State Precipitation & Temperature Update for Arizona

Conditions through March 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 4/27/2010. The data are preliminary.

Precipitation Percentiles by Watershed (through March 2010)

Temperature Percentiles by Climate Division (through March 2010)

SHORT TERM CONDITIONS: 1-6 MONTHS

March precipitation was near or above average everywhere in Arizona. Even the Little Colorado watershed was at the 40^th percentile. The wettest watersheds are along the northern and western borders of the state. Temperatures in March were near average everywhere except the south and southeastern counties, which had cooler than normal conditions. The three-month period, January through March, was extremely wet across the entire state, with all watersheds above the 82^nd percentile, and all but two above the 85^th percentile. The wetter than average conditions are the result of the El Niño circulation pattern that has brought winter storms south along the California coast where they have combined with subtropical moisture and moved eastward across the southern tier of states. Three-month temperatures were cooler than average in the eastern half of the state, at the 28^th percentile, and near or slightly warmer than average in the western climate divisions. The six-month period precipitation, from October through March, was also wetter than average in all watersheds, above the 52^nd percentile. All watersheds except the Little Colorado were above the 63^rd percentile. Temperatures were near or slightly above average everywhere except the Colorado Plateau which was much colder than normal, at the 22^nd percentile. The warmest counties, Maricopa and Pinal, were at the 70^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	40.00	CD1	59.91
Upper Colorado	85.00	CD2	43.53
Little Colorado	40.00	CD3	44.40
Verde	52.50	CD4	47.41
Bill Williams	65.00	CD5	47.41
Agua Fria	70.00	CD6	43.53
Lower Gila	70.00	CD7	28.45
Salt	55.00
Lower Colorado	72.50
Upper Gila	55.00
Santa Cruz	55.00
San Pedro	65.00
Willcox Playa	60.00
San Simon	45.00
White Water Draw	55.00

MARCH 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	82.05	CD1	70.43
Upper Colorado	92.50	CD2	28.45
Little Colorado	84.62	CD3	46.55
Verde	85.00	CD4	43.10
Bill Williams	87.50	CD5	68.10
Agua Fria	90.00	CD6	62.50
Lower Gila	95.00	CD7	28.88
Salt	90.00
Lower Colorado	95.00
Upper Gila	92.50
Santa Cruz	92.50
San Pedro	95.00
Willcox Playa	89.74
San Simon	87.50
White Water Draw	89.74

JANUARY 2009 - MARCH 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	67.57	CD1	61.74
Upper Colorado	82.05	CD2	22.61
Little Colorado	52.63	CD3	49.57
Verde	71.05	CD4	47.83
Bill Williams	74.36	CD5	54.35
Agua Fria	79.49	CD6	70.00
Lower Gila	76.92	CD7	47.83
Salt	69.23
Lower Colorado	84.62
Upper Gila	69.23
Santa Cruz	71.79
San Pedro	72.97
Willcox Playa	63.16
San Simon	64.10
White Water Draw	63.16

OCTOBER 2009 – MARCH 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 is still the driest short term period, but only one watershed, the Little Colorado, is below average at the 33^rd percentile. All others are above the 43^rd percentile and five are above the 61^st percentile. Temperatures remain warmer than average in all climate divisions, except the Colorado Plateau, with the warmest conditions in Maricopa and Pinal Counties, at the 95^th percentile.

The 24-month period has the most variability in precipitation, with seven watersheds near average, three watersheds in southwest and central Arizona wetter than average, and five watersheds drier than average. The driest, the Little Colorado and Virgin, are at the 21^st and 16^th percentiles, respectively. Temperatures for the 24-month period are warmer than average across northern and southeastern Arizona, near average in Gila County and much warmer than average in Yuma, Maricopa and Pinal counties.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	45.95	CD1	69.57
Upper Colorado	71.79	CD2	43.48
Little Colorado	33.33	CD3	73.91
Verde	51.28	CD4	66.09
Bill Williams	51.28	CD5	80.87
Agua Fria	64.10	CD6	95.65
Lower Gila	76.92	CD7	73.48
Salt	53.85
Lower Colorado	66.67
Upper Gila	58.97
Santa Cruz	56.41
San Pedro	61.54
Willcox Playa	44.74
San Simon	43.59
White Water Draw	44.74

APRIL 2009 – MARCH 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	16.67	CD1	70.18
Upper Colorado	57.89	CD2	63.16
Little Colorado	21.05	CD3	80.70
Verde	28.95	CD4	53.51
Bill Williams	47.37	CD5	90.35
Agua Fria	39.47	CD6	100.00
Lower Gila	81.58	CD7	74.56
Salt	63.16
Lower Colorado	60.53
Upper Gila	52.63
Santa Cruz	39.47
San Pedro	52.63
Willcox Playa	47.37
San Simon	47.37
White Water Draw	42.11

APRIL 2008 – MARCH 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 continues to be the wettest long term interval, with four watersheds wetter than average, six watersheds drier than average, and five watersheds near average. The wet watersheds are the upper Colorado in the north, the Salt and upper Gila in east central Arizona, and the lower Gila in the southwest. Climate division temperatures over the three-year period have dropped a bit with cooler than average conditions over the past three months. All climate divisions are still warmer than average, but two are below the 80^th percentile, and only one, Maricopa and Pinal Counties, is above the 90^th percentile.

The 48-month period is now the driest long-term period, which is good news if the current wet year continues, as dry months from four years ago would be replaced by wetter months this year, indicating a long-term improvement in the drought. Currently only one watershed, the lower Gila is wetter than average at the 72^nd percentile, but eight watersheds are near average, and only six watersheds are drier than average, with four below the 25th percentile. The four-year period remains the warmest interval, with all climate divisions above the 76^th percentile, and four climate divisions above the 86^th percentile. Maricopa and Pinal Counties continue to have the warmest four year interval since 1895.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	8.57	CD1	70.80
Upper Colorado	67.57	CD2	80.97
Little Colorado	43.24	CD3	85.40
Verde	35.14	CD4	73.89
Bill Williams	35.14	CD5	87.61
Agua Fria	35.14	CD6	100.00
Lower Gila	83.78	CD7	89.38
Salt	72.97
Lower Colorado	54.05
Upper Gila	64.86
Santa Cruz	35.14
San Pedro	51.35
Willcox Playa	40.54
San Simon	59.46
White Water Draw	35.14

APRIL 2007 – MARCH 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	6.06	CD1	76.99
Upper Colorado	52.78	CD2	84.38
Little Colorado	33.33	CD3	86.16
Verde	25.00	CD4	82.14
Bill Williams	16.67	CD5	91.07
Agua Fria	22.22	CD6	100.00
Lower Gila	72.22	CD7	91.96
Salt	58.33
Lower Colorado	41.67
Upper Gila	58.33
Santa Cruz	33.33
San Pedro	55.56
Willcox Playa	58.33
San Simon	44.44
White Water Draw	52.78

APRIL 2006 – MARCH 2010 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

April 2010 Arizona Drought Update (based on precipitation data through March 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, January through March, was extremely wet across the entire state, with all watersheds above the 82^nd percentile, and all but two above the 85^th percentile. The wetter than average conditions are the result of the El Niño circulation pattern that has brought winter storms south along the California coast where they have combined with subtropical moisture and moved eastward across the southern tier of states. Three-month temperatures were cooler than average in the eastern half of the state, at the 28^th percentile, and near or slightly warmer than average in the western climate divisions.

The 6-month period precipitation, from October through March, was also wetter than average in all watersheds, above the 52^nd percentile. All watersheds except the Little Colorado were above the 63^rd percentile. Temperatures were near or slightly above average everywhere except the Colorado Plateau which was much colder than normal, at the 22^nd percentile. The warmest counties, Maricopa and Pinal, were at the 70^th percentile.