Southwest Climate Outlook September 2016

Date issued

Precipitation & Temperature: August precipitation totals were above average across most of Arizona and New Mexico (Fig. 1a), buoyed by a surge of monsoon storms that started in late July and extended through the first week of August, and a surge of moisture linked to Tropical Storm Javier in mid-August. August temperatures were mostly average to below average in Arizona and New Mexico (Fig. 1b), a decline that did not alter the overall seasonal pattern of very warm temperatures observed during the summer months (Fig. 2). September precipitation to date (Sept 1 – Sept 14) ranges from well above average in southeastern Arizona and portions of New Mexico, tied mostly to heavy rains during Hurricane Newton, to well below average in other areas of the region that did not record as much activity during this time (Fig. 3). Water year precipitation to date (Oct 1, 2015 – present) is below average in much of the Southwest, particularly in Southern California, most of southern Arizona, and western New Mexico (Fig. 4).

Monsoon: With two weeks remaining in the 2016 monsoon (June 15 – Sept 30), seasonal precipitation totals to date are generally below average in much of Arizona, except for clusters in the southeastern corner of the state. During the same time frame, precipitation totals are average to above average in most of New Mexico. These totals gloss over the spatial and temporal variability of the monsoon, but they do provide a rough measure of the monsoon’s performance in terms of intra-regional comparisons and in comparison to prior years. Tropical storm activity (primarily Javier and Newton in 2016) provided a boost to seasonal monsoon totals (for more detailed discussion, see Monsoon Tracker).

Drought & Water Supply: Long-term drought persists across the Southwest (Fig. 5). The Sept. 15 U.S. Drought Monitor designated all of Arizona and much of western and central New Mexico as experiencing some form of drought. The northwest and southeast portions of Arizona, along with most of the designated areas in New Mexico, were classified as abnormally dry (D0), while much of southwestern and northeastern Arizona were designated as experiencing moderate drought (D1). The far southwestern corner of Arizona was designated as experiencing severe drought (D2), reflecting the persistent multi-year drought conditions in central and Southern California.

La Niña & Drought: Sea-surface temperature anomalies and atmospheric patterns all generally indicate ENSO-neutral conditions. Previous forecasts pointed towards the formation of a weak La Niña. In the last month, model consensus has shifted toward an increased probability of an ENSO-neutral winter, with a declining (but still present) chance of a weak La Niña event (see La Niña Tracker). An ENSO-neutral winter would be less likely to lead to the drier-than-average conditions associated with La Niña, but given the wide range of observed precipitation totals over ENSO-neutral winters (see Fig. 6, La Niña Tracker), this shift does not necessarily lead to increased certainty in the seasonal precipitation forecasts.

Precipitation and Temperature Forecasts: The Sept. 15 NOAA Climate Prediction Center’s seasonal outlook for October calls for equal chances of above- or below-average precipitation for most of the Southwest (Fig. 6 top) and increased chances of above-average temperatures across the western U.S. and the Southwest in particular (Fig. 6 bottom). The three-month outlook for September through November calls for increased chances of above-average temperatures across the U.S., including the Southwest, while calling for equal chances of average, above-average, or below-average precipitation.

Published by the Climate Assessment for the Southwest (CLIMAS), with support from University of Arizona Cooperative Extension, the Arizona State Climate Office, and the New Mexico State Climate office.

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