Update Sat AM:

Big day here at the Allegretto house with my sons 5th birthday party.  I went through all the model runs this morning and not much change from yesterday.  The storm may have slowed slightly with precip beginning Sunday afternoon.  Two distinct waves of precip Sunday afternoon and Monday afternoon with light showers in between.  Both waves stay West of the basin with most of the precip not pushing over the crest.  No change to the snowfall forecast below, expecting very light amounts at lake level and a few inches on the mountains.  Cold air returns for a few days before warming by next weekend.  Next chance for a storm not until around the 17th-18th.

From Yesterday:

Summary:

Temperatures are a little warmer today and Saturday back into the 40's with sun ahead of the next cold system.  We will see snow return on Sunday into Monday with cold air returning for the beginning of next week.  Snowfall amounts will be light with 1-3 inches at lake level, and 3-6 inches on the mountains.  High pressure builds in next week with temperatures warming back into the 40's by the end of the week. 

Forecast models are split on how far South storms will come next weekend.  If they stay North we could see a warm-up into week 2, if they are further South we could see some colder air with more rain and snow.  

Details:

Some changes on the forecast this morning.  First is to speed up the storm on Sunday.  We could see rain and snow start as early as Sunday morning.  Second is to raise the snow levels slightly to start.  They should start near to just above lake level, so we may start as rain before snow levels fall Sunday afternoon.  Third is to lower the snow ratios with the highers snow levels and the precip falling during the day Sunday.  Fourth is to cut back on totals as there appears to be quite a bit of rain shadowing East of the crest.

The snow showers should continue Sunday and the latest model runs show a 2nd weak wave moving in Monday with some more showers.  Total precip amounts for the East side of the basin may only be around .1 to .25 inches, with .25 - .5 inches on the West side.  

You can see here on the Canadian precip forecast that an inch or more could fall West of the crest.  The areas that will be interesting are most of the ski resorts located West of the lake along the crest.  For snowfall we could see a coating up to a couple of inches on the East side of the basin, and 2-4 inches on the West side.  On the mountains we could pick up 1-3 inches on the East side of the basin, and 3-6 inches on the West side.  Ski resorts along the crest could see up to 9 inches up top.  This is by Monday morning.  So a small storm by Tahoe standards for a 24 hour period.

The temperatures behind the cold front will be cold again with highs in the 20's up on the mountains and 30's at lake level to start next week.  High pressure builds off the coast and moves closer by the end of next week.  That will bring a dry pattern and warming temps back into the 40's by the 2nd half of the week.

For next weekend most forecast model runs were keeping the storms to our North into the Pacific NW.  That would bring a continued warming trend next weekend into week 2.  The European model run last night on the 0z run dug the Friday storm much further South into Northern CA with a cold front and more snow for Tahoe.  We will have to keep watching to see if that is a fluke or a trend or coming further South like we saw with the last 2 storms.  Either way quite a bit of precip will fall over the Pacific NW next week.

Long-Range:

Looking at the long-range ensemble runs of the models they are still pointing towards a pattern change towards the end of week 2 with a trough digging into the West.  Some have the trough along the West Coast and some a bit East over the West like the Canadian run below.  That could bring another pattern of some colder weather and storms if it holds starting around the 19th.  

The Past & Future:  

November was never expected to be a wet month although historically during a strong Nino event November has had above average snowfall.

Here was the forecast for precip in November, which should be wrong in the Pacific NW after next week.

So we have been pleasantly surprised by some early season precip and snowfall.  During the month of October the Tahoe Basin picked up 107% of average precipitation, and the Truckee River basin picked up 130% of average precip.  Temperatures averaged around 3 degrees above average for the month.  We had a nice start to November with the rain and snow with the last storm, and a little more with the next storm.  Hopefully we see some bigger storms before the end of the month.  October was the first month of the water year so let's keep this above average trend going!

So what about Winter?  I started off the Winter discussions early in the Summer and started by countering the El Nino hype with scenarios I was seeing that could bring us average or even below average precip this Winter.  Then I followed up with reasons why we could see average to above average precip and possibly average to above average snowfall.  A lot of people are just looking at the last super strong El Nino during the 97/98 season and assuming we will see the same pattern this Winter.

Here is a look at November 97 Sea Surface Temps on the left and this November on the right.  You can see 3 distinct areas that are not the same that I have circled.  First, the temperatures in the Eastern Pacific off the West Coast are the opposite with much warmer temps this year.  Second, the temperatures in the Indian Ocean are the opposite with much warmer temps this year.  Third, the water was warmer on the surface along the equator in 1997, and the warmest water was closer to South America.

I don't know how you can look at that and say it's guaranteed to be the same pattern.  The forecast for the Nino region is for the warmest Water further West this Winter in region 3.4 slightly more towards but not quite a Modoki pattern.  That could mean a colder Eastern U.S. vs the 97/98 event.  We saw a modoki El Nino last Winter but weaker.  The water was also warm off the West Coast and once the continent cooled during Winter we saw high pressure setup along the West Coast and the cold lock in over the East, while the trough over the Pacific sat North of Hawaii over the cold pool that is also still there.

The forecasts for this Winter have the trough further East just off the West Coast with the ridge over the Northwest, and storms coming into CA and across the Southern U.S. which is a typical El Nino pattern.  The super strong El Nino we currently have should help to bring us that pattern.  But not all climate forecast models agree.  That and the Sea Surface Temp pattern we have that is unlike one we have seen during a super strong El Nino, has kept me from going all in on forecast for big snow this Winter.  I have continued to be cautiously optimistic.

Here is the CMC forecast for precip Dec-Feb.

But here is the GFDL for the same time period keeping the above average precip in Southern California.

Looking at 9 climate model forecasts for Winter about 1/3 show us on the edge of average to below average, and 2/3 above average.  The method I usually use to forecast the snowfall for the season looks historically at the ENSO state, the PDO (Pacific Decadal Osciallation), the QBO (Quasi Biennial Oscillation), and some other factors, and compares it to the current and forecast patterns for those variables.  Then I rank each season by how many matching variables it has and give it a rank.  That showed above average snowfall for the 10/11 season and below average for the last 4 seasons, which came out right.  But using that method for this season I come up with 154% of average snowfall for us.  So I am not going with that, but just thought I'd mention it.

Our climatologist put the Opensnow forecast together using a similar method but only using the sea surface temps for each region historically versus the forecast for this Winter.  Using Sugar Bowl as an example that is giving us a forecast of 97% - 133% of average snowfall.

Historically we applied this method agains actuals and came up with an accuracy of around 50%.  This forecast covers a nice range of slightly below average snowfall to well above average.   I think that shows the uncertainty we face going into this season.  We could see slightly below average snowfall even with above average precip if we have high snow levels.  We could also see a big season if the trough sets up right along the West Coast steering storms into all of CA all Winter.  People have been asking me to make a wager on my feeling and I would feel most comfortable looking at the data with a snowfall forecast of 95%-110% of average snowfall.

There just seems to be a lot more uncertainty in the forecast models and among forecasters than what the media would lead you to believe.  Look at the CPC forecast for the next 3 months.  Equal chances of above or below average precip with the above average to our South.  That is a nice blend of the climate model forecasts.

So no one knows what will happen until it happens, but it should be a much more active and interesting season than the last 4.  The Brazilian forecast that just came out is encouraging showing the trough nosing right into CA this Winter. 

Whatever El Nino does do for us precip wise we expect it to be seen in the heart of Winter with January to March showing the highest chances of above average precipitation.  So whatever snow we get this month and December could be a bonus ahead of the stormy months.  Let's hope we see the storms continue.

Stay tuned....BA