State Precipitation & Temperature Update for Arizona

Conditions through March 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 4/25/2007. The data are preliminary, and some data are missing from the Upper Colorado and Santa Cruz watersheds.

Precipitation Percentiles by Watershed (through March 2007)

Temperature Percentiles by Climate Division (through March 2007)

SHORT TERM CONDITIONS: 1-6 MONTHS

March precipitation was below average across the northern half of the state, near normal in the southwest and above average in the southeast watersheds. The near average precipitation in the Bill Williams and Lower Colorado watersheds will help offset extremely dry conditions the previous two months. The high temperatures of March (all watersheds were above the 89^th percentile) melted virtually all of the snowpack around the state, and caused much of the precipitation to fall as rain rather than snow. The 3-month period of January through March was below the 25^th percentile for the upper, lower and Little Colorado watersheds, as well as the Bill Williams in west central Arizona. The central and southern watersheds were also dry, with only White Water Draw above the 56^th percentile. The typical winter storm track is across the northern half to two-thirds of the state, while an El Niño winter generally brings moisture to the central and southern watersheds. This year we saw neither the usual winter pattern nor the typical El Niño pattern. Although January was much colder than normal, both February and March were warmer than average, pushing the 3-month temperatures above the 50^th percentile in all climate divisions. Fall and winter precipitation, represented by the 6-month period of October through March, was extremely dry, below the 44^th percentile in all watersheds, with the upper Colorado being the wettest. The Santa Cruz and San Simon watersheds were the driest at the 14^th percentile. In the six-month period, temperatures across the state were well above average, with the cooler areas in the Northeast plateau and the southwest.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	32.43	CD1	94.69
Upper Colorado	37.84	CD2	93.81
Little Colorado	21.62	CD3	92.04
Verde	29.73	CD4	97.35
Bill Williams	43.24	CD5	92.04
Agua Fria	43.24	CD6	92.04
Lower Gila	54.05	CD7	89.38
Salt	32.43
Lower Colorado	54.05
Upper Gila	62.16
Santa Cruz	51.35
San Pedro	64.86
Willcox Playa	78.38
San Simon	48.65
White Water Draw	83.78

MARCH 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	19.44	CD1	85.84
Upper Colorado	21.62	CD2	69.47
Little Colorado	25.00	CD3	66.37
Verde	27.03	CD4	84.96
Bill Williams	18.92	CD5	65.93
Agua Fria	35.14	CD6	84.96
Lower Gila	35.14	CD7	50.44
Salt	27.03
Lower Colorado	21.62
Upper Gila	48.65
Santa Cruz	29.73
San Pedro	51.35
Willcox Playa	55.56
San Simon	27.03
White Water Draw	63.89

JANUARY 2006 - MARCH 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	23.53	CD1	81.42
Upper Colorado	44.44	CD2	65.49
Little Colorado	25.71	CD3	70.35
Verde	28.57	CD4	76.11
Bill Williams	22.22	CD5	71.24
Agua Fria	22.22	CD6	80.53
Lower Gila	22.22	CD7	82.30
Salt	22.22
Lower Colorado	22.22
Upper Gila	36.11
Santa Cruz	13.89
San Pedro	32.35
Willcox Playa	31.43
San Simon	13.89
White Water Draw	40.00

OCTOBER 2006 – MARCH 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 half of the state continues to be very dry for the 12 month period that began in April of 2006, with only the highest elevation watersheds of the Salt, upper Gila, Little Colorado and southeastern Arizona experiencing near to above average precipitation. Much of that 12-month precipitation was the result of a wet monsoon in those areas. The wettest watersheds were the San Pedro and Willcox, just above the 62^nd percentile. Temperatures for the previous 12 months continue to be well above average, with all climate division above the 80^th percentile.

The two-year period map again shows the longer term drought condition. It seems that an occasional wet season, such as the winter of 2005 is completely offset by an exceptionally dry season, such as the winter of 2006, within the two year window. This alternating of wet and dry years prevents the wet years from being effective in alleviating the 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 85^th percentile, exacerbating the dry conditions. Again, the southeast climate division is the hot spot at the 100^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	17.65	CD1	83.04
Upper Colorado	30.56	CD2	82.14
Little Colorado	41.67	CD3	90.18
Verde	27.78	CD4	80.36
Bill Williams	8.33	CD5	91.96
Agua Fria	27.78	CD6	92.86
Lower Gila	27.78	CD7	96.43
Salt	30.56
Lower Colorado	33.33
Upper Gila	55.56
Santa Cruz	36.11
San Pedro	66.67
Willcox Playa	62.86
San Simon	22.22
White Water Draw	60.00

APRIL 2006 – MARCH 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	36.36	CD1	73.87
Upper Colorado	11.43	CD2	88.29
Little Colorado	5.71	CD3	85.59
Verde	8.57	CD4	92.79
Bill Williams	2.86	CD5	86.49
Agua Fria	2.86	CD6	93.69
Lower Gila	8.57	CD7	100.00
Salt	2.86
Lower Colorado	37.14
Upper Gila	17.14
Santa Cruz	14.29
San Pedro	34.29
Willcox Playa	40.00
San Simon	5.71
White Water Draw	40.00

APRIL 2005 – MARCH 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 has now fallen below the 21st percentile for three watersheds in the south central desert, and the Little Colorado watersheds is below the 40^th percentile. Only the Virgin, upper, and lower Colorado are above the 60th percentile. The 36-month^-temperature pattern remains unchanged for the past 3 months, with Gila County and the southeast climate division above the 95^th percentile for temperature, and only the northwest below the 74^th percentile.

The 48-month precipitation pattern shows the eastern parts of the state below the 25^th percentile, and the western desert only slightly better off just below the 40^th percentile. The upper and lower Colorado River basins are near to slightly above average. Unfortunately, the long-term temperature pattern remains unchanged, with all areas of the state above the 77^th percentile, with the hottest temperatures in Gila County and the southeast climate division, both still above the 96^th percentile.

Watershed	Precipitation Percentile	Climate Division	Temperature Percentile
Virgin	84.38	CD1	73.18
Upper Colorado	67.65	CD2	88.18
Little Colorado	38.24	CD3	86.82
Verde	55.88	CD4	95.45
Bill Williams	52.94	CD5	86.36
Agua Fria	44.12	CD6	90.91
Lower Gila	52.94	CD7	98.18
Salt	41.18
Lower Colorado	79.41
Upper Gila	47.06
Santa Cruz	5.88
San Pedro	20.59
Willcox Playa	41.18
San Simon	11.76
White Water Draw	50.00

APRIL 2004 – MARCH 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	77.06
Upper Colorado	48.48	CD2	89.91
Little Colorado	21.21	CD3	91.74
Verde	30.30	CD4	96.33
Bill Williams	33.33	CD5	89.45
Agua Fria	21.21	CD6	93.58
Lower Gila	39.39	CD7	100.00
Salt	24.24
Lower Colorado	66.67
Upper Gila	21.21
Santa Cruz	12.12
San Pedro	18.18
Willcox Playa	18.18
San Simon	21.21
White Water Draw	36.36

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

April 2007 Arizona Drought Update based on Precipitation (data through March 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

March - precipitation was below average across the northern half of the state, near normal in the southwest and above average in the southeast watersheds. The near average precipitation in the Bill Williams and Lower Colorado watersheds will help offset extremely dry conditions the previous two months. The high temperatures of March (all watersheds were above the 89^th percentile) melted virtually all of the snowpack around the state, and caused much of the precipitation to fall as rain rather than snow.

Three-month period – The 3-month period of January through March was below the 25^th percentile for the upper, lower and Little Colorado watersheds, as well as the Bill Williams in west central Arizona. The central and southern watersheds were also dry, with only White Water Draw above the 56^th percentile. The typical winter storm track is across the northern half to two-thirds of the state, while an El Niño winter generally brings moisture to the central and southern watersheds. This year we saw neither the usual winter pattern nor the typical El Niño pattern. Although January was much colder than normal, both February and March were warmer than average, pushing the 3-month temperatures above the 50^th percentile in all climate divisions.

Six-month period – Fall and winter precipitation, represented by the 6-month period of October through March, was extremely dry, below the 44^th percentile in all watersheds, with the upper Colorado being the wettest. The Santa Cruz and San Simon watersheds were the driest at the 14^th percentile. In the six-month period, temperatures across the state were well above average, with the cooler areas in the Northeast plateau and the southwest.

Twelve-month period – The western half of the state continues to be very dry for the 12 month period that began in April of 2006, with only the highest elevation watersheds of the Salt, upper Gila, Little Colorado and southeastern Arizona experiencing near to above average precipitation. Much of that 12-month precipitation was the result of a wet monsoon in those areas. The wettest watersheds were the San Pedro and Willcox, just above the 62^nd percentile. Temperatures for the previous 12 months continue to be well above average, with all climate division above the 80^th percentile.

Two-year period - The two-year period map again shows the longer term drought condition. It seems that an occasional wet season, such as the winter of 2005 is completely offset by an exceptionally dry season, such as the winter of 2006, within the two year window. This alternating of wet and dry years prevents the wet years from being effective in alleviating the 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 85^th percentile, exacerbating the dry conditions. Again, the southeast climate division is the hot spot at the 100^th percentile.

Three-year period - The 36-month precipitation has now fallen below the 21st percentile for three watersheds in the south central desert, and the Little Colorado watersheds is below the 40^th percentile. Only the Virgin, upper, and lower Colorado are above the 60th percentile. The 36-month^-temperature pattern remains unchanged for the past 3 months, with Gila County and the southeast climate division above the 95^th percentile for temperature, and only the northwest below the 74^th percentile.

Four-year period - The 48-month precipitation pattern shows the eastern parts of the state below the 25^th percentile, and the western desert only slightly better off just below the 40^th percentile. The upper and lower Colorado River basins are near to slightly above average. Unfortunately, the long-term temperature pattern remains unchanged, with all areas of the state above the 77^th percentile, with the hottest temperatures in Gila County and the southeast climate division, both still above the 96^th percentile.