The University of Arizona

Monthly Archive | CLIMAS

Monthly Archive

Feb 2018 Southwest Climate Outlook - La Niña Events in the Southwest

Monday, February 19, 2018

Winter precipitation (Dec-Feb (DJF)), during most weak La Niña events (ENSO Index Value between -0.5 and -1.0) has been below average, although a few years (1968, 1985) were notable outliers (Figs. 5-6). The monthly breakdown of weak, moderate, and strong La Niña events reveals that while the DJF totals for Tucson, AZ and Las Cruces, NM have been mostly below average (Figs. 7-8), there have been individual months that recorded precipitation above the monthly average (represented by black lines on the plots). The most likely outcome for the Southwest this year is below-average precipitation totals for the winter season, but the way that these events unfold will have an impact on how residents perceive and experience this La Niña event (see the following page for examples from Arizona and New Mexico during La Niña events).

Recent La Niña Events - Winter Temperature & Precipitation (Dec 1 - Feb 14)

Temperature anomalies (show below as departures from normal) have been mostly warmer than average during the core of this winter season (Dec 1-Feb 14) across the Southwest (Fig 9). The accumulation plots in Figure 10 display the average precipitation for this timeframe (blue), the observed precipitation this year (green), and the observed precipitation for two recent La Niña events (red, purple) (Fig. 10). These plots reveal similar accumulation patterns, especially in the southern locations, and highlight just how far behind the normal accumulation we are in most of the Southwest.

Feb 2018 Southwest Climate Outlook - La Niña Tracker

Friday, February 16, 2018

La Niña conditions continued for another month, with both atmospheric and oceanic conditions demonstrating a La Niña pattern (Figs. 1-2). Forecasts continue to suggest a weak-to-moderate La Niña event that has likely peaked and will gradually weaken this spring. On Jan. 30, the Australian Bureau of Meteorology saw evidence in recent observations that the event has peaked and is likely already in decline. On Feb. 8, the NOAA Climate Prediction Center (CPC) continued its La Niña advisory based on oceanic and atmospheric conditions, but identified a 55-percent chance of a transition to ENSO-neutral in the spring. On Feb. 8, the International Research Institute (IRI) issued its ENSO Quick Look calling for La Niña to last into the spring (Fig. 3) as a weak-to-moderate event, with a likely return to neutral conditions by mid-spring. On Feb. 9, the Japanese Meteorological Agency (JMA) identified ongoing La Niña conditions straddling weak to moderate strengths and called for a 70-percent chance that the event will end this spring. The North American Multi-Model Ensemble (NMME) is consistently indicative of a weak La Niña event returning to neutral conditions by spring (Fig. 4).

 

Summary: This La Niña event has hovered in the weak-to-moderate range, although it appears to have finally reached moderate strength at the time of this writing. La Niña strength matters in the Southwest, but intensity is not the only factor that affects winter temperature and precipitation patterns. Warmer- and drier-than average winter conditions are associated with La Nina events of any strength, so the presence of La Nina is certain to heighten concerns about winter precipitation and drought, regardless of strength. At the same time, Southwest winters are relatively dry to begin with, so the existence of La Nina does not necessarily bring winter conditions that depart radically from normal, even as they are reliably not wetter than average. However even ENSO-neutral winters have included some of driest (as well as wettest) winters on record. One notable linkage when looking at past events is La Niña conditions generally take wetter-than-average winters off the table. The recent winter storms in the Southwest represent a welcome change, but given the conditions observed so far this winter, a warmer- and drier-than-normal winter certainly appears to be the most likely trajectory.


Online Resources

  • Figure 1 -Australian Bureau of Meteorology - bom.gov.au/climate/enso
  • Figure 2 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov
  • Figure 3 - International Research Institute for Climate and Society - iri.columbia.edu
  • Figure 4 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov

Southwest Climate Outlook February 2018 - Climate Summary

Thursday, February 15, 2018

Precipitation & Temperature: January was warm and dry across the Southwest. Precipitation was average to below average in most of Arizona, and below average to much-below average in New Mexico (Fig. 1a). Temperatures were much-above average to record warmest in Arizona, and ranged from near average to much-above average in New Mexico (Fig. 1b). Looking to the water year (Oct. 1-present), much of Arizona and New Mexico have been recording below-normal precipitation (Fig. 2) and above-average temperatures (Fig. 3) for the period.

Snowpack & Water Supply: Snowpack and snow water equivalent (SWE) are below average across the Southwest (Fig. 4), with most stations in Arizona and New Mexico having recorded less than 25 percent of normal, until recent storms in mid-February boosted SWE in central Arizona. La Niña typically brings warmer and drier conditions to the Southwest in winter, so these patterns are not unexpected, but they do raise concerns about drought impacts on water resource management, reservoir storage levels, rangeland and agricultural conditions, and wildfire risk.

Drought: Drought-designated areas were further expanded and intensified in the Feb. 13 U.S. Drought Monitor, with both Arizona and New Mexico documenting increases in the extent and intensity of drought since January’s outlook. The predominant classification in both states was severe drought (D2), with moderate drought (D1) covering the remaining areas except for small pockets of extreme drought (D3) (Fig. 5). These designations reflect short-term precipitation deficits and warm temperatures at monthly and seasonal timescales, as well longer-term drought conditions that track the cumulative effect of extended periods of warmer- and drier-than-normal conditions. A winter storm is bringing substantial moisture to southern and central Arizona at the time of this writing, which will help moderate short-term conditions but do little to alleviate long-term drought and its impacts.

Wildfire: Warm and dry conditions this winter, in conjunction with above-normal fine fuel loading and continuity, have led to a relatively early start to fire season, thus we are initiating the seasonal fire risk outlooks sooner than in previous years. The National Significant Wildland Fire Potential Outlook for February and March identifies above-normal wildland fire risk for southeastern New Mexico and portions of the borderlands region in southwestern New Mexico and southeastern Arizona (Fig. 6). The extended outlook for April and May identifies above-normal wildland fire risk in nearly all of Arizona and New Mexico. Notably, two fires are already burning in southern Arizona, including the Altar fire and the Knob Hill fire.

ENSO & La Niña: Oceanic and atmospheric conditions continue to indicate an ongoing La Niña event of near-moderate strength. The event is starting to show signs of returning to ENSO-neutral, and most forecasts and outlooks indicate a gradual decay to ENSO-neutral this spring. In the Southwest, La Niña events tend to produce drier-than-average winters, and given the observed conditions this fall and winter, the La Niña influence continues to cause concern in the Southwest in terms of winter precipitation, drought, and water resource management.

Precipitation & Temperature Forecast: The three-month outlook for March through May calls for increased chances of below-average precipitation (Fig. 7, top) and increased chances of above-average temperatures (Fig. 7, bottom) for the southwestern United States.


Online Resources

  • Figure 1 - National Centers for Environmental Information - ncei.noaa.gov
  • Figures 2-3 - High Plains Regional Climate Center - hprcc.unl.edu
  • Figure 4 - Western Regional Climate Center - wrcc.dri.edu
  • Figure 6 - U.S. Drought Monitor - droughtmonitor.unl.edu
  • Figure 7 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov