We are in the middle of another snow drought here so it’s a good time to recap the January numbers. January was a warm month with below average precip despite the big snow the third week of the month. February is not looking much better so far.
I have not been writing as ofter as I laid out what I think could happen with the pattern this month and now I’m just waiting to see if the forecast models catch on. Even when I’m not writing I’m spending a lot of time everyday studying the pattern and watching the forecast models. The entire U.S. is quiet right now but something has to give with the above average snow and below average temps in other parts of the Northern Hemisphere. I would expect some major changes are coming to the U.S. pattern this month at some point.
I was riding this morning and thinking about how East Coasters in Tahoe must have the edge right now. Usually riding knee to waist deep snow is a skill you have to learn if you come to Tahoe, but riding hard pack and groomers everyday is something you learn in the East. I have never tuned my edges living in Tahoe as the snow is usually fresh or soft, but it may be time.
The only precip we really had in January was the rainy/snowy 5 day period during the third week of the month. We ended the month at 90% of average in the Tahoe basin for precip and 88% in the Truckee River basin. That brings us to 49% and 51% respectively on the water year. The snowpack ended the month at around 25% of the April 1st average. Temperatures ran at 2.9 degrees above average reported by the Truckee Airport reporting station.
I have been looking for answers to try and understand the season so far. Looking at the La Nina conditions they have begun to weaken. The Western equatorial Pacific has had strengthening La Nina conditions but the Eastern equatorial Pacific has been weakening faster. Currently the sea surface temperature departures are around -0.85 which is up from -1.0 earlier in January. The ONI which is the 3 month average was at -0.80 at the end of December. The new number comes out this week for January. A moderate La Nina is an ONI of -1.0 or higher.
That number is what the correlations are usually based on for La Nina strength vs. CA precip. At the end of last season it looked like we would have a weak La Nina this season and I immediately started saying we would have a below average season right through the summer. I think the very first guess at the snowfall for this season was 75-85 percent of average and that was based on history. Here is the precip anomaly for a weak La Nina based on the average since 1950. The orange is below average and green above average.
At the end of the summer the CFS Nino forecast showed it going super strong. I didn’t believe that but did believe moderate which is what it began to pull back towards in its forecast during the Fall. The precip anomaly for a moderate La Nina looks like this. No color is average precip.
La Ninas during a cold PDO tend to have a better chance of being above average. The PDO during its cold phase has colder than avarage water temps in the Eastern Pacific North of the equator. I went over research done on this in a post during the Fall. Here is the anomaly from that research for La Ninas during a cold PDO showing above average precip in black.
I took that and added it to the moderate La Nina forecast and came up with 95-100% precip forecast for the seasona and 105% snowfall based on the extra cold and snow fluff factor. That cold hasn’t made it much further South than Alaska where they just had one of the coldest Januarys in history. That is most likely due to the positive Arctic Oscillation we had until recently that tends to keep the cold and arctic jet to the North with the strong polar vortex.
With the ONI at only -0.80 at the end of December and now weakening it looks like we may not get to moderate with the La Nina this season. Here is the forecast going forward.
There are lots of factors that could be leading to the dismal season but the fact that it looks like we will stay in a weak La Nina would correlate us with below average precip. Last season we had a strongly moderate La Nina tetering on strong with an ONI of -1.4. -1.5 is strong. It was also a cold PDO phase. Here is what the precipitation anomaly is for a strong La Nina.
There is a nice looking storm heading our way for Tuesday but it will fall apart as it comes onshore and hits the ridge. The models are in better agreement now and they have the storm weakening and splitting with the Southern piece going South into the Baja. We should see a little light snow especially along the crest but not more han a couple inches.
Next weekend there is some agreement that the ridge will setup out around 140w off othe coast of CA allowing storms to return to the Pacific NW. The Euro has the ridge a bit closer to 150w allowing a cold and snowy pattern to setup with storm down the coast then into CA.
I do still think we could see the storms begin to come into CA by mid-month. We also have to keep watching the MJO as it is now in phase 7 and forecasted into phase 8. That could mean the subtropical jet breaks into CA week 2 and is not yet being picked up by the models. Until then make the best of the groomers and hard pack. I’ll be all over the first sign of a good storm, stay tuned…BA
Yes I’m watching the Super Bowl but it’s a team that is the rival of my team vs. a team that always wins so looking for the next big dump took precedence.
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