Temperatures since the water year began on October 1 are averaging between 60 and 75 degrees Fahrenheit in the southwest deserts and along the Arizona-California border; 55 to 65 degrees F in southeastern Arizona, along the New Mexico-Mexico border, and in southeastern New Mexico; and 45 to 55 degrees F in central and northwestern New Mexico and across the Colorado Plateau in Arizona (Figure 1a). The highest elevations are seeing temperatures between 35 and 45 degrees F. These temperatures have been 1–2 degrees F warmer than average across parts of Arizona and most of New Mexico (Figure 1b). The highest above-average temperatures have been in Otero County along the New Mexico-Mexico border. The warm conditions are due to a persistent high pressure ridge over the area which suppressed monsoon precipitation.   

Temperatures during the past 30 days have been warmer than average across most of Arizona and all of New Mexico (Figures 1c–d). In the southwest Arizona deserts, temperatures increased by about 5 degrees F over the previous month due to increased humidity and warmer nighttime temperatures. New Mexico has experienced the warmest conditions. Temperatures have been progressively warmer to the southeast, which matches the drought pattern in recent weeks—the driest and hottest conditions have been toward southeastern New Mexico.  
 

Precipitation since the water year began on October 1 generally  has ranged from 130 percent of average in the northwest corner of Arizona to less than 25 percent of average in the southeastern corner of New Mexico (Figures 2a–b). The wet-to-dry gradient continues to run diagonally across both states. The Colorado Plateau and central counties of Arizona, as well as the northwest and northern borders of New Mexico, have received between 50 to 90 percent of average precipitation. The southern Arizona counties and the southeastern two-thirds of New Mexico have received 25–50 percent of average.  Eddy, Chaves, and Lea counties in southeastern New Mexico have received even less.

In the last 30 days, monsoon storms have delivered copious rains to parts of southeastern Arizona including Graham, Greenlee, and western Cochise counties, as well as to central Coconino County in northern Arizona and southern Hidalgo and Luna counties in southwest New Mexico (Figures 2c–d). However, most of the Southwest has received less than 70 percent of average rainfall in the last month, most notably western Arizona and eastern New Mexico, which have received less than 50 percent of their average.

Most of the western U.S. remains drought-free after a banner wet winter and spring. The exceptions are Arizona and New Mexico, where drought conditions continued to occupy nearly all of both states. The monsoon started with a bang in a few parts of Arizona—although precipitation was not widespread or heavy enough to improve drought conditions—and a bust for most of New Mexico; precipitation during the last 30 days has also been slightly below average in most of the two states except for the southeastern and southwestern corners of Arizona and New Mexico, respectively. Across the West, the percent of area covered by abnormally dry conditions or a more severe drought category remained virtually unchanged from one month ago and currently sits at about 25 percent, according to the August 16 update of the U.S. Drought Monitor (Figure 3).

Drought conditions also remain unchanged in Texas, were exceptional drought conditions currently occupy 75 percent of the state.

Monsoon thunderstorms have been spottier than usual and relatively infrequent over much of Arizona over the past 30 days, bringing little relief to drought conditions plaguing much of the state. Drought expanded across western Arizona, while conditions eased slightly in far southeast Arizona in the last month, according to the August 16 update of the U.S. Drought Monitor (Figures 4a–b). In far northwestern Arizona, incursions of moisture and thunderstorms have been few and far between, leaving mounting precipitation deficits and the return of abnormally dry conditions to this region—abnormally dry conditions are not a drought category but signal drought will develop if dry conditions continue. In southeastern Arizona, a handful of widespread precipitation events over Cochise and Graham counties during the last 30 days have slightly reduced extreme and exceptional drought, but overall drought conditions are still very severe due to long-term precipitation deficits and a lackluster monsoon season so far. Reports submitted through Arizona DroughtWatch
(http://azdroughtwatch.org) for southeast Arizona continue to portray very poor rangeland conditions and impacts to livestock that include calling herds, hauling water, and providing supplemntal forage due to continuing extreme drought conditions.

New Mexico generally has received less than 70 percent of average rainfall in the past month. The exception has been in the southwest corner of the state, where  storms have delivered more than 130 percent of average. As a result, the entire state is still classified with some drought category (Figures 5a-b). About 42 percent of the state is pegged with exceptional drought, which is defined as a drought that occurs, on average, once in every 50 years. Another 35 and 16 percent of the state is experiencing extreme and moderate drought, respectively. Compared to one month ago, exceptional drought declined by about 6 percent, extreme drought increased by about 4 percent, and moderate drought increased by about 2 percent. The NOAA-Climate Prediction Center September forecast calls for slightly increased chances for below-average rainfall. In addition, the probability for a return of La Niña this winter is increasing. Both these forecasts suggest that drought conditions will not improve and may actually intensify and spread.

Combined storage in Lakes Mead and Lake Powell increased by almost 2 million acre-feet during July. As of July 1, Mead and Powell storage was at 61 percent of capacity (Figure 6), which is around 10 percent more than a year ago. On July 30, the elevation of Lake Powell peaked for the water year at 3,660.9 feet, which is 39.1 feet below full capacity. The projected unregulated inflow to Lake Powell for the 2011 water year is 17.0 million acre-feet, or 141 percent of average. Storage in other reservoirs within Arizona’s borders decreased by more than 116,000 acre-feet in July. San Carlos Reservoir, in drought-stricken southeastern Arizona, is at a mere 1 percent of capacity.

The increase in Lake Mead’s level, which is currently about 20 feet higher than it was one year ago, allowed the U.S. National Park Service to reopen several boat-launch ramps along the lake’s National Recreation Area (Las Vegas Review Journal, August 7).

The total reservoir storage in New Mexico declined by about 160,000 acre-feet in July (Figure 7). There were substantial decreases in storage in the state’s largest reservoirs—Navajo and Elephant Butte declined by 39,200 and 60,100 acre-feet, respectively. Compared with one year ago, storage declined in every New Mexico reservoir included in Figure 7, except Abiquiu, which contains only 700 acre-feet more than one year ago.

In water-related news, the Buckman Direct Diversion project, which brings Rio Grande water to Santa Fe, was closed for about a month after rain washed ash and debris from the Las Conchas Fire into the river system (Santa Fe New Mexican, August 6). The closure prevented the ash from clogging filters and required Santa Fe, whose local reservoirs are only around one-third full, to pump groundwater.
 

Wildfires have abated since the monsoon began in early July and storms have helped quell many large fires, including the record-setting Wallow Fire that burned more than 538,000 acres in eastern Arizona and western New Mexico. Between July 20 and August 16, more than 150,000 acres burned across Arizona and New Mexico, according to Predictive Services at the Southwest Coordination Center. Since the beginning of the calendar year, more than 970,000 acres in Arizona and 1 million acres in New Mexico have burned in wildfires (Figure 8a), which is about 900,000 more acres burned then the previous record set in 2002. In Arizona, most wildfires occurred in the central and southern parts of the state (Figure 8b), while the eastern areas of New Mexico have experienced the highest fire activity (Figure 8c).    

As of August 18, 11 fires larger than 100 acres were burning in Arizona. Most of these were relatively small, having charred less than 5,000 acres. In New Mexico, seven fires were burning and all but one covered fewer than 300 acres; the largest fire has burned fewer than 5,000 acres.

The first two months of the monsoon season have been underwhelming and spottier than normal in many parts of Arizona and New Mexico despite persistant high humidity. Although moisture has been present, a lack of strong winds aloft and atmospheric stability has prevented widespread and constant rains. As a result, rainfall between June 16 and August 14 in New Mexico and Arizona generally has been less than 3.5 inches, with precipitation deficits ranging from 1.5 to 4.5 inches in New Mexico (Figures 9a–b). Rainfall has measured less than 75 percent of average in most of New Mexico, with the driest conditions occurring in the southeast corner (Figure 9c). Only parts of southeast and southwest Arizona and the Four Corners region have experienced above-average rainfall. The drier-than-average conditions in New Mexico can be blamed in part on the position of the subtropical high, or the monsoon ridge, which has hovered too far to the east to deliver copious rains to most of the state. This extensive dome of high pressure has generally extended from the East Coast to eastern New Mexico, causing winds over New Mexico to waft generally from the east instead of the south. The drier-than-average conditions have not helped improve widespread and intense drought for most of the region. On August 16, 12 and 77 percent of Arizona and New Mexico, respectively, were pegged with extreme or exceptional drought. Two months earlier, at the onset of the monsoon season, those numbers were 18 and 68 percent.

The seasonal temperature outlooks issued by the NOAA-Climate Prediction Center (CPC) in August call for increased chances for temperatures to be similar to those of the warmest 10 years of the 1981–2010 period through the spring. For the September–November period CPC outlooks call for greater than a 50 percent chance that temperatures will resemble the warmest years in the climatological record in most of Arizona and southern New Mexico (Figure 10a). These forecasts are based in part on decadal trends and statistical and dynamical forecasts. The forecast issued for the October–December and November–January periods calls for temperatures in most of Arizona and in New Mexico to have greater than a 40 percent probability of being similar to those of the warmest 10 years in the climatological record, with slightly higher probabilities in southern parts of both states (Figures 10b–c). For the December–February period, temperatures have an equal chance of being above-, below-, or near-average in Arizona and slightly enhanced odds for warmer-than-average temperatures in New Mexico (Figure 10d).

The seasonal temperature outlooks issued by the NOAAClimate Prediction Center (CPC) in August call for slightly increased chances for precipitation during September–November and October–December to be similar to the driest 10 years of the 1981–2010 period (Figures 11a–b). The greatest chances are in the southern portions of both states. These forecasts are based in part on current dry soil moisture conditions and trends for drier conditions during these periods. For November–January, the CPC calls for equal chances of above-, below-, or near-average conditions (Figure 11c) for most of the region. The southern tier of the region has slightly enhanced odds at drier-than-average conditions for the December–February period (Figure 11d). This forecast is influenced in part by the increasing likelihood that a La Niña event will develop this winter. La Niña events historically bring dry conditions to the Southwest.

This summary is partially excerpted and edited from the August 16 Seasonal Drought Outlook technical discussion produced by the NOAA-Climate Prediction Center (CPC) and written by forecaster D. Miskus.

Monsoon rainfall began in earnest during the first half of July across portions of the Southwest, primarily in Arizona, Utah, and Colorado. In New Mexico, however, drought remained entrenched in the eastern half of the state, while some monsoon showers aided the far western areas. In recent weeks, monsoon activity has been centered near the Arizona and New Mexico border with some showers spreading into northeastern New Mexico and the Texas and Oklahoma panhandles. However, storms have missed southeastern New Mexico and far western Texas. Short -and medium-term forecasts spanning 6–10 and 8–14 days favor drier weather for the western sections of the Southwest, and near-average precipitation for the eastern parts. The NOAA-Climate Prediction Center (CPC) monthly and seasonal outlooks support increased chances of below-median rainfall and above-average temperatures across the entire Southwest monsoon region. Also, there are increasing chances for the re-emergence of a La Niña event this winter. In the past, the second winter in back-to-back La Niña events has delivered below-average precipitation to the Southwest. Based on these forecasts, drought is forecast to persist from Arizona into New Mexico, with possible development in western Arizona and southern Utah and Colorado (Figure 12). The CPC assigns a medium confidence for this forecast.

A persistent ridge of high pressure has maintained hot and dry conditions across the south-central U.S. for the second consecutive month, exacerbating the drought in the southern Plains and contributing to below-average rainfall in many parts of New Mexico. Texas and Oklahoma experienced the warmest July in the last 117 years, while Texas had the second driest July on record. For the May–June period, Texas and New Mexico experienced the second driest period on record, while February–July was the driest on record for New Mexico.

Significant fire potential is expected to remain normal across most of Arizona and New Mexico for the September–November period, according to the Predictive Services at the Southwest Coordination Center (Figure 13). Only the far eastern edge of New Mexico, where conditions have been hotter and drier than average, shows signs of above-normal significant fire potential. Significant fire potential is the likelihood that a wildland fire event will require additional fire management resources from outside the region where the fire originated. Temperature outlooks issued by the NOAA-Climate Prediction Center (CPC) show an increased likelihood for aboveaverage temperatures for the September–November period.

CPC precipitation forecasts for the same time period show slightly increased chances for below-average rainfall across most of the Southwest (see Figures 10a and 11a). However, significant fire potential remains normal due to monsoon-related moisture. Although actual rainfall has been variable across the region, high day and night humidity levels accompanying the monsoon have helped and will continue to help mitigate fire potential through September. High nighttime humidity is particularly important because it allows vegetation to regain moisture, making these potential fuels less likely to burn. Additionally, the recent lack of windy conditions has diminished the occurrence of large wildfires. If the number of wind events remains low, wildfires will have less potential to grow into significant events in the coming months.

Sea surface temperatures across the central and eastern equatorial Pacific Ocean were close to average again this month, signaling the continuation of ENSO-neutral conditions. Southern Oscillation Index (SOI) values are also near zero, additional evidence for neutral conditions (Figure 14a). However, similar to last month, the NOAA-Climate Prediction Center (CPC) states there are several weak atmospheric circulation patterns characteristic of La Niña that continue to linger from last winter’s La Niña event, including slightly enhanced easterly winds along the equator and suppressed convection in the eastern Pacific.

The La Niña-like conditions in the atmosphere, albeit weak, and a pool of below-average ocean temperatures below the surface in the eastern Pacific have caused models to increase probabilities for a return of La Niña as early as this fall. Forecasts issued by the International Research Institute for Climate and Society (IRI) indicate a 44 percent chance that La Niña conditions will develop during the November–January period, an increase from 26 percent issued last month. It is important to note that the probability of neutral conditions continuing this fall is 54 percent; the chance for the development of El Niño is very low at 2 percent (Figure 14b).

Seasonal precipitation forecasts for the Southwest reflect in part the idea that a weak La Niña may return and persist through the fall and winter season. An increased chance of below-average precipitation across southern Arizona and New Mexico shows up in seasonal precipitation forecasts issued by the NOAA-CPC for December 2011 through April 2012. This is consistent with dry conditions characteristic of a La Niña event and would be the continuation of a very dry pattern for a second year in a row in the Southwest. The prospect of back-to-back dry winters is bad news for drought-stricken areas in Arizona and New Mexico.