Update 9 AM

New 12z NAM model run is now further North for Monday with total precip in line with the other forecast models.

From 6 AM:

Summary:

Cold storm set to arrive this afternoon with a second wave keeping snow showers going through Monday into Monday night.  Several inches of snow could fall at lake level with up to a foot of snow on the mountains.  Cold temperatures will start the week and will warm slowly into the 40's the 2nd half of the week.  The next storm could arrive next Sunday into Monday with some stronger storms possible the week of the 16th.

Details:

After the post yesterday morning the forecast models started to slow the storm down and to slightly increase precip amounts.  They have continued backtracking this morning towards the timing and increased precip from a few days ago.  The details are slightly different though.  

We could see precip reach the crest by midday but with limited spillover into the Tahoe basin.  Snow levels will start above lake level but should mostly be snow along the crest with most elevations above 7000 feet.  Later this afternoon the cold front will approach and the precip will spill over into the basin as well as snow levels falling below lake level.  The snow will be light to moderate and will turn showery by Monday morning.  Total precip with the front is still expected to be quite light, with .1 - .25 inches on the East side of the basin, and .25 - .5 inches of liquid on the West side.

Here is a look at the GFS forecast model for total precip by Monday morning from the 6z run.

Compare that to the previous run and it's not much different.

The other forecast models show similar amounts with the first part of this storm.  With the slowed timing the snow will fall at night and with the cold front, so we should see a bit more snow than we were thinking yesterday.  On the East side of the basin we could see 1-2 inches at lake level, and 2-4 inches on the mountains.  On the West side of the basin we could see 2-4 inches at lake level, and 3-7 inches on the mountains, with up to 9 inches tops West of the basin along the crest.  

Where things get interesting is with the 2nd wave of precip that moves in Monday afternoon.  This will be associated with the cold unstable air behind the front.  When systems like this hit the mountains we usually see some heavier bands of snowfall breakout.  You can see the popcorn shaped clouds behind the front off the coast which indicates much colder air behind the front.

The last couple of days the forecast models were trending this 2nd wave to our South towards Mammoth.  Last night the European and Canadian forecast models were the first to shift it further North towards Tahoe on the 0z runs, and then the GFS followed on the 6z run.  Only the NAM as of early this morning is still South.  We will have to keep watching today on the next few model runs to see if the trend North continues.  If not then we most likely only see a dusting of additional snow showers Monday as the system passes to our West and South Monday like we were thinking yesterday.  Maybe a few additional inches on the crest.

Here is a look at the 0z run of the GFS last night through Tuesday morning for the entire storm.  If you compare with the one above through Monday morning you can see not really much more precip across the Tahoe basin Monday, most falls South of us.

 

Now on the 6z run... The precip amounts are doubled or maybe slightly more than doubled by the 2nd wave Monday afternoon and evening.

That is similar to what the European model starting showing on the 0z run as well as the Canadian model.  Here is the Canadian through Monday morning showing actually lighter amounts than the GFS.

But then heavier amounts with the 2nd wave by Tuesday morning, but similar totals to the Euro and GFS forecast models.

The NAM keeps amounts light with the 2nd wave staying South like the other models were showing yesterday.  So with 3 models trending further North this morning we will be watching closely today.  This trend would make a big difference in total snowfall by Tuesday morning.  This 2nd wave will be colder with higher snow ratios so totals could be double or slightly more, especially East of the crest with some better spillover Monday.  

Here is my updated snowfall forecast by region, day, and elevation based on the latest runs of the GFS, Euro, and Canadian combined.

Again, this assumes the trend continues with a further North track with the 2nd wave Monday.  If go goes South then we end up with just the Monday totals.  Yesterday the thinking was that more of the precip would fall during the day today so I had trended towards the lower end of the Monday morning totals, and now with it falling more overnight I am trending towards the middle.  So a very interesting day ahead seeing how this trends.

Behind tonight's cold front the weather is cold again through Tuesday with highs only in the 30's at lake level and 20's on the mountains.  That will keep the snow guns firing.  Then the 2nd half of the week into next weekend we will moderate back into the 40's.  There will be a flat ridge in the East Pacific with the storms continuing the 2nd half of the week and into the weekend over the Pacific NW.

The GFS has also now trended towards the European and Canadian forecast models for next Sunday into Monday with pushing the storm track further South into CA.  The scenarios are a little different, but the idea is that the trough either sags into Northern CA next Sunday, or digs down off the coast and pushes inland in the Sun-Tue time frame.  So after this storm will will be watching the same time period next week for a possible accumulating snowfall event.

Here is the 10 day snowfall forecast map from the GFS which looks promising for the West.

Long-Range:

The long-range of the models and the ensembles are still in decent agreement that we could see the trough dig into the West Coast the week of the 16th, which could lead to a decent storm or two.  Here is a look at the 500mb pattern on the GFS ensemble run for Thursday the 19th.

It also shows the trough hanging around into the week of the 22nd.

The Canadian and European ensemble runs also show the trough possibly hanging around and they also show some blocking over the top in Canada.

Of course this is all out in "fantasy" range of the unreliable models.  But at least for now the weather looks to remain active and interesting, a big change from last Winter's weather.

Stay tuned, storm updates starting this afternoon on the FB page, Twitter, and Instagram....BA

P.S.  Make sure you check out all of the new charts and info on our newly designed resort pages.  Also, the weather maps are still available on our Tahoe Info page along with the new webcam image from the office at Donner Summit.  Working on getting it clickable to a bigger image...  Bookmark it!