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Update 6:00 PM
Snow levels were up around 9000 ft around 1:00 this afternoon, but temperatures have slowly been falling ever since. I had reports to 8000 ft at around 4:00 pm, and then I got a surprise at 4:30 when I was told it was already snowing on Donner Summit at 7k. That is over 1000 feet lower than expected for this evening. Forecast models have been wrong before about the timing of cold air moving in. Snow level could still rise a little this evening, but we are still expecting more cold air moving in tonight.
If snow levels stay lower than expected tonight, then we would have to increase the snowfall forecast back to what I had yesterday at 7000 and 8000 ft. We will keep an eye on this all night as wherever the snow level sits will make a huge difference in the snowfall totals with all this moisture.
It is snowing to the base of Mt. Rose, Sugar Bowl, and Boreal this evening, and it should be getting close to the base at Alpine.
From This Morning
Precipitation has started moving into the area this morning. With the dry air in place over the area we did see the wet-bulb effect to start this morning as the initial moisture evaporated dropping temps and snow levels below 7000 feet briefly. Now that the air is becoming saturated the temps and snow levels are headed back up.
So what has changed in 24 hours? The GFS, NAM, and WPC models have become much wetter with up to 6 inches of liquid near the crest. The European, Euro EPS, and Canadian models are still at up to 4 inches of liquid. So now we have a 2 inch variance as the storm is starting...
See the nice 11 inch bullseye to our NW on the GFS?! It looks like the GFS and the other wetter models are keeping the warm atmospheric rive moisture over the area longer before the cold front pushes it South tomorrow. It's interesting to see a big change on half the models right as the storm is starting. The GFS also has the Southern edge of the heavy precip today a little further South near Tahoe on the latest run, which seems to be the case looking at the radar.
So who is right? The European and others who bring in the cold front faster and have less total precip, or the GFS and others that are slower and wetter? Nobody knows...
Take a look at the freezing level forecast on the GFS yesterday for 10 a.m. tomorrow (top), and on today's run (bottom)
You can see how the 8k freezing level is across the lake on yesterday's run, and well NW of the lake on today's run. The 7k line yesterday was right behind it near Donner Summit as cold air is moving in. Today it is up near Lassen. When colder air is moving in like that the snow level can be 1,000 feet below the freezing level, or lower when it's snowing hard. So yesterday snow levels are 7,000 feet by tomorrow mid-morning and falling towards lake level. Today they are at 8,000 feet still mid-morning tomorrow.
If the GFS and other warmer wetter models are correct that would affect the snowfall below 9000 feet, and especially below 8000 feet. The GFS could be suggesting snow levels stay near 9000 feet today through tonight falling to 8000 feet tomorrow morning, and then staying there most of tomorrow before crashing below lake level during the evening as the storm is winding down.
For my snowfall forecasts I average the models for the total precip, but normally for temperatures I use the GFS model. That should make the final snowfall forecast conservative, especially if the snow levels are lower. So after several days of the 8000 foot snowfall forecast holding steady, I may be going in the opposite direction of other forecasts today in lowering that forecast based on snow levels possibly being above 8k tonight during the heaviest precip.
You can see that the all of the forecasts below 9k have come down today with the possibility of the longer duration of warm air, but that the 9k forecast has not changed. This storm has been tricky all week and the last minute change on half of the models this morning is just adding to the headache. I think now all we can do it nowcast as the storm happens over the next 36 hours. Snow levels could sit down to 8k tonight with the heavy precip and then the snowfall would have to go back up from a forecast of 1-2 feet back up to 2-3 feet.
I plan to be out on the mountains tonight and tomorrow monitoring and posting updates over social media. Be sure you are following the TahoeWeather Facebook, Twitter, and Instagram pages to follow along.
It should be a nice weekend with temperatures warming into the 40's on the mountains and 50's at lake level.
Looking at the Monday storm the GFS is now looking more like the European model with a splitting trough and a colder and drier storm possibly brushing the area as it moves through to our North. The European model is still opening the door enough for a storm by Thanksgiving while the GFS keeps us dry next week.
P.S. This should be a nice start to the water year with all the liquid wit this storm over Northern CA!
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