State Precipitation & Temperature Update for Arizona

Conditions through November 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 12/26/2007. The data are preliminary.

Precipitation Percentiles by Watershed (through November 2007)

Temperature Percentiles by Climate Division (through November 2007)

SHORT TERM CONDITIONS: 1-6 MONTHS

November was dry in the northern half of the state and near or slightly above average for the southern half of the state. After 28 days of dry conditions, most of the state received two days of moderate, steady rainfall at the end of the month that prevented November from being one of the driest on record. The big winners were the lower Gila and San Pedro watersheds in the south, as the warm storm system moved northward through Arizona from the Gulf of California. Due to the consistent high pressure position over the western US, November was in the top 3% warmest since 1895, everywhere in the state. The three-month period of September through November was unusually dry everywhere in the state, but especially so across the northern half of the state, on the Colorado Plateau. The southern half of the state benefited from the end of the monsoon in September, which brought a few storms to the southern watersheds. The clear skies and dry weather during the fall have pushed the temperatures above the 91^st percentile everywhere in the state. The southern half of the state was above the 97^th percentile. The 6-month period rainfall was near average for most of the state. The lower Gila had above-average rainfall, while the Salt and Agua Fria watersheds in central Arizona, and the Santa Cruz and San Simon watersheds in southern Arizona, had slightly below-average rainfall. The Virgin River in northwest Arizona was very dry, below the 3^rd percentile. Temperatures everywhere except the lower Colorado River were above the 95^th percentile for the six month period. The lower Colorado River was still warm, with temperatures between the 86^th and 94^th percentiles.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	4.17	CD1	98.23
Upper Colorado	10.81	CD2	100.00
Little Colorado	18.92	CD3	97.35
Verde	35.14	CD4	98.23
Bill Williams	16.22	CD5	98.23
Agua Fria	56.76	CD6	100.00
Lower Gila	78.38	CD7	97.35
Salt	45.95
Lower Colorado	45.95
Upper Gila	40.54
Santa Cruz	56.76
San Pedro	70.27
Willcox Playa	51.39
San Simon	48.65
White Water Draw	56.76

NOVEMBER 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	5.71	CD1	91.15
Upper Colorado	10.81	CD2	94.69
Little Colorado	8.11	CD3	92.92
Verde	24.32	CD4	94.69
Bill Williams	16.22	CD5	91.15
Agua Fria	24.32	CD6	97.35
Lower Gila	40.54	CD7	97.35
Salt	21.62
Lower Colorado	32.43
Upper Gila	16.22
Santa Cruz	24.32
San Pedro	27.03
Willcox Playa	22.22
San Simon	24.32
White Water Draw	21.62

SEPTEMBER 2006 - NOVEMBER 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	2.86	CD1	86.73
Upper Colorado	43.24	CD2	98.23
Little Colorado	40.54	CD3	95.58
Verde	51.35	CD4	96.46
Bill Williams	43.24	CD5	93.81
Agua Fria	29.73	CD6	99.12
Lower Gila	86.49	CD7	99.12
Salt	35.14
Lower Colorado	56.76
Upper Gila	40.54
Santa Cruz	37.84
San Pedro	45.95
Willcox Playa	44.44
San Simon	32.43
White Water Draw	50.00

JUNE 2006 – NOVEMBER 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 continues to be extremely dry across the entire state. Four watersheds in the central part of the state, and one on the southern border, were below the 11^th percentile. All but one of the other 10 watersheds were below the 39^th percentile. Statewide temperatures were above the 85^th percentile during the previous 12 months, while the Colorado Plateau and southern Arizona were above the 96^th percentile.

The driest interval remains the 24 month period, with 12 of 15 watersheds below the 20^th percentile. Eight watersheds in northwest, central, and south central Arizona are below the 15^th percentile. Only the San Pedro, Willcox, and White Water Draw watersheds have had near normal precipitation in the past two years. In the long term, only Northwestern Arizona has remained below the 81^st percentile for temperature. The rest of the state has been above the 91^st percentile, and the two southern climate divisions were above the 98^th percentile for temperature.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	2.94	CD1	85.71
Upper Colorado	25.00	CD2	96.43
Little Colorado	13.89	CD3	94.64
Verde	11.11	CD4	91.07
Bill Williams	11.11	CD5	90.18
Agua Fria	11.11	CD6	96.43
Lower Gila	55.56	CD7	96.43
Salt	16.67
Lower Colorado	16.67
Upper Gila	30.56
Santa Cruz	16.67
San Pedro	19.44
Willcox Playa	30.56
San Simon	11.11
White Water Draw	38.89

DECEMBER 2006 – NOVEMBER 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	3.03	CD1	80.18
Upper Colorado	14.29	CD2	93.69
Little Colorado	17.14	CD3	91.89
Verde	11.43	CD4	93.69
Bill Williams	2.86	CD5	93.69
Agua Fria	5.71	CD6	98.20
Lower Gila	17.14	CD7	100.00
Salt	11.43
Lower Colorado	20.00
Upper Gila	20.00
Santa Cruz	8.57
San Pedro	34.29
Willcox Playa	48.57
San Simon	8.57
White Water Draw	42.86

DECEMBER 2005 – NOVEMBER 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 is the closest to normal of all time periods. It combines two dry years (2004 and 2006) with one very wet year (2005) Most of western Arizona is near average, while eastern Arizona is below average at the 26^th to 39^th percentile, and southern Arizona is much below average at the 8^th to 12^th percentile. This shows that although a good wet year is helpful, it cannot erase the deficit. Temperatures over the three-year period are similar to the two-year period, with the northwest below the 79^th percentile, and the others all above the 88^th percentile. Southern Arizona has been extremely warm the past three years, above the 98^th percentile.

The 48-month period precipitation is also near average across the western part of the state, and well below-average in eastern and southern Arizona. The Virgin watershed in the northwest and the lower Colorado watershed in the southwest had above-average precipitation for the four-year period. Ten of the fifteen watersheds were well below the 50^th percentile. Three climate divisions, all in the southern half of the state, were above the 96^th percentile for temperature, and two were above the 99^th percentile for the four-year period. The warm temperatures have added to the evaporative demand, enhancing the dry conditions.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	46.88	CD1	78.18
Upper Colorado	47.06	CD2	93.64
Little Colorado	29.41	CD3	92.73
Verde	41.18	CD4	93.64
Bill Williams	17.65	CD5	88.18
Agua Fria	29.41	CD6	98.18
Lower Gila	50.00	CD7	100.00
Salt	38.24
Lower Colorado	55.88
Upper Gila	35.29
Santa Cruz	11.76
San Pedro	26.47
Willcox Playa	41.18
San Simon	8.82
White Water Draw	44.12

DECEMBER 2004 – NOVEMBER 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	63.33	CD1	77.06
Upper Colorado	57.58	CD2	89.91
Little Colorado	21.21	CD3	92.66
Verde	42.42	CD4	96.33
Bill Williams	30.30	CD5	88.99
Agua Fria	21.21	CD6	99.08
Lower Gila	48.48	CD7	100.00
Salt	24.24
Lower Colorado	63.64
Upper Gila	33.33
Santa Cruz	6.06
San Pedro	24.24
Willcox Playa	36.36
San Simon	9.09
White Water Draw	45.45

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

December 2007 Arizona Drought Update based on precipitation data through November 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

The 3-month period of September through November was unusually dry everywhere in the state, but especially so across the northern half of the state, on the Colorado Plateau. The southern half of the state benefited from the end of the monsoon in September, which brought a few storms to the southern watersheds. The clear skies and dry weather during the fall have pushed the temperatures above the 91^st percentile everywhere in the state. The southern half of the state was above the 97^th percentile.

The 6-month period rainfall was near average for most of the state. The lower Gila had above-average rainfall, while the Salt and Agua Fria watersheds in central Arizona, and the Santa Cruz and San Simon watersheds in southern Arizona, had slightly below-average rainfall. The Virgin River in northwest Arizona was very dry, below the 3^rd percentile. Temperatures everywhere except the lower Colorado River were above the 95^th percentile for the six month period. The lower Colorado River was still warm, with temperatures between the 86^th and 94^th percentiles.