Thursday, January 15, 2015

Mother Nature Is Putting the "Squeeze" on Us

The loop below shows how Mother Nature is putting the squeeze on us.  In the previous post we discussed how you can warm the air through subsidence or sinking motion and you can see that very well in the evolution of upper-level sounding profiles below which shows a strengthening and lowering of the inversion over the previous two days.

Yesterday afternoon low clouds covered much of the Salt Lake Valley and many of the other valleys and basins of northern Utah.  Below shows the view from our mountain meteorology lab.

Although dismal and grey, I was actually hoping that those clouds would hang on.  There is often a layer with good mixing beneath stratus and stratocumulus clouds of that type that is much deeper than we see during our typical inversion events.  Indeed that was the case yesterday and infact there was a deep surface based mixed layer that extended to the clouds, enabling our pollution to mix through a layer that was about 3000 feet deep.  That helps keep the pollution diluted.

Unfortunately, with those clouds gone now and I suspect we will see strengthening of the inversion at lower levels, with the mixing depth lowering and pollution concentrations increasing more rapidly.   Plus, there's also reports of dense fog near the Great Salt Lake.  Yes, Mother Nature is going to squeeze us further, although we have ourselves to blame for the pollution.

There is some good news.  We will get clipped by a weak system late Friday and Friday night, so hopefully that will stir things up a bit and keep things from getting out of hand.

Announcement for Utah County readers:

I will be giving a talk at Utah Valley University (Building/Room SB 260) at noon next Tuesday, January 20, 2015 on my book Secrets of the Greatest Snow on Earth.  The talk is open to the public and we are hoping (likely, but not firm yet) that there will be a book sales and signing event immediately following.

Air Quality Links:

A number of you have asked where you can find air quality monitoring data.  Here are the sites I use most frequently:

DAQ observations from Hawthorne Elementary:
University of Utah:
Neil Armstrong Academy:
TRAX mobile obs:

The University of Utah and Neil Armstrong Academy links above will provide data in tabular form.  If you want a graph, click on "New Graphical Display" in the left hand bar and select "PM_2.5 Concentration" under one of the variable selectors.  TRAX data is not always available since the car is not always in service.


  1. Do you have any reason to believe the numbers either at DAQ or Mountain Met are off somehow? The values for Hawthorne seem to be about 10 ug/m3 lower than the other stations posted.

    1. The sensors at MTMET, NAA, and on TRAX are the same and thus differences should be useful for identifying areas that are more or less polluted. The sensor DAQ has at Hawthorne is different and it provides hourly averages rather than high frequency data like MTMET, NAA, and TRAX. I think it is reasonable to expect that there will be some difference between DAQ and the other three sites, but at this point that difference and how it varies with PM2.5 concentration has yet to be quantified.

      Observations from 11-12 this morning did suggest MTMET was running ~22 ug/m3 (eyeball hourly average) vs. 13 at DAQ/Hawthorne. In the previous inversion, MTMET was not systematically higher and sometimes was much lower. Thus, I don't think the current difference necessarily reflects a systematic bias, but work will need to be done to confirm that and understand these contrasts.

  2. Thank you for the additional explanation and data. I got burned on my forecast promising sunny skies. I did travel out of town towards Colorado. As soon as I hit Price, sunny skies.

  3. It is interesting to compare today to yesterday... yesterday (Jan 14) the eastern side of the Great Salt Lake Basin, including the Wasatch Front, was cloudy while west of the lake it was sunny. Today, it is the opposite. I suspect that a shift in the low-level pressure gradient may be responsible, with subsidence bringing clearing and a lowering inversion to areas east of the lake and perhaps the opposite happening on the west side, out near the NV border. Anyway it is an interesting contrast.