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Monthly Archive | CLIMAS

Monthly Archive

August 2018 SW Climate Update - ENSO Tracker

Friday, August 17, 2018

The Southwest remains in an ENSO holding pattern, with oceanic and atmospheric conditions still within the range of ENSO neutral over the last month (Figs. 1-2), and the forecasts and outlooks reflect that. On Aug. 9, the NOAA Climate Prediction Center (CPC) continued its El Niño watch, identifying persistent neutral conditions at present but with seasonal outlooks and models picking up on an increased likelihood of El Niño later this year despite a recent decrease in equatorial sea surface temperatures (see Niño 3.4 plot in Fig. 2 & sidebar for more information). CPC’s outlook indicates a 60-percent chance of an El Niño event developing this fall and a 70-percent chance of El Niño conditions this winter. On Aug. 9, the International Research Institute (IRI) issued an ENSO Quick Look noting neutral conditions in the oceans and atmosphere now but with warming subsurface oceanic waters pushing forecast probabilities for an El Niño event to just over 70 percent by the end of 2018 (Fig. 3). On Aug. 10, the Japanese Meteorological Agency (JMA) also identified neutral conditions in oceanic and atmospheric indicators and a 60-percent chance of El Niño by this fall. On Aug. 14, the Australian Bureau of Meteorology maintained its “El Niño Watch,” although most indicators were within the range of neutral. They, too, noted the warm subsurface waters in the Pacific Ocean despite recent cooling of surface waters and predicted a 50-percent chance of El Niño formation by the end of 2018. The North American Multi-Model Ensemble (NMME) is demonstrating the steady trend in observations and forecasts towards warmer-than-average ocean temperatures and is zeroing in on a weak to borderline-moderate El Niño event by the end of 2018 (Fig. 4).

Summary: Despite a recent dip in surface temperatures in the Pacific Ocean, most outlooks have maintained an increased chance of a weak to borderline-moderate El Niño forming in 2018 with virtually no chance of a La Niña. Warm subsurface waters persist, and the forecasts suggest a return to warming sea-surface temperatures in the coming months along with a transition to atmospheric patterns more indicative of El Niño. However, the formation of an El Niño event is still far from certain; the probabilities for neutral conditions range from 30 to 50 percent, depending on the agency and the timeframe, but are near zero for a La Niña event (see Fig. 3 for an example). Presuming an El Niño event does form in 2018, the onset timing and intensity of the event will play a role in how much it affects tropical storm activity this fall and cool-season precipitation this winter and spring.

Online Resources

  • 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 -

August 2018 SW Climate Outlook - Monsoon Tracker

Friday, August 17, 2018

Monsoon precipitation totals vary considerably across the Southwest. Monthly totals for select locations reveal near or below-average amounts compared to long-term averages (Fig. 1). There are widespread regions with above-average totals as well (see p. 5), revealing the challenge of characterizing monsoon performance using single stations. The monthly breakdown illustrates the sporadic nature of monsoon activity that affects how each locale reaches its seasonal totals and demonstrates how particular events can boost monthly totals in some locations but not others—such as how TS Bud in June affected Tucson but not Phoenix. Daily precipitation plots for the same stations (Fig. 2) further demonstrates the intermittent nature of monsoon precipitation and distinguishes areas that have had frequent events (e.g. Tucson, Flagstaff) from those with fewer ones (e.g. Phoenix, El Paso).


As discussed last month, increasing dewpoint temperature was the old metric by which monsoon onset was determined. This year, the onset of monsoon precipitation was relatively closely aligned with increasing dewpoint temperatures in early July, but the precipitation/dewpoint relationship since then illustrates why elevated dewpoint is an imperfect measure of likely precipitation. Although dewpoint temperatures were elevated for much of the last month, precipitation was not consistent. In fact, sustained periods of high dewpoints without precipitation led to extreme heat warnings in the region, with heat indices over 110 degrees in some locations, and persistent warm overnight temperatures. Without storm-induced cooling, elevated dewpoint temperatures can be downright miserable, especially for households that rely on evaporative coolers for interior climate control.

Seasonal totals to date (Fig. 3), the percent of normal precipitation (Fig. 4) and percent of days with rain (Fig. 5) all help characterize the spatial variability and intensity of the monsoon thus far.

A look at monsoon precipitation across the Tucson metropolitan area illustrates the spatial heterogeneity of monsoon events. Some areas receive frequent and/or abundant precipitation, while others–often nearby–do not (Figs. 6-7). Individual stations (e.g. the Tucson Airport) track long-term comparisons to normal at that single location, but can not capture this variability. Higher elevation areas are expected to receive more precipitation, but the range found in lower elevation locations highlights how daily and cumulative totals can vary across a remarkably short distance.

Online Resources

  • Figures 1-2 - CLIMAS: Climate Assessment for the Southwest -

    • Figure 1 Data:
    • Figure 2 Data:
  • Figures 3-5 - UA Climate Science Application Program -
  • Figures 6-7 - CLIMAS: Climate Assessment for the Southwest -

    • Figures 6-7 Data: & Pima County Flood Control District

Southwest Climate Outlook August 2018 - Climate Summary

Thursday, August 16, 2018

Precipitation and Temperature: Precipitation in July ranged from below average to much-above average in Arizona and New Mexico (Fig. 1a), illustrating the extent to which monsoon precipitation varies across the region. July temperatures were warmer than average in nearly all of Arizona and New Mexico (Fig. 1b), and since July 1, most of the daily temperature anomalies (deviations above or below the average temperature) have been warmer across the region (Fig. 2). Year-to-date precipitation is above average to record driest while year-to-date temperatures have been much-above average to record warmest (Fig. 3a-b).

Monsoon Tracker: The monsoon is going strong with prevailing conditions favorable to storm activity. Arizona and New Mexico have had nearly daily storms since early July, but as is typical this time of year, the actual precipitation totals vary considerably across the Southwest at regional and even local scales due to the intense but localized nature of monsoon events (see Monsoon Tracker for details).

Drought: Water-year precipitation to date reveals persistent cumulative deficits across nearly all of Arizona and much of New Mexico (Fig. 4). The Aug. 14 USDM responded to recent precipitation and scaled back some of the drought designations in southern Arizona and New Mexico (Fig. 5), although the Four Corners region remains in exceptional drought (D4). Drought experts continue to discuss the extent to which short-term upticks in summer precipitation can truly reverse months of deficit. This is our annual conundrum: How much does monsoon precipitation mitigate drought conditions in the Southwest? High-intensity precipitation is subject to loss via runoff and evaporation, yet it can help quickly recharge reservoir storage and irrigate summer forage crops that are dependent on the timing of the precipitation, thus the answer depends on what type of drought you are tracking. Furthermore, the spatial variability of monsoon events can lead to a sense of winners and losers for monthly and seasonal totals during the monsoon, even while both are still subject to the longer-term, cool-season precipitation deficits.

Wildfire: Widespread moisture and monsoon activity helped tamp down fire risk in July and August (so far). The period of highest wildfire risk is over for the Southwest, but convective activity associated with the monsoon does bring additional ignition sources for wildfire, and wildfire totals in Arizona and New Mexico as of Aug. 7 saw modest increases in lightning-caused fires over the last month (see Fig. 6 for a seasonal summary).

El Niño Tracker: Neutral conditions are present in oceanic and atmospheric indicators and are expected to remain neutral through summer. Seasonal outlooks indicate increasing chances of an El Niño event in 2018, with El Niño conditions likely to emerge by fall or winter (see ENSO Tracker for details). Above-average winter precipitation is one characteristic of El Niño in the Southwest, but if the event develops earlier rather than later this fall, it also could help enhance eastern Pacific tropical storm activity. This in turn could promote increased precipitation in the Southwest this fall, especially if these tropical storms bend back into the Southwest and drive moisture into the region. By way of comparison, last year—a La Niña year—brought little tropical storm activity to augment precipitation totals for either the monsoon or the fall season.

Precipitation and Temperature Forecast: The three-month outlook for August through November calls for increased chances of above-normal precipitation in Arizona and most of New Mexico (Fig. 7, top), and increased chances of above-average temperatures for the entire western United States (Fig. 7, bottom).

Online Resources

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