Thursday, April 30, 2015

// // 3 comments

Climate Data Mining in the Sierra Nevada

California and the Sierra Nevada are well know for the Gold Rush years of the mid 1800s, but for weather weenies like myself (and you likely fall into this classification if you are reading this blog) there is a wealth of beautiful long term climate records for the region just waiting to mined. As a weather and climate researcher data mining is a regular part of my job, and the long term observations really fascinate me.

Dr. James E. Church, who originally came to Reno in the late 1800s to teach foreign languages at UNR, developed the Mount Rose snow sampler in 1906, and the Mount Rose site now has one of the longest snow water equivalent records in the country.


Figure: Dr. James E. Church,  http://www.wcc.nrcs.usda.gov/factpub/wc_ss.html

Donner Summit and Mount Rose both have snow course records archived back to 1910, and can be found at the same pages as the Natural Resources Conservation Service SNOTEL data (http://www.wcc.nrcs.usda.gov/snow/). Below I have plotted up both sites showing the measured snow water equivalent on April 1st, which is considered about the time of maximum snow pack in the Sierra.

Some interesting things stand out when comparing the two sites. First, when considering the current drought 2014 and 2015 are the two lowest values in the Donner record, but at Mount Rose 2015 is tied for third lowest rank with 1948. The lowest value at Mount Rose was in 1924 followed by 1931. There are likely two main factors contributing to these difference: (1) orographic effect (Donner situated just west of the Crest, and Mount Rose in the Carson Range) and (2) elevation. From a skiers perspective, we know that during many storms, Donner and Rose can get similar snowfall or often times Rose is shadowed and Donner gets more, and rarely (during upslope events) Rose can be the big winner. The high freezing levels (ridiculously warm temperatures) during the past two winters is likely the main reason for Donner snow water equivalent being so much lower than Rose (~2000 feet elevation difference), and has played big role in the "snow drought" (here and in the Pacific Northwest).


Streamflow records can tell you quite a bit about drought conditions as well, particularly when you accumulate the streamflow throughout the course of the water year. The Merced River at Happy Isles in Yosemite has one of the longest records in the Sierra, dating back to the early 1900s. 



Shrad Shukla and Andy Wood developed the Standardized Runoff Index (SRI; http://www.hydro.washington.edu/forecast/monitor/info/Shukla_Wood_SRI_GRL08.pdf) to quantify streamflow drought based on the historical distribution. Below is the water year SRI from the Merced River, which is showing the accumulated streamflow throughout each water year. For the SRI, negative values mean drought, and positive values mean wet. This one only goes through 2014, but tells a similar story as the Mount Rose snow course: 1924 and 1931 were worse single year drought than 2014. Based on this SRI 1977 was actually the worst single year drought. Looking at the abysmal snow pack for this year, the 2015 water year SRI may actually be the new worst. 



There are many things to consider when looking at the current drought, and depending elevation, orographic positioning, and variable being considered you will find different results. I've only considered single year droughts here, and this multi-year event (four years now) is certainly one of the most severe in the past 100 years.

Well, I'm droughted out! Hopefully in the near future when can discuss extremes on the opposite end of the spectrum!
Read More

Wednesday, April 22, 2015

// // 7 comments

The Drought: Type 2 Fun



Western Basin and Range Province, http://bmvgallery.com/tag/pyramid-lake/
The ongoing western U.S. drought (Water Year (WY) 2012-present) presents a fine example of how variable the climate in this region of the world can be when compared with the more bountiful of cold seasons. Prolonged dry periods are not abnormal on geologic timescales and may be the rule rather than the exception, contrary to what we would prefer. Of course, present-day temperature anomalies worsen the effects as increases in temperature results in greater atmospheric water demand and less precipitation falling as snow. The result is less runoff, which in a society that dramatically undervalues the true value of water and overvalues activities that favor water waste creates myriad problems. Such problems span the gamut of socioeconomic and ecologic spectra and will require both creativity and sacrifice to solve.

Since the end of WY2011, which ATLiens four light years away are now observing ("mmmmmm Eagle's Nest izzzz looking gooooooood"), we have been shown that our "Western Heritage" is in jeopardy. Society has been bumping up against the speed bump guarding an irreversible state change of California (pun intended) and may roll over into the abyss should the drought persist. What's four years when 100-200 years are possible? Should the next couple of years be 'normal' (wouldn't that be nice) or even 'above-normal' (WHAT?! 118%! No way!) the current level of freakout might be climatically-mitigated and we can write about how rad it was to ski Tom and climb 15 stars worth of evening 5.11 at the Gorge in the same day. Pow to corn to pump to Las Palmas, oh yea! Or, the drought will continue in year 10 and maybe then your average Californian could explain to you where their water actually originated. Time will tell.

A golden opportunity awaits the Golden and Silver States to rapidly reorganize and shore up the fortifications of climate resiliency that are presently weakly, if at all, existent. Nearly infinite obstacles are in the way of such change, remnants of the Manifest Destiny still woven thickly through our softshells and Prana shorts. How to surmount such challenges I cannot know. I have removed over 2000sq ft of turfgrass on my property, reducing the water usage by 50%, all the while planting copious pollinator-friendly, climatically-adapted plants. Any water I free up in the system will be quickly snapped up by someone else for a use they deem worthwhile. On goes the cycle.

I've waxed and waned, but let me return to my thesis statement. Climate in the Pacific Southwest has and always will be highly variable. For many of us, previously extended dry periods are at best faint memories. We have now gotten a taste of what is possible and how to adapt our recreational activities and perceptions accordingly. Most likely, a decent or even great shred year is on the horizon within the next few years, but this is not a guarantee by any means. Life is all about gaining perspective. Seeing how one's perspective shifts in light of new evidence is a fantastic learning experience. To be sure, not all learning experiences are fun while they happen. But when you can reflect back with a higher level of understanding and say, "Well, that really wasn't SO bad..." the experience is usually recorded as a positive one. This process is often qualified as "Type 2 Fun." When you know an activity is going to be Type 2 Fun heading into it (or realize it before it ends), you might gain the psychological momentum to keep pushing forward despite the challenges. I see the drought situation in a similar light. Make the best of it, learn from it, and be stoked to capitalize on new opportunities. Once seasonal Type 1 Fun returns, 2011-XXXX will be just a long string of bike rides, hand cracks, slushy jibs, bolts, and core shots.
Read More

Saturday, April 4, 2015

// // Leave a Comment

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.



Read More

Monday, March 30, 2015

// // Leave a Comment

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.











Read More

Sunday, March 22, 2015

// // Leave a Comment

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.    

Read More

Thursday, March 19, 2015

// // Leave a Comment

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!


Read More

Saturday, March 14, 2015

// // Leave a Comment

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.


Read More

Tuesday, March 10, 2015

// // Leave a Comment

A Little Somethin'

The ridge of steel has been slowly pushing east across the Great Basin today and will take a temporary hiatus tomorrow as a mature closed low currently over the eastern Pacific pushes northeast into the WA/OR border overnight. As it does so, two small pieces of energy will break southeastward into the Sierra (Figure 1). The first piece will arrive early Wednesday morning and the second during the afternoon. Precipitation will be light on the west slope (0.45"of liquid +/-) and limited amounts east of the Crest (Figure 2). Conditions will cool down with time, but snow levels with remain above 7000 ft with light accumulation possible, particularly above 7500 ft. Over the next 24 hours, we can expected:


  • Mild and overcast this evening with increasing SW winds (breezy overnight)
  • Light rain (snow) over Tahoe below (above) 7500 ft by Wednesday morning
  • Precip will become isolated around mid day with another light pulse in the afternoon
  • Temperatures cooling through the day on Wednesday
  • 2-5 inches of snow possible above 7500 ft with a few wet snowflakes below 
  • Ridge builds back on Thursday with north winds keeping temps cooler
  • Rebounding temps on Friday as winds turn easterly
  • Ridging Friday-Saturday with another mild event possible by Sunday evening


Figure 1 illustrating the synoptic situation over the mid troposphere this afternoon. The departing ridge over the Great Basin with the closed low over the eastern Pacific and the 2 small pieces energy expected to arrive over the Sierra Wednesday.


Figure 2 illustrating the liquid precipitation expected over the Sierra through Thursday.


Read More

Sunday, March 8, 2015

// // Leave a Comment

Recapping a Bummer (Future?) Winter

Well it's March now and if you felt like we didn't really have a winter (December through February), you are somewhat correct. The Sierra and the Cascades had a warm winter as evident in Figure 1. The Cascades received approximately their average precipitation, but as you may have noticed, we did not (Figure 2).
 Figure 1. Average temperature departure from average from December 8 through March 7. 

Figure 2. Water year (since October 1) precipitation percentage of normal. 

Record to near record winter temperatures (Figure 3) significant hurt snowfall totals leading to much below average snow-water equivalent percentages (Figure 4) and record to near record low snowpack in the Sierra (Figure 5). All of this means less spring skiing and a small window for that desired corn cycle we enjoy in March and April each year. Low snowpack equates to quicker melting, which not only hurts our spring skiing, but has major implications for water especially in a historical drought.

Figure 3. Average temperature ranks for climate divisions across the United States for December through February.

Figure 4. Snow-water equivalent percentage of normal for March 8.

Figure 5. Snowpack percentage of average for March 3 and April 1. Also shows the minimum and maximum snowpack on record. 

Is this a sign of things to come for future winters? That is the million (trillion?) dollar question. Some climate projections under climate change forecast rising snow levels. Dr. John Abatzoglou addresses this question (and others) in a great blog post located here: https://climateinw.wordpress.com/2015/03/07/coming-soon-the-new-normal/.

Is there any good news? Possibly. We do have a weaker storm moving through this week (Wednesday-Thursday). However, as of now, it's not anything to get too excited about. Additionally,  models forecast the Madden-Julian Oscillation (MJO) to amplify and move into phases favorable for moisture transport into the western United States. However, the GFS model forecasts a larger MJO amplification than other models (Figures 6-7).

Figure 6. MJO phase diagram with GFS ensemble forecast (green lines). Phases 6-8 can be favorable for western United States moisture transport. 

Figure 7. MJO phase diagram with statistical forecasts (green, pink, blue lines). Phases 6-8 can be favorable for western United States moisture transport. 

If this occurs, we can expect some atmospheric river events for the West Coast. Those events are wet and usually warm, especially during spring. Any precipitation is welcomed especially for drought stricken California. However, it probably won't do much for the snowpack and it could actually hurt it with any rain on snow.

Read More

Wednesday, March 4, 2015

// // Leave a Comment

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!





















Read More

Saturday, February 28, 2015

// // Leave a Comment

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!



Read More

Thursday, February 26, 2015

// // Leave a Comment

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!


Read More

Tuesday, February 24, 2015

// // Leave a Comment

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!
Read More

Sunday, February 22, 2015

// // Leave a Comment

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.
Read More

Friday, February 20, 2015

// // Leave a Comment

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.


Read More