State Precipitation & Temperature Update for Arizona

Conditions through December 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 01/31/2008. The data are preliminary.

Precipitation Percentiles by Watershed (through December 2007)

Temperature Percentiles by Climate Division (through December 2007)

SHORT TERM CONDITIONS: 1-6 MONTHS

December was extremely wet everywhere in the state; between the 75^th and 84^th percentile in the southern watersheds; between the 89^th and 95^th percentile in the central watersheds; and between the 89^th and 100^th percentile in the northern watersheds. Most of the precipitation fell in a five day period from the 6^th through the 11^th, as part of a major winter storm that brought significant snowfall to the mountains. The series of cold fronts that passed through the state lowered temperatures dramatically from the previous month. November had been the 3^rd warmest year since 1895, but December temperatures were near average along the lower Colorado River and well below average elsewhere, with Yavapai County at the 24^th percentile. The three-month period of October through December had nearly average precipitation in the northern and southeastern watersheds, and well above average precipitation in the central and southwestern watersheds. The wet conditions are mostly a result of the very wet December across the state. The cold December, averaged with the very warm October and November, brought the three-month average temperatures down near the 80^th percentile in most climate divisions. Even the hotter climate divisions of Gila, Maricopa and Pinal Counties fell below the 93^rd percentile. The 6-month period precipitation was near average in the southeast, and well above average in all other watersheds. This period reflects both the wet monsoon and the wet early winter. The wet December brought the Virgin River watershed from the 3^rd to the 17^th percentile. The hot summer and fall have kept the six-month temperatures up above the 85^th percentile everywhere in the state. The hottest conditions were still in the Maricopa-Pinal County climate division at the 96^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	100.00	CD1	45.13
Upper Colorado	89.19	CD2	36.28
Little Colorado	97.30	CD3	24.78
Verde	94.44	CD4	46.46
Bill Williams	89.19	CD5	44.25
Agua Fria	89.19	CD6	26.99
Lower Gila	89.19	CD7	30.97
Salt	91.89
Lower Colorado	83.78
Upper Gila	83.78
Santa Cruz	83.78
San Pedro	77.14
Willcox Playa	75.68
San Simon	83.78
White Water Draw	75.68

DECEMBER 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	50.00	CD1	82.30
Upper Colorado	40.54	CD2	80.53
Little Colorado	54.05	CD3	74.78
Verde	63.89	CD4	92.92
Bill Williams	54.05	CD5	79.20
Agua Fria	70.27	CD6	89.38
Lower Gila	75.68	CD7	81.42
Salt	70.27
Lower Colorado	70.27
Upper Gila	51.35
Santa Cruz	59.46
San Pedro	54.29
Willcox Playa	52.78
San Simon	72.97
White Water Draw	54.05

OCTOBER 2007 - DECEMBER 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	17.14	CD1	85.40
Upper Colorado	70.27	CD2	92.04
Little Colorado	75.68	CD3	92.04
Verde	77.78	CD4	93.81
Bill Williams	62.16	CD5	90.27
Agua Fria	59.46	CD6	96.46
Lower Gila	91.89	CD7	91.15
Salt	75.68
Lower Colorado	70.27
Upper Gila	56.76
Santa Cruz	54.05
San Pedro	48.57
Willcox Playa	50.00
San Simon	67.57
White Water Draw	52.78

JULY 2007 – DECEMBER 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 is now about average for precipitation in most watersheds with the wet second half of the calendar year balancing out the dry first half of the calendar year. Notable exceptions are the very dry Virgin, Bill Williams and Agua Fria watersheds and the very wet lower Gila watershed. The past 12 months have continued to be very hot with temperatures above the 83^rd percentile in all climate divisions.

The 24 month period is yet again the driest period, although now only 3 watersheds are below the 12^th percentile, and five are near or above average for precipitation. The dry watersheds are toward the north half of the state, indicating that the 24-month deficit is due more to winter dryness than summer dryness. Temperatures are all above the 81^st percentile with the southern 1/3 of the state above the 98^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	2.86	CD1	83.04
Upper Colorado	37.84	CD2	94.64
Little Colorado	48.65	CD3	91.96
Verde	43.24	CD4	91.96
Bill Williams	18.92	CD5	92.86
Agua Fria	24.32	CD6	96.43
Lower Gila	75.68	CD7	94.64
Salt	56.76
Lower Colorado	40.54
Upper Gila	56.76
Santa Cruz	35.14
San Pedro	40.54
Willcox Playa	54.05
San Simon	45.95
White Water Draw	59.46

JANUARY 2007 – DECEMBER 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	11.76	CD1	81.98
Upper Colorado	27.78	CD2	93.69
Little Colorado	36.11	CD3	90.99
Verde	19.44	CD4	90.99
Bill Williams	8.33	CD5	92.79
Agua Fria	11.11	CD6	98.20
Lower Gila	44.44	CD7	99.10
Salt	27.78
Lower Colorado	22.22
Upper Gila	55.56
Santa Cruz	30.56
San Pedro	47.22
Willcox Playa	66.67
San Simon	16.67
White Water Draw	58.33

JANUARY 2006 – DECEMBER 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 period has nine watersheds near normal for precipitation, and only three at or below the 20^th percentile. The Santa Cruz and San Simon watersheds in southern Arizona have been extremely dry for the three year period, as has the Bill Williams in central Arizona. Again, temperatures over the three-year period are extremely high with only the northwest climate division below the 80^th percentile, and the southern climate divisions above the 98^th percentile.

The 48-month period again shows above average precipitation across the western part of the state, and near average precipitation in eastern and southern Arizona. The exceptions are the Santa Cruz and San Simon watersheds, both below the 15^th percentile, and the San Pedro below the 30^th percentile. There are still three climate divisions in the southern half of the state above the 96^th percentile for temperature. Only the northwest climate division, most of Mohave County, is below the 78^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	51.52	CD1	79.09
Upper Colorado	45.71	CD2	92.73
Little Colorado	45.71	CD3	91.82
Verde	37.14	CD4	94.55
Bill Williams	17.14	CD5	89.09
Agua Fria	31.43	CD6	98.18
Lower Gila	54.29	CD7	100.00
Salt	45.71
Lower Colorado	48.57
Upper Gila	51.43
Santa Cruz	20.00
San Pedro	34.29
Willcox Playa	48.57
San Simon	17.14
White Water Draw	57.14

JANUARY 2005 – DECEMBER 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	64.52	CD1	77.06
Upper Colorado	67.65	CD2	90.83
Little Colorado	35.29	CD3	91.74
Verde	55.88	CD4	96.33
Bill Williams	41.18	CD5	88.07
Agua Fria	41.18	CD6	97.25
Lower Gila	61.76	CD7	99.08
Salt	50.00
Lower Colorado	67.65
Upper Gila	44.12
Santa Cruz	8.82
San Pedro	29.41
Willcox Playa	52.94
San Simon	14.71
White Water Draw	55.88

JANUARY 2004 – DECEMBER 2007 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

January 2008 Arizona Drought Update based on precipitation data through December 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

December was extremely wet everywhere in the state; between the 75^th and 84^th percentile in the southern watersheds; between the 89^th and 95^th percentile in the central watersheds; and between the 89^th and 100^th percentile in the northern watersheds. Most of the precipitation fell in a five day period from the 6^th through the 11^th, as part of a major winter storm that brought significant snowfall to the mountains. The series of cold fronts that passed through the state lowered temperatures dramatically from the previous month. November had been the 3^rd warmest year since 1895, but December temperatures were near average along the lower Colorado River and well below average elsewhere, with Yavapai County at the 24^th percentile.

The 3-month period of October through December had nearly average precipitation in the northern and southeastern watersheds, and well above average precipitation in the central and southwestern watersheds. The wet conditions are mostly a result of the very wet December across the state. The cold December, averaged with the very warm October and November, brought the three-month average temperatures down near the 80^th percentile in most climate divisions. Even the hotter climate divisions of Gila, Maricopa and Pinal Counties fell below the 93^rd percentile.

The 6-month period precipitation was near average in the southeast, and well above average in all other watersheds. This period reflects both the wet monsoon and the wet early winter. The wet December brought the Virgin River watershed from the 3^rd to the 17^th percentile. The hot summer and fall have kept the six-month temperatures up above the 85^th percentile everywhere in the state. The hottest conditions were still in the Maricopa-Pinal County climate division at the 96^th percentile.

The 12-month period is now about average for precipitation in most watersheds with the wet second half of the calendar year balancing out the dry first half of the calendar year. Notable exceptions are the very dry Virgin, Bill Williams and Agua Fria watersheds and the very wet lower Gila watershed. The past 12 months have continued to be very hot with temperatures above the 83^rd percentile in all climate divisions.

The 24 month period is yet again the driest period, although now only 3 watersheds are below the 12^th percentile, and five are near or above average for precipitation. The dry watersheds are toward the north half of the state, indicating that the 24-month deficit is due more to winter dryness than summer dryness. Temperatures are all above the 81^st percentile with the southern 1/3 of the state above the 98^th percentile.

The 36-month period has nine watersheds near normal for precipitation, and only three at or below the 20^th percentile. The Santa Cruz and San Simon watersheds in southern Arizona have been extremely dry for the three year period, as has the Bill Williams in central Arizona. Again, temperatures over the three-year period are extremely high with only the northwest climate division below the 80^th percentile, and the southern climate divisions above the 98^th percentile.

The 48-month period again shows above average precipitation across the western part of the state, and near average precipitation in eastern and southern Arizona. The exceptions are the Santa Cruz and San Simon watersheds, both below the 15^th percentile, and the San Pedro below the 30^th percentile. There are still three climate divisions in the southern half of the state above the 96^th percentile for temperature. Only the northwest climate division, most of Mohave County, is below the 78^th percentile.