Poster Session P10.2 Subtle Radar Signatures in the West Brookfield, MA Tornado of 23 July 2002

Thursday, 7 October 2004
Glenn A. Field, NOAA/NWS, Taunton, MA; and D. R. Vallee

Handout (602.4 kB)

Tornadic storms in New England tend to be subtle and difficult to detect. The F1 tornado that occurred in West Brookfield, MA on 23 July 2002 was no exception. On that day, a cold front was moving through western New York state and a weak short wave trough was moving through the eastern Great Lakes. Convective Available Potential Energy (CAPE) and vertical wind shear were such that multicellular storms, in the form of a squall line, were expected over southern New England. Indeed, a squall line did form. A weak F1 tornado formed on a break in the Line Echo Wave Pattern (LEWP). It is theorized that this occurred at the apparent intersection of a rear flank downdraft and a developing outflow boundary, which may have helped 'spin up' the tornado. The tornado was very short-lived and occurred before the rain arrived.

WSR-88D imagery displayed a short-lived weak hook echo, associated with a gate to gate couplet of 51 knots at 0.5 degrees, 44 nm northwest of the radar. This signature lasted for only one volume scan and based on spotter reports and eyewitness accounts, it occurred shortly after the tornado had already touched down. Although classified as a weak tornado, it managed to lift water 30-50 feet into the air from a lake and tear the roof off a house, nailing it to a tree across the street.

This presentation will show the radar signatures associated with this weak tornado and discuss how low-level influences, such as outflow from adjacent storms, may have played a key role in its evolution. Examining extremely subtle radar signatures will aid forecasters in improving tornadic detection and warnings.

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