December deluge moistens 2008

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By Scot Johnson

How much snowfall does Los Alamos collect each year? Three feet? Four feet?

It may surprise you to learn that we get five feet – 58.7 inches to be exact – on average.

Five feet per year, on average, measured from 1971 through 2000, for the year.

This December brought 29 inches of snowfall to Los Alamos, which is half the average for the entire season already!

Expect the other half to be spread out over the remainder of the winter, given the return of mild La Niña conditions which bodes for warmer and dryer months ahead.

Wind speed, like snowfall, was well above normal in December. Temperatures were average in December and 2008 overall.

Snowfall was recorded on 13 days in Los Alamos during December, not surprising given the low pressure trough present on so many days over the southwest USA.

Marking the U-shaped southern boundary of this trough was the jet stream, which ran right over New Mexico. In other words, New Mexico lay right in the storm track.

The southern dip of the jet stream, veering clockwise to the east as it crossed New Mexico, also brought more moisture from the warmer, lower elevations to the south.

The 29 inches of snow in December far exceeded the average of 11 inches for the month in Los Alamos.

The liquid equivalent was 1.6 inches, compared to 0.9 inches for an average December.

White Rock measured 1.3 inches of liquid equivalent, almost double the average 0.7 inches there.

In 2008, Los Alamos recorded a total of 17.4 inches of precipitation, 92 percent of the average 19 inches recorded per year.

December and August were particularly soggy, bringing nearly double the average for each month and helping to make up for the very dry months of April, June, and September.

The average temperature in Los Alamos and White Rock in December was just under 30 degrees, which is normal.

The average high of 39 degrees in Los Alamos was a degree less than the usual maximum of 40 while the average low of 20 degrees exceeded the normal 19.

In White Rock, the average high of 41 degrees was less than the normal 43 degrees and the average low of 18 degrees exceeded the usual December minimum of 16 degrees there.

In 2008, the average temperature in Los Alamos was 48 degrees, right on the 1971 to 2000 average.

With the jet stream overhead on so many days in December, it is not surprising that winds were well above normal.

The average wind speed in Los Alamos and White Rock was over seven miles per hour, about 50 percent above normal in both towns. Winds gusted beyond 40 mph on five days in Los Alamos and three days in White Rock.

Some 40 mph-plus gusts are normal on only two days in Los Alamos and one day in White Rock in December.

The Climate Prediction Center’s long-term forecast has changed this month to include warmer-than-normal temperatures and below-average precipitation through spring 2009.

This change in the forecast from nearly normal conditions is in response to the strengthening of mild La Niña conditions in the equatorial Pacific which are expected to be present for the next few months.

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