Tahoe Daily Snow
By Bryan Allegretto, Forecaster Posted 2 months ago December 9, 2023
Dry and seasonal through next Friday. A storm could move through at some point between the 16th and 20th. A drier pattern is possible for a few days leading up to Christmas Eve. A stormier pattern is possible from around Christmas through the last week of December.
Short Term Forecast
No big changes to the forecast this morning other than trying to forecast the track of a possible cut-off low next weekend. First, we have a dry 7+ days starting today (Saturday).
It's a cold Saturday morning with temperatures in the teens for the lower valleys near lake level, but with the lighter winds, we saw inversions form overnight. We can see this clearly looking at the Palisades Tahoe weather sensors that show the coldest air at the base with temperatures in the teens, helping to displace the warmer air upward toward the summit with temperatures rising into the 30s at the same time.
This doesn't mean too much usually but when temperatures rise above freezing when they are trying to make snow on the upper mountains they are limited to making snow, and the best snow, at the bottom of the mountains.
We don't usually get into too much, but we have a week ahead of mostly sunny days and highs into the 40s, so it's one of the only interesting things happening this week. Highs for the upper mountains should be colder during the day in the 30s above 8000 ft.
With the dry week ahead all eyes are still on the long-range forecasts as we wait for more storms and our first big storm of the season.
The latest model runs have started to change a bit for next weekend. They still show the trough trying to push into the West Coast opening up the door to a storm moving through, but the latest runs now show the trough becoming pinched off by high pressure to the north.
That has the trough and associated low-pressure system that spins up into the trough becoming cut-off from the east-west flow. They are also encountering the high-pressure ridge over the West. Both of these are causing the models to now show a slower-moving trough through could sit near the coast from next weekend into the first few days of the following week.
The storm that spins up into the trough off the coast could form into a closed or cut-off low and spin off the coast before eventually moving inland. The latest GFS model runs has it off the coast all weekend and then moves it through southern CA mostly missing us, which is why the snowfall forecasts have dropped this morning for Saturday-Sunday.
More progressive scenarios like the European model have the system tilting negatively with a south-to-north flow which is not good for pushing moisture into the Sierra, and it weakens and splits as it encounters the mountains. Overall the message is that this system could be a real pain in the #%s to forecast over the next week, and we could see very light snow, a few days of snow showers, or even a day or two of steadier snow.
The ensemble mean models show light-moderate amounts of precipitation falling near the Sierra between the 16th-20th. We'll likely be swinging the forecast a bit up and down as we try to nail the forecast down over the next week.
The long-range models still show high-pressure building back in whenever that trough finally finishes moving through. The latest model runs show high pressure building back in by the 21st through the 24th vs the 18th - 24th on the previous model runs the last few days.
We have started to speculate the last few days about a possible Christmas Miracle. By the time we get to Christmas Day, we are more than 2 weeks out at 16 days from today. All we can look at out that far if we even dare to speculate that far, is what the weather patterns could do and if that could lean toward storms or dry weather.
I've been looking at and talking about the weather that far out for the last few days for two reasons: 1) we are still waiting on our first big storm, and 2) there's been some online hype about the possible jet stream strength and position the last week of December. It amazes me all the time that people still trying to talk in certainties about the weather more than two weeks out, but we have been discussing that the weather pattern currently forecast does look interesting.
By the 25th the long-range ensemble mean models are still in good agreement on a pattern that has a very large low-pressure trough over the northeast Pacific.
That would allow some pretty big storms to form over the Pacific and to head toward the West Coast. What would be even more helpful would be a strong jetstream to help push them into CA. We have been watching the forecasts for a strong jet stream to extend east off of Japan across the Pacific, and hoping that as we get into the last week of the month the forecasts continue to extend it all the way to the West Coast.
Well, that is what is happening on the latest model runs...
A parade of storms could be lined up across the Pacific being steered toward the West Coast by Christmas Day, with a moisture tap all the way west across the Pacific to help feed them.
IF this pattern were to continue to hold over the next two weeks, it could mean that storms unleash on northern CA starting around Christmas through the last week of December.
We have to remember that this is still 16+ days out in the Fantasy range. I wish other forecasters weren't making such a big deal out of it yet on social media. Forecasts this far out change all the time and people will get excited and then be let down. But the ingredients are there and we are anxiously awaiting our first big storm series.
Let's just hope that it's not a repeat of Christmas to New Year's 2005 (Google it if you weren't here)...