Not much change in the overall forecast this morning for the short term with a warm and wet storm moving in this week.  Most changes are in the long-term.  We have a lot of details that are changing daily that we need to keep updating.  

I hope you can all appreciate the difficulty in forecasting snowfall when snow levels are fluctuating up and down over the course of long duration precip event.  I spent 2 hours this morning just trying to calculate the snowfall forecast for each elevation after looking at all of the forecast model data.

We are still watching to see if we see a few snow showers this afternoon as a reinforcing cold front moves through with more cold air.  I think the GFS could win round 2 today if we see a dusting or less.  But the European model looks like it will win rounds 3 and 4 from the case study we started last Thursday.  The European model saw the heavy precip event for this Thursday and the storms for next week while the GFS was drier for Thursday and had the storms staying North next week.

I'm trying to think of the best way to organize the precip amounts, snowfall amounts, snow levels, and precip timing over the next 10 days without you getting lost.  Maybe we can break it out by 12 hour periods for the short term.

Wednesday Night:

Light snowfall moves in as warmer air ahead of the atmospheric river overrides the cold air in place.  Snow levels will be below lake level and we could see couple inches of snow at lake level, and a few inches on the mountains.  Snow levels begin to rise overnight, but I think they could stay to lake level until sunrise.

Thursday:

One of the changes this morning is that the forecast models now have the heaviest precip with the atmospheric river pushing in during the day Thursday.  With the storm pulling in moisture all the way from Hawaii, warmer air moves in quickly with snow levels rising above 8000 feet by afternoon.  Possibly capping out around 8500-9000 feet.  So the snow accumulation stops at lake level.  At 7000 feet another inch or two before a changeover Thursday morning.  At 8000 feet we could see a few inches of snow before a changeover to rain by afternoon.  At 9000 feet or wherever it stays all snow we could see 3-6 inches of snow.  

Thursday Night:

The precip lightens with continued showers.  Snow levels may drop back down near 8000 feet.  From there and up we could see a few more inches of heavy wet snow.

Friday:

Even lighter showers, or the precip may even end for a little while East of the crest over the Tahoe basin.  Snow levels hover around 8000 feet.  We could maybe see another inch along the crest.  

Overall the forecast models are drier through Friday.  The GFS maxes out near the crest at 1.5 inches of liquid.  That's close to yesterday but the European model that was showing 3 inches of liquid near the crest now is closer to the GFS with only 1.3 inches of precip along the crest.  On the East side of the lake the GFS still shows a lot more shadowing with only up to 0.3 inches as a max and the European is wetter with up to 0.7 inches.

Friday Night:

This is another change to the forecast this morning.  All of the forecast models now pick up on a 2nd wave of heavy precip moving in Friday night.  The European is wetter than the GFS.  This 2nd wave is still warm as it moves in from the West off the Pacific, but at the same time a cold front is pushing down from the North.  The GFS shows snow levels falling to lake level overnight Friday night.  We could see a few inches of snow at lake level and several inches on the mountains.

Saturday:

The GFS ends the storm by Saturday morning with colder air moving in for the weekend.  The European model has heavy precip continuing into Saturday.  This is making for a significant difference in the forecast for Saturday between the 2.  The GFS ends the snowfall while the Euro brings enough precip for up to a foot at lake level and 1-2 feet on the mountains.

So we will have to keep an eye on this 2nd wave Friday night into Saturday, and how it interacts with the cold front pushing down from the North.

Here is a look at the total precip forecast on the last 2 runs from the GFS.

Here is a look at the Canadian model which is similar.  The European model is similar through Friday night before the spread on Saturday.

Taking into account the fluctuating snow levels here is my forecast for total snowfall through Friday night.  I left out Saturday with the heavy snowfall on the Euro.  Most of the lake level and 7000 ft. snowfall comes Wednesday night and Friday night, with rain in between.

The winds will be strong up high through the period.  So if you decide to brave the rain watch for wind holds.

We may have a break in the action Saturday night through Sunday night with colder air in place behind the cold front.

The forecast models are in decent agreement for a week+ out with the forecast next week.  It is looking more and more like we may see another warm atmospheric river event setup on Monday.  This time it may last even longer through Thursday.

The GFS is coming in much wetter than the other models next week.  If we see another moisture stream from Hawaii to CA and it takes aim far enough South at our area, then we could see quite a bit of rain and some snow.  

Here is a look at the storm next Tuesday on the GFS.

There is a high pressure ridge Southwest of CA and a low off the Pacific NW coast.  The moisture is streaming in between and helping to be fed by that low to the North of Hawaii.  You can see on the height pattern that we are right between the ridge and the trough.

A shift slightly North and we may not get the heavier precip next week.  For now the forecast models say we do.  If the current forecast were to hold, we would see snow levels rise up near 9000 feet Monday night and stay there through Tuesday night as the heavy precip streams in.  Above 9000 feet we could see a couple feet of heavy wet snow.

They are showing the low North of Hawaii moving into CA Wednesday as a cold front pushes down from the North, similar to what we could see this Friday night.  That would lower snow levels back to lake level next Wednesday, so we could see snowfall for all elevations at the end.

Of course 9 days out this is all speculation and could change as we get closer.  The main takeaway is the chance for another AR event next week with snow possible at the end.

Here is a look at the 10 day total precip forecast from the GFS.

and here is the Canadian...

The 10 day difference between the GFS and Euro for total precip along the crest is 8.5 inches vs 6.6 inches.  Both significant amounts of precip.  Currently we have fallen slightly below the wettest year but we are still well above average for precip so far this water year.  If the forecast holds, 10 days from now we would be back ahead of 82-83.

What is interesting is that 82-83 was a strong El Nino, not weak La Nina/ENSO neutral.

Trying my best to take into account the snow levels fluctuations here is the 10 day snowfall forecast.  I don't normally forecast out more than 5 days, but some of you are looking at unreliable computer generated forecasts that don't understand the snow levels and you are seeing snowfall amounts that are way to high for how warm these storms are aloft.

Looking beyond 10 days the GFS ensembles show the trough staying along the West Coast.  European ensembles show the ridge building over the Southwest with the storm track shifting to our North starting the weekend of the 17th.  The Canadian ensembles keep us between the 2 like we see next week.

Plenty to look at the next 2 weeks.  Unfortunately most of what is coming is rain.  Let's hope we see a cold pattern setup after mid-month.

Stay tuned...BA

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Geography Key:

East

Mt. Rose, Heavenly, Diamond Peak

Central

Northstar

West

Tahoe Donner, Homewood, Bear Valley, Dodge Ridge

Crest

Boreal, Donner Ski Ranch, Sugar Bowl, Squaw, Alpine, Sierra, Kirkwood

*Boreal and Donner Ski Ranch are forecast with the "West" mountains in higher snow levels events.