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Welcome back.. I didn't get a chance to post in August although I have been watching and reading all of the Winter forecasts coming out and signals developing.
Our words of caution here at Opensnow since last Spring about El Nino not looking too strong for the upcoming season are now becoming relevant. The computer models this past Spring and early Summer once again tried to predict a Strong El Nino and many forecasters or media outlets took the bait and started hyping the upcoming season. Back in July I posted about taking caution in reading the early forecasts. Since then the forecast models have continued to weaken the outlook for El Nino this Winter, with the latest update from NOAA yesterday now saying only a 65% chance we even see an El Nino develop.
If one does develop it now looks to be weak at best. The good news is that we can now take the moderate El Nino years out of the analogs if the trend continues, and just look at weak events for now. The 4 ENSO regions this week are averaging 0.5c above average, just barely a weak El Nino signal. The ONI which is the 3 month average through July was only at 0.1. Still waiting to see the average through the end of August. The ONI would need to be at least 0.5 for 5 consecutive months in order to have an official El Nino event. Below is the latest CFS forecast for Nino 3.4 through the Winter peaking just barely above 0.5 now.
So now that the El Nino hype is gone let's look at some other factors that could affect the pattern this Winter. None of the things we will look at are for sure, but an entertaining look at possibilities using some things we know and trends from the past.
There was a warm pool of water in the Northeast Pacific last Winter and the warm water has now spread down the West Coast. That warm water was blamed for high pressure up in Canada last Winter that helped to send cold into the Central and Eastern U.S. The PDO (Pacific Decadal Oscillation) has flipped to a warm phase this Summer. That will change one of the variables we use in comparing past Winters in our analogs. Take a look at the sea surface temps 2 years ago in the Summer of 2012. Notice all of the cold water off the coast in a classice cold phase of the PDO look.
See the warm pool develop in the Northeast Pacific in 2013
and now look at all of the warm water off the coast... With the look of a warm phase of the PDO.
What is interesting is that the water down along the equator still has a lot of negative values which is why there is no clear El Nino signal yet. The forecast is for a Central Pacific modoki El Nino pattern to develop by Winter, if it does develop.
The warm water off the coast is most familiar in recent years to 2004 below. Biggest difference is the colder water off of Mexico. We will take note of that as we look at the analog years later in the post.
Another oscillation we can try to forecast this far out is the QBO (Quasi Biennial Oscillation). Looking at the latest readings it is currently in its Easterly phase and forecast to continue that way into the Winter. This is also the opposite of last season. So is it a good thing we have an opposite PDO and QBO compared to this time last year?. Most of you would probably take anything the opposite of last year as a good sign, but lots of warm water off the coast could mean a Western ridge again this Winter.
Let's take a look at some past weak El Nino seasons Oct-Apr, and the precipitation anomalies for them compared to the long-term averages. First, let's look at all of the weak El Nino seasons.
Not looking too good just based on the strength of the El Ninos alone. In comparison let's look at just the moderate El Nino seasons.
Now while these look much better there may be other factors that can split apart the moderate years as well between dry and wet seasons. Looking at the warm phase of the PDO years like we have now the average snowfall on Donner Summit is only 84% of average, while moderate El Ninos during a cold PDO are averaging 144% of average snowfall. So while a moderate El Nino as was possible when we looked earlier this Summer and may have increased our chance of an average season, with the warm PDO historically it may not have.
Now before I show you I can tell you that looking at the last 60+ years weak El Ninos in a warm phase of the PDO with an Easterly QBO phase like we could have this Winter, the average snowfall is very similar to a weak El Nino in a cold PDO and a moderate El Nino in a warm PDO phase. Below is the analog of the years that weighted the highest score when looking at these 3 factors this far in advance of the upcoming season.
You can see the Southern jet stream is supressed well to our South with average precip for SoCal which is good news, and across the Southern U.S.
The only time Donner Summit runs above average for snowfall on average during weak-moderate El Ninos is during moderate El Ninos in a cold PDO. Maybe due to increased chance for West Coast troughing with the cold water off the coast.
The one thing with an Easterly QBO and the low solar activity continuing the country from the Rockies East could be very cold again this Winter, With above average snowfall in the Southeast.
The exact number for average snowfall at the Donner Summit snow lab is 323 inches or 84% of the 411 inch annual average during a weak El Nino in a warm PDO with an East QBO. The outlier is 2004-2005 which I mentioned above with when look at the sea surface temp comparison to this summer. The 04-05 season was a weak El Nino in a warm phase PDO with an Easterly QBO, but it had 482 inches of snowfall on Donner Summit at 117% of average. So yes, that year busts the analog average and is a possibility this year. (Thanks to Randall at the Snow Lab for all the data on Donner Summit snowfall)
These of course are only 3 factors and there are more that we will be able to look at as we get closer to Winter. Let's hope that we start to see some positive signs for the Winter. As I said this is just an entertaining way to look at the past and try to guess the future using it. It's not an exact science. Just like the forecast models change on a dime anything could happen this Winter. As of right now however, I am not seeing anything yet that is pointing towards a good chance of an above average snowfall this Winter.
Tis the season for looking at the forecast models more closely moving forward. We could see our first dusting on the mountains in September, it's not unusual here. Looking at the Fall for weak El Nino seasons they average 13 inches of snow in October, 26 inches in November, and 60 inches in December on Donner Summit. We do tend to start the season a little earlier. Despite being below average years they do have snow through the Winter. Let's hope we see it early and throughout this Winter!!!
Stay tuned.....more updates on Winter and the lookout for the first flakes coming soon.....BA
The Upcoming Winter:
It has been over 2 months without a post. I would love to say I have been watching the weather everyday, but I have taken a break over the past 2 months. During this time I have been doing plenty of reading and monitoring for the upcoming season. I have been watching the ENSO state and forecasts and other patterns. I have noticed quite a few Winter forecasts coming out in July. The weather models are forecasting for the Winter already, but this far out it is still quite an inaccurate science.
Most of the forecasts are factoring El Nino as the major player in the pattern. The forecast models have been over forecasting the strength of El Nino events however the past several years. The strong El Nino forecast from Spring has already been downgraded to a Weak to Moderate El Nino forecast for this Winter, in line with the what the models have been doing in recent years. Chances are increasing though that we will see a weak or moderate El Nino pattern evolving by Winter. Currently we are still in an ENSO neutral state with the equatorial ENSO region ocean temps cooling recently. Not a good sign for a stronger El Nino.
Here in Tahoe we are on the borderline between Northern and Central CA, and between the Pacific NW and the Southwestern U.S. With El Nino having a much stronger correlation with Southern CA weather and the Southwestern U.S. it is hard to say what it would mean for us here in Tahoe. Historically Strong El Ninos or La Ninas have a much better chance of bringing us above average precip here in the Tahoe Basin. Unfortunately that is not looking likely this upcoming Winter so the forecast will be tricky and other variables in the weather pattern may push us one way or the other. So we may be in for another season of frustrating forecasting.
Golden Gate weather has a nice site with historical data for El Nino and La Nina precip in Northern CA. Back in May they put out a list of myths about El Ninos commonly regurgitated around CA in discussions about weather and Winter snowfall. Below is their "Myth #5" that I thought would put the upcoming Winter forecasts into perspective.
"Myth 5: When there is an El Niño, there is lots of rain in California. No! -- The answer is NOT always and NOT everywhere. Historical records for the past six plus decades for Central California show that during the 22 El Niño events the rainfall has been above normal half the time and below normal the other half. If just the 6 strong El Niño events are looked at then the rainfall has been above normal 4 of the 6 seasons. However, if only the weak and moderate El Niños are examined then it is seen that 6 of the 16 years received below normal rainfall, 5 near normal and 5 above normal.
Over the same span, Northern California had 3 wet years years during the 5 strong events, with 5 above-normal seasons during the 16 weak-to-moderate El Niños.
Southern California showed more of a wet bias during strong El Niños with above-normal rain in 4 of the 5 seasons, near normal the fifth year. During weak to moderate events Southern California precipitation was above normal 6 of the 16 seasons, near normal 5 seasons and below normal the remaining 5 years.
The bottom line is that California can get wet during El Niño, but not always. As a matter of fact, the California drought in the 1976-77 winter was during a weak El Niño. It is important to keep in mind that El Niño is not the only thing happening in the atmosphere and that other patterns can either enhance or detract from its overall impact."
So just looking at historical records since 1950 Central and Northern CA have a 31% chance of above average precip this upcoming Winter. The better news is that there is a 63% chance of at least an average season for precip.
I am going to take the historical snowfall on Donner Summit and break it down by year and month in the weak to moderate El Nino years. I will also add in other variables and come up with my analog years as we get closer to Winter. We will take another look at the trend for El Nino in August and analyze the snowfall for Tahoe in past years during El Ninos.
Meanwhile, don't read between the lines on the Winter forecasts coming out. Stay grounded in the historical facts.
An area of low pressure spinning off the Pacific NW coast will head South through CA over the next few days. The winds have already been gusty this weekend and the temperatures have cooled slightly.
Clouds and colder temperatures will push in with the low Monday. The best chance for showers looks to Monday night through Tuesday night. Snow levels on Tuesday will drop as low as 7000 ft., but will hover between 7000-8000+ ft. during the event. We could see several inches of snow above 8000 ft. by Wednesday morning. We may even see some flakes below 7000 ft. Tuesday during heavier showers.
The low kicks East Wednesday with warming temps Thursday into next weekend.
Clouds and wind will be on the increase today. A cold trough is digging down the West Coast and it could bring in precip by this evening. Snow levels will drop below lake level overnight and we could see a coating to an inch on cold surfaces.
The snow showers will linger through the day on Tuesday as the low swings through. We could see 1-3 inches in total on the mountains on the East side of the lake and 3-6 inches on the West side by Tuesday evening. Highest amounts above 8000 ft. along the crest.
We begin to warm up on Wednesday but another system moves through to our North Thursday night into Friday. The computer models have been trending further South with this system so we could see some light rain and snow showers.
Next weekend into the following week it looks like we will warm back up with quiet weather for a while.
After temperatures in the 70's the past couple of days we have breezy conditions and cooling temps this weekend as the high pressure breaks down. A cold trough will drop down the West Coast Monday and Tuesday dropping temps into the 40's by Tuesday. We could see some rain and snow showers Tuesday as the trough moves through.
The forecast models are still showing enough liquid that the mountains could see a few inches of snow with this system. We could see up to 6 inches along the crest above 8000 ft.
The trough moves East and we begin to warm the second half of the week but only into the 60's not the 70's. More active weather may return around the middle of the month. The climate models have been showing precip for May and we will take as much rain or snow as we can get to help with the drought.
The month of April the Tahoe Basin picked up 66% of average precip bringing us to 66% of average for the water year. The temperatures at the Truckee airport averaged 1.4 degrees above average for the month.
Another update Monday on the details of snowfall potential for the mountains...BA