We are only 2 days out from what should be the first measurable snowfall of the season.  We have decent agreement for the Wednesday storm details among the forecast models, but there are some differences on the Friday storm.  So let's go through the details.

Wednesday:

Not much change to the forecast for the first storm on Wednesday.  We are expecting rain and snow to push in by afternoon with snow levels around 7,000 feet.  Then Wednesday night snow levels could drop to lake level.  Good agreement that we could see up to an inch of liquid west of the lake near the Sierra crest, but this system has a Southerly flow which is not great for pushing the moisture to the other side of the lake.

We could see snow to lake level Wednesday night.  This could be the only chance for accumulating snows that low from these storms.  We could see 1-3 inches at lake level by Thursday morning.  For the mountains, we could see 5-10 inches of snow above 7,000 feet.  With the highest amounts west of the lake.

Thursday:

It still looks like we will have a break in the action Thursday into Thursday night.  We could maybe see some lingering snow showers hang up along the crest.  Snow levels stay low but not expecting enough moisture to pick up more than a dusting Thursday.  Thursday night the European model is a little faster with the arrival of the next storm, so we could see 1-2 inches of snow on the mountains later in the night.

Friday:

Friday the next storm moves in.  A decent stream of moisture pushes into Northern CA bringing heavy rainfall to our North.  Where the models split is how far South the stream of moisture pushes before it cuts off and how much forcing there is to push the moisture into the Tahoe basin.  The European model is very wet and brings over 2 additional inches of liquid to the crest through Friday night and over 1.25 inches to the East side of the lake.

In contrast, the GFS now has very little moisture making as far south as Tahoe with no push to the East side of the lake.  It only brings up to 1/4 inch of liquid near the crest.  That is a huge difference from the other models.  You can see that it maxes out a storm total near 1.4 inches of liquid.

It has been doing this for several runs now.  Meanwhile, the rest of the models are bringing in at least another inch of liquid.  The model average of all the model runs this morning is a storm total around 2.4 inches of liquid near the crest.  That is about the average between the 3.2 inches on the Euro and the 1.4 inches GFS.  Here is a look at the WPC model that blends several models, and has up to 2.5 inches of liquid near the crest.  With lesser amounts go east across the lake.

The GFS is the outlier and really so is the European on the other end of the scale with over 3 inches of total liquid.  So I think using the average of the 2 is a good method for now. 

The other issue is snow levels.  With the deep moisture feed that this 2nd storm is initially pulling from, it will bring in warmer air.  Snow levels could start around or even below 7,000 feet Friday morning.  But they rise above 7,000 feet by Friday afternoon and could peak out close to 8,000 feet.  Then some colder air moves in Friday night and snow levels could fall back to 7,000 feet by the time the storm ends.

So as you can imagine, the snowfall forecast for the Friday storm is tricky.  As of this morning, I have it at 3-7 inches above 7,000 feet by Saturday morning, and 5-10 inches above 8,000 feet.

Storm Totals:

Here is the updated table for storm totals.  If the European model is right these amounts will be higher.  If the GFS is right they will be much lower.  This is taking the model average.  The bold amounts above should tie out to the 8,000-foot forecast below for the ski resorts.  Some of the lower mountains like Boreal and Homewood should be tied to the 7,000 ft. amounts.

Behind the storm we should have colder air in place next weekend with highs only in the 40's.  Overnight lows down into the teens and 20's.  So the ski resorts should have good snowmaking weather with some natural snow to blow on top of. 

The week of the 26th should start dry as high pressure builds in over the West Coast next weekend.

But a large trough looks like it will set up across the North Pacific...

With a strong Pacific jet stream underneath across the Pacific aimed at the West Coast by the 29th...

That may flatten any ridge trying to build off the coast and be strong enough to push storms into the Western U.S. ridge into CA.  The long-range runs of the GFS and European models show several storms pushing into CA from the 28th/29th through the first week of December.  We'll see...

Stay tuned...BA