Monday, November 30, 2015

November: Average Temperatures But Below Average Precipitation

November is almost in the record books and it looks like we're going to be pretty close to average for temperature and below average for precipitation.

At the Salt Lake City airport, the trough-a-week pattern dominated the month, yielding fairly typical late fall ups and downs in temperature.  The last trough decided to hang around for a few extra days, yielding our current cold stretch.

Source: NWS
With one day left to go (today), the average temperature for the month is 40.15ºF compared to a long-term average (1981–2010) of 40.0ºF.  We'll probably end up just a hair below that long-term average after today is factored in.

For precipitation, the airport received 0.40", well below the average of 1.45".  Overall it was a decent month for artificial snowmaking, but Mother Nature had her struggles.  The thin natural snowpack is now quite weak and will be a prime concern for backcountry travel if it ever starts to snow again.

Sunday, November 29, 2015

Avenues Skiing and Medium-Range Prospects

Ah, freshies were had in the Avenues Foothills.  Not today, but five years ago today.  I just wanted to share that memory as that was the start of the epic 2010–11 ski season that we all remember so well.

The 2015-16 ski season is getting off to a slower start.  SNOTEL stations in the central Wasatch sit at 60–71% of average.  Average this time of year is not huge, so we're basically one good storm short of average.  If only we could get that one good storm!

Unfortunately the pickings are pretty slim in the medium-range forecasts.  The European ensemble shows very little outside of some snow showers today and tonight through at least December 4th.  Similarly, the North American Ensemble Forecast System (NAEFS) plume for Alta-Collins produces some snow showers through tonight, followed by a flat line until December 4th.  At that point, a few of the ensemble members bring a storm in, but others keep us mainly dry.
Thus, the upcoming work week looks like a good one for putting in some longer hours.

Saturday, November 28, 2015

Sometimes It Doesn't Take Much

There is not always a direct relationship between the amount of new snow and road-weather impacts.  Sometimes a little is enough to create problems.

The snow that fell late last night didn't come fast and furious.  It started at the Salt Lake City airport at around 4:50 AM MST and has added up to a whopping .03" of water equivalent through 8:40 am this morning.  That's probably pretty close to what I got in the Avenues foothills.

However, after the cold weather the past couple of days, the road surfaces are cold and the snow is sticking.  In addition, I suspect the road crews were caught off guard and nothing was plowed when I woke up this morning in my neighborhood.  Further, Commuterlink at 8:48 AM MST showed fairly slow going for a Saturday along much of I-15 and I-215 through the Salt Lake Valley.

Source: UDOT
Traffic cameras showed the light snow covering all but the busier lanes.

Source: UDOT
An inch at Alta so far.  It's not much, but I'm starting to learn to appreciate anything we get.

Friday, November 27, 2015

Black Friday

Black Friday is here.  Despite the thin snowpack, I'm going skiing.  I don't recommend shopping, but if you must, my book Secrets of the Greatest Snow on Earth makes a great gift.

The first print run is almost sold out.  A second is in process, but if you have to have it for the holidays, get it now to be sure.  Options are direct from University Press of Colorado, Amazon, Barnes and Noble, and great local bookstores like King's English at 15th and 15th, Weller Book Works in Trolley Square, and Dolly's on Main Street in Park City.  If you by direct from University Press of Colorado, enter 50for50 at checkout for 50% off.

Thursday, November 26, 2015

Thank You Mother Nature

Although I'd rather talk about snow, Mother Nature just keeps giving interesting weather and I experienced the full force of it on my pre-Turkey hike this morning.

While hiking in the Avenues Foothills, I experienced increasingly strong, cold easterly flow as I hiked eastward and upward to the top of the Avenues Twin.  It was absolutely frigid on top, with screaming easterlies of perhaps 25–30 mph.  I wasn't dressed for that!

Observations from the University of Utah show the development of the easterlies this morning with gusts reaching about 40 mph around 11 am.

Source: MesoWest
As is often the case, there was a well developed "Sandy Eddy" with the easterly flow turning cyclonically (counterclockwise) and becoming northwesterly or westerly flow over the Salt Lake Valley and upslope flow over the Wasatch Range near the Cottonwood Canyons.

Source: MesoWest
The Sandy Eddy has a very apparent signature when viewed from the Avenues foothills.  There is typically very clear air in the easterly flow over the northern Salt Lake Valley, but haze where the flow is northwesterly or westerly and impinging on the Wasatch.  I'm not sure if the haze reflects pollution, higher relative humidity in the upslope flow (which leads to the formation of haze particles), or some combination of those two factors.  Today there were also some small cumulus forming in that area.  

As I looked westward toward the airport, I also saw evidence of a pronounced hydraulic jump where the flow separates from the surface and rises rapidly.  An example of such a jump is provided by the figure below, which is based on an idealized numerical simulation.

Source: Doyle and Durran (2007)
Sometimes there is an opposing return flow downstream of the jump and that was indeed the case today as if you look at the MesoWest plot above the flow at the airport was northwesterly even as the winds were cranking out of the east at the University of Utah.

Cumulus clouds just near downtown provided evidence of the strong ascent associated with the hydraulic jump this morning.

This cumulus cloud and scd clouds extended northward just west of the Wasatch foothills (photo below taken ~15 min earlier than the one above).

Happy Thanksgiving!

Wednesday, November 25, 2015

This Storm Could Be a Turkey

Ah, it's a beautiful morning in Salt Lake.  The sun is shining.  Temperatures are around 50ºF.  Gorgeous.

The loop below shows very nicely the situation that has proven to be the bane of forecasters for so long.  As mentioned in earlier posts on this event, we have a situation of large-scale Rossby-wave breaking, with the upper-level trough forming rapidly over the Pacific States overnight last night.

All the action right now is to our north and west, although it's less impressive than I hoped it would be prior to moving into the Wasatch Front (thinking from a skier's perspective here, not a commuter's).  Each successive model run slows the system down a bit more and that continued to be the case through this morning.  Here's yesterday's NAM time-height for Salt Lake City showing frontal passage around 2100 UTC (2 PM MST) this afternoon, as well as a slug moisture in the pre-frontal southerly flow for this morning and the early afternoon.

Now here's today's.  Frontal passage is after 0000 UTC (5 PM MST) and the prefrontal environment is much drier.

Snow will eventually kick in later this afternoon over the mountains, but totals by tomorrow morning are going to perhaps only be in the 3-6 inch range in the upper Cottonwoods.  I haven't been putting any numbers on this event over the past few days as it seemed so hopelessly unpredictable, as we have discussed at length in early posts, so there's always the hope that I'm overly pessimistic, but I doubt it.  Right now, I think we'll escape the evening rush hour along the Wasatch Front without major weather problems, but keep an eye on things just in case.