Tuesday, November 30, 2010


Lots of clouds around today through Thursday, but the most they will do is maybe drop a flake or two. They will also keep the night temps warmer and the sun from melting the snow during the day. The cold front is stalled over Northern CA and that is where most of the precip will stay until Friday. Lots of people have been asking me about the "Big Storm" for this weekend. When looking at 7 day forecasts on the Weather Channel and such don't forget to look at percentage chances of snow. 20% every day this week means an 80% chance that you will not see any snow. Like anything else you want odds greater than 50% to get your hopes up.

The problem this week is that there is a giant ridge of high pressure out in the Pacific to the North of Hawaii. The jetstream across the Pacific is split going around the ridge to the North and South of it. Whenever that happens we tend to get pieces of storms, weak storms, or lows that cut-off from the jetstream and wobble all over the place. That is what we will be dealing with through the weekend before the pattern changes.

We also have a building ridge over the Rockies. A few days ago it appeared that the cold front would move right through Tahoe on Thursday and a cut-off low would follow for the weekend. Because the ridge is a bit stronger over the Rockies and the storms are a bit weaker becuase of the split flow, the cold front is being blocked to our North. On Friday a weak storm will move in off of the Pacific and push the precip into our area. Right now snowfall on Friday looks to stay in the 3-9 inch range over Tahoe. Models are now in agreement that the cut-off low will come in over Southern CA on Monday and miss us.

Next week the pattern over the Pacific changes. The high pressure ridge in the Pacific is crushed by a big storm moving into the Gulf of Alaska. A new ridge will form over Alaska and off the coast of Southern CA. This will open the storm door for the Pacific NW and Northern CA by the middle of next week. Several storms will be directed into the coast underneath the large low pressure in the Gulf of Alaska. They will be able to draw in moisture from across the Pacific as the jetstream has a nice straight fetch. We should see storms every couple of days starting as early as next Tuesday.

The only question will be the snow levels. It all depends on how much warm sub-tropical moisture the storms pull in and where the jet sets up. The position of the ridge off of Southern CA will dictate the position of the jetstream into CA. A little to our North and we could have high elevation snow and low elevation rain. A little to our South and we have large quantities of snow. This new pattern will be discussed a lot over the next week.

As we go through December and into January the jetstream will strengthen and the storm door should stay open as we get into a true La Nina pattern. If we can get good snow in December it should just be a bonus to what we could see in Jan. & Feb. Stay tuned......BA

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