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

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

Recent Annual Climatology of Severe Weather TypeNumber Events Significant Reports Hail Wind Tornadoes All MonthTotal January3 February4 March57 April112 May164 June135 July87 August63 September43 October11 November15 December6

Focus Upon Cold Season Severe February 28, 2007 Previous studies focused on yearly activity and ENSO phase (Mayes et al., 2006, Agee and Zurn-Birkhimer, 1998, Browning, 1998). Situational awareness

50+ Year Climatology of Cold Season Severe

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

Incidence of Severe Events during Cold Season for the ENSO Phases La Nina EL Nino Neutral

Incidence of Severe Type Event during ENSO Phases

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%)

Results Concurrent5 Months Prior Overall severe event incidence is more prevalent during cold phase of ENSO (La Nina) 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

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 Study area limited to CWA, may need to expand to larger domain 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

Future Work Compositing Expansion of domain? Analysis of specific severe type frequency