Tuesday, December 15, 2009

A Mouthful.........

After 7+ feet of snow on Northstar in the past week, the weather pattern is going to start to slow down for a while.

Ridge continues to build after the storm with warmer temps into the 40's Wed.-Sat. Next storm associated with some colder air from the North tries to move in around Monday. Not looking too impressive at the moment, but it should bring in colder air to start next week. Meanwhile, the jet is strengthening over the Pacific with increased increased tropical convection in the equatorial Pacific thanks to El Nino. MJO has emerged in phase 4 and forecast to slowly strengthen and move East. Current thinking is that the forecast for strengthening could be the models catching on to affects from El Nino as well. This could be dejavu of the past week with another period of heavy snowfall starting sometime around Christmas or Christmas weekend.

Some people have been asking the status of El Nino since I don't talk about it like I did in the summer and fall. Then, I was looking at analogs to come up with theories on the upcoming winter. Basically I was looking for the conditions in the past that were most closed related to this year to see how the following winter panned out. In the summer I was hoping for a repeat of the huge winter of 1951-52. We had an overall cold PDO with a la nina the winter before and a weak el nino that faded out by Feb. Moving away from that year now because the current El Nino conditions are moderate as of this month with an ONI of 1.2, and although forecasted to peak this month, are forecasted to last into the summer. In 1951 it only reached .8 in Nov. before fading out and the PDO went way negative in January.

The closer years now are 68-69 and 94-95. In 68-69 ONI peaked at 1.0 in Feb. & March before fading into the summer, with a PDO right where we are now in Nov. at -.4 and then heading below -1 by Jan. This was an above avg. snow year with 50 feet of snow on Donner Summit. 94-95 didn't have a la nina the year before and an overall cold PDO the few years prior, but is the only year with a moderate strength El Nino during a negative PDO like we have now. That year peaked at 1.3 in Feb. before fading out in May. That was another 50 foot year on Donner Summer.

Looking at the below avg. precip during weak and moderate El Nino years they were during warm PDO years with the exception of 63-64, but that year the El Nino conditions faded out by March. Analogs are not great forecasting tools because of the short span of records over the past 60 years, but they are fun to play around with when looking for what could happen when these conditions happen. Lots of talk around Tahoe about how the start of this winter compares back to 94-95. We'll just have to wait and see.....BA

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