WELCOME BACK! Be sure to check out our inaugural Anti-Seasonal Outlook, Seasonal Outlook: A Four Part Series. We will have a new post each day, Monday through Thursday (10/20-10/23). Also, we will have new and improved content through the season, so be sure to come back often!

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Saturday, April 4, 2015

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Winter Clings to Life

Well, mother nature sure has a sick sense of humor. We will probably see the coldest or close to the coldest storms all winter over the next 5 days...in April. Makes me think of that classic line, 'Isn't it ironic? Don't you think?' from that even more classic Alanis Morissette song, 'Ironic'. I don't know if our coldest storms coming in April at the tail end of a warm, drier winter qualifies as irony, but hey, Alanis Morissette didn't really understand irony either.

Figure 1. Storm total precipitation for the Saturday/Sunday storm(s).

ANYWAYS...look for snow possibly tonight, but for sure tomorrow afternoon and evening. We expect 3-6" of snow with some areas seeing near ~8" and snow levels down to 4000-5000' (Figures 1-2). A bigger storm comes through Tuesday into Wednesday. This storm is trying to push more south than east, which could limit the impact around Tahoe. This storm is cold and wet though, so let's hope it swings more to the east.
Figure 2. 9,000-10,000 ft. winds, temperature, and heights. Very cold storms will be moving through the Tahoe area.

If the second storm takes a more easterly track, the Sierra and around Tahoe could see 8-14" with some of the highest elevations pushing 18". As of right now this isn't happening, so a more conservative estimate would be 4-8" (Figure 3).
Figure 3. Showing total precipitation from Saturday morning to Thursday morning. 

If this was December or January, I would be pumped, but it is April and we have 5% of the normal snowpack. However, with the drought, this is much needed and welcomed and it may extend some backcountry excursions for another week or two.

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Monday, March 30, 2015

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Classic April Roars In

Been enjoying those calm 70+ degree days with blue and sun. Been out cycling/running/something staring at your unused skis as you return. That's over for a few days, maybe longer. An early April Fools? NFW! Classic April roars in a day early tomorrow bringing a pattern change and Wind putting a damper on those plush warm days. The breakdown over the next couple days goes as follows:

  • Wind and slightly cooler overnight with cool fropa 
  • Wind re-intensifies with another cool front on Tuesday 
  • Another more impressive cold front on Wednesday associated with a strong shortwave
  • Some light snow and snow showers above 5000 ft on Wed/Thr can't be ruled out
  • And this is just setting the table for early next week after a brief rebound/hiatus Friday
  • Yes, a colder situation is looks promising beginning Sat. night onward, could be interesting
A rather dramatic pattern shift began this afternoon, although April is notorious for such events, with a series of shortwaves hitting the West coast. The first (#1) passing through tonight across the Pacific northwest tightening the pressure gradient and dragging cooler across Tahoe and western Nevada. Another shortwave (#2) moves across the southern Oregon on Tuesday prompting more wind for our area. And then a quite impressive wave (#3) on Wednesday night is something to watch bringing strong upper-level dynamics and much colder air (Figures 1 and 2). After a brief hiatus on Friday (Figure 3), another strong shortwave (#4) approaches Tahoe Saturday night into Sunday. In addition to strong dynamics, this time there is some moisture to work with (Figures 4 and 5). This is really something watch!

Figure 1. Illustrating shortwaves #1 and 2 via 500 mb heights/vorticity.
Figure 2. Illustrating shortwave #3 via 500 mb heights/vorticity.

Figure 3. Friday hiatus with temporary ridge, made of paper not steel, via 500 mb heights/vorticity.

Figure 4. Illlustrating impressive wave #4 for Saturday night via 500 mh heights/vorticity.

Figure 5. Illustrating some moisture associated with impressive wave #4 via precipitable water and lifted index.

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Sunday, March 22, 2015

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Too little too late

The first spring storm of the year will begin impacting the Sierra this evening with light snow accumulations below 7000 feet and up to a foot at the highest elevations along the crest.  Light and scattered snow showers will persist into Tuesday night before the ridge begins to rebuild to its former glory....

- Snow beginning this evening with snow levels dropping to lake level tomorrow morning.
- Light accumulations below 7000 feet with generally 3- 8 inches above and up to a foot along the highest peaks of the crest. 
- Snow amounts will drop off south of Tahoe and increase as you head north.
- This storm will do little to save the rapidly disappearing snow pack.

Current storm is slowly getting its act together and is spreading some showers into Northern California.  Not much in the way of moisture with this storm as there is no significant subtropical tap as can be seen in Figure 1. 

Figure 1: Forecasted precipitable water (the amount of precipitation that would occur if all of the moisture in the column was wrung out) for this evening at 1700 in centimeters.
The dynamics are also rather benign with a very weak trough passing to the north of Tahoe along the CA/OR border.  However, a respectable shot of cold air  (for this season...) will accompany this system (see Figure 2) and allow the snow level to fall to Lake level as 700 mb temps drop to around -6 C.

Figure 2: 700 mb (~10,000 ft) temperature (colored contours) in Celsius and relative humidity (color fill) for 5:00 am tomorrow morning.
As can be seen in Figure 2, the bulk of the high humidity air is behind the -5 degrees Celsius contour which for us back to back World War champs is a chilly 23 degrees Fahrenheit. This will allow the majority of the precipitation to fall as snow down to about 7000 feet providing a fresh new coating of white. However, due to the lack of moisture and dynamics, that coating will only be enough to cover small obstacles and fill in some bare spots.  Figure 3 shows the forecasted precipitation amounts from a high resolution model. The crest will be favored with precipitation amounts dropping off as you head south of Lake Tahoe.  Meanwhile, high elevations north of Lake Tahoe, like Mt. Shasta, look to do quite well with several feet of snow above 8,000 feet or so.

Figure 3: Forecasted accumulated precipitation (in inches) over the next 72 hours. 

Although this storm will help give everything a fresh coat, it is merely a drop in the bucket as the snow pack is disappearing at an astonishing rate.  Figure 4 shows just how early and scary the loss of snow is. 

Figure 4: Current snow water equivalent (bold blue line) and total precipitation (bold red line) from the start of the water year for various Snotel sites near Lake Tahoe.  The non-bold red and blue lines are the median (or "normal") precipitation and snow water equivalent.
The observations speak for themselves.  This winter, or lack there of, has been dismal except for at the highest elevations.  The "Spring" run off has started as much as two months early and is going to provide little relief to the already depleted water supplies across the region.

But to end on a more positive note, get out there and make some turns in the fresh snow before you either have to hike up Shasta or fly south, way south for the Summer.    

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Thursday, March 19, 2015

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Pleasant end of the week and a breezy weekend

  • Seasonable to slightly above average temperatures with a cooling trend into the weekend
  • Light winds today/tomorrow turning breezy out of the southwest
  • Possible precipitation in the northern region of CA, better chances for Tahoe on Monday

Keep those fingers crossed for some! any! Pacific moisture to make it into our parched region. A few small storms this spring could actually keep a little bit of skiing going into April or even longer if we get lucky. I recall an Amazing April where 110" of snow fell (~13" liquid); this would nearly double what we have accumulated during snow drought 2015. Fairly slim chances on this, but if we knew the answer, there would be no fun in playing the game!
 If this verifies, this weak trough might produce some of the lower snow levels experienced this winter. Yikes.

Should the Monday event be realized, we could see 6+ inches of snow fall above 7000ft. Not much help for the snowpack, but it will fill in a few skiable lines with a fresh coat of shreddability! The only place to really ski in CA, Mt. Shasta, will again be a big winner!

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Saturday, March 14, 2015

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Warm, Cloudy, and Possibly a Few Showers

Above normal temperatures will continue for much of the western U.S. with no real end in site. The plot below shows the temperature for the last 7 days at the Reno UNR weather station. We've been in the upper 60's and low 70's for the last week which is well above the normal for this time year, about 57-60 F.

You'll notice that we have had several nights with very warm lows, around 50 F. These warm nights coincide nicely with the incoming longwave radiation plot below. This is due to the abundant cloud cover, which absorbs shortwave radiation, and then emits longwave radiation towards the surface (throughout the night), keeping things much warmer than clear sky nights.

Today's clouds are due to an active, mostly meridional (south to north orientation), jet stream off the CA coast that is directed at the Pacific Northwest region. The storm shows up nicely on satellite, with a stream of moisture extending from the tropics.

Unfortunately, the main impacts for the Sierra will be strong winds tonight and tomorrow, with a few very light showers possible tomorrow. You can see that we are on the southern edge of a fairly strong 700 mb (~10,000 ft level) jet core by 18Z (10:00 AM) tomorrow morning. 
We will remain in this type of pattern for several days, with plenty of clouds, warm temps, and a better possibility of some showers (high snow level) by Tuesday or Wednesday, according to the GFS. Even if this does pan out, it won't do much for our snow pack. Get some turns while there is still snow, or do like many have already done, and make the transition to summer activities! No signs of a March Miracle at this point.

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