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Normally, it is early September when monsoon moisture diminishes in Los Alamos.
And, as a rule of thumb, 2 inches of precipitation can be expected during September, splitting the difference between 3 inches during each of July and August and 1 inch during every other month.
This year, however, the monsoon ended with the closing of August.
A normally moist September threatened to go into the books as unusually dry until a tropical storm kicked moisture to the north on Sept. 22.
This moisture teamed up with a well-timed pressure trough from the west to dump rain across New Mexico last Wednesday.
Aside from that day of drenching, there was almost no rain during the month in Los Alamos County. Precipitation events on the Sept. 8 and the Sept. 14 were consistent with a continuing monsoon pattern, but were barely enough to moisten the ground.
Thanks to the fluke event of Sept. 22, the month’s precipitation total was 1.32 inches in Los Alamos, two-thirds of the normal 2 inches. All but 0.04 inches came during that storm. In White Rock, the total was 0.78 inches, a little over half the normal 1.52 inches there. The annual total in Los Alamos is right on track with 15.5 inches thus far. White Rock remains an inch ahead of schedule at nearly 12 inches.
Along with the dryness in September came heat. While temperatures usually drop nine degrees during September, from an average of about 65 at the start of the month to 56 at the end, temperatures were oddly constant during the month at a daily average of 65 in Los Alamos.
And with the heat came new temperature records, not surprisingly during the second half of the month.
The high of 83 in Los Alamos on Sept. 29 broke the 2003 record of 81.
The high minimum that day of 54 broke the old record of 53 set in 1954. In White Rock, new highs of 87 on Sept. 15 and Sept. 18 broke the old records of 86 on both days, set in 2007 and 1997 respectively.
The high of 88 degrees on the Sept. 29 broke the old record of 86 set in 2003.
Wind speed averaged about seven miles per hour in both Los Alamos and White Rock. That’s about 15 percent, or one mile per hour, higher than normal. Daily maximum wind gusts were near the average of 24 mph. It is old news by now that the El Niño event from last winter that brought so much snow to Los Alamos has begun to swing to the opposite extreme.
We are expecting a moderate to strong La Niña this coming fall and winter. Although this see-saw of warm and cold water in the top few hundred meters of the Pacific Ocean takes place far away, there are distinct teleconnections to the weather over the USA.
Unfortunately, the climate forecast for New Mexico includes drier than normal conditions from now through spring of 2011. The temperature forecast is for above normal temperatures.