Wednesday, June 26, 2013

Dry and Hot

I'm back in town after a quick trip to Boulder and the National Center for Atmospheric Research.  Apparently I missed out on the "big" precipitation event, which gave us a trace of rain Monday at the Salt Lake City International Airport.  That may have ended our stream of days without precipitation, but the streak of days without measurable precipitation continues.

Source: NWS
There is a very real chance that we will make it through June without measurable precipitation.  Only a rogue convective storm could ruin that streak.

We are now about to enter what should be a hot stretch.  We mentioned a few days ago that the GFS was going for extremely warm temperatures for later this week, with forecast 700-mb temperatures near 20ºC, which is on the outer edge of our current climatology (I emphasize current because higher temperatures are coming in future decades).  The good news is that the latest forecast are slightly cooler, putting the 700-mb temperature for Friday afternoon near 18–19ºC, but the bad news is that's still damn hot.

I mentioned in that earlier post that days with 700-mb temperatures near or above 20ºC are very rare (note: we use 700-mb, which is at about 10,000 feet, as an indicator of the overall warmth of the airmass).  Trevor Alcott of the National Weather Service recently sent me some numbers illustrating that this is truly the case.  In fact, days above 19ºC are pretty exceptional, as can be inferred from the 10 highest 700-mb temperatures observed at the Salt Lake City airport since 1956.

Courtesy Trevor Alcott
Here are the peak 700-mb temperatures forecast by the GFS for the approximate time of the upper-air soundings on Friday, Saturday, Sunday, and Monday afternoons:

Friday: 18.2ºC
Saturday: 19.1ºC
Sunday: 19.5ºC
Monday: 19.2ºC

Yup, that's rarified air, probably good for maximum temperatures at the airport in the triple digits.  Nasty!  In addition, I need to note that this is JUNE (Monday is July), and all the top-10s above are in July and August.  So, this is especially rarified air for this early in the year.  We'll have to keep an eye on things to see if we can break into the top-10 for all-time 700-mb temperature.  If you are keeping score at the ground, the records at the airport for Friday Saturday, and Sunday, are 102, 104, and 103, respectively.  


  1. That July 13, 2002 day with 20.2C at 700 mb tied the all-time record high at the airport of 107F. It's interesting that the July 26, 1960 record high of 107F didn't make the top 10 warmest 700 mb temperatures.

    It would be interesting to see a top 10 organized by event. The 1st, 2nd, 4th, and 7th temperatures are all the same heat wave, while the 5th, 8th, and 9th are also the same heat wave.

    1. Adam:

      Yes, that would be interesting.

      There is a good, but not perfect correlation between 700-mb temperature and the maximum temperature during the summer. Events with southerly flow tend to get a bit warmer at the airport. This might be an issue for Sunday. The GFS has a top-10 700-mb temperature, but also NW large-scale flow in the afternoon. If that verifies, it might keep us a couple of degrees cooler than if we had a south wind. Time will tell...


    2. Good point. Although the GFS doesn't even know about the Salt Lake valley, I think the northwest winds are a good bet. Showers and thunderstorms could also play a role on some of these upcoming days.

      In terms of correlating surface high temperature and 700-mb temperature, I suppose you can always have the situation of the high temperature occurring before 0Z and then have some cooling at 700 mb through advection or evaporating precipitation before the sounding is launched.

    3. 00Z 27 July 1960: 700-mb temp was 18.6C. There are a multitude of reasons why this doesn't jive with the record temp. I'll leave you to place blame on one observing system or the other.

  2. Dr Jim, What is the average for 100+ degree days in SLC? What is the record? With one down this year we should have half a dozen by next week.

    1. I think they are 5 and 22, but don't hold me to that.