This is going to be a long post today as there is a lot of weather and data to dissect, as well as conversations about the change in collecting data and making forecasts as we switch more towards backcountry skiing with the closing of the resorts.

Resort Closings:

Most of you know by now that all ski areas around Tahoe are closed today due to containment efforts for the COVID-19 virus. It looks like Dodge Ridge will be reopening on Tuesday & Donner Ski Ranch & China Peak Thursday after they dig out from the big snowfall. The rest of the ski areas are closed indefinitely.

Most of us will either not be skiing, transitioning to other outdoor activities, or backcountry skiing. For the latter be sure you have been trained in backcountry skiing and avalanche courses, are carrying all the safety gear, and skiing with friends. The avalanche risk remains high in the Sierra.

For my forecasts, most of you are looking at them for these activities outside of resort skiing. For my forecast tables for the ski areas, they are still relevant for backcountry skiing as they show snowfall up to 9000 ft. The ski area pages on our site put out a forecast for mid-mountain. For the peak forecasts in the backcountry download and use our app or website OpenSummit.com. That will give you the forecast details for the top peak of all the mountains. You can email us if an area you ski is missing & we can add it.

Collecting the Data:

Most of the ski areas have stopped reporting snowfall now that they are closed. The few ski areas that are still open are reporting, and Mammoth is still reporting even though they are closed. This makes it hard for me to get the snowfall numbers from the mountains.

After my post yesterday about not having snowfall data reported, I got a lot of messages from readers and from some ski areas. Several of the ski areas not reporting have confirmed to me that they are still measuring and keeping records, just not reporting. So we will eventually have access to those official numbers at some point which is great!

We've had a lack of data from the Snow Lab all season with Randall retiring and no one hired yet to take official snowfall measurements. We have to rely on the snotel sensors that use sonar from about 30 feet up and bounce that off the snow surface to estimate the snow depth. The problem with that is that the snow depth is compacted snow and not snowfall that is measured every 12 hours and cleared, as per the NWS official snowfall measuring guidelines.

https://www.weather.gov/media/ffc/snow_measurement_guidelines.pdf

We can look at the increase in snow depth by the hour to try and get an idea of the snowfall, but the daily reported depths are too low for official snowfall numbers with the compacting of the snow as it piles up. I am looking at the snow depth changes by the day and the total precipitation. If I estimate the increase in liquid by day and multiply by the assumed snow ratios for the day, I can come up with a good guess at how much snowfall we saw. 

I also have readers sending me reports, some of whom live near the base of several of the ski areas. This morning I spent a lot of time calculating a good guess at the snowfall numbers based on the snotel data and reader reports. It's not official though until we get the numbers from the ski areas. We will never get the official numbers from the Snow Lab this season with no one measuring, after decades of data.

Please comment your reader reports at the bottom in the comments if you can. I read them all and it's easier to compile vs getting them through email and social media channels. Please use the NWS guidelines in the link above when measuring. Posting in the comments is also great for others to see your reports!

Storm Totals So Far:

The 4-day storm continues Monday. We have picked up big totals so far from this storm as we were expecting. Tahoe is buried under 2.5 to 6 feet of new snow since Friday night!

This may be a tease to see these pictures and total if you are not able to ski, but I'm planning to keep forecasting and reporting daily until the snow stops flying.

From all the data I've collected, it looks like we saw an additional 6-12 inches over the past 24 hours at lake level, and 1-2 feet on the mountains. That brings the storm totals to 2.5 - 5 feet at lake level (highest on the west side of Truckee & the West Shore of the lake, and 3 - 5.5 feet on the mountains!

The snowfall average for the ski areas was near 63% of average for the date on Friday and is now around 76% of average as of this morning. A nice jump over the weekend!

The snowpack jumped from 35% of average on Friday up to 46% of average today. That is a measure of the water content in the snow on the ground, not snowfall which measures the amount of snow that falls every 12 hours. The snowfall numbers have been running higher as a % of average all season with mostly cold storms this season & high snowfall ratios.

I was able to sneak in one last powder day yesterday at Homewood while Powder Chaser Steve was in Tahoe this weekend and went to Mt. Rose. It was a good way to end the season if this was the end... You can read his Tahoe report here. https://opensnow.com/dailysnow/chase

I'm not sure how fair it is to critique myself without official snowfall numbers, but I enjoy the critique as it helps me to fine-tune my forecasting techniques, and keeps me transparent and honest. We know that cold orographically driven storms like this tend to over-produce vs what the models are showing as I mentioned leading up. We also saw my forecasts come in under the totals quite a few times last February with similar storm setups. But I still can't find the courage to forecast the high end of the models even with these storms because if we don't get those totals then I will get massacred in the comments.

For the keep me honest report it is comparing my final forecast as the storm approached vs the approximated totals this morning. You can see much higher totals east of the crest for the west shore mountains & mid basin mountains. Then several inches over for several mountains along the crest, with 4 mountains coming in within the final forecast range.

This is an ugly report, maybe the worst ever, but a) no one complains on the over & b) we don't know if these are the real totals, but they should be pretty darn close based on observations. This storm was a good one and came at the perfectly wrong time!

The Storm Continues:

The area of low pressure spinning near the CA coast has slowly shifted south as of this morning.

That has continued the snowfall over the Sierra but also turned the flow to southerly. The winds have backed off this morning and are gusting from the south to around 10-20 mph over the ridges. The southerly flow decreases the orographic enhancement of the precipitation by the mountains as the flow is parallel to the mountains. 

We are expecting the steadiest precipitation to fall Monday morning and then become lighter & more scattered into the afternoon. The heaviest precipitation shifts south towards Mammoth. Going into Monday night and Tuesday the precipitation becomes more scattered as the low continues to move south. The flow becomes easterly with some upslope enhancement possible on the east side of the Sierra. 

Total precipitation amounts through Tuesday are ranging between 0.7 - 1.4 inches on the latest model runs. The NAM & ICON models being the wettest. The 100 model average is around 0.97 inches on teh high end by Tuesday night. Here is the total precipitation forecast for additional precip Monday through Tuesday night on the WPC's blended model.

Winds are expected to stay light. Temperatures in the 20s for the upper mountains and 30s for lake leve through Tuesday. Snow levels rising to around 5500 ft. Monday and dropping below 3000 ft. again Monday night. Then rising to around 4500 ft. Tuesday. Snow ratios around 11-14:1 Monday and then rising again Monday night to around 14-19:1.

Based on the average of the models here is the final forecast for potential additional snowfall from 4 AM Monday through 4 AM Wednesday. Some of which has already accumulated this morning.

Wednesday - Friday:

The area of low pressure off the coast moves through southern CA Wed - Thu, and the next system approaches Friday. That could bring clouds and sun over the 3 days, with a chance for isolated snow showers to pop up over the mountains under the unsettled pattern. Highs warming into the 30s on the mountains and 40s at lake level.

The Weekend:

The next system moves down from the north towards CA for the weekend. The forecast models are not in agreement yet on the track. Some models keep the low off the coast with a mostly dry weekend, while other models like the GFS drop the system south through CA with light-moderate snow possible on the mountains.

We will have to continue to fine-tune the forecast all week as the models come to a consensus on the track of this system.

The long-range models continue to show a trough over or near the West Coast through the end of the month.

(yes, mother nature is giving us the finger...)

That would keep the storm door open for CA. The models that have the low off the coast for the weekend move it inland by next Monday with more snow for the Sierra. The long-range models show that system as well as another right behind it for early next week.

Fantasy Range:

The active pattern may continue through the end of the month if the current pattern forecast holds. We will have to watch the track of each system to see how much moisture it could pull into CA. We will assume weak systems for now and then watch to see if we could see another strong system before the end of the month. The CFSv2 model shows above-average precipitation continuing for CA week 2.

Contributing to the confidence that a stormy pattern could continue are the teleconnection forecasts. The PNA pattern is forecast to stay negative through the end of the month, which is a West Coast trough pattern. You cand see it went negative briefly in mid-January when we had the last double-digit snowfall before March, and then negative again the first week of March setting up a stormy pattern so far this month.

The MJO is forecast to finally move through phases 1-2-3 in the Indian Ocean over the next 2 weeks. This usually causes a shift in the pattern to trough near the West Coast, and historically is a wet pattern for CA, wetter each phase as it moves into phase 3.

This is the pattern we have been hoping for a repeat of since we saw it in December which was a stormy month. Unfortunately, it waited until all the ski areas closed to finally show up...  The CFSv2 climate model shows above-average precipitation continuing for CA through the end of the month during weeks 3 & 4.

Sea Surface Temps:

We continue to watch things evolve over the ocean as we wind down this season and look towards next season. It appears that a warm tongue of water is trying to form east of Japan towards north of Hawaii, with a cold horseshoe trying to form around the north, east, & south sides. That would be a negative (cold) PDO pattern.

The climate models continue to suggest a La Nina pattern setting up along the equator next season, possibly a moderate to strong one. A cold PDO & moderate/strong La Nina pattern can bring CA a colder winter, and sometimes a snowy one as well like the 10/11 season. Although that season also saw a westerly phase of the QBO and we just switched to an easterly phase.

I thought maybe some of you would be bored today and would enjoy a good long post. Others may be a little depressed so I thought I'd try to bring some good news to the weather forecast for the rest of the season and possibly for next season...

Stay tuned, stay sane, stay kind...BA

P.S. If you love our app & site, and use it for your forecasting needs, please consider signing up for our All-Access Pass. Usually, most of the funds go towards developing cool new forecasting products, but now will go towards keeping us going as ski industry advertisers, that keep most of this site free, continue to cancel their advertising. Plus you'll love the All-Access features & it's good for OpenSummit as well for only $19 a Year!

Also, please support local businesses and those who have lost their jobs in the tourism & restaurant industries due to the shutdowns & containment efforts. #mountaincommunity #tahoestrong

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