Friday, February 27, 2015

I Need Some "Forecaster Friend"

What I wouldn't give for a slam dunk, strongly forced, relatively high predictability snowstorm over northern Utah.  We keep getting these amplifying and digging upper-level troughs with hit and miss snowshowers and snowbands that are tough to anticipate.  In times like these, I find myself consuming a few too many of these.

Forecaster's Friend was brewed by Utah Alum Kyle Tietze.  Kyle was a great student who
passed away unexpectedly a few years ago.  We miss him greatly.
The loop below shows the NAM forecast of 500-mb heights, clouds (b/w), and precipitation (color fill) through Sunday morning.  The main upper-level trough digs down the California coast and were mainly dealing with periods of snow showers that eventually concentrate in a snowband over central Utah on Sunday morning.  

Direct NAM model output for Alta-Collins shows a few snow showers later today (tallying about an inch), dry conditions overnight, and then more snow showers tomorrow adding up to another 3 or 4 inches.

The challenge with forecasts like this is that that the location and intensity of these snow showers and snowbands are somewhat chaotic, and that increases the uncertainty of the forecast for any specific location.  This also explains why you may have noticed some jumpiness in the forecasts for this weekend.  In addition, this is low density snow, so it stacks up fast, further exacerbating the challenge of forecasting snow amounts.

As things stand now, I'd probably call for 0-2 inches today, 0-1 inches tonight, and then 3-6 inches late tomorrow and tomorrow night in the upper Cottonwoods.  Given how little snow we have had this year, your best option is to go and ski and take advantage of whatever comes whenever it comes.  After Tuesday, we could be dealing with winter interuptus again.

Thursday, February 26, 2015

Snow Returns!

I was unusually excited about the inch or two of snow that fell at the U today.  It's amazing what a snow drought will do.  In case you are wondering, two inches so far at Alta-Collins (as of 2 PM).

I have a busy day today, so consult with our students at for a forecast.

Wednesday, February 25, 2015

Utarado Snowpack Comparo

In a bad year like this, I sometimes feel jealous of my friends to the east in Colorado as I hear they are having a good year, and then I look at the data and I don't feel so bad.

Below is a comparison of the  year-to-date long-term median and 2015 snowpack snow-water equivalent (SWE) at Snowbird and selected SNOTEL stations in Colorado.  Snowbird is on the left after which they are ordered in terms of descending median snowpack SWE.  I have included some of the snowier SNOTELs in Colorado along with a few from selected locations near major resorts.

You can see why I jokingly say that a bad year in Utah is better than a good year in Colorado (or, more correctly, a bad year in Little Cottonwood is better than a good year at the resorts near and along I-70).  Although we are running well behind median at the Snowbird SNOTEL, we are still ahead of the SNOTELs near and along I-70 (Loveland Basin, Vail Mountain, Berthoud Summit, Copper Mountain, Beaver Creek Village), despite the fact that the latter are running near median.

Of course, one can see from this chart that there are some areas in Colorado that do get some decent amounts of snow climatologically (see the median bars, red).  One area is in the Park Range and Zirkel Mountains north of Steamboat Springs (i.e., the Tower and Zirkel SNOTEL stations).  Tower in particular, located at Buffalo Pass, always generates some big numbers and I've often thought of visiting the area just to check it out for confirmation purposes.  There are also the usual suspects in favored areas of the San Juan Mountains (Wolf Creek Summit, Cumbres Trestle), as well as Schofield Pass in the Elk Mountains.  The San Juans and Elks are running farther below average, but will do some catching up over the next few days.  In fact, depending on how things play out the next few days, my friends in Colorado may be asking for an update of this post.

Tuesday, February 24, 2015

Possible Ice and Snow Records: East and West

It's been a remarkable winter and we have the potential for ice and snow records in both the east and the west in the coming days.

East: Great Lakes Ice Cover

The snow and wintery weather back east have gotten quite a bit of press, but I haven't seen a lot on the Great Lakes ice cover.  Modis imagery from yesterday shows Lake Erie to be frozen over and Lakes Superior and Huron to be predominantly frozen over.  Lake Michigan is still hanging on with some open water (and producing some lake-effect clouds and snowfall), as is western Lake Ontario.  If you click on the image to enlarge it, you have a great view at the complexities of pack ice, especially on Lake Huron where large leads (cracks with open water) and openings can be found as the ice is pushed around by wind and currents.

The NOAA Great Lakes Environmental Research Laboratory has some great products for monitoring the ice cover of the Great Lakes (available here) and allowing for comparisons back to the early 1970s.  As of yesterday, the median ice concentration across most of the lake surfaces, with the exception of portions of Michigan and Ontario, exceeded 90%.  I've been watching these analyses over the past week and have noticed both Michigan and Ontario are slowly but surely seeing the median ice concentration increase in their open regions.  They peg the Great Lakes total ice cover at 85.6%.

Last year the ice cover peaked at 92.5% on March 6th, the 2nd highest since the early 1970s (the highest ice cover of 94.7% occurred in 1979). If we compare yesterday to last winter on the same date (below), we find that we are currently running ahead of last year's pace.

Given the cold weather expected over the next several days, it will be very interesting to see if we can take a run at the post-early-1970s record.

West: Alta Snowfall

Despite the snowstorm this weekend, we're still flirting with record low snowfall at Alta for the month of February.  Before proceeding, I need to note that I don't have access to the official records for the Alta cooperative observer site, so there is some uncertainty in this analysis.  However, records at the Utah Avalanche Center suggest that the minimum February snowfall at Alta Guard is 34 inches.  I can access unofficial snowfall records for that site and it appears they've had 19 inches so far this month.  The ski area snowfall history reports 25 inches for the month.  I've been looking at the model runs for the next few days and it appears we will miss a storm passing to our east of us on the 25th, have a weak system coming through on the 26th,  and then are on the fringes of a storm that digs down the Pacific coast and penetrates into southern Utah on the 27th and 28th.  The net impact of this is that in the latest (0600 UTC) GFS, the heaviest precipiation through the end of the month falls to our west, south, east, and north and we're left in a low precipitation region.  If this forecast verifies, we'll probably see some snow before the end of the month, but perhaps not enough to avoid the record.  On the other hand, a shift in storm track or intensity and we might do better, and avoid the dubious honor.

Of course there are the usual problems with snowfall records (see Limitations of Long-Term Snowfall Records), so in the end, there still might be debate about whether or not February 2015 was indeed the worst snow month on record.  The combination of forecast uncertainty and observational uncertainty should make for lively discussions around the office over the next few days!

Monday, February 23, 2015

Easterly Winds

As Napoleon learned all to well, all bad things come from the east.  A walk on campus this morning is a bit more challenging that it has been in a few weeks given the cooler weather and the blustery winds.  Here are a few peak gusts since 11 PM last night from around the area:

Farmington/I-15: 68 mph
Mouth Parleys Canyon: 62 mph
Centerville: 54 mph
Bountiful Bench: 54 mph
University of Utah: 53 mph
Hill Field: 52 mph
Fruit Heights: 51 mph

Pretty much everyone is getting in on the action in this one. [Addendum @ 11:08 AM: Everyone along the east bench of the Salt Lake Valley and the northern Wasatch Front - JS].

The time series from the Mouth of Parley's is quite interesting.  Winds have been steadily out of the east since late Saturday.  Although it is not unusual to have strong easterly flow at this location at night and in the morning, note that the easterlies persisted through the day yesterday, and then reached their maximum strength this morning with a peak gust of 62 mph (right hand side of the graph).

 Note how the speed goes down and the wind direction becomes erratic from around noon to 1600 yesterday.  The surface heating and associated turbulent mixing acts to weaken the strength of the downslope flow in these events.  As a result, they often reach their maximum intensity overnight and in the early morning and slacken during the day.  

More information on this phenomenon can be found by examining our previous posts on downslope winds

Sunday, February 22, 2015

Limitations of Long-Term Snowfall Records

This snowfall measurement brought to you by The Home Depot
In a season in which we are seeing seeing remarkable snowfalls in the east (a lot of snow) and in the west (not enough), I've been dealing with a number of questions concerning long-term snowfall trends and records.  Answering these questions is sometimes complicated by the warty nature of our long-term climate records.  We have a saying in meteorology that all observations are bad, but some are useful, and this is especially true for snowfall observations, which are probably the worst of the lot.

Here are just a few things that affect snowfall observations:
  1. On what surface was the snow depth measured?
  2. How frequently were observations taken?
  3. Was the measurement taken right after the storm or a couple hours later?
  4. Was the measurement taken right after the precipitation changed to sleet/freezing rain/rain or a couple of hours later?
  5. How hard was the wind blowing?
  6. Was the measurement location sheltered or wind affected?
  7. Was there any tree or building intercept?
  8. Who collected the data?

And, when we compare contemporary observations with those in the past, changes in observing techniques and site characteristics can make a big difference and in some (most) cases, these changes are poorly documented.  In addition, when one goes into the distant past, the measurement techniques can be far removed from what we do today, at least at some locations (e.g., Looking Back and the World 24-Hour Snowfall Record)

Based on the long-term record at the Utah Avalanche Center, we are making a run at the lowest February snowfall at Alta-Guard.  Those observations are collected today by the Utah Department of Transportation, and in the past by USFS Snow Rangers like Monte Atwater (Note: These are not equivalent to the ski area observations which, at least in recent years, have been collected independently).  The previous record is 34 inches in February 1950.  We are still below that, but have some potential to climb closer depending on how things play out the next several days.

Ultimately, comparing the two Februaries is perhaps not an apple to oranges comparison, but a bit of a gala to Braeburn comparison since the details of the snow measurements in February 1950 are probably lost in the sands of time (one of you historians should do some digging).  Assuming we get no more snow, we can probably say with some confidence that February 2015 was worse.  If we do get more snow, and we end up within a few inches of 34, it will be less clear which February is the "winner."