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Monthly Archive

SW Climate Outlook Jan 2018 - Climate Summary

Thursday, January 18, 2018

December Precipitation & Temperature: December precipitation ranged from average to much-below average across most of Arizona and New Mexico, with record-dry conditions along the western edge of Arizona and in pockets of central and eastern New Mexico (Fig. 1a). December temperatures were above average to record warmest in both states (Fig. 1b), continuing the pattern observed during fall 2017.

Water Year (to-date) and 2017 Precipitation and Temperature: 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 (for more details see the water year to date summary). Annual precipitation in 2017 ranged from much-below average to average in Arizona, and from below average to much-above average in New Mexico (Fig. 4a), while average annual temperatures were record warm across most of Arizona and New Mexico (Fig. 4b).

Snowpack & Water Supply: Snowpack and snow water equivalent (SWE) are below average across the Southwest (Fig. 5), with most stations in Arizona and New Mexico recording SWE of less than 25 percent of normal. The above-average temperatures and dry conditions that drove this pattern are attributable, at least in part, to the ongoing La Niña event. If warm and dry conditions persist through winter—not uncommon in a La Niña event—this will have implications for drought and water resource management throughout 2018 (see Arizona and New Mexico reservoir volumes).

Drought: Above-average temperatures and below-normal precipitation are reflected in the expanding areas of drought designation in the Jan. 17 U.S. Drought Monitor (Fig. 6), with Arizona and New Mexico documenting increases in extent and intensity of drought since the December outlook. Most of both states was classified as moderate drought (D1), but severe drought (D2) was noted over a large area along the Arizona/New-Mexico border and in a smaller region of eastern New Mexico. Below-average precipitation in the Southwest over the last few months is a primary driver for these designations, but the drought monitor authors also considered the effect of long-term drought in their designations.

ENSO & La Niña: La Niña conditions continued for another month, although the event may have reached its peak intensity. Current forecasts suggest this weak-to-moderate event will last through winter 2018 before weakening this spring. In the Southwest, weak La Niña events tend to produce drier-than-average winters, but moderate events have resulted in more consistently dry conditions over the winter (see La Niña Tracker and DJF La Niña Precip in the SW for details). Given the drier-than-average conditions in the Southwest last fall and so far this winter, the presence of a 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 February through April calls for increased chances of below-average precipitation for all of Arizona and New Mexico (Fig. 7, top), and increased chances of above-average temperatures for the entire southwestern United States (Fig. 7, bottom).

Online Resources - Image Credits

  • Figures 1,4 - National Centers for Environmental Information -
  • Figures 2-3 - High Plains Regional Climate Center -
  • Figure 5 - Western Regional Climate Center -
  • Figure 6 - U.S. Drought Monitor -
  • Figure 7 - NOAA - Climate Prediction Center -

SW Climate Outlook - La Niña Tracker - Jan 2018

Thursday, January 18, 2018

La Niña conditions have continued for another month at weak-to-moderate strength, with both atmospheric and oceanic conditions, including sea-surface temperatures (SSTs), demonstrating a consistent La Niña pattern (Figs. 1-2). Forecasts continue to suggest that a weak-to-moderate La Niña event will last through the winter before weakening this spring.

On Jan. 11, the Japanese Meteorological Agency (JMA) identified ongoing La Niña conditions and called for a 70-percent chance of these conditions persisting through spring 2018. On Jan. 11, the NOAA Climate Prediction Center (CPC) continued its La Niña advisory, identifying an 85-95-percent chance of La Niña conditions lasting through the winter, with a transition to ENSO-neutral in the spring. On Jan. 11, the International Research Institute (IRI) issued its ENSO quick look, calling for La Niña to last into the spring (Fig. 3) as a weak event, but with recognition that the conditions were very close to the threshold for a moderate event. On Jan. 16, the Australian Bureau of Meteorology updated its ENSO tracker to reflect continued La Niña conditions, but noted that this event “may be nearing its peak,” with a return to neutral values by spring 2018. The North American Multi-Model Ensemble (NMME) is consistently indicative of a La Niña event of weak to moderate intensity this winter (Fig. 4).

Summary: Given the consistent La Niña patterns observed in both oceanic and atmospheric indicators, seasonal outlooks forecast that La Niña will last through the winter. Current conditions reflect a borderline weak-to-moderate event. Warmer- and drier-than-average winter conditions are associated with La Niña of any strength in the Southwest, so the presence of La Niña is certain to heighten concerns about winter precipitation and drought. Southwestern winters are already relatively dry, however, so La Niña does not ensure an exceptionally dry winter (although this is the trajectory much of the Southwest appears to currently be on), but it does take a wetter-than-average winter off the table based on past La Niña events. If the La Niña strengthens to moderate intensity, the likelihood of an even drier Southwest winter increases (see the following page for a few examples).

Online Resources / Image Credits

  • Figure 1 - Australian Bureau of Meteorology -
  • Figure 2 - NOAA - Climate Prediction Center -
  • Figure 3 - International Research Institute for Climate and Society -
  • Figure 4 - NOAA - Climate Prediction Center -

Dec-Feb La Niña Precip in the SW

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.

Online Resources / Image Credits

SW Climate Outlook Jan 2018 - Water Year To-Date (Oct 1 – Jan 15, 2018)

Thursday, January 18, 2018

The year 2017 was record warm across most of Arizona and New Mexico, in no small part thanks to the exceptionally warm conditions during the final three months of the year (and November in particular).

These months were also very dry, with limited eastern Pacific tropical storm activity making its way into the Southwest during the fall and very little early winter precipitation, further exacerbating the dry conditions brought about by a relatively early end to the monsoon last summer.

Looking to a selection of weather stations in Arizona (below) and New Mexico (p. 7), water-year temperature and precipitation departure from normal since Oct. 1 demonstrate just how warm and dry conditions have been across the region.

Figures 1-3 - West Wide Drought Tracker -

Figures 4-7 - CLIMAS: Climate Assessment for the Southwest -