We have been talking about these incoming storms for a couple weeks now, but now it is the big headline in Northern CA as everyone is getting excited for the rain and snow starting tomorrow.  We can see the first storm approaching the coast on satellite.

I have been spending the past few mornings over-analyzing the forecast models.  There is still good agreement on the first storm for Wednesday, but still some discrepancies for Thursday into Friday.  Let's go through the latest trends.

Wednesday:

There is good agreement among the models on the trend of slowing the first system slightly.  We could see light rain and snow move in during the afternoon, but it looks like the heavies precip may hold off until evening.

Wednesday night the heaviest push of moisture moves in.  Snow levels drop to 7,000 feet Wednesday afternoon at the start and then could lower close to lake level Wednesday night.  In my snowfall forecast I have the assumption that snow levels are down to lake level Wednesday night.

The latest 12z GFS model run came in a little wetter with up to 1.3 inches of liquid near the Sierra crest.  The European model has only up to 0.6 inches, but the average of all the models seems to be around an inch.  That should be enough for 1-4 inches of snow at lake level and 5-11 inches of snow on the mountains above 7,000 feet.

Here is a look at the Canadian forecast for the first system showing up to an inch of liquid near the crest.

Thursday:

The trend for Thursday is for moisture from the next system to possibly start to push in earlier.  But still expecting only light snow showers with snow levels hovering around lake level.  We could see a dusting to an inch of snow during the day.

Thursday night the GFS has the push of heavier precip moving in late in the night by early morning Friday.  But the trend on the European model has been for heavy precip to push in earlier Thursday night.  It has over an inch of liquid now for Thursday night along the crest and up to 3/4 of an inch to the East side of the lake.

Snow levels rise with this next system as it taps some warmer moisture before pushing in.  If the Euro is right bringing in the heavy precip Thursday night, the snow levels may rise through the night to 7,500 feet by Friday morning.  The timing will determine how much snow falls at night, but taking a split of the models we could see an additional 2-6 inches of snow above 7,000 feet.

Friday:

Friday a 2nd wave of heavy precip may push into Northern CA.  Yesterday the GFS model was not pushing this moisture as far south or with enough forcing to push it into the Tahoe basin.  This morning it has the heavier moisture pushing further south to Tahoe in line with the other models, but still has a tough time pushing it east across the Tahoe basin.  West of the lake near the Sierra crest it brings an additional 0.8 inches of liquid with not much making it across the lake.

Meanwhile, the European model is much wetter still and is actually wetter today than yesterday.  It is bringing over 3 inches of additional liquid to the crest and pushing over 2 inches to the east side of the lake.  In my experience, these systems tend to push more moisture into the basin more in line with the Euro.  But it is still running at 4x the precip amounts as the GFS 3 days out.  So that will have to be decided as we get closer.

Snow levels may rise up to 7500-8000 feet on Friday and stay there into Friday night with while the heaviest precip is falling with this storm.  Above the snow line we could see 6-13 inches of additional snowfall.  But only rain expected below that for most of this 2nd storm.

Storm Totals:

Here is a look at the Canadian total precip forecast which is close to the average of all the models for the storms.

Looking at all the other model runs like the Canadian, NAM, WPC, etc., and ensemble runs of the GFS and Euro, they show storm totals of 2-3 inches of liquid along the crest.  The average is 2.8 inches.  You can see the forecast graph below for the Snow Lab in Soda Springs that uses an average of the Canadian and their ensembles, shows a similar average total storm precip amount.

It also shows an average total snowfall forecast of around 18 inches of snow at 6,883' at the Snow Lab.  My 7,000 foot forecast for the crest which would include that area caps out around 15 inches.

You can see the drop off in snowfall below 8,000 feet as the lower elevations should receive most of their snow with the first storm.  On the ski resort pages you'll see that the mountains with most of their terrain below 8k like Boreal and Homewood have their forecast tied to the 7k forecast.

Behind the storms we should see drier weather for the weekend with cold air in place and highs only in the 40's.  The colder air behind the storms should make for some decent snowmaking conditions.

It still looks like high pressure will build over the West Coast this weekend into early next week.  But it also still looks like a large trough in the Eastern Pacific and strong jet stream could push more storms into CA by next Wednesday.

Both the GFS and European models are showing storms from the middle of next week into the weekend of the 1st.  

In the uber long-range the GFS ensembles keep the trough near the coast with more storms pushing into CA through the first week of December.

Stay tuned...BA

P.S.  Check out the new I-80 forecast page complete with graphs and cams!

https://opensnow.com/dailysnow/i80/post/12068