Thursday, July 20, 2017

One Streak Ends, Another Continues

At just before 1 AM MDT on 19 July, a weak thunderstorm moved over the Salt Lake City International Airport, producing .01" of rain.  The thunderstorm was isolated in nature, but was enough to produce measurable precipitation at the airport for the first time in 34 days.

So that streak, although not even close to record breaking, is over.  If my notes are right, the record at the Salt Lake City airport for consecutive days without measurable precipitation is 63 days and there have been 9 instances of 40 or more.  Of course, .01" isn't really much in July when it evaporates off in a few minutes.

Getting to record breaking streaks, our consecutive day streak with minimum temperatures above 70 continued through yesterday and now sits at 17.  The overnight low this morning was only 77 or 78 degrees, so that streak will go to 18 unless we can get some thunderstorm cooled air to drop things to below 70 this afternoon or evening.

Speaking of thunderstorms, we noted on Tuesday that a monsoon surge and associated thunderstorm activity would push right to the doorstep of Salt Lake County tomorrow afternoon and that's pretty much what happened.  Below is the precipitable water analysis (contours, a measure of how deep the water would be if you condensed out all of the water vapor in the atmosphere) for 0000 UTC (6 PM MDT) yesterday afternoon.  Note the sharp dropoff from central Utah to the northwest Utah border.

Some strong storms popped over Utah, Summit, and Wasatch Counties and did try to sneak into Salt Lake County, but for the most part, we missed out on the action.  Pity, although the cloud cover and cooler outflow was appreciated.

Some of that monsoon moisture remains in the area today, so there's still the hope of something popping and giving us some rain this afternoon or evening.  Keep your fingers crossed.

After that, we see a shift in the flow and drier air moving into northern Utah.  By Saturday afternoon, precipitable water values over northern Utah are less than 15 mm, greatly reducing the thunderstorm threat, which will likely consists of just isolated storms over the highest terrain (Uinta Mountains, you know who you are).

With drier air moving in, there is a chance that we might actually see a minimum temperature below 70 if not with a storm this afternoon (low chances) then sometime over the next few days.  Another reason to keep your fingers crossed!


  1. Got a wild hair and pulled the data back to 2014.

    Average min temp Jul 1 to Jul 19 was 69.2 in 2014, 67.7 in both 2015 and 2016, and a whopping 74.1 this year.

    Last year we had that delightful September in July when the overnight low was 51 on the 11th. Nights warmed after that w 81 on the 18th, and an average of 70 for the month.

    Average low for 2015 was 65.5, max of 79 on the 4th, min of 53 on the 29th, the 28th was 54 and the 30th was 58.

    Average low for 2014 was 68.3, max of 77 on the 15th, min of 58 on the 1st, the only day below 60 for the month.

    There's something unusual going on in 2017 not directly related to the urban heat island or climate change. Could just be a random warm streak related to the monsoon as I surmise, or something else. If the next 10 days cool down overnight, the month of July 2017 could end up looking about the same in terms of average, min and max as the past three years. Getting to an average near 70, like 2014 and 2016 would require a string of days w lows in the 50s. One can only pray.

    Hopefully it will bring a snowy winter.

    1. Yes, natural variability is also playing a role this year.