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Monthly Archive | CLIMAS

Monthly Archive

SW Climate Outlook - Monsoon Case Study - Pima ALERT Network

Monday, August 21, 2017

Comparison of the current totals at regional weather stations to normal precipitation-to-date and average seasonal totals gives a better sense of how locations across the region are faring in the monsoon (Fig. 1). Most of the stations in Fig. 1 recorded average to above-average precipitation to date, and a few (El Paso and Tucson) exceeded the monsoon seasonal average (June 15 – Sept 30). Daily cumulative precipitation plots (Figs. 2a-c) show how stations reached their current totals, documenting the intensity of individual days, as well as their contribution to the seasonal total.

Individual station values provide insight into the regional variability of the monsoon, but what about the local variability? Looking at the Pima County ALERT network sensors (Fig. 3) reveals just how variable the monsoon can be within a region, as well as the fact that daily & cumulative single-station values may not reflect the range of precipitation values observed in the monsoon.

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SW Climate Outlook - ENSO Tracker - Aug 2017

Sunday, August 20, 2017

Oceanic and atmospheric indicators remain within the range of neutral (Figs. 1-2). Seasonal outlooks and forecasts generally agree that ENSO-neutral conditions are the most likely outcome through winter 2017-2018. On Aug. 10, the Japanese Meteorological Agency (JMA) identified a continuation of ENSO-neutral conditions with a 60-percent chance of El Niño conditions until winter 2017-2018. On Aug. 10, the NOAA Climate Prediction Center (CPC) observed that oceanic and atmospheric conditions remained within the range of ENSO-neutral conditions, and that “the majority of models favor ENSO-neutral for the remainder of 2017.” They identified an 85-percent chance of neutral conditions through September 2017, and a 55-percent chance through February 2018. On Aug. 15, the Australian Bureau of Meteorology ENSO tracker remained at neutral/inactive, highlighting that every indication (models and forecasts) suggested ENSO-neutral conditions through 2017. On July 20, the International Research Institute for Climate and Society (IRI) and CPC identified a high likelihood of ENSO neutral conditions for the rest of 2017 (Fig. 3). The North American Multi-Model Ensemble (NMME) is ENSO-neutral as of August 2017. The model spread indicates a range of outcomes for the rest of 2017 (Fig. 4), but the ensemble mean indicates ENSO-neutral as the most likely outcome.

Summary: As with last month, ENSO indicators remain well within the bounds of ENSO-neutral, and there is little to suggest any other outcome in winter 2017-2018. An interesting detail has emerged from a few of the forecast discussions, however: the appearance of a slight uptick in the likelihood of a La Niña event in 2017-2018, running counter to discussion of the last few months. What’s going on? In Fig. 3, subtracting the current forecast percentage (bars) from the seasonal climatological probability percentage (lines) flattens the plot and reveals the deviation from normal climatology these forecast percentages represent (Fig. 5). Under this formulation, neutral conditions are forecast well above their climatological average through winter 2017-2018, while both El Niño and La Niña conditions are below their climatological average. This corresponds with current forecasts discussed above, and given the expected uncertainty associated with longer-term forecasts, the forecast percentages converge on climatological averages by the Mar-Apr-May period of 2018.

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SW Climate Outlook - Monsoon Tracker - Aug 2017

Friday, August 18, 2017

After a relatively late start to the monsoon across much of the Southwest, early-mid July through early August saw an impressive run of storms. Above-average cumulative (through Aug. 14) precipitation is widespread across much of Arizona (Fig. 1a) and New Mexico (Fig. 1b). Exceptions—regions with average and below-average precipitation—occur mostly in Arizona and include the southwest portion of the state, the highlands of the Mogollon Rim, and the north rim of the Grand Canyon, as well as the Four Corners region. These figures highlight the spatial variability of monsoon precipitation and the difficulty of scoring or grading the monsoon performance using single stations or summary maps (but we’re still trying!). Another useful metric that characterizes a different aspect of the monsoon is the percent of days with rain, which, when used with the precipitation maps, distinguishes areas that have received more frequent and moderate precipitation from those in which just a few extreme events boosted seasonal totals. In Arizona, the eastern two-thirds of the state has seen consistent precipitation, ranging from 35 percent to as high as 50 percent of days (Fig. 2a).  In contrast, Phoenix and the western edge of the state have had far fewer days with rain. Precipitation frequency is even more uniform across New Mexico, with nearly the entire state recording precipitation on 30 to 50 percent of days (Fig. 2b).

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SW Climate Outlook August 2017 - Climate Summary

Thursday, August 17, 2017

Precipitation and Temperature: July precipitation ranged from below average in the southwest corner of Arizona to average to much-above average across the rest of the state (Fig. 1a). Central New Mexico recorded mostly below-average precipitation in July, while the northern and southwestern portions of the state recorded average to much-above average precipitation (Fig. 1a). July temperatures were average to much-above average in Arizona and New Mexico (Fig. 1b), although regular monsoon events helped tamp down daily average temperatures in southeastern Arizona and southwestern New Mexico. Year-to-date precipitation ranks reveal mostly average to above-average precipitation in Arizona and New Mexico, with drier pockets in the borderlands region of Arizona and in central and southeastern New Mexico (Fig. 2a). Year-to-date temperature ranks are much-above average across the Southwest (Fig. 2b), with small areas of Arizona and much of the Rio Grande Basin in New Mexico recording record-warm yearly average temperatures (Jan-July 2017).

Monsoon Tracker: The monsoon started a bit later than average in 2017 but more than made up for the delayed start with numerous precipitation events throughout much of July and early August (see Monsoon Tracker for details). Notably, Tucson recorded its wettest July on record and second-wettest month on record, and it and many other stations across the region have surpassed their normal cumulative values, with some approaching or even exceeding their seasonal (June 15 – Sept. 30) climatological average (Fig. 3).

Drought & Water Supply: With monsoon precipitation catching up in the northern halves of Arizona and New Mexico, the U.S. Drought Monitor (USDM) has removed those regions from the short-term drought designation of the previous month. However, the borderlands region of southern Arizona remains designated as either D0 (abnormally dry) or D1 (moderate drought), emphasizing long-term drought conditions linked to below-average winter precipitation that are not typically ameliorated by monsoon precipitation (Fig. 4).

Health & Environmental Safety: Wildfire season is effectively over in Arizona and New Mexico, with monsoon precipitation and increased relative humidity tamping down fire risk across the region. Wildfire totals for the 2017 season are approximately 370,000 acres burned in Arizona (roughly 220,000 acres attributed to lightning ignition and the remainder to human causes), and approximately 128,000 acres burned in New Mexico (105,000 acres due to lightning and 23,000 acres from humans). With the return of the monsoon, the region has also seen an uptick in pollen counts from plants that take advantage of seasonal moisture: chenopod and ragweed pollen are particularly severe following abundant monsoon precipitation.

El Niño Southern Oscillation: Models and forecasts continue to suggest the most likely outcome is ENSO-neutral conditions through winter 2017-2018 (85 percent chance through the fall, then 55 percent chance over winter - See ENSO Tracker for details). The chances of El Niño or La Niña this winter are fairly low, at 15-20 percent and 25-30 percent, respectively.

Precipitation and Temperature Forecast: The Aug. 17 NOAA Climate Prediction Center’s outlook for September calls for equal chances of above- or below-average precipitation in Arizona and New Mexico, and increased chances of above-average temperatures in most of Arizona. The three-month outlook for September through November calls for equal chances of above- or below-average precipitation in Arizona and New Mexico (Fig. 5, top). Increased chances of above-normal temperatures are forecast for the entire United States (Fig. 5, bottom).

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