April 2024: Southwest Climate Outlook

The Southwest Climate Outlook is published by the Climate Assessment for the Southwest (CLIMAS), with support from University of Arizona Cooperative Extension, and the New Mexico State Climate office.

Questions/Contact: Stacie Reece, sreece@arizona.edu

March precipitation was above normal to much-above normal across much of Arizona and large parts of New Mexico. Precipitation in southern and eastern New Mexico ranged from near normal to below normal.

March temperatures were near normal across most of Arizona and New Mexico, ranging into below normal temperatures in parts of Arizona, and above normal in parts of New Mexico.

January – March 3-month precipitation accumulation was above normal across Arizona and western and northern parts of New Mexico. Central, southern, and eastern parts of New Mexico saw near normal to below normal precipitation over those three months.

January – March 3-month average temperatures varied across space, with large parts of Arizona and New Mexico seeing temperatures near normal, but areas including much of the Colorado Plateau, Rio Grande Valley, and southeastern plains of New Mexico seeing above normal averages. In some isolated areas, mostly in Arizona, temperatures averaged below normal.

Water year precipitation so-far (October 2023 – March 2024) has been near normal across most of Arizona and New Mexico, but above normal in parts of southern and eastern Arizona, and in some places across New Mexico. Precipitation has lagged below normal in parts of northwestern Arizona and southern New Mexico over those six months.

The U.S. Drought monitor highlights less-than-ideal conditions for Arizona and New Mexico as we enter the hot and dry season—drought conditions are affecting about three quarters of New Mexico and about one quarter of Arizona; an additional near-half of Arizona, and nearly all the remaining portion of New Mexico is classified as abnormally dry. The area facing the most acute drought conditions is southern New Mexico, where conditions are classified extreme to exceptional for over 13% of the state’s area.

NIDIS Improved and Expanded State Pages on Drought.Gov

We are now well into the melting season for snowpacks in the Southwest, and basin-average snow water equivalent (SWE) estimates reflect measurements from fewer sites because the climatological normal (period-of-record median SWE) is zero or missing for this time of year. Only one station in Arizona is contributing data to SWE estimates as of April 29, and as normal approaches zero, percent-of-normal will become meaninglessly large, as seen in a few Arizona basins. Elsewhere, warm temperatures have rapidly melted snow that was, when at peak snowpack, near normal SWE. Estimates of near normal to below normal SWE from more northern or higher elevation basins are more reflective of snow storage conditions.

Streamflow forecasts vary from below normal expected flows in basins of the San Juan and Rio Grande rivers to much-above normal flows in basins of the Salt, Verde, and Gila rivers.

Water storage in reservoirs is broadly near-to-above normal in Arizona and below normal in New Mexico. Lakes Mead and Powell are well below normal (long term average), but levels have increased over last year’s. The same is true of many larger New Mexico reservoirs including Elephant Butte and Navajo.

 _{The map gives a representation of current storage for reservoirs in Arizona and New Mexico. Reservoir locations are numbered within the blue circles on the map, corresponding to the reservoirs listed in the table. The cup next to each reservoir shows the current storage (blue fill) as a percent of total capacity. Note that while the size of each cup varies with the size of the reservoir, these are representational and not to scale. Each cup also represents last year’s storage (dotted line) and the 1991–2020 reservoir average (red line). The table details more exactly the current capacity (listed as a percent of maximum storage). Current and maximum storage are given in thousands of acre-feet for each reservoir. One acre-foot is the volume of water sufficient to cover an acre of land to a depth of 1 foot (approximately 325,851 gallons). On average, 1 acre-foot of water is enough to meet the demands of four people for a year. The last column of the table lists an increase or decrease in storage since last month. A line indicates no change. These data are based on reservoir reports updated monthly by the  Natural Resources Conservation Service - National Water and Climate Center (USDA)  .} 

Sea surface temperatures (SSTs) in March showed warm SST anomalies in the central equatorial Pacific persisting from the El Niño event that peaked over the winter, while SSTs in the eastern equatorial Pacific tended toward normal. The western equatorial Pacific featured warm SST anomalies that would be consistent with an expected development of La Niña later this year.

Forecast SSTs for May – July show expansion of warm SSTs in the western tropical Pacific and a cohesive region of cool SSTs in the eastern equatorial Pacific, in a pattern consistent with the development of La Niña conditions.

SSTs within the four ENSO diagnostic regions have continued to decline, and although regions Nino 3 (eastern equatorial Pacific), Nino 4 (central equatorial Pacific) and Nino 3.4 (a region spanning parts of Nino 3 and 4) have not yet returned to ENSO-neutral SSTs (-0.5°C < SSTA < 0.5°C), the coastal-eastern Pacific region Nino 1+2 has shown cool-anomaly SSTs beginning in March.

The probabilistic summary of ENSO model forecasts favors ENSO-neutral conditions for the coming months, through the June – August prediction interval. La Niña conditions are the most likely state expected for the latter half of the year (2 out of 3 odds of La Niña conditions in October – December), but there is still uncertainty—probabilities >25% of ENSO-neutral conditions.

Among individual ENSO forecast models, the majority predict La Niña conditions by September – October; some models indicate a very strong La Niña event while others indicate a more subdued event. A few models predict ENSO-neutral conditions through year end, and one model indicates a return to weak El Niño conditions.

The May – July seasonal precipitation forecast leans toward below normal precipitation for an area that includes New Mexico and eastern Arizona. Ensembles of weather prediction models contribute to these forecasts; the “leaning below” outlook in this case corresponds to 33%-50% of individual model ensemble members indicating precipitation totals in the lower tercile of the precipitation climatology for the season.

The May – July seasonal temperature forecast leans toward above normal temperatures for Arizona, and favors above normal temperatures for New Mexico with greater likelihood.

Areas of central and southeastern Arizona, southern New Mexico, and the Rio Grande Valley are expected to have above normal potential for significant wildland fire in May and June. Reasons for the elevated potential include an abundant accumulation of fine fuels and expected hot, dry conditions.  

In this month’s Southwest Climate Podcast hosts Zack Guido and Mike Crimmins look back at winter to share insights on the late-loaded precipitation, as well as current snowpack conditions and streamflow forecasts.  The hosts discuss how El Niño played out as it starts its transition to La Niña and what to look out for this coming spring setting up this year’s monsoon season.  

And stay tuned for news on this year's Monsoon Fantasy competition on the next Pod being released next week!

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The Climate Assessment for the Southwest (CLIMAS) program was established in 1998 as part of the National Oceanic and Atmospheric Administration’s Climate Adaptation Partnerships (CAP) Program (formerly known as Regional Integrated Sciences and Assessments, or RISA). CLIMAS—housed at the University of Arizona’s Institute of the Environment—is a collaboration between the University of Arizona and New Mexico State University. The CLIMAS team is made up of experts from a variety of social, physical, and natural sciences who work with partners across the Southwest to develop sustainable answers to regional climate challenges.