Tuesday, October 25, 2016

Yesterday's "SnowEater" Conditions

Yesterday was a net loss for what little snowpack that we had at pretty much all but the highest elevations.  We didn't have a lot of snow on the ground yesterday morning, but a couple of inches was lingering on shady north aspects, and most of that snow is gone today.

Yesterday.  Source: Alta.com.
Today.  Source: Alta.com.
Here's another perspective looking up Collins Gulch.  Yesterday there was a white strip in High Rustler and environs, and spotty snow down almost all the way to the base (unfortunately I didn't grab an image).  Today, gone.

Today.  Source: Alta.com
During fall and winter, it's very hard to melt snow on north aspects when skies are clear, even when the temperature is well above the melting point (0ºC).  On these aspects, there is simply not enough energy from the sun to melt snow when the sun angle is low, and the energy transferred from the relatively warm atmosphere to the snowpack is insufficient to drive significant snowmelt.

Yesterday, however, we had a boost in energy input to the snowpack from two additional sources.  One was the rain, which when it hits the snowpack cools to 0ºC, releasing energy for the melting of snow.  The other was the cloud cover, which provides long-wave radiation for snowmelt, a process sometimes referred to as "greenhousing" and which also results in cloudy nights not being as cool as clear nights.  Thanks to those two energy sources, poof, what little snow we had is now gone except in the highest elevations.

During winter, when the sun angle is low, the worst-case scenario for snowmelt is not a warm, sunny day, but a warm foggy day with rain.  A couple of hours of snowmelt is about all you get on a warm, sunny day during winter, but fog and rain work 24/7.  In the eastern United States, warm, foggy, rainy days just destroy the snowpack, creating "snoweater" conditions.  Here in Utah, such effects are sometimes seen in the lower elevations.  For example, in December and January, snow will linger in shady areas in the Salt Lake Valley under clear skies even if it is well above the melting point, but if you get a day with rain and low clouds, it can melt away.

Monday, October 24, 2016

Perspectives on the Snow Season So Far

Yeah, it's only October, but it's worth a quick look at the snow season so far.

Outside of Utah, aggressive resorts are getting on it, mainly with the help of artificial snow.  Arapahoe Basin, CO opened last weekend.  Killington, VT opens this week.  Mt. Rose, NV planned to open October 31 based on early-season natural returns, although looking at their web cams, I wonder if that is now a pipe dream.  You want natural snow?  Grand Targhee remains the big winner in the interior west so far, as we mentioned previously, and some high-altitude areas of the North Cascades might offer up some skiing as well.  The Northwest Avalanche Center observing site at Washington Pass has a 21 inch base this morning.  If you really want to feel jealous, even Vermont got some this weekend.
Here in Utah, we remain on hold.  I did some stomping around upper Albion Basin yesterday and snow remains limited to a couple of inches in shady upper-elevation aspects.

Portions of the Catharines area almost looked skiable.  Ah, wishful thinking.

The snow distribution pictured above is typical of a dry, continental climate.  When the humidity is low, it's hard to melt snow without the help of the sun and that's why it lingers for so long on shady aspects.  On those shady aspects this time of year, snow losses are due largely to sublimation, or ice transitioning to vapor, rather than melt.

Things are changing, however, today, but depending on elevation, not necessarily for the better.  We've had a surge of moisture from the sub-tropics into Utah, or what I'll call the last gasp of the 2016 monsoon.  The analysis below shows a tongue of high precipitable water air extending northward across southern California and southern Nevada and into Utah.

Temperatures at 700 mb are fairly high and around +4ºC.

A look at surface observations shows Alta-Collins (~9700 ft) is sitting at about 38ºF and Mt. Baldy (11,000 ft) at 30ºF as of 8 am.  Thus, we have a snow level sitting around 10,000 feet, which is roughly consistent with what I'm seeing on the Alta web cams.  Note the thin layer of sticky snow on the dormant snow gun near Germania Pass, which is near the bottom of the melting layer.

Source: Alta.com
Although there may be some fluctuations in snow level today, snow will be confined primarily to the highest peaks.  Below 9500 feet or so, we might see a net loss of snow today as the combination of higher humidity and cloud cover is more favorable for melt on those north-facing aspects.

No need to panic, however, as it's only October.  Nevertheless, the natives are starting to get restless...

Saturday, October 22, 2016

Inversion Season Is upon Us

A quick look at yesterday afternoon's sounding shows that inversion season is indeed upon us.  The afternoon boundary in which surface heating drives turbulence and mixing, extended to only 850 mb, just a couple hundred meters or so above the valley floor.  This mixed layer was capped by a series of stable layers and inversions, effectively putting a cap or lid on the valley atmosphere.  In other words, what you emit is what you breath.  

Source: SPC
Welcome to late October.  We are now moving into the time of year during which surface heating is often not enough to mix out the valley atmosphere.  In other words, its inversion season.  However, don't blame the inversion for our air pollution problems.  In fact, meteorologists like myself hate it when people say "the pollution is bad because of the inversion."  Nope.  The pollution is bad because of emissions.  We have met the enemy and it is us.  

A shallow layer of pollution could be spied in all directions while on my bike ride this morning.  

And, in case you were wondering, PM2.5 concentrations at Hawthorne Elementary have been running in what I'll call the "Low Moderate" category at around 20 ug/m3.  

Source: DAQ
With southwesterly flow on tap for the next couple of days, this should be a brief-lived, moderate episode without major concerns.  It is, however, a stress test for the coming winter.  

Friday, October 21, 2016

One Last Monsoon Surge?

As future Senator Blutarski said in Animal House, nothing is over until we decide it is.

Or, in the case of the seasons, nothing is over until Mother Nature decides it is, and she still hasn't decided to call it over on the 2016 monsoon season.

Model forecasts are showing another monsoon surge into Utah late on Sunday, with the potential for some scattered showers and thunderstorms through Monday night.

Right now, it appears we'll squeak the UAE (Utah Education Association) weekend in with good weather, although there's a chance something will sneak into southern Utah late on Sunday.  After that, we'll see how things look in a couple of days.

Thursday, October 20, 2016

September Temperatures: Pleasantly Near-Average Locally, Hot Globally

With the climate data now in and processed, I thought we would take a quick look back at the month of September locally and globally.

For the State of Utah, the mean temperature for September was about as close as you can get to the 20th century average.  
Source: NCEI
Given that September is typically a "Goldilocks Month" in the Salt Lake Valley (not too hot, not too cold, but just right), the month overall rated as quite pleasant in my book, requiring neither air conditioning or heating of the home and most of the days.  

While the whims of the jet stream looked favorably on us, globally September was still beastly warm, rating as the 2nd hottest in the instrumented record.  

Source: NCEI
That's a fairly significant change as the last month that did not set a record for the hottest all time based on analyses by the National Centers for Environmental Information was April 2015.  That's quite a stretch of record setting warmth, although there are a few months in there where 2016 and 2015 are probably statistically indistinguishable (i.e., so close that they are essentially tied).  Even September 2016 and 2015 might fall into that category.

For the year to date, 2016 easily remains the hottest on record, 0.99ºC warmer than the 20th century average.  

Source: NCEI
Developing La Nina conditions in the tropical Pacific will knock the global temperatures down just a touch in the coming months, so the "race" between 2015 and 2016 will probably get a bit tighter between now and the end of December, but it's a virtual lock that 2016 will be the warmest calendar year on record.  

Wednesday, October 19, 2016

You Could Be Skiing This Weekend

Yes, you could be skiing this weekend, but not in the Wasatch Range.

A quick look at the snowpack snow water equivalent (SWE) at western U.S. SNOTELs shows the highest values are nearby at the 9200 foot Grand Targhee site.  Take a quick gander, and you'll see a yellow dot near the Wyoming–Idaho border at that site.

Source: NRCS
Observations show a snowpack SWE of 8.1 inches.  Pretty healthy for October and the equivalent to the climatological median in late November.

Source: NRCS
Web cams show a wintery scene.

Source: Grand Targhee
If you go, add your report to the comments.

Note: To my knowledge, the ski area will not be open.  I don't know their policy for access this time of year.  You will need to earn your turns, possibly outside the resort boundary.