Sunday Morning Update:

Some precipitation is moving in this morning ahead of the main storm and cold front.  The fronts arrival has slowed even more with arrival now early this afternoon.  That is when the heavier precip will move with falling snow levels.

Summary:

We have a break today before a cold storm moves through on Sunday.  We will see snow down to lake level Sunday with a an inch or two possible, and several inches of snow for the mountains.  

There will be another break Monday before we could see some light snow Monday night into Tuesday with a few more inches for the mountains.

Then the ridge builds in over the West and we could see dry weather the first 2 weeks of November as the ridge keeps the storms to our North.

Details:

We do have some changes to the forecast over the past 24 hours.  The storm is digging a little more off the coast today and tonight.  That will slow its arrival with the window for heaviest precip now 10 a.m. to 4 p.m. on Sunday.  It will also move through faster which will limit the snowfall amounts.

Last Storm:

We do have a decent little fall storm still on tap that will bring us several inches of snow to the mountains!  First though, let's look at the wet and warm storm that just rolled through.  Here are are some of the storm totals for rain from the CNRFC (Calilfornia Nevada River Forecast Center)

What is interesting is the amounts over 2 inches near Donner Lake.  Before this storm here are the top 4 wettest Octobers on record back to 1870.

If you add 2 inches to this October we move into 4th place ahead of 2010, and wettest October in 53 years!  We could get another inch of liquid tomorrow, so we may bump 1883 for the 3rd spot!

Sunday Funday:

So about that storm.  I have been analyzing all of the computer models this morning trying to figure out the snowfall.  2 days ago I had rough estimates of 6-12 inches for the mountains with up to 18 inches along the crest.  Now with the slower arrival and then faster speed of the front moving through on Sunday the total precip numbers have come down a little.

 

That is the latest GFS forecast and here is the WPC blended forecast model forecast which is similar.

Also with the storm coming through during the day it will be slightly warmer with lower snow ratios and making it harder to stick at lake level.  Snow levels start around 7500 feet Sunday morning but look to drop pretty quickly to near lake level by early afternoon.  Here is a look at the NAM radar forecast for Sunday.

You can see the front moving through pretty quickly.  This is a typical cold front storm we see here in Tahoe with 3-6 hours of heavier snowfall and then lingering snow showers.  We will see snow showers linger near the crest into Sunday evening.

I blew the dust off the snowfall calculator and plugged in the numbers for the first time this season.  Here is my official day before forecast for this storm.  I know I will get a little grief because my numbers are lower than the NWS.

As a refresher for this season, I will explain my calculator.  It takes the input from the latest GFS and European forecast model runs for precipitation and temperature at each location and elevation.  It averages them together.  It creates a snow ratio based on the temperature at each elevation.  Then it multiplies the total precip high and low end by the snow ratio.  That gives us a snowfall forecast.  I then tweak the numbers slightly based on timing of snow level drops.

So we should see a decent little October storm with several inches of snow for the mountains by Sunday night.  At lake level we will have to see how fast snow levels drop and if snow can accumulate.

What's Next?:

There is another weak and cold storm that will move through Monday night into Tuesday morning.  The GFS shows another 1-3 inches possible for the mountains.  The Euro is more agressive with 3-5 more inches on the latest run.  Snow levels again will be near lake level.  We will take another look at this one Monday morning.  Temperatures through the week at night may be just cold enough to blow some snow.

Long-Range:

I am sticking to my forecast of a dry start the first 2 weeks of November for now.  If you have been running the GFS model at home you probably keep thinking I'll be wrong as it always shows storms breaking through week 2.  But if you notice each day it keeps pushing those out to 2 weeks and keeping us dry through the first week.  

What is happening is that the trough in the Northeast Pacific will be pulling back slightly West and the ridge will be building over the Western U.S. the first week of November.  Storms will try to break through the ridge and will bring some precip to the Pacific NW, but won't hold together long enough to make it to Central CA.

Here is a look at the pattern next Saturday as forecast on the GFS ensemble mean, which is similar to the European model that was first to catch the pattern change.

and then the following Saturday...

you can see the trough shifting slightly further West with time and the ridge as well, and the trough in the East.  So if this verifies we may be going into a drier pattern for at least a couple of weeks.

Winter Forecast Ramblings:

This pattern is not that far off the pattern weatherbell.com is forecasting for the Winter, and here is their latest winter snowfall forecast update.

Storms spend the Winter trying to break through the ridge and enough make it into the Pacific NW for them to get a typical La Nina boost to their snowfall.

If you have been reading along this Fall you know my initial snowfall forecast back in September for Tahoe was 85-92% of average snowfall.  I didn't come out with a final forecast yet because of the uncertainty still about the state of the ENSO and North Pacific temperatures.  

Still seeing some conflicting signals as the SOI (Southern Oscillation Index) is tanking negative.  This creates westerly wind bursts along the equator.  That is what strengthens an El Nino not a La Nina.  So even though we have weak La Nina currently, I'm not sure if the latest flip back to a forecast for weak La Nina won't flip again back to a forecast for ENSO neutral conditions this Winter.

Of course there are many other variables and many other Winter forecasts out there that we will continue to look at this Fall.  I am hoping my initial forecast is wrong and we continue to get lots of storms like we have been seeing in October.  It is a difficult Winter to forecast and it could go either way.  It only takes a few big storm series in Tahoe to bury us and have a great Winter, and a so called "average" Winter of 400-500 inches on the mountains is a great Winter.

Ok that's enough rambling for this morning.  Let's concentrate on snow coming the next few days and then worry about the future.  

Stay tuned...BA

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