Chase Log: April 06th, 2006
Click on any of the SPC products below (Convective Outlooks, Watches, or MCDs) to see the SPC's "Severe Thunderstorm Events" page pertaining to this event.
Total Distance: 560 miles
Target Area: Bartlesville, OK
Chase Area: Bartlesville, OK, to Carney, KS, to Pryor, OK
Maximum SPC Risk category: High
Watches:
PDS Tornado Watches 154, 157, and 159, Tornado Watches 155, 158, Severe Watch 156
Mesoscale Discussions (MCDs):
Another synoptically-evident severe weather setup today, with a VERY deep cylone along the central NE/KS border (~980mb) associated with an intense cut-off low moving out of the western US. The operational models weren't consistent with the location of the dryline, however. Several days before the event, the models began shifting the dryline forecast position from western MO/AR, westward to near the I35 by afternoon. However, starting the day before the chase, the NAM began shifting the dryline forecast position farther east again, with the 12z 4/5/06 run indicating that the dryline would be in western MO by 0z. With that trend, opposite of what we had seen up to that point in the season, I was feeling quite pessimistic about the chase potential, and I had full plans to stay home.
Well, the 0z models rolled in on 4/5, and that all changed. The WRF and NAM were now forecasting the dryline to be along I35 by 18z, shifting eastward to eastern OK/KS by 0z. Cha-ching! With model forecasts of 2000-3000 j/kg CAPE, and strong low-level shear profiles, I quickly changed my plans. Since midlevel flow was progged to be out of the south north of the OK/KS border (resulting in shear vectors that were not very normal to the dryline), I knew I wanted to stay in OK as much as possible. Unfortunately, the heart of the 85-95kt 500mb jet streak was also progged to pass through OK, so very fast storm motions was going to be an issue.
I chased with several folks today (Gabe, Brandon; then caravaned with JR, Justin, Adam, and Robin) in northeastern OK and extreme southeastern KS. We targeted Bartlesville, and were quite pleased to see that hte storms that developed near I35 north of OKC were taking aim at our location. We meandered north from Bartlesville towards Dewey to get a good view of the storm as it approached. We knew it was tornado-warned, and the south side of the updraft was quite rigid. However, in time, it's radar appearance dropped... We headed north into extreme southern KS (in Carney), to watch this storm further. There was plenty of turbulent motion, but nothing too organized. We then dropped back south into OK, as radar showed addl storms developed that way. There was a nice RFD occlussion with the storm near the OK/KS border, but we thought that a storm to that one's south that was precipitating into the inflow of the that northern storm would squash the chances for a tornado with that one... So, we dropped south further, hearing of a new tornado-warned supercell southwest of Bartlesville. After getting to just east of Nowata, everything looked quite poor. With a nowcast update from Phil H., we dropped south again, hoping to catch a tornado-warned supercell very near the Tulsa 88D / radar site. We punched the core, making it to Pryor before trying to head east. At this time, the supercell was tornado warned again... On our way out of Pryor, we experienced very strong RFD winds, breaking a small tree not too far ahead of us. The storm exhibited a pretty nice RFD clear slot, but it was quite wet at that time. We tried to keep up with it, but we lost it on the most pathetic of roads that is Hwy 20 south of Langley (east of Lake Hudson). The somewhat saving grace was experiencing the intense RFD in Pryor.
In all, however, this chase falls in line with the other high-hype chases of the year (including 3/30 and 4/1), which is disappointment and frustration. I wish I had the will-power to just stay away from these early season setups, since they almost always seem to fail for one reason or another. Overall, another rather disappointing chase. The structure wasn't particularly noteworthy, and cloud-base rotation was weak. I noticed that, on radar, many of the cells exhibit some anticyclonic rotational tendencies intermittently.
Looking at the RUC/SPC mesoanalysis valid for 0z, it's no wonder why storms struggled, with only ~500 j/kg CAPE near the storms in northeastern OK and southeastern KS. The 0z NAM initialized 750-1250 mlCAPE in the same area. Similar to what happened on 3/30, I think one of the main failure modes was lack of strong instability in the face of strong shear (the supercell that moved from Paul's Valley to McAlester on 3/30 was also located in marginal CAPE -- 250-500 j/kg CAPE per SPC mesoanalysis by late afternoon and early evening). 0z NAM initialization indicates 0-6km shear of 70kts, with 80-85kt 500mb winds across that area at 0z. Broken strato-cu developed east of Osage county through the afternoon, which kept temps largely in the low-mid 70s. Farther west near and just east of I35, temps rocketed into the 80s. I don't think it's any coincidence that storm updrafts looked quite solid as they first approached Bartlesville, before turning more "mushy" in appearance as they marched northeastward. With relatively cool sfc temps, CINH was relatively significant. I do think that some storms were able to sustain themselves long enough to establish decent vertical perturbation PGF fields, which helped maintain the storms as they moved into the weaker/weak instability in se KS and ne OK. I do think we would have seen an event more like what was forecast if temps had warmed a bit and Tds would have risen a few more degrees. 0-1km SRH wasn't a problem, with RUC mesonanalysis at 0z indicating >400 0-1km SRH in se KS / ne OK. I think the cooler surface temps likely prevented storms from ingesting surface-based parcels (or at least not stretching them much owing to relatively weak CAPE), which is turn made the very strong low-level shear rather irrelevant.
