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Cold season severe weather climatology

Cold season severe weather climatology . What is the impact of ENSO Cycle? Suzanne Fortin. Outline. Recent Annual Severe Weather Climatology Distribution of of Severe Events During the Cold Season Analysis of Severe Events and ENSO Cycle Significance of ENSO Cycle to Severe Incidence.

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Cold season severe weather climatology

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  1. Cold season severe weather climatology What is the impact of ENSO Cycle? Suzanne Fortin

  2. Outline • Recent Annual Severe Weather Climatology • Distribution of of Severe Events During the Cold Season • Analysis of Severe Events and ENSO Cycle • Significance of ENSO Cycle to Severe Incidence

  3. Recent Annual Climatology of Severe Weather

  4. Focus Upon Cold Season Severe • February 28, 2007; January 8, 2009 • Previous studies focused on yearly activity and ENSO phase (Mayes et al., 2006, Agee and Zurn-Birkhimer, 1998, Browning, 1998). • Situational awareness • Initial study conducted on CWA only, study expanded to encompass area roughly defined by 36-41N and 92-96W • Initial study analyzed 50+ years

  5. 50+ Year Climatology of Cold Season Severe

  6. ENSO Phases Since 1950 Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI)*

  7. Incidence of Severe Events during Cold Season for the ENSO Phases

  8. Incidence of Severe Type Event during ENSO Phases TORNADO WIND HAIL

  9. Methodology • Used compositing methodology developed by NWSH, CPC and NWS field • Test of statistical significance performed on statistical analysis to determine if deviations from normal climatology are significant (90%)

  10. Results • Overall severe event incidence is more prevalent during cold phase of ENSO (La Nina) • Weak signal that severe is more likely during early cold season in La Nina phase • Mixed signal during late winter, with severe events occurring during both cold and warm phases of ENSO • “Signal” that severe incidence in late winter greater when cold phase (1) or neutral phase (2) during late summer/early fall Concurrent 5 Months Prior

  11. What’s in store this year? • Compared 2008-2009 ONI with previous years • Found similarities with ONI during lead in to winters of1964-1965*, 1986-1987,1994-1995*, 2002-2003, 2004-2005* • No noticeable increase in tornado incidence throughout warm phase of ENSO cold season • During 1996-1997 and 2006-2007 analogs, severe events started about one month earlier than “normal” start of late March

  12. Summary • Scaled analysis to the past 30 years due to limited dataset prior to 1970s • Statistical analysis also showed severe weather frequency greater during warm phase (El Nino) of ENSO for certain periods • Initial study area encompassed only CWA, expansion to larger domain (36-40N, 92-99W) resulted in even more mixed signals • Signal that severe weather frequency greater during cold season during concurrent cold phase of ENSO • Signal that severe weather frequency during later part of cold season greater if cold/neutral phase of ENSO during late summer/early fall

  13. Future Work • Compositing • Further redefining of domain? • Analysis of specific severe type frequency

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