Sunday, February 19, 2017

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Under the hose again

We've had a few small-to-moderate storms, for Sierra standards, over the past week that have led to continued fantastic snow sliding conditions. I don't need to tell you this, but the snow is getting deep. Here are a couple of shots from Alpine Meadows on last Friday, 2/17.

The next storm system is already beginning to impact the Sierra, and it will be another doozy. A strong jet, 150-170 knots at the core, will direct heavy precipitation and dangerous winds into the Sierra for several days...again.

Figure: 250mb winds (jet stream level) showing a powerful jet aimed at the northern Sierra. Forecast shown is for Sunday morning through Tuesday afternoon.

Heavy precipitation is all but guaranteed, but once again the snow levels will be the deciding factor in snow accumulations below about 7000 feet.

Figure: Total precipitation from GFS through early Thursday morning. There is a 6-10 inch bullseye over Tahoe and northern Sierra. Not good for the Oroville dam flooding concerns.

The storm will start cold enough for all snow in Tahoe, then some warm air creeps in, and then back to all snow during the end of the event. Snow levels could get up above 7500 feet for a short period, but heavy precipitation rates might allow for lower snow levels.

Figure: 700 mb (~10,000 feet) forecast Sunday morning through Tuesday afternoon from the NAM. The green shading (with red line) shows the 0 degree, or approximate freezing line. 

Forecast from the National Weather Service shows snow levels rising above Donner pass for a few hours on Monday.

Figure: Snow level forecast from the National Weather Service, Reno office.

By the end of the storm expect 4-6 FEET of snow above 7500 feet with several feet likely between 6500 and 7500 feet. Lake level snow will be tricky and depend how much (and fast) snow levels rise. Flooding, avalanches, and mudslides will once again all be a concern. Monday will likely be a don't go out there kind of day.

We will likely see several more small storms Wednesday through Friday that will be colder bringing a nice fresh coating on top of the massive pineapple pow that is on the way.

Be safe out there!


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