December 3rd, 2009

The buzz has been going around. “Dude, we are gonna get dumped on next week,” or “Hear about the big storm coming next week?” – Wherever you have heard it or read about it, it appears there is some precipitation coming our way. – This isn’t a detailed forecast but I think it is an honest one from – Keep those fingers crossed! – – – December 12, 2009 Tahoe still has at least two more days of comfortable fall weather before a major change in the pattern is expected to take hold. Things will be getting colder this weekend, then wetter by next week. But the details beyond Sunday remain elusive. Here is what is in the mix: A high pressure system over the Eastern Pacific is retrograding toward the north, opening the door to a series of storms that should impact the Sierra starting this weekend. But first we will have an “inside slider,” a storm that has ridden up and over the ridge, into British Columbia and then south through the interior west. These storms tend to be cold and also dry, because they don’t sweep over the Pacific scooping up- moisture before they arrive in the Sierra. And that’s how this one looks. It will be cold, with temperatures dropping at least 10 degrees from Friday’s highs. It will also be windy. And it will be dry, with well under an inch of precipitable water. But the conditions will be ideal for snow creation if there is any moisture at all to work with. Depending on how far west the system drifts as it heads south, this could mean a dusting for Tahoe late Saturday and early Sunday or several inches of snow.

What happens then is the real question. A cold low from the north is expected to take hold over the Great Basin for several days. At the same time, a warm, wet moisture plume is setting up in the Pacific on a track headed for California. How these two systems interact as they collide will determine how much rain and snow the Sierra gets next week. If the cold low prevails, it will push the moisture track to the south, leaving the Sierra with less precipitation but also colder temperatures. If the cold low stays east of the Sierra, however, that subtropical moisture plume would likely bring a series of warm, wet storms to the area. The first one, due to arrive Sunday and Monday, will probably be all snow, mixing with the cold air already present. The Tahoe high country could see a foot or more of beautiful dry powder from this event. The second wave, now timed for a Wednesday or Thursday arrival, looks like snow at the passes and rain below. But each successive wave should be warmer as the cold air gets pushed out and replaced by the tropical influences from the west. And if that happens, it’s possible by the end of the week we could be looking at rain at 7000 feet. It’s a quantity versus quality thing. The more moisture we get, the higher the snow levels are going to be, and the greater chance that we will get rain at 7000 or even 8000 feet. We tend to root for the colder, drier storms here, but with the snow pack still so meager, it wouldn’t hurt to get a nice big, wet base down to start the season. As long as it doesn’t rain. Sorry we can’t be more definitive. But it’s early yet. With the computer forecast models giving mixed signals, it’s impossible to say this far out when it will snow, or how much.