Atmospheric River…One Of The Toughest Forecasts In Tahoe

There’s growing confidence that something is about to change with our weather, and every time we look, it’s sooner and sooner. That means that we can be pretty confident in the forecast. One indication that the event is fairly certain is when the weather forecasters start putting specific numbers down for precipitation. It’s kind of like a card player keeping their cards close to their chest, with everyone waiting for what the other guy says. People started laying down their cards today.

Focusing on Thursday’s main event, here’s the numbers for Alpine Meadows:

• Reno NOAA: 4-8 inches of snow at mid mountain
• BA at OpenSnow: Reduced his number from 8-18 inches to 8 inches at 7000 feet
• Weather Geek at TahoeLoco.com: Calls for 1-2 feet at 8000 feet and smaller amounts at lower elevations
• Paul at TahoeWeatherBlog.com: Paging Paul….

Now those numbers are a far cry from some of the other numbers we have heard this week. That number can still go up or down, and it will be very difficult to say until it happens. Welcome to the forecasters world of the “atmospheric river”, which is the currently the in vogue term for a “pineapple express”. Maybe forecasters don’t want people to confuse their forecast with the 2008 stoner action comedy “Pineapple Express”.

We covered this topic back in late November. The atmospheric river represents a lot of moisture being pulled up from the tropics, often Hawaii. This flow is often quite warm. We get some great storms when it gets pulled into a cold front arriving from Alaska. If the front moves slow and we stay on the south side of the jet, we get hosed, literally. If the front pushes through and we end up on the cold north side of the jet, we can get massive amounts of snow. The problem lies in that 100 miles of movement in the wrong direction can be the difference between happy times and disappointment city.

Here’s the latest run of the GFS for Thursday. In this model run, Tahoe keeps on the southern edge of the jet, which would lead to a tendency toward higher snow levels.  We hope that changes over the next two days. The NAM shows the system losing the tropical tap by Thursday. The Ensemble also keeps Tahoe at the southern edge.

In this scenario, lower level resorts would not benefit much from this storm. Northstar and Squaw Valley could experience more rain than snow at the bases, with Alpine Meadows only slightly better. Mount Rose stands to gain the most, with a much higher base elevation. Bear Valley and Kirkwood also have the elevation but are possibly too far south to catch much snow before the ridge builds back in.

The Reno NOAA office did a nice summary of the situation via Youtube today. Note the emphasis on low confidence in snow amounts due to the difficulty of pinpointing the exact location of the cold front. Expect that this forecast may change again in the next 24 hours.