The Light at the End of the Inversion

February 11, 2016 Taylor McCorkle

This goes without saying, but its downright gross outside.  This is the my first time to ever experience a true Salt Lake Valley inversion episode, and its just about as bad as everyone said.  PM2.5 skyrocketed yesterday, landing us in the Department of Air quality's "Unhealthy" category. With 24 hour averaged values of PM2.5 hovering around 60 micrograms per cubic meter, we are nearly double the ambient air quality standard of 35 micrograms per cubic meter averaged over a 24 hour period... That's bad y'all.  

The good news is, in the valley, the poor visibility you are seeing is not a direct result of the pollution.. It's a low cloud layer! Why I'm excited about this is because these low clouds are indicative of a shallow mixed layer.  A mixed layer is caused by turbulent heat fluxes which in a sense "stir up" the air, moving around some of that stagnant, polluted air we've been breathing.  This should curb the further deterioration of the air quality at least for now.  Looking forward into the weekend, we might have a chance to possibly flush out this air.  Models are in agreement that northern Utah will be clipped by a weak shortwave trough Saturday night in to Sunday.  This will result in a chance of rain the valley and some light snow in the mountains.  

Unfortunately we will be in the grips of yet another round of high pressure for most of the week next week.  Though, approximately 180 hours out, the GFS is producing a solution where we will experience our first real front in weeks.  While the uncertainty is high still being over a week out, this system could refresh our deteriorating snow pack and help us Utahns breathe a little easier. 

About a half-Beijing

February 10, 2016 Ian Glenn

Imagine someone enclosed you on a football field, in a giant glass box the length and width of the field, with a sealed top at the height of the goal posts. Imagine they also put an idiling car in there with you too. I've heard our good old Prof. Steenburgh use this frightening analogy to communicate the approximate amount of air available per Salt Lake City resident during an inversion event like we are experiencing. How long would you let that car idle if you knew you were going to be stuck in that box for 10 days? How long would it take to fill the box with hazy, exhaust filled air? Now of course we all have work and business to do in this city, but I think this analogy makes it clear how important even little things you can do can be. Less idling time, more public transport per person can really make a difference.

PM2.5 measurments went well above 100 ug/m^3 at their peak today in the Salt Lake Valley. Beijing was around 200 ug/m^3 today, so we're at about a half-Beijing. Looks like freaking Blade-Runner out there.

Now back to the weather... The NAM and GFS have the inversion slightly weaken Thursday night into Friday, but not enough to give any relief. I'll be interested to see how this plays out in the soundings though. The best hope is Saturday afternoon into Sunday morning. No chance of precip, but cold air aloft and increasing wind could remove a good amount of the pollution.

The next chance of precipitation is at 8 days out in the GFS, a time frame where we can't trust the details like amount and timing, but the gist of it is usually correct. A trough passage somewhere around Wednesday - Friday next week, snowfall amounts not predictable yet.

I don't have much to add about mountain temperatures, what Wyndam and Matt said is still holding true. One note about the warm temperatures that my award winning super-forecaster officemate Andrew Lesage pointed out is how peaked Alta's temperature trend is. For example, Collins mid-mountain hit 42F around 3pm today, but was around 35F and lower just an hour or two before and after. It's 8:30 PM and most of Alta's stations are just now below 32F. Though the entirety of Park City and Canyons terrain are still above the melting temperature according to MesoWest.

Hot and Dirty

February 9, 2016 Wyndam Lewis

We weren't kidding about the spring-like conditions in the Wasatch this week, as most resorts saw upper 40s and even 50s today.  Alta's weather station at 10,400 feet reported 52 degrees F at 1pm today, with nearby stations off the summit reaching mid to upper 40s.  Meanwhile, KSLC remained in the 30s.  

A continuous supply of powder is obviously preferable this time of year, but it's all relative.  Skiing in pleasant weather and clean mountain air sounds like a pretty good option when the valley's aesthetics resemble post-apocalyptic ruin.  Concentrations of particulate matter (PM 2.5) in the valley will continue to worsen throughout the week, and are currently impinging on the lower end of "unhealthy" for all groups at roughly 140% of the EPA Clean-Air Act standards.  It's truly alarming when we are forced to breathe the accumulation of pollution we emit every day.  

The ridge encompassing the Western US will persist for the remainder of the week, peaking Friday with ridge level temperatures around 40F.  On Saturday, the ridge will flatten in the wake of a weak shortwave disturbance.  According to the EC, any significant precipitation with this system is expected to miss to the north.  Ridge level temperatures will dip back below freezing, and there is potential for some air quality relief.

Albeit 10 days out, both the EC and GFS indicate the presence of a longwave trough around the end of next week.  Let's keep our expectations at bay for now, and we'll continue to provide updates as this feature in the models evolves. 

Because I was Inverted

February 8, 2016 Matt Jeglum

The inversion in the valley is unmistakable Monday and its only gonna get worse. The Euro ensemble has Utah completely dry until at least next Saturday, when we might see a weak trough passage. The GFS has an even weaker trough Sunday. It is possible that we make it through the weekend with no new snow and the inversion still around. But that is getting pretty far out into model wonderland. At the very least don't expect any new snow until at least Saturday.

But wait, there's more! Temperatures aloft will be near recond highs for the month of February in the Wasatch. It will be spring this week at the resorts. Bring some shorts if you are going touring. It's going to be warm for so long that some proto- corn might start to form on south aspects. Only high elevations on the north half of the compass will be able to stay winter-like. If nothing else going skiing will get you out of the dirty air in the valley.

It is times like this that I like to remember that it is still Early February and we live in Utah. We have more pow days left than Summit County, CO will get all year.

Last Cool Day

February 6, 2016 Peter Veals

The weather was absolutely perfect for skiing today: sunny, mild but not warm, and almost no wind. I think most of the USW forecasters were out on the slopes today, hopefully you got out to enjoy it too. Tomorrow will be a similarly awesome ski day, although with slightly more wind and some high clouds. Nothing too bad though.

As Tom mentioned, a strong ridge of high pressure will be taking over the Western U.S. for the next week or so. The big warm up really starts on Monday...temps in the 30s and 40s in the mountains and poor air quality in the valleys. The south, east, and west facing slopes will go through a melt-freeze cycle all week, but *fingers crossed* the north-facing slopes above 9,000ft will hopefully avoid the crustiness as long as no mid-level clouds move in during this warm spell. This phenomenon is known as "greenhousing," but it looks like we'll avoid it...skies will be sunny through at least mid week.

When will the ridge break down? This is difficult to tell, as these events (particularly the strong ones) tend to be very persistent. Looks like at least 7 days. We'll keep you posted, but enjoy the sun and almost spring-like warmth in the meantime.

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