Saturday, January 31, 2015

Don't Be So Colorado!

Yesterday afternoon my twitter feed became populated with claims of everything from great powder to free refills in the Wasatch.  Is this really what it has come to?

I know things have been really really hard this January, but buck up.  This is Utah not Colorado!  We don't get excited about snow until we hit English measurement double digits, meaning 10 inches or more.  We thumb our noses at metric measurement double digits, meaning 10 cm (4 inches), something that nobody even reached yesterday.  I'm sure the 2–3 inches of snow that fell on the Park City side improved the skiing, but you are snow snobs.  Don't stoop to such levels!

A few more ensemble members and the GFS have recently shifted to pulling the storm track further south and giving us some action Tuesday and Wednesday.  Keep your fingers crossed that the low probability outcome discussed in the post from Thursday verifies.  Sometimes Mother Nature does roll snake eyes.

Friday, January 30, 2015

This Is a SAD Weather Day

"And then depression set in"
- John Winger, Stripes

If you are trying to avoid Seasonal Affective Disorder (SAD), today's weather is not for you.  It's about as grey and drab as it can get.  Our camera peering at the Wasatch Range from the University of Utah upper campus shows thick cirrostratus clouds, but further adding to the darkness is the valley smog/haze, evident on the right side of the photo.  

Source: MesoWest
Here's a view looking at the Wasatch Range from the west showing the nicely layered atmosphere with the valley smog and cirrostratus deck separated by a clear layer aloft.  I guess the place to be today is somewhere in that clear layer.  

Source: MesoWest

Thursday, January 29, 2015

The Snow Potential (or Lack Thereof) from Brush By Storms

If the forecast from the 0600 UTC GFS verifies, the central Wasatch will remain sandwiched between storms to our south or storms to our north over the next week, getting just what we can from brush-by precipitation events.

First we have the system moving into the southwest today and giving them precipitation through Saturday.  We are expected to be on the northern edge of this system.  

Once that system moves downstream, the we get brushed by systems to our north.  Again, we're right on the edge of the action.  

In situations like this, a slight shift in storm position can make a difference and I like to consult forecast ensembles to get an idea of range of possibilities.  Let's start with the Short Range Ensemble Forecast System (SREF), from which we can examine the potential for precipitation as the system affecting the southwest brushes by us the next couple of days.  There are 22 members of this ensemble, of which only 9 produce any precipitation at all at the Salt Lake City grid point, with two generating over 0.15".  

A forecast like that suggests we may see a few valley showers and mountain snow showers tonight through early Saturday morning, but accumulations will probably be minimal.  The odds of a few inches during this period in the upper Cottonwoods aren't zero, but they're pretty low (less than 10%).

For the next week, we can look at our ensemble of downscaled forecasts from the North American Ensemble Forecast System (NAEFS) for the 7-day period beginning yesterday afternoon and running through next Wednesday afternoon.  As can be seen below, the probability of at least 6 inches of total snow accumulation in this period is fairly low, maxing out in the central Wasatch at about 60 or 70%.  The odds of more than 24 inches isn't zero, but it's less than 10%.  We would need one of those systems to shift southward for that to happen.  

Here's another way to look at it.  Below we've extracted the accumulated water equivalent (top) and snowfall (bottom) from the downscaled NAEFS ensemble members for Alta.  The vast majority of the members are producing 8 inches or less of snow for the entire period.  There is one member, from the Canadian Ensemble, that is very excited about a huge storm late in the period (this always seems to be the case with the Canadian Ensemble.  The Canadians clearly love snow!).    

So, looking at all these ensembles, the most likely forecast scenario for the next week (i.e., through Wednesday) in the central Wasatch is that we continue to see drier than average weather, with just a few periods of snow showers or snow as we are brushed by systems to the south or north.  Although not zero, the odds of a major storm are low and would require a more direct hit than forecast by most of the ensemble members.  

REI Talk Tonight

I'll be giving a talk on my book Secrets of the Greatest Snow on Earth, including a look at topics such as the real reasons why Utah snow is so great, where to find deep powder around the world, and the avalanche history of Little Cottonwood Canyon, at 7 PM tonight (Thursday) at the Salt Lake City REI (3285 E 3300 S).  The talk is free and open to the public, although REI does request that you register by clicking here.  My friends from Weller Book Works will be selling copies of the book if you haven't picked one up yet.  I'll be happy to sign any copies you bring or buy at the event.  

Wednesday, January 28, 2015

Time to Head South

The highest elevations of Arizona, New Mexico, southern Utah, and southern Colorado will be getting some late Thursday through Saturday thanks to moisture streaming into the region from the south and east as shown in the integrated water vapor and 850-mb wind forecast for 0600 UTC 30 Jan (late Thursday).

This leads to the development of wide-spread precipitation across the region. as illustrated by the forecast below for 1800 UTC (1100 MST) Friday 30 January.

The northern Utah mountains are skunked in the forecast for that time and that is largely the case through the weekend, although we may see a few lingering snow showers today and then perhaps a stray snow shower or two through Friday.  Although a few inches fell in the northern Wasatch last night (the central Wasatch go the shaft), it appears we will make it through January with only one major storm.  What a pity.

Those of you considering a southern road trip should keep an eye on the forecasts.  It's a complex system and the timing and intensity of snowfall will vary by location and I can't possibly hope to summarize that here!

Tuesday, January 27, 2015

An Impressive Record Aloft

Yesterday afternoon's sounding from the Salt Lake City International Airport recorded a 700-mb (~10,000 ft) temperature of 7.8ºC.  This is the highest 700 mb temperature ever recorded between December 17 and March 21 and in line with what we typically observe in mid June.  I've annotated the observation on the sounding climatology below to show how anomalous the temperature is for January.  The red trace represents the highest 700-mb temperatures at each of the twice-daily sounding times during the year.

Source: SPC
Perhaps not surprisingly, Alta set a record high for the day of 58ºF.  This beat their previous record of 43ºF for the date by 15ºF!

Source: NWS
That's a huge trouncing, but the previous 43ºF record for yesterday was the lowest maximum temperature record during January (tied with Jan 3rd).  The record for the entire month of January remains 59ªF, set on January 12, 1996 and January 20, 2005 (the latter noted above).  Thus, the max temperature at Alta yesterday was pretty damn impressive, but not an all-time record breaker for the month.  

Valley showers and mountain snowshowers are on tap for today and tonight and possibly a bit tomorrow.  This looks to be a sporadic, hit and miss event and the models continue to flounder around on accumulations, but continue to call for a modest event.  Through late tomorrow, the 6Z NAM is going for about 3 inches at Alta, whereas the 6Z GFS is in there for 7.5 inches, with most of this falling this afternoon and tonight.  I'll stick with 3–6 inches for a storm total as that seems to be in the heart of the distribution and I'm not sure how much to weight the new high-res GFS for mountain precipitation.  

Monday, January 26, 2015

Welcome to Bizzaro world.

Consider yourself transported to a Bizzaro world, one in which the upper-level flow is from the east and you can ski in short sleeves in January.

Here's the view of the Bizzaro world this morning.  The upper-level flow is what we call highly amplified, with a ridge over western North America and a deep trough over the eastern United States (Northeast skiers rejoice, dumpage is coming your way!).  There is also a closed upper-level low off of Baja California that will provide us with more Bizzaro weather in the near future.

Here's this morning's sounding from the Salt Lake City airport.  Note the deep easterly flow from 800–550 mb.  It will be an unusually short flight if you are coming to Salt Lake City from Chicago today.  Temperatures increase from 0ºC at the surface to 7.2ºC at 775 mb.  At 700 mb, roughly 10,000 feet, the free atmosphere temperature was 5.2ºC.

Source: University of Wyoming
That's quite steamy for late January.  The graph below shows the daily minimum (blue line), median (black line), and maximum (red line) 700-mb temperature in all available soundings taken at the Salt Lake City or Ogden airports since 1948.  I've annotated with the green line this morning's 700-mb temperature.  The record for the month of January is 7.2ºC (12Z Jan 20).  However, from January 21 to 10 March the highest on record is 5.8ºC (Feb 1).  So, we are very close to as hot as it gets at 700-mb for this time of year.  In fact, this morning's 700-mb temperature is about the median for June 1st.  If we had the June sun rather than the January sun, I'd be calling for a high at the airport of 73ºF.

Source: SPC
That closed low will move northward and bring a monsoon-like surge of moisture into the southwest that will spread into Utah tonight and tomorrow.  That sounds exciting, but we're missing the surface heating of summer and the models can't seem to get their act together and converge on a solution.  The 12Z NAM is going for only 0.11" of snow-water equivalent through 11 PM Wednesday, whereas the 6Z GFS is going for 0.8" (the 12Z run isn't available as I write this).  Your guess is as good as mine.  Hold a gun to my head and I'd go for 3-6" in upper Little Cottonwood by 11 PM Wed.