Sunday, May 24, 2015

Great Colorado Ski Conditions

I have a reputation for giving Coloradoans a hard time about their lack of snow, but it is well worth a trip to the Centennial State when they are having a spring like this one.

Most of Colorado did not have a great ski season if you measure it by the peak snowpack.  However, the spring has been outstanding for two reasons.  First, it has stayed cold and snowy.  Second, a lot of that snow has been of the sticky, high density variety and it has coated just about everything and the cover is exceptional above 11,000 feet.

Here's an example from the Grizzly Peak snotel at 11,100 ft in Arapaho Basin.  The highest snowpack snow water equivalent of the water year is right now.  It's about at the median peak for this site, but that typically happens in early April rather than late May, putting them way above average for so late in the year.

Source: NRCS
For the Memorial Day holiday, my son and I decided to check out this snowpack for ourselves.  We spent the day yesterday at A-basin experiencing a mixture of sun and snow, as well as a one-hour lightning shutdown about mid morning.  Once that was over, conditions were great for late May with some fine cream on crust conditions.

Today we spent touring near Independence Pass and had another great day, bagging our first 13er on skis.

 Low angle, but we're not used to climbing at 12,000+ feet.  Missing those Wasatch Ohs.
By Colorado standards, the snowpack is bomber, with mainly new snow instabilities to deal with.
A little shameless U of U promotion in the Sawatch 
Happy summiters.
The kid getting some creamy goodness.
We even ran into a fan of Secrets of the Greatest Snow on Earth, who somehow recognized me from the back cover photo.  Great to hear Coloradans are reading it.

I guess this year provides a great example of why you should never give up on the ski season.  I've had more fun skiing in April and May than I did during much of the winter.

Thursday, May 21, 2015

The Memorial Day Weekend Forecast

In the Harold Ramis directed movie Groundhog Day, a weatherman played by Bill Murray relives the same day over and over and over again.  

I've thought of that movie a lot the past week or two and it suspect you will to as we move forward through Memorial Day weekend.

The bottom line is that the unsettled weather will likely persist over the state through the weekend.  Just watch the NAM forecast below which runs through Sunday afternoon and you get a good idea of what we're looking at.  

Yup, showers and thunderstorms with some variations in the timing, coverage and intensity of precipitation from day to day.  That's the pessimistic view.  The optimistic view is that there will be  some breaks where you can get in outdoor activities and there are no unusually cold airmasses making an appearance.  Nevertheless, keep the shower and thunderstorm threat in mind during your outdoor recreating.  Move indoors or into a closed vehicle if you can hear thunder, etc.

If you are thinking of skiing, this is a pattern of primarily hit-and-miss upper-elevation snow showers that are impossible to time.  Really for good freshies this time of year you want something to keep it snowing fairly hard for an extended period as happened last weekend, but right now I don't see anything to organize the precipitation in that manner.  Nevertheless,  this is an extended forecast and I can't rule it out if we get a bit better large-scale forcing than advertised in the latest model runs. I expect snow levels to be fairly high this weekend, perhaps in the 8500-9500 foot range, except during periods with stronger precipitation when they might lower temporarily.  Daytime maximum temperatures will probably reach near or above freezing even at 11,000 feet.  What can I say, it's late May.  Get on it if it starts snowing hard for an extended period, otherwise be thankful the snirt is still buried.

Wednesday, May 20, 2015

An Evolving El Nino

For a good part of this past Northern Hemisphere winter, above average sea-surface temperatures (SST) persisted near the dateline (180ยบ) in the equatorial Pacific.  For example, the image below shows the weekly SST anomaly (anomaly means departure from a 30-year climatology) for the last week of February with the positive SST anomalies centered on the dateline in the equatorial Pacific.
Source: ESRL/PSD
Since then, positive SST anomalies consistent with weak to moderate El Nino conditions have strengthened and developed across the eastern Pacific and now extend to the coast of South America.

Here's another perspective based on a loop of the SST anomalies since late February, showing very nicely the development of the weak to moderate El Nino.  
Source: CPC
Concurrently, enhanced convection and cloud cover developed over most of the central and eastern tropical Pacific, especially just to the north of the equator along the Intertropical Convergence Zone (ITCZ).  This is reflected in negative outgoing long-wave radiation (OLR) anomalies over the past month.  More cloud cover (especially upper-level clouds) means less outgoing long wave radiation at the top of the atmosphere.

Source: CPC
And, along with this convection, we've seen anomalous upper-level anticyclones to the north and south of the equator, the former associated with the active subtropical jet we've seen across the southwest the past couple of weeks.  

Source: CPC
The latest diagnostic discussion from the Climate Prediction Center calls for a 90% chance of El Nino to continue through the Northern Hemisphere summer and a greater than 80% chance it will last through 2015, but also notes that there is considerable uncertainty regarding the strength of the event.  As we have discussed in the past (e.g., Outlook for the 2013–2014 Ski Season), the potential existence of El Nino does not strongly load the dice one way or the other for snowfall in the Wasatch Range next ski season.  Nevertheless, it would probably mean a different large-scale flow pattern than the one we had last season, which would provide much needed new material for this blog!

Tuesday, May 19, 2015

It's Been Pouring Cats and Dogs!

I haven't read it yet, but given the weather we have had the past two weeks, I think we should all run out and pick up Cynthia Barnett's new book Rain.  

Over the past 14 days, precipitation is well above average statewide, with large portions of the state running more than 300% above average.  
In the Salt Lake Valley, Alta is the climatologically wettest regular observing site and has picked up 7.65 inches of precipitation so far this month (not including overnight and possibly part of the day yesterday).  A good chunk of that total fell over the weekend when the upper elevations got 16 inches of high density snow.  

Source: NOAA Regional Climate Centers
The Salt Lake City International Airport is the climatologically driest location and has still recorded 3.38" of precipitation (through midnight MST last night), nearly three times average.   

How does that stack up relative to past Mays?  Records are pretty spotty at Alta, but May 1981, 1983, and 1986 produced more than 9 inches of precipitation.  

At Salt Lake City, the 3.38" we had through May 18th would be good for the 16th wettest (time series below based on observations from the Salt Lake City area prior to the establishment of the Salt Lake city International Airport).  Two Mays have had more than 5 inches of precipitation, 2011 (5.14") and 1908 (5.76").  We have some time to catch up though as those are totals for the entire month.  

Surely you remember May 2011?  If not, let me refresh your memory as I always like looking back on the winter of 2010/11.

Memorial Day Weekend, May 30, 2011
It's wind scoured here, but at 8 am that morning Alta-Collins had recorded 10" new with a 193" settled snow depth
BDOME: Best Day of May Ever
There may be some variations in precipitation coverage and intensity from day to day, but the weather looks unsettled for the next 7 days.  We will probably be climbing up the rankings for May rainfall.  A minus with regards to skiing this weekend is that it appears it will be a bit warmer than last weekend and I'm not seeing a precipitation system as organized as what we got Saturday night.  Nevertheless, one can always hope as we see how things come together.  

Monday, May 18, 2015

Sunday, May 17, 2015

Huge Spring Dump, Avalanches Likely

After depriving us of quality powder for most of the winter, Mother Nature turned on the spigot big time last night.  Automated observations from the Alta-Collins observing station (9662 ft) show the total snow depth increasing from around 64 inches yesterday (multi-hour average) to 80 inches as of 7 am this morning.  I'm calling it a 16 inch storm total, although it looks like 14 inches of that fell after 6 PM yesterday.  Total water during this period was a whopping 2.41 inches.  

Radar images from last night show the remarkably juicy northwesterly flow and how Alta was fortuitously located in the narrowing band as the night dragged on.  

Source: NCAR/RAL
Source: NCAR/RAL
I've looked at some radar loops and there may have been some lake augmentation at times, but the large-scale precipitation band was an important component of this storm (note how it extends well upstream of the lake in the images above).  

The Utah Avalanche Center is closed for the season, but they did issue a tweet overnight highlighting that avalanches are likely, including terrain within closed ski areas, which is de facto backcountry right now.  

As much as I was hoping to get out this morning and followup on yesterday's creamy turns, I'm electing to stay home.  Today is the epitome of too much of a good thing