Mesoscale Analysis of Wintertime Nonmesocyclone Tornadogenesis in Northwest Texas: 27 December 2007

Mark Conder, Todd Lindley, and Gary Skwira NOAA/National Weather Service, Lubbock,

Texas

Impacts

Goal of Study

Picture of the first non-mesocyclonic tornado taken around 2320 UTC

The second tornado observed over S.E. Lubbock County at 2330 UTC.

At Least Two Brief “landspout”

Tornadoes near Lubbock

Intense Convective Snow Showers

Strong Wind Gusts Up to 23 m/s

Critical Fire Weather Conditions

Examine the mesoscale evolution of this event – particularly the surface features – in order to

understand the conditions which caused a wide variety of impact weather to the area

Meteorological Overview

A potent upper level trough emerged over West Texas providing lift during the afternoon and evening hours

Low clouds persisted north of a stationary front that bisected the Lubbock CWA from northwest to southeast. Differential heating reinforced the front through the day. The insolation also promoted deep mixing with strong winds and dry air advancing eastward behind a dryline into the south-central South Plains during the afternoon.

Meteorological Overview

Water vapor satellite imagery from 1815 UTC (left) and 0015 UTC 28 (right) December 2007. Lighter colors represent greater amounts of moisture. Overlaid

are the 0000 UTC RUC40 wind barbs (kts) and isotachs (kts) at 500 hPa.

Meteorological Overview II

Visible satellite picture from 20:01 UTC 27 December 2007. CWA

Boundaries in red.

WRF-NAM12 6-hour forecast cross-section of RH (image) and omega

(-ubars/s) fields valid at 00 UTC

Radar Analysis

KLBB WSR-88D 0.5º reflectivity on 27 December 2007 at: (a) 2300 UTC, (b) 2333 UTC, and (c) 2357 UTC. The top image is a large view, with a corresponding zoomed in view below. Lubbock is located in the center of the ground clutter. County lines are in gray, and CWA boundaries in red.

(a) (b) (c)

(a) (b) (c)

Surface Analysis: 2100 UTC 27 Dec 2007(a) (b)

(c) (d)

(a) Station plot; (b) Frontogenesis; (c) Relative Vorticity & Convergence; (d) Equivalent Potential Temperature

Surface Analysis: 2330 UTC 27 Dec 2007(a) (b)

(c) (d)

(a) Station plot; (b) Frontogenesis; (c) Relative Vorticity & Convergence; (d) Equivalent Potential Temperature

Surface Analysis: 0030 UTC 28 Dec 2007(a) (b)

(c) (d)

(a) Station plot; (b) Frontogenesis; (c) Relative Vorticity & Convergence; (d) Equivalent Potential Temperature

Sounding Analysis

WRF-NAM 6-hr forecast sounding at Lubbock, valid at 0000 UTC 28 Dec 2007.

Summary Although seasonal climatology and synoptic-scale

meteorological conditions were not supportive of the development of tornadoes near Lubbock, two non-mesocyclonic tornadoes formed during the late afternoon of 27 December 2007. The tornadoes formed along a broken line of cumulus towers on the dryline; concurrent radar only depicted a faint “fineline” in the reflectivity and velocity moments.

A number of environmental factors supportive of non-mesocyclonic tornadogenesis including: strong surface convergence, vertical vorticity, frontogenesis, and equivalent potential temperature were maximized near Lubbock around 2330 UTC. Also supportive were steep low-level lapse rates of approx. 9.5 °C km-1, weak amounts of Convective Available Potential Energy, and no Convective Inhibition.

From a forecasting perspective, although difficult to foresee, a number of factors were present to suggest a brief window during which the environment was supportive of non-mesocyclonic tornadoes.

Questions???

For additional information, please contact:Mark.Conder@noaa.govTodd.Lindley@noaa.govGary.Skwira@noaa.gov