The Sawmill fire (Fig. 1) started, reportedly by recreational shooting, on April 23, 2017 in a grass- and shrub-covered area of low-elevation Arizona state lands approximately 40 miles south of Tucson. The fire spread quickly due to dry and windy conditions that day: the temperature reached 98 degrees, relative humidity ranged between 4 and 18 percent, and sustained winds reached 20 mph with gusts up to 30 mph. High winds, high temperatures, and low relative humidity continued through much of the following week, driving rapid growth of the fire (Fig. 2). (read more)
Precipitation & Temperature: April precipitation was average to above average in New Mexico, while most of Arizona was below average, including much-below average and record-dry conditions in the southwestern corner of the state (Fig. 1a). April temperatures were above average in nearly all of Arizona and New Mexico, with much-above average temperatures in southern Arizona (Fig. 1b). May has been dry in southern Arizona and New Mexico, while parts of northern Arizona and northern and eastern New Mexico have picked up decent precipitation relative to the normally dry May climate (Fig. 2). May temperatures in Arizona and New Mexico have ranged from 4 degrees below to 4 degrees above normal, while temperatures in higher latitudes and upper elevations (e.g. Upper Colorado River Basin, California Sierras, etc.) have been generally warmer than average, ranging from 0 to 8 degrees above normal. Water year precipitation has been normal to above normal across most of Arizona and New Mexico aside from a small pocket of dry conditions along the Arizona-Mexico border (Fig. 3). (read more)
Oceanic and atmospheric indicators are still within the range of neutral (Figs. 1-2), although sea-surface temperatures have more consistently hinted at El Niño compared to atmospheric indicators. Outlooks and forecasts generally agree that ENSO-neutral conditions are likely to remain through the summer, but by mid-to-late 2017, chances of an El Niño event emerging become approximately equal to the chances of continued ENSO-neutral conditions. (read more)
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Similar to last month, oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) are in the range of neutral (Figs. 1-2), and these conditions are forecast to last through the spring and summer. Most forecasts and outlooks indicate that El Niño conditions could return in mid-to-late 2017, but these assessments come with the annual caveat of increased uncertainty associated with the “spring predictability barrier”, during which time the specifics regarding the possibility, timing, and intensity of an El Niño event are elusive. At any rate, the models and forecasts indicate a near-zero probability of La Niña in 2017, leaving forecasters to decide between the probability of neutral or El Niño conditions in later 2017. (read more)
Precipitation & Temperature: March precipitation totals were average to below average in most of the Southwest except for the northeastern corner of New Mexico (Fig. 1a). March temperatures were much-above average across the entire Southwest, with record warm temperatures in the southeast corner of Arizona and most of New Mexico (Fig. 1b). April precipitation to date has been below average for much of southern Arizona and New Mexico (Fig. 2), while April temperatures have been between 0 and 6 degrees above normal for most of the region. Water year precipitation has been normal to above normal for most of Arizona and New Mexico, aside from a dry region along much of the Arizona-Mexico border (Fig. 3). (read more)
Precipitación Y Temperatura: En febrero, Arizona experimentó precipitación media a precipitación por arriba del promedio, mientras Nuevo México experimento precipitación que osciló entre media a por arriba de la media (Fig. 1ª). Temperaturas muy por arriba del promedio se observaron en la mayor parte de la región; el este de Nuevo México experimento las temperaturas mas altas registradas (Fig. 1b). Las primeras dos semanas de marzo fueron secos para el Suroeste, una inversión de las condiciones mojadas del inicio del invierno (Fig. 2ª). Temperaturas por arriba del promedio se observan en marzo también (Fig. 2b) y incluyen un serie de temperaturas casi record en el mediados de marzo. Para el año pluviométrico, el Suroeste ha experimentado precipitación y temperaturas por encima del promedio (Fig. 3). (Resumen completo)
This event began in fall 2016, ended in early February 2017, and throughout the period oceanic and atmospheric indicators generally hovered near the boundary between weak La Niña and ENSO-neutral conditions. According to CPC criteria, this was a weak La Niña event (but just barely); other agencies use slightly different criteria (see last month's ENSO tracker for details), highlighting the difficulty in categorizing these borderline events. This weak strength also affects how precipitation and temperature patterns are interpreted. In the Southwest, a La Niña event is more likely than not to bring warmer- and drier-than-average conditions over the cool season, but a weak La Niña event might not even stand out from the normal seasonal variation of typically dry southwestern winters (Fig. 5).
So how did this La Niña event stack up compared to expectations? (read more)