Tahoe Daily Snow

Monday Morning Powder...

Summary

- We have a break in the storms on Saturday with some sun and breezy winds. Highs in the 40's with upper mountain wind gusts to 40 mph. Sunday the clouds and winds increase ahead of the next storm. - The next storm moves in Sunday evening and lasts into Monday morning. We could see 3-11 inches of snow on the mountains by midday Monday. - High pressure builds in quickly behind the storm bring dry and mild weather for the rest of the week. Highs will be in the 40's on the upper mountains and near 50 at lake level Tuesday through Friday. - In the long-range, it looks like storms could return between the 23rd - 26th through the end of the month.

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Short Term Forecast

All eyes are on the Sunday night storm as it will be the first measurable snowfall in 11 days, and there is a week of dry weather behind it.  It's the main event of the week, so let's over-analyze it this morning as I know you love to do!

Saturday/Sunday:

We saw wind gusts on the ridges up to 117 mph yesterday!  That did shut down lifts on the mountains.  Those gusts have come down to 50 mph this morning and should come down to 30-40 mph today.  We should have clouds and sun into Sunday morning with highs into the 40's.  Sunday the winds increase again so watch for lift issues.

The Storm:

The latest model runs show snow showers arriving as early as 4 PM on Sunday, but the heaviest snowfall is between 10 PM to 6 AM.  Then the storm moves out by Monday afternoon.

The trend the last 3 days has been slightly wetter.  Even with the GFS model trending drier yesterday it has come back wetter again this morning.  This trend, however, is an increase in the average model precipitation of around a tenth of an inch per day.  That has been adding about an inch to the forecast the last 3 days, not a foot.

The storm looks pretty impressive on satellite this morning.  This is the way a storm usually looks that will bring us significant snowfall.

satellite

But we have seen good looking storms all week move into the West Coast and fall apart by the time they reach us.  Yesterday was another example where a band of heavy rain pushed into NW CA and completely dried up by the time it reached Tahoe.  The wettest forecast models had an inch or two of snow for Donner Summit and we saw nothing.  So keep that in mind as this next storm moves in.

We have a high-pressure ridge over the Western U.S. that these storms are running into.  Sunday night into Monday we also have high-pressure building in from the South.  The difference with this storm is that it is the strongest of the week and pulling in a lot of moisture.  So it's a battle as it pushes through CA.  But it will be weakening and splitting apart by Monday, and the southerly flow is not good for pushing precip over the crest.  So the question is how much moisture can it push in over Tahoe.

gfs

This morning we have the NAM model showing a high end of 1.2 inches of liquid west of the lake along the crest...

nam

The Canadian model is the driest showing only up to 4 tenths of an inch along the crest and less as you go east across the basin.

canadian

You can see that they are both bringing a similar amount of heavy precip over Northern CA, but completely different amounts are being pushed over the Tahoe basin.  These two models are the outliers and are not being used in my snowfall forecast.  They are averaged into the model average though, which has increased from a high end of 0.71 inches of liquid yesterday to 0.81 inches of liquid today.

The GFS and European ensemble mean runs both show up to 0.80 inches of liquid, right in line with the model average.  The European and GFS operational runs used in the snowfall forecast show up to 0.80 - 0.90 inches of liquid with an average of 0.85 inches on the crest.  Close to the model average. 

I like the trend of increasing the average a tenth each day, but I'm not buying into the NAM showing over an inch of liquid yet.  This storm has the potential to push in more moisture than the models are showing and we get more than forecast.  But the way the storms have been splitting apart over CA all week, it also has the potential to bring the low end as well.

Here is the updated snowfall forecast showing a low end of 3 inches on the east side of the lake on the mountains, up to 11 inches on the highest peaks on the west side of the lake.  Snow levels look to be around 6,000 feet Sunday night falling to 5,500 feet by Monday morning.

snowfall forecast

If the trend continues tomorrow, we could add another inch pushing the high end up to a foot.  I wouldn't be shocked if a mountain NW of the lake hit a foot if the forecast holds.  But I'm trying to stick to the model average and technique I've used over the last 13 years.  I also show my score the day after the storm, showing the actual versus the predicted amounts, so nothing to hide here.  

NWS Offices:

The Northern Sierra forecasts are split between two NWS offices.  To the west side of the crest it's the Sacramento office, and from the crest east to NV it's the Reno office.  I wanted to try and help you understand why the two offices have different forecasts and advisories.

As an example, the NWS Sacramento put out a Winter Storm Watch yesterday for their zone for 10-18 inches of snow with up to 24 inches.  That prompted some local media around the lake to put out articles claiming up to 2 feet of snow was coming to Tahoe.  But the NWS office in Sacramento doesn't forecast for Tahoe.  The NWS Reno does, and they have no advisories issued.  Looking closer, the highest snowfall forecast I could find from the NWS Reno was up to 13 inches NW of the lake along the crest near the top of Squaw.

This morning I took the WPC total precipitation forecast for the storm and zoomed in to show you what I'm talking about.  I put a straight black line from north to south down the Sierra crest to show the dividing line between the two forecast offices. 

wpc

I circled in black the heavy precip on the west slope from Mt. Lassen down to Tahoe.  That is where they have a Winter Storm Watch for 10-18 inches up to 24 inches above 5,000 feet.  The 24 inches is for Mt. Lassen where I put a triangle on the north end of the circle.  I also put one up near Mt. Shasta where over 3 feet of snow could fall.  Sugar Bowl, Sierra, and Kirkwood fall right on the eastern edge of their forecast zone where the lowest amounts of precip are forecast.

In red I made a circle that shows where most of the ski resorts sit.  You can see it has greens and blues, not yellows and oranges.  So the forecast would be from the low end of the Sac office forecast and lower.  So 12 inches or less as you go east.  The NWS Sacramento advisories are really important because they cover the heaviest snowfall areas of I-80 and 50, the two major routes into the Tahoe area.  So you will have to drive through that heavy snowfall.  But the NWS Reno covers most of the ski resorts which are east of the crest around the lake and east of the Sacramento office zone.

This why my forecast and the NWS Reno office forecasts are much lower for the ski resorts and Tahoe basin than the Watch put out yesterday by the Sacramento office for the Sierra.  You have to be careful of that with each storm, or you will be disappointed in the snowfall amounts around the lake.  I break down the forecast even further and pinpoint the amounts at each elevation for each mountain using my own techniques.

Extended Forecast

High pressure builds in quickly behind the storm bringing dry weather and mild temps into next weekend.  The ridge looks a little dirtier next weekend as it weakens and we could see some clouds from storms moving through to the north.

The long-range ensemble mean runs still agree we could see a pattern change around Christmas with the ridge shifting off the coast opening the storm door.

storm door

The majority of the long-range models now point towards a negative PNA pattern the last week of the month.

pna line

PNA map

The EPO forecast is towards positive as well.  So that trough on the image above would be centered more over the West Coast with the high north of Hawaii not as far north.  That could bring colder air and storms from around Christmas through the end of the month. 

The GFS model runs bring in the first storm around the 26th.  The European model runs show a nice storm Christmas Eve laying a carpet of white ahead of Santa's sleigh.

Stay tuned...BA

P.S.  The beard is getting pretty long.  I started it in July on the RV trip to the National Parks.  I was thinking that I would wait for a mountain to report 3 feet in 24 hours this season, and then shave it off.  What do you think?

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