Sitting here this morning looking out the office window there is not a cloud in the sky and no wind. We are expecting highs into the 50s at lake level this weekend. It should be a beautiful weekend, but that will change fast-starting Monday.

Colder Air:

We have a much colder pattern coming starting Monday. For Monday we are only expecting a drop in temperatures with highs in the 30s on the mountains and 40s at lake level. We should stay dry into Tuesday morning. Winds will start to pick up Monday afternoon with gusts to 25 mph, and then really start to pick up Tuesday with strong gusts on the mountains ahead of the incoming storm.

The Storm:

We are still 3 1/2 days out from the initial storm moving in as early as Tuesday afternoon. We are still dealing with differences in the track of the storm on the forecast models which is fluctuating the total precipitation forecasts and snowfall forecasts. We are confident a very cold storm will bring snow Tuesday night with lingering snow showers possible through Thursday night. But we are not confident yet in snowfall totals.

For example, let's look at the track of the storm on the last 2 runs of the GFS forecast model. Here is the 6z run showing the center of low pressure tracking down the CA and into Central CA Tuesday night.

Now here is the latest 12z run of the GFS model showing the center of the low moving in on the CA/OR border Tuesday night.

Here is a look at the difference in total precipitation forecasts. The first run would bring the heaviest precipitation to the south of Lake Tahoe.

The second run would bring the heavier precipitation farther north...

It may not look like a big difference, but 8 tenths of an inch more precipitation near Donner Summit at 8k with 20;1 snow ratios would be a 16-inch difference in snowfall totals.  I just wanted to show you what we deal with when forecasting with the run to run changes in the forecast models. This is just 2 runs of one model. We are looking at a dozen different models that each run 4 times a day.

Taking an average of the latest model runs let's try to break down the storm by day through Thursday.

Tuesday:

Tuesday expect increasing clouds and winds. We could see light snowfall start to push in by later in the afternoon. Expecting the heaviest snow for overnight Tuesday night. This is when travel gets really difficult with heavy snow and wind blowing around the powdery snow.

Snow levels could start as low as 4,000 feet and drop below 3,000 feet Tuesday night. That means we could see chain controls on up to 60+ miles of road on I-80. Taking the model average, we could see 6-12 inches of snow at lake level and 1-2 feet of snow on the mountains by Wednesday morning.

Wednesday:

After the initial low moves through with the heavier snow, we could see a 2nd low form near the CA coast and slowly move south along the coast. This is not a great setup for heavier precipitation to able to push into the Tahoe Basin. We may just see scattered light snow showers through Wednesday night with the best chance west of the lake along the crest and especially southwest of the lake near Sierra and Kirkwood. This pattern favors snow farther south near Mammoth.

It is very cold with highs only in the 20s and overnight lows in the teens. Snow levels could fall as low as 2,000 feet in the foothills. This will continue high snow:water ratios with very fluffy/powdery snow falling. We may only see 1-2 tenths of an inch of total precipitation along the crest, but there will be a lot of fluff factor making for higher snowfall accumulations than we would normally be able to get from such little precip. The latest forecast model average shows we could see an additional 1-3 inches of snow.

Thursday:

Thursday could be more of the same with low pressure moving inland across Southern CA. That continues to favor precipitation over Southern CA. We could continue to see some scattered snow showers into Thursday night. There some model runs that suggest a third wave could slide south down the coast which could bring us a better chance of seeing snow showers continue over the Tahoe Basin.

It continues to be very cold with high snow ratios. We could see another 1-3 inches of fluffy snow accumulate. Winds should start to come down some on Thursday.

Totals:

The latest GFS/European model average is around 1.6 inches of total precipitation near the crest. Whether that is along the entire area from NW to SW of the lake depends on the track of the storm Tuesday night. A farther south track would put the higher totals SW of the lake. The WPC's blended forecast model shows similar total precipitation amounts through Thursday night.

Looking at the 100 model average the total precipitation average is around 1.3 inches west of the lake along the crest. About 3 tenths less than the WPC and Euro/GFS average. Snow ratios through the period could average around 15:1 at lake level and 20:1 at 8,000 feet. That brings the 100 model snowfall average for the storm to a high end of around 27 inches along the crest at 8k.

Here is my updated total snowfall forecast broken down by zone and elevation by Friday morning.

What I am leaving out is the potential for lake enhanced snow NE of the lake over Mt. Rose with the very cold air moving over a relatively warm lake from SW to NE. Something to keep an eye on.

We will continue to fine-tune this as we get closer and get a better idea of the track of the storms. One thing is for sure, this will be a cold pattern with temperatures running up to 20 degrees below average through the period.

If you are coming up I would leave by Tuesday morning or expect a lot of headaches. Even if the snow is tapering off to scattered snow showers Wednesday, we will still have gusty winds with powdery snow that will easily blow around. This is not good snow for building the starting base on the mountains, but it will help as a layer for them to blow snow on top of.

Black Friday into the Weekend:

We could see some lingering snow showers into Friday, but it looks like we could also start to clear out. It could be a dry weekend with some sun, but it should remain cold. Especially at night with snow on the ground and clear skies. We could see temperatures in the valley really bottom out with the radiational cooling.

The Week of the 2nd:

The forecast models have lost the potential storm for Sunday night dropping down from the north. They now show a large area of low pressure sitting off our coast by Sunday. The GFS and European models show a Rex Block pattern setting up with high pressure sitting over the low pressure off the coast.

That pattern has the low off the coast sitting there through most of the week and not progressing east into CA until the end of the week around the 6th of December. That would bring a week of drier weather from the 30th through the 5th.

The Canadian model and some of the ensemble runs of the GFS and European models show the low off the coast progressing right into CA by Monday the 2nd.

When the low does move into CA it could bring another round of heavy snow to the mountains. So we will be watching the trend on the models closely to see if we will have a week of drier weather, or if the storms will continue into the week of the 2nd.

Stay tuned...BA