Thursday, July 9, 2015

The Amazing Strobe-Light Storm

Although I was in desperate need of a long night's sleep, last nights spectacular lightning display kept me mesmerized and jacked up through about midnight.

The system swept through the Salt Lake Valley from about 9 PM to 1 AM MDT.  It featured a number of strong convective cells, followed by a more continguous region of precipitation in their wake.

The system was highly electrified.  Although frequent lightning of this type is common east of the Rockies and sometimes in the southwest U.S., I don't know if I've ever seen such a long period of frequent lightning before in northern Utah.  Hence, I'll call this the Strobe-Light Storm since the combination of thunder, heavy rain, and lightning gave it a discotheque feel.

Some of the most intense precipitation fell at about 11 PM MDT near downtown Salt Lake City and especially near the junctures of I-215, I-80, and I-15.  At this time, a broad swath of heavy precipitation with radar reflectivities exceeding 50 dBZ, with maxima above 60 dBZ, pummeled the area.

Storm-total radar-estimated precipitation in this area peaked at a whopping 2.5 inches (brownish pixels below) with a large area exceeding 1.5 inches.  The average July rainfall at the Salt Lake City Airport is only .61 inches.

The maximum radar-estimated 1-h accumulation in that area was near 2 inches.  Such an hourly rainfall rate has a return interval of about 200 years at that area of the Salt Lake Valley according to data on the the NOAA Precipitation Frequency Data Server.  Although there are a variety of problems with the use and interpretation of those intervals, especially in a changing climate, such numbers illustrate that it was "raining like hell" in that area last night by Salt Lake City standards.

Showers and thunderstorms are possible again today.  What a great start to July.


  1. The Radar pattern for this storm is quite interesting in that it can be seen how the Wasatch Front concentrated the rainfall over the Salt Lake area. As the storm approached it was oriented in an elongate NW-SE direction and was moving to the NE. As this line approached the Wasatch the SE edge contacted the Wasatch near Provo and Mt. Timp. This caused the rainfall to "bunch-up" in that area and move in a more northerly direction. As the rest of the line continued to move NE while the SE limb moved north. The storm concentrated upon itself right over SLC.

  2. I was impressed by the explosive development of the 50+ dBZ area on radar considering that light precipitation had already been spreading into the valley, which often leads to more stratiform-type rain as time goes on. The 0000 UTC sounding last evening showed a surface dew point of 49 and a CAPE of 643. Dew points rose into the mid 50s not long after 0000 UTC which, looking at the Skew-T, probably added a considerable amount of CAPE to the mix.

  3. I shot a couple of video clips looking north from Taylorsville around 10:30 to 11:00 last night as that main cell was developing. It had lightning about once per second during that time, and looked like the vast majority of it was in-cloud.

  4. it looks like the airport reported less than an inch