Thursday, November 20, 2014

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Lil' Somethin' Better Than Nothin'

In the nouveau climate of enhanced aridity in the Sierra Nevada, we have become accustomed to long stretches of little to no precipitation during the cool season. Hopes are high that this season will buck that trend but the possibilities are wide ranging. That said, the recent storms, albeit weak, have provided much needed moisture for parched soils, dry vegetation, and empty reservoirs. Trail conditions could not be better at lower-mid elevations and many resorts are producing snow. The storm making its way into the Sierra this afternoon and another tomorrow (Friday) evening will continue to moisten soils and provide much-needed natural snow to augment snow-making efforts for Thanksgiving groomer runs.

Precipitation from today's event will begin during the early afternoon in the Sierra and continue into the evening. Snow levels will start around pass level and fall rapidly to 5500ft, possibly lower. Favorable orientation of lower and upper level winds will provide orographic and dynamic lifting. Total snowfall on the crest will be in the neighborhood of 8-10". Totals at 6k will be in the 4-8" range. These values are higher than the 3am NWS discussion, but I am using the most recent WRF and GFS simulations; perhaps they are more favorable.

The Friday evening-Saturday morning event will sing a different tune. Copious moisture provided by an errant tropical Pacific moisture plume will result in an enhanced positive moisture flux into northern California. However, the Sierra will be located under the warm sector of the jet stream and snow levels will be around 8k. Low-mid level wind are also oriented much less favorably for enhancing precipitation over the mountains. Therefore, at least 6" of sticky (GOOD!) snow can be expected with this event along the crest. If the jet migrates southward a few 100km, these totals could easily double. The WRF simulation is a bit bullish with over an inch of liquid precipitation for the northern Sierra, given the northwesterly 700mb flow, although the happy face side of the jet exit region does nose into Nevada County and will briefly provide a lifting mechanism. BUT! If it verifies, and we see a foot of rock hiding stump gobbling glop, nobody will be sad.

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