State Precipitation & Temperature Update for Arizona

Conditions through September 2009

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 10/19/2009. Maps and tables only. The data are preliminary.

Precipitation Percentiles by Watershed (through September 2009)

Temperature Percentiles by Climate Division (through September 2009)

SHORT TERM CONDITIONS: 1-6 MONTHS

September precipitation was near or slightly below average in 12 of 15 watersheds. Thunderstorms brought measureable rainfall somewhere in the state on 22 of the 30 days of the month. Many places had significant rainfall from individual storms. On the 10^th, Sedona had 2.50” which caused significant damage due to flash flooding through town. Yuma received more than half its annual rainfall during a single storm on September 5^th, as a result of remnant moisture from Hurricane Jimena. September temperatures were above average in all climate divisions, but the warmest areas were along the lower Colorado River and the metropolitan Phoenix area of Maricopa County. The three-month period of July through September represents the monsoon, which was virtually non-existent in all watersheds except the lower Gila. Ten watersheds were below the 13^th percentile and four more were between the 15^th and 25^th percentiles. Temperatures for the three-month period were above the 95^th percentile in the south central deserts and central mountains, including Maricopa, Pinal, Gila, Yuma and La Paz counties. The six-month period also had all but one watershed with below average precipitation. The lower Gila is at the 69^th percentile, but all other watersheds are below the 40^th, and ten are below the 24^th percentile. Temperatures over the last six months were again well above average statewide, with the coolest climate division on the Colorado Plateau at the 73^rd percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	67.57	CD1	93.91
Upper Colorado	35.90	CD2	70.87
Little Colorado	46.15	CD3	84.35
Verde	43.59	CD4	72.61
Bill Williams	30.77	CD5	93.04
Agua Fria	35.90	CD6	93.04
Lower Gila	43.59	CD7	77.83
Salt	43.59
Lower Colorado	53.85
Upper Gila	53.85
Santa Cruz	28.21
San Pedro	28.21
Willcox Playa	69.23
San Simon	61.54
White Water Draw	48.72

SEPTEMBER 2009: 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	24.32	CD1	90.35
Upper Colorado	10.26	CD2	86.09
Little Colorado	7.69	CD3	90.43
Verde	7.69	CD4	96.52
Bill Williams	12.82	CD5	95.65
Agua Fria	7.69	CD6	99.13
Lower Gila	66.67	CD7	93.04
Salt	7.69
Lower Colorado	23.08
Upper Gila	17.95
Santa Cruz	12.82
San Pedro	12.82
Willcox Playa	12.82
San Simon	15.38
White Water Draw	5.26

JULY 2008 - SEPTEMBER 2009 (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	16.22	CD1	78.95
Upper Colorado	28.21	CD2	73.04
Little Colorado	20.51	CD3	85.22
Verde	17.95	CD4	81.30
Bill Williams	10.26	CD5	88.70
Agua Fria	12.82	CD6	95.65
Lower Gila	69.23	CD7	85.22
Salt	25.64
Lower Colorado	11.54
Upper Gila	38.46
Santa Cruz	12.82
San Pedro	20.51
Willcox Playa	30.77
San Simon	23.08
White Water Draw	21.05

APRIL 2008 – SEPTEMBER 2009 (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 precipitation was below average in all watersheds with eleven watersheds below the 25^th percentile and seven watersheds below the 17^th percentile. The driest watersheds were again in the southeast, plus the Virgin watershed in the northwest. During the past 12 months, temperatures have been above the 75^th percentile in all areas of the state. Maricopa and Pinal Counties have been above the 97^th percentile.

The 24 month period is still the wettest long-term period; with only the Salt and lower Gila watersheds receiving above average precipitation. Six watersheds were below the 25^th percentile and four more were between the 27^th and 38^th percentiles. Temperatures over the past two years were above the 76^th percentile in all climate divisions except the northwest, where Mohave County is at the 71^st percentile. The Pinal-Maricopa County climate division remains the warmest, above the 98^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	5.56	CD1	76.32
Upper Colorado	26.32	CD2	85.09
Little Colorado	21.05	CD3	86.84
Verde	21.05	CD4	76.75
Bill Williams	21.05	CD5	89.47
Agua Fria	23.68	CD6	97.37
Lower Gila	36.84	CD7	92.11
Salt	36.84
Lower Colorado	36.84
Upper Gila	10.53
Santa Cruz	2.63
San Pedro	5.26
Willcox Playa	16.22
San Simon	15.79
White Water Draw	10.53

OCTOBER 2008 – SEPTEMBER 2009 (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	2.94	CD1	71.68
Upper Colorado	45.95	CD2	79.20
Little Colorado	24.32	CD3	84.07
Verde	21.62	CD4	76.11
Bill Williams	27.03	CD5	89.38
Agua Fria	29.73	CD6	98.23
Lower Gila	72.97	CD7	84.96
Salt	67.57
Lower Colorado	40.54
Upper Gila	37.84
Santa Cruz	16.22
San Pedro	32.43
Willcox Playa	18.92
San Simon	59.46
White Water Draw	18.92

OCTOBER 2007 – SEPTEMBER 2009 (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 with above average precipitation, the Upper Colorado, lower Gila and Salt Rivers. Of the remaining 12 watersheds, six are below the 14^th percentile, and the other six are between the 19^th and 28^th percentiles. Temperatures over the three-year period remain well above average, with only the northwest climate division below the 76^rd percentile, and the Pinal-Maricopa County division continues to be the warmest at the 99^th percentile.

The 48-month period continues to be the driest long-term period, and if the forecasts for a La Niña winter hold true, it will continue to be a dry period as the winter of 2010 replaces the dry winter of 2006 in the 4-year period. While the wettest watershed was the lower Gila at the 40^th percentile, the only other watersheds above the 23^rd percentile were the Salt River and Willcox Playas at the 28^th percentile. Nine watersheds are below the 15^th percentile, and four are below the 4^th percentile. The four-year temperatures are above the 89^th percentile in all but the northwest climate division, and the two southern climate divisions remain at the 100^th percentile as the hottest since 1896.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	2.94	CD1	75.00
Upper Colorado	44.44	CD2	86.61
Little Colorado	22.22	CD3	88.39
Verde	13.89	CD4	80.36
Bill Williams	11.11	CD5	91.07
Agua Fria	11.11	CD6	99.11
Lower Gila	63.89	CD7	93.75
Salt	52.78
Lower Colorado	27.78
Upper Gila	27.78
Santa Cruz	5.56
San Pedro	11.11
Willcox Playa	25.00
San Simon	22.22
White Water Draw	19.44

OCTOBER 2006 – SEPTEMBER 2009 (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	3.12	CD1	75.68
Upper Colorado	17.14	CD2	89.19
Little Colorado	8.57	CD3	90.99
Verde	5.71	CD4	91.89
Bill Williams	2.86	CD5	92.79
Agua Fria	2.86	CD6	100.00
Lower Gila	40.00	CD7	100.00
Salt	28.57
Lower Colorado	14.29
Upper Gila	22.86
Santa Cruz	2.86
San Pedro	11.43
Willcox Playa	28.57
San Simon	11.43
White Water Draw	22.86

OCTOBER 2005 – SEPTEMBER 2009 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

October 2009 Arizona Drought Update based on precipitation data through September 2009)

The following summary describes the heat and dryness across the state for the 1-, 3-, 6-, 12-, 24-, 36-, and 48-month periods.

SUMMARY

September precipitation was near or slightly below average in 12 of 15 watersheds. Thunderstorms brought measureable rainfall somewhere in the state on 22 of the 30 days of the month. Many places had significant rainfall from individual storms. On the 10^th, Sedona had 2.50” which caused significant damage due to flash flooding through town. Yuma received more than half its annual rainfall during a single storm on September 5^th, as a result of remnant moisture from Hurricane Jimena. September temperatures were above average in all climate divisions, but the warmest areas were along the lower Colorado River and the metropolitan Phoenix area of Maricopa County.

The 3-month period of July through September represents the monsoon, which was virtually non-existent in all watersheds except the lower Gila. Ten watersheds were below the 13^th percentile and four more were between the 15^th and 25^th percentiles. Temperatures for the three-month period were above the 95^th percentile in the south central deserts and central mountains, including Maricopa, Pinal, Gila, Yuma and La Paz counties.

The 6-month period also had all but one watershed with below average precipitation. The lower Gila is at the 69^th percentile, but all other watersheds are below the 40^th, and ten are below the 24^th percentile. Temperatures over the last six months were again well above average statewide, with the coolest climate division on the Colorado Plateau at the 73^rd percentile.

The 12-month period precipitation was below average in all watersheds with eleven watersheds below the 25^th percentile and seven watersheds below the 17^th percentile. The driest watersheds were again in the southeast, plus the Virgin watershed in the northwest. During the past 12 months, temperatures have been above the 75^th percentile in all areas of the state. Maricopa and Pinal Counties have been above the 97^th percentile.

The 24 month period is still the wettest long-term period; with only the Salt and lower Gila watersheds receiving above average precipitation. Six watersheds were below the 25^th percentile and four more were between the 27^th and 38^th percentiles. Temperatures over the past two years were above the 76^th percentile in all climate divisions except the northwest, where Mohave County is at the 71^st percentile. The Pinal-Maricopa County climate division remains the warmest, above the 98^th percentile.

The 36-month period has three watersheds with above average precipitation, the Upper Colorado, lower Gila and Salt Rivers. Of the remaining 12 watersheds, six are below the 14^th percentile, and the other six are between the 19^th and 28^th percentiles. Temperatures over the three-year period remain well above average, with only the northwest climate division below the 76^rd percentile, and the Pinal-Maricopa County division continues to be the warmest at the 99^th percentile.

The 48-month period continues to be the driest long-term period, and if the forecasts for a La Niña winter hold true, it will continue to be a dry period as the winter of 2010 replaces the dry winter of 2006 in the 4-year period. While the wettest watershed was the lower Gila at the 40^th percentile, the only other watersheds above the 23^rd percentile were the Salt River and Willcox Playas at the 28^th percentile. Nine watersheds are below the 15^th percentile, and four are below the 4^th percentile. The four-year temperatures are above the 89^th percentile in all but the northwest climate division, and the two southern climate divisions remain at the 100^th percentile as the hottest since 1896.