I was just looking at the Pacific Sattelite and it’s nice to see that storm swirling in the Gulf of Alaska, the seasons are changing and Winter is coming. I have have been doing a lot of research since the last post and doing some analoging.

There are are a lot of forecasters who will analog before a Winter, which means they will take various current and forecasted conditions and compare them against past years to see which line up the closest. It’s not always an accurate way to predict a Winter, but it gives you the averages from the past for similar conditions. There are some websites that actually run contests where the forecasters can put their Winter forecasts up against others and you can see their analogs.

One of the problems that you can run into trying to make a forecast like that is that you can have several years that were very dry and several very snowy. That would tell you we could have an average year when historically we’ve only had dry or snowy years under the same conditions. The more years that fall to either side the more confidence you would have in a forecast.

For example, two years ago with the Strong La Nina 4 out of 5 have had above average snowfall for us so the analog was pretty straight forward. With the weak El Nino we have now it’s not so straight forward and I threw several more variables into the equation. Still, we are averaging out some pretty big swings. I have 8 analog years this year in which there is 51/52 with 196% of average snowfall, and 76/77 with 45% of average snowfall. There is also 68/69 with 146% of average and 06/07 with only 67% of average.

The variables we are dealing with this upcoming season are a weak El Nino (Central Pacific centered), a cold PDO, an East QBO, and coming off a La Nina. I don’t give much weight to the last one, but I scored the rest against all El Nino’s to come up with a score for each year with 0 being no match and 4 being a perfect match. The highest score was 69/70 with 3 and the other 7 analog years 2.5 points.

If you just look at weak El Nino years you have us averaging 107% of average snowfall, but of course take out 1951-52 and you drop below average to 94%. El Nino years with a cold PDO we average 109% of average snowfall, and after a La Nina year 115% of average snowfall. But the QBO (Quasi Biennial Oscillation) which can affect the entrance point of the jet into the West Coast is trending into the East phase for this Winter, and in an East QBO state we only average 89% of average snowfall.(You will have to research the QBO yourself, not enoght time to bore you here)

The other factor that I think is important is where the core of the warm water is located, which I have not been able to find enough data on back to 1950. This season the models are forecasting Central equatorial Pacific as you can see here.

You can also see with the cold PDO we still have a lot of cold off the West coast and the warm pool to the North/Northeast of Hawaii.  This is looking like ingredients for a East Pacific-West Coast ridge and North America trough pattern.  The warm North Atlantic may favor a block and negative NAO pattern which may block up the pattern and help to keep ridges in place longer.

Let’s take a look at what the forecast models are showing for the Winter Precip.

The red being below average and blue above average.  You can see the jet is coming into Mexico and thenm up the East coast.  So what about the analogs and the history of years with similar conditions forecasted?  Well the year that scored a 3 was 69/70 with 74% of average snowfall.  All of the other East QBO years were either with a warm PDO or with a strong El Nino which we won’t have.  After two years of La Nina this looks like just a sloshing back of the warm water and it is being kept at bay by the cold water to the North. 

Now the El Nino has been weakening, but several models still do forecast it to come back and possibly hit moderate status (above 1) in December-January.

If that were to happen we could throw 02/03 back into the mix which was a 97% of average snowfall year.  If QBO state were to switch to Westerly than we can throw back in the other 3 weak El Nino years during a cold PDO in which 61%, 91%, and 146% averages out to 101% of average snowfall. 

Basically to summarize the forecast using the analogs I came up with, 6 out of the 8 closest analog years are below average snowfall which only average out to slight above average snowfall because the other 2 years were monster snow years.  Those 2 years however were during a West QBO.  Was that the magic combination or just coincindence?  That is the question.  The data set is still not that large and this season could create it’s own original data and bring us a big snow year.  It’s still really early and I will be updating the Winter forecast into October, but right now I am going to go with 70-80% of average snowfall, more spreadout across the season.

With the El Nino inspired Subtropical jet across the Southern U.S. with its lower pressures and trough across the U.S., it may turn out to be a fairly cold Winter across most of the U.S. including into the Sierra.  Here is the current model forecast for Winter temperatures with below average in blue.

I already talked about some reasons we could see a cold Fall as well in my previous posts.  Those new snowmaking systems may come in handy this year. 

I will keep on tracking everything as it develops as we head into the Fall so that I can fine tune the forecast.  I’m on vacation next week so the next post will be at least another 10 days out.  We will start to see the ridge breakdown this weekend with some cooler weather and then rebuild next week.  The first sign of some weather in the long-range models is the first week of October so we’ll have to keep an eye on that.

If you have any thoughts on the upcoming Winter feel free to email me.  Stay tuned……BA

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