State Precipitation & Temperature Update for Arizona

Conditions through January 2011

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. The percentiles have shifted to reflect the percentile categories used in the National Drought Monitor. Current update is 2/23/2011. The data are preliminary.

Precipitation Percentiles by Watershed (through January 2011)

Temperature Percentiles by Climate Division (through January 2011)

SHORT TERM CONDITIONS: 1-6 MONTHS

January was extremely dry across all watersheds in Arizona, with the wettest watershed, the Virgin, at the 10^th percentile. All the other watersheds were below the 8^th percentile for January precipitation. This was due to the La Niña circulation keeping winter storm tracks north of Arizona. January temperatures were near normal with some warmer than average periods and a few extremely cold periods during the month, including numerous freeze warnings and hard freezes in central and southern Arizona. The three month period was near average in the northern watersheds and well below average in the central and southern watersheds. The near average conditions in the northern half of the state occurred because the extremely dry conditions of January were balanced out by wetter than average conditions in December. Temperatures were somewhat warmer than average in the northern 2/3 of the state and near average in Yavapai, Gila and the southeastern counties. The six-month period was near average in most watersheds in central Arizona, and drier than average (below the 20^th percentile) in the Lower Colorado, Willcox, and White Water Draw watersheds, and at the 5^th percentile in the Santa Cruz and San Simon watersheds. Only the Upper Colorado watershed was wetter than average, at the 80^th percentile. Six month temperatures were much warmer than average, with all counties above the 81^st percentile, and the southern counties above the 87^th percentile. Maricopa and Pinal counties were above the 96^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	10.00	CD1	79.06
Upper Colorado	4.88	CD2	39.32
Little Colorado	2.50	CD3	63.68
Verde	4.88	CD4	59.40
Bill Williams	3.66	CD5	82.48
Agua Fria	4.88	CD6	68.80
Lower Gila	7.32	CD7	55.98
Salt	4.88
Lower Colorado	6.10
Upper Gila	7.32
Santa Cruz	4.88
San Pedro	2.44
Willcox Playa	2.44
San Simon	4.88
White Water Draw	5.00

JANUARY 2011: 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	31.58	CD1	84.48
Upper Colorado	45.00	CD2	76.72
Little Colorado	33.33	CD3	75.00
Verde	43.59	CD4	74.14
Bill Williams	45.00	CD5	82.76
Agua Fria	32.50	CD6	83.62
Lower Gila	17.50	CD7	70.26
Salt	32.50
Lower Colorado	30.00
Upper Gila	10.00
Santa Cruz	7.50
San Pedro	7.89
Willcox Playa	5.13
San Simon	7.50
White Water Draw	7.69

NOVEMBER 2010 - JANUARY 2011 (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	51.35	CD1	81.90
Upper Colorado	80.00	CD2	83.62
Little Colorado	41.03	CD3	82.76
Verde	51.28	CD4	87.07
Bill Williams	42.50	CD5	87.93
Agua Fria	22.50	CD6	96.55
Lower Gila	22.50	CD7	93.10
Salt	37.50
Lower Colorado	20.00
Upper Gila	35.00
Santa Cruz	5.00
San Pedro	26.32
Willcox Playa	17.95
San Simon	5.00
White Water Draw	17.95

AUGUST 2010 – JANUARY 2011 (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 short term interval with eight watersheds near average, two watersheds in northern Arizona wetter than average, and five watersheds in south central and central Arizona drier than average. The driest watershed was the San Simon, at the 5^th percentile. Temperatures were only slightly warmer than average, between the 65^th and 71^st percentiles in most counties, except Maricopa and Pinal counties that were above the 84^th percentile.

The 24-month period is the driest long-term interval, with ten watersheds drier than average, four near average and one, the upper Colorado, wetter than average. The wet conditions in the upper Colorado are due to the winter storms over the past two winters that have consistently crossed the northern edge of the state. Temperatures for the 24-month period are slightly warmer than average across northern Arizona, and much warmer than average in the southern counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	60.53	CD1	70.69
Upper Colorado	77.50	CD2	68.10
Little Colorado	55.00	CD3	65.95
Verde	40.00	CD4	68.53
Bill Williams	22.50	CD5	71.12
Agua Fria	17.50	CD6	84.48
Lower Gila	40.00	CD7	73.28
Salt	35.00
Lower Colorado	50.00
Upper Gila	30.00
Santa Cruz	12.50
San Pedro	40.00
Willcox Playa	32.50
San Simon	5.00
White Water Draw	37.18

FEBRUARY 2010 – JANUARY 2011 (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	27.03	CD1	68.70
Upper Colorado	64.10	CD2	65.22
Little Colorado	35.90	CD3	79.13
Verde	28.21	CD4	68.70
Bill Williams	25.64	CD5	80.43
Agua Fria	25.64	CD6	92.17
Lower Gila	51.28	CD7	81.74
Salt	38.46
Lower Colorado	46.15
Upper Gila	28.21
Santa Cruz	10.26
San Pedro	30.77
Willcox Playa	20.51
San Simon	7.69
White Water Draw	20.51

FEBRUARY 2009 – JANUARY 2011 (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 drier than average, three watersheds near average and three watersheds wetter than average. The driest watersheds are the Santa Cruz at the 11^th percentile, the San Simon at the 15^th, the Virgin at the 17^th, and Verde and Agua Fria at the 18^th percentile. The wettest watershed is the lower Gila at the 68^th percentile. Temperatures for the three year period were warmer than average in all counties, with Yuma, La Paz, Maricopa and Pinal counties above the 85^th percentile.

The 48-month period is the wettest long term interval with three watersheds above the 62^nd percentile, five watersheds near average and only seven watersheds drier than average. The driest watersheds are the Virgin at the 6^th percentile and the Santa Cruz at the 11^th percentile. The San Simon, Bill Williams and Agua Fria are also all below the 19^th percentile. The 48-month temperatures are well above average, with only Mohave County below the 77^th percentile. Maricopa and Pinal counties are now at the 100^th percentile, the warmest 4 year interval on record.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	16.67	CD1	69.30
Upper Colorado	60.53	CD2	78.95
Little Colorado	28.95	CD3	78.07
Verde	18.42	CD4	58.77
Bill Williams	21.05	CD5	85.09
Agua Fria	18.42	CD6	98.25
Lower Gila	68.42	CD7	83.77
Salt	60.53
Lower Colorado	44.74
Upper Gila	31.58
Santa Cruz	10.53
San Pedro	42.11
Willcox Playa	23.68
San Simon	15.79
White Water Draw	21.05

FEBRUARY 2008 – JANUARY 2011 (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	5.88	CD1	72.81
Upper Colorado	62.16	CD2	85.84
Little Colorado	48.65	CD3	82.30
Verde	32.43	CD4	77.88
Bill Williams	16.22	CD5	87.61
Agua Fria	16.22	CD6	100.00
Lower Gila	72.97	CD7	90.27
Salt	62.16
Lower Colorado	37.84
Upper Gila	45.95
Santa Cruz	10.81
San Pedro	32.43
Willcox Playa	27.03
San Simon	18.92
White Water Draw	27.03

FEBRUARY 2007 – JANUARY 2011 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

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

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 near average in the northern watersheds and well below average in the central and southern watersheds. The near average conditions in the northern half of the state occurred because the extremely dry conditions of January were balanced out by wetter than average conditions in December. Temperatures were somewhat warmer than average in the northern 2/3 of the state and near average in Yavapai, Gila and the southeastern counties.

The 6-month period was near average in most watersheds in central Arizona, and drier than average (below the 20^th percentile) in the Lower Colorado, Willcox, and White Water Draw watersheds, and at the 5^th percentile in the Santa Cruz and San Simon watersheds. Only the Upper Colorado watershed was wetter than average, at the 80^th percentile. Six month temperatures were much warmer than average, with all counties above the 81^st percentile, and the southern counties above the 87^th percentile. Maricopa and Pinal counties were above the 96^th percentile.