State Precipitation & Temperature Update for Arizona

Conditions through February 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 5/6/2011. The data are preliminary.

Precipitation Percentiles by Watershed (through February 2011)

Temperature Percentiles by Climate Division (through February 2011)

SHORT TERM CONDITIONS: 1-6 MONTHS

February was extremely dry across the southeastern watersheds in Arizona, and near or slightly wetter than average across the northern and central watersheds. The southeastern watersheds were between the 21^st and 39^th percentiles, meaning out of 100 years, 61 years were wetter and 20 years were drier. The steering of winter storms north of Arizona is typical of the La Niña circulation and was a prominent feature of the February weather pattern. February temperatures were much colder than normal statewide, as the tail end of several cold winter storms passed through the state, leaving their precipitation in Utah and the Sierra Nevada, but delivering cold air to Arizona. The three month period was near average in the northern watersheds and well below average in the central and southern watersheds, again, very much the typical La Niña pattern. Temperatures were only slightly warmer than average statewide. The six-month period was near average in the Upper Colorado, Bill Williams and Verde watersheds, but much drier than average, below the 15^th percentile in the southern watersheds. This reflects both the dry winter and the early end to the monsoon in early September. The Lower Gila watershed was at the 25^th percentile while the Agua Fria was at the 17^th percentile. Six month temperatures were also only slightly warmer than normal, with Maricopa and Pinal counties at the 84^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	58.54	CD1	29.06
Upper Colorado	80.49	CD2	35.47
Little Colorado	68.29	CD3	22.22
Verde	58.54	CD4	27.78
Bill Williams	41.46	CD5	14.96
Agua Fria	36.59	CD6	33.33
Lower Gila	56.10	CD7	16.67
Salt	51.22
Lower Colorado	70.73
Upper Gila	24.39
Santa Cruz	29.27
San Pedro	21.95
Willcox Playa	30.00
San Simon	39.02
White Water Draw	21.95

FEBRUARY 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	58.97	CD1	67.67
Upper Colorado	67.50	CD2	64.22
Little Colorado	56.41	CD3	64.66
Verde	48.72	CD4	72.41
Bill Williams	50.00	CD5	63.79
Agua Fria	43.75	CD6	65.52
Lower Gila	32.50	CD7	56.47
Salt	45.00
Lower Colorado	55.00
Upper Gila	20.00
Santa Cruz	12.50
San Pedro	10.53
Willcox Playa	10.26
San Simon	22.50
White Water Draw	7.69

DECEMBER 2010 - FEBRUARY 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	64.86	CD1	72.41
Upper Colorado	67.50	CD2	65.95
Little Colorado	38.46	CD3	64.66
Verde	48.72	CD4	74.14
Bill Williams	42.50	CD5	69.83
Agua Fria	17.50	CD6	84.48
Lower Gila	25.00	CD7	74.14
Salt	35.00
Lower Colorado	40.00
Upper Gila	15.00
Santa Cruz	10.00
San Pedro	10.53
Willcox Playa	10.26
San Simon	10.00
White Water Draw	7.69

SEPTEMBER 2010 – FEBRUARY 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 four watersheds near average, two watersheds in northern Arizona wetter than average, and eight watersheds in south central and central Arizona drier than average. The driest watersheds are the San Simon and Santa Cruz, at the 5^th percentile. Temperatures were only slightly warmer than average, between the 61^st and 72^nd percentiles in most counties, except Maricopa and Pinal counties that were above the 77^th percentile.

The 24-month period has eleven watersheds drier than average, three near average and one, the upper Colorado, wetter than average. The wet conditions in the upper Colorado are due to the winter storms during the previous two winters that have consistently crossed the northern edge of the state. Temperatures for the 24-month period are near average across the Colorado Plateau, and slightly warmer than average in the southern counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	31.58	CD1	63.79
Upper Colorado	75.00	CD2	66.81
Little Colorado	62.50	CD3	61.21
Verde	47.50	CD4	65.52
Bill Williams	25.00	CD5	63.79
Agua Fria	15.00	CD6	77.59
Lower Gila	42.50	CD7	71.55
Salt	50.00
Lower Colorado	50.00
Upper Gila	27.50
Santa Cruz	5.00
San Pedro	22.50
Willcox Playa	20.51
San Simon	5.00
White Water Draw	20.51

MARCH 2010 – FEBRUARY 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	29.73	CD1	69.57
Upper Colorado	76.92	CD2	57.39
Little Colorado	38.46	CD3	73.48
Verde	28.21	CD4	68.70
Bill Williams	20.51	CD5	78.26
Agua Fria	20.51	CD6	92.17
Lower Gila	58.97	CD7	76.52
Salt	41.03
Lower Colorado	51.28
Upper Gila	30.77
Santa Cruz	12.82
San Pedro	33.33
Willcox Playa	30.77
San Simon	10.26
White Water Draw	17.95

MARCH 2009 – FEBRUARY 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 is now the driest long-term interval with ten watersheds drier than average, two watersheds near average and two watersheds slightly wetter than average. The driest watersheds are the Santa Cruz at the 11^th percentile, the San Simon and Agua Fria at the 13^th, and the Virgin at the 17^th. The wettest watershed is the lower Gila at the 71^st percentile. Temperatures for the three year period were warmer than average in all counties except Gila, with Maricopa and Pinal counties above the 95^th percentile.

The 48-month period is the still the wettest long term interval with three watersheds above the 62^nd percentile, three watersheds near average and nine watersheds drier than average. The driest watersheds are the Virgin at the 3^rd percentile and the Agua Fria at the 16^th percentile. The Santa Cruz, Bill Williams and Willcox Playa are also all below the 25^th percentile. The 48-month temperatures are well above average, with only Mohave County below the 72^nd percentile. Maricopa and Pinal counties are now at the 99^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	16.67	CD1	69.30
Upper Colorado	55.26	CD2	71.93
Little Colorado	28.95	CD3	79.82
Verde	21.05	CD4	57.89
Bill Williams	26.32	CD5	85.09
Agua Fria	13.16	CD6	97.37
Lower Gila	71.05	CD7	79.82
Salt	60.53
Lower Colorado	52.63
Upper Gila	36.84
Santa Cruz	10.53
San Pedro	28.95
Willcox Playa	23.68
San Simon	13.16
White Water Draw	21.05

MARCH 2008 – FEBRUARY 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	2.94	CD1	71.93
Upper Colorado	67.57	CD2	82.30
Little Colorado	45.95	CD3	83.19
Verde	32.43	CD4	75.22
Bill Williams	24.32	CD5	85.40
Agua Fria	16.22	CD6	99.12
Lower Gila	78.38	CD7	87.61
Salt	62.16
Lower Colorado	43.24
Upper Gila	43.24
Santa Cruz	18.92
San Pedro	27.03
Willcox Playa	24.32
San Simon	32.43
White Water Draw	27.03

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

March 2011 Arizona Drought Update (based on precipitation data through February 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, again, very much the typical La Niña pattern. Temperatures were only slightly warmer than average statewide.

The 6-month period was near average in the Upper Colorado, Bill Williams and Verde watersheds, but much drier than average, below the 15^th percentile in the southern watersheds. This reflects both the dry winter and the early end to the monsoon in early September. The Lower Gila watershed was at the 25^th percentile while the Agua Fria was at the 17^th percentile. Six month temperatures were also only slightly warmer than normal, with Maricopa and Pinal counties at the 84^th percentile.