State Precipitation & Temperature Update for Arizona

Conditions through April 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. Current update is 7/7/2011. The data are preliminary.

Precipitation Percentiles by Watershed (through April 2011)

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Temperature Percentiles by Climate Division (through April 2011)

SHORT TERM CONDITIONS: 1-6 MONTHS

April was near or wetter than average across all watersheds except the far southeast. Once again the storm tracks bypassed the southeastern parts of the state. While the few storms that occurred in April passed through the northern part of Arizona, the moisture remained in the western half of Arizona. April temperatures were much warmer than normal in the southern counties and only slightly warmer than average across the northern counties. The three month period was drier than average in all watersheds except the upper and lower Colorado River basins. The driest watersheds continue to be the southeastern basins. The three month temperatures were near average in Yuma, La Paz and Yavapai counties, and much warmer than average in the southern counties. The six-month period is now the driest short-term interval with only one watershed near average, ten below the 23^rd percentile, and all six in the southeast at or below the 10^th percentile. Six month temperatures were slightly warmer than average, in the northern and western counties, and above the 81^st percentile in the southeastern counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	6.10	CD1	71.79
Upper Colorado	78.05	CD2	73.93
Little Colorado	39.02	CD3	68.38
Verde	56.10	CD4	92.31
Bill Williams	68.29	CD5	80.77
Agua Fria	60.98	CD6	87.18
Lower Gila	78.05	CD7	91.45
Salt	51.22
Lower Colorado	75.61
Upper Gila	58.54
Santa Cruz	63.41
San Pedro	37.80
Willcox Playa	31.71
San Simon	80.49
White Water Draw	30.49

APRIL 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	24.39	CD1	63.36
Upper Colorado	60.98	CD2	67.95
Little Colorado	26.83	CD3	47.86
Verde	31.71	CD4	79.49
Bill Williams	36.59	CD5	56.41
Agua Fria	24.39	CD6	82.05
Lower Gila	34.15	CD7	78.63
Salt	19.51
Lower Colorado	48.78
Upper Gila	9.76
Santa Cruz	9.76
San Pedro	4.88
Willcox Playa	10.00
San Simon	31.71
White Water Draw	7.32

FEBRUARY 2011 - APRIL 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	21.05	CD1	70.94
Upper Colorado	57.50	CD2	70.09
Little Colorado	28.21	CD3	67.52
Verde	33.33	CD4	84.62
Bill Williams	32.50	CD5	73.08
Agua Fria	22.50	CD6	82.05
Lower Gila	17.50	CD7	81.62
Salt	20.00
Lower Colorado	32.50
Upper Gila	10.00
Santa Cruz	5.00
San Pedro	7.89
Willcox Playa	2.56
San Simon	10.00
White Water Draw	5.13

NOVEMBER 2010 – APRIL 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 the upper Colorado wetter than average and the Little Colorado near average. Eight watersheds were below the 23^rd percentile. The Santa Cruz and San Simon were at or below the 5^th percentile. Temperatures were much warmer than average in all counties except Mohave and Yavapai.

The 24-month period is the driest long-term interval with two watersheds wetter than average, one near average, 12 below the 39^th percentile and 7 below the 25^th percentile. Temperatures for the 24-month period were slightly warmer than average across northern Arizona, and much warmer than average in the southern counties, with the warmest conditions continuing to be found in Pinal and Maricopa counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	28.95	CD1	68.10
Upper Colorado	62.50	CD2	78.02
Little Colorado	57.50	CD3	71.55
Verde	40.00	CD4	80.60
Bill Williams	22.50	CD5	79.31
Agua Fria	15.00	CD6	87.93
Lower Gila	27.50	CD7	88.79
Salt	40.00
Lower Colorado	37.50
Upper Gila	22.50
Santa Cruz	5.00
San Pedro	12.50
Willcox Playa	15.38
San Simon	2.50
White Water Draw	15.38

MAY 2010 – APRIL 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	67.83
Upper Colorado	74.36	CD2	70.43
Little Colorado	35.90	CD3	76.52
Verde	28.21	CD4	77.39
Bill Williams	23.08	CD5	80.00
Agua Fria	23.08	CD6	93.91
Lower Gila	61.54	CD7	83.91
Salt	38.46
Lower Colorado	43.59
Upper Gila	33.33
Santa Cruz	15.38
San Pedro	33.33
Willcox Playa	23.08
San Simon	10.26
White Water Draw	17.95

MAY 2009 – APRIL 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 the most variable across the state with wet watersheds in the north and central parts of the state and dry watersheds across central and southern Arizona. Temperatures for the 36-month period were slightly warmer than average across northern Arizona, and much warmer than average in the southern counties, with the warmest conditions continuing to be found in Pinal and Maricopa counties.

The 48-month period is still the wettest long term interval with three watersheds above the 60^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 and Willcox at the 16^th percentile. The 48-month temperatures are much warmer than average, with only Mohave County below the 78^th percentile. Maricopa and Pinal counties are at the 99^th percentile, and the southeastern counties are at the 91^st percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	16.67	CD1	69.30
Upper Colorado	60.53	CD2	77.19
Little Colorado	34.21	CD3	78.07
Verde	28.95	CD4	58.77
Bill Williams	26.32	CD5	84.21
Agua Fria	21.05	CD6	98.25
Lower Gila	68.42	CD7	81.58
Salt	55.26
Lower Colorado	52.63
Upper Gila	44.74
Santa Cruz	15.79
San Pedro	26.32
Willcox Playa	21.05
San Simon	15.79
White Water Draw	18.42

MAY 2008 – APRIL 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	69.03
Upper Colorado	70.27	CD2	82.30
Little Colorado	45.95	CD3	81.42
Verde	27.03	CD4	78.76
Bill Williams	24.32	CD5	84.07
Agua Fria	18.92	CD6	99.12
Lower Gila	72.97	CD7	91.15
Salt	64.86
Lower Colorado	43.24
Upper Gila	37.84
Santa Cruz	16.22
San Pedro	21.62
Willcox Playa	16.22
San Simon	32.43
White Water Draw	24.32

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

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

April was near or wetter than average across all watersheds except the far southeast. Once again the storm tracks bypassed the southeastern parts of the state. While the few storms that occurred in April passed through the northern part of Arizona, the moisture remained in the western half of Arizona. April temperatures were much warmer than normal in the southern counties and only slightly warmer than average across the northern counties.

The 3-month period was drier than average in all watersheds except the upper and lower Colorado River basins. The driest watersheds continue to be the southeastern basins. The three month temperatures were near average in Yuma, La Paz and Yavapai counties, and much warmer than average in the southern counties.

The 6-month period is now the driest short-term interval with only one watershed near average, ten below the 23^rd percentile, and all six in the southeast at or below the 10^th percentile. Six month temperatures were slightly warmer than average, in the northern and western counties, and above the 81^st percentile in the southeastern counties.

The 12-month period had the upper Colorado wetter than average and the Little Colorado near average. Eight watersheds were below the 23^rd percentile. The Santa Cruz and San Simon were at or below the 5^th percentile. Temperatures were much warmer than average in all counties except Mohave and Yavapai.

The 24-month period is the driest long-term interval with two watersheds wetter than average, one near average, 12 below the 39^th percentile and 7 below the 25^th percentile. Temperatures for the 24-month period were slightly warmer than average across northern Arizona, and much warmer than average in the southern counties, with the warmest conditions continuing to be found in Pinal and Maricopa counties.

The 36-month period is the most variable across the state with wet watersheds in the north and central parts of the state and dry watersheds across central and southern Arizona. Temperatures for the 36-month period were slightly warmer than average across northern Arizona, and much warmer than average in the southern counties, with the warmest conditions continuing to be found in Pinal and Maricopa counties.

The 48-month period is still the wettest long term interval with three watersheds above the 60^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 and Willcox at the 16^th percentile. The 48-month temperatures are much warmer than average, with only Mohave County below the 78^th percentile. Maricopa and Pinal counties are at the 99^th percentile, and the southeastern counties are at the 91^st percentile.