November 25, 2009

Thanksgiving is shaping up to be a beautiful fall day across the Tahoe region, and the holiday weekend should be crisp but mostly fair and maybe a bit breezy. The next major storm for the basin is probably at least a week away.

A deep low pressure system in the Gulf of Alaska and a ridge of high pressure over the West are dictating our weather pattern for the moment. The low is sending out waves of energy, but as they approach the west coast of the U.S., these waves are being pushed back to the north and into the Northern Rockies. Nothing for the Sierra. Nothing for Tahoe.

The latest wave of energy is headed our way late on Thanksgiving Day or early Friday. It will likely bring some high winds and cloud cover, and perhaps a snow shower or two. But it appears certain to break apart as it hits that ridge, with most of its energy going north, and what remains falling completely apart before it reaches as far south as Interstate 80. If we get any snow at all it will be light and scattered and should not amount to much accumulation. Another piece of energy might ride south on northerly winds aloft on Saturday, but that piece looks aimed more for eastern Nevada and Utah than the Sierra. This "inside slider" would have to veer hundreds of miles off its current path, drifting west instead of south and east, in order to bring snow to Tahoe. The winds carrying that system on a north to south trajectory, however, could also bring us cooler temperatures for the weekend.

Then the ridge of high pressure will rebuild and temperatures should warm a bit on Monday and Tuesday. There are some signs of a pattern change by the middle of next week, with a warmer, wetter flow trying to establish itself from the Central Pacific to the coast of California. That wouldn't necessarily be what we are looking for, since it could mean rain at higher elevations. But it would be consistent with the El Nino condition that has not begun to shape our weather as much as it should be. And it might be the start of something big -- if that moisture plume could hook up with a blast of cold air from Alaska.

Have a safe and Happy Thanksgiving. Think snow. We will continue to post updates on our web site through the weekend.

Check www.tahoeloco.com for the first word when the next storm appears on the horizon.

El Nino Watch
Sea Surface temperatures held steady in the week ending Nov. 23, with temperatures at 1.7 degrees Celsius above average in the central Pacific tropical region most watched by El Nino forecasters and observers. Temperatures further west held firm at 1.5 degrees above normal, and in the cooler region off the South American coast, temperatures remained .5 degrees above normal, which is the threshold for being classified as an El Nino condition. The temperatures in zone 3.4 are high enough to be classified as a strong El Nino if they hold there for several more months. As it is, we still need to wait until the end of November for this El Nino to be officially in the books as an El Nino episode. And what that happens, the avearges up until now will classify it as a moderate El Nino episode. Whatever the stats say, however, we should start seeing some effect on our weather from this condition in the next several weeks. We'll be writing about those potential changes in future installments of El Nino Watch at www.tahoeloco.com.

MONTHLY WEATHER ALMANAC FOR NOVEMBER TO DATE

TRUCKEE
High: 72 on Nov. 3
Low: 10 on Nov. 21
Average temp: 36.3
Departure from norm: -0.3
Precipitation: 0.94
Normal precip: 3.83
Percent of normal: 25%
Total snowfall: 7.6 inches.

SOUTH LAKE TAHOE
High: 68 on Nov. 2
Low: 17 on Nov. 8, 15
Average temp: 39.6
Departure from norm: +4.4
Precipitation: .19 inches
Normal precip: 4.70 inches
Percent of normal 4%
Total snowfall 0.5 inches.

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