1. Improving Tornado Detection and
Lead Time: The July/August, 2018 Tornadoes in Southern New England
Joseph W. DelliCarpini
NOAA/NWS Boston/Norton, MA
Jonathan E. O’Brien
UAlbany
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2. Motivation and Objectives
Verification showed a need to improve tornado detection and lead time in southern New England (BOX CWA)
Improve understanding of synoptic and mesoscale patterns associated with these tornadoes in order to raise situational awareness
Improve recognition of radar signatures that may indicate a tornado is developing
Development of a “detection scale” to assist forecasters in the warning decision making process
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3. Methodology
Update of previous study (Brooks et al, 2008) which included tornadoes in the WFO BOX County Warning Area from 1997 to 2006
Reviewed 17 of the 22 tornadoes between 2007 and 2017
Most were EF-0 (9) or EF-1 (6)
One EF-2 (Chelsea/Revere, MA in July, 2014)
One EF-3 (Westfield/Springfield/Monson/Brimfield/Charlton in June, 2011)
Data Sources
North American Regional Reanalysis (NARR) for synoptic environments
SPC Mesoanalysis Archive for mesoscale environments
GR2Analyst for radar data
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4. Synoptic Classification: Type A
Closed 500 hPa low over Ontario or Hudson Bay
Divided into 3 sub-categories based on closed low placement
9 of 17 events fall in this group;
“Dominant” SNE tornado pattern A3 A1 A2
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5. Type A Example
June 1, 2011 Westfield-Springfield-Monson- Brimfield-Charlton EF-3
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6. Synoptic Classification: Type B-1 (Zonal Jet)
Open trough near the western Great Lakes
with a shortwave near New England
5 of 17 events (2 of 5 were B-1)
June 23, 2015: Wrentham, MA EF-0
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7. Synoptic Classification: Type B-2 (Disjointed Jet)
Open trough near the western Great Lakes
with a shortwave near New England
5 of 17 events (3 of 5 were B-2)
September 1, 2013: Shutesbury, MA EF-0
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8. Synoptic Classification: Type C
Deep trough over the East-Central US
Strong right entrance jet positioning
2 in this study
July 1, 2013: Enfield, CT EF-1
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9. Synoptic Classification: Type E
Cold pool aloft hPa temperatures 8-10°C colder than in other events
Steep lapse rates, other parameters less favorable
May 9, 2013: Stoughton, MA EF-0
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10. Storm-Relative Helicity
Instability and Shear
Surface-Based CAPE
Storm-Relative Helicity
(0-3 km)
Type A and B:
Usually 1000 J Kg-1 or more but can vary widely
Type C: 600 J kg-1
Type D: 500 J kg-1 [remnants of Allison (2001) from prior study]
Type E: 350 J kg-1
Types A, B, C, and D:
150 m2s-2 or higher, can be lower in A and B if CAPE is high
Type E:
100 m2s-2 or less
Some events with lower 0-3km SRH make up for it by concentrating most SRH in the lowest 1 km
0-1km SRH >=150 m2s-2 -or m SRH >=95 m2s-2 is especially conducive to tornadoes
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11. Moisture: Dew Point and Precipitable Water
Types A, B, C, and D:
Average 20-23°C (68-73°F)
Type E:
Average 10-15°C (50-60°F)
Types A and B:
Average 43 mm (1.7”)
Type C:
Average 48 mm (1.9”)
Type D:
Average 38 mm (1.5”)
Type E:
Average <=25 mm (<=1”)
Higher moisture = Lower LCL
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12. Summary of Synoptic and Mesoscale Environments
Tornadoes in southern New England formed in one of a few prevailing synoptic patterns
Closed 500 hPa lows accounted for a majority of the events
Mesoscale parameters can vary widely and often “trade” with one another
CAPE and 0-3km shear, in particular
“Tropical” moisture and presence of a surface boundary is necessary
Stronger tornadoes are rare and need high CAPE and shear (6/1/11)
Similar to environments in the Plains
0-1 km SRH (150+) and especially m SRH (95+) seemed to be the best discriminators between tornadic and non-tornadic events
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13. Tornado Detection Scale
Goal: Provide more accurate and consistent guidelines to help forecasters issue Tornado Warnings
Empirical scale based upon past tornado events and “false alarms”
Largely based upon radar signatures
Rotational velocity [Vr = (Inbound+Outbound)/2]
Normalized Rotation (“NROT”)
Also includes some environmental factors
Highly recommend VCP 212 with SAILS 3 for one-minute low level scans!
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14. Boston/Norton, MA NROW XIX Albany, NY NATIONAL WEATHER SERVICE
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15. Testing The Scale: Detection
Radar data for 21 of 22 tornadoes from
4 score as a zero
Not detected by radar, including two “fair weather” tornadoes
3 score below a 9 (2 below a 5)
Marginal cases
14 score as a 9+ at or before touchdown:
“Reasonably detectable” cases
POD = 0.67
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16. Testing The Scale: False Alarms
Data for 23 “False Alarm” Tornado Warnings reviewed from
13 of 23 would have scored 9+ on the scale
Shows potential for lowering false alarm rate (by 43% in this case)
“Control Cases”
Reviewed a similar number of storms that did not have Tornado Warnings issued, did not produce tornadoes, but would have scored 9+ on the scale
There were only a couple of cases
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17. BOX Tornado Verification Statistics
POD = 0.52
FAR = 0.81
Average Lead Time = 9 minutes
2018 (July/August)
POD = 0.60
FAR = 0.20
Average Lead Time = 10 minutes
2018
POD = 0.67
FAR = 0.54
National GPRA Goals:
POD 0.72
FAR 0.71
Lead Time 13 minutes
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18. Ashford, CT EF-0 Tornado: 1957 UTC July 17
0.5 REF and SRM
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19. Boston/Norton, MA NROW XIX Albany, NY NATIONAL WEATHER SERVICE
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20. Douglas, MA EF-1 Tornado: 0627 UTC July 26
0.5 REF and SRM
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21. Boston/Norton, MA NROW XIX Albany, NY NATIONAL WEATHER SERVICE
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22. Woodstock, CT & Dudley/Webster, MA Tornadoes: 4 Aug
Woodstock, CT 0.5 SRM
1334 UTC
Dudley/Webster, MA 0.5 SRM
1356 UTC
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23. Woodstock, CT Boston/Norton, MA NROW XIX Albany, NY
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24. Dudley/Webster, MA Boston/Norton, MA NROW XIX Albany, NY
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25. Future Work Update the tornado database with the 8 tornadoes in 2018:
Ashford, CT EF-0 (July 17)
Douglas, MA EF-1 (July 26)
Upton, MA EF-1 (July 26)
Woodstock, CT EF-0 (August 4)
Dudley/Webster, MA EF-1 (August 4)
Mansfield, CT EF-0 (October 2)
North Providence/Lincoln, RI EF-1 (October 23)
Norton, MA EF-1 (October 23)
Hardwick, MA EF-1 (October 23)
Hubbardston, MA EF-0 (October 23)
Woods Hole, MA EF-0 (October 29)
Continue to test and tweak the detection scale based upon recent events
Share with neighboring WFOs and add nearby events
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26. References
*Brook, D. 2008: Reanalysis of Southern New England Tornado Events from 1997–2006 to Improve Forecast Verification, Lyndon State College, 32
*Brook, D., J. DelliCarpini, and D. Vallee, 2008: WFO Taunton Southern New England Tornado Playbook. 11 pp.
*Gibson Ridge Software, 2013: GR2Analyst Version
*LaPenta, K. D., L. F. Bosart, T. J. Galarneau Jr., and M. J. Dickinson, 2005: A Multiscale
Examination of the 31 May 1998 Mechanicville, New York, Tornado. Wea. Forecasting,
20, 494–516.
*Mesinger, F. et. al., 2006: North American Regional Reanalysis. Bull. Amer. Meteor. Soc.,
87, 343–360.
*National Weather Service Weather Forecast Office Louisville, KY, cited 2017: What is Dual-
Polarization Radar and What Can it do for Me? [
*Rasmussen, 2003: Refined Supercell and Tornado Forecast Parameters. Wea. Forecasting, 18,
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