State Precipitation & Temperature Update for Arizona

Conditions through March 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 5/6/2011. The data are preliminary.

Precipitation Percentiles by Watershed (through March 2011)

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Temperature Percentiles by Climate Division (through March 2011)

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SHORT TERM CONDITIONS: 1-6 MONTHS

March was extremely dry across all watersheds in Arizona, with the wettest watershed, the upper Colorado, at the 41^st percentile. All the other watersheds were below the 29^th percentile for March precipitation. The La Niña circulation continued to steer winter storms north of Arizona. March temperatures were much warmer than normal for all counties except those along the California-Arizona border. The three month period is the driest short-term period with eleven watersheds below the 15^th percentile. Two more watersheds were between the 19^th and 23^rd percentiles. The wettest watersheds were the upper and lower Colorado, at the 39^th and 29^th percentiles, respectively. The three month temperature average was near normal statewide, with the northwest and southwest corners being slightly warmer than average. The six-month period is now the wettest short-term interval with slightly wetter than average conditions in the upper Colorado watershed (67^th percentile), and near average precipitation in the Virgin, Bill Williams and Verde watersheds. The other eleven watersheds had lower than average precipitation, with the southeastern watersheds below the 15^th percentile. Six month temperatures were slightly warmer than average, in the northern and western counties, and above the 78^th percentile in the southern counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	24.39	CD1	78.21
Upper Colorado	41.46	CD2	88.89
Little Colorado	17.07	CD3	85.47
Verde	24.39	CD4	91.45
Bill Williams	29.27	CD5	81.20
Agua Fria	21.95	CD6	90.60
Lower Gila	21.95	CD7	92.31
Salt	24.39
Lower Colorado	29.27
Upper Gila	12.20
Santa Cruz	12.20
San Pedro	7.32
Willcox Playa	7.32
San Simon	12.20
White Water Draw	12.20

MARCH 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	22.50	CD1	62.50
Upper Colorado	39.02	CD2	53.42
Little Colorado	12.50	CD3	44.44
Verde	14.63	CD4	59.83
Bill Williams	19.51	CD5	51.28
Agua Fria	14.63	CD6	59.40
Lower Gila	14.63	CD7	61.54
Salt	14.63
Lower Colorado	29.27
Upper Gila	7.32
Santa Cruz	7.32
San Pedro	7.32
Willcox Playa	7.50
San Simon	9.76
White Water Draw	7.50

JANUARY 2011 - MARCH 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	52.63	CD1	70.94
Upper Colorado	67.50	CD2	69.23
Little Colorado	35.90	CD3	70.51
Verde	48.72	CD4	82.05
Bill Williams	42.50	CD5	70.09
Agua Fria	25.00	CD6	82.91
Lower Gila	22.50	CD7	78.21
Salt	35.00
Lower Colorado	40.00
Upper Gila	12.50
Santa Cruz	10.00
San Pedro	7.89
Willcox Playa	7.69
San Simon	15.00
White Water Draw	5.13

OCTOBER 2010 – MARCH 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 had no watersheds wetter than average, two near average, five slightly drier than average, and eight watersheds much drier than average. The driest watershed was the San Simon, below the 3^rd percentile. Temperatures were only slightly warmer than average, between the 65^th and 73^rd percentiles in the northern counties, and above the 82^nd percentile in the southern counties.

The 24-month period is the driest long-term interval, with ten watersheds drier than average, four near average and one, the upper Colorado, wetter than average. The wet conditions in the upper Colorado are due to the winter storms over the past two winters that have consistently crossed the northern edge of the state. Temperatures for the 24-month period are slightly warmer than average across northern Arizona, and much warmer than average in the southern counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	28.95	CD1	65.52
Upper Colorado	60.00	CD2	73.28
Little Colorado	55.00	CD3	66.81
Verde	35.00	CD4	69.83
Bill Williams	17.50	CD5	67.67
Agua Fria	7.50	CD6	87.07
Lower Gila	30.00	CD7	82.76
Salt	37.50
Lower Colorado	32.50
Upper Gila	22.50
Santa Cruz	5.00
San Pedro	17.50
Willcox Playa	20.51
San Simon	2.50
White Water Draw	17.95

APRIL 2010 – MARCH 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	24.32	CD1	68.70
Upper Colorado	71.79	CD2	61.74
Little Colorado	35.90	CD3	74.78
Verde	30.77	CD4	71.30
Bill Williams	20.51	CD5	78.70
Agua Fria	23.08	CD6	90.43
Lower Gila	58.97	CD7	80.87
Salt	41.03
Lower Colorado	46.15
Upper Gila	28.21
Santa Cruz	15.38
San Pedro	33.33
Willcox Playa	28.21
San Simon	10.26
White Water Draw	17.95

APRIL 2009 – MARCH 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 period with eleven watersheds drier than average, three watersheds near average and one watershed wetter than average. The driest watersheds are the Santa Cruz and Virgin at the 11^th percentile. Five other watersheds are below the 24^th percentile. The wettest watershed is the lower Gila at the 68^th percentile. Temperatures for the three year period were much warmer than average in all counties, with Maricopa and Pinal counties above the 95^th percentile.

The 48-month period is still the wettest long term interval with three watersheds above the 64^th percentile, five watersheds near or slightly drier than average and seven watersheds much drier than average (below the 25^th percentile). The driest watersheds are the Virgin at the 9^th percentile and the Santa Cruz at the 14^th percentile. The Willcox Playa, Bill Williams and Agua Fria are also all below the 22^nd percentile. The 48-month temperatures are much warmer than average, with only Mohave County below the 71^st percentile. Maricopa and Pinal counties are at the 98^th percentile, and the southeastern counties are at the 89^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	11.11	CD1	68.42
Upper Colorado	55.26	CD2	76.32
Little Colorado	34.21	CD3	78.95
Verde	28.95	CD4	54.39
Bill Williams	23.68	CD5	83.77
Agua Fria	15.79	CD6	97.37
Lower Gila	68.42	CD7	79.82
Salt	50.00
Lower Colorado	52.63
Upper Gila	39.47
Santa Cruz	10.53
San Pedro	26.32
Willcox Playa	21.05
San Simon	15.79
White Water Draw	18.42

APRIL 2008 – MARCH 2011 (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	8.82	CD1	70.80
Upper Colorado	70.27	CD2	82.30
Little Colorado	37.84	CD3	82.30
Verde	27.03	CD4	75.22
Bill Williams	21.62	CD5	84.51
Agua Fria	18.92	CD6	98.23
Lower Gila	75.68	CD7	89.38
Salt	64.86
Lower Colorado	43.24
Upper Gila	35.14
Santa Cruz	13.51
San Pedro	24.32
Willcox Playa	18.92
San Simon	32.43
White Water Draw	24.32

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

April 2011 Arizona Drought Update (based on precipitation data through March 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

The 3-month period is the driest short-term period with eleven watersheds below the 15^th percentile. Two more watersheds were between the 19^th and 23^rd percentiles. The wettest watersheds were the upper and lower Colorado, at the 39^th and 29^th percentiles, respectively. The three month temperature average was near normal statewide, with the northwest and southwest corners being slightly warmer than average.

The 6-month period is now the wettest short-term interval with slightly wetter than average conditions in the upper Colorado watershed (67^th percentile), and near average precipitation in the Virgin, Bill Williams and Verde watersheds. The other eleven watersheds had lower than average precipitation, with the southeastern watersheds below the 15^th percentile. Six month temperatures were slightly warmer than average, in the northern and western counties, and above the 78^th percentile in the southern counties.