- We have a break for Thursday into Friday with some sun. Highs in the 30s. Lighter winds Thursday morning start to increase during the afternoon gusting to 20+ mph over the ridges. Then Friday they are gusting to 50+ mph increasing to 70+ mph through the afternoon likely affecting lift operations. - The next storm will move in Friday evening and lasting into Sunday. This storm will start a little warm and will have falling snow levels. We could see several inches of snow at lake level after a change from rain to snow Saturday, and 1-3 feet of new snow to the mountains by Sunday evening. Snow levels could start around 6500-7000 feet Friday night, then falling to near lake level by Saturday evening, and below lake level Saturday night into Sunday. - We may see a break for the week of the 9th. The forecast models disagree on how long the pattern change to a drier pattern will last. They show better chances for a more active pattern after mid-month.
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Short Term Forecast
We have a short recap of the weak system that moved through Wednesday. We saw scattered snow showers through the evening. The heaviest showers fell west of the lake along the crest and south of the lake. The forecast was for 1-4 inches across the mountains. Totals this morning being reported are a coating up to 6 inches. Lightest amounts north and northeast of the lake, with the highest amounts south and southwest of the lake.
This was just the icing on top of the big snow from the past week, and we have another storm inbound after a short break from Thursday into Friday.
The Weekend Storm:
For Friday we may see partly sunny skies in the morning with increasing clouds and winds. We are expecting high winds with this storm over the mountains. We could see winds gusting to 50+ mph on the ridges by Friday morning, increasing to 90+ mph by Friday night.
The latest model runs have slowed the arrival. What is happening with the first wave of precipitation is that we will have a southerly flow ahead of the front which usually slows eastward movement and limits spillover past the crest into the Tahoe Basin. The forecast models have a range of arrival times near the crest of 6 pm to 1 am. I would expect a start time around 5-10 p.m. We can take a final look on Friday morning.
Timing start times of snow down to the hour or less 6+ hours out is not very easy. The advancement of precipitation speeds us and slows down and is made more difficult with the interaction with the mountains. I have been getting some requests to be more specific with exact start times for driving. I can't do that and will not take on the liability of your driving decisions cutting it close to start times. As with this storm with a start time of 6 pm to midnight, I will usually just say after 4 p.m. I would highly suggest being finished driving by then over the passes.
The precipitation with the front Friday night will also have higher snow levels. The latest forecast model runs haven't changed much and are still showing snow levels in the 6500-7000 feet range Friday night. That is rain for lake level and snow for the mountains. There may be decent shadowing to the east side with the first round of heavy snow. The models show half of the total precip as the west side near the crest. We could see 1-3 inches on the east side and 3-6 inches on the west side mountains above 7k by early Saturday morning.
Saturday - Saturday Night:
It still looks like we could see a small break in the heavy precip rates Saturday morning with light-moderate rain/snow. Snow levels don't come down much behind the cold front, maybe a few hundred feet as some warmer air may work in ahead of the 2nd wave coming as low pressure off the coast moves into northern CA later Saturday. Then the models show a 2nd push of heavy precipitation sometime between Saturday afternoon and evening lasting into Saturday night.
This looks like the heaviest snow of the storm. The south winds switch to the southwest which is more favorable for precipitation to spill over the crest across the Tahoe Basin, and is better for orographic enhancement. Winds could continue to gust to 70+ mph over the ridges causing upper mountain lift closures.
Snow levels Saturday could start to come down, especially later in the day with the 2nd round of heavy precipitation. They may come down near 6200 feet (lake level) during the afternoon. I have the snow levels for the day at 6200-6700 feet. Then dropping to 5200-5700 feet Saturday night, that maybe when they drop to all elevations including lower valleys like Truckee. We could see 5-10 inches at lake level and 1-2 feet of additional snowfall above 7000 feet by Sunday morning.
The European model clears us out quickly Sunday morning with little if any additional snowfall. The GFS model shows a final wave bringing snow showers through the day before ending by Sunday evening. Snow levels staying in the 5500 feet range. Taking the model average, snow showers could bring a final 1-3 inches on the mountains, slightly more if the GFS is right.
The latest model run averages are slightly wetter this morning but not much. The European model is slightly drier with more shadowing Friday night and an earlier finish Sunday. The 6z GFS was still trying to show 5 inches of total precipitation near the crest. I waited for the new 12z run before posting. That came down to 4 inches, with only 3 inches by Sunday morning, then adding an inch Sunday with the 3rd wave. The total model average this morning is up 1 tenth to 2.7 inches.
Here is the WPC model is showing up to 3 inches which is in line with the German model, the NAM, and the GFS/Euro model average.
The updated snowfall forecast through Sunday still shows a big drop off at 6k due to rain through at least Saturday morning. Amounts could be slightly higher at lake level if it switches earlier. Then you can also see the shadowing to the east side due to the first round of precip. Totals have gone up a couple of inches over yesterday with the slightly wetter model runs this morning.
You will also notice I added the NWS forecast for 8k at Squaw to the table. I get a lot of questions about the difference in winter storm warning amounts or NWS forecasts vs what we forecast. The NWS is an amazing resource that we use a lot. They have a lot of necessary data that helps forecasters. I read their discussions every day. The NWS Reno is the office for the Tahoe basin. They cover from the crest east across the Tahoe Basin.
They are looking at the same data and models as we are, and are putting out a forecast for safety reasons for anyone traveling or in the outdoors. They will usually cover up to the worst potential in order to keep people safe, including the higher end of snowfall potential. That is why their forecast has a larger range and higher-end usually. You can see above a 16-inch range in totals based on drier and wetter models. The NWS also won't forecast snowfall amounts until within 3 days of a storm.
We are forecasting specifically only for ski resorts and elevations from the base to the top of ski resorts for skiers to get an idea of what to expect at their mountain. Our automated mountain forecasts use pin drops at the base, mid-mountain, and summit of each ski resort that average together dozens of models, and within 3 days we also average in the NWS forecast. Taking the average we have a smaller range usually in the middle of the models. Our formulas attempt a snowfall forecast for each mountain up to 10 days, but I personally won't discuss it until within 5 days. I shoot at a much smaller forecast range window, usually only 3-6 inches for each elevation.
So that is the main difference and why forecasts are sometimes different. I hope that answers some of the questions we get. I thought maybe I would add the NWS forecast for 8k at Squaw just so you can see the difference. When the wettest models end up being right we will at times get the highest end of the range instead of the average.
Behind the Storm:
High pressure builds in behind the storm by Monday. The long-range models want to keep the ridge over CA through the 2nd week of December, but some model runs show weakened storms trying to push some precip into northern CA on Wednesday and again around the 14th.
The MJO is still dead and we are still waiting to see if it re-emerges in the Indian Ocean and has any effect on the long-range forecast. In the meantime, we may have a dry or at least drier pattern for the 2nd week of December. The long-range ensembles do try to suggest a weakening of the ridge or a trough going into the 3rd week of December.
Plenty of time to look at the long-range after this storm. The mountains will have plenty of snow by Monday to get through a short dry spell. Highs next week should warm into the 40s at lake level and 30s for the upper elevations.
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