May 9, 2017 Colorado Chase

by John Farley

This would not be a day in which I would see any severe weather by the official definition, but it still turned out to be an interesting chase day, in which I could document the wide variety of weather that can occur in Colorado in May, and would finish the day getting a couple nice lightning shots along with hail video only about five miles from home.

After overnighting in Walsenburg, CO following the previous day's chase on the Palmer Divide, my initial plan was to just head home to Pagosa Springs, hoping perhaps to encounter some thundersnow in Wolf Creek Pass on the way home. However, after looking at weather online in the morning, I decided to hang around the I-25 corridor a little longer. Upslope flow would be present again, along with decent wind shear as the slow-moving storm to the southwest continued to drift slowly eastward. SPC had most of CO and NM along and east of I-25 in a slight risk, with 5% tornado probabilities in much of SE Colorado. Additionally, the forecast discussions from the NWS office in Pueblo were very bullish on northweard moving supercells in the I-25 corridor including near the cities of Trinidad and Pueblo, with early initiation of severe storms (by 1:00 p.m., maybe earlier). Since I woke up smack in the middle of this area, I decided to hang around for a while and see what would happen. Though I must admit I was skeptical because of widespread morning rain and cool temperatures across the area. The temperature was around 50 with light rain and occasional rumbles of thunder in the Walsenburg area, which did not seem conducive to severe storms to me - but with moist and warmer air being pumped in from the southeast, I did not totally discount the possibility, either.

By around 10:45 a.m., after the first batch of thundershowers (too light to really call them storms) had moved through, I could see that a much stronger storm had developed over the mountains just west of Raton, NM, and was now moving into the Trinidad area. I decided to head south to try to intercept this storm. Just as I was about to get on I-25 to head south, I stopped to take a picture of the Spanish Peaks, where accumulating snow had fallen overnight, and now presented a nice contrast with the dark updraft base in the background. (The updraft base was extending westward from the Raton/Trinidad storm, and looked to be elevated - not surprising considering how cool the surface temperatures were.) This picture was taken around 10:55 a.m.:

It soon became evident that if I kept going toward Trinidad on I-25 I would drive right into the storm, thus having no visibility and potentially ending up in a hail core. So I turned around at the first exit and headed back north to Walsenburg. By now, the updraft base extending westward from the storm had turned in to a line of storms, and I had seen some CG lightning, so when I got to Walsenburg I headed a few miles west of town to a good viewing spot where there was also a roof available in front of a lodge that I could get under if I got caught in hail. This line of storms was clearly elevated, but rather photogenic and very likely producing some hail. Here is a picture taken from this location around 11:15:

At this time the line of storms was near the Spanish Peaks and extending westward from there into the Cuchara area. After fifteen minutes or so it began to weaken, though, and as it moved in to my region it was just a cool, rainy thundershower much like the earlier one. However, radar showed that the Raton/Trinidad storm had passed over Trinidad and continued to move north or NNE and, if it held together, would be easy for me to intercept along CO Route 10 somewhere between Walsenburg and La Junta. At first the storm was obscured by rain, but once I got closer to it, storm features became visible, including what looked like hail shafts at times and occasionally some lowered areas under the flanking line that extended SW from the SE end of the storm. Eventually I caught up with the storm about 30 miles NE of Walsenburg and was able to follow it with a good view for about 20 miles. The storm remained very strong, but had become somewhat linear in contrast to its earlier cellular character. The NWS in Pueblo issued a significant weather advisory on the storm at 12:21 for half-inch hail and 50-55 mph wind, and then at 12:44, a flash flood warning. So definitely a potent storm, though never severe-warned. Here is how the storm looked at 12:25:

By around 1:00 the storm began to look a little weaker and less organized, and since I wanted to get back to Pagosa Springs by evening I knew it was time to let it go, head back to Walsenburg for lunch, and start home. It was also becoming increasingly evident that if any severe weather occurred in CO, it would be in the far eastern part of the state, not along I-25. (Though farther south in NM, severe storms were beginning to occur along I-25, but since I needed to get home, that was not an option.) While I was in Walsenburg yet another thunderstorm moved over town and this one actually contained a little pea-sized hail. This was around 2:00 p.m. By now, it had been storming off and on there for around 24 hours, and the rain totals in the area were becoming significant. Later in the day flash flood warnings were issued in this general area and I believe there was some flash flooding, especially in the more mountainous areas on the east slopes of the Sangre de Cristos and near the Spanish Peaks. By evening of the next day (May 10), some areas near the Spanish Peaks had 3-day totals of around 6 inches of rain, with significant snow in the very highest elevations.

As I headed west, I gradually ran out of the rain near La Veta Pass, but then as I headed into the San Luis Valley I could see it was snowing and raining to my south, in the Sangres of northern New Mexico and the southern San Luis Valley. By the time I was nearing Alamosa it was raining hard, with temperatures in the low to mid 40s. I gradually ran out of this rain west of Alamosa, though. I noticed some accumulated hail along the side of the road just west of Monte Vista. Earlier, strong thunderstorms had moved through the western and northern part of the San Luis Valley. Between Del Norte and South Fork, I encountered a swath a mile or two wide of accumulated hail from these earlier storms - there was lots of it along the road and in the fields, and it extended up into the mountains to the north. Some of it may have been graupel or snow as well. In any case, here is a picture I took around 4:15 p.m., well after the storm had passed:

By now, the precipitation had moved well to the north, and I could see clear sky to the west. However, as I got up into Wolf Creek Pass, there was fresh snow. Around 4:50 p.m. I stopoed to photograph the fresh snow in Wolf Creek Pass, where about an inch of new snow had fallen earlier in the day:

Around 5:10, as I was heading down the west side of Wolf Creek Pass toward Pagosa Springs, I noticed an overshooting top looking to my SW, associated with a line of storms in northern NM about to cross into Colorado. By around 5:30, I was home. But I was soon to be back out, with strong storms approaching the Aspen Springs area, which is located along Route 160 about 5 miles southwest of our house. By 6:25, I was getting ligntning pics from along Route 160 as the storm was nearing Aspen Springs:

I guess you would call this cloud-to-ground lightning, but it certainly took a roundabout route! Notice also that a shelf cloud has formed along the leading edge of the storm, which was moving directly toward my postion.

This might be my favorite picture from my entire 2-day trip. Notice how this picture shows that lightning does NOT always strike in the highest place - this one struck right in the valley along Route 160, rather than in the higher terrain on either side.

A few minutes later, around 6:30, the storm arrived with an intense burst of pea-sized hail. The hail was not large, but there was a LOT of it! It quickly covered the ground and eventually the roads, up to a half-inch deep in spots. It was enough that CDOT sent out a plow to clear the hail off Route 160. I later found out from someone who lives in Aspen Springs that hail was still on the ground next morning. Here is my video of the hail as the storm hit Aspen Springs:

In addition to accumulating on the ground, the hail piled up quite a bit on my car, too:

Like I said at the start, although I saw no officially severe weather and certainly never came close to seeing a tornado (those were in New Mexico, where the atmosphere was less worked-over from yesterday's and overnight convection - at least seven tornadoes in NM), this still turned out to be an enjoyable chase day because of the icredible variety of weather that I saw - hailstorms, spectacular lightning, fresh snow - you can see a lot of different things chasing storms in Colorado in May!

Chase distance for day 338 miles. Chase distance for 2-day trip 868 miles including Aspen Springs segment.

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