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April 2018 SW Climate Outlook - Cool Season Precip Summary (Oct - Mar)

Wednesday, April 25, 2018

From the April issue of the CLIMAS Southwest Climate Outlook

Monthly and cool-season (Oct-Mar) precipitation totals demonstrate how this La Niña year compares to previous years, and helps characterize the influence of ENSO on cool-season precipitation. Figures 5a-8a describe monthly and cool season precipitation totals at four weather stations (Flagstaff, AZ; Tucson, AZ, Albuquerque, NM, and El Paso, TX), where each dot corresponds to observed monthly and cool-season precipitation for each year since 1950, color coded by the ENSO status of that year, and the horizontal black lines correspond to 2017-2018 precipitation. Figures 5b-8b are scatterplots of ENSO index vs. precipitation totals for the regional climate division that contains each weather station.

A closer look at individual stations highlights some notable observations. Flagstaff recorded almost no precipitation ​from October through December, and ​the corresponding climate division recorded record​-​dry conditions for the ​entire ​Oct​ober​-through-Mar​ch​ period. ​In Tucson​, nearly all of the October-through-March precipitation fell over just a few days, and ​the plot illustrates the ​role ​that those​ few storms play​ed​ in boosting seasonal totals. Albuquerque had a run of months with near​-​zero precipitation ​broken by a ​few storms in February that boosted the station from record​-​dry to ​merely top​-five driest, while the ​regional climate division was just below average. El Paso fared better than many regional stations, but still recorded generally below​-​average precipitation.


April 2018 SW Climate Outlook - La Niña Tracker

Monday, April 23, 2018

From the April edition of the CLIMAS Southwest Climate Outlook

Oceanic and atmospheric conditions over the last month remained generally consistent with a La Niña event (Figs. 1-2), but given the rapid decline of these conditions and the imminent seasonal transition, it is only a matter of time before ENSO-neutral conditions return. The current ENSO forecasts reflect this steady weakening, with most indicating a likely transition to ENSO-neutral conditions over the spring, and others having already declared an end to this La Niña event. On April 10, the Japanese Meteorological Agency (JMA) identified ongoing La Niña conditions but called for a 90-percent chance that this event will end in spring. On April 10, the Australian Bureau of Meteorology maintained their ENSO Outlook at “inactive,” stating “there is little sign of El Niño or La Niña developing in the coming months.” On April 12, the NOAA Climate Prediction Center (CPC) continued its La Niña advisory but expected a transition to ENSO-neutral conditions by May and forecast a greater-than-50-percent chance of ENSO-neutral lasting through summer. On April 19, the International Research Institute (IRI) issued its ENSO Quick Look, which still identified weak La Niña conditions present but called for a rapid transition to ENSO-neutral conditions over spring (Fig. 3). The North American Multi-Model Ensemble (NMME) is consistently indicative of a return to ENSO-neutral conditions, but with greater uncertainty over what the latter half of 2018 might hold (Fig. 4).

Summary: In the Southwest, the effects of La Niña events can be difficult to distinguish from normal winter conditions. La Niñas are associated with warmer- and drier-than-average winters, but as Southwest winters are relatively dry to begin with, La Niña does not always reflect a radical departure from normal. That said, the above-average temperatures and below-average precipitation of this winter and spring have been characteristic of a La Niña year. The resulting reduction in snowpack and snow water equivalent across the western United States raises concerns about water resource management since the region relies on snowmelt and streamflow to provide a steady supply of water for the region. Thus the impacts of a seasonal event like La Niña, especially in a drought-sensitive area such as the Southwest, can extend far beyond the duration of that event to affect long-term strategies to manage demand, use, and supply in a resource-constrained environment. Water systems in the Southwest are designed with arid conditions in mind, but accumulated precipitation deficits associated with long-term drought, seasonal climate phenomena like La Niña, and the variability of weather all threaten the stability of these systems and the communities and sectors that depend on these water resources.

Southwest Climate Outlook April 2018 - Climate Summary

Friday, April 20, 2018

From the April edition of the CLIMAS Southwest Climate Outlook

Precipitation and Temperature: Precipitation varied across the Southwest in March, but temperatures remained warm throughout the region. Precipitation amounts ranged from record driest to above average (Fig. 1a). Temperatures ranged from average to above average in Arizona, and from above average to much-above average in New Mexico (Fig. 1b). 2018 year-to-date (Jan-Mar) precipitation ranged from near average to much-below average (Fig. 2a), while temperatures for the same period were above average to much-above average (Fig. 2b).

Snowpack and Water Supply: Above-average temperatures and below-average precipitation resulted in snowpack and snow water equivalent (SWE) values that are well-below average across the Southwest (and much of the western United States) (Fig. 3). These warm and dry conditions also affected streamflow and runoff timing: streamflow forecasts for Arizona and New Mexico are all well-below normal (Fig. 4).

Drought: Drought-designated areas were expanded in the April 17 U.S. Drought Monitor, with Arizona and New Mexico documenting increases in the extent and intensity of drought. Nearly 90​ ​percent of Arizona is class​i​f​ied​ as experiencing severe (D2) or extreme (D3)​ drought​, with a pocket of exceptional drought (D4) in the north​-​central region (Fig. 5). Approximately 70​ ​percent of New Mexico is classified as experiencing severe (D2) or extreme (D3)​ drought​, with a notable increase ​in drought intensity ​​from south to north, where exceptional drought (D4) has emerged. These designations reflect short-term precipitation deficits, above-normal temperatures at monthly and seasonal timescales, and longer-term drought that tracks the cumulative effect of extended periods of warmer- and drier-than-normal conditions.

Wildfire: The National Significant Wildland Fire Potential Outlook for May identified above-normal wildland fire risk for eastern New Mexico and the borderlands region in New Mexico and southeastern Arizona, as well as higher-elevation regions in the Upper Colorado River Basin (Fig. 6). The June outlook expands above-normal fire risk to include nearly all of Arizona and New Mexico. Warm and dry conditions this winter, in conjunction with above-normal fine-fuel loading and continuity, are major drivers of the elevated risk, and the Southwest Coordinating Center increased to preparedness level 3 on April 12, reflecting growing concern about fire risk.

ENSO & La Niña: Oceanic and atmospheric conditions remain broadly indicative of a weak La Niña event, but are clearly waning, and trends in these anomalies indicate an imminent return to ENSO-neutral conditions. Most forecasts and outlooks are tracking the gradual decay to ENSO-neutral conditions over spring, and some agencies have already declared this La Niña event over (see La Niña tracker for details). Regardless of when this La Niña event officially ends (or ended), the onset of the characteristically warmer and drier spring conditions in the Southwest means the region is unlikely to see much if any additional precipitation before this summer’s monsoon. Looking back over cool-season precipitation (see Cool Season Precipitation Recap for details), the low seasonal total and relatively few number of days with measurable precipitation are certainly consistent with the reduced precipitation we might expect in a La Niña year.

Precipitation and Temperature Forecast: The three-month outlook for April through June calls for equal chances of above- or below-average precipitation in Arizona and New Mexico (Fig. 7, top) and increased chances of above-average temperatures (Fig. 7, bottom) for the entire southwestern United States.