State Precipitation & Temperature Update for Arizona

Conditions through May 2008

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 06/23/2008. The data are preliminary.

Precipitation Percentiles by Watershed (through May 2008)

Temperature Percentiles by Climate Division (through May 2008)

SHORT TERM CONDITIONS: 1-6 MONTHS

May is normally very dry statewide, but this year it was exceptionally wet in many locations, as three wet low pressure systems moved across the state. Some of the higher elevations even had snow. Precipitation was above the 52^nd percentile for all watersheds except the Virgin in NW Arizona. The wettest watershed was the Little Colorado, at the 86^th percentile. As a result of the storm systems, which brought unseasonably cold air, all climate divisions except the NW had temperatures near or below average for the month. The three-month period of March through May was drier than average, since both March and April were very dry across the state. The lower Colorado and lower Gila watersheds were the only watersheds above the 21^st percentile for precipitation. Central and southeastern Arizona were especially dry, below the 15^th percentile. The three month temperatures were near or slightly above average as numerous cold fronts passed through the state, keeping temperatures down. The 6-month period precipitation, from December through May, was near average in the southeast and above average in the rest of the state, due to the wet months of December through February. Ten watersheds were between the 62^nd and 79^th percentiles. The driest watersheds, in the southeast, should start to recover as the monsoon develops. Temperatures were near average in the southern and western parts of the state, and cooler than average on the Colorado Plateau. Gila County was slightly warmer than average.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	31.58	CD1	62.72
Upper Colorado	63.16	CD2	29.39
Little Colorado	86.84	CD3	28.07
Verde	85.53	CD4	50.88
Bill Williams	81.58	CD5	55.26
Agua Fria	84.21	CD6	45.18
Lower Gila	94.74	CD7	44.74
Salt	94.74
Lower Colorado	92.11
Upper Gila	89.47
Santa Cruz	52.63
San Pedro	73.68
Willcox Playa	81.58
San Simon	57.89
White Water Draw	76.32

MAY 2008: 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	5.26	CD1	69.30
Upper Colorado	21.05	CD2	43.86
Little Colorado	15.79	CD3	53.51
Verde	10.53	CD4	70.18
Bill Williams	13.16	CD5	65.35
Agua Fria	7.89	CD6	66.67
Lower Gila	31.58	CD7	60.09
Salt	15.79
Lower Colorado	50.00
Upper Gila	13.16
Santa Cruz	10.53
San Pedro	13.16
Willcox Playa	18.42
San Simon	13.16
White Water Draw	21.05

MARCH 2008 - MAY 2008 (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	50.00	CD1	53.51
Upper Colorado	75.68	CD2	30.70
Little Colorado	77.78	CD3	39.47
Verde	63.89	CD4	62.28
Bill Williams	64.86	CD5	46.93
Agua Fria	67.57	CD6	46.93
Lower Gila	75.68	CD7	52.19
Salt	78.38
Lower Colorado	64.86
Upper Gila	62.16
Santa Cruz	59.46
San Pedro	48.57
Willcox Playa	47.22
San Simon	72.97
White Water Draw	50.00

DECEMBER 2008 – MAY 2008 (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 near- or below-average precipitation in 5 watersheds in west central and southeastern Arizona, and above-average precipitation on the Colorado Plateau and in southwestern Arizona on the lower Gila River watershed. The cooler temperatures in May brought the twelve month temperature average down slightly on the Colorado Plateau, and in west central and southwestern Arizona. However, temperatures are still high, with all climate divisions above the 70^th percentile.

The 24-month period was slightly wetter than last month, with three watersheds now above average for the 24-month period. The lower Gila, Willcox Playa and Whitewater Draw have moved up to the 61^st percentile. The rest of the state is near or slightly below average, with the Bill Williams and Agua Fria the driest, below the25th percentile. Temperatures for the 24-month period cooled slightly so that all climate divisions are below the 93^rd percentile and climate division 1 in the NW is at the 75^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	5.71	CD1	70.80
Upper Colorado	70.27	CD2	71.68
Little Colorado	70.27	CD3	82.30
Verde	62.16	CD4	89.38
Bill Williams	45.95	CD5	79.65
Agua Fria	51.35	CD6	85.84
Lower Gila	70.27	CD7	88.50
Salt	72.97
Lower Colorado	59.46
Upper Gila	45.95
Santa Cruz	37.84
San Pedro	37.84
Willcox Playa	33.33
San Simon	54.05
White Water Draw	38.89

JUNE 2008 – MAY 2008 (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	5.88	CD1	75.00
Upper Colorado	47.22	CD2	79.02
Little Colorado	58.33	CD3	86.61
Verde	33.33	CD4	88.39
Bill Williams	16.67	CD5	87.50
Agua Fria	22.22	CD6	91.07
Lower Gila	61.11	CD7	92.86
Salt	55.56
Lower Colorado	38.89
Upper Gila	52.78
Santa Cruz	36.11
San Pedro	52.78
Willcox Playa	61.11
San Simon	38.89
White Water Draw	61.11

JUNE 2007 – MAY 2008 (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 driest long-term period, with most of the southeast and central watersheds at or below the 20^th percentile. All watersheds remain below the 32^nd percentile, and seven watersheds are below the 15^th percentile. For temperature, the southeast climate divisions remain above the 95^th percentile and even the coolest climate division, in the northwest, is still above the 75^th percentile.

The 48-month period had dry conditions in the southeast, and near average conditions in central Arizona, and wet conditions in central and western Arizona. The 48 month period includes the winters of 2004-05, 2005-06, 2006-07, and 2007-08 and the summers of 2004 – 2007. In central and northern Arizona watersheds, 2005 was the wettest of the past four years, while in the driest southeast watersheds, 2004 was the wettest year. All climate divisions are above the 74^th percentile for temperature, but the southwest climate division has dropped below the 85^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	9.09	CD1	75.23
Upper Colorado	31.43	CD2	88.29
Little Colorado	28.57	CD3	89.19
Verde	11.43	CD4	92.79
Bill Williams	5.71	CD5	90.09
Agua Fria	5.71	CD6	95.50
Lower Gila	28.57	CD7	100.00
Salt	20.00
Lower Colorado	31.43
Upper Gila	14.29
Santa Cruz	8.57
San Pedro	17.14
Willcox Playa	31.43
San Simon	5.71
White Water Draw	31.43

JUNE 2006 – MAY 2008 (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	45.16	CD1	74.55
Upper Colorado	70.59	CD2	88.18
Little Colorado	38.24	CD3	86.36
Verde	58.82	CD4	94.55
Bill Williams	47.06	CD5	83.64
Agua Fria	41.18	CD6	90.91
Lower Gila	63.24	CD7	98.18
Salt	44.12
Lower Colorado	76.47
Upper Gila	32.35
Santa Cruz	8.82
San Pedro	11.76
Willcox Playa	35.29
San Simon	17.65
White Water Draw	41.18

JUNE 2005 – MAY 2008 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

June 2008 Arizona Drought Update (based on precipitation data through May 2008)

The following summary describes the heat and dryness across the state for the 1-, 3-, 6-, 12-, 24-, 36-, and 48-month periods.

SUMMARY

May is normally very dry statewide, but this year it was exceptionally wet in many locations, as three wet low pressure systems moved across the state. Some of the higher elevations even had snow. Precipitation was above the 52^nd percentile for all watersheds except the Virgin in NW Arizona. The wettest watershed was the Little Colorado, at the 86^th percentile. As a result of the storm systems, which brought unseasonably cold air, all climate divisions except the NW had temperatures near or below average for the month.

The 3-month period of March through May was drier than average, since both March and April were very dry across the state. The lower Colorado and lower Gila watersheds were the only watersheds above the 21^st percentile for precipitation. Central and southeastern Arizona were especially dry, below the 15^th percentile. The three month temperatures were near or slightly above average as numerous cold fronts passed through the state, keeping temperatures down.

The 6-month period precipitation, from December through May, was near average in the southeast and above average in the rest of the state, due to the wet months of December through February. Ten watersheds were between the 62^nd and 79^th percentiles. The driest watersheds, in the southeast, should start to recover as the monsoon develops. Temperatures were near average in the southern and western parts of the state, and cooler than average on the Colorado Plateau. Gila County was slightly warmer than average.

The 12-month period had near- or below-average precipitation in 5 watersheds in west central and southeastern Arizona, and above-average precipitation on the Colorado Plateau and in southwestern Arizona on the lower Gila River watershed. The cooler temperatures in May brought the twelve month temperature average down slightly on the Colorado Plateau, and in west central and southwestern Arizona. However, temperatures are still high, with all climate divisions above the 70^th percentile.

The 24-month period was slightly wetter than last month, with three watersheds now above average for the 24-month period. The lower Gila, Willcox Playa and Whitewater Draw have moved up to the 61^st percentile. The rest of the state is near or slightly below average, with the Bill Williams and Agua Fria the driest, below the25th percentile. Temperatures for the 24-month period cooled slightly so that all climate divisions are below the 93^rd percentile and climate division 1 in the NW is at the 75^th percentile.

The 36-month period is the driest long-term period, with most of the southeast and central watersheds at or below the 20^th percentile. All watersheds remain below the 32^nd percentile, and seven watersheds are below the 15^th percentile. For temperature, the southeast climate divisions remain above the 95^th percentile and even the coolest climate division, in the northwest, is still above the 75^th percentile.

The 48-month period had dry conditions in the southeast, and near average conditions in central Arizona, and wet conditions in central and western Arizona. The 48 month period includes the winters of 2004-05, 2005-06, 2006-07, and 2007-08 and the summers of 2004 – 2007. In central and northern Arizona watersheds, 2005 was the wettest of the past four years, while in the driest southeast watersheds, 2004 was the wettest year. All climate divisions are above the 74^th percentile for temperature, but the southwest climate division has dropped below the 85^th percentile.