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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
This was written Wed Morning but didn't post....another update Friday night or Saturday morning.
I am still watching the weather even though the ski resorts will all be closed by Sunday. This morning the forecast models all came into much better agreement on the pattern for next week. It looks like it will feature a cold trough dropping down the West Coast the first half of the week and settling in over the West.
Much colder air will move in by Monday with snow showers possible Monday throughTuesday. The European model keeps the trough far enough West all week to bring more waves of precip in, while other models just keep the cooler air in place. The snow levels will be near lake level to start the week. We could see several inches of snow on the mountains.
Another update later this week...BA