Things are still looking good for a pattern change next week and we will start it off with the chance of some light snow with the cold trough this weekend.  I know that everyone is getting tired of the dry pattern and looking at the current snowcover from the GFS model it is not looking very pretty.

As you can see with the storms coming down to our East over the past two weeks the Rockies are off to a good start. This time last year we had already had one 100 inch week in November and were getting ready for another one in December. We are off to a much slower start this season, with one of the biggest differences being that there is no blocking with the AO Arctic Oscillation being so positive.

I have gotten a few emails about making a page with a glossary of common terms. That is something I will work on in the off-season when time permits, but until then I setup the site this year so that any of the teleconnections that I refer to are on the site. If you look at the top there are the NAO & AO, and on the right sidebar is the MJO. If you click on them it brings you to the NOAA page that describes what they are.

So back to the forecast.  The pattern is going to become more progressive with the ridge moving to our East and new ridges forming further out in the Pacific near 160w.  That will briefly open the storm door and then the ridges will come East again blocking storms before the cycle begins again.  This isn’t a locked in trough along the West Coast pattern that brings the storm train, but it gets things moving and begins to bring chances of snow.

We will see this happen this weekend as a cold trough drops down the West coast behind the departing ridge.  We could see some light snow Sunday night as the cold front moves through.  Then the ridge shifts back East in the Pacific causing a wave to split off from the trough and spin down the coast.  The track of the low is not certain yet, but if it comes down over Tahoe or inland just to our South we could see some more light snow on Monday.

The ridge shifts back again in the Pacific the middle of next week which will open the door for another storm to dive in out of the Northeast Pacific.  This storm looks like it could pick up a little more moisture and bring some snow on Thursday.  This has been the overall trend on the models until this evenings 18z GFS that showed the possibility of high pressure forming in the Gulf of Alaska and shifting the jetstream South in the Pacific, almost like a block forming briefly.

We will have to watch if that continues to show up or not because that could bring in much more moisture off of the Pacific.  Here is a shot of what the latest GFS suggests for the jetstream for next Thursday and then the storm it shows.

Right now I am not buying into that scenario yet. I think that the jetstream will stay up into the Pacific NW and we could see some lighter snow on the South side of the storm.  The pattern should continue going into the weekend of the 17th with the jetstream possibly flattening out as the wavelengths lengthen.  That would allow the storms to pick up more moisture and take more of a West to East aim at Tahoe.

Right now the forecast models are showing the possibility of some stronger storms the weekend of the 17th and going into the week before Christmas.  Right now the forecast for both the PNA and NAO are both neutral, and the MJO looks to die, so none of them look to affect the pattern which is why I think it will stay progressive.

The La Nina conditions strengthened last week with all 4 regions cooling with 3 of them now below -1 into moderat La Nina territory.  This would lead me to believe that the -PNA has to eventually come back and bring more permanent troughing to the West Coast as we head into the Winter.  For now it’s just nice to see some movement in the overall pattern away from the blocking ridge.  Here is the snowcover map for the weekend of the 17th.

This is much prettier picture than what we started with. This shows a fresh 2 foot snowpack along the crest.  You can find these snowcover forecast maps at policlimate.com.  Stay tuned….BA

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