Presentation on theme: "20 Years of Connecticut Tornadoes Ryan Hanrahan / WVIT-TV NBC Connecticut."— Presentation transcript:
20 Years of Connecticut Tornadoes Ryan Hanrahan / WVIT-TV NBC Connecticut
Introduction A look at Connecticut tornado climatology in the WSR-88d era Radar characteristics of Connecticut tornadoes A few unique examples Better warnings in future?
Introduction 31 Tornadoes 1995- Present 2 significant tornadoes (F2 or greater) All different storm modes (QLCS, supercell, etc.) Frequently little advanced warning on radar
Tornado Climatology Of the 31 tornadoes… – 2 were landspouts (excluded from research) – 1 storm was missing all radar data (7/23/1995); 3 tornadoes (6/30/1998) only patchy data (and level 3) available. – All other storms were analyzed using Level 2 radar data from NCDC at the nearest site available (OKX, ENX, BOX)
Low Level Rotation 0-5 minutes before Tgen Mean LLDV of 44 knots Median = 43 knots Maximum LLDV of 74 knots BUT…. 6 events (out of 25 with radar data) had NO discernible low level rotation at all!
Low Level Rotation 5-10 minutes prior to Tgen Mean LLDV of 41 knots Median = 35 knots Maximum LLDV of 77 knots BUT…. 8 events (out of 25 with radar data) had NO discernible low level rotation at all!
Radar Characteristics Only 2 of 11 QLCS cases featured ANY low level rotation on radar 9 of 14 supercell cases DID exhibit low level rotation approximately 10-15 minutes prior to tornadogenesis 3 Volume Scans Prior to Tornadogenesis
QLCS Vs. Supercell Rotation For Scan Immediately Prior to/During Tornadogenesis Of storms with low level rotation… Supercell median LLDV of 46 knots Only 2 of 14 cases didn’t feature a low level mesocyclone Of storms with low level rotation… QLCS median LLDV of 41 knots 4 of 11 cases didn’t feature a low level mesocyclone
Radar Characteristics What about reflectivity signatures? SUPERCELLS Only 1 of 14 storms had a classic “hook echo” QLCS Of 11 events… 3 occurred in a “inflow notch” and 2 featured an appendage
Other Clues… Supercell in Litchfield County and Bristol, CT on 7/21/2010 produced significant severe and several tornado touchdowns.
Warning Dilemma Nearly 1/4 of CT tornadoes in the 88d era were virtually impossible to detect on radar. Why? – Beam too high (closest radars all out of state) – Parent mesocyclone too small for radar’s resolution (especially far from radar site) – No parent mesocyclone (landspout)
Significant Tornadoes Scan Prior to Tornadogenesis 48 knots of gate-to-gate shear in Torrington, CT case 46 knots of gate-to-gate shear in Greenwich, CT case (storm was in Rockland County NY at this time) Not surprisingly, greater than mean/median of all tornado cases
Speaking of Torrington… One of the more unusual cases on radar!
June 23, 2001 Litchfield Hills Tornadoes Only 3 severe weather events were reported in the northeastern U.S. on 6/23/2001 – 3 separate tornadoes from 2 separate mini supercells in Connecticut.
June 23, 2001 Litchfield Hills Tornadoes No warning for all 3 tornadoes Likely no lightning during the three tornadoes Storm Data entry was incorrect (including times) which is one of several errors I found during research
What Can Help? Dual Polarization radar has shown great promise revealing lofted tornado debris in the northeastern U.S. While not predictive (can not provide lead time) this can provide confirmation of a tornado touchdown or provide warning to areas next in a tornado’s path.
Tornado Debris Signature Lofted tornado debris has a unique dual polarization signature on radar. It’s easy to identify and provides confirmation of a tornado touchdown. According to NWS Warning Decision Training Branch guidance a TDS is “more reliable than a spotter report of a tornado”
Dual Pol Refresher Dual-polarization radar sends out 2 pulses (a vertical and horizontal pulse) Allows user to know more about size, shape, and variety of targets
Correlation Coefficient Measures how similarly horizontal and vertical pulses behave. Low CC indicates large variety in type, shapes, orientation of targets.
Differential Reflectivity Difference between horizontal and vertical reflectivity factors ZDR near 0 for spherical objects (drizzle) and >1 for horizontally oriented targets (rain)
Tornado Debris on Dual Pol Large variability in shapes of tornado debris reduces correlation coefficient. “Tumbling” of tornado debris makes it appear spherical to radar thereby reducing ZDR near 0.
What’s a Tornado Debris Signature? High reflectivity (Z) CC < 0.80 ZDR near 0 ALL COINCIDENT WITH STRONG ROTATION/TVS
Tornado Debris Signature Reflectivity CC ZDR Velocity Chemung County, NY 9/2/2014
Tornado Debris Signature Chemung County, NY 9/2/2014 Gate-to-Gate Delta V of only 40-50 knots Tornado in rear inflow notch TDS for 10 minutes Borderline case with no tornado warning
Revere, Mass TDS 7/28/2014 at 1334 UTC 7/28/2014 at 1330 UTC
Revere, Mass TDS Strong low level rotation picked up only after tornado had touched down. By the time TVS appeared a TDS had also appeared. Guaranteed had touched down!
Stamford, CT TDS?????? 7/1/2013 @ 15:04 UTC (KOKX)
Stamford, CT TDS?????? Probably radar detected debris 47 knot gate-to- gate delta-V High Z (50 dBZ) Low CC (0.80-0.90) ZDR near 0
Stamford, CT TDS?????? EF-0 tornado 3.7 miles in length Debris detected nearly 3,000 ft above the ground from a fairly weak tornado.
What to Do Use all available radar data for tornadoes – particularly difficult to spot QLCS spin-ups. Recognize that not all tornadoes can be detected on radar – particularly in areas poorly served by 88d coverage. Be aware of many different environments that can produce tornadoes – low CAPE/high shear being a big culprit.
What to Do While can’t be used for positive lead time on warnings – the TDS has shown great promise in the northeast in detected tornado touchdowns.