A very strong bomb cyclone with moisture from an atmospheric river will continue to soak the Sierra with heavy rain and mountain snow this week. Due to a bit of an unusual storm track, retreating up and being absorbed into another storm in the Gulf of Alaska, weaker waves will be ejected inland providing moderate snow totals for the rest of the West. The pattern will remain active through the weekend and beyond, with storms lined up across the Pacific for the foreseeable future. 

Short Term Forecast

Some light snow from the previous storm will linger in the Southwest today, bringing moderate totals of 3-6\ in Arizona, Colorado and New Mexico by tomorrow morning. Our eyes then shift to the next powerful storm that will impact the Sierra Wednesday through Friday. The main components of this storm are a strong surface and upper level low pressure system and an atmospheric river. We call this storm a \"bomb cyclone\" because the surface low will rapidly strengthen over a short period of time, often resulting an intense storm with large impacts. This type of atmospheric river is called a \"Pineapple Express\" because the origin of this river of water vapor in the upper atmosphere originates near Hawaii, which you can see below. 


You can see the plume of moisture stretching from Hawaii all the way to the California coast. 


Compared to some recent atmospheric events, the precipitation amounts and wind speeds won't be as long lasting or extreme, but this will be a significant storm nonetheless. With the massive amount of recent rains, soils are already quite saturated outside of the mountains, increasing the threat for flooding this week and moving forward. The storm will actually remain over the ocean, off the coast of California/Oregon, but the associated warm/cold fronts and other impacts will certainly impact the Sierra. This is why further inland will see only moderate snow from this storm though. You can see the storm strengthen off the coast, linger there for a bit, then retreat to the northwest. 


The snow will start Wednesday morning in the Sierra and continue through Friday morning, with the heaviest Wednesday night through Thursday afternoon. Temperatures will be warming through midday Wednesday, and then begin to gradually fall Wednesday afternoon as the cold front approaches. Snow levels could rise up to 7500 feet on Wednesday before starting to lower in the afternoon, and likely falling to lake level between midnight and 6am. Snow quality will be better Thursday morning, but still on the denser side. The last few hours of snow. before the lifts open on Thursday should be better quality. Lower density will continue Thursday into Friday, but not as heavy. Models diverge on the extent of the moisture overnight. Still, Friday morning will feature the best quality snow, and if there are closures on Thursday, you may get to ski/ride the storm total on Friday with some better density snow on top. At no point though do the temperatures ever get really cold, so at best the snow will be medium density. 

Resorts along the Crest should see between 1 to 3 feet (base to summit), with lesser amounts as you move east into the basin on the west side of Lake Tahoe, and even less east of the lake. Storm totals from the National Blend of Models (NBM) below.


Everywhere Else

For the rest of the West, this storm should deliver moderate snow totals in Washington, Oregon, Idaho, Utah, Wyoming and Colorado. Again, since this storm is staying off the coast and retreating north and west, so the atmospheric river will not penetrate much beyond California and thus available moisture will be limited. From Wednesday afternoon through Friday, light snow will be falling in Oregon, with 3-6\" expected during that time. From Wednesday night through Friday in Washington, light to moderate snow will be falling. Expect 3-6\" here as well, with perhaps a little more in the southern Cascades. From Wednesday night through Friday in Idaho, light snow will fall and pile up around 3-6\" there as well. In Utah, snow starts Thursday afternoon/evening and continues through Friday morning, with 6-10\" of snow expected. In Wyoming, light snow will fall from Thursday afternoon through Friday, with 4-8\" possible before the snow winds down. And finally, from Thursday night through Saturday, snow will be falling in Colorado too, with 4-8\" falling across most of the mountains.

Temperatures will be on the warmer side to start in all these areas, and the cold front that does move through is not all that cold. Therefore snow will be on the denser side, and there isn't a lot of moisture expected once temps do cool off either. In all of this, the best picks for powder are Utah/Wyoming on Thursday. Some light snow will be falling in northern Arizona and northern New Mexico during this time as well. Storm totals for the rest of the West below, from the American model below, through Friday night. Note the higher amounts in southern Utah due to the addition of today's snowfall. 


Of interest are the snow totals in Washington, Oregon, Idaho, Wyoming, Northern Utah, and Colorado resulting from this late week storm. 

Long Term Forecast

Starting this weekend, another storm will move into the west coast. Snow should start flying Saturday afternoon in Washington and California, and last through the weekend. Some of this moisture will move inland to Idaho and Wyoming as well, with northern Utah and Colorado seeing more snow as well. This storm has the potential to drop another couple feet in Tahoe, 8-16\" in Washington, and 4-8\" elsewhere. Since we are still 5 days out for this storm, those totals will be updated as we get closer. As previously mentioned, the models show storms continuing to pound the western US over the next few weeks, with storms possible through the third week of the month. 

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Stay tuned for updates as this active pattern continues. Thanks for reading.



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