Monday, April 11, 2016

Why Utah Meteorologists Love Tax Day

If you are a meteorologist in Utah, there are few days on the calendar as fun as tax day.

It seems like something exciting happens every year on or about April 15, and there are good reasons for it.  April 15 lies at the beginning of the Intermountain cyclone season, which spans from April to early June and frequently features the development of strong troughs or low pressure systems over the Great Basin downstream of the Sierra Nevada.  Such systems frequently bring strong winds and blowing dust.  April 15 also lies in the heart of the wettest month climatologically in Salt Lake, with April averaging a whopping 2.10 inches of precipitation, good for big storms.  Finally, April 15 is in the middle of the transition from winter to summer and we can get some extremely large temperature swings in April and everything from deluges to dumps.  If you don't like the weather in April, wait 5 minutes.

Perhaps the biggest and baddest example of extreme weather on April 15 is the 2002 Tax Day storm, which produced the second lowest sea level pressure observed in Utah since observational records began in 2002 and the strongest cold-front passage observed in recent decades.  With frontal passage in Salt Lake City, temperatures fell 13ºF in 10 seconds and 34ºF in 2 hours.  Blowing pre-frontal dust produced by the storm forced the closure of US-6 and left a chocolatey-brown coat of dust on the mountain snowpack for the remainder of the snowmelt season.

The storm advertised for later this week isn't as exciting, but will probably make things more meteorologically interesting.  As predicted by this morning's 1200 UTC NAM, a surface cyclone and frontal precipitation band are predicted to develop over the Great Basin by Wednesday afternoon (0000 UTC 14 April).

The surface trough and frontal band linger to our northwest for some time, but the NAM eventually brings them into the Salt Lake Valley in earnest on Thursday morning.

Yes, I know that's 14 April, not Tax Day, but that's close enough for Rock 'n' Roll.

As things stand now, the event looks like a modest spring storm for northern Utah, certainly not of the caliber of the 2002 Tax Day Storm and many other strong spring events in Salt Lake City.  If the NAM were to verify, we would, however, see some significant changes in weather including some bench snow on Thursday, and perhaps some decent powder skiing in the mountains on Friday.

However, I've done this gig long enough to know not to read too much into the small-scale details of an Intermountain front event that is still about 3 days away.  There's a lot of sensitivity of these events to the track, speed, and structure of the primary upper-level trough and its interaction with the Sierra Nevada.

Thus, don't bet the farm on this morning's NAM forecast.  A lot could change the next couple of days.   Let's see how things look on Wednesday.  


  1. Jim - For those of us with short memories, last year was plenty dramatic as well:

    "At the University of Utah, yesterday's maximum temperature was 71ºF, achieved just before frontal passage, which occurred between 2:45 and 2:50 PM MDT. The temperature changes accompanying the frontal passage include

    12.4F in 5 min,
    17.8F in 10 min,
    21.1F in 1 h, and 29F in 2 h.

    The total temperature change from 71F at 2:30 to 32F at 8:05 was 39F."


    1. Ah yes, that was a good one. My short-term memory isn't what it used to be!

  2. I'm running in the SLC marathon on the 16th...No snow please!! :)

  3. Even though the IRS pushed tax day back to next was a beautiful powder day on the upper half of Snowbird! I loved this tax day! :)