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July was a good monsoon month

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By Scot Johnson

Los Alamos County had rain on 20 days in July, so the monsoon appeared to be in full swing. But how much the monsoon is to be credited for the rain is questionable.

Indeed, the first major storms of the month, which brought a combined 1.3 inches of rain on July 5th and 6th and the largest hail this meteorologist has ever seen, had perfect monsoon conditions associated with them.

These include very high dewpoint temperatures in Tucson, Phoenix, and El Paso shortly beforehand, indicating mucho moisture in the atmosphere there, plus strong high pressure over Texas sweeping this abundant moisture up from the south.

The golf ball sized hail of Monday, July 6th, was so large that the projectiles, in order to accrete ice as much as they did, must have made several passes up and down a convective column (a cloud) of deep vertical development, courtesy of violent updrafts, before falling down onto local cars and roofs.

From July 7th through 19th, however, only 0.07 inches of rain was measured in Los Alamos.

The storm that relieved the dry-spell on July 20th and 21st was not due to the monsoon but came from the north.

And although it rained nearly every day during the last week of July, leaving the impression of a monsoon in full swing, the dewpoint temperatures in Tucson, Phoenix, and El Paso had already dropped below the threshold at which a monsoon is defined to be active.

As of August 7th, these dewpoints are still below monsoon threshold.

Despite the sputtering monsoon, Los Alamos measured 4 inches of rain in July, where 3 inches is normal (the other rain gauges in the network measured about 3 inches).

White Rock had 2 inches which is just about normal there. The 2009 total in Los Alamos so far is 11.6 inches, 117 percent of the normal 9.9 inches. In White Rock, the year’s total of 6.7 inches is just behind the normal pace of 6.9 inches at the end of July.

Average temperatures were 69 degrees in Los Alamos and 72 degrees in White Rock, a degree warmer than normal in both towns.

The mean maximum and minimum temperatures in Los Alamos were a degree warmer than normal at 81 and 56 degrees, respectively.

In White Rock, the mean maximum of 88 was two degrees warmer than normal. The mean minimum of 56 degrees was right at normal.

Average wind speeds and maximum daily gust speeds were about normal in Los Alamos during July, averaging 6 and 24 miles per hour respectively. White Rock’s numbers were about 7 and 30 miles per hour, around 10 percent above normal there.

The climate forecast for this fall and winter is becoming interesting. Up until a month ago, it was expected that there would be neither an El Niño nor La Niña event in the tropical Pacific later this year.

But now weak El Niño conditions have appeared and are expected to grow into a weak-to-moderate event during autumn. The El Niño is expected to strengthen to a moderate to strong event this winter, increasing the likelihood of snow here.

Scot Johnson, Meteorologist is with Waste and Environmental Services Division, Environmental Data and Analysis Group, Los Alamos National Laboratory.