May 4 was a day I was looking forward to chasing up to five days in advance. For one it would be a Sunday, which is my only day off work. The computer forecast models were already indicating the potential of a severe weather outbreak in the southern Plains that day - finally forecasting decent moisture to move into the region ahead of a strong surface low and impressive dry punch. The ETA and GFS were in a lot of disagreement in the days leading up to the event as to how far east the low and the dryline would be on Sunday, but I was suspecting both were placing them too far east, as disturbances were ejecting from the West Coast trough slower than the models were indicating. Even as late as Saturday, the models were pointing towards this outbreak being mainly a Missouri/Arkansas event - but with the low still in eastern Colorado and dryline way back in western Texas late Saturday night - I was hopeful I would not have to travel too far east to see severe weather on Sunday.
I woke up around 11am on Sunday morning to take a look at data. The low had begun moving eastward through northwest Kansas and the dryline was rapidly mixing eastward through western Oklahoma. My goal today was to try for the tail end cell, which would have access to the most unstable air. The night before I had been thinking that might occur as far south as northeastern Texas, but with the strength of the cap (over 20C at 850mb) I was not as confident things would happen that far south. So I continued to look at data and satellite trying to pin down a target. By 1:30pm, the dryline had almost made it to I-35, and towering cumulus were bubbling up in north central Oklahoma. This made me hopeful things would happen in northeastern Oklahoma, but I was still not convinced to blow off things further south. With skies rapidly clearing from the west and winds beginning to crank out of the west-southwest here in Norman, it really was time to go, so after downing a tasty bacon cheddar sandwich at Sonic I high tailed it out of Norman at 2pm.
From Norman I took I-35 up to Oklahoma City. I then went east on I-40, which would give me options both north and south. With limited visibility due to haze and smoke I would not be able to see storms firing to my distant north, but with cumulus towers eating away at the cap to my east I became more optimistic about my south target. I blasted east on I-40, listening in amazement at the NOAA Wx Radio as OKC had a temp/dewpoint of 90/46 by 3pm (it was 84/66 at 1pm!). Updrafts would repeatedly launch and fizzle as they worked at the cap, but by around 4pm the cumulus towers were gone. This led me to believe that storms had fired elsewhere, but due to poor visibility I couldn't see any signs of storms to my north or south. I then learned on NOAA Wx Radio that storms had begun forming in Coal and Hughes Counties to my south. By this time I was crossing Lake Eufaula and was coming up on the intersection of I-40 and US 69, and once I came to this intersection I headed south on US 69. Almost immediately upon turning south on US 69 numerous warnings came over the radio for the developing storms to my southwest. Through the haze I could begin to make out a backsheared anvil to my southwest, and before long, anvil rain blown well downstream began hitting my car. I got gas in Eufaula, then punched through this northeastward racing left split to get to an eastward moving cell further south. I started getting into some intense rainfall about 10 miles north of McAlester, which dramatically dropped off in intensity as I arrived in McAlester just before 5pm. I pulled over in a parking lot near the intersection of US 69 and US 270 to try to get a visual and listen for further warnings. Scud was surging southward and winds were out of the north, so I felt I was in a fairly safe spot. A tornado warning then came over the radio stating a doppler indicated circulation near Kiowa, which was to my southwest. So I cautiously proceeded eastward hoping to eventually get ahead of this thing. A sense of urgency took over once I got into Alderson and I noticed that winds were now out of the south! Why they were now out of the south I didn't know and didn't really have time to find out, so I just calmly headed east through intense rainfall hoping for the best. After getting into some dime sized hail in Hartshorne, I finally broke free of the precip. Winds here were fairly light and out of the southwest, so I felt safe but still knew I needed to continue east. A split in the road came east of town, with US 270 continuing northeast and Hwy 1/63 heading southeast. With a nasty looking, hail filled rear flank downdraft looming to my northwest, I felt it would probably be best to take 1/63.
Hwy 1/63 was not a good route for chasing with numerous curves, hills, and trees, but it was keeping me south of the storm. Periodically I was able to get good views of the storm from high vistas along the road, and I pulled off on one to take some video of this HP supercell and its hail laden RFD as it screamed eastward, displaying impressive mid level rotation and pulling in tufts of scud from the southeast. This thing was really booking it eastward, so my stop was a brief one. I eventually lost sight of this storm, as well as good Wx Radio reception, as I continued into the hilly, curvy roads and extensive forests of Latimer County. I got into better terrain once I was further east into LeFlore County, where I learned of a tornado warned storm to my east. As I passed through the towns of Summerfield and Wister, I could sporadically see leaves which had been ripped off trees - apparently from wind/hail. Numerous residents of Wister were standing around the post office looking westward, as if they were looking for a tornado....the town was under a warning at the time. The only problem was that the storm was off to their southeast. I tried to keep up with the storm all the way to Poteau, but by now the storm was well into Arkansas and racing off to the east, and with nothing off to my west I decided to call it a day and head home.
Some interesting surprises came upon returning home and checking reports and radar data. One was that the supercell I tracked was a single storm. I had initially thought that the cell in LeFlore County was a new cell that formed to the east of the one I had been tracking, but it turned out the supercell I initially intercepted near McAlester just zoomed right past me as I was winding through the hills and forests of Latimer County. This storm was apparently just an HP "hurricane hailer", producing numerous reports of baseball sized hail and 80 mph winds between Wilburton and Poteau....and apparently was one of the only non tornado producing storms of the day. This could be because the RFD was filled with hail, which may have made the RFD cold. Recent research suggests that cold RFD's are detrimental to tornadogenesis - tornadoes appear to form in association with warm RFD's. Another interesting surprise came when I learned that railroad cars were overturned in Alderson, very close to the time I passed through there. Remember that my winds went from north to south somewhere between McAlester and Alderson. I never experienced winds that seemed strong enough to do any damage, however. Radar indeed showed a circulation embedded in precip in that area around that time, with the cell merging with another cell to its southwest shortly thereafter. I have not heard what the exact cause of the Alderson damage was at this time, however.
Today's chase gets a 10 out of 18. The frustrating terrain and fast storm movement made this chase a challenge, but the sight of an HP beast cranking along at more than 50 mph was definitely one to remember.
Total Mileage: 477 miles
Total Driving Time: 8 hours, 16 minutes