Friday, January 30, 2015

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Fingers Crossed

Lets start with good news: there is ONE model indicating a wet storm could impact the Sierra by early next weekend. The GFS brings heavy precipitation into NorCal and the northern Sierra by late Friday night (February 6th). The other THREE models that I've looked at keep the main moisture plume to the north to start the weekend.

 Source: tropicaltidbits.com

The only reason I'm even posting a 198 hour forecast is because there has been nothing exciting for nearly a month now (over a month?)! The bad news: the figure above shows rain and snow, with nothing but rain in CA (including the Sierra). This appears to be an atmospheric river type event, with warm origins (wah wah wah, no bueno). Any liquid is good for CA, but we really need the snowpack. OK, we will just have to wait and see how this plays out next week, because the forecast will undoubtedly change.

 This weekend into next week will remain balmy and dry in the Sierra, while the northeast is under the gun again with another developing Nor'easter. This is a common pattern when a blocking ridge sets up in the west.
Source: tropicaltidbits.com

Oh, hey, here is where all our snow is going! Nova Scotia, awesome!

This should come as no surprise, but we could expect another mid-winter heat wave by early next week in the west...I wish I had some good news. 850 hPa represents about 5000 ft. above the surface, or around the elevation of Reno, NV.

Source: tropicaltidbits.com

Maybe for once things will change in our favor by next weekend, and the atmospheric river will couple with cold air from the north (doubt it)! Until then, keep working on your tan and getting in shape for summer activities.

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Monday, January 26, 2015

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Enough to Rinse Off the Chalk!

A nice little tropical dose over the next 24 hours should dampen the soil and rinse off the tickmarks on your projects. Tropical moisture exports are important components of the planetary circulation.
The highly amplified southern stream is contributing to blowing up eastern North America.
Between 0.25-0.5 inches of liquid will be welcomed by all living things in the central and southern portions of the Great Basin. Snow will be falling in the higher country with light accumulations.
Probably a good weekend to avoid climbing in the southern regions!

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Saturday, January 24, 2015

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Six more weeks of Summer


Put up the skis and break out the swim trunks and sun screen.  Two more days of near record or record high temperatures across the Sierra before a weak system moves in from the south and brings some light precipitation over the area.

-Above normal temperatures continue for the foreseeable future
-A weak system will bring some light snow to the high elevations on Tuesday
-Possible storm for the Southern Sierra at the end of the work week

This system will do little more than drop the temperatures and bring a couple of inches of new snow to the higher elevations.  Models have trended a bit wetter as can be seen in Figure 1.  Hopefully the trend continues and this system exceeds expectations.

Figure 1: Comparison between the 00z GFS (on the left) and the 18Z GFS (on the right) for accumulated precipitation from now through Thursday at noon 
Another storm is forecasted to impact the Southern Sierra on Friday but confidence is low this far out, especially this winter...

Unfortunately, there isn't much relief in sight for the drought or for the dwindling snow pack. The Climate Prediction Center (CPC) has above average temperatures and below average precipitation for the next 6-10 and 8-14 days (see Figure 2).  For our sake, let's hope the CPC is misguided and their forecasts are a bust.

Figure 2: Climate Prediction Center's 6-10 day temperature (upper left) and precipitation (upper right) forecast and their 8-14 day temperature (lower left) and precipitation (lower right) forecast

Looks like the Omegasaurus is here to stay for the foreseeable future...


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Wednesday, January 21, 2015

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DROUGHT: Juneuary Style

Drought. Dry. Arid. Barren. Parched. You can find more synonyms to describe our current situation in a thesaurus like I did. You may have heard the Sierra Nevada and the vast majority of Nevada and California are in a drought. The Sierra and areas adjacent to the Sierra currently exist somewhere between the 1 and 13th percentile for precipitation during the past 24 months. 

We thought we saw the light at the end of the tunnel with the precipitation we received in November and December. We were wrong. While the precipitation helped, the high snow levels mitigated some of the effects and optimism. Additionally, we have been bone dry all of January. 

HOW DRY DO YOU ASK?! Drier than drinking Extra Brut Champagne, while eating saltine crackers during the summer in the Atacama Desert….that might be slightly exaggerated but you get the point. 

Figure 1: Tahoe City January precipitation (in.) from 1910-2015. The average January Tahoe City precipitation is 5.83". 

Currently, Tahoe City has received 0" of precipitation in January (Figure 1). Tahoe City has never received 0" of precipitation during January. NEVER. The lowest was 0.08" in 1991 and the next lowest was 0.35" in 1985. Tahoe City has received less than 1" of precipitation in January only 9% of the time and 3% of the time Tahoe City received less than 0.5".

Including 2015, the past five Januaries (2011-2015) have had below average precipitation. Tahoe City has had four previous instances where five or more consecutive Januaries received below average precipitation (record was 9: 1984-1992). However, the past five Januaries have yielded a total of 8.99" of precipitation. That is 2.47" below the next lowest total (for consecutive Januaries) for the period of record. 

Figure 2: Tahoe City January snowfall (in.) from 1930-2015. The average January Tahoe City snowfall is 45"

When examining the Tahoe City snowfall record, it is even more bleak (Figure 2). It has received 0" of snowfall this year (duh) and the only time that has occurred before this year was 1991 and essentially 1934 (0.1"). This is the lowest snowfall period since the aforementioned mid 1980s to early 1990s. The past five Januaries (2011-2015) have yielded 32.5" of snow. That is below the monthly average for ONE January. The next lowest five consecutive Januaries' total was 66.4" from 1983-1987. 

Granted, low precipitation or snowfall in January does not always result in a dry winter. In 2011, Tahoe City received 0.84" of precipitation and 7" of snowfall, but it was one of the wettest, snowiest winters on record in the Sierra. This is only one location, but I use it as an example of the larger area (the Sierra). Figure 3, a table from the National Weather Service Reno office, demonstrates how dry the past few winters have been. 

Figure 3: Snowfall totals (in.) from the past six winters with seasonal averages. Via NWS Reno.

Our friends (Nina O.) at the Western Regional Climate Center (WRCC), developed a precipitation probability analysis for stations in the Sierra. Currently, Blue Canyon has a 3.82" deficit of precipitation for the current water year and needs 38.28" to reach or maintain normal precipitation by September 30, 2015. The probability of reaching normal is approximately 33%. That's basically the same chance Armando Benitez gave the Giants of converting a save opportunity from 2005 to 2007.

Looking out, there is the possibility of receiving precipitation and snow next week. However, the way the models have teased us and completely switched multiple times during this season, we are very skeptical. Be sure to check out the Sierra Avalanche Center for all of the backcountry skiing conditions and keep the following video in mind as we wait for snow…



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Saturday, January 17, 2015

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A Little Perspective on the Current Situation (Drought!)

Will it ever snow again in the Sierra?  Probably, but not likely in the next 7 days.  Omegasaurus (see our last post if you are not familiar with this beast) will continue to dominate our weather pattern in the near future.  I'm not going to get into details about the long-range forecast, as we've had our hopes built up just to get let down a few too many times this season.

Source: NOAA/NCEP

As a graduate student at the Desert Research Institute my main area of research has been drought.  So, many of you may be tired of hearing about the current drought, but where this one falls into the last 120 years of records is pretty interesting to a drought nerd like myself!  I put together an analysis from the Tahoe City COOP station.  This station is part of the US Historical Climatology Network because it has a long and consistent period of record dating back to the late 1800s.

Let me break down this figure for you.  In each panel the black line is the same, and shows the water year (September-October) percent of normal precipitation.  A red bar indicates the start of a drought period.  For the top panel a drought is classified as <100% of normal for 3 consecutive years.  The middle is same threshold, but for 4 consecutive years, and bottom has a threshold of <75% of normal for 3 consecutive years.  


Source: Dan McEvoy, Desert Research Institute

There were actually 9 years in a row below normal during the 90's, nearly the entire decade (top panel).  But, a couple of those years were 90-98% of normal, which still a lot of precipitation.  Focusing on the bottom panel, there have only been 4 cases since 1896 that have seen 3 years in a row with <75% of normal precipitation (including 2012-2014).  At this particular station there has never been 4 years in a row below 75% of normal...lets hope we don't break that record this year!

Lets not forget that we have evidence that suggests much drier periods than this one lasting for several decades, as Ben alluded to in the last post.  My analysis is based only on one weather station record.

Well, I'm off to hit the mountain bike trails in Reno, which are riding pretty awesome right now! Enjoy the weekend, and make the best of what have right now!
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Wednesday, January 14, 2015

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Cool Summer Continues!

Conditions are going to continue to be perfect for cool summer activities with a late-week cooling trend as the upper level flow becomes more west-east. The southern PeeEnDub will be the place to be if you are psyched to slide on snow and rocks!


Too bad they don't have much of a snowpack!




Better to head east but hide those Cali plates.

Meanwhile, Nevadastan is producing solar energy (photo courtesy Sir Sieczkowski):

In the ever-so-subtropical Sierra Nevada, keep spinning tires, clipping bolts, SENDING THE DAWN WALL (Congratulations, Tommy and Kevin, for a true opus of a rock climb at the planet's finest venue), and skateboarding. T-shirts for the day, a layer or two on Friday, and a windbreaker for the weekend. Omegasaurus will snooze a bit but otherwise keep things nice and dry.


One more key point to make, my dear snow-lovers. There may not be an end in sight. Not in our lifetime and perhaps not in anyone who will be born during the next 100 years. Stine's Trees silently pass this wisdom on to us. These Jeffery Pines grew for 100-200 years over two separate periods when Baghdad was the place to be. To enable their growth, most of these years had smaller or similar seasonal snowfall totals as the past three years. Behold the power of Omegasaurus!




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Thursday, January 8, 2015

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Wet at the End of the Ridge?

A weak series of systems will undercut the ridge this weekend bringing a shot at some light snowfall for the northern half of the Sierra, better air quality to valley locations and dropping temperatures closer to normal.  A major pattern shift looms on the horizon.
  • Weak system impacts the Northern Sierra late Sunday through Monday with light snowfall possible
  • Temps become more seasonal behind the system
  • Major pattern change possible for the end of next week
The typical January, or more aptly named Juneuary, ridge that has brought bitter cold to the eastern 2/3 of the country and well above average temps for us will be undercut by a series of weak waves starting tomorrow.  The first wave will bring some high clouds to the region tomorrow morning and a possible stray snow shower to the Tahoe area by evening.  Attention then turns to Sunday night as the next wave begins to approach the Northern Sierra.  This system bears watching as the latest runs of the GFS (the American, Global Forecast System) have come in stronger and wetter.  If this morning run verifies then Lake Tahoe and points northward could see a couple of inches of snow by Monday evening. 

A Pattern Change
Models continue to come into better agreement on a major pattern shift occurring towards the latter half of next week.  As can be seen in Fig. 1, all of the ensemble members of the GEFS (the American, Global Ensemble Forecast System) show the ridge weakening and moving east between now and next Friday.  The European model is also coming into line with the GEFS, further increasing the confidence of a pattern change arriving towards the end of next week.



Figure 1.The 5400 and 5820  meter height contours from 20 different ensemble members over the North Pacific.  The farther south (north) the height contour, the colder (warmer) it is. Current height contour locations are shown in the top image and the bottom image shows the forecasted height contour location for next Friday afternoon.

Trying to nail down the exact storm track and precipitation amounts this far out is a dangerous game but the GEFS ensembles are showing surprisingly high confidence in precipitation impacting Northern California.  The last few model runs have had a 50% chance of greater than a .25 inch of precip in a 6 hour period for next Saturday as can be seen in Figure 2. 

Figure 2. The probability of precipitation exceeding .25 inches in a 6 hour period derived from 20 ensemble members.  This forecast is valid for next Saturday afternoon.

It is extremely important to stress that the devil is in the details and even though the models are showing a pattern change that favors moisture reaching the Sierra, nothing is guaranteed.  At this point, we can only hope that Ullr is generous and blesses us with copious amounts of moisture with this pattern change.

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Monday, January 5, 2015

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The Ridge of Steel

Since this past weekend, temperatures have been on the increase and will continue to do so through Thursday as the ridge of steel continues to build and park itself over the west-central Great Basin. The scenario for this week in a nutshell features:

  • Morning inversions in the valleys with moderate air stagnation; 
  • Unseasonably mild with temps pushing 60+ during the day in the arid valleys; 
  • High elevations will be most pleasant with snow re-softening by mid-late morning; 
  • Lots of sun and blue sky with only occasional high clouds at times; 
  • Friday the ridge breaks temporarily and allows for some westerly flow and air cleansing

The current longwave pattern for us and the rest of the Country reveals a classic (positive) wintertime Pacific/North American (PNA) signature with a ridge over the Pacific NW and a broad trough over the upper Midwest and Great Lakes region. Over the next 24 to 72 hours, this pattern amplifies significantly bringing unseasonably mild temperatures to the West and a healthy bout of Arctic air across the eastern two-thirds of the US (Figure 1).

Figure 1. 250 mb (Heights/Winds) GFS model prog illustrating the ridge of steel over the West and a broad trough over the eastern two thirds of the Country. Courtesy of NCAR RAL web page.

A positive phase PNA anomaly is quite common for this time of year, particularly the first week or two in January. In general, the prominent weather that ensues with such a pattern is above (below) average temperatures (precipitation) over extreme western Canada/US and the opposite scenario for the central-eastern US. A negative phase PNA anomaly tends to feature the reverse ridge/trough signature over the US.

The dynamics of the PNA anomaly are a function of the upstream environment. In large, it is controlled by the sea surface temperature anomalies over the south Pacific (e.g, El Nino/La Nina), which modulate the behavior of the Asian-Pacific jet. The phase duration of the PNA can be persistent or highly variable at times where changes every 7-10 days are not uncommon. Persistence or (high variability) has been linked to stronger (weaker) signals in the El Nino Southern Oscillation (ENSO). The short term forecast for the PNA anomaly is depicted in Figure 2. As noted in an earlier post, a few weeks back, the current ENSO signal teeters toward weak El Nino. Therefore, we can watch and see if the positive PNA (and the associated ridge of steel) is short lived...let's hope so, or the beast reforms and drives us crazy.

Figure 2. The daily PNA pattern from September 2014 to present, including a 7-day model projection set. Courtesy of the NOAA Climate Prediction Center. 



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Thursday, January 1, 2015

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Bluebird Days and Cold Nights


Through mid next week expect:
  • Ample blue sky,
  • Rebounding daytime temps with light winds,
  • Very cold mornings, strong inversions in the valleys,
  • Enjoy the high elevations being mindful of the evolving thaw/freeze snowpack conditions
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Arctic air remains in the wake of the recent storm system and the strong cold front of this past Tuesday. The origin of the current airmass stems from the north pole. Figure 1 highlights the southwesterly journey taken by the air via the tropopause pressure field (left panel) and the 200 mb meridional (north-south) wind field (right panel). Note the black-line arrow along the pressure gradient trail (north to south) from the pole into the Sierra and points southward (left panel). Along the same trajectory, the corresponding north-to-south wind maxima is illustrated by the cool colors (blue-purple, right panel).

Figure 1. Tropopause pressure (left) and the 200 mb meridional (north-south) wind field (right) illustrating the origin and trajectory of the current Arctic airmass. Courtesy of the NOAA-ESRL Global Reanalysis plotting page. 
Since its arrival on Tuesday, the airmass has finally begun to modify as an upper-level ridge continues to build overtop (Figure 2). This evolving pattern will dominate our weather for the next several days (into the middle of next week) yielding nice bluebird skies and daytime temperatures rebounding gradually over the period. Evenings will be very cold with intense morning inversions, particularly in the lower valleys where light-moderate snowpack exists. With such a pattern, higher elevations should be pleasant from mid-late morning through the day and be an escape from the morning inversion air that will deteriorate a little bit more each day.

The new topcoat of snow should be light and powdery for the next day or so, before some decent melting begins to take shape. By the weekend, daytime melting and nighttime refreezing will be in full force with the snowpack consistency changing along with it, so plan your outdoor excursions accordingly.

Figure 2. NAM model 250 mb forecast (heights/winds) for Saturday late morning. Note the strong upper-level ridge continuing to build into/across the western US. Courtesy of the NCAR Real-time weather data page.



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