Extended Abstract (80K)P8.3
The Climatology and Character of Pennsylvania Severe Weather
John J. LaCorte, NOAA/NWS, State College, PA; and R. H. Grumm
An examination of 50 years of storm data was conducted to define the climatology and character of severe weather over Pennsylvania. Storm data were loaded into a relational database for rapid examination of severe weather. Severe weather reports, associated with convection, increase rapidly in late spring (June) and peak in early summer (July). There is a minor secondary severe weather maximum in November. These data revealed that the majority of severe weather events are small, consisting of fewer than 5 reports of severe weather. Only about 10 percent of the events were large events, associated with more than 40 reports of severe weather. The majority of severe weather events occurred in the afternoon peaking around 1700 LST. A convective minimum occurs between about 0100 through 1000 LST. During the winter months, the convective maximum is between 1100 and 1200 LST. There is a small secondary convective maximum, about 10 percent of the afternoon value, around midnight. Using the large event dates and the re-analysis data, an examination was made of the large-scale meteorological features associated with these events. Preliminary results suggest several large-scale features provided clues to the potential occurrence of large events. These features include a strong surface cyclone moving over the Great Lakes, a strong low-level southerly wind anomaly, and a surge of anomalous moisture into the region from the southwest. A similar examination of tornadic activity was extracted from the database. These data revealed the same seasonal trends as the general convective activity. The peak month for tornadoes was June followed closely by July. June was also the peak month for strong and violent tornadoes followed by May and July respectively. The peak time of tornado occurrence was approximately 1700 LST. An examination of the NCEP reanalysis data during strong (F2 and F3) and violent (F4 and greater) tornadic events revealed several strong signals. All F2 and greater events were associated with an anomalously deep low-pressure center moving over the central Great Lakes. No strong or violent tornadic event has been observed where the mean-sea level pressure of the surface cyclone has not been at least 1.5 standard deviations below normal. Preliminary results suggest other features include an anomalously deep 500 hPa trough northwest of the surface low and anomalous moisture and strong low-level southwesterly winds ahead of the surface low. Additionally, there appears to be a general southwest to northeast cold frontal boundary associated with the strong tornadic events.
Poster Session 8, Climatological Studies of Severe Local Storms
Wednesday, 14 August 2002, 3:00 PM-4:30 PM
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