State Precipitation & Temperature Update for Arizona

Conditions through August 2007

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 8/15/2007. San Pedro and Virgin River are missing data. The data are preliminary, and there are no data for the Virgin River watershed, and the San Pedro watershed data are provisional as several stations have not reported for August.

Precipitation Percentiles by Watershed (through August 2007)

Temperature Percentiles by Climate Division (through August 2007)

SHORT TERM CONDITIONS: 1-6 MONTHS

August, like July, is generally a wet month across Arizona, but this year the precipitation was not equally distributed across the state. The Colorado plateau, higher elevations of the White Mountains in the east, and the southeast corner of the state received higher than average rainfall, but the central watersheds were just below average and the southern watersheds were much drier than average. The lower Colorado River basin, including Yuma was exceptionally dry. Yuma has had no measureable precipitation through August, although they received 1.79” in one day of early September when moisture from hurricane Erin moved north. Temperatures across the state were well above average, with all climate divisions above the 89^th percentile. Due to the wet July, the 3-month period of June through August, is well above average for 11 watersheds and near average for three watersheds. The big winners of rainfall were the northern watersheds on the Colorado plateau. The wet conditions in the north helped to decrease temperatures below the 95^th percentile, where they had been for the previous 3 month period. The 6-month period was slightly above the average rainfall in the north, along the lower Colorado River in the west, in the eastern mountains, and in the southeast corner. The central part of the state, including the Salt, Verde, Agua Fria, San Pedro and San Simon watersheds was slightly below average. The dry winter, spring and early summer led to temperatures above the 95^th percentile everywhere in the state except the northwest, which was at the 92^nd percentile, for the 6-month period.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	-99	CD1	92.92
Upper Colorado	89.19	CD2	91.15
Little Colorado	78.38	CD3	92.92
Verde	48.65	CD4	90.27
Bill Williams	35.14	CD5	98.23
Agua Fria	13.51	CD6	97.35
Lower Gila	64.86	CD7	89.38
Salt	43.24
Lower Colorado	35.14
Upper Gila	81.08
Santa Cruz	18.92
San Pedro	21.62
Willcox Playa	62.16
San Simon	16.22
White Water Draw	70.27

AUGUST 2007: 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	-99	CD1	95.58
Upper Colorado	91.89	CD2	94.69
Little Colorado	86.49	CD3	94.69
Verde	81.08	CD4	98.23
Bill Williams	67.57	CD5	90.27
Agua Fria	56.76	CD6	98.23
Lower Gila	94.59	CD7	93.81
Salt	78.38
Lower Colorado	83.78
Upper Gila	75.68
Santa Cruz	51.35
San Pedro	59.46
Willcox Playa	62.16
San Simon	59.46
White Water Draw	66.67

JUNE 2006 - AUGUST 2007 (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	-99	CD1	92.92
Upper Colorado	81.08	CD2	96.46
Little Colorado	64.86	CD3	96.46
Verde	40.54	CD4	97.35
Bill Williams	37.84	CD5	95.58
Agua Fria	40.54	CD6	99.12
Lower Gila	89.19	CD7	98.23
Salt	43.24
Lower Colorado	67.57
Upper Gila	78.38
Santa Cruz	35.14
San Pedro	51.35
Willcox Playa	72.97
San Simon	48.65
White Water Draw	69.44

MARCH 2006 – AUGUST 2007 (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 combines the dry winter of 2006-07 with the slightly above-average summer monsoon of 2007. The southeast, eastern, and lower Gila watersheds were very near average, while the rest of the state had a very dry year. Even though conditions were much warmer than average, only two climate divisions were above the 90^th percentile. The very cold weather that came through the state in late December and early January helped to bring the average temperatures down for the year, somewhat balancing out the warmer than average summer.

For the two-year period, we continue to see the cycle of an extremely dry year occurring at least every two years. One year ago, the 12-month period had almost every watershed below the 15^th percentile. Now that dry year has moved into the two-year period, and it continues to show the driest conditions of all periods, as it did last month. Only the far southeastern corner of the state has had near normal precipitation during the two-year period. That is mostly due to two consecutive wet monsoons in that area, as monsoonal moisture was drawn toward New Mexico. Temperatures in the state for the two-year period reflect the absence of storms systems with all climate divisions except the northwest above the 90^th percentile. The extremely dry conditions in south central Arizona are consistent with the temperatures above the 97^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	-99	CD1	83.04
Upper Colorado	50.00	CD2	82.14
Little Colorado	33.33	CD3	87.50
Verde	25.00	CD4	90.18
Bill Williams	25.00	CD5	83.93
Agua Fria	22.22	CD6	89.29
Lower Gila	44.44	CD7	93.75
Salt	25.00
Lower Colorado	38.89
Upper Gila	55.56
Santa Cruz	19.44
San Pedro	41.67
Willcox Playa	57.14
San Simon	16.67
White Water Draw	55.56

SEPTEMBER 2006 – AUGUST 2007 (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	-99	CD1	82.88
Upper Colorado	22.86	CD2	93.69
Little Colorado	20.00	CD3	91.89
Verde	11.43	CD4	93.69
Bill Williams	2.86	CD5	90.09
Agua Fria	2.86	CD6	97.30
Lower Gila	14.29	CD7	100.00
Salt	5.71
Lower Colorado	20.00
Upper Gila	22.86
Santa Cruz	2.86
San Pedro	25.71
Willcox Playa	51.43
San Simon	2.86
White Water Draw	45.71

SEPTEMBER 2005 – AUGUST 2007 (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 precipitation period shows the results of the wet winter of 2004-05 in northern and western Arizona. The rest of the state is near or below average for the three-year period. This oscillation back and forth between wet and dry years is not unusual for desert climates where precipitation is generally low most of the time. It is, however, difficult to manage water resources when the variability is so extreme, and the current long-term drought has contributed to that variability. The 36-month^-temperatures remain very high with the southeast climate division continuing to be the hottest on record.

The 48-month period precipitation is above average across the northern part of the state, and well below average in south central Arizona. Ten of the fifteen watersheds are below the 40^th percentile, and the Santa Cruz is at the 6^th percentile. The warm conditions continue as the two southern climate divisions are above the 99^th percentile for temperature, and all climate divisions are above the 78^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	-99	CD1	75.45
Upper Colorado	70.59	CD2	90.91
Little Colorado	38.24	CD3	88.18
Verde	55.88	CD4	94.55
Bill Williams	50.00	CD5	85.45
Agua Fria	47.06	CD6	95.45
Lower Gila	64.71	CD7	100.00
Salt	44.12
Lower Colorado	82.35
Upper Gila	52.94
Santa Cruz	11.76
San Pedro	23.53
Willcox Playa	44.12
San Simon	14.71
White Water Draw	55.88

SEPTEMBER 2004 – AUGUST 2007 (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	-99	CD1	78.90
Upper Colorado	69.70	CD2	89.91
Little Colorado	30.30	CD3	93.58
Verde	39.39	CD4	95.41
Bill Williams	27.27	CD5	88.99
Agua Fria	21.21	CD6	99.08
Lower Gila	48.48	CD7	100.00
Salt	27.27
Lower Colorado	72.73
Upper Gila	36.36
Santa Cruz	6.06
San Pedro	24.24
Willcox Playa	39.39
San Simon	18.18
White Water Draw	48.48

SEPTEMBER 2003 – AUGUST 2007 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

September 2007 Arizona Drought Update based on Precipitation (data through August 2007)

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

SUMMARY

August, like July, is generally a wet month across Arizona, but this year the precipitation was not equally distributed across the state. The Colorado plateau, higher elevations of the White Mountains in the east, and the southeast corner of the state received higher than average rainfall, but the central watersheds were just below average and the southern watersheds were much drier than average. The lower Colorado River basin, including Yuma was exceptionally dry. Yuma has had no measureable precipitation through August, although they received 1.79” in one day of early September when moisture from hurricane Erin moved north. Temperatures across the state were well above average, with all climate divisions above the 89^th percentile.

Three-month period – of June through August, was well above average for 11 watersheds and near average for three watersheds, due to the wet July. The big winners of rainfall were the northern watersheds on the Colorado plateau. The wet conditions in the north helped to decrease temperatures below the 95^th percentile, where they had been for the previous 3 month period.

Six-month period –was slightly above the average rainfall in the north, along the lower Colorado River in the west, in the eastern mountains, and in the southeast corner. The central part of the state, including the Salt, Verde, Agua Fria, San Pedro and San Simon watersheds was slightly below average. The dry winter, spring and early summer led to temperatures above the 95^th percentile everywhere in the state except the northwest, which was at the 92^nd percentile, for the 6-month period.

Twelve-month period – combines the dry winter of 2006-07 with the slightly above-average summer monsoon of 2007. The southeast, eastern, and lower Gila watersheds were very near average, while the rest of the state had a very dry year. While conditions were much warmer than average, only two climate divisions were above the 90^th percentile. The very cold weather that came through the state in late December and early January helped to bring the average temperatures down for the year, somewhat balancing out the warmer than average summer.

Two-year period - continues to show the cycle of an extremely dry year occurring at least every two years. One year ago, the 12-month period had almost every watershed below the 15^th percentile. Now that dry year has moved into the two-year period, and it continues to show the driest conditions of all periods, as it did last month. Only the far southeastern corner of the state has had near normal precipitation during the two-year period. That is mostly due to two consecutive wet monsoons in that area, as monsoonal moisture was drawn toward New Mexico. Temperatures in the state for the two-year period reflect the absence of storms systems with all climate divisions except the northwest above the 90^th percentile. The extremely dry conditions in south central Arizona are consistent with the temperatures above the 97^th percentile.

Three-year period - The 36-month precipitation period shows the results of the wet winter of 2004-05 in northern and western Arizona. The rest of the state is near or below average for the three-year period. This oscillation back and forth between wet and dry years is not unusual for desert climates where precipitation is generally low most of the time. It is, however, difficult to manage water resources when the variability is so extreme, and the current long-term drought has contributed to that variability. The 36-month^-temperatures remain very high with the southeast climate division continuing to be the hottest on record.

Four-year period - The 48-month period precipitation is above average across the northern part of the state, and well below average in south central Arizona. Ten of the fifteen watersheds are below the 40^th percentile, and the Santa Cruz is at the 6^th percentile. The warm conditions continue as the two southern climate divisions are above the 99^th percentile for temperature, and all climate divisions are above the 78^th percentile.