State Precipitation & Temperature Update for Arizona

Conditions through April 2010

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 6/2/2010. The data are preliminary.

Precipitation Percentiles by Watershed (through April 2010)

Temperature Percentiles by Climate Division (through April 2010)

SHORT TERM CONDITIONS: 1-6 MONTHS

April precipitation was drier than average in northern and central Arizona, and wetter than average in the southern watersheds. Most of the storms that had been moving across the state in March shifted north into Utah in April. Temperatures were near to slightly cooler than average across the state. The three-month period, February through April, was wetter than average across the northern border watersheds, and in southern Arizona, but was near or slightly drier than average throughout the central watersheds. Three-month temperatures were cooler than average in the eastern half of the state, at the 30^th percentile, and near average in central Arizona, including Maricopa, Pinal and Yuma counties. Only Mohave County was warmer than average. The six-month period precipitation, from November through April, was much wetter than average in all watersheds, above the 65^th percentile, and in seven watersheds covering northern and southeastern Arizona, it was above the 76^th percentile. This was due to the El Niño circulation that brought subtropical moisture up from the east central Pacific Ocean to provide moisture to the winter storms that also had a more southerly track this winter. Temperatures were near average in most areas, with the Colorado Plateau slightly colder than average, and Maricopa, Pinal and Mohave counties slightly warmer than average.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	62.50	CD1	46.12
Upper Colorado	32.50	CD2	40.95
Little Colorado	37.50	CD3	28.45
Verde	25.00	CD4	56.47
Bill Williams	27.50	CD5	27.16
Agua Fria	25.00	CD6	40.09
Lower Gila	67.50	CD7	50.86
Salt	20.00
Lower Colorado	20.00
Upper Gila	30.00
Santa Cruz	77.50
San Pedro	77.50
Willcox Playa	62.50
San Simon	87.50
White Water Draw	52.50

APRIL 2010: 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	77.50	CD1	60.43
Upper Colorado	70.00	CD2	30.17
Little Colorado	30.00	CD3	31.90
Verde	37.50	CD4	43.97
Bill Williams	52.50	CD5	44.83
Agua Fria	62.50	CD6	45.69
Lower Gila	72.50	CD7	27.16
Salt	45.00
Lower Colorado	60.00
Upper Gila	57.50
Santa Cruz	70.00
San Pedro	77.50
Willcox Playa	69.23
San Simon	72.50
White Water Draw	67.50

FEBRUARY 2009 - APRIL 2010 (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	72.97	CD1	62.07
Upper Colorado	84.62	CD2	29.31
Little Colorado	65.79	CD3	42.24
Verde	68.42	CD4	49.57
Bill Williams	74.36	CD5	54.31
Agua Fria	82.05	CD6	68.10
Lower Gila	82.05	CD7	49.14
Salt	71.79
Lower Colorado	87.18
Upper Gila	74.36
Santa Cruz	79.49
San Pedro	81.08
Willcox Playa	71.05
San Simon	76.92
White Water Draw	68.42

NOVEMBER 2009 – APRIL 2010 (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 Little Colorado, drier than average, due to the wet El Niño winter. Ten watersheds are near average and four are wetter than average. This wet year has alleviated short-term drought across most of the state, except a portion of the central Colorado Plateau. Temperatures have been warmer than average across most climate divisions, with the Maricopa and Pinal counties being the warmest, and the Navajo, Apache and Coconino counties being cooler than average.

The 24-month period has four watersheds wetter than average, (Salt, Lower Gila, Lower Colorado, San Simon), three drier than average (Virgin, Verde, Little Colorado), and nine near average. Temperatures for the 24-month period are warmer than average across all counties except Gila, which had near average temperatures. The warmest counties were Yuma, Maricopa and Pinal counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	48.65	CD1	70.43
Upper Colorado	76.92	CD2	40.00
Little Colorado	30.77	CD3	71.30
Verde	48.72	CD4	66.96
Bill Williams	48.72	CD5	79.13
Agua Fria	56.41	CD6	90.43
Lower Gila	74.36	CD7	68.70
Salt	56.41
Lower Colorado	64.10
Upper Gila	56.41
Santa Cruz	48.72
San Pedro	64.10
Willcox Playa	47.37
San Simon	51.28
White Water Draw	44.74

MAY 2009 – APRIL 2010 (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	19.44	CD1	69.30
Upper Colorado	57.89	CD2	65.79
Little Colorado	23.68	CD3	80.70
Verde	26.32	CD4	51.75
Bill Williams	44.74	CD5	85.09
Agua Fria	44.74	CD6	98.25
Lower Gila	81.58	CD7	73.68
Salt	63.16
Lower Colorado	60.53
Upper Gila	55.26
Santa Cruz	44.74
San Pedro	55.26
Willcox Playa	50.00
San Simon	65.79
White Water Draw	42.11

MAY 2008 – APRIL 2010 (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 remains the wettest long term interval, with five watersheds wetter than average (Salt, Upper Gila, Upper Colorado, Lower Gila, San Simon), five watersheds drier than average (Virgin, Agua Fria, Verde, Bill Williams, White Water Draw), and five watersheds near average (Little Colorado, Lower Colorado, San Pedro, Santa Cruz, Willcox Playa). However, there is no spatial pattern to the wet and dry conditions. Climate division temperatures over the three-year period remain much warmer than average in five climate divisions, and slightly warmer than average in Mohave and Gila counties.

The 48-month period remains the driest long-term period, with six watersheds drier than average (Virgin, Little Colorado, Verde, Bill Williams, Agua Fria, Santa Cruz), and only one wetter than average (Lower Gila). The other eight watersheds are near average. The four driest watersheds are below the 25^th percentile. The four-year period remains the warmest interval, with all climate divisions above the 75^th percentile, and three climate divisions above the 90^th percentile. Maricopa and Pinal Counties were above the 99^th percentile. The significance of the 4-year period being the driest interval means that a wet winter in 2010-11 would further improve the long-term drought (water supply) conditions.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	8.57	CD1	70.80
Upper Colorado	70.27	CD2	77.88
Little Colorado	48.65	CD3	83.19
Verde	37.84	CD4	74.34
Bill Williams	37.84	CD5	85.40
Agua Fria	35.14	CD6	99.12
Lower Gila	83.78	CD7	84.51
Salt	72.97
Lower Colorado	54.05
Upper Gila	62.16
Santa Cruz	40.54
San Pedro	51.35
Willcox Playa	40.54
San Simon	64.86
White Water Draw	35.14

MAY 2007 – APRIL 2010 (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	6.06	CD1	75.00
Upper Colorado	52.78	CD2	83.04
Little Colorado	36.11	CD3	83.93
Verde	25.00	CD4	79.91
Bill Williams	16.67	CD5	91.96
Agua Fria	22.22	CD6	99.11
Lower Gila	72.22	CD7	90.18
Salt	58.33
Lower Colorado	41.67
Upper Gila	58.33
Santa Cruz	33.33
San Pedro	58.33
Willcox Playa	58.33
San Simon	44.44
White Water Draw	52.78

MAY 2006 – APRIL 2010 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

May 2010 Arizona Drought Update (based on precipitation data through April 2010)

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, February through April, was wetter than average across the northern border watersheds, and in southern Arizona, but was near or slightly drier than average throughout the central watersheds. Three-month temperatures were cooler than average in the eastern half of the state, at the 30^th percentile, and near average in central Arizona, including Maricopa, Pinal and Yuma counties. Only Mohave County was warmer than average.

The 6-month period precipitation, from November through April, was much wetter than average in all watersheds, above the 65^th percentile, and in seven watersheds covering northern and southeastern Arizona, it was above the 76^th percentile. This was due to the El Niño circulation that brought subtropical moisture up from the east central Pacific Ocean to provide moisture to the winter storms that also had a more southerly track this winter. Temperatures were near average in most areas, with the Colorado Plateau slightly colder than average, and Maricopa, Pinal and Mohave counties slightly warmer than average.