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Monthly Archive

SW Climate Outlook - ENSO Tracker - Oct 2017

Monday, October 23, 2017

Oceanic and atmospheric indicators remain generally within the range of ENSO-neutral but have shifted more towards La Niña conditions in the past month (Figs. 1-2). Most seasonal outlooks and forecasts reflect these changes, and continue to call for the formation of a La Niña event as the most likely outcome by the end of fall and continuing into this winter. On Oct. 10, the Australian Bureau of Meteorology noted that all oceanic and atmospheric indicators remained ENSO-neutral, and highlighted recent short-term warming of sea surface temperatures in the tropical Pacific after a longer period of cooling. On Oct. 11, the Japanese Meteorological Agency (JMA) forecast a 50-50 chance of either ENSO-neutral conditions persisting through winter or La Niña conditions developing in fall or winter. On Oct. 12, the NOAA Climate Prediction Center (CPC) observed that while oceanic and atmospheric conditions remained ENSO-neutral, they had “edged closer to La Niña conditions,” with a 55- to 65-percent chance of a La Niña event this winter. On Oct. 19, the International Research Institute for Climate and Society (IRI) and CPC briefing noted further short-term cooling in sea surface temperatures, and forecast a 70-percent chance of La Niña by the end of 2017. The North American Multi-Model Ensemble (NMME) is borderline weak La Niña as of October 2017 (Fig. 4), with a majority of the models predicting a weak La Niña this winter.


Summary: The seasonal outlooks have turned more bullish on a weak La Niña event developing this fall, if you can call tentative forecasts that hint at the possibility of a short and weak La Niña “bullish.” Despite the fact that many ENSO indicators have remained within the range of neutral, forecasters are seeing enough evidence in the data to be relatively certain that a La Niña event is the most likely outcome this winter. It is late in the forecast window for so much uncertainty about the upcoming winter; the signal is usually clearer by mid-October. Last year, the sea surface temperature anomalies had already consolidated into weak La Niña status by October, whereas this year there is still quite a bit of movement around the boundary between ENSO-neutral and weak La Niña. Given the warmer- and drier-than-average winter conditions associated with La Niña in the Southwest, the possibility of a La Niña forming might generate concern regarding winter precipitation and persistent drought in the Southwest. However, it may not ultimately make much difference whether the conditions resolve into weak La Niña or borderline weak ENSO-neutral: southwestern winters are relatively dry and neither scenario is likely to bring much precipitation.



SW Climate Outlook Monsoon Recap - Oct 2017

Friday, October 20, 2017

The North American Monsoon was quiet for much of the Southwest through early July. The rest of July was active and numerous locations approached or set single-month precipitation records. August saw a widespread shutdown of monsoon activity across much of Arizona, which lasted for the rest of the official season. During the same period, New Mexico saw more consistent precipitation activity, including a last gasp in late September when a cluster of storms hit both central and far southern parts of the state. Weather stations in regional metropolitan areas recorded mostly average to above-average totals (Fig. 3 on p.2), with the larger anomalies in Tucson and El Paso attributed to near-record July precipitation. Conversely, Yuma and Albuquerque had been lagging behind their seasonal averages but received late-season boosts to their seasonal totals.

Precipitation rank maps reveal July was mostly above normal (top 33 percent) and much-above normal (top 10 percent) across nearly all of Arizona and much of western and northern New Mexico (Fig. 1). August flipped that script, with most of Arizona and western New Mexico recording below-normal or much-below-normal precipitation, and with a large pocket of dry conditions centered over the Four Corners region even while eastern New Mexico was much-above normal to record wettest (Fig. 2). September was a variation on that theme, with most of Arizona and southwestern New Mexico recording below-normal or much-below-normal precipitation while northwestern Arizona and northern and eastern New Mexico recorded above-normal to much-above-normal precipitation (Fig. 3).


The cumulative seasonal precipitation totals diminish the more extreme monthly variations (Fig. 4), with percent of total and days with rain revealing a high degree of spatial heterogeneity of precipitation totals and frequency across the region (Figs. 5-6 on p.4).

SW Monsoon - Station Case Studies

Cumulative precipitation maps help illustrate where monsoon precipitation fell, and the monthly maps on p.3 narrow down when it fell, but a closer look at individual stations reveals the variety of ways the monsoon can progress. The cumulative plot for Tucson (KTUS: Fig. 7a) shows the slightly-behind-normal start, the strong series of storms from mid-July to early August, and the complete shutdown of monsoon activity after mid-August. Albuquerque, on the other hand, had an early event but then lagged behind the seasonal total for most of the monsoon before a run of storms pushed the city just over its seasonal average at the end of September (KABQ: Fig. 7b). El Paso looks to be the best of both worlds, with an early start, a strong set of storms in the middle, and a season-ending event that pushed the total even further past the seasonal average (KELP: Fig. 7c). A closer look at the daily rainfall totals reveals a vast majority of El Paso’s monsoon rainfall fell during a small number of intense rainfall events. Each of the three cities had similar overall results – above-average monsoon totals – but each followed a different pattern to reach those totals.


CLIMAS developed an experimental product using the Pima County ALERT network data that further reveals the range of precipitation totals that occur during monsoon events. Figure 8 plots the daily precipitation totals from the KTUS NWS station used for Figure 7a, along with the range of precipitation totals recorded at the various network stations around Pima county.

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SW Climate Outlook Oct 2017 - Climate Summary

Thursday, October 19, 2017

Precipitation & Temperature: September precipitation was much-below average to below average across central and southeastern Arizona and southwestern New Mexico, while northeastern New Mexico recorded above-average to much-above-average precipitation for the month (Fig. 1a). September temperatures were average to much-above average in New Mexico, and below average to much-above average in Arizona (Fig. 1b). October temperatures to date have been quite warm, especially in the southern portions of Arizona and New Mexico. Year-to-date precipitation ranges widely from much-below average in southeastern Arizona to much-above average to record wettest in northeastern New Mexico (Fig. 2a). January through September temperatures have been consistently warmer than average, with nearly all of Arizona and New Mexico recording much-above average temperatures, including small pockets of record-warmest conditions in both states (Fig. 2b).



Monsoon Tracker: Persistent dry conditions in September meant 2017 monsoon precipitation totals saw little change in the last weeks of the monsoon, especially in Arizona. New Mexico recorded a late-season surge, with heavy rainfall observed in a number of locales just in time to be counted in the seasonal totals (Figs. 3, 5a; see Monsoon Tracker for more details).



Drought & Water Supply: Arizona has seen a return to short-term drought designation (D0: abnormally dry) in eastern and southeastern regions. This designation, in addition to the long-term drought designations (D0: abnormally dry and D1: moderate drought) that are persisting along the U.S.-Mexico border in southwest Arizona, mean that well over 50 percent of Arizona had some form of drought designation as of October 2017. New Mexico is nearly free of drought designation, with just one small area of D0 (abnormally dry) in the western part of the state (Fig. 4; also see Arizona and New Mexico reservoir storage and water supply).

Water Year 2017: Water-year (Oct 2016 – Sept 2017) precipitation was normal to above normal in most of New Mexico, while Arizona ranged from well-below normal in southern and eastern areas to above normal in the northwest part of the state (Fig. 5b). Notably, the pattern of below-normal precipitation extended into the Upper Basin of the Colorado River (in Utah and Colorado), an important fact to monitor going into this next winter and water year given the strong influence that drought in the Upper Basin can have on Lower Basin water availability and management.


El Niño Southern Oscillation: Current conditions are generally in the range of ENSO-neutral, while seasonal outlooks and forecast models continue to suggest La Niña as the most likely outcome this winter (See ENSO Tracker for more details).

Tropical Storms: The eastern Pacific tropical storm season has been active in 2017 with 17 named storms, including nine hurricanes of which four were major (greater than category 3), and the season is not yet over. This is in line with the seasonal outlook for 2017, which predicted 14-20 named storms, 6-11 hurricanes and 3-7 major hurricanes. Despite an average to above-average number of storms, they have not been active in driving moisture into the Southwest. This is one factor that has contributed to the drier-than-average conditions observed in late August and most of September, which often sees increased precipitation linked to tropical storm activity.

Precipitation & Temperature Forecast: The three-month outlook for October through December calls for increased chances of below-average precipitation for most of Arizona and New Mexico (Fig. 6, top), and increased chances of above-normal temperatures for the entire southwestern United States (Fig. 6, bottom).


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