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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Wednesday, March 4, 2015

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The Unwelcomed Guest Returns

After a welcomed moderate snowfall this past weekend, our wintertime foe, aka Omegasaurus Rexbloxus, the Ridge of Steel, the Impenetrable Wall, or the Unwelcomed Guest, returns for another extended visit for the unforeseeable future. Figure 1 illustrates the flow blocking demon reestablishing a presence.
Figure 1. 300 mb wind/height illustrating the intensifying ridge off the California coast. Courtesy of Golden Gate Weather Services.
The day/night trend ahead, at least for the next week, will be a familiar one with the following expected:
  • Rebounding daytime temperatures with mainly sunny skies
  • Light north winds becoming easterly with time 
  • Cold mornings in the valleys with moderate inversions and slow mix out
  • Pleasant and milder at higher elevations with south-facing snow softening by mid-late morning
Much attention centers on the root cause of the persistent ridging we've been experiencing throughout the winter. In fact, the last three winters have been pretty exhausting for Sierra snow enthusiasts. An overwhelmingly positive Pacific North American (PNA) pattern with a dominant ridge off the west coast of California and a trough over the eastern two thirds remains a consistent theme. PNA behavior has been linked to all the prominent intraseasonal (within season) modes of variability such as the Arctic Oscillation, North American Oscillation, and not excluding the more slowly changing Madden Julian Oscillation. Interseasonal (between season) variability such as El Nino/La Nina modulates the behavior of the former intraseasonal indices as well. The full extent of the interaction amongst these modes remains unclear despite all the teleconnection studies that have been published. The near-neutral (macroscopic) signal for El Nino/La Nina over the last three winters is the only persistent observation to be gleaned. It sure seems like there's a larger component of this puzzle at work. The elusive nature cries out to lesser understood phenomenon such as a natural external forcing mechanism (e.g., the variation in solar activity), or an internal forcing mechanism as part of the oceans?

For now, put on the sunblock and shades and enjoy our "not too shabby" snowpack while we have it!

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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.


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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