A new closed low was forming over AZ/NV near the southern end of a persistent western trough that had been hanging around for about a week. This was pumping in very moist air to NM with near daily-record PW (precipitable water - a measure of the amount of moisture through all layers of the atmosphere) in the morning in Albuquerque. The dew point was around 60 in Santa Fe - not overly humid by Midwestern standards but VERY humid by the standards of north-central New Mexico. Shear and CAPE would be favorable for supercells, with SE surface winds veering and strengthening with height - 35-50 knots of shear were predicted, with good directional shear. CAPE was predicted by the RAP model to be in the 800-1600 j/kg range - plenty for severe weather at the high altitude of New Mexico.
Around 2:00 p.m., I noticed on radar that a strong storm, almost certainly a supercell, had developed and was just east of Grants. Before it even got a SVR warning, GRL3 radar indicated a 3.25" hail marker, though in all likelihood the hail was not really that big. Also there was a TVS (tornado vortex signature) for a couple scans. Eventually, though, SVR warnings for the storm did mention potential for 2-inch hail. The first SVR warning for this storm was issued at 2:30. The storm was indicated in the warning as 14 miles E of Grants and was moving slowly to the NE at just 15 mph. I watched for a while, then decided around 3:00 p.m. to head out, figuring I could intercept the storm, which was moving in my general direction, somewhere around or just W of Bernalillo, NM at the north edge of the ABQ metro, perhaps a little before 4 p.m.
My plan worked pretty well. By the time I got to the US 550 exit from I-25 at Bernalillo, around 3:50 p.m. I could see the storm to my WSW with lowerings under the updraft base. I went SW off 550 on Paseo del Volcan, stopping once or twice for pics but eventualy going all the way to where it T-intersects with Unser, then N and W slightly from there, to a high spot in Rio Rancho, NM with a good westward view. It gradually became evident from this viewpoint that the storm was HP (a high-precipitation supercell), with a wall cloud near the center of its leading edge, a low shelf cloud at the leading edge of the heavy RFD (rear-flank downdraft) precipitation south of the wall cloud, and another shelf cloud along the leading edge of the forward flank precipitation NE of the wall cloud. You can see that structure in this picture taken around 4:25 p.m.:
The wall cloud/meso is about straight down the road in the picture. Just to its left is the low-hanging shelf cloud on the leading edge of the wet RFD gust front. And to the right of the wall cloud is the shelf cloud associated with the forward-flank gust front. For the next several hours after this, the storm continued to get new SVR warnings shortly after each one expired - eventually a total of six.
At the south end of the RFD gust front and precipitation, condensation was forming near the ground where the precipitation interacted with the ambiant warm air, and then was drawn back up into the base of the cloud. This created the appearance of lowerings from the cloud base to the ground, but actually these were forming near the ground and being drawn up.
The wall cloud appeared to extend to the ground at times, but it was still pretty far away when this occurred and the storm never had a tornado warning. It did have warnings for hail to 2" and wind to 70 mph, and after a while also began to get flash flood warnings. It eventually got four of those, and several were verified by reports of flash flooding from Sandoval County eventually up through Santa Fe County south of Santa Fe. I watched the storm as it drew closer to my position, displaying its menacing HP supercell structure.
Eventually the RFD gust front and precipitation were getting close enough that I needed to move, and I figured I could basically stay ahead of the storm as I retreated back to the NE. Near Unser and Paseo del Volcan, the outflow ahead of the precipitation core caught up to me and I was blasted with blowing dust. But I got back ahead of it heading E then NE on Paseo del Volcan to Bernalillo, where I made a quick gas stop. Now the wall cloud was just a mile or two to my NW. Here is a picture of the wall cloud looking NW from the gas station:
By the time I finished my pit stop, the outflow wind had again caught up and dust was being blasted across the gas station - more of it this time because of a construction project across the street. I then headed up I-25 back toward Santa Fe, getting back ahead of the storm and making picture stops at the Budaghers exit and again at the Cochiti Pueblo/Cochiti Lake exit at the bottom of La Bajada hill. Now I was directly in the path of the storm and staring straight into the notch at the HP meso. At the first stop (Budaghers), there was some visible cloud-base rotation as well as dust being lofted in the air (I am pretty sure from outflow and/or a gustnado, nothing more) along the leading edge of the storm. Here is a picture from that location.
At the second stop at the base of La Bajada, the storm was getting very close, along with CG lightning, so I videoed mostly from inside the car. Here is a video frame capture of some of the lightning - it is somewhat blown out by the brightness of the lightning but gives you an idea of the intensity of the CG lightning barrage:
That was pretty much the end of the chase, because I had to continue toward Santa Fe to stay ahead of the storm, but new storms were now going up around and ahead of the syupercell. From one of these I got torrential rain and a little hail at I-25 and NM 599. I figured then that the supercell would be absorbed into what seemed to be a developing MCS, but it managed to keep its supercell character as it moved through the Galisteo area and on to the south of Las Vegas NM. In those areas it triggered flash flooding and road washouts along with reports of penny-sized hail. All told, the storm lasted at least 9 and a half hours as it tracked from near Grants (around 2 p.m.) to at least midway between Las Vegas, NM and Tucumcari, NM (by around 11:30 p.m.). All in all, a very impressive HP supercell storm, reminiscent of what I used to often chase in IL and MO, but with better visibility of the storm. Not too surprising to get this type of storm, I guess, with very high moisture along with veering wind profiles but not super-strong upper winds.
ADDENDUM: Although it did not make the local storm reports or the news media at the time, this storm caused extensive damage, largely from flooding, on the Acoma Pueblo, which is located just southeast of Grants. Various structures and infrastructure were destroyed, and ten miles of roads were rendered unusable. With damages estimated to be at least $2 million, the Pueblo and the NM congressional delegation requested a federal Major Disaster declaration. That request was approved December 21, and the Pueblo will receive much-needed federal assistance.
Total chase distance: 112 miles.
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