Analysis of 3/30 Tulsa Tornado Environment
Rotation data, courtesy: NWS Tulsa
A tornado affected the north and northeast suburbs of Tulsa, Oklahoma early yesterday evening. Despite the conditions in place, a Tornado Watch was not in effect, as instead, a Severe Thunderstorm Watch had been issued by the Storm Prediction Center (SPC). Severe thunderstorms can and sometimes do produce tornadoes and the environment across northeastern Oklahoma late Wednesday was favorable for tornadoes. It’s not always a clear-cut forecast and the environment across the Plains and Mississippi Valley yesterday was quite complex with mixed storm modes and several boundaries in play. Below is a quick look at some mesoanalysis graphics and other images to get a better idea of how the event unfolded.
A line of discrete thunderstorms was ongoing late Wednesday from southeastern Kansas into portions of north-central Oklahoma. A Severe Thunderstorm Watch was in place and the SPC outlined the threat for severe weather downstream, into northeastern Oklahoma and surrounding areas. Large hail was the primary threat, due to moderate instability and steep mid-level lapse rates. The surface wind barbs in the mesoscale discussion to the right show that winds were backed (southeasterly) ahead of the line of storms. This was an immediate red flag that there may be a tornado threat with any of the more dominant cells.
The image below, on the left side, shows low-level instability and vorticity. To the bottom right, the vertical wind profile (VWP) from Tulsa during and shortly before the time of the tornado shows considerable veering with height.
This wind pattern was supportive of enlarged low-level hodographs, creating an environment where thunderstorms could gain rotation and potentially spawn tornadoes. In this case, a cell on the north side of Tulsa did just that. Another tornado was reported just to the northwest, in far southern Kansas, in Cowley County. Some have asked why a tornado threat wasn’t more substantial from eastern Kansas toward the Kansas city area. Looking above, the surface wind fields were beginning to veer (wind shift to the south-southwest or southwest), resulting in less of a tornado threat. The above left image also shows that surface vorticity was maximized near and immediately ahead of a surface low, while this vorticity tended to decrease with northward extent.
As of midday Thursday, the strength of the tornado has not yet been made official by the National Weather Service (NWS). Some of the damage suggests that one or more of the paths was related to a strong (EF-2 or greater) tornado. The Significant Tornado Parameter (STP), a function of instability, storm relative helicity, wind shear, lifted condensation levels and convective inhibition, showed values in excess of 1 to 2 in northeastern Oklahoma, as the discrete cells intensified. While STP is helpful in assessing strong tornado potential (particularly when STP values are greater than 1), it should be one of many tools used to evaluate the environment. Nonetheless, in this case, a discrete cell formed in an area that had the ingredients in place to support vigorous rotation and the development of tornadoes.
Later NWS surveys will have more details on the tornado or tornadoes, but early evidence suggests there may have been multiple damage swaths from the parent supercell. This article will be updated with subsequent information.
A special thanks goes out to the NWS, SPC and College of DuPage for providing some of the graphics and images used in this article. Below are some additional graphics to get a better idea of how the mesoscale environment looked ahead of the Tulsa tornado.
The tornado formed near the frontal boundary/dryline/low pressure triple point:
A rough look at the surface analysis from 23z Wednesday, including radar imagery.
