Tahoe Daily Snow

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By Bryan Allegretto, Forecaster Posted 6 years ago December 14, 2017

Last Day of the Western Ridge?...

Summary

Sunny and mild through Friday with highs in the 50's and lows in the 20's with inversions leading to lows only in the 30's on the mountains. Winds are a little gusty this morning up high but should come down a bit this afternoon. Friday night into Saturday morning a cold front moves through. That will lower high temperatures for the weekend to highs in the low 40's at lake level, and 30's on the upper mountains. Overnight lows will drop into the 20's for all elevations Saturday night. Next week we may warm back into the 40's on the mountains and near 50 at lake level on Monday and Tuesday. Then another cold front moves through from the North Wednesday bringing colder air again. This time we could see some light snowfall accumulations with the cold front. The cold air may hang around this time right through Christmas with high temperatures near to below average. We could see more dry systems move through and try to bring light snow. We are still watching to see if some wetter storms can break into CA by the end of the month.

Short Term Forecast

The good news today is that the pattern will finally begin to change Friday after being stuck with a large area of high pressure over the West the last 10 days.

current ridge

The ridge of high pressure is going to reform off the coast this weekend which will help a cold trough to drop in from the North.  The trend on the models has been for the trough to dig a little further West over the area instead of to our East.  That is why the temperature forecast is getting colder for the weekend, and now we have a chance for a few snow flurries Friday night into Saturday morning.

Still, it is not a deep trough and won't back far enough West to pull in any moisture off the ocean.

weekend trough

Here is a look at the meager precip forecast.

gfs precip this weekend

At least it will be nice to see a pattern change to colder and maybe some flakes in the air.

High pressure builds in over the Northeast Pacific into next week.  That is a position that should help another cold trough to dig down from the North on Wednesday.  We have been talking about this one for a while now as the first chance to break the dry spell.  The forecast models have been all over the place the past week with the track of the trough as it moves South.  That has been causing forecasts for no snow or moderate snow among the runs.

We have been using the ensemble mean runs of the models to try and cutout the outlier forecasts.  It seems to be working because now that we are within a week we can look at the operational model runs, and they are starting to agree with what we were seeing on the ensemble mean runs.  A consensus that the trough may dig right down the Sierra bringing colder air and the possibility of some light snowfall.

Here is the latest GFS model forecast for total precip for next Wednesday.

gfs next wed

The European model...

euro next week

The Canadian...

canadian next wed

Here is the WPC's model forecast which looks at I believe 47 different model runs now.  In the latest discussion I believe they said they were cutting it down from 71 to 47 in an effort to cut out the least accurate models after looking at verification after storms.  So unlike the ensemble mean runs of the models that take the average of all of their own model members, the WPC is pulling in all different models that they believe to be the most accurate. 

wpc forecast

Tomorrow we will be in the 5 day window so I will start to put out a snowfall forecast if the current model runs that show precip hold.  A quick glance at the average of the above model runs would be 1-4 inches of snow.  The good news is that the model runs are all starting to agree as we get closer.

If the dry spell is broken next Wednesday that would cap the dry spell at 16 days.  Here is a look a the record Winter dry spells as a comparison, so you can see this is not that long of dry spell if it ends.

dry spells

Extended Forecast

The forecast for the area of high pressure in the Northeast Pacific to shift towards Alaska the last week of the month is not changing, but what is changing is the GFS (top) and European (bottom) ensemble models keeping the trough int the West after next Wednesday.  The trend has been to keep a over the West through Christmas with a ridge building over the Southeast.

gfs christmas

eps christmas

If that happens and the strong high pressure is in the Gulf of Alaska as shown, that could really drive some cold air into the West for the weekend of the 23rd and into Christmas Day.  The GFS ensemble control run really drives us into the freezer.

cold

You could then see systems dive into the trough and try to bring light snow which is what some model runs are showing, and if they dig West off the coast and pick up Pacific moisture that gets even more interesting.  Let's not get the cart ahead of the horse yet though.  Let's just stop at the trend is for a pattern that could possibly bring and hold cold over the West starting next Wednesday.  

With the strong high pressure centered up near Alaska the last week of the month we have been talking about the possibility of storms breaking underneath into CA the last week of the month.  We continue to show some model runs showing that and others keeping us dry.  Looking at the latest ensemble member runs of the GFS we have increased from 30% to 40% of the members showing this happening by the end of the month.  So at least we are trending the right direction. 

Here is a look at the GFS ensemble mean run through the 29th.

gfs ens mean eom

Here is the European ensemble mean run...

euro ens mean eom

With the pattern that is forecast to setup it is still giving us hope for snow the last week of the month.  The odds are still against us, but lots of interesting things happening in the long-range with the pattern.  So we will continue to watch with hope.  There is plenty of potential for surprises!

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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