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Brian J. Frugis NWS WFO Albany, New York

A Case Study of the August 25, 2007 Severe Weather Event in Eastern New York and Western New England. Brian J. Frugis NWS WFO Albany, New York. Brief Introduction of Event. 17 confirmed individual severe weather events One of the largest events of the summer of 2007 for ALY CWA

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Brian J. Frugis NWS WFO Albany, New York

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  1. A Case Study of the August 25, 2007 Severe Weather Event in Eastern New York and Western New England Brian J. Frugis NWS WFO Albany, New York

  2. Brief Introduction of Event • 17 confirmed individual severe weather events • One of the largest events of the summer of 2007 for ALY CWA • Storms generally occurred between 19Z-01Z (3pm-9pm EDT)

  3. Surface Setup • Tropical air surged northward along the coast • Temps 32-35°C (lower to mid 90s °F) • Dewpoints 23-25 °C (mid 70s °F)! • Frontal boundary over eastern Great Lakes • Pre-frontal trough was the focus for convection

  4. Special 18Z Sounding • Massive amounts of CAPE (nearly 5000 J/kg) • Dry layer between 700-500 mb • Very moist low levels • Modest wind shear • 0-6 km shear: 30 kts • 0-3 km helicity: 116 m²/s² • Freezing level rather high • Located at 15.5 kft

  5. Convective Available Potential Energy (CAPE) • Impressive surface based CAPEs up and down Hudson Valley • 19Z LAPS analysis shows values over 4000 J/kg common • Previous ALY study by LaPenta & Maglaras (2002) of “major” severe weather events (10+ reports) had a mean CAPE of 2272 J/kg • Double the average of other major severe events in the ALY CWA

  6. Helicity • 18Z LAPS 0-1 km analysis shows not overly impressive amounts • Values generally 80-150 m²/s² • Indicated tornadic threat was limited

  7. Lifted Index (LIs) • 19Z analysis shows very low values of -6 to -8°C across most areas (exception was northern Adirondacks) • Lowest values in mid Hudson Valley would suggest best area for explosive convective development if storms can be triggered • Previous ALY case studies by LaPenta & Maglaras (1995) showed “major” severe events to have a mean of -6 °C.

  8. Mid-Level Lapse Rates • 19Z 850-500 mb level lapse rates shown here • LaPenta & Maglaras (2002) found 800-600 mb level best to look at, but unavailable for analysis • Values not overly impressive • Between 5.85 and 6.5°C • Generally values above 6.5 °C considered good for severe weather according to SPC • Showed convectively unstable in most areas, except extreme north • Values were higher in morning, decreased throughout the afternoon

  9. Downdraft CAPE (DCAPE) • DCAPE is an estimate of kinetic energy available to a downdraft parcel due to negative buoyancy • Impressive amounts indicated damaging wind potential • Lapenta & Maglaras (2002) case study showed mean value of major severe events studied was 353 J/kg • Highest values of 900 J/kg found in Hudson and Mohawk Valleys at 18Z

  10. Severe Thunderstorm Watch • Mesoscale discussion issued at 1630Z (1230 PM EDT) concerning watch potential • Actual watch issued at 1755Z (155pm EDT), valid until 0100Z 8/26 (9 PM EDT)

  11. Storm #1 - Adirondacks • First severe t-storm warning of the day issued for Herkimer County at 1904Z (304 PM EDT) • Developed in a pocket of higher CAPE values as depicted on LAPS • Around 3000 J/kg • VIL values up to 70 kg/m² • Produced significant tree damage in towns of Ohio and Russia in Herkimer County

  12. Storm # 1 - Adirondacks • Storm continued eastward through Adirondacks • Photo of damage from town of Ohio in Herkimer County • Warning for Hamilton and northwestern Fulton counties issued at 322 PM and 342 PM respectively • Moved through unpopulated area of forest and lakes • No verification from this area

  13. Storm #1 - Adirondacks • Storm continued into northern Saratoga and Warren counties towards area of CAPE values over 4000 J/kg • Nickel sized hail at Hadley, Saratoga County at 2030Z (430 PM EDT) • Only severe hail report of the day • VIL values over 60 kg/m²

  14. Storm #1 - Adirondacks • Storm reaches the Lake George & Glens Falls area • VIL image taken at 2041Z (441 PM EDT) • Values approaching 70 kg/m² on eastern shore of Lake George

  15. Storm # 1 - Adirondacks • 4 Panel reflectivity from 2041Z (441 PM EDT) • 55 dBZ up to 35,000 feet • Extensive wind damage countywide in Warren County • 13,000 people were without power at one point • Many trees and power lines down across roads near Lake George • Elevated core passed over Glens Falls • Little damage within the City of Glens Falls

  16. Storm # 1 – Adirondacks • Core finally falls across northern Washington County • 0.5 radial velocity image taken at 2058Z • Extensive tree and wire damage in towns of Kingsbury, Fort Ann and Whitehall

  17. Storm #2: Capital Region/Taconics/Berkshires • Storm developing over Helderbergs in western Albany County around 2147Z (537 PM EDT) • 4 panel image from Binghamton (BGM) radar • Storm had a few pixels of ~50 dBZ in mid-levels, but considered marginal for warning

  18. Storm #2: Capital Region/Taconics/Berkshires • Storm was headed towards the axis of very high CAPE values • Values at 21Z (last available time during reanalysis) were still over 4000 J/kg in the Hudson Valley • Decided to warn based on the track of storm towards very unstable air even though dBZ was marginal • Warning for Albany and Rensselaer counties issued at 2216Z (616 PM EDT)

  19. Storm #2: Capital Region/Taconics/Berkshires • Widespread tree and wire damage across the town of Bethlehem in extreme eastern Albany County at 2216Z (616 PM EDT) • Less than a minute lead time • Storm continued to maintain strength as it headed across Rensselaer County • Warning issued for Berkshire, Mass. at 2253Z (653 PM EDT)

  20. Storm #2: Capital Region/Taconics/Berkshires • 0.5 radial velocity image taken at 2306Z (706 PM EDT) • 45 kts pixel right over KAQW (North Adams, Mass.) at 4000 feet AGL • Wind gust at KAQW to 70 MPH (60 Knots) at 708 PM

  21. Storm #2: Capital Region/Taconics/Berkshires • Pea and marble size hail reported at North Adams as well • Storm continued across northern Berkshire County • Trees down in Savoy, Mass. at 2340Z (740 PM EDT)

  22. Thunderstorms developed and were prolonged due to extreme instability and high moisture Lots of CAPE can go a long way, despite modest shear Both storms examined were long-lived, despite not having supercell structures LAPS data useful in determining best areas of explosive thunderstorm development Bethlehem wind damage was an example of this Lead time can be improved by warning on marginal storms if they are headed towards areas of extremely high CAPE Anomalously large amount of DCAPE was supportive of wind damage potential Conclusions of Study

  23. Conclusions of Study • 18Z RAOB observation was very useful • Sounding was representative of mesoscale environment • Actual convective parameters measured helped determine severe threat was real • More useful than modifying 12Z sounding since it accurately depicts if the cap is definitely broken

  24. Acknowledgments • Much thanks to ALY forecasters Tom Wasula, Neil Stuart, and Joe Villani for their help with this study!

  25. Questions? Mammatus Clouds over Dolgeville, New York on August 25, 2007, courtesy of Matt Lanza, WKTV-Utica

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