Sierra Forcasters will have a somewhat easier time with the forecasts the next few days as the precipitation that falls over the Mono County Area Friday and Saturday will certainly be all snow! Questions still remain about how much snow will fall as the system  itself  is currently pretty dry but will pick up moisture as it develops off shore. The QPF from California Rivers Forecast Center paints about an inch and a half over the crest by Saturday AM, giving the upper elevations a good 2 to 3 feet. This is considering the cold nature of the storm and the potential ratio of snow to water….. 20:1 to 25:1.  The big question remains about the possibility that this system may tap some deeper moisture from the central pacific Friday that would help boost QPF totals….hence this is still a very much developing storm that may prove to be a bigger precip producer for the high country than what the models are currently showing. Of course, if it does tap central pacific moisture, that may moisten the system up a bit with the ratios not quite as high as we currently expect.

What We Know:

1. A very deep upper low will form off the coast of Vancouver by Thursday Night

2.  This upper trof will then sag southward just off the coast of the Columbia River by early Thursday and continue to shift southward down the west coast through Saturday Morning. Deep layered onshore flow will exist in the mid and lower levels for a prolonged period of time….. and so what we will experience is really one big ocean type Lake Effect into the sierra beginning Thursday night into Friday afternoon. If the central pacific moisture gets tapped, that would be the bonus.  So again….A combination of onshore flow, UVM, orographics and strong upper jet dynamics will keep this a major storm to contend with. At the moment, a good 2 to 3 feet of snow is certainly possible by Saturday morning. Will update on the estimated amount of snowfall Thursday morning.

3. The other big issue here is the Arctic air dropping in over California from the north instead of back dooring us from the northeast. The new 12z WRF has -18C over Mammoth Mountain at 10,000 feet Saturday mid morning. That is -4 F. and temps in the town of Mammoth will probable be in the low single digits Saturday morning. Any wind at all will create a significant wind chill factor Saturday. Up slope conditions may develop Saturday afternoon into the evening.

4. The best part of this storm is that it is pure Western Canadian Born. In perspective, it is rare that Mammoth gets the potential for large amounts of snow at ratios of 20:1 to 25:1. Saturday for those that want to experience deep cold dry powder will want to have the right warmth for the elements. And  to experience the possibility,  of true Canadian type powder! 

Dr Howard and the Dweebs……………………….:-)

Reference Glossary of Weather Terms
Disclaimer: I have been a hobbyist meteorologist for over 30 years here in the Mammoth area and I do this for my personal enjoyment. The National Weather Service saves lives every day . . . I do not. When making important planning decisions please use information provided by the National Weather Service as they are the most knowledgeable and accurate information source available today.