An atmospheric river will deliver serious moisture to California starting tonight and lasting through the weekend with snow levels starting at 6500′ before a cold front brings flakes down to 4,500′.
According to NOAA, the heaviest precipitation will occur on Friday during the day before a second wave of snow hits after nightfall. The cooling trend will begin in the early morning hours on Saturday.
“The trend over the past several model runs has been taking the deeper moisture farther south, which has led to increased storm total precipitation values in Mono Co.” – NWS Reno
While the upper elevations surrounding Tahoe should benefit from the storm, our sights are currently on Mammoth Mountain, Kirkwood, and June– al of whom boast a southern positioning that should account for higher precipitation totals that will also be accompanied by cooler temps.
LET IT SNOW!
Area Forecast Discussion [NWS Reno]
Dry and warmer conditions are expected today, though clouds will be abundant. Winds will begin to increase this afternoon, followed by a sharp change to a cooler and wetter pattern with periods of stronger winds Thursday through the weekend. The best chances for heavy rain and higher elevation snow are from late Thursday night into Saturday morning with a moderate atmospheric river. Additional weaker systems remain possible into next week.
SHORT TERM: Today through Saturday Night…
Weak ridging with abundant mid and high level clouds will be the main story today. Take this opportunity to prepare for the upcoming storm for the end of the week into the weekend. Another atmospheric river (AR) storm is headed our way late Thursday through Saturday and if anything the integrated water vapor transport detection tools have only continued to show it strengthening. While this storm is nothing like the monster storms we saw back in January and February, it is an unusually strong storm for April. Confidence is high for heavy precipitation late Thursday night through Saturday, but lower for snow levels and subsequently snow totals and flood potential.
*Here are the highlights with regards to this storm event:
Warm air advection Thursday ahead of the main storm will bring isolated areas of light rain, with the main AR moisture push coming Thursday night into Friday. The period for peak precipitation rates still looks to be on Friday, followed by a secondary wave Friday night. The trend over the past several model runs has been taking the deeper moisture farther south, which has led to increased storm total precipitation values in Mono Co. Rain and snow will turn more showery on Saturday in a cold and unstable atmosphere as the upper low shifts through the region. Overall, liquid precipitation totals haven`t changed much with 2-5 inches along the Sierra crest and 1-3 inches in the Tahoe Basin, eastern Sierra foothills, and northeast California. However, totals are now more likely to be on the higher end of the range for the southern Sierra. 0.5-1 inch is possible along the Sierra Front with lesser amounts into west central Nevada.
This will be the key to the forecast and is also where the greatest uncertainty lies. Snow levels look to start in the 6500-7500 foot range (lowest closer to the Oregon border), but the question lies in the Friday afternoon time frame. The shortwave that was causing the mid-level flow to turn more southerly during the time frame is not as pronounced in the latest forecast guidance.
While some warmer air is advected northward, it doesn’t appear to be quite as much of a warm nose in forecast soundings as what was present in yesterday`s model runs. In addition, snow level deviations among available guidance has dropped from 3000 feet to 1500 feet. However, this deviation can still make an appreciable difference in the forecast. The biggest potential variation in snow totals will be in the 6000-7500 foot range where there is less certainty in the heavier rounds of precipitation falling as rain or snow.
A cold front looks to shift through the region Friday night, which will take snow levels down to 4500-5500 feet by Saturday morning. A mix of rain and snow, or possibly even pellet showers will be likely on Saturday down to all valley floors.