Storm Update:

The first real storm of the season moved through yesterday afternoon and overnight. Low pressure is still spinning over the area this morning.

The center of the low pressure dropped to the lowest recorded level for CA as it moved in over Crescent City last night.

It pushed a cold front through during the evening that brought is heavy snow across the Tahoe Basin. We saw road closures pretty quickly due to accidents. I-80 west was closed again this morning. For 24 hour snowfall, we have reports so far of 6-14 inches at lake level, and the ski resorts are reporting 10-22 inches as of early this morning.

That is around 5-8 inches less than the range we were expecting for the first 24 hours of the storm (15-30 inches). The GFS and NAM models may have been a little too wet. Temps did come up a little ahead of the front lower snow ratios during the evening, and maybe a little windblown up high too.

Looking at the snotel sensors near the ski resorts along the crest there was around 2 inches of total precip, at 12:1 that would be 24 inches of snow. The Snow Lab sensor is showing 26 inches on the ground. I'll have the "forecast-actual variance" report out after the storm on Friday.

We have snow showers firing up behind the front this morning. That will continue throughout the day. It also looks like some lake enhanced bands possibly forming northeast of the lake which I circled in red.

The Rest of the Storm:

The snow showers will be more scattered east of the west side of the lake, with breaks of sun. The steadier snow showers along the crest should become more scattered Wednesday night into Thursday. The forecast models show scattered showers possibly lingering into Thursday night, then clearing for Friday.

The average of the latest models shows an additional 3/4 of an inch of precipitation along the crest by Friday. Similar to what the latest NAM model runs is showing.

Snow levels are 3,000 feet or lower and snow ratios are high in the 15-20:1 range. That will bring some fluffy accumulations wherever the snow showers fall. Here is the updated snowfall forecast for Wed - Thu.

Most of that falls by Thursday morning, with a dusting up to 3 inches possible Thursday depending on where snow showers fall. The wild card is the lake effect snow bands northeast of the lake that could boost snowfall amounts near Mt. Rose. That should diminish Thursday.

The winds were still gusting to 60+ mph this morning from the southwest. They will come down through the day on Wednesday.

We will see much lighter winds for Thursday and Friday. Highs only in the 20s through Friday with overnight lows in the teens. That will keep the resorts making snow around the clock on top of the fresh snow.

The Weekend Storm:

By Saturday the next storm is off the coast, and it is a cold day again here in the Tahoe Basin. Highs only in the 20s. 

This will be a much warmer storm as it draws in subtropical moisture and aims a small AR (atmospheric river) at CA. That will push in moderate-heavy precipitation by later Saturday, with the storm possibly lasting into Monday. There are differences in the models on how long the storm lasts, how high the snow levels rise, and how much total precipitation we could see. All making for a complicated forecast.

The latest trend on the models is to delay the onset of the precipitation until Saturday afternoon or evening. Initially, the forecast models show the AR pointed to our south. Then Saturday night through Monday as the storm spins off the coast the stream lifts from south to north taking direct aim at Tahoe at some point and then lifting out of the area. This process will also continue to push in warmer air through the 3 day period.

The Canadian model has the moisture lifting out of the area by Sunday evening, while the GFS and European model runs don't lift it out until Monday evening. Just that will make for big precipitation differences. Most of the ensemble mean models and deterministic models show 3-4 inches of additional precipitation near the crest from Saturday - Monday, on top of the lighter precip through Wed-Thu.

The GFS model shows up to 6 inches, so I threw that out this morning so it doesn't push up the snowfall forecast.

The snow levels are the tricky part of this forecast. The models are showing warmer air this morning. There is stubborn cold air in place to start, so snow levels should stay near to below lake level at the start Saturday night. Then the warm air should start to erode that away Sunday. The GFS model shows snow levels rising to around 6,500 feet Sunday into Monday. The Euro shows snow levels rising to 7,500 feet. I took the average and assumed 7,000 feet in the updated snowfall forecast.

The forecast is down some today due to eliminating the wetter GFS model, due to higher snow levels and lower snow ratios, and due to a change to rain below 7k.

This is still a lot of precipitation that could fall, and we could see high amounts like the GFS is showing. Below 7k it looks like a mess with several inches of snow Saturday night changing to rain Sunday. Above 7k on the upper mountains, this could bring the base building snow we need. 

Winds could be gusty through the weekend as well. Increasing with gusts to 50 mph Saturday into Sunday on the upper mountains.

We will have to continue to fine-tune the details as we get closer.

We should see a break next Tuesday. The forecast models are at odds with what happens to the low off the coast. Some show it moving in on Wednesday bringing more rain and snow, while others show it moving into southern CA and giving us a break Tue-Wed.

Then another storm is shown upstream that could move into the West Coast next Thursday-Friday bringing more precipitation to California.

Going into the 2nd week of December some of the models, like the GFS ensemble mean model, show a large trough in the Gulf of Alaska with the active pattern continuing for the West Coast.

Others, like the Canadian ensemble mean model, show the trough a bit farther west with a ridge building over the West.

The difference would make a big difference in whether or not the storm track stays south into CA or shifts north for the 2nd week of December.

Plenty to deal with in the meantime, and I'm off to have an early Thanksgiving meal with family today.

Stay tuned...BA

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