State Precipitation & Temperature Update for Arizona

Conditions through May 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 06/22/2009. The data are preliminary.

Precipitation Percentiles by Watershed (through May 2009)

Temperature Percentiles by Climate Division (through May 2009)

SHORT TERM CONDITIONS: 1-6 MONTHS

May precipitation was well above average throughout the state, as a persistent low pressure system off the California coast pulled sub-tropical moisture into Arizona and it rained somewhere in the state every day after the 18^th of the month. The first half of the month was unusually hot with a record string of 100^o+ days. May was the 2^nd hottest on record in Flagstaff and Tucson and the 4^th hottest in Phoenix. The three-month period of March through May was slightly drier than average in northern Arizona, and much drier than average in the southern half of the state. The only watersheds wetter than average were Willcox Playa and White Water Draw in the southeast corner. Temperatures for the three-month period were well above average statewide. The six-month period precipitation was near or above average in the northern two thirds of the state, except the Virgin River watershed, which continues to be exceptionally dry. The period was slightly drier than average in the southern half of Arizona, and well below average in the San Pedro watershed. Temperatures over the last six months were well above average in all climate divisions.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	33.33	CD1	94.78
Upper Colorado	97.44	CD2	97.39
Little Colorado	94.87	CD3	95.65
Verde	89.74	CD4	95.65
Bill Williams	64.10	CD5	97.39
Agua Fria	92.31	CD6	98.26
Lower Gila	89.74	CD7	96.52
Salt	84.62
Lower Colorado	67.95
Upper Gila	76.92
Santa Cruz	79.49
San Pedro	66.67
Willcox Playa	89.74
San Simon	100.00
White Water Draw	84.62

MAY 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	7.69	CD1	83.33
Upper Colorado	28.21	CD2	83.48
Little Colorado	35.90	CD3	78.26
Verde	25.64	CD4	88.70
Bill Williams	12.82	CD5	84.78
Agua Fria	25.64	CD6	91.30
Lower Gila	23.08	CD7	91.30
Salt	20.51
Lower Colorado	7.69
Upper Gila	20.51
Santa Cruz	17.95
San Pedro	20.51
Willcox Playa	61.54
San Simon	38.46
White Water Draw	64.10

MARCH 2008 - MAY 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	76.32
Upper Colorado	65.79	CD2	84.21
Little Colorado	56.76	CD3	79.82
Verde	54.05	CD4	80.26
Bill Williams	50.00	CD5	82.46
Agua Fria	50.00	CD6	92.98
Lower Gila	42.11	CD7	93.86
Salt	65.79
Lower Colorado	52.63
Upper Gila	34.21
Santa Cruz	26.32
San Pedro	25.00
Willcox Playa	40.54
San Simon	52.63
White Water Draw	35.14

DECEMBER 2008 – MAY 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 near average statewide. The driest watersheds were the Virgin, at the 6^th percentile, and the Little Colorado at the 29^th percentile. The wettest were the Lower Gila and Salt at the 68^th and 63^rd percentiles, respectively. Gila County was only slightly warmer than average, at the 66^th percentile, while all other counties were above the 78^th percentile for temperature over the past year.

In the past 24 months, six watersheds received near average precipitation, four were slightly wetter than average and four were slightly drier than average. Temperatures in six climate divisions are above the 78^th percentile, and the southern half of the state is above the 91^st percentile, while Mohave County in the northwest is only slightly warmer than average.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	5.56	CD1	78.95
Upper Colorado	50.00	CD2	83.33
Little Colorado	28.95	CD3	88.60
Verde	42.11	CD4	65.79
Bill Williams	39.47	CD5	93.86
Agua Fria	36.84	CD6	99.12
Lower Gila	68.42	CD7	89.47
Salt	63.16
Lower Colorado	52.63
Upper Gila	57.89
Santa Cruz	39.47
San Pedro	52.63
Willcox Playa	43.24
San Simon	63.16
White Water Draw	45.95

JUNE 2008 – MAY 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	72.57
Upper Colorado	64.86	CD2	85.84
Little Colorado	56.76	CD3	86.73
Verde	45.95	CD4	78.76
Bill Williams	43.24	CD5	91.15
Agua Fria	37.84	CD6	98.23
Lower Gila	78.38	CD7	97.35
Salt	72.97
Lower Colorado	51.35
Upper Gila	48.65
Santa Cruz	29.73
San Pedro	35.14
Willcox Playa	43.24
San Simon	67.57
White Water Draw	37.84

JUNE 2007 – MAY 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 had near or below average precipitation across the northern half of the state, and was slightly wetter than average in two watersheds in southern Arizona. The lower and upper Gila watersheds are above the 63^rd percentile. The Santa Cruz is below the 31^st percentile. Temperatures over the three-year period remain high with only the northwest climate division below the 78^th percentile, and the two southern climate divisions are above the 96^th percentile.

The 48-month period remains the driest long term period, as the very dry winter of 2008-2009 replaced the very wet winter of 2004-2005. Only the Lower Gila watershed is near average at the 46^th percentile. Four watersheds are below the 9^th percentile, and five others are between the 14^th and 23^rd percentiles. The four-year temperatures continue to be extremely high, with six climate divisions above the 89^th percentile, and the southern third of the state still at the 100^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	2.94	CD1	77.23
Upper Colorado	44.44	CD2	87.50
Little Colorado	50.00	CD3	90.18
Verde	30.56	CD4	83.93
Bill Williams	19.44	CD5	94.64
Agua Fria	22.22	CD6	99.11
Lower Gila	69.44	CD7	96.43
Salt	58.33
Lower Colorado	41.67
Upper Gila	63.89
Santa Cruz	38.89
San Pedro	58.33
Willcox Playa	58.33
San Simon	50.00
White Water Draw	55.56

JUNE 2006 – MAY 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	3.12	CD1	75.89
Upper Colorado	22.86	CD2	89.19
Little Colorado	28.57	CD3	89.19
Verde	8.57	CD4	90.09
Bill Williams	2.86	CD5	90.99
Agua Fria	2.86	CD6	100.00
Lower Gila	45.71	CD7	100.00
Salt	31.43
Lower Colorado	22.86
Upper Gila	25.71
Santa Cruz	14.29
San Pedro	17.14
Willcox Playa	31.43
San Simon	20.00
White Water Draw	34.29

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

June 2009 Arizona Drought Update based on precipitation data through May 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 March through May was slightly drier than average in northern Arizona, and much drier than average in the southern half of the state. The only watersheds wetter than average were Willcox Playa and White Water Draw in the southeast corner. Temperatures for the three-month period were well above average statewide.

The 6-month period precipitation was near or above average in the northern two thirds of the state, except the Virgin River watershed, which continues to be exceptionally dry. The period was slightly drier than average in the southern half of Arizona, and well below average in the San Pedro watershed. Temperatures over the last six months were well above average in all climate divisions.

The 24 month period: six watersheds received near average precipitation, four were slightly wetter than average and four were slightly drier than average. Temperatures in six climate divisions are above the 78^th percentile, and the southern half of the state is above the 91^st percentile, while Mohave County in the northwest is only slightly warmer than average.