For the past week we have been talking about a pattern change to cold and light snow around the 3rd with possibly some bigger storms behind that. That is still in the cards but some interesting developments the last 24 hours.
High pressure is still forecast to develop over Southern Alaska this weekend which will help to drive the coldest air of the season into the Western U.S. The question when a large trough is digging into the West is how far West will it dig. If it stays over land we just get colder air and maybe some light snow which is what it has looked like on the forecast models for the past week. Over the past 24 hours the models have been digging the trough further and further West out off the West Coast. That allows it to pick up moisture from the Pacific and throw it back into the cold air.
These setups if they setup just right can produce a lot of fluffy snow of the Sierra. We are still about 6 days away so we have to keep watching how this develops, but let's take a quick look at what the forecast models are trending towards and what it could mean next week.
The cold front is forecast to move through sometime next Monday with some light snow, and then low pressure developing just off the coast drawing in moisture off the ocean into the cold air for a few days. The Canadian and European forecast models show a 3 day event with low pressure slowly working down the coast and then inland. The GFS forecast model suggests a second area of low pressure following the first and keeping the snow going through the week.
The total precipitation forecast for the week is currently around 1-2 inches of liquid. What makes this whole setup interesting and worth watching is that the forecast models tend to under forecast the total precip on these systems, and with air as cold as what is coming the snow:water ratios would be really high. As an example: the European forecast model's total snowfall forecast is showing 1-2 feet of snow over the Tahoe Basin next week. It assumes a 10:1 snowfall ratio, but with the amount of cold air that is coming down from Canada we could see 20:1 snowfall ratios which would mean double the amount of snow for the mountain.
When the forecast models begin to trend towards a scenario like this I like to look at as many runs as possible and not jump the gun. After looking at around 16 runs in a row I would say that the chances for snow next week continue to look promising. Still being a week out I wouldn't get overly excited yet as there is still time for things to change. The colder air and at least some snow falling from the sky look to be certain next week. The potential snowfall amounts will be something we have to monitor daily.