Back in the saddle today and ready for the upcoming Winter.  The frequency of posting will rely on the activity in the weather.  Let's hope there is a lot to write about this Fall.

August was a drier month after a few wet months for the Tahoe basin.  We saw only 33% of average precip for the month.  Temperatures the last 2 months have been running around 2 degrees below average based on the Truckee airport readings, after several months of above average temperatures.  Not that many big heat waves this Summer.

I had planned to write earlier this week but I had to spend more time than expected looking at the data.  NOAA decided this Summer to reanalyze past ENSO events and they changed the ranking of several past events.  Much like how they have changed the temperature data twice now.  It messes with all of the analogs I have built in spreadsheets based on the strengths of the Nino events.  I had to adjust their rankings which changed a some of the data.

For example, weak nino events historically averaged well below average snowfall on Donner Summit, moderate was slightly above average, and strong was slightly more above average.  Now with the reanalysis weak El Ninos have historically average near average snowfall, moderate is now below average, and strong well above average. 

I also use these past events and combine them with the PDO, QBO, and the prior Winter's ENSO state to come up with an analog ranking for the upcoming Winter based on what we think will happen.  I had to redo that chart as well.  What does all that mean?  I am not an expert on how they decide to change past data, but it definitely affected our forecast models and analog forecasts that use past data.  

The forecasts now show more precip and snowfall for this upcoming Winter when pulling the new historical data.  One reason is that the 87-88 season, which used to be ranked as a Strong El Nino and only brought 58% of average snowfall to Donner Summit, has now been ranked as a moderate event.  That makes 4 out of 5 strong events now that brought above average snowfall, and raises the average snowfall for strong events to 513 inches, or 125% of average.

Here is a look at the historically precipitation against the average for the 5 strong nino events.

Currently we are into Super Strong El Nino conditions with Nino 3.4 at 2.2 degrees celcius above average on the latest update.  Doing the weighted scale that I have used in past seasons that has worked out fairly well with putting together an idea of how much snow could fall, I come up with 3 seasons 57-58, 82/83, and 97/98.  57-58 was not a super strong event, but QBO is one of the the several factors I throw into the mix for weighting and 57-58 saw mostly a west phase like 82/83, and 97-98 had East.  So 82-83 came up as my highest analog year with the other 2 close behind.  But anyway those three seasons all had above average snowfall and the average on Donner Summit was 668 inches.

That is not my forecast for this season, but that is historically what we have seen under several similar conditions as we are seeing now.  I purposefully wrote a post earlier this Summer about the reasons why could not see a big Winter, knowing that just looking at the current El Nino and PDO conditions things look very positive for us this Winter.  I remain cautiously optimistic after so many bad seasons in a row.  The potential is definitely there though to snap the drought and it is time for it to snap historically after 3-4 drought years.

It has been interesting reading around on the blogosphere all of the different forecasts for this Winter.  Most show a wet CA and a cold and snowy Southeast which is typical for El Nino.  Many forecasters are telling everyone why their forecast is right and sometimes why others is wrong.  I get a chuckle from that since no one actually knows.  Those who think they are smarter than everyone else need a large slice of humble pie.  I am not a climatologist but ours is working hard on the official Opensnow Winter Forecast that will be out soon.  I am a snow forecaster trying to nail down storms and snowfall amounts, although the past few seasons without storms I have had to resort to trying to forecast long range patterns.  I use history a lot more than some in coming up with forecasts. 

Many forecasts are using only the CFSv2 to back up their forecasts for a wet Winter in CA.  With the skill that version 2 has shown the last couple years I would equate using the CFS to using a guy who picked the wrong winning team in the NFL work pool every time last season, and you hire him as your consultant to pick your teams this season...  Not every climate forecast model is showing the deep Gulf of Alaska trough hugging the West Coast this Winter.  Some are showing the trough further West off the coast and a ridge over the Coast.  Putting all of the models together last month Tahoe was still sitting on the fence between above and below average precip, similar to what the Climate Predictions Center is still showing in the most recent forecast for this Winter.

Northern CA actually became drier on the forecast from July on the right to August on the left, before coming in a little wetter again for Central CA on the latest forecast above.

Models like the NCEP CA model are going back and forth as well with how close to the coast the trough sits and how far East the enhanced jet stream extends across the Pacific.

If you want to back up historical precip or to get the result you want if you think the pattern will bring us well above average precip, you can use the CFSv2.  Below is the pattern forecasted with the trough close to the West Coast which would be ideal for both branches of the jet stream to steer storms into CA.

And the resulting precip......

I get flashbacks looking at these to all the times the CFS forecasted above average precip 30 days out last season and we got nothing...  

The JAMSTEC tends to be a more reliable climate model, and it has been increasing the precip forecast as we get closer to Winter.

Instead of only using one unreliable model I'd rather use as many as possible and take an average.  The European model which most of us are not allowed to post, shows the trough further off the West Coast and a drier Winter for Northern CA.  The Jamstec and Euro are thought by some to be the more reliable models.  Weatherbell tends to put out Winter forecasts that are the opposite of other outlets.  Last season they got the snowfall wrong for the Sierra as they forecasted average amounts, but they got the pattern right for the rest of the country.  They are leaning towards the European runs with their Winter forecast.

The forecast for the South, East, and NW looks similar to other outlets and El Nino, but CA is much different.  Still watching for some of the major weather outlets to release their Winter forecasts.  Like many of the forecasts that have come out, I'm expecting them to have a wetter and snowier CA than above.

From what I have been noticing looking at of the forecast models is a trend towards a wetter forecast for CA as we get closer to Winter.  The NMME uses a blend of models and this is what it has been forecasting.

It has been interesting reading the arguments between whether high pressure the last few Winters has caused the blob, or the blob caused the high pressure.  Also, if or how fast the water will cool with an active storm pattern into the West Coast.  If the blob is a result and not a cause of the ridge then it won't have any affect.  If when the land cools and the warm water has more of an influence on the air patterns and that is what helped to cause ridging then maybe it does affect the storm pattern in the heart of Winter.  There are arguments that the cooling Western Pacific will change the long wave pattern enough for a persistent deep trough close to the coast and an extended East Asian jet into CA.  Other forecasters argue the Northern Pacific is so warm as a whole that we will not see the extension into the West Coast.

It is definitely a Sea Surface Temperature pattern I can't remember seeing with 3-4 distinct warm blob areas in the Pacific.  I am not going to to claim to know what is going to happen.  I am going to enjoy seeing what does happen either way.  For now I am hoping for and preparing for a big Winter based on historical snowfalls during similar PDO and El Nino conditions.  But I won't be astonished if this unusual pattern brings a pattern we are not expecting.  For now I am only expecting a greater than 50% chance we could see at least slightly above average precip as far North as Tahoe, and hoping that if we do the snow levels are low enough to equate to above average snowfall to the base of the mountains.  Above average precip doesn't necessarily equate to above average snowfall down to lake level.

Historically if we do see above average snowfall the months we will see it are November, January, and February based on monthly stats from the Central Sierra Snow Lab on Donner Summit.  Will we finally get a Winter without a doughnut hole of no snow in Janaury?

I plan to update as storm activity picks up.  We have had cooler weather the last few days from a trough that moved through the Pacific NW bringing snowfall to the Northern Rockies.  We will ridge back up along the coast and see warmer weather return this week.  Next chance for some cooler weather looks to be at least 2 weeks away.  

Stay tuned.....BA