1. Identifying key features to predict significant severe weather outbreaks in the northeastern U.S. Neil A. Stuart NOAA/NWS Albany NY NROW XIII 3 November 2011

2. Inspiration for this study Study of mid-Atlantic significant severe weather outbreaks presented at SLS 2004 Focus on comparison/contrast of significant severe weather outbreaks and forecast busts Recent 2 outbreaks in April in the Carolinas and Virginia and 1 June outbreak in the northeastern U.S. Similarities between mid-Atlantic and northeastern U.S. significant severe weather outbreaks and forecast busts

3. Definitions Significant severe weather outbreak – Large hail of ≥ 2 Inches – Winds of ≥ 65 MPH – Tornadoes ≥ F2/EF2 Forecast bust – Moderate Risk indicated in SPC severe weather outlook – Tornado Watch with no severe weather Outlier event – Significant severe weather in a weak low-level forcing environment – Significant severe weather observed in a weak instability/shear environment Mid-Atlantic U.S. – North Carolina to Maryland and Delaware Northeastern U.S. – Pennsylvania, New Jersey and New York through New England

4. What we will be looking at Character of cold fronts – key to low-level forcing – Low-level wind shift, dew point boundary and leading edge of cold advection often displaced Low level forcing – Need a parameter that encompasses moisture and temperature – Minimize discontinuities from the friction layer 850 hPa ϴ e gradients – accounts for temperature and moisture 850 hPa wind maxima – maximum low-level jet energy

5. What we will be looking at Instability – 4-layer best lifted index Upper dynamics - Eastward progression of 500 hPa vorticity maxima and attendant low level features Upper jet structure – 250 hPa wind maxima

6. Cases studied

9. Let’s start with 500 hPa heights April 2002 LaPlata, MD F4 tornado -Progressive eastward moving -Crossed well east of Appalachians in 24 hours May 2003 forecast bust -Very little eastward movement -Just about reached the Appalachian Mountains in 24 hours

10. Let’s start with 500 hPa heights June 2011 – Springfield, MA EF3 tornado -Progressive eastward moving -Crossed well east of Appalachians in 24 hours June 2010 forecast bust -Very little eastward movement -Just about reached the Appalachian Mountains in 24 hours

11. Next – 250 hPa winds May 2002 mid-Atlantic widespread winds and large hail - Mid-Atlantic in right entrance region of strong upper jet May 2003 forecast bust Eastern U.S. not in favored region of much weaker upper jet

12. Next – 250 hPa winds June 2011 – Springfield, MA EF3 tornado - Northeastern U.S. in right entrance region of cyclonically-curved relatively weak upper jet June 2010 forecast bust Northeastern U.S. not in favored region of relatively strong upper jet

13. Next – 850 hPa parameters - winds April 2002 – LaPlata, MD EF4 tornado April 2011 – Mid-Atlantic multiple EF2+ tornadoes (1 st of 2 outbreaks in April 2011) Note wind cores exit east of the Appalachian Mountains

14. Next – 850 hPa parameters - winds June 1953 – Worcester, MA F4 tornado June 2011 – Springfield, MA EF3 tornado Note wind cores exit east of the Appalachian Mountains

15. Next – 850 hPa parameters - ϴ e March 1984 – Multiple F2+ tornadoes in NC/VA April 2011 – Multiple F2+ tornadoes NC/VA (2 nd outbreak of 2011) Note Δϴ e of ≥ 25K over the mid-Atlantic region associated with a tight ϴ e gradient

16. Next – 850 hPa parameters - ϴ e May 1985 – Multiple F2+ tornadoes in OH/PA July 1989 – Multiple F2+ tornadoes NY and New England Note Δϴ e of ≥ 25K over the northeastern U.S. associated with a tight ϴ e gradient

17. Next - Instability May 1995 – Great Barrington, MA F4 tornado May 1998 – Mechanicville, NY F3 tornado Note Lifted Indices exceeding -2 over the northeastern U.S. during the period of maximum instability

18. Next - Instability May 1998 – Mechanicville, NY F3 tornado November 1992 – Multiple F2+ tornadoes NC/VA Note Lifted Indices exceeding -2 over the northeastern U.S. (left) and mid-Atlantic (right) during the period of maximum instability

19. Forecast Busts – 1 st – May 2003 Low-level jet core never crossed the mountains Low-level ϴ e gradient outran the low-level jet core

20. Forecast Busts – 2 nd – May 2004 Low-level jet core weak and never crossed the mountains Low-level ϴ e gradient weakened and outran the low-level jet core

21. Forecast Busts – 3 rd – June 2010 Low-level jet core right at the 35 kt threshold Low-level ϴ e gradient well below the ≥ 25K threshold

22. Outliers – Significant severe weather with weak forcing August 1973 – Stockbridge, MA F4 tornado Lack of low-level wind core Lack of low-level ϴ e gradient Impressive instability

23. Outliers – Significant severe weather with weak forcing October 1979 – Windsor Locks F4 tornado Low-level wind core close to the 35 kt threshold Marginal instability Low-level ϴ e gradient below the 25K threshold

24. Outliers – Significant severe weather with weak forcing August 1993 – Petersburg, VA F4 tornado July 2003 – Multiple F2+ tornadoes in NY/PA Low-level wind core well south Low-level wind core met 35 kt threshold Low-level ϴ e gradient did not meet the 25K threshold in both events

25. In summary It is not often that the low-level forcing, shear and instability exist simultaneously in one region east of the Appalachian Mountains That is why significant severe weather outbreaks are so rare in the mid- Atlantic and northeastern U.S. Significant severe weather outbreaks occur when all these parameters are present – 500 hPa and 850 hPa systems cross east of the Appalachian Mountains within 24 hours – 500 hPa system may be a well-defined impulse tracking around the periphery of a parent upper low – Favorable upper jet structure – Coincident Low-level features and instability Core of ≥ 35 Kt 850 hPa winds passes through the region 850 hPa ϴ e gradient of 25K tracks through the region in 24 hours 4 layer Lifted Index exceeding -2

26. Caveats Each severe weather event is unique – – Weaker tornadoes, < 2” hail and wind damage can occur if one threshold for one parameter is met – Important that 850 hPa features cross east of Appalachian Mountains in 24 hours Outlier significant severe weather events can occur under much weaker atmospheric conditions but are extremely rare Analysis of 850 hPa winds and ϴ e can be subjective depending on if it is based on observations or Global Reanalysis sets

27. Future Work Resolving the different analyses of low-level features and instability between observations and Global Reanalysis Historical RAOB data to analyze CAPE, shear and elevated mixed layers – Source of Skew-T analyses important as different sources show different CAPE, shear and midlevel lapse rates HYSPLIT 24 hour Parcel trajectories - 1500m (~850 hPa), 3000m (~700 hPa) and 5000m (~500 hPa) to investigate advection of elevated mixed layers, rising and sinking motions

28. Thank you for your time – Questions, comments or suggestions? June 1953 Worcester, MA - Courtesy Worcester Telegram and Gazette May 1985 - Hermitage, PA Courtesy Harkphoto.com – Hermitage, PA May 1985 June 2011 Springfield, MA - Courtesy Matt Putzel June 2011 Agawam, MA - Courtesy Paulina Dusza September 2001 University of Maryland - Courtesy Ecampus.com April 2002 LaPlata, MD tornado crossing Chesapeake Bay – Courtesy Johns Hopkins Univ. April 2011 Wilson, NC – Courtesy Steven Hoag April 2008 Suffolk, VA - Courtesy Coastal Carolina Weather Examiner July 1976 - New York City, NY June 2011 Windsor, MA - 4” hail June 2011 Shaftsbury, VT - 3” hail Acknowledgments: Thanks to NCEP NOMADS for Global Reanalysis wind and Lifted Index plots, Storm Prediction Center for Upper Plots and Plymouth State archive for Global Reanalysis and observed ϴ e plots