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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Monday, October 20, 2014

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Anti-Seasonal Outlook, Seasonal Outlook: Part I

            Over the next four days, Powdiction will bring you the inaugural Anti-Seasonal Outlook, Seasonal Outlook: A Four Part Series. Each day, a different aspect of seasonal outlooks will be discussed hopefully in a coherent manner. I know you are thinking we may have gone all Peter Jackson with splitting this up and dragging it out. However, we hope this will inform our readers about the current state of the climate (spoiler: not good), what could change it, how it’s forecasted, and the difficulties in doing so.
            The Sierra Nevada mountain range is in extreme to exceptional drought, which are the two highest categories. Essentially all of California and Nevada are drought stricken with it being the worst in recorded history in some areas of California. This drought started way back in 2011, after we had an epic powder year. Then the drought progressively worsened each year.
            Some areas in the Sierra had above average precipitation over the summer, but it barely made a dent into the drought. That is due to the low monthly precipitation averages during the summer (June-August), which makes it easier to be above normal. For example, Tahoe City averages 0.30” of precipitation in August, and this August Tahoe City received 0.89” of precipitation, which is nearly three times the average. Furthermore, Tahoe City averages 5.55” of precipitation in December. So 300% of average precipitation in August is only about 16% of normal December precipitation.
            Most precipitation in December falls as snow, which acts as a water reservoir through the spring and into the summer. Compared to summer thunderstorms, which are usually short, intense rainfall events, snowmelt is preferable due to the increased duration and the gradual nature of the water moving into the soil, plants, lakes, rivers etc. One caveat this year is the rain event we had associated with a tropical disturbance moving along the Sierra August 4th and 5th that brought mostly steady rain. Bottom line, we need a good winter to bust this drought as the below graphic eloquently illustrates.

            The Sierra depends heavily on cold season precipitation. The majority of the precipitation falls November through March. For example, Tahoe City and Truckee receive more than 70% of their annual precipitation in these five months.  So what’s on tap for this winter?
            For the past 29 months, the El Niño-Southern Oscillation (ENSO) has been neutral. This represents the 3rd longest ENSO neutral period since 1950. And examining ENSO’s history, each instance where ENSO has been neutral for more than 13 months, an El Niño has followed.
            Well there has been a forecast of El Niño for the past several months. While the Southern Oscillation Index (SOI) has been borderline El Niño since July, the sea surface temperature (SST) anomaly has been stuck in neutral. The SST anomaly is much closer to an El Niño than La Niña currently and has been since the spring.
            The reason I am discussing ENSO is it can be a strong influence on the weather and climate, and for us to bust the drought; we need a change in the atmosphere. Ridges control the weather and they tend to establish over areas of drought. That does not bode well for us. So a change in ENSO or other atmospheric-oceanic circulations needs to occur to break this rut. 

            In the subsequent posts, we will discuss ENSO, some of the other atmospheric-oceanic circulations, seasonal forecast guidance, the complexity of seasonal forecasting, and how it all affects the Sierra and Tahoe. Stay tuned for Part 2 of Powdiction’s inaugural Anti-Seasonal Outlook, Seasonal Outlook: A Four Part Series!
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Monday, May 5, 2014

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Corn Window Open

After a bad week for freezing temperatures at lower and upper elevations, the recent cold front has brought the recipe for perfect corn conditions to the region. Higher elevations will now have had a solid freeze since the last snowfall and middle elevations will have finally experienced sustained cold temperatures at night for several days in a row. This means excellent spring skiing is ahead! As if it wasn't already pretty good in select locations, now it will be super duper everywhere once the wind abates.

Tuesday will have continued cool temperatures, cloud cover, and some light precipitation but by late Wednesday we will be transitioning back into seasonal conditions. For Wednesday, blustery northerly winds and slightly lower than normal temperatures will keep the corn window cracked but only with wise choices of terrain and aspect. Thursday onward should be straight up awesome. Get some!

Tales of coverage and quality remain great given the lackluster totals this season. Saddlebag Lake road should open any day with many fun steep runs to be enjoyed. Solstice, Ripper, Chute Out, and others are skiing well and should have sufficient coverage for a short while. Shasta's south side is still in play, the east side should be coming into awesomeness now that a few warm days helped transition to spring, and the north side has lots of walking. Lassen is likely still a ton of fun with some Devastated walking required (not sure on the south side entrance situ, should be open anytime if not already). Tahoe is just about dun-dilly unless you don't mind a long stroll. 

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Thursday, April 24, 2014

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How Bout Some Late April Pow

Interesting start to the weekend as a strong polar jet amplifies over the northeast Pacific this evening (see Figure 1) prompting a moderate shortwave pulse to impact the Sierra. Two bursts of precipitation are expected on Friday. The first in the morning associated with strong cold advection, and the second during the afternoon-evening as the upper-level energy works through. Snow accumulations of 12-18 inches will remain concentrated near and above 7,500 ft, particularly further south in around the Mammoth Lakes area, with a coating to a couple inches possible below the 7,000 ft level.

Figure 1 illustrating the location of the upper-level amplification of the polar jet west of British Columbia. 
The mid to upper level cold air associated with this late April storm is quite impressive (Figure 2) and shall enhance the volume of snow accumulation at high elevation. Figure 3 reveals a broad area of 1-2+ inches of liquid precipitation across the Sierra. As cold fropa approaches tonight, winds will continue to ramp up from the southwest. Cold air arrives early Friday morning along with the first burst of precipitation. Intermittent to moderate snow showers continue through the day Friday before a heavier second burst in the afternoon-evening associated with the upper-level vorticity advection. The vorticity advection and central core of the upper trough appear to take a more southern trajectory across the Sierra prompting a bit more orographic enhancement further south along the Crest (Figures 4).

Figure 2 illustrating the cold air advection at 700 mb. Note the perpendicular nature and intersection of the blue-dotted isotherms and black-solid height contours. 

Figure 3 illustrating the broad swath of liquid precipitation across the Sierra through Sunday AM. 

Figure 4 illustrating vorticity advection (red) further south coming into the Sierra. 
As this system exits to the east Saturday, residual snow showers will be frequent with minor additional accumulations likely. Then on Saturday evening, another weak shortwave attempts to press south from the Pacific NW, although the amplifying ridge off the southern California coast assumes control Sunday night. Ahead of this ridge building, a period of convective snow showers associated with a pulse of mid level moisture will be the feature on Sunday. 

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Monday, April 21, 2014

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Mother Nature pulls a Lee Corso on us and says NOT SO FAST! to summer. The next 7 to 10 days will be a reminder that it is still spring. MJO is in an active phase for the west coast, PNA is in a somewhat favorable phase, and AO is more favorable than unfavorable, which all together leads to stormy weather.

 Mother Nature pulling a Lee Corso and saying, 'NOT SO FAST!' for summer weather.

The first storm will impact the Sierra tonight and tomorrow, dropping 0.1-0.5" of precipitation and 1-3" of snow. It will get cold with snow levels dropping below lake level tomorrow. The next storm beginning Thursday evening and lasting through Saturday will be stronger and drop 0.5-1.5" of precipitation and 4-8" of snow with some high elevations areas possibly reaching 1". That is a little further out, so we will keep monitoring the storm for any changes.

HPC 5-day precipitation forecast. 0.5-2" across the Sierra.

 9-10,000' winds, temperatures, and heights. Will get cold tomorrow and again late this week. 

Now you may ask how rare is this? Well after digging around with the help of WRCC data, I found that it is not that rare. Looking at the last 15 days of April since 1960 the Central Sierra Snow Lab (~7000' near Soda Springs) has had 294 days with precipitation and 197 days with snow. The average precipitation per day was 0.15" and average snowfall per day was 1.18". The average snow depth for the 2nd half of April was 63" or just over 5'. The average maximum temperature was 47 degrees and minimum temperature was 25 degrees.

So, about 1 out of every 3 days during the 2nd half of April has precipitation and 1 in 4 days has snow. Compare this to Reno for the same period and only 1% of days saw snow and 4% of days recorded precipitation.

Bottom line is, this is pretty normal and we should be happy because it will slow the decline of the snowpack and extend spring skiing/snowboarding just a bit longer. We will have another post up mid-week getting more into the specifics of the late week storm.

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Friday, April 18, 2014

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Big Line Spring Window: Get It While It's Open!

Many of our favorite spring ski areas now have road access, including Tioga Pass (120, to the bathrooms), Sonora Pass (108), South Lake (167) and Lassen (89 to the Devastated Area). The low snowpack allowed these roads to open soon, but the sharp edge of the sword means that good skiing will not last as long as we like. The North Peak/Conness zone and Brewer Creek sides of Shasta will be some of the only good May options, barring a final Pacific blast of winter. As awesome as snowboarding North Peak in June or July is (as JimW caught me doing in 2010), those months will be better spent on the rocks, trails, or other ranges.

To keep things rolling into June and onward, the Cascades (Mt. Hood north) and Tetons are going to be the best options.

When on the search for the ultimate corn descent, especially on volcanoes, the following two parameters are of key interest:
  • 700mb winds and temperatures: These can make or break your spring ski run. Too cold and breezy and you better hope you sharpened your edges. Too warm and it's a slush fest complete with wet slides. A volcanic note of importance is that due to their mass ripping into the troposphere, cloud formation can take place very quickly while all other free atmosphere regions at the same level remain clear. This makes for changing conditions (lack of melting, rapid refreezing) and visibility challenges. Always watch the clouds.
  • Overnight lows: If it doesn't get close to 32 (or lower in ideal cases), you are hosed. Slarving slush is fun at the resort but laying globatacular trenches on beautiful stratovolcanoes is poor form. Recently, we have had rather warm overnight temps that have wrecked havoc on the snowpack, as melting was able to occur 24 hours a day instead of during a 10 hour window. 34 or 35F is around the limit for acceptable freezing of the snow surface, but it is far better when a solid freeze takes place with regards to safety and fun.

Yikes! Let's hope for some cooler weather.

Conditions on Tioga have been reported as very good, we skied Lassen's north face with excellent results last week and the Trinity Chutes on Shasta (6400 vertical foot run to the car!) were stellar. Get it while you can!!!!
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