State Precipitation & Temperature Update for Arizona

Conditions through December 2010

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 1/20/2011. The data are preliminary.

Precipitation Percentiles by Watershed (through December 2010)

Temperature Percentiles by Climate Division (through December 2010)

SHORT TERM CONDITIONS: 1-6 MONTHS

December was much wetter than normal across the western border and the northern half of the state, and even the southern half of Arizona received near- or above-average precipitation. The only watersheds with below average precipitation were the Willcox Playa and White Water Draw in the SE corner. December temperatures were well above average statewide due to persistent cloud cover that held nighttime temperatures up, as well as a few very warm ridges of high pressure over the state in December. The three month period was also much wetter than average across the northern watersheds, near average across central Arizona and much drier than average across the southern third of the state. December and October were both quite wet in northern Arizona, while November was dry everywhere in the state. Temperatures were well above average for the three month period, led by December, which was among the top 10 hottest Decembers in most Arizona locations. The six-month period, which includes the monsoon, was also wetter than average in the northern half of the state and near average or drier than average across southern Arizona. The driest basins were the San Simon, Santa Cruz, both below the 23^rd percentile. Six month temperatures were much warmer than average, with all counties above the 82^nd percentile, and Yuma, La Paz, Maricopa and Pinal counties above the 96^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	95.00	CD1	94.83
Upper Colorado	85.00	CD2	99.14
Little Colorado	82.50	CD3	93.97
Verde	82.05	CD4	97.41
Bill Williams	80.00	CD5	95.69
Agua Fria	70.00	CD6	98.28
Lower Gila	60.00	CD7	97.41
Salt	72.50
Lower Colorado	75.00
Upper Gila	60.00
Santa Cruz	50.00
San Pedro	57.89
Willcox Playa	35.00
San Simon	52.50
White Water Draw	30.00

DECEMBER 2010: 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	92.31	CD1	85.65
Upper Colorado	90.00	CD2	93.10
Little Colorado	62.50	CD3	71.55
Verde	87.18	CD4	87.07
Bill Williams	72.50	CD5	89.66
Agua Fria	55.00	CD6	90.52
Lower Gila	45.00	CD7	78.45
Salt	55.00
Lower Colorado	65.00
Upper Gila	45.00
Santa Cruz	32.50
San Pedro	21.05
Willcox Playa	12.82
San Simon	30.00
White Water Draw	12.50

OCTOBER 2010 - DECEMBER 2010 (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	65.79	CD1	86.96
Upper Colorado	87.50	CD2	94.83
Little Colorado	82.50	CD3	82.76
Verde	69.23	CD4	89.66
Bill Williams	45.00	CD5	96.55
Agua Fria	37.50	CD6	98.28
Lower Gila	52.50	CD7	92.24
Salt	72.50
Lower Colorado	55.00
Upper Gila	45.00
Santa Cruz	22.50
San Pedro	44.74
Willcox Playa	33.33
San Simon	7.50
White Water Draw	41.03

JULY 2010 – DECEMBER 2010 (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 the wettest interval with 11 watersheds above the 65^th percentile, eight watersheds above the 77^th percentile, and the upper Colorado above the 97^th percentile. The wet conditions in the southern watersheds are due to the wet El Niño winter last year. Temperatures are slightly warmer than average, though Maricopa and Pinal counties are above the 86^th percentile.

The 24-month period is the driest long-term interval, though it has significant variability from basin to basin. Only one basin, the upper Colorado, is wetter than average, while five basins, are near average, six are slightly drier than average, two, the Bill Williams and Santa Cruz, are much drier than average, and one basin, the San Simon, is below the 6^th percentile. Temperatures for the 24-month period are only slightly warmer than average across northern Arizona, but the southern counties are much warmer than average, with Maricopa and Pinal counties again above the 96^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	68.42	CD1	72.17
Upper Colorado	97.50	CD2	71.30
Little Colorado	88.75	CD3	66.96
Verde	77.50	CD4	73.04
Bill Williams	65.00	CD5	76.52
Agua Fria	72.50	CD6	86.09
Lower Gila	85.00	CD7	72.17
Salt	90.00
Lower Colorado	82.50
Upper Gila	80.00
Santa Cruz	52.50
San Pedro	82.50
Willcox Playa	57.50
San Simon	42.50
White Water Draw	52.50

JANUARY 2010 – DECEMBER 2010 (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	32.43	CD1	72.81
Upper Colorado	66.67	CD2	72.81
Little Colorado	43.59	CD3	80.70
Verde	28.21	CD4	73.68
Bill Williams	23.08	CD5	82.89
Agua Fria	25.64	CD6	96.49
Lower Gila	58.97	CD7	88.60
Salt	58.97
Lower Colorado	51.28
Upper Gila	35.90
Santa Cruz	15.38
San Pedro	46.15
Willcox Playa	28.21
San Simon	5.13
White Water Draw	25.64

JANUARY 2009 – DECEMBER 2010 (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 three watersheds wetter than average, four near average and seven drier than average. The driest watersheds are the Virgin at the 14^th percentile, and the Santa Cruz and White Water Draw between the 21^st and 24^th percentiles. The wettest watershed is the upper Colorado at the 76^th percentile. Temperatures for the three year period are warmer than average with all counties except Gila county above the 69^th percentile. Maricopa and Pinal counties are above the 97^th percentile.

The 48-month period remains the driest interval with four watersheds below the 25^th percentile. Four others are below the 36^th percentile for precipitation. Four watersheds are near average and only three are wetter than average, between the 62^nd and 79^th percentiles. The 48-month temperatures are well above average, with the coolest county – Mohave, above the 72^nd percentile. Maricopa and Pinal counties are now at the 99^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	13.89	CD1	69.91
Upper Colorado	76.32	CD2	77.88
Little Colorado	50.00	CD3	77.88
Verde	39.47	CD4	58.41
Bill Williams	34.21	CD5	84.96
Agua Fria	39.47	CD6	97.35
Lower Gila	73.68	CD7	82.30
Salt	68.42
Lower Colorado	47.37
Upper Gila	55.26
Santa Cruz	23.68
San Pedro	47.37
Willcox Playa	26.32
San Simon	26.32
White Water Draw	21.05

JANUARY 2008 – DECEMBER 2010 (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	7.35	CD1	72.32
Upper Colorado	72.97	CD2	86.61
Little Colorado	51.35	CD3	82.14
Verde	29.73	CD4	79.46
Bill Williams	16.22	CD5	87.05
Agua Fria	24.32	CD6	99.11
Lower Gila	78.38	CD7	87.50
Salt	62.16
Lower Colorado	43.24
Upper Gila	51.35
Santa Cruz	21.62
San Pedro	40.54
Willcox Playa	29.73
San Simon	29.73
White Water Draw	35.14

JANUARY 2007 – DECEMBER 2010 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

January 2011 Arizona Drought Update (based on precipitation data through December 2010)

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 was also much wetter than average across the northern watersheds, near average across central Arizona and much drier than average across the southern third of the state. December and October were both quite wet in northern Arizona, while November was dry everywhere in the state. Temperatures were well above average for the three month period, led by December, which was among the top 10 hottest Decembers in most Arizona locations.

The 6-month period, which includes the monsoon, was also wetter than average in the northern half of the state and near average or drier than average across southern Arizona. The driest basins were the San Simon, Santa Cruz, both below the 23^rd percentile. Six month temperatures were much warmer than average, with all counties above the 82^nd percentile, and Yuma, La Paz, Maricopa and Pinal counties above the 96^th percentile.