Tahoe Daily Snow

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By Bryan Allegretto, Forecaster Posted 6 years ago January 27, 2018

What's Next?...

Update

Ok, so we finally got a few weeks of storms starting on January 4th and ending yesterday.  They started weak and ended moderate in the past week.  They started with high snow levels and ended with the coldest and strongest storm.  In total we saw 2-4 feet of new snow on the upper mountains.  For the ski resorts to the South side of the lake that is more than November, for the North side November is still the snowiest month this season for most.

season totals

We finally had 5 ski resorts on the North side break 100 inches for the season this week.  It's the taller ski resorts on the North side that got a head start in November on the upper mountains above 8,000 feet during the warm storms.  We actually ended November with several ski resorts above average for snowfall on the upper mountains.

Then we had a dry December and a wetter but still below average January for total precipitation and snowfall.  Below is a chart showing the stats of where we stand so far.  I don't have the final numbers for January from the Central Sierra Snow Lab, so for snowfall I used the average of the ski resort reports above, and total precipitation I used the 8-station Northern Sierra Index from the CDEC.

stats

You can see that we are only 43% of the way through an average season so far, so still plenty of Winter left, more than half a season!  The upper mountains are at around 48% of average snowfall YTD.  Meanwhile for total precip we are closer to 73% of average.  So you can see the variance caused by lots of warmer storms this season. 

Below that the variance is even greater.  Guessing the snowfall at the Central Sierra Snow Lab for January, I would say we will be around 31% of YTD average by the end of January.  The snow lab sits just below 7,000 feet.

Thanks to 2-3 feet of colder snow in the past week from 3 storms, the conditions on the mountains are pretty good considering the lack of snow.  They have also been able to make a lot of snow with the colder air this month.

What's Next?

Starting tomorrow we look to have at least a week of sunny weather with highs in the 40's on the upper mountains and 50's at lake level.

We are transitioning back towards a pattern that looks similar to December.  We have high pressure building off the West Coast that could anchor there for a couple weeks, and cold trough that could dig in over the East again.  Here is the GFS ensemble mean height forecast and anomaly for February 12th.

ridge

Some of the forecast models show a negative EPO (eastern pacific oscillation) pattern, which would have the highest pressures further North over Alaska.  A lot of people are talking about how strong the MJO is forecast to be as it moves through the Western Pacific.  While moving into phase 6 & 7 can help to build a ridge and bring drier weather to the West Coast, as it moves into phases 8 & 1 we can see an extension of the East Asian jet stream towards the West Coast Sometimes that will cause an AR event for the West Coast with heavy precip as the jet stream cuts under the ridge to the North.

But this year we have a La Nina along the equator with colder than average sea surface temps.  As the MJO encounters that colder water it weakens considerably as it moves into phases 8 & 1.

ssts

We saw that happen in December and we didn't see any change in the dry pattern as the MJO moved through the Western Pacific.  This time it is much stronger moving into the Western Pacific.  So many are hopeful we could see an extension of the jet stream towards the West Coast mid-month.  But the forecast sees it dying again when it hits the cold water. 

mjo

The other difference to December is that the La Nina has weakened and the water is not as cold along the equator.  So could the MJO activity survive moving through the Pacific with how strong it is and with the water not as cold?  Who knows we can just wait and see.  If there is no effect on the pattern other than building a ridge near the West Coast, we could be in for several weeks of dry weather.

Here is the 10 day precip forecast off the Euro this morning.

euro

The GFS has several runs showing and the Euro had some too, where the ridge shifts towards the Gulf of Alaska by next weekend.  That could help to drive some colder air South into CA around next Sunday-Monday.  It could also bring some light snow with the cold front.  That seems to be our best chance for snow the next 10 days.  You can see some precip showing up on the 10 day GFS forecast.

gfs

So do we see the ridge shift NW a bit next weekend allowing for some colder air and light snows the following week?  Do we see the jet stream break into CA mid-month?  Or do we see the ridge just sit near the West Coast with several weeks of dry weather?  We will continue to watch the trend on the models.  It could go either way, but it won't be easy to get significant snow into CA with the overall pattern of ridge in the West and trough in the East through February.

Looking at the current weak La Nina, the negative/East QBO (quasi biennial oscillation), and the warm PDO (pacific decadal oscillation), we can look back at the last 70 years to see what other seasons were like.  

Weak La Nina - The 11 weak La Nina's as a whole have historically brought average snowfall to the Snow Lab in Soda Springs when averaged together.  We have a low end of 56% of average snowfall, and a high end of 146% of average snowfall.

Warm PDO -  Warm PDO's on their own have historically brought 90% of average snowfall, versus 101% in a cold PDO phase.  But mix warm PDO conditions with a weak La Nina, and we average 103% of average snowfall, versus only 97% of average in a cold PDO.  We have a low end season of 84% of average snowfall, and high end of 140% (16/17 season).

East QBO -   This could have the most significant effect on the pattern so far this Winter.  I have read some other forecasters that have attributed a lot of the dry season to this.  During East QBO winters as a whole, we have seen 94% of average snowfall versus 99% in a West QBO.  Throw that in with a weak La Nina and a warm PDO and we historically have seen only 94% of average snowfall.

8 of 11 weak La Nina's have had an East QBO phase.  Of the 3 that had a West QBO phase, 2 of those were in a cold PDO.  The only season since 1950 with a weak La Nina with a West QBO and warm PDO was last season, where we saw 140% of average snowfall.  So the QBO seems to be one of the biggest differences to last season.  So maybe our key to a snowy weak La Nina season is a warm PDO and West QBO, not East.

That's the stats for today.  I most likely won't post tomorrow with the stagnant forecast for the next week.  But I'll update on the long-range Monday, and try to find some more fun stats to look at while we await the return of Winter.

Stay tuned...BA

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About Our Forecaster

Bryan Allegretto

Forecaster

Bryan Allegretto has been writing insightful posts about snow storms for over the last 15 years and is known as Tahoe's go-to snow forecaster. BA grew up in south Jersey, surfing, snowboarding, and chasing down the storms creating the epic conditions for both.

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