 - SEPTEMBER 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	35.90	CD1	65.52
Upper Colorado	56.10	CD2	61.11
Little Colorado	56.10	CD3	84.62
Verde	31.71	CD4	96.58
Bill Williams	7.32	CD5	84.62
Agua Fria	9.76	CD6	88.89
Lower Gila	46.34	CD7	94.02
Salt	36.59
Lower Colorado	26.83
Upper Gila	29.27
Santa Cruz	17.07
San Pedro	51.22
Willcox Playa	31.71
San Simon	7.32
White Water Draw	25.00

APRIL 2011 – SEPTEMBER 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 is the driest short-term period, with only one watershed, the upper Colorado, with near average precipitation. Eight watersheds are below the 13^th percentile, and three more are below the 23^rd percentile. This interval captures the drier than average winter, the dry spring and the slightly drier than average monsoon season. 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 85^th percentile.

The 24-month period is still the wettest long-term period with the Upper Colorado at the 79^th percentile, and four other watersheds above the 41^st percentile. Otherwise, it wasn’t very wet, as two watersheds are below the 8^th percentile, four more are below the 24^th percentile, and four others are between the 28^th and 39^th percentiles. From this month forward, the forecast is for a second consecutive La Niña event, so it is doubtful that the long-term conditions will have any improvement until next summer. Temperatures on the Colorado Plateau were near average, and Mohave, La Paz and Yuma counties just below the 73^rd percentile. The other counties were all above the 77^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	39.47	CD1	63.79
Upper Colorado	60.00	CD2	57.76
Little Colorado	27.50	CD3	85.34
Verde	35.00	CD4	92.24
Bill Williams	20.00	CD5	78.45
Agua Fria	7.50	CD6	86.21
Lower Gila	12.50	CD7	90.52
Salt	22.50
Lower Colorado	20.00
Upper Gila	7.50
Santa Cruz	2.50
San Pedro	5.00
Willcox Playa	10.26
San Simon	5.00
White Water Draw	5.00

OCTOBER 2010 – SEPTEMBER 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	31.94	CD1	62.61
Upper Colorado	79.49	CD2	50.43
Little Colorado	53.85	CD3	77.39
Verde	38.46	CD4	80.43
Bill Williams	23.08	CD5	72.17
Agua Fria	28.21	CD6	85.22
Lower Gila	43.59	CD7	83.91
Salt	41.03
Lower Colorado	51.28
Upper Gila	23.08
Santa Cruz	7.69
San Pedro	38.46
Willcox Playa	20.51
San Simon	5.13
White Water Draw	20.51

OCTOBER 2009 – SEPTEMBER 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 only one watershed above the 40^th percentile for precipitation. Temperatures for the three year period were warmer than average with the four northern counties below the 73^rd percentile. Gila, La Paz, Yuma, and Yavapai counties were all near the 80^th percentile. Maricopa and Pinal, plus the seven south and southeastern counties, were all above the 92^nd percentile.

The 48-month period has extremes both wet and dry. Two watersheds (Upper Colorado and Lower Gila) were wetter than average (above the 64^th percentile) and three (Virgin, White Water Draw, and Santa Cruz) were much drier than average (below the 9^th percentile). Six of the other ten are below the 25^th percentile. Temperatures for the four year period continue to be warmer than average in all counties, with Maricopa and Pinal above the 98^th percentile. The seven southeastern counties are above the 89^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	22.22	CD1	67.54
Upper Colorado	60.53	CD2	72.37
Little Colorado	39.47	CD3	80.70
Verde	18.42	CD4	80.70
Bill Williams	13.16	CD5	82.89
Agua Fria	13.16	CD6	95.61
Lower Gila	34.21	CD7	92.11
Salt	39.47
Lower Colorado	39.47
Upper Gila	7.89
Santa Cruz	2.63
San Pedro	10.53
Willcox Playa	13.16
San Simon	2.63
White Water Draw	7.89

OCTOBER 2008 – SEPTEMBER 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	8.82	CD1	66.37
Upper Colorado	67.57	CD2	73.45
Little Colorado	35.14	CD3	81.42
Verde	21.62	CD4	79.65
Bill Williams	16.22	CD5	81.42
Agua Fria	16.22	CD6	98.23
Lower Gila	64.86	CD7	89.38
Salt	51.35
Lower Colorado	32.43
Upper Gila	24.32
Santa Cruz	5.41
San Pedro	29.73
Willcox Playa	16.22
San Simon	16.22
White Water Draw	8.11

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

October 2011 Arizona Drought Update (based on precipitation data through September 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

September was wetter than average in the northern and some of the southeastern watersheds. Only the Salt and lower Colorado watersheds were slightly drier than average. Six watersheds had near average precipitation. September temperatures were very hot, similar to the August temperatures. September was slightly cooler due to more thunderstorm activity. All counties were above the 87^th percentile.

The 3-month period is still the wettest short-term interval (for drought purposes – we don’t use the 1 month interval), with three watersheds wetter than average, five watersheds near average, and four slightly drier than average. However, three watersheds were below the 18^th percentile. Temperatures in the three-month period were again much warmer than average, mostly as a result of the August heat. All the southern counties plus Yavapai County were above the 96^th percentile.

The 6-month period was very dry in the Bill Williams and Agua Fria watersheds, which were both below the 10^th percentile, along with San Simon down on the southern border. Eight watersheds were below the 25^th percentile and four more were near average. Six month temperatures were slightly warmer than average in northern Arizona, and much warmer than average in the southern half of the state.

The 12-month period is the driest short-term period, with only one watershed, the upper Colorado, with near average precipitation. Eight watersheds are below the 13^th percentile, and three more are below the 23^rd percentile. This interval captures the drier than average winter, the dry spring and the slightly drier than average monsoon season. 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 85^th percentile.

The 24-month period is still the wettest long-term period with the Upper Colorado at the 79^th percentile, and four other watersheds above the 41^st percentile. Otherwise, it wasn’t very wet, as two watersheds are below the 8^th percentile, four more are below the 24^th percentile, and four others are between the 28^th and 39^th percentiles. From this month forward, the forecast is for a second consecutive La Niña event, so it is doubtful that the long-term conditions will have any improvement until next summer. Temperatures on the Colorado Plateau were near average, and Mohave, La Paz and Yuma counties just below the 73^rd percentile. The other counties were all above the 77^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 only one watershed above the 40^th percentile for precipitation. Temperatures for the three year period were warmer than average with the four northern counties below the 73^rd percentile. Gila, La Paz, Yuma, and Yavapai counties were all near the 80^th percentile. Maricopa and Pinal, plus the seven south and southeastern counties, were all above the 92^nd percentile.

The 48-month period has extremes both wet and dry. Two watersheds (Upper Colorado and Lower Gila) were wetter than average (above the 64^th percentile) and three (Virgin, White Water Draw, and Santa Cruz) were much drier than average (below the 9^th percentile). Six of the other ten are below the 25^th percentile. Temperatures for the four year period continue to be warmer than average in all counties, with Maricopa and Pinal above the 98^th percentile. The seven southeastern counties are above the 89^th percentile.