We are about 4 days away from the beginning of the big pattern change that promises lots of snow for Tahoe. We will start with more cold than snow as we progress into the new pattern and then more snow than cold as we get it going. The teleconnections are lining up and the ridge is set to begin it retrogression from 140w towards 150w and then further out to 160w next week. That will swing the storm door wide open.

The first storm associated with the strong cold front for Friday was not expected to bring a large amount of snowfall, but it was looking like we could see around a foot. Over the past 24 hours though the models have developed a second low that is coming down behind the first one. This low looks like it will kick the first low inland over Washington or Oregon instead of it coming further down the coast. The further down the coast it comes the more moisture it can draw in off the ocean into our area. The GFS now shows it drier with the low coming in over Washington while the Euro is wetter with the low being kicked in over Oregon.

So that is the kicker and the low responsible is then projected to come down off the coast and then come inland just to our South like the storm this past Friday. Total precip through Saturday averaged out across the models is .25 – .75 inches of liquid. This is a cold storm so snow ratios will increase Friday night. Even with that it looks like a few inches in the basin with several inches possible above 7000 ft. Best case scenario with the drier track and the storm coming in to our North looks to be up to a foot along the crest. We still have a few days here to watch the exact track.

Then the pattern becomes more established the beginning of next week as the ridge shifts further West in the Pacific allowing the trough to broaden off the West Coast. Meanwhile a huge low moves into the Gulf of Alaska and it looks like it should send the jetstream into CA around Wednesday or Thursday of next week. We have been watching the teleconnections point to this for a while now and the models have been showing it since last week. If things continue to develop this is a storm we should start to get excited about. The amount of precip that kind of a setup is capable of producing can bring several feet to the Sierra.

The pattern looks to hold for about a week with more big storms possible going inot the final weekend of the month. This could be score number 2 for the MJO already this season. The PNA should stay negative a lot of this season with the moderate La Nina so troughing will want to be near the West Coast, but when the MJO cycles through phases 7,8,1 it should be game on. Last season we got pummeled thanks to blocking that formed from the extremely negative AO which is also shown at the top of this post. Right now it’s positive so we are not looking for any blocking yet out near the dateline that would lead to a suppressed jetstreams across the Pacific into CA or in Western Canada that would hold the lows in place in the Gulf of Alaska.

Without the blocking the pattern should stay progressive so the storms will take a shots and leave for now. That could change so watch for the AO to go negative this Winter. The only danger with the -AO is that the cold builds up in Western Canada and if the NAO goes negative the cold spills into the East and can lock a trough in place there and a ridge over the West. We saw this happen last January. Right now more and more models are showing the NAO going negative towards the end of the month which could lead to an East Coast trough.

We can have a trough on both coasts if the wavelengths or ridge/trough stay short, but more common is that the trough along the West Coast backs up into the Pacific and a little ridge pops up over CA. This has been my theory for a while now and that we would get quiet at the end of the month after we get dumped on. The super long-range models are beginning to show this possibly beginning to happen at the end of the month. Hopefully by then we have plenty of snow on the ground. Stay tuned…..BA

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