November 7, 2017 Winter Convection and Thunderstorms,
Pagosa Springs, CO Area

by John Farley

Interesting weather occurred in and around Pagosa Springs, CO the afternoon and evening of November 7. With west-southwesterly jet stream winds overhead and a cold front approaching from the north, moisture, orographics, and atmospheric dynamics combined to produce numerous convective showers and thunderstorms. It was cold enough for winter mixed precipitation with these showers and storms in the San Juan River Valley around Pagosa Springs (elevations 7000-8000) with substantial snow accumulations in the higher mountains (above 9000 feet elevation).

Around 1:30 I left home to go pick up routine medication for our cat at the San Juan Veterinarian Clinic which is a mile or two northeast of Pagosa Springs along U.S. 160. I figured that while I was out, I would also head up toward Treasure Falls to see if I could get any decent pictures of the snow that had been falling higher up in the mountains. However, this ended up being more of a winter storm chase, as that opportunity presented itself and with the low visibility, any snow photography would have required driving well up into the mountains. In town, there had been rain off and on overnight and into the morning. However, by now, the precipitation had become more scattered and convective, and in town, the sun had been out for a while. As I got to Piņon Lake, not far from home, I noticed a line of fairly decent convection to the north, with shafts of what looked like frozen precipitation coming out of the cloud base:

The temperature was in the mid-40s, and that was where it would stay until I eventually entered the precipitation. After I stopped at the vet office and picked up the medication, I could see that the broken line of convection was not far to my north. One heavier cell along the line was to my west, likely moving in to the Pagosa Springs area. There was another cell in the same line farther ENE, with precipitation moving across 160 a few miles up the road to my NNE. Figuring there was at least some potential for thundersnow, I headed that way, and as I crossed through the precipitation, I encountered a mix of rain and graupel (snow pellets). The temperature on my car thermometer now fell to the upper 30s, and that is where it remained the rest of the time I was out. Once I passed through the precipitation, I noticed that there was another line of convection parallel to the one I had just passed through, but farther north. The following picture is of that line, looking NNE right along route 160 toward Treasure Falls:

I reached this line of convection a little before Treasure Falls, near the chain station right before the road turns from two to four lanes. This was heavier than the previous cell I had passed through, producing a burst of graupel/snow pellets, sleet, and rain. I stopped for a little while hoping for some lightning and thunder, but decided to move to the Treasure Falls parking lot because at the chain station, I could only park in a position where the precipitation was blowing into the car if I had the window down for video. However, Treasure Falls was on the back edge of the line of convection, and the precipitation was lighter there. Nonetheless, I sat and waited for a while to see if there would be any lightning or thunder, but there was none. So after a while I headed for home. A half mile or so before I passed the vet office again on the way home, I noticed that the ground was white and the road, for a short distance, was also covered with graupel, sleet, snow, and/or hail. Obviously when the first of the two lines of convection passed through here, it had been heavier than anything I had driven into. From a little past here into the east end of town, there were a few patches of white, but not as much as in the narrow swath just northeast of the vet office. The rest of the way home it was wet. The sky to the southeast was dark, but it was now clearing in the Pagosa area, and the more northern band of convection had shifted east into the mountains. When I got home, my wife said it had rained hard at the house, with one rumble of thunder, but she did not see any precipitation other than rain.

For a while after that the weather stayed calm, but with lots of showers on radar to the west and northwest, I figured that would change. Intermittent light rainshowers returned during the early evening, with occasional distant rumbles of thunder. The lightning tracker showed one cluster of strikes near Arboles,CO and Navajo Lake early in the evening, then another around Chama, NM later. There were also a handful of strikes in the San Juan Mountains east of Chama and Pagosa Springs, likely indicating some mountain thundersnow. Starting around 9 p.m., there were occasional heavier showers of mixed rain, graupel, and snow at our house. Around 9:40, there was a loud rumble of thunder, indicating lightning pretty close. I decided to try getting some video looking out of the garage onto the driveway. P-type when I started was mainly graupel (snow pellets) with perhaps a little rain mixed in, but after a few minutes the graupel increased and mixed with a little hail. Then a flash of lightning, followed in a few seconds by thunder, indicating the lightning was less than a mile away. The precipitation decreased shortly after that, mixed with ordinary snow, and then abruptly stopped - with another flash of lightning just then. Only about 3 seconds between the flash and the thunder, so the lightning was barely more than a half mile away. There were two more flashes after that, and another burst of graupel/snow pellets. By around 10 p.m., the mixed winter precipitation and lightning were over. Here is a video capture of one of the flashes of lightning:

Here is video showing the mixed winter precipitation and 4 flashes of lightning:

As this winter thunderstorm was occurring, the temperature in Pagosa Springs in the mid to upper 30s. The 9 p.m. temperature at the Pagosa Springs airport was 38, and 37 with a thunderstorm at 10 p.m. Also at this time Wolf Creek Pass was receiving thundersnow with a temperature of 23. Over the period from Monday night through Tuesday night, significant snow accumulations occurred in the San Juan Mountains, where a winter weather advisory was in effect. The Wolf Creek ski area received 10 inches of snow. Here are a couple pictures of the fresh snow in the mountains:

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