Reanalysis ofReanalysis of

Southern New EnglandSouthern New England

TornadoesTornadoes

To Improve Warning VerificationTo Improve Warning VerificationDaniel Brook, Lyndon State College*

Joseph DelliCarpini, NOAA/NWS Taunton, MADavid Vallee, NOAA/NWS NERFC, Taunton, MA

*Present affiliation: Meridian Environmental Technology

1953 Worcester Tornado (Stanley H. Smith/Library of Congress Photo)

BackgroundBackground

Verification data showed a need to Verification data showed a need to improve tornado detection in BOX CWAimprove tornado detection in BOX CWA– Low frequency, high impact eventsLow frequency, high impact events

14 cases included, dating back to mid 14 cases included, dating back to mid 1990s (WSR-88D implementation)1990s (WSR-88D implementation)July 3, 1997 was most significant, with 4 July 3, 1997 was most significant, with 4 tornadoes in one afternoon near southern tornadoes in one afternoon near southern New HampshireNew Hampshire

Purpose and MethodologyPurpose and Methodology

Help operational forecasters improve warning Help operational forecasters improve warning performanceperformance– Identify days with tornadic potentialIdentify days with tornadic potential

Improve forecaster situational awarenessImprove forecaster situational awareness

– Identify critical signatures on radar Identify critical signatures on radar

Compile days with tornadoes to determine Compile days with tornadoes to determine underlying causes.underlying causes.– Synoptic and mesoscale composite analysesSynoptic and mesoscale composite analyses– WSR-88D data from KBOX, KENX, and KOKXWSR-88D data from KBOX, KENX, and KOKX– Re-classify intensities to EF scale for consistencyRe-classify intensities to EF scale for consistency

Classification SystemClassification System

A.A. Southern Ontario Closed Low (7)Southern Ontario Closed Low (7)

B.B. Open Great Lakes Trough (3)Open Great Lakes Trough (3)

C.C. Deep Great Lakes Trough (1)Deep Great Lakes Trough (1)

D.D. Tropical Remnant (1)Tropical Remnant (1)

E.E. Cold Pool Aloft (2)Cold Pool Aloft (2)

A: Southern Ontario Closed LowA: Southern Ontario Closed Low

High CAPEHigh CAPE– Over 1500 J/kgOver 1500 J/kg

Strong ShearStrong Shear– More than 160 mMore than 160 m22/s/s22

High PWHigh PW– Greater than 2 inchesGreater than 2 inches

Example – July 3, 1997Example – July 3, 1997 EF2 – Greenfield, NHEF2 – Greenfield, NH

Discrete cellsDiscrete cells– Storm that produced the EF2 had a history of Storm that produced the EF2 had a history of

producing three EF1 tornadoesproducing three EF1 tornadoes

Subtle indication in reflectivity dataSubtle indication in reflectivity data

Velocity data shows gate-to-gate rotation Velocity data shows gate-to-gate rotation (50 kt) as the event takes place(50 kt) as the event takes place– Little indication beforehandLittle indication beforehand

2357z | 03-Jul-1997

Base Reflectivity

Greenfield, NH

EF2

Storm-Rel. Velocity

B: Open Great Lakes TroughB: Open Great Lakes Trough

Moderate CAPEModerate CAPE– 1000-1500 J/kg1000-1500 J/kg

Moderate shearModerate shear– Near 150 mNear 150 m22/s/s22

Moderate PWModerate PW– Near 1.5 inchesNear 1.5 inches

Example – June 2, 2000Example – June 2, 2000EF1 Leeds/Northampton, MAEF1 Leeds/Northampton, MA

Tornado developed on a squall lineTornado developed on a squall line

Subtle hook echo visible in reflectivitySubtle hook echo visible in reflectivity

Broad rotationBroad rotation– Sampling at mid levelsSampling at mid levels

2102z | 02-Jun-2000

Base Reflectivity

Leeds, MA

EF1

Storm-Rel. Velocity

C: Deep Great Lakes TroughC: Deep Great Lakes Trough

Low CAPELow CAPE– 200-400 J/kg200-400 J/kg

Moderate shearModerate shear– Up to Up to 150 m150 m22/s/s22

Moderate PWModerate PW– Near 1.5 inchesNear 1.5 inches

Example – June 23, 2001Example – June 23, 2001EF0 – East Hartland, CTEF0 – East Hartland, CT

Good example of how surrounding radars Good example of how surrounding radars can be very important to examine.can be very important to examine.– Nothing significant seen from KBOXNothing significant seen from KBOX– KENX much more usefulKENX much more useful

Discrete low topped cellsDiscrete low topped cells– Subtle indication in reflectivity dataSubtle indication in reflectivity data– Broad rotation in velocity dataBroad rotation in velocity data

1911z | 23-Jun-2001

Base Reflectivity

Data fromKENX

East Hartland, CT

EF0

Storm-Rel. Velocity

D: Tropical RemnantD: Tropical Remnant

Low CAPELow CAPE– 400-600 J/kg400-600 J/kg

Moderate shearModerate shear– 120 m120 m22/s/s22

High PWHigh PW– Over 2 inches Over 2 inches

Example – June 17, 2001Example – June 17, 2001EF2 – Princeton, MAEF2 – Princeton, MA

Remnants of Tropical Storm AllisonRemnants of Tropical Storm Allison– HP supercell (bookend?) embedded within HP supercell (bookend?) embedded within

line of convectionline of convection

Best radar signature in the studyBest radar signature in the study– Strong Mesocyclone statusStrong Mesocyclone status– Rotational velocity of 40 ktRotational velocity of 40 kt

One of few cases where rotational couplet One of few cases where rotational couplet takes up several pixels instead of a few.takes up several pixels instead of a few.

1536z | 17-Jun-2001

Base Reflectivity

Princeton, MA

EF2

Storm-Rel. Velocity

E: Cold Pool AloftE: Cold Pool Aloft

Low CAPELow CAPE– 200-400 J/kg200-400 J/kg

Little or no shearLittle or no shear– Light wind profile Light wind profile

Low PW Low PW – Less than 1 inchLess than 1 inch

Example – May 20, 2006Example – May 20, 2006EF0 - Portsmouth, RIEF0 - Portsmouth, RI

Formed along line of low-topped Formed along line of low-topped convectionconvection

Very subtle reflectivity signatureVery subtle reflectivity signature

SRM shows no sign of rotationSRM shows no sign of rotation

2242z | 20-May-2006

Base Reflectivity

Portsmouth, RI

EF0

Storm-Rel. Velocity

Summary:Summary:Synoptic/Mesoscale FindingsSynoptic/Mesoscale Findings

Key points foundKey points found– Usually a strong upper level jet in vicinityUsually a strong upper level jet in vicinity– ““Tropical” airmass – Dewpoints of 70° or higherTropical” airmass – Dewpoints of 70° or higher

Low LCLsLow LCLs

– Moderate to highly sheared environmentModerate to highly sheared environment

Helicity – at least 120 m²/s²Helicity – at least 120 m²/s²– Over 1000 J/kg of CAPEOver 1000 J/kg of CAPE

Found to be less consistent than shearFound to be less consistent than shear– Sharp gradients as important as actual valuesSharp gradients as important as actual values– Low level boundary present for “spin up”Low level boundary present for “spin up”

Stronger TornadoesStronger Tornadoes

High-end EF1 and EF2 usually requireHigh-end EF1 and EF2 usually require– Moderate/High ShearModerate/High Shear (130 m(130 m22/s/s22))– High CAPE High CAPE (1500 J/kg)(1500 J/kg)– Moderate PWModerate PW (1.5 inches)(1.5 inches)

A limited amount of “trading” can occur A limited amount of “trading” can occur between each criteria above.between each criteria above.

Without a combination of these, weaker Without a combination of these, weaker tornadoes form (EF0, low-end EF1)tornadoes form (EF0, low-end EF1)

Summary:Summary: Radar Findings Radar Findings

Radar signatures can be found with a Radar signatures can be found with a trained eye …trained eye …– But many are comprised of very few pixels But many are comprised of very few pixels

and some don’t show up at all (most EF0s)and some don’t show up at all (most EF0s)– Few have very prevalent signatureFew have very prevalent signature

Summary:Summary: Warning Strategy Warning Strategy

Use multiple radars Use multiple radars Issue SVRs for “short lived” EF0 Issue SVRs for “short lived” EF0 tornadoestornadoes– Difficult to detect with subtle signaturesDifficult to detect with subtle signatures

Issue TORs for EF1 and stronger Issue TORs for EF1 and stronger tornadoestornadoes– 25 kt rotational velocity with depth and 25 kt rotational velocity with depth and

persistencepersistence

Integrating Research into Operations:Integrating Research into Operations:July 23, 2008July 23, 2008

EF1 Tornado EF1 Tornado – Warren RI and Swansea MAWarren RI and Swansea MA

Forecasters recognized synoptic pattern Forecasters recognized synoptic pattern and were aware of tornadic potentialand were aware of tornadic potential– Type A: Southern Ontario Closed Low Type A: Southern Ontario Closed Low

As event unfolded, utilized warning As event unfolded, utilized warning strategy (SMW strategy (SMW SVR SVR TOR) TOR)

A: Southern Ontario Closed LowA: Southern Ontario Closed Low

High CAPEHigh CAPE– 1800 J/kg1800 J/kg

Strong ShearStrong Shear– 150 m150 m22/s/s22

Moderate PWModerate PW– 1.8 inches1.8 inches

Example – July 23, 2009Example – July 23, 2009EF1 - Warren, RI / Swansea, MAEF1 - Warren, RI / Swansea, MA

HP supercell formed along line of HP supercell formed along line of convection moving NE from Long Islandconvection moving NE from Long Island

Subtle hook signature on reflectivity data Subtle hook signature on reflectivity data prior to tornado formationprior to tornado formation

Velocity data showed subtle gate-to-gate Velocity data showed subtle gate-to-gate (45 kt) signature(45 kt) signature

1946z | 23-July-2008

Base Reflectivity

Warren, RI / Swansea, MA

EF1

0.5 Velocity

GR2 Analyst GR2 Analyst Cross Section of Storm Cross Section of Storm just West of Bristol, RIjust West of Bristol, RI

2000 UTC2000 UTC

Barrington Beach, RIBarrington Beach, RI

Credit: Chris Legro, NWS Davenport, IACredit: Chris Legro, NWS Davenport, IAFormer NWS Taunton student intern Former NWS Taunton student intern

VerificationVerification

SMW issued at 335 PMSMW issued at 335 PM– Mentioned waterspoutMentioned waterspout

SVR issued at 350 PMSVR issued at 350 PM

TOR issued at 404 PMTOR issued at 404 PM– Touched down 405 PMTouched down 405 PM

First tornado warning issued First tornado warning issued andand verified with tornado verified with tornado report since July 1997report since July 1997– Cheshire County, NHCheshire County, NH

NWS Taunton Storm Survey PhotosNWS Taunton Storm Survey Photos

NWS Taunton Storm Survey PhotosNWS Taunton Storm Survey Photos