Only three storms have penetrated the Southwest since the water year began on October 1, and precipitation deficits continue to mount. Arizona and New Mexico have received less than 25 percent of average precipitation in the last 60 days and no rain or snow fell in many places in the last month. January was the second driest on record in Arizona and the driest recorded in New Mexico. Temperatures were very warm in the past 30 days (Figure 1), exacerbating dry conditions by ramping up evaporation and more rapidly melting snowpacks. All of the basins in Arizona and New Mexico report below-average snowpacks (Figure 2), with several snow monitoring sites in the Gila Mountains and Upper Rio Grande Basin measuring snow water equivalent values in the driest 10 percent of their historical record. Consequently, streamflow forecasts are well below average for streams that draw water predominately from the higher elevations of either state. Precipitation in the Upper Colorado River Basin has been above average, however and has helped compensate for below-average snows in other parts of the basin. Nonetheless, February 1 projections for inflow into Lake Powell still favor slightly below-average streamflows.
The dry conditions also have caused drought to intensify from moderate to extreme in central areas of Arizona (Figure 3). In the last month, severe and extreme drought increased by 22 and 7 percent, respectively. Similarly, the area covered in New Mexico with severe and extreme drought rose by 24 and 11 percent, respectively.
A persistent ridge of high pressure parked off the West Coast has causedwarm and dry conditions over Arizona and New Mexico, as well as record-setting dry weather in California. This pattern has driven storms north of the region where it has entrained cold air before moving east over the Rocky Mountains in Montana and Wyoming and then south into Colorado and eastern New Mexico. While the moisture has been largely sapped from the air before leaving Colorado, the cold air has driven down temperatures in New Mexico (Figure 1). This atmospheric circulation resembles a classic La Niña pattern, although sea surface temperatures in the tropical Pacific Ocean have been near average, or ENSO-neutral. When a resilient atmospheric pattern sets up, like the one in place this winter, forecasts usually favor persistence. The seasonal drought forecasts call for elevated chances for drought to persist or intensify, while temperature forecasts favor above-average conditions; precipitation forecasts are a coin flip.