Today will be mostly sunny with highs in the 40's. The winds will be picking up again on the mountain tops with gusts to 50 mph. That increases to 60 mph tonight. For Wednesday we have a storm moving in with rain for most elevations and snow levels around 9000 feet, falling closer to 8000 feet by evening. Wednesday night snow levels continue to slowly fall with snow starting to accumulate above the 8000 foot level. We could see 5-10 inches of snow above 8000 feet Wednesday night. Thursday we have a cold front moving through dropping snow levels below lake level. There will be heavier snow with the front and then we could see snow showers continue into Thursday night as low pressure moves through the area. We could see snow accumulate at all levels. We could see 3-11 inches at lake level, and 5-25 inches on the mountains. The highest amounts as you go up the mountain and West of the lake. Friday we should clear out with the sun returning and temperatures in the 30's. Over the weekend we should see milder air move in with high temperatures back into the 40's. We could see another wet storm move in Sunday night into Monday with high snow levels. There is still a lot of uncertainty with this storm. The forecast models are split on the pattern we see Thanksgiving week with some keeping us dry all week and other bringing in a storm on Thanksgiving.
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Short Term Forecast
Ok, so we have a lot to go over today so this will be a long post but with a lot of images. We have to quickly review the storm that moved through last night, then talk about the complex storm that moves in tomorrow, and then I will be looking at the long-range again today.
First off the storm last night. I usually send out tweets through the storm on the TahoeWeather twitter page. I sent one out at the start of the storm last night saying that the precip seemed to be making it easily to the East side of the lake, and that the snow levels were a little lower than expected NW of the lake near Donner Summit, where it was snowing down to 7000 feet from the beginning.
We are actually getting quite a few snowfall reports this morning from the ski resorts, enough to post the usual report chart. The forecast was for 1-3 inches on the East side of the lake above 8000 feet, and 3-6 on the West side. You can see most ski resorts fell within the forecast range except for Mt. Rose coming in an inch over forecast, and Sierra & Homewood an inch under. But overall this storm did what we expected bringing a few inches above 8000 feet, and even a couple down to 7k near Donner Summit.
For Boreal and Mt. Rose today it's a little breezy but the sun is out with fresh snow on the hill.
I wish I was up taking a few turns but these storms have me stuck in looking at models all morning...
Yesterday we went into a lot of detail on the storm moving in tomorrow. The main message was that we have mostly a rain event Wednesday into Wednesday night, and then a snow event Thursday into Thursday night. The question was how much precip falls in the warm part and the cold part?
Whenever we get a big storm, especially the first big storm, people are always very cautious about believing a forecast, and rightly so. I get nervous myself anytime I put big numbers on a snowfall forecast as I don't like to be wrong. When it's complex with snow levels I like to really explain how I came up with the numbers. It's important people are reading the explanation and not just looking at the forecast, so that they know the possible errors that I explain.
The storm for tomorrow, as some of you know already, has trended wetter for Northern CA and also warmer. Looking at the total precip forecasts they are still showing up to 4-5 inches of total liquid West of the lake near the Sierra Crest. Now if this was a cold storm with 12:1 ratios that would be a forecast of 48-60 inches of snow on the mountains. The forecast all week has been half of that due to the warm nature of the storm, so we are accounting for the warm air, there is just a lot of moisture with this storm, and the question is still how much precip falls after colder air moves in.
Look at the nice moisture feed that this storm taps into on Wednesday!
I am going to start again by showing 6 model runs from wettest to driest for total precip forecast by Friday morning, and then I'm going to get into both parts of the storm again and show something interesting I'm noticing this morning.
Now, when people are saying much wetter model runs this morning they are talking about the GFS and NAM. The rest of the models are pretty similar. BUT here is the thing I notice. The totals around Lake Tahoe are not much different on any of the models (except the NAM).
The wetter model runs this morning are from more moisture being pulled in from a tropical system with the AR (atmospheric river) of moisture that moves into Northern CA on Wednesday with the warm air. But the latest model runs seem to be trending towards that precip hitting further North, to the NW of our area on Wednesday.
Then as the cold front moves South Wednesday night towards Norther CA it begins to push that moisture feed further South towards the Tahoe basin. At the same time it starts to push colder air in aloft. So for Wednesday I am expecting higher snow levels around 9000 feet during the day and then the latest model runs would suggest them falling near 8000 feet by evening. So the only snow expecting is maybe a couple inches of wet snow above 9000 feet.
Then Wednesday night the snow levels look to sit around 8000 feet for most of the night as heavier precip pushes into the area. That should keep the snow nice and wet for that elevation and rain below that. Below is the snowfall forecast through Wednesday night, and you can see that my thinking is that by the Thursday morning reports we are looking at 5-12 inches at best from the ski resorts up top. So as I have been explaining all week, no need to get overly excited and to hype the storm.
So rule #1 with this storm is no posting about a lack of snowfall in the comments on Thursday morning.
The latest model runs are suggesting that the cold front and colder air move in sometime Thursday morning. That will bring another period of heavy precip and falling snow levels. We should see snow levels fall to 7000 feet during the morning, and then below lake level during the afternoon.
I'm expecting some good post cold front snow showers to setup as well as cold unstable air moves in. Then as the center of low pressure moves inland to our North that could continue snow showers into Thursday night. This second part of the storm is what is tricky and critical to the snowfall forecast. You have the timing of the heaviest precip moving through with the front, the amount of moisture behind the front, the amount of moisture with the low, versus the falling snow levels and rising snow ratios.
This is where all the math and formulas come in. My forecast for the 2nd half of the storm follows the snow level timing above combined with the GFS elevational temperature forecast for snow ratios, and the GFS/European model average for precipitation. It would have to come together with the exact timing, temps, and totals in that formula to have the part 2 forecast pan out. The good news is that this morning the GFS and European models have almost the exact same forecast for total precip along the crest of 4+ inches, but the European model as usual is wetter on the East side of the lake.
The timing on the models is more in sync as well with the heaviest precip Wednesday night now, but the GFS is wetter on Thursday now more in line with the Euro. They have about 60% of the moisture falling in the warm half of the storm and 40% in the colder half. Thursday night the Euro is much wetter with the low moving through. Overall much lighter showers Thursday night, but the snow ratios jump with the much colder air which is why the snowfall shows several inches possible.
Here is the updated total snowfall forecast with the resort reporting levels at 8k in green. That is the comparison to totals reported on Friday. This really hasn't changed at all over the last several days. Like I said yesterday, even if you kept the whole storm warm with snow ratios of 8:1 average at 9k through the storm you would get 32-40 inches along the crest with the 4-5 inches of liquid the models are spitting out. Can you tell I'm as nervous about forecasting the first possible significant snowfall as you are about receiving it?
The NWS is more conservative and doesn't like to put out specific snowfall numbers until a couple days out. Looking at the point an click map they have 22-36 inches for 8k at Squaw Valley by Friday on today's forecast and I have 29-37.
Also, they are finally talking about 2-3 feet along the crest above 8k in their discussion,
and they have 12-18" for 7k over Donner Pass and I have 11-17" for 7k on the crest...
I do my own calculations and forecast and don't usually show theirs, but hoping it makes you feel better like it does me!
We should clear out on Friday with a nice weekend, especially Saturday with sun and highs in the 40's. We have more ski resorts opening for the weekend, Squaw, and Heavenly, so this storm should help!
There is another storm moving towards the West Coast next weekend as we have been watching all week. The question continues to be the overall pattern for the West Coast, with the GFS keeping the trough off the coast.
and the European model into the coast...
There is another nice moisture feed possibly setting up for Monday...
The difference this time is that the GFS has the cold area of low pressure in the North Pacific with no cold air moving in with this storm. That would mean a big rain event for Monday if the moisture feed pushes into Central CA.
The European model does push in some colder air so it would bring some snow to the upper mountains. I really don't want to get too much into it yet with the model differences. Just know that we are tracking another storm that could potentially tap a lot of moisture for Monday.
The interesting things about the European solution is that it also kicks the trough off the East coast of the U.S. so that by Thanksgiving the trough in the East Pacific is closer to the West Coast. Which could allowing another storm in for Thanksgiving.
The GFS and several other models ridge up the Western U.S. next week with dry pattern, which is what I have been leaning towards all week, but the Euro does keep it interesting.
Another interesting thing is the big crash in sea surface temps in the ENSO region of the equator this week. We were barely in week territory last week and now well into moderate in all regions this week excpet Nino 4.
So we will be watching that as well for the upcoming season.
Ok, gotta run, DMV appointment awaits, I can't wait! (sarcasm)
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