The first half of December has been one of the driest on record so far according to the NWS in Reno. In the Sierra if it doesn’t snow by the end of the month it will be one of the least snowy December’s on Record and it’s looking like that is a possibility. The Pacific NW is normally the area that gets above average precip in a La Nina and the Southwest below average, but Taos, NM is having one of the wettest and snowiest starts to December on record.
This is really going to hurt a lot of the local ski areas as the Holidays approach and there is not much snow to ski on. The resorts with the most open terrain are those that have large snowmaking systems, but even those have limited terrain. This story is the same across the country as the storms have been staying up into Alaska and Canada, except for the Southwest where waves from the cold troughs have been cutting off and then tapping the subtropical jetstream.
Everyone is going crazy looking at the forecasts and looking for when this dry pattern might finally break. At this point even a little storm would be nice just to remind us that it’s Winter. I had forecasted a late start to this Winter and a dry December back in November, but even a dry December usually means at least some snow. Some people aren’t complaining like the ice climbers and ice hockey players because no snow and lots of cold has meant perfect ice conditions.
Some of the differences between this time last year and this year in the atmophere are the AO (Arctic Oscillation) was negative last year, the PNA (Pacific North American) teleconnection was negative, and the warm pool of water in the Western Pacific was not extended quite as far to the East North of Hawaii. All of those factors have somewhat contributed to the ridge of high pressure anchoring itself off the coast. Last year if you followed the PNA alone we had the big storms when it was negative and dry conditions in January when it was positive.
The first day of Winter is on Thursday, the La Nina has been strengthening, and the PDO is negative. That all tells me that the PNA can’t stay positive forever and it should go back to its usual La Nina negative state as we go into the Winter. That will bring the trough back down the West Coast and the storm track into the Pacific NW. On top of that the AO should also go negative if the stratospheric warming continues over Siberia pushing North and East.
In the Pacific NW as we head into January it should be game on. The cold could be as impressive as the snowfall if we can get the Arctic air from the stratospheric warming over the Arctic to come South down the West Coast. The storm train is already starting to show up on the models starting next week in Washington and Oregon. The record dry conditions up there should be wiped out right before the month ends, but down it Tahoe it may stay dry just past the end of the year.
Tahoe will need the jet stream to push further South down the coast. One way is for the ridge to retrograde allowing the trough to dig off the coast, but that is not showing up yet because of the positive PNA keeping the ridge off the coast. The other way is for the jet stream to be pushed South by blocking setting up to the North and an Arctic plunge down the coast crushing the ridge.
The latter scenario is starting to show on the forecast models as about 50% of the ensembles and 50% of the operational runs are showing the jetstream crashing into Tahoe around or just after the New Year. Let’s Look at some of the model runs in the past 24 hours.
Here is the 18z GFS jetstream forecast from Sunday for the 2nd of January.
Here is Sunday’s 00z GFS forecast for Jan 2nd.
And here is Sunday’s 12z GFS forecast for Jan. 2nd…
Also, here is the 8-16 day precip forecast through Jan. 3rd from a mix of several models including those not showing a big storm yet.
50% of the models showing this possibility more than 2 weeks out is not a bad start. We can never trust the models this far out on any specific storm, just look to see if they are recognizing a pattern change and they are. It may take a little longer to change but we are heading in the right direction.
Until then there is another trough dropping down to the East of CA on Thursday bringing another shot of cold with it into Tahoe. Then the ridge is going to shift closer to the coast next weekend and then inland which could bring some milder weather next weekend. Next week the storm activity will start to pick up in the Pacfic NW. It’s possible that the storm mid-week comes far enough South for a little snow but nothing big.
For now all eyes are on the first week of January to see if the pattern change being suggested by the models comes to fruition. Until then keep the faith, it only takes a big week of Tahoe snow to erase the memory of a 6 week drought. BA