- Sunny and warm Sunday into Monday with highs in the 60s. - Tuesday we have increasing clouds and wind as a storm moves in. We could see some light showers later in the afternoon. Tuesday night we could see some light rain and snow with snow levels lowering to around 7,000 feet. Wednesday the light showers could continue. We could see a coating up to a few inches of snow above 7k. - Cooler weather behind the system with highs in the 40s and lows in the 20s. Expecting a drier pattern Thursday into next weekend. We could warm a few degrees going into the weekend with highs near 50 at lake level. - The week of the 25th we could see a weak system move through. No signs of any stronger systems until the first week of December.
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Short Term Forecast
We are enjoying warm and dry weather this weekend, but all eyes are on a system moving through this week that will bring colder air and the possibility of some light snow on the mountains.
A strong area of high pressure over CA bringing warm/dry weather this weekend...
...will be replaced by a trough digging into CA this week.
An area of low pressure will move south through CA and NV bringing the chance for light rain and snow to the Sierra, and even a few spots that could see some heavier precipitation.
We have been watching this system all week and trying to get an idea of what it might do. Cut-off lows are notoriously hard to forecast as they are cut-off from the flow of the jet stream and can move in various directions and at various speeds.
They can also have a deformation zone of heavier precipitation that develops on the north/northwest side of the circulation that can sit over a small area and drop heavier precipitation. Where that band sets up can make a big difference in total precipitation amounts.
We are also dealing with counterclockwise rotations with an east flow when the lows are sitting to our south. That increases the orographic lifting effect of the mountains on the east side of the Sierra instead of the west side like we normally see with storms moving in from west to east off of the Pacific.
All of this makes for tricky forecasting and it's why I have stayed away from trying to make any snowfall forecasts yet. You can see the computer-generated forecast on the right sidebar showing higher snowfall amounts for the ski resorts on the east side of the lake.
We could see some light precipitation make it to the Tahoe basin by Tuesday afternoon along with some gusty winds and cooler temperatures. Then Tuesday night into Wednesday we could see some steadier precipitation set up as the low draw in more moisture as it sits over southern CA and NV. Where those areas of steadier precipitation setup is complicated due to the reasons stated above.
Looking at some of the forecast model runs this morning, we see the Canadian model showing some heavier precipitation over the area with up to an inch of total precip near Heavenly through Wednesday.
The GFS is a bit drier around the area with up to half an inch of total precipitation on the south side of the lake.
The NAM model is even drier with a band of heavier precipitation setting up to our south from around Mammoth east into central NV. It has only very light precip amounts for the Tahoe basin if any.
So you can see why a forecast is still complicated only 2-3 out. We will have to continue to watch this system closely as it gets closer, but we may not know where the heaviest precipitation will fall until the storm arrives and we see where any bands of heavier precipitation set up.
Snow levels look to start around 8,000 feet Tuesday afternoon and could fall to 7,000 feet Tuesday night. The GFS model has them as low as 6,000 feet on Wednesday. If we do see a band of heavier precipitation set up over the lake, or some orographic enhancement on the east side of the lake, we could see accumulating snow on the mountains. The best chance to see more than a coating of snow would be on the east side of the lake where the computer-generated forecasts are showing up to 3-5 inches for the upper mountain for Mt. Rose down to Heavenly through Wednesday.
We will also see much colder air push into the area with and behind this system for the 2nd half of the week. Highs dropping into the 40s and lows in the 20s bringing much better snowmaking conditions.
High pressure builds back in starting Thursday and going into next weekend, but a bit off the coast and not as strong as this weekend. We may warm back into the low 50s next weekend at lake level, but not as warm as this weekend.
For the week of the 25th, the long-range models show weakening high pressure off the coast and shifting west slightly. That could allow a weak system or two to sneak in before the end of the month. But overall nothing showing up of any significance through the end of November right now.
Here is the total precipitation forecast from the GFS ensemble mean run through the 30th showing the heavy precipitation chances staying to our north in the Pacific NW and British Columbia.
Forecasts beyond 2 weeks (10 days really) are unreliable as the forecast models lose most of their accuracy. But it can be fun to look at some of the climate models and long-range forecasts that try to forecast the long-range pattern.
Looking at the CFSv2 model we can see it has a below-average precipitation forecast for northern CA week 1 and week 2 through the end of the month.
Then going into the first 2 weeks of December it shows average precipitation amounts possible the first week, and possibly above-average precipitation chances for the 2nd week of December.
But overall for December NOAA is forecast below-average precipitation for CA.
Then better chances for average precipitation as we go into January.
That would not be unlike last season. We did see some snow the last week of November last year, but below average for the month and below average again in December. By the end of December, we only recorded 57% of average snowfall. The first 2 weeks of January were also dry. By the 15th of January last season we were running at the 6th lowest snowfall totals for the date over the last 50 years.
It wasn't until January 16th and beyond that last season got going and we ended up above average for snowfall by the end of February. The overall pattern this season does suggest a bias towards below-average precipitation for northern CA. But we can have patterns that set up and drop big snowfall and change the season quickly. Will it wait until January again this season? Hopefully not. Let's hope we can get some decent storms starting in December.