Mid-April, 2016 Winter Storm in Colorado

by John Farley

The Setup

A strong low pressure system tracked southeastward from the northern Pacific, reaching land a little south of Portland, OR and continuing southeastward across Oregon, northeastern Nevada, and Utah to the Four Corners area where, by April 16, it would become cut off from the jet stream flow and continue meandering over New Mexico and then Colorado through April 19. With an Omega block pattern and high pressure stuck over the Midwest, the storm system simply could not move eastward. Drawing moisture from both the Pacific and the Gulf of Mexico, this system produced severe weather from southeastern Colorado to the Texas and Oklahoma Panhandles on April 15, and periods of heavy snow across much of Colorado and northern New Mexico from April 15 through April 18, with some snow still lingering on April 19. As discussed below, snow totals would exceed 50 inches in parts of Colorado, and an impressive range of winter and severe weather would occur across the state over a period of five days, before the low pressure finally drifted northeast into Nebraska by the 20th.

Day 1, April 15

On Friday, April 15, the storm system began to impact Colorado with heavy snow, including several areas of thundersnow, in the mountains and severe weather, including 3 tornadoes and hail up to tennis ball size in the eastern plains of Colorado.

A map from SPC showing the day's severe weather can be seen here, and storm chaser reports for the day including some nice pictures of the Colorado tornadoes can be seen here. (Note: Although the storm chaser report thread's title does not mention Colorado, it does include some nice pictures of Colorado tornadoes from this system.)

I knew that thundersnow was a possibility in the San Juans (though in the Pagosa Springs area it was initially too warm for snow, and precipitation during the day was in the form of rain), so I remained on the alert. By mid-afternoon, thundersnow was occurring near the Crested Butte and Purgatory ski areas, and not long after, in the Cumbres Pass area northeast of Chama, NM. By around 4:00 p.m., radar was showing a strong squall producing snow and rain (depending on elevation) near the CO/NM state line around the Chromo, CO area and moving northeast into the South San Juan Wilderness and nearby areas. I decided to head out and see what I could see. Looking southeast from the Archuleta County fairgrounds just east of Pagosa Springs, what was developing into a thundersnow storm was quite visually impressive:

While watching the storm from here, I did not see any lightning or hear any thunder, but it seemed to be intensifying, and radar suggested it would pass close to or over Wolf Creek Pass. At first I had thought it might pass southeast of there and thus be inaccessible to me, but as I watched the radar it seemed to be turning a little to the left, so I figured it could be intercepted in the pass. So I headed up. By the time I reached the scenic overlook, the northwestern edge of the storm was dropping snow just behind me to my southwest, surging toward my position there. I waited a short time but heard no thunder, so I decided to head further up the pass to get deeper into the core of the cell. By the time I reached the summit, it was snowing heavily:

I waited there and ran the video camera, hoping for thundersnow. The snow came down very heavily for a while, but I experienced no thunder or lightning. As it turns out, though, there was some, apparently while I was changing locations. The lightning tracker indicated 4 CG lightning strikes between Wolf Creek Pass and the NM state line on the west side of the divide. One of them was within a mile or two of route 160, the road that goes over the pass. So my ideas for chasing thundersnow with this storm were good, but I guess my timing was slightly off for actually getting any. At the time I was at the top of the pass, about 3 inches of fresh snow and graupel had accumulated. The p-type while I was up there was mainly ordinary snow, but it did go back and forth between ordinary snow and graupel (snow pellets) a couple times.

On a non-weather note, while going up to the pass and coming back down, I saw the largest herds of bighorn sheep that I have ever seen in the Wolf Creek Pass area. It is common to see them near the scenic overlook (the upper of the two sharp switchbacks on the lower part of the west approach to the pass, elevation about 8,800), but usually just one or two. On the way down this day, though, I counted a total of 17 sheep in two herds. Here is a picture of the larger herd, along the road a little below the scenic overlook:

Note that there is no snow at this location. By the next morning, it would be very snowy, with several inches on the ground and the road in poor condition.

Day 2, April 16

My main personal focus for this day was skiing, as the Wolf Creek ski area re-opened for the weekend to take advantage of the powder after closing for the regular season on April 3. Only a dusting of snow had fallen in town, as the p-type had been rain for part of the night, but the snow cover quickly increased as I headed east of town toward the pass. When I got to the ski area, about 8 more inches had fallen overnight on top of the 3 from the previous day. Terrific powder! Here is a picture showing how much there was; one of those sets of tracks is mine!

Snow continued to fall through the day, lightly at times but quite hard at others. Sometimes it was ordinary snow, sometimes graupel, as it kind of went back and forth. At the end of the day the ski area was reporting a storm total of 13 inches, and when I left the ski area around 2:00, worn out from skiing powder since around the time it opened, the snow was coming down heavily.

As I got into the area around the scenic overlook - the same place where I saw the sheep the previous day (none in sight today; they found shelter somewhere!), I noticed that the trees were spectacularly coated with the rather wet, sticky snow. I decided a good place to get a picture of this would be at Treasure Falls, which is located where the highway transitions from the valley to going up the pass. The elevation of the parking lot for the falls is about 8,100, though the falls itself is quite a bit higher. Here is a picture of Treasure Falls as it appeared in this mid-April snowstorm:

I ran into a gap in the snowfall a few miles west of the falls, but there was noticeably more snow on the ground in the valley than there had been in the morning, and by the time I got back home it was snowing again, with a couple inches of new snow on the ground.

With the low pressure system cut off from the jet stream and unable to move east due to the Omega block, areas of heavy snow were meandering around various parts of Colorado. Very heavy snow set up in the afternoon and evening in the foothills and east slope of the Rockies west of Denver, where one location reported 5 inches of snow in an hour and a half. Heavy snow would continue through the night in that area.

Day 3, April 17

Again I headed up to Wolf Creek to ski, possibly for the last time of the season. Not much snow had fallen overnight, but conditions remained good from the previous day. When I got there it was partly sunny with some light flurries in the area, which gradually evolved into a steady light snow, but without much accumulation until around 1 p.m. Then the snow (and occasionally graupel) became heavier, with a new inch or two by around 3 p.m. This made for terrific skiing during the afternoon. When I headed down, it was not snowing much in the pass, but I could see that there was a heavy snow shower coming up the valley. As I drove through this, snow began to accumulate in the valley where it had melted earlier in the day. I ran out of this snow shower before reaching town, but not long after I got home, heavy snow redeveloped.

These "gorgo" flakes came down for a while, then got smaller, but within an hour and a half of when the snow began at 5:30, two inches had accumulated. By 9:00 p.m., the accumulation was up to 3.7 inches. After 9, the snow became lighter and more intermittent, but did additionally accumulate.

Day 4, April 18

By morning, the accumulation at our house from the snow that began late the previous afternoon had reached 5 inches. Meanwhile, the heavy snow had continued in the foothills and east slope of the Rockies west of Denver and Colorado Springs. A local storm report from the Boulder NWS showing some of the massive accumulations, in one case over 50 inches, west of Denver can be seen here. Note that a number of locations in Jefferson, Boulder, and Gilpin Counties got over 40 inches. And near Pinecliffe was not the only place that got 50 inches or more. A Denver TV station that evening did a report from a ranch near Golden that had gotten 50 inches. The report showed a horse up to its belly in the snow and a cow up to its shoulders! The ranchers had to work frantically, but managed to keep all their livestock safe.

Meanwhile, the storm was not quite finished with Pagosa Springs. We continued to get occasional snow showers through the day, though the warm ground and above-freezing temperatures prevented accumulation and allowed some of the overnight 5 inches of snow (which had accumulated mainly on grassy and elevated surfaces) to melt. But then around 7 p.m., something a little different came along. The sky darkened, and what I at first thought was graupel began to fall. But it was not graupel. Its rate of fall toward the ground was a lot faster than any of the graupel we had been getting, and it started making loud bangs as it hit the roof. It was not graupel, it was hail! The biggest ones were only about 1/4 inch or a little bigger, but it was definitely hail, not graupel. The temperature, incidentally, was in the upper 30s. The hail lasted about 2 minutes, then changed to graupel. It was still chunky and bouncing when it hit, but falling much more slowly and not making anywhere near as much noise. Then after a minute or two that changed to ordinary snow. So there it was: hail, graupel (snow pellets), and ordinary snow, all in less than 5 minutes and all from the same storm. It is only the second or third time I have observed the rare combination of hail and snow from the same storm! The snow continued for another 10 minutes or so, with the sun coming back out before it stopped. The hail, graupel, and snow all accumulated a little on the ground, but never more than a tenth of an inch or so. Out of curiosity I checked the lightning tracker, although I had heard no thunder, and discovered that this cell had produced a couple CG strikes as it moved toward Pagosa Springs from the southwest. One occurred about 15 miles to our southwest not too far from Pagosa Junction, and another a little farther SW over Navajo lake. Interesting weather, to say the least!

Day 5, April 19

Although the storm system was weakening and trying to move away, Colorado was still not entirely finished with it. Additional snow fell in some mountain areas in southern Colorado and northern New Mexico, and intermittent rainshowers in Pagosa Spring. Finally in the evening the low began to drift northeast into Nebraska as the blocking pattern began to break down. Although isolated showers would still continue into the next day in parts of Colorado, the significant precipition associated with this system was finally coming to an end.

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