Strong Storms with Hail Northeast of Pagosa Springs, CO
May 11, 2020

by John Farley


From a couple days ahead, there were indications of potential for strong thunderstorms across western Colorado on this day, as a shortwave crossed the area. By the morning of the event, it was evident that there would be plenty of moisture, with seasonally high precipitable water of .5-.75 inch and dewpoints in the 40s and 50s. Plenty of instability, too, with CAPE of 1000 j/kg or higher. And there would be wind shear, too, with bulk shear of 30-40 kt, favoring some potential for storm rotation. Now, these parameters would not be overly exciting for storm chasers in the plains or Midwest, but for the higher elevations that exist in places like Colorado and New Mexico, they are more than enough for strong to severe storms. Interestingly, although it seemed to me that a marginal risk would have been warranted for much of western and southern Colorado, the Storm Prediction Center did not issue any risk area for this region. However, the NWS in Grand Junction was on top of things, mentioning the potential for strong storms a day or two ahead of the event. I thought there was potential both for thundersnow in the highest elevations and for strong to marginally severe storms throughout the area, so I was watching the weather while I tended to other tasks as the day unfolded. The biggest uncertainty in the forecast was whether clearing from early morning precipitation would occur in time for the atmosphere to destabilize, but most of the convection-allowing models (CAMS) suggested that it would. And by mid-day, clearing was under way in eastern Utah and far western Colorado, and spreading east. So it was looking more and more like game on.

Around 3:15, I noticed on the lightning tracker that there had, in the past few minutes, been a number of lightning strikes on the southwest slopes of the San Juan Mountains west of Wolf Creek. Checking radar, I could see that an isolated strong cell had formed in that same area. Since the Webcam at Wolf Creek Ski Area showed snow falling at the time, my initial thinking was that this could be a thundersnow opportunity, although the heaviest part of the storm, as it moved to the ESE, would probably pass southeast of the ski area. But I knew it could also become a strong storm with good potential for hail, so either way, it was go time. As I waited for a light a mile or so from home, I could clearly see the storm to my north, and got this picture with my phone around 3:25:

As I got through Pagosa Springs and closer to the storm heading northeast on U.S. 160, I could see storm structure that suggested a pretty strong storm. Once you're out of town, cell service disappears quickly, so you have to rely on your eyes with no help from radar or the lightning tracker. But it was clear that this was a pretty strong storm, and not far out of town, around 3:40, I could see this lowered area which appeared to something of a shelf cloud/wall cloud hybrid:

The left part of the lowering was under the main updraft of the storm. As I continued to drive toward the storm, I could see occasional lightning and, as I got closer, rather violent cloud motion, although no clear rotation, in the cloud base. Here are a picture and a video capture showing the storm at this time (around 3:45):

The lowerings in the second picture briefly took on the appearance of funnels, but again, despite violent cloud motion, there was no real evidence of rotation, so I do not think that they were. Still, the amount of turbulence suggested a strong storm, and I was sure there would be hail, as indeed there did turn out to be.

The storm crossed the road a few miles ahead of me, and I continued to the path, where I found hail on the ground, and some on the road, intermittently for about 3 miles beginning just before the Archuleta-Mineral County line, up toward Treasure Falls. I got out and inspected the hailstones, which were hard, true hail, not graupel, and mainly pea-sized. I got pictures of the hail on the ground and on the road.

By now, the storm had moved off to the ESE into the mountains, where it undoubtedly produced thundersnow, probably along with hail in places. I headed back toward town, since at the time it did not appear that another storm in this area was imminent. When I got back to the east edge of Pagosa Springs, I could see a fairly strong storm to my southeast, and since radar showed it was over U.S. 84, I probably could have gotten to it. But it looked like it was at its peak strength and perhaps about to weaken, and was moving away from me. At the same time, I could see a line of TCU extending to the WNW from the storm I had been on, along the southwest slopes of the San Juans. I watched a while, saw that some of these were developing into storms, and ultimately decided to head back where I had been. By the time I was about halfway there, I could see that several storms had developed in the line, and were tracking through the same general area as the storm I had been on earlier. Basically, the storms were training through the same area, resulting in repeated storms occurring in the same places. I was on the edge of the storms by the time I reached the turnoff for the East Fork Campgroud, next to the East Fork of the San Juan River. This was around 4:45, and it was evident that hail was falling heavily just to the north and northeast of my location. I stopped there, and soon hail was falling and lightning was zapping down. One bolt appeared to strike the top of a mountain a mile or so away:

In the picture, you can also see hail fog near the ground on the left and clouds rising up the side of the mountain that probably originated as hail fog. I was at the southwest edge of the storm, and could hear the hail roar as the hail hit the trees on the mountain and between me and the mountain. I had thought that the core of the next cell in the line would move over me, but it continued on the same path as the earlier storms, producing the heaviest hail just to my north near the county line of Archuleta and Mineral Counties, and never fully moving over my location. When the heaviest of the hail passed, I decided to get back on 160 and drive a mile or so to the path where the heaviest hail occured. As I did, a mixture of rain, hail, and graupel or wet snow fell, the temperature having fallen from near 60 before the storms to the upper 30s now. The hail had accumulated to about an inch on 160, the road was very slippery, and many vehicles had stopped to wait out the storm. I managed to safely drive through the hail swath, getting some video as I went. The swath of hail was a mile or so wide, and ended quite abruptly on the other (northeast) side. I turned around and drove through the swath again, now encountering some slightly larger (around .3") hail falling as a tail-end cell moved over, along the same path as the others. I stopped, waited out the hail, and got a couple pictures of the hail, which by now had accumulated to a depth of about an inch on the highway:

The first picture is looking NNE on U.S. 160 toward Treasure Falls. You can see the Mineral County sign on the right of the road, indicating that I was right at the county line. The second picture is looking the opposite direction on the highway, toward Pagosa Springs. These pictures were taken after the last burst of hail ended, though a little rain was still falling. When crossing the swath just before I stopped at this location, I noticed that a pickup truck had slid off the road and ended up overturned just over the fence on the southwest-bound side of the road. The truck and trailer on the side in the first picture was stopped next to the location of the overturned truck and appeared to be providing assistance. Shortly after this picture a tow-truck arrived and the truck and trailer that had been stopped continued on their way. It thus appeared there were no injuries, so I also returned to Pagosa at that point. On the way back, I met a couple of Pagosa Fire vehicles on the way to assist, but no ambulances. While out taking the pictures above, I determined that the depth of the accumulated hail on the highway was around 1 inch.

That was the end of this line of storms, but not the last of the day's storms. As I came back into Pagosa, I could see another line of storms to my WSW, still pretty far away. I thought about going after it, but decided to head home. After getting home, I noticed reports that the approaching storm had produced 50-55 mph winds as it moved through both the Cortez and Durango areas. It arrived at our house around 6 p.m., producing a burst of strong outflow wind, then a brief shower of small hail, then a steady light to moderate rain for 45 minutes or so. Very little in the way of thunder and lightning, though. Just after 6 p.m., a wind gust of 59 mph was recorded at the Pagosa Springs airport, so the storm met severe thunderstorm criteria. I don't think it was that strong at our house, though. I don't have my rain gauge out yet because of concerns about freezing, but gauges nearby generally recorded .15-.25 inches of rain. Much needed, since the west side of Pagosa had not gotten any significant precipitation since late March.

The video linked below shows the rapid cloud base motion associated with the first storm, hail, lightning, and thunder from the second storm from near the East Fork Campground turnoff, and a drive through the hail swath near the county line during the later stages of the second storm

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