Friday, February 14, 2014

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A Nice Weekend Topcoat

Don’t despair just yet Pow seekers. Despite the unseasonably mild temperatures that will persist into Saturday, a sizable cement base will endure from mid-mountain and up (~7500 ft). And Saturday night into Sunday features a promising opportunity for the remaining snowpack to receive a nice white topcoat. 

Late Saturday into Sunday a moderate snowfall is expected to blanket the northern Sierra, as an amplifying trough drops out of the Gulf of Alaska, with sufficient cold air, and plows into the Pacific Northwest (~ just south of the WA/OR border). In the immediate wake of this system, a moderate piece of trailing wave energy branches southward into the northern Sierra (Figure 1). At this time, it appears snow levels will drop fast Saturday night to Lake level yielding an estimate of 3-5” near the mountain base, 5-8” at mid-mountain, and 8-12” at the top with some isolated areas receiving 12”+ (Figure 2).

Figure 1 illustrating the large wave pushing into the Pacific NW with trailing shortwave energy headed toward the northern Sierra.

Figure 2 illustrating expected precipitation amounts from the weekend system.
Preceding and accompanying this system, strong jet dynamics aloft and moderate mid-level baroclinicity will tighten the low-level pressure gradient and create strong winds of 40-50 mph sustained with gusts exceeding 70 mph at times near the Crest. Downsloping winds on the leeside could be equally if not more impressive (Figure 3). As the main system works into the Pacific Northwest, the winds will ramp up quickly Saturday morning and rage most of the day prompting impressive leeward lenticulars. Rain showers are expected Saturday evening, but colder air will work in rapidly as the main energy arrives just before midnight (Figure 4). 

Figure 3 illustrating strong wind speeds along the northern Sierra, near Lake Tahoe, and on the leeward side.
Figure 4 illustrating the cold air advection, relative humidity, and tightening pressure gradient just before midnight on Saturday.
Figure 5 depicting column precipitable
water and the subtropical plume associated
with the Saturday night event. 

Although the infusion of the cold air is impressive given the mild state ahead of this system, like the previous storm, this event will have a subtropical connection reducing the fluff factor (Figure 5). 

Things should taper off quickly Sunday morning perhaps offering a Sunday afternoon for Pow and fresh tracks. Take advantage!

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