State Precipitation & Temperature Update for Arizona

Conditions through April 2007

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 4528/2007. The data are preliminary, and some data are missing from the San Pedro and Santa Cruz watersheds.

Precipitation Percentiles by Watershed (through April 2007)

Temperature Percentiles by Climate Division (through April 2007)

SHORT TERM CONDITIONS: 1-6 MONTHS

April brought three different precipitation regimes to the state. The northernmost watersheds had near average precipitation, while the watersheds across central Arizona had precipitation well below average, and the southern watersheds had above average precipitation. The lack of rainfall across the forested watersheds worsened the wildfire conditions. Temperatures across the state were again well above average, but unlike March, only 2 climate divisions were above the 85^th percentile for temperature. Precipitation for the 3-month period of February through April was below the 40^th percentile everywhere in the state except the southeast corner. The combination of extremely dry conditions and temperatures above the 95^th percentile on the Colorado Plateau during the past 3 months hastened the snowmelt and contributed to dangerous fire conditions. The 6-month precipitation map shows the effects of the dry fall and winter with only five watersheds above the 25^th percentile and only two above the 40^th percentile. Temperatures were above the 75^th percentile everywhere in the state for the 6-month period, probably as a result of the lack of winter storms.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	54.05	CD1	87.17
Upper Colorado	43.24	CD2	82.74
Little Colorado	21.62	CD3	80.97
Verde	13.51	CD4	95.58
Bill Williams	13.51	CD5	75.22
Agua Fria	21.62	CD6	76.99
Lower Gila	64.86	CD7	78.76
Salt	37.84
Lower Colorado	55.41
Upper Gila	62.16
Santa Cruz	64.86
San Pedro	54.05
Willcox Playa	70.27
San Simon	70.27
White Water Draw	78.38

APRIL 2007: 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	21.62	CD1	93.81
Upper Colorado	24.32	CD2	95.58
Little Colorado	16.22	CD3	88.50
Verde	21.62	CD4	95.58
Bill Williams	18.92	CD5	84.07
Agua Fria	27.03	CD6	92.04
Lower Gila	32.43	CD7	82.30
Salt	27.03
Lower Colorado	37.84
Upper Gila	37.84
Santa Cruz	24.32
San Pedro	35.14
Willcox Playa	50.00
San Simon	29.73
White Water Draw	56.76

FEBRUARY 2006 - APRIL 2007 (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	14.71	CD1	86.73
Upper Colorado	16.67	CD2	78.76
Little Colorado	11.43	CD3	76.99
Verde	14.29	CD4	89.38
Bill Williams	8.33	CD5	77.88
Agua Fria	13.89	CD6	83.19
Lower Gila	16.67	CD7	81.86
Salt	16.67
Lower Colorado	16.67
Upper Gila	33.33
Santa Cruz	11.11
San Pedro	35.29
Willcox Playa	45.71
San Simon	11.11
White Water Draw	48.57

NOVEMBER 2006 – APRIL 2007 (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 western deserts and Verde watershed continue to have well below average precipitation for the 12 month period that began in May of 2006, with watersheds on the Colorado Plateau having only slightly below average precipitation. The San Pedro, Willcox Playa, and White Water Draw watersheds remain above average, mostly as a result of the wet monsoon in 2006. Temperatures for the previous 12 months continue to be well above average, with all climate divisions remaining above the 84^th percentile.

The two-year period has shown very little improvement over last month with the Salt River watershed moving from the 5^th percentile to the 6^th percentile for precipitation. The previous 24 months continue to be the driest period in the past 4 years, indicative of the persistence of the long term drought. The wettest watersheds are at the 40^th percentile, and the driest are below the 3^rd percentile. For temperature, all divisions except the northwest are above the 89^th percentile, exacerbating the dry conditions. The southeast climate division remains at the 100^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	23.53	CD1	84.82
Upper Colorado	33.33	CD2	85.71
Little Colorado	27.78	CD3	85.71
Verde	19.44	CD4	91.07
Bill Williams	5.56	CD5	91.96
Agua Fria	22.22	CD6	91.07
Lower Gila	25.00	CD7	92.86
Salt	33.33
Lower Colorado	33.33
Upper Gila	55.56
Santa Cruz	41.67
San Pedro	66.67
Willcox Playa	65.71
San Simon	22.22
White Water Draw	62.86

MAY 2006 – APRIL 2007 (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	21.21	CD1	74.77
Upper Colorado	8.57	CD2	90.09
Little Colorado	5.71	CD3	89.19
Verde	2.86	CD4	92.79
Bill Williams	2.86	CD5	90.09
Agua Fria	2.86	CD6	94.59
Lower Gila	8.57	CD7	100.00
Salt	5.71
Lower Colorado	28.57
Upper Gila	17.14
Santa Cruz	11.43
San Pedro	34.29
Willcox Playa	40.00
San Simon	5.71
White Water Draw	40.00

MAY 2005 – APRIL 2007 (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 precipitation is well below average in the south central deserts and slightly below normal in most other watersheds. Since last month’s update, the northern and western watersheds have dropped from above to near average precipitation for the 3-year period. The 36-month^-temperature pattern continues unchanged for the past four updates, with Gila County and the southeast climate division still above the 95^th percentile for temperature, and only the northwest below the 75^th percentile.

The eastern watersheds remain below the 25^th percentile for the 48-month period. The only change from last month’s update is the Salt River watershed which moved up to the 27^th percentile. In this longest term, only the lower Colorado watershed remains above normal at the 66^th percentile. The long-term temperature pattern has become even warmer with climate division 6 (Maricopa and Pinal counties) moving from below the 95^th percentile to the 97^th percentile. Climate division 7 in the southeast remains at the 100^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	75.00	CD1	74.55
Upper Colorado	58.82	CD2	89.09
Little Colorado	29.41	CD3	86.36
Verde	44.12	CD4	95.45
Bill Williams	41.18	CD5	86.36
Agua Fria	32.35	CD6	91.82
Lower Gila	47.06	CD7	97.27
Salt	38.24
Lower Colorado	76.47
Upper Gila	32.35
Santa Cruz	5.88
San Pedro	20.59
Willcox Playa	38.24
San Simon	8.82
White Water Draw	47.06

MAY 2004 – APRIL 2007 (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	-99.99	CD1	77.98
Upper Colorado	48.48	CD2	91.74
Little Colorado	21.21	CD3	93.58
Verde	30.30	CD4	96.33
Bill Williams	27.27	CD5	90.83
Agua Fria	21.21	CD6	97.25
Lower Gila	39.39	CD7	100.00
Salt	27.27
Lower Colorado	66.67
Upper Gila	24.24
Santa Cruz	12.12
San Pedro	15.15
Willcox Playa	18.18
San Simon	21.21
White Water Draw	36.36

MAY 2003 – APRIL 2007 (48-month): percentiles of temperature, and precipitation for the 15 Arizona watersheds and percentiles of temperature for the 7 climate divisions.

May 2007 Arizona Drought Update based on Precipitation (data through April 2007)

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

SUMMARY

April brought three different precipitation regimes to the state. The northernmost watersheds had near average precipitation, while the watersheds across central Arizona had precipitation well below average, and the southern watersheds had above average precipitation. The lack of rainfall across the forested watersheds worsened the wildfire conditions. Temperatures across the state were again well above average, but unlike March, only 2 climate divisions were above the 85^th percentile for temperature.

Three-month period – Precipitation for the 3-month period of February through April was below the 40^th percentile everywhere in the state except the southeast corner. The combination of extremely dry conditions and temperatures above the 95^th percentile on the Colorado Plateau during the past 3 months hastened the snowmelt and contributed to dangerous fire conditions.

Six-month period – The 6-month precipitation map shows the effects of the dry fall and winter with only five watersheds above the 25^th percentile and only two above the 40^th percentile. Temperatures were above the 75^th percentile everywhere in the state for the 6-month period, probably as a result of the lack of winter storms.

Twelve-month period – The western deserts and Verde watershed continue to have well below average precipitation for the 12 month period that began in May of 2006, with watersheds on the Colorado Plateau having only slightly below average precipitation. The San Pedro, Willcox Playa, and White Water Draw watersheds remain above average, mostly as a result of the wet monsoon in 2006. Temperatures for the previous 12 months continue to be well above average, with all climate divisions remaining above the 84^th percentile.

Two-year period - The two-year period has shown very little improvement over last month with the Salt River watershed moving from the 5^th percentile to the 6^th percentile for precipitation. The previous 24 months continue to be the driest period in the past 4 years, indicative of the persistence of the long term drought. The wettest watersheds are at the 40^th percentile, and the driest are below the 3^rd percentile. For temperature, all divisions except the northwest are above the 89^th percentile, exacerbating the dry conditions. The southeast climate division remains at the 100^th percentile.

Three-year period - The 36-month precipitation is well below average in the south central deserts and slightly below normal in most other watersheds. Since last month’s update, the northern and western watersheds have dropped from above to near average precipitation for the 3-year period. The 36-month^-temperature pattern continues unchanged for the past four updates, with Gila County and the southeast climate division still above the 95^th percentile for temperature, and only the northwest below the 75^th percentile.

Four-year period - The eastern watersheds remain below the 25^th percentile for the 48-month period. The only change from last month’s update is the Salt River watershed which moved up to the 27^th percentile. In this longest term, only the lower Colorado watershed remains above normal at the 66^th percentile. The long-term temperature pattern has become even warmer with climate division 6 (Maricopa and Pinal counties) moving from below the 95^th percentile to the 97^th percentile. Climate division 7 in the southeast remains at the 100^th percentile.