Saturday, February 28, 2015

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Not Too Shabby

I woke up this morning and the first thing I did was check the ski resort snowfall totals. Alpine Meadows: 17". Squaw Valley: 17". Sugar Bowl: 8-12". Sierra at Tahoe: Trace. Heavenly: 0". Wow! North Shore wins by a land slide! This was a cold and unstable weather system, with little moisture and a lack of good orographic forcing (strong W or SW jet stream over the Sierra). Much of the snow was produce via convective instability, making it extremely difficult for a forecast model to identify the exact location of the heaviest bands.

I skied Alpine Meadows today and it felt great just to be out there skiing in the cold while it was snowing. It was also nice to not have to worry about snow levels for once this season. Conditions were great with plenty of light, fluffy pow to go around. Plenty of obstacles lurking just beneath the surface, so be careful out there.

The area of low pressure that brought us the snow will shift south tomorrow leaving us plenty cold, with maybe a few lingering snow showers.

weather.rap.ucar.edu

We remain under the influence of a trough through early next week, with the possibility of some light snow. At this point, accumulation looks pretty meager.


We ridge back up by next weekend, so enjoy the fresh snow while we have it!



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Thursday, February 26, 2015

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Wintry weekend ahead

Upcoming weather highlights:

  • 4-12+ inches of snow throughout the Intermountain West
  • Cold temperatures, light winds
  • Increasing northerly winds early next week

The seasonable temperatures this week have been a welcome change from the outrageously anomalously warm weather that has plagued the eastern Pacific for much of the winter season.


The expected temperature asymmetry under Omegasaurus Rexbloxus (higher min than max) has not been realized which is worthy of further investigation. Either way, the snowpacks of the Pacific cordillera have been getting demolished in many ways this year, be it rain (PNW and CA), no precipitation (CA), and anomalously higher temperatures (CA). Yikes.




Back to the upcoming snow. The formation of a deep closed low over the region this weekend will bring chilly temperatures and snow to the much of the western U.S.
Expect totals to range from 4-18 inches over the course of the Saturday-Tuesday in the Basin and Range with the bulk of the precipitation falling over the weekend.
This will be low density snow, so choose your runs wisely as sharks are lurking! The northerly winds will pick up early next week and will have no problem redistributing that champagne quicker than Kanye on the way to the Grammys. Keep a look out for graupel as well, a classic indicator of an unstable atmosphere that favors convective snowfall.
While it is not the 6-10" liquid soaker we'd love to see, anything falling from the sky is welcome particularly if it comes in a frozen form. Have fun!


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Tuesday, February 24, 2015

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Seasonable and Breezy

Seasonable temperatures and cool northerly winds will continue through the middle of the week before picking up ahead of the deep continental low that will (likely) swing through this weekend. The Four Corners looks to be the place to go if you are looking for a weekend wintery getaway, although the Great Basin should pick up a few inches of fluff. Good enough for harvesting turns if you are into it! For the midweek fun, the cool temperatures should make for enjoyable groomer runs so get out and work on that form!
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Sunday, February 22, 2015

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Back to reality

The current storm system will continue to produce snow over the southern Sierra with Mammoth and points southward picking up another couple of inches overnight. The next storm looks to impact the region next weekend. Temperatures return back to normal after almost two months of above average and record setting temps.

-Additional accumulations of 6 to 12 inches over the Southern Sierra tonight
-Temperatures return back to normal for the foreseeable future
-Next storm looks to impact the the area next weekend

The low pressure system impacting the Southern Sierra will continue over night with additional accumulations of 6 to 12 inches over the higher elevation and some locations seeing even more. Snow will begin tapering off in the predawn hours with light snow showers continuing over the high Sierra until noon or so.

A major pattern shift is underway as the high pressure ridge that has plagued the west coast retrogrades (fancy term for moves to the west) offshore.  Just how warm has it been? Figure 1. shows temperature compared to normal since the beginning of the year at South Lake Tahoe.
Figure 1. Temperature (top) and precipitation (bottom) compared to normal for 2015 at South Lake Tahoe
 The above average and record setting temperatures have caused snow melt to occur much earlier than normal.  Figure 2. shows the rapid loss of snow water equivalent at the Central Sierra Snow Lab.
Figure 2. Snow Water Equivalent (blue line) and precipitation (red line) observed at the Central Sierra Snow Lab near Truckee since October 1st.  The light blue and light red are the average snow water equivalent and precipitation respectively.
Rapid snow melt has occurred since the beginning of the year and intensified over the last week as temperatures soared into the 60's and the sun angle continues to rise in the sky.

Luckily for the snow pack and water interests, the westward motion of the ridge will allow colder air to make its way into the Western U.S., ultimately slowing the snow loss and open the door for storms to reach the Sierra.  The next of these storms looks to arrive at the end of the week and into next weekend.  Hopefully all of our prayers to Ullr are being heard and winter will begin to make a comeback.
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Friday, February 20, 2015

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Inside Slider Just in Time for Pitchers and Catchers Reporting

Well, I could talk about how depressing the snowpack is or I could talk about the storm coming in this weekend. Let's talk about the relatively good news first. We have a nice inside slider moving into the Great Basin and Sierra late this weekend and early next week that will bring us some snow. Not a lot, but some.

Figure 1: Storm total precipitation via the CNRFC 
  • Snow begins early Sunday morning stretching north to south from Portola towards Bishop and further south
  • Areas around Tahoe will receive 1-4" of snow with some isolated areas near the Sierra Crest and east receiving twice that depending on where convective snow showers develop
  • Kirkwood (4-8") and Mammoth (6-12") should receive the most snow
  • There isn't a lot of moisture with this storm, but it is cold and snow levels will be to valley floors
  • Very dry snow = powder


Figure 2: 1-hour precipitation total color shaded and snow levels color contoured valid Sunday morning via CANSAC

What is an inside slider? I'm glad you asked. An inside slider is an upper level trough that develops just east of a ridge centered over the eastern Pacific. Due to the amplitude (how far north the ridge stretches) of the upper level ridge and the cold air distribution and overall flow pattern across Canada, a trough slides down along and east of the Cascades and the Sierra. It usually possess a positive tilt (axis of trough looks like this: /) and moves north to south along the mountains.

Figure 3: 500mb (~9,000-10,000 ft.) heights, winds, and temperature. Notice the upper level trough across the northern Great Basin and Pacific NW and its orientation as a positively titled trough. This will slide south over the weekend and into early next week.

This storm will be cold therefore snow levels will not be a problem. Due to the trajectory of the storm, there will not be more snow along the crest and west. More than likely there will be more snow along the crest and east due to the upslope flow residing on the east side for this storm. The snow will be very dry and powdery and there is a slight chance of some thunder snow (cue Jim Cantore's reaction).
Figure 4: Water Year (since October 1) Precipitation % of Normal by Basin

Now, the bad news. I will make it brief. The good part of the bad news is that we are near normal or close to it for precipitation since October 1 (I'm fudging a bit here calling 55-65% near normal) (beginning of the water year) (Figure 4). However, as we have said, too much of that precipitation has fallen as rain with the higher snow levels we have seen with our biggest storms this Fall/Winter. We are way below normal for snow-water equivalent (Figure 5). The rain has helped with the drought, but it would have been much better if it had fallen as snow. With a better snowpack, then the water storage lasts longer into the warm season and does more to help alleviate the drought.

Figure 5: Snow Water Equivalent (SWE) % of Normal by Basin

We will have another post up this weekend detailing the upcoming storm and a look into a (hopefully) snowy future.


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Friday, February 13, 2015

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Holy Inversion Batman!

I'll start by being straight forward and saying that we have no hope of any significant (or weak, really) storms within the next 7 days. The figure below has been way too familiar this winter over the western US. White blob of nothingness over the Sierra Nevada, boo!


That doesn't mean there is nothing interesting to talk about weather wise. The persistent ride of high pressure over the west has led to some rather extraordinary temperature inversions for the Reno-Tahoe region. The sounding, showing weather balloon data, from the Reno NWS office is shown below. Weather balloons are released twice a day around the globe at exactly the same time, which provides valuable input data for the atmospheric models that produce our forecast. Pretty amazing!

Even more amazing is the strength of the inversion found in the vertical profile, and just the general nature of the early morning heat wave. The x-axis of the graph is temperature (red line air temperature and green line dew point temperature) and the y-axis is elevation (pressure units are shown in mb, but that is easily translated to elevation, and 700 mb is ~10,000 ft.). At the surface, the temperature was about 45 F at 4:00 AM and a whopping 55 F at ~7500'. Toasty!

Figure: Sounding from Reno NWS at 4:00 AM on 2/13/2015. Source: weather.rap.ucar.edu


Figure: The yellow dots show the locations of all the global sounding release points. At each location a balloon is released at 00Z and 12Z every day.

This inversion translated to some really warm temps at the ski resorts this morning. Check out the Alpine Meadows sensor at 7800'. It was 65 F at 9:00 AM today! There is basically no hope for a good corn cycle in the near future, until we start to get down near or below freezing at high elevation overnight.

This could turn out to be a fun weekend for resort skiing, pond skimming, and beer drinking. Get it while there is still snow!




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Monday, February 9, 2015

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Climate System 3 : 4 Sierra Nevada

After a truly grueling match between the dueling planetary forces of land against coupled climate system, the match ends. That was a close one! Things could have been a lot worse, but we won't go there because now there is new snow in high places and IT SKIED AWESOME! There is something special about proper Sierra Cement with some cold smoke on top...

Let's see how the match was decided:

Climate System 1:0 Sierra Nevada
While we did get snow, compared to normal (albeit modeled) we need a lot more! A few choice locations faired well, however. Time to burn some dinosaurs?

Climate System 2:0 Sierra Nevada

Of course the gradient of precip was the largest just before getting into the BEST terrain and what will support a sweet terminal lake! Yellow Card, Paoha Island, for aggressive tackle after the goal.

What snow we ended up with sure is soaked! The amount of water that can be absorbed into a unit volume of snow before producing runoff is impressive. Then you freeze it at saturation and start stacking new flakes on top. Not a bad recipe for hiding rocks and other hazards. The 10 inches that fell at 7k into early Saturday morning broke the stride of the Climate System and acted as a serious sponge and buffered what might have been irreversible damage done to the snowpack. It is always worth skiing in the rain every once in a while. Real west coast slidaz know what I'm sayin'!

Climate System 2:2 Sierra Nevada
t
We got snow. Yes. Not everywhere, but somewhere, and that is all that matters.

Climate System 2:3 Sierra Nevada

The Sierra Nevada supports almost all the remaining perennial Great Basin terminal lakes, most of which are some of the coolest features on the planet for various reasons.


Lots of water into Pyramid Lake!!!!

Climate System 3:3 Sierra Nevada

Given it's location, movement, epoxy, fixed gear and view, the Totem Pole was one of my favorite climbs on Donner Summit. Yes, I clipped the bolts, and I know the Queen is angry. Hopefully those who climbed this route enjoyed it! This is the second catastrophic failure of Donner Summit aka Chossville; the other being on the Stealth Wall. They are similar types of granite I believe, but we'll have to consult R. Putnam of Sonora, CA for the full rundown (maybe a guest post in the future).  Geologic forces at work in fine style over many scales of time:


Climate System 3:4 Sierra Nevada


What better day to do a classic kayak run than a standard rain on snow day! Folks were loving the conditions.

Get it while you can!

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Friday, February 6, 2015

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One, Two, Update


As Mathew McConaughey would say,

Snow levels have been lower than expected but should unfortunately continue to rise over the next few hours as warm moist tropical air continues to stream into the Sierra. The snow levels bottomed out around lake level earlier this evening with about two inches of accumulation near Tahoe City.  Radar observations showed snow levels dropped to as low as 4700 feet at one point which is really quite impressive considering the warm nature of this storm.  This is in large part due to two atmospheric phenomena, wet bulbing and an isothermal layer.  

Wet bulbing occurs when precipitation falls through dry air. The precipitation evaporates and cools the air as it falls through the dry air like sweat on Randy Daytona.

Meanwhile an isothermal layer occurs when the temperature remains the same throughout a vertical layer of the atmosphere. For example the temperature above Incline Village was the same as it was at Verdi.  Today, the isothermal layer allowed snow levels to drop much lower than forecasted and gave motorists quite a surprise over Donner Pass.  

Below are some videos from Mt. Rose Summit this afternoon and the surf on Tahoe which a couple of surfers were taking advantage of.







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One, Two... Dump

Deep tropical moisture from east of Hawaii will finally make its way into the Sierra this afternoon and hang around through Monday morning.  Two wet and unfortunately for all of us skiers, warm systems will impact the region this weekend.  The first is currently knocking on the door with moderate to heavy rain currently overtaking the Central Valley. The second system is scheduled to move in on Sunday and persist through Monday morning.

-Two very moist systems will clobber the Sierra this weekend thanks to an Atmospheric River
-Due to the tropical nature of the moisture, snow levels will be high (7400-8200 feet) before dropping to lake level Sunday night
-Sierra Cement will pile up above 8200 feet with 4+ feet possible on the highest peaks


Precipitable water from the 06Z GFS model showing an Atmospheric River stretching from east of Hawaii into the Norther California.

The first system will dump two to three inches of precipitation over the Tahoe Basin by tomorrow afternoon.  The crest and points northward will likely see more with some some locations getting as much as six inches of precip.  The storm will begin to wind down tomorrow morning but moisture will continue to stream into the region throughout the day providing additional precip accumulation of an inch or two. Before another colder system moves in Sunday and drops another two to three inches of precip over the area.  The Weather Prediction Center (formerly the Hydrometeorological  Prediction Center) has as much as 11 to 13 inches of precipitation along the crest through Monday afternoon...

Forecasted total precipitation amounts through Monday at 4 pm PST

We haven't had this much precipitation in the Sierra in a three day period in over two years!

Unfortunately for us skiers, the majority of this precipitation will fall as rain from 7800 feet down, at least until Sunday night when snow levels drop to lake level. The majority of ski areas will see significant degradation of their snow pack from lower mid-mountain down.

Where snow does fall it will be very heavy with snow to liquid ratios of 6-8 to 1.  That means classic Sierra Cement and even some "dippin-dots" (technically known as graupel) at times due to the very deep moisture in the atmosphere.

The precipitation amounts will drastically drop off east of the crest with the first storm. Leaving higher elevations of the Carson Range with 7 to 14 inches of snow through Saturday. The second storm is much more favorable for spillover as the atmosphere will be more unstable and could see some areas of the Carson Range with 2 feet of the snow.

Bottom line stay up high and enjoy the Sierra Cement.  Places like Kirkwood, Heavenly and Mt. Rose look to do extremely well this weekend due their higher altitude.





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Tuesday, February 3, 2015

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The 2014-15 Sierra Winter is at a Crossroads

WE HAVE WEATHER TO TALK ABOUT! LET US ALL REJOICE!

OK, I got that out of my system. We have an atmospheric river (Pineapple Express; Figure 1) event occurring late this week and into early next week bringing much needed precipitation to Northern California and the Pacific Northwest. However, per usual, there is some uncertainty associated with the event.

Figure 1. Precipitable water forecast valid Friday afternoon. Notice the higher precipitable water values stretching from Hawaii to the California coast. 

WHAT WE KNOW
  • An atmospheric river (Pineapple Express) has set up across the eastern Pacific
  • This will bring significant precipitation to Northern California including the Sierra and the Pacific Northwest through the weekend
  • Multiple atmospheric waves will move over the Sierra Friday through Monday
UNCERTAINTY
  • Everything else…just kidding…but seriously…
  • SNOW LEVELS: These will fluctuate throughout the event with the passage of multiple waves, uplsope cooling, development of isothermal layers (temperature remains relatively consistent in the vertical through a layer), and some wet bulbing due to dry layers in the atmosphere (good explanation by my former colleagues: http://www.mesonet.org/files/materials/Classroom_Winter_2006-07.pdf)
  • Ratio of snow and rain, which is highly dependent on the snow levels
  • Total amount of precipitation especially east of the Sierra Crest and in the southern Sierra
SCENARIOS
Scenario #1. Probability of occurring 50% 
The core of the upper level jet moves directly over Tahoe and the deepest moisture associated with the atmospheric river doesn't reach the crest and the central and southern Sierra. This scenario would be similar to what we have seen with previous atmospheric river events this winter; good precipitation, but with higher snow levels. 

Figure 2. Accumulated liquid precipitation forecast amounts for the next 7 days. Via the WPC. 

Snow levels would hover around 8000 ft., but would fluctuate between 7000 and 9000 ft. over the weekend including dropping early Saturday and again on Monday. If this occurs and with the precipitation forecast of 2-6" (Figure 2) of liquid precipitation, snowpack below 7000 ft. (what's left of it) would be decimated and snowpack above 8000 ft. would receive 1-2 ft. of heavy Sierra cement snow depending on location and elevation. 

Scenario #2. Probability of occurring 30%
The upper level jet stays to our north, the area receives 20-50% less precipitation than Scenario #1, and snow levels remain around 9000 ft. until Monday. 

If this occurs, GAME OVER. BYE BYE WINTER. SELL YOUR SKIS. 

This would equate to 1-5" rain below 9000 ft., which as you know is most of the ski-able terrain in the Sierra near Tahoe. Scenario #2 would be catastrophic to the snowpack and for the winter moving forward. We would essentially have to start over. 

Figure 3. Probability of the 500mb (mid-level) heights in the upper or lower third of climatological data over the weekend. Essentially, if it is red, you have ridging (warmer, less weather) and blue is troughing (colder, more active weather)

Figure 3 shows that the Sierra and Tahoe are once again in a transition zone. The lower heights, colder air stays to the west and north. The ridge does flatten, but it doesn't fully break down (stubborn Omegasaurus). Without strong cold air accompanying the jet and pushing east to southeast, the ridge flattens but doesn't go away. This is one reason why snow levels could be higher and that the storm track could shift slightly to the north.

Scenario #3. Probability of occurring 20% 
The upper level jet slides south of Tahoe, we receive about the same amount of precipitation as Scenario #1 (2-6"), maybe a little more, and snow levels would fluctuate between 6000 and 8000 ft. This is obviously the best case scenario with snow down to and below lake level for at least part of the storm with snow above 7000 ft. for the majority of the event. This event will also promote more spillover precipitation, so Mt. Rose, Heavenly and western Nevada would see more rain and snow. This would drop 1-3 ft.+ of some prime sticky Sierra cement. 

Models recently have trended to a slightly more southerly track for the jet. IF this continues and colder air can make a strong push to the east/southeast, the probability of Scenario #3 occurring increases. HOWEVER, I am skeptical of any significant southerly storm track change due to the presence of the ridge, the orientation of the waves, and what we have seen recently. 

If you are still reading at this point, congratulations. As the title of the post says, this weekend represents a crossroads of sorts for the 2014-15 Sierra winter. And when I think of crossroads, I think of Bone Thugs. And if you don't, shame on you. 


The crossroads facing the Sierra doesn't include missing Uncle Charlie (RIP Uncle Charlie) but it does include the three scenarios described above. This event could bring some needed precipitation that will help fill reservoirs in Northern California, but with high snow levels. This event could also decimate the snowpack with a major rain on snow event. And finally, it could provide a nice reprieve from the bummer of the winter we've had and refresh the snowpack for most of the resorts, especially the higher elevation ones (Kirkwood, Mt. Rose, Heavenly, etc.).

We will have updates throughout the week, so stay tuned. 




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