Blame it on La Niña.

Pushing the jet stream and the storms it carried north of the region, La Niña played a starring role in a record-dry winter in the Southwest this past year.

The lack of rain and snow led to extensive fires in Arizona and New Mexico, skimpy irrigation allotments and withered vegetation in the spring. Now mounting evidence suggests that after a brief summer hiatus La Niña may be back.

This would not be welcome news for most of the Southwest, and especially those areas mired in extreme and exceptional drought, particularly since the second year in back-to-back La Niña events is often drier than the first.

During the 20 winters since 1950 in which La Niña was present, precipitation has been, on average, below-average across the region. Last winter upheld this dry pattern, as a moderate to strong La Niña event developed in June 2010 and dissipated in April.

At the onset of winter, in the beginning of November, only about 3 percent of Arizona was classified with moderate drought conditions; New Mexico was drought-free. By the beginning of the 2011 monsoon season in mid-June, however, 56 and 99 percent of Arizona and New Mexico, respectively, were in the grips of moderate, if not more severe, drought.

Drought also intensified in nearly every region. By mid-June, nearly 6 and 45 percent of Arizona and New Mexico, respectively, were pegged with the most severe drought category – exceptional drought, which occurs once in every 50 years; about another 13 and 23 percent were classified with extreme drought, which occurs once in every 20 years.

With the region desiccated in the lead-up to the summer rains, climatologists at the University of Arizona and National Drought Mitigation Center at the University of Nebraska stated that an average monsoon season would be insufficient to significantly improve drought conditions.

The region needed constant and copious moisture. In most of New Mexico and all of Texas, the October-July period was either the first or second driest in the last 117 years, while southeast Arizona ranked in the top six.

To date, however, the thunderous storms have been inconsistent and spottier than usual, and most of the region continues to accumulate rainfall deficits. It is unlikely that summer rains will provide widespread drought relief this late in the season.

The NOAA-Climate Prediction Center, or CPC, assigns less than a 3 percent chance that moisture in the upcoming four months will be sufficient to erase drought conditions in southern Arizona and New Mexico where drought conditions are most severe.