A little more active is better than nothing…

I have to admit, it’s been pretty refreshing to be in the valley and see snow flurries on and of throughout the day today, even if it hasn’t amounted to much in the way of accumulations. The cold front that came through last night was weak and poorly defined but ample cold air and winds for mixing scoured out the last of the pollution and have us all breathing easy today.

Recap of today's weather with visible satellite, radar, and surface wind vectors
Recap of today’s weather with visible satellite, radar, and surface wind vectors

As far as snow totals – well, the weak wave that progressed into the region is exactly that. Resorts are reporting 1″ new if any at all, with just 0.01″ of water at Alta-Collins snow stake. Our friends to the north in the Cache valley seem to have done a little better, with ~3″ of snow reported in the Logan area, so if you’re really jonesing for a Sunday tour on some fresh… Overall, I wouldn’t expect much in the way of additional snow in the mountains tonight, just a trace to 1″.

—————————–
So what’s next? There’s hope, right?

ECMWF
ECMWF Ensemble forecast meteogram. Next indicated event beginning late on the 20th/early 21st

At this range I’d rather keep looking at ensembles than go one deterministic run to another. Both the GEFS and ECMWF EPS indicate, as Trey previously mentioned, a trough moving into the region midweek. The agreement among members and models here is fairly good, though they are agreeing on a slightly weaker outcome than we might hope for. Both models bring in ~0.2-0.3 SWE, though the ever terrain-happy deterministic GFS suggests closer to 0.8″ in the Wasatch.

Far too early to put value on any numbers right now, I’ll say this – we can expect something with a little more punch than today’s trough, but not much more than a modest snowfall mid-week.

At this point I’ll take any snow we can get, but man, I’m still crossing my fingers for the big one and wondering when we’ll see it.

 

A Welcome Sight

Short Range

As Peter alluded to in his forecast, a quick-hitting storm will impact Northern Utah tomorrow through tomorrow night. While accumulations aren’t looking overly impressive, I think we’ll take just about anything at this point. Also, the cold air aloft + precipitation should be enough to mix out any inverted valley locations..hooray! For totals I’m expecting 2-4 inches of snow in most mountain locations above 7500 feet. Because of the cold temperatures aloft, this snow will be mostly of the low density variety. This could also lead to totals being slightly on the higher end for a few locations. Overall, it’s not enough for a powder day, but a nice refresher and clean valley air will be very much welcomed.

Mid-Long Range

The weather will likely be quiet early next week as the upper level ridge parked over Utah for much of December remains relatively entrenched. Fortunately, it should retrograde far enough towards the west allowing a storm to drop down into Utah from the NW by mid-week. The animation below shows the ECMWF depiction of the this overall wave pattern in the mid-upper atmosphere. The warmer colors indicate ridging aloft (typically dry conditions), while the cooler coolers are often associated with upper level troughs (storms) and colder air.

ecmwf_z500_mslp_npac_fh0-240

While it’s still too far out to get into specifics, early indications are that the potential storm for mid-next week may be a bit better than this weekend’s. Beyond that storm, I’m still not liking the overall pattern with a high amplitude blocking pattern and a ridge dominating the West Coast. Obviously that can and hopefully will change in future forecasts.

Finally, I do want to point out one additional long range possibility, since I do study tropical cyclones. The GFS and ECMWF are keying in on potential typhoon development near the Philippines late next week. Depending how strong the typhoon gets (and whether or not it recurves) could have big implications on the downstream atmospheric wave pattern. If it doesn’t recurve (as most models currently suggest) than I could foresee an amplification of the West Coast/Gulf of Alaska ridge. This would likely be bad for us unless the ridge axis was also far enough west to get “backdoor” NW flow storms. On the other hand, a recurving storm would entirely throw a wrench in the current global wave pattern. We could certainly use that right now! Any potential outcomes are purely speculation at this point, but it’ll be something to keep an eye on next week.

Screen Shot 2017-12-15 at 4.29.26 PM

Response to the Powder Buoy

A couple days ago I made a post where I said to not trust the Powder Buoy. I should have been a bit more specific and said “don’t trust that the Powder Buoy provides any useful, skillful information (i.e., better than climatology)”, but I figured our readers got the point.  There was no hate directed at the Powder Buoy, I was simply stating that claims that it is skillful are false.  If we were propagating misinformation, I sure hope someone would correct us.

Here’s a simple explanation.  There are several claims that the buoy is right about 75% of time when given a “flex” day (the guy who runs the page said this yesterday).  I understand that there’s a lot of uncertainty regarding how this validation was done, but I responded to him with the following statement and got no response, so I assume my assumptions were correct:

“The issue is that the claims that it is skillful are false. For example, on average, Alta receives snowfall on about 50% of days during the winter (last year 100 out of 180 days recorded snowfall). That plus the fact that you gave yourself flex days means that about 75% of the days would count as storm days. I could have randomly chosen days and 75% of them would have storms. In other words, random guessing does just as good as the buoy.”

Time and time again peer-reviewed studies have shown that models do not contain skill beyond about the 10 day period.  I guarantee that a buoy is not out-forecasting models that cost hundreds of millions of dollars to develop and operate.
The unfortunate outcome for simply calling out a false scientific claim is that we were called trolls, haters, and other unnecessary names in the more than 200 comments that the post generated (https://www.facebook.com/powderbuoy/posts/1447875505309994).  This turned out to be an example of a lack of scientific understanding and reasoning – something prevalent in today’s world.

Good News…well decent news

As Taylor called for yesterday, we had a little bit of relief in the form of a weak shortwave trough scooting through last night. It brought a dusting of snow up high and took a bite out of the valley inversions, cutting pollution levels in half. Fortunately, we’ve got more (and better) relief on the way!

Details
The ridge will rebuild tomorrow with temperatures once again warming in the mountains and strengthening valley inversions. This will be short-lived though, as a stronger and colder shortwave trough comes in Saturday morning. This trough won’t bring much snow, but it *should* be cold enough and windy enough to completely scour out the valley inversions. As for snowfall, I’d expect something like 1-4″ in most mountain spots, so don’t break out the powder boards just yet.

With the cold temperatures that this storm will be packing, snow density will be fairly low, so the blower pow could stack up a bit deeper than expected. This certainly doesn’t help for base building though…we could use some heavy dense snow.

ECMWF Weather Model
Precip for the Sat-Sunday storm from the ECMWF model. Calling for somewhere around 0.2″ of water, which should translate to a few inches of snow.

Long Range
After that, the ridge rebuilds a bit, but not completely. The storm action looks to stay to our north, but that could change, and the models are bringing our next storm in midweek. Too early to tell much, but it looks like it could be cold one. I labelled the time-height diagram from the GFS to illustrate the forecast for the next week:

GFS weather model
Time-height cross section from today’s GFS model run.

“Oh The Weather Outside is Frightful…”

“But the…. ” Actually there’s nothing delightful about what’s going on outside right now.

Grumpy Cat's take on the inversion
Grumpy Cat’s take on the inversion

I mean really, the air is borderline toxic and it hasn’t been snowing. If you can’t make it up to the mountains, I would suggest staying inside, watch holiday movies and bake cookies! Or at least that’s what I have been doing when I’m not working.

PM2.5 trend, with 24hr values in the "Unhealthy" levels (air.utah.gov)
PM2.5 trend, with 24hr values in the “Unhealthy” levels (air.utah.gov)

Here’s what you can expect in the near future:

The next 24 hours:
More of the same. This evening, we get a brush-by from a weak, and I mean WEAK, short-wave trough. You can see what I’m talking about in the dynamic tropopause map below.. Essentially a dynamic tropopause map shows the pressure level where the top of the troposphere is currently. “Higher” values (cooler colors) means the tropopause is dipping lower in the atmosphere, which is typically associated with colder air mixing down in the troposphere.. Remember pressure varies inversely with height (highest pressures located at ground level, decreasing with height above ground). Note the dark blue colors extending down from the polar regions, over the great basin.

GFS forecasted dynamic tropopause map valid around midnight.
GFS forecasted dynamic tropopause map valid around midnight.

Another way to look at this is with our trusty time-height cross section, which depicts moisture moving in and a weak wind shift.  Remember time increases to the left.  Unfortunately, I don’t think this “frontal passage” will be enough to mix out the inversion.. Note where the green starts, the theta-e lines are still increasing with height, indicating the atmosphere is still stable at low levels. Above crest-level, some instability may give way to meager snow showers.. A trace accumulation of snow likely, an inch at the very best.

Time-Height cross-section for KSLC (weather.utah.edu)
Time-Height cross-section for KSLC (weather.utah.edu)

Finally, to support this, here’s a forecast sounding valid around 5 pm this evening (time of the anticipated “fropa”).  Note the line on the left (which represents the vertical profile of the dew point temperature) is bent inward and is nearly touching the air temperature line on the right from 650-550mb, which corresponds to heights just about crest level. This  means the air is saturated here, which we typically see with a front.. A wind shift and influx of moist, cooler air, which destabilizes the atmosphere.  This FROPA doesn’t ever make it down to the surface, leaving the soupy mess to stick around a bit longer.

GFS BUFR Forecast Sounding, valid 00Z or 5pm MST (weather.utah.edu)
GFS BUFR Forecast Sounding, valid 00Z or 5pm MST (weather.utah.edu)

 

Long-Range:
This looks a bit more promising, as a stronger (relatively speaking) and colder trough is anticipated to move through state on Saturday.. It looks like this time the frontal winds will reach the surface, hopefully mixing out some of the pollutants that have been trapped in the valley for the past week or so. Precipitation amounts are still pretty pathetic, but at this point, I’d take anything

NAM 500mb hgt and vorticity valid Fri. 5p-Sat. 5p (pivotalweather.com)
NAM 500mb hgt and vorticity valid Fri. 5p-Sat. 5p (pivotalweather.com)

Light at the End of the Tunnel?

I think I speak for everyone when I say that I am sick (figuratively and possibly literally) of this stagnant, foggy, polluted air in the valley.  PM 2.5 levels have been in the unhealthy category for days making it unwise to exercise outside.  It would be nice if we could escape to the mountains and get a few turns in, but that too is unadvisable in most of the Wasatch due to a lack of snow.

This Week: The cold pool that’s been causing the build-up of pollution in the valley will persist for a few more days.  Friday night a weak front will cross through the region.  Although it’ll be moisture starved, it should be accompanied by strong enough winds to wipe out the cold pool.  We’re not expecting more than a few inches in the mountains with this system.  As the NAEFS below depicts, a good deal uncertainty still exists with this system. We’re not optimistic given how this fall has gone so far.

NAEFSPL_CLN2017121212F168

Long range: The long-range models are starting to indicate that we may undergo a major pattern change around Christmas time.  Below is ECMWF EPS 500mb ensemble mean height anomaly for 12/24.  Essentially, it’s predicting a a period of lower than normal heights, which are accompanied by troughs and often stormy weather.  Keep you fingers crossed.

eps_z500a_b_noram_276

 

One more thing…I trust that our readers understand the immense amount of data, computational power, and research necessary to create and operate skillful weather models, but I just have to say it – don’t believe a word this guy says:

Screenshot 2017-12-12 21.31.27

Breath of Fresh Air?

Air quality in the valleys really took a dive today. Many sites in the Salt Lake Valley, from valley floors all the way to the benches, saw spikes of PM 2.5 larger than the increases from day-to-day last week and over the weekend.

For example, the Utah Department of Environmental Quality sensor at Hawthorne Elementary school (~4300 ft) in Salt Lake City saw tremendous spikes of PM 2.5 into the ‘Unhealthy’ range for 1 hour average which allowed the 24 hour average to migrate into the ‘Unhealthy for Sensitive Groups’ range.

121117
PM2.5 concentrations measured at Hawthorne Elementary for the last several days. A very noticeable spike in concentrations is visible midday on Monday, Dec. 11th. Image and data courtesy of Utah Dept. of Environmental Quality and available at air.utah.gov.trendcharts.php

Up near the University of Utah, observations available from MesoWest show similar features in PM 2.5 concentrations at WBB (~4800 ft) and MTMET (~5000 ft).

121117(1)121117(2)

Yep, it’s getting pretty nasty out there and it’s going to get worse before it gets better. But when will it get better?

There is potential that a cold front will sweep through Northern Utah on Friday or Saturday with power to mix out the valley inversions and horrid pollution. If the system this weekend doesn’t have the oomph to do it, the next chance of clearing our air isn’t for almost another week after that. Unfortunately, neither of these systems look benefit the Wasatch much in terms of snow.

So, it’s going to be a long week (or more) of this inversion episode. Do whatever you can to reduce your emissions! Enjoy the sun and groomers if you get a chance to escape from the valleys, and keep checking back for updates.

 

There’s a Snow Storm on the Horizon

TLDR: 

Skiers enjoy the fresh air on another smoggy day for SLC Valley. Our next good storm could bring snow to the resorts next weekend as early as Friday night. Stay tuned for more updates every day this week!

The Recap

“What would you be doing … if skiing had never been invented?” – Warren Miller

This weekend specifically? Taking in big gulps of cold exhaust fumes…

Poor souls trapped beneath the inversion Sunday evening. As seen from LCC (credit to the author)
Poor souls trapped beneath the inversion Sunday evening. As seen from LCC (photo credit to the author)

It’s days like this when, despite the hard luck in snowfall I couldn’t be happier to escape the city and ski.

In other LCC news, the Snowbird Tram woke up today:

And to expand, here’s an *unofficial* stats update for some resorts:

Resort            Trails       Base      Lifts

Snowbird      10/189      26″      4/11

Alta                  10/116      23″      4/10

Brighton        19/66       25″      5/6

Solitude          5/77          22″      3/8

Park City        13/347      18″      11/41

Deer Valley    14/101      20″      10/21

Snowbasin     12/104     18″       3/11

The Pattern Change

When is our next snow storm? We were told many times over that we’d be cold and dry for at least a week, but I hath seen the horizon and ’tis promising.

The first hint at change comes Thursday. We are still cold and dry, but a shortwave feature speeding through the Northern US precedes the movement of our ridge toward the West. This means that we are allowed access to some strong flow in the jet stream, which happens to be a major player in the next potential snow storm. Read the caption below the GIF for more details.

GFS 500 hPa Pressure Level Vorticity (shaded), winds (barbs) and heights (solid black lines). Notice the strong vorticity bullseye in the first few frames moving from S.E. Canada into the Midwest. This marks the regime change I mentioned above (courtesy of tropicaltidbits.com)
GFS 500 hPa pressure-level vorticity (shaded), winds (barbs) and heights (solid black lines). Notice the strong vorticity bullseye in the first few frames moving from S.E. Canada into the midwest US. This marks the regime change I mentioned above (courtesy of tropicaltidbits.com)
The Forecast

Additionally, winds over the Northwest US increase early Saturday. We are looking at a low level jet making its way through the weakening ridge. Let’s take a closer look at both the Euro (top) and GFS (bottom) forecasts for comparison.

ECMWF forecasted 700 hPa Winds (shaded) for 5PM Saturday (courtesy weather.us)
ECMWF forecasted 700 hPa winds (shaded) for 5PM Saturday (courtesy weather.us)

 

GFS forecasted 700 hPa Winds (shaded) for 11AM Saturday (courtesy weather.us)
GFS forecasted 700 hPa winds (shaded) for 11AM Saturday (courtesy weather.us)

You’ll notice the difference in the timing (the GFS prefers an earlier event), but the big takeaway is the surprising consensus in the models for this type of synoptic setup.

We have strong crest-level flow and a weakening ridge for the Northwest and Intermountain states sometime Saturday. Next, I want to look for moisture. We can find this in the following graphs for both the Euro (top) and the GFS (bottom). They will also clue us into why this snow event is occurring as I’ll explain later.

ECMWF
ECMWF forecasted 700 hPa relative humidity (shaded) for 5PM mountain time Saturday. Notice the stream of moisture flushing in from the Pacific (courtesy weather.us)
GFS
GFS forecasted 700 hPa relative humidity (shaded) for 5PM mountain time Saturday. Again, notice the stream of moisture flushing in from the Pacific (courtesy weather.us)

Given good agreement on sufficient moisture at low levels, I will place my bets on a good snow storm sometime next weekend, with a day or so flexibility in timing.

Zooming out we see that the moisture source is our pineapple express tapping moisture from the tropics, shown below:

ECMWF forecasted Relative Humidity (shaded) shown for 5PM Saturday over the entire Eastern Pacific. Note in green the atmospheric river flow from the Hawaii islands to the Pacific Northwest US.
ECMWF forecasted relative humidity (shaded) shown for 11AM Saturday over the entire eastern Pacific. Note in green the atmospheric river flowing from the central Pacific Ocean to the Pacific Northwest US (courtesy weather.us)
The Details:

Timing: earliest friday night, latest perhaps sunday evening

Amounts: too early

Other questions:

Will lake effect play a role in this storm? I will leave that talking point for other posts this week, but something to consider if the air pushing through is cold enough. I think the northwesterly flow, upstream moisture source, and warm lake temperatures help maintain the possibility that lake effect snow periods could occur during the event.

Are we going to see any snow before Saturday? Aside from changes in the timing for this storm, I don’t think so. At least nothing major, and in my opinion probably nothing minor either. We are cold, stable, and dry most likely until Thursday, if not later.

Stay tuned this week as more details emerge! And do whatever ritual you do to keep the models pumping snow for the weekend.

Happy skiing!

-Marcel

No News

We are in the middle of a long stretch of sameness. A week of perfect bluebird skies. Temperatures on the mountains are hovering around freezing, and wow is it dry up there. The dew point temperature at Solitude Apex as I write is near -19°F, meaning that a cloud wouldn’t form up there unless it were -19°F. That gives a relative humidity of 9%–chap stick weather for sure.

Screenshot_20171209_200653
9 Dec 2017 8 PM MST dew point temperatures around the Cottonwoods via MesoWest

This is the time of the year that I like to call the longest nights. The earliest sunset of the year here was the 7th, and the latest sunrise is on January 3rdsource, and I find these to be convenient boundaries to demarcate the darkest part of winter. Where I’m going with this is that the north slopes are hardly getting any sunlight at all, and that will keep them relatively fresh through this long stagnant period.

Sameness will dominate for the first half of the week, but some changes are on the way for the last half. It’s far too early to make promises on what’s coming, but it’ll be a change at least. Until then, resorts can take advantage of these extremely dry conditions by pumping out snow and opening up terrain.

Valley Haze and Clear Mountain Skies.

Unfortunately, inversion season is upon us in northern Utah.  The last few days have been tolerable with just enough mixing in the low levels of the atmosphere to keep the air quality from deteriorating rapidly.  Below is a sounding from this morning at the Salt Lake City airport.  The inversion can be identified between 700 mb and 800 mb in this sounding.

 

Screen Shot 2017-12-08 at 1.35.32 PM
Salt Lake City observed sounding from Friday morning. Courtesy of http://www.spc.noaa.gov/exper/soundings/

Looking ahead to the weekend, the ridge will slide eastward and the inversion is expected to strengthen.  Below is a forecast sounding from the NAM model for Saturday morning.  The layer between 700 mb and 800 mb has warmed significantly.  Also take note that the inversion has lowered closer to the surface.  In conclusion, over the next few days, the inversion will become stronger and move closer to the surface.  This will create a tight lid over valley locations, trapping all emissions and leading to air quality concerns.

NAMSKEWT_KSLC2017120812F029
Salt Lake City forecast sounding for Saturday morning from the NAM model. Courtesy of weather.utah.edu

Models continue to show no real signs of a quick change in the pattern anytime soon.  In the far extended, there is a chance of a pattern change around Christmas.  The ECMWF ensembles and CFS are suggesting the possibility of an active pattern beginning sometime around the beginning of 2018.  In the meantime, the ridge will keep a firm grip across the western U.S. through next week.  Below is a cross-section of relative humidity and wind speed over Salt Lake City.  The blue line is the freezing level.  This is one of the driest cross-section I have ever seen for Salt Lake City is my days of forecasting.  The good news, though is resorts should be able to continue to make snow and possibly open up additional terrain.

GFSET_KSLC2017120812F120
Salt Lake City GFS cross-section of relative humidity and wind speed. Courtesy of weather.utah.edu

-Alex L.