| Autor: |
Bodner, Michael J., Junker, Norman W., Grumm, Richard H., Schumacher, Russ S. |
| Předmět: |
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| Zdroj: |
National Weather Digest; Dec2011, Vol. 35 Issue 2, p103-119, 17p |
| Abstrakt: |
The synoptic-scale atmospheric patterns and the most extreme 13-day rainfall periods during the 1993 and 2008 historic Midwest flood events are compared. Over the north central part of the United States, these two 13-day periods were the two wettest during the warm season over the past 60 years. The 500-hPa geopotential height, mean sea level pressure, 250-hPa u-wind and 850-hPa v-wind component anomaly patterns associated with the two periods were found to be remarkably similar. A correlation of .939 was found for the 500-hPa height anomalies between the two periods. The synoptic patterns associated with both periods facilitated the development of a plume of anomalously high precipitable water and moisture flux around the periphery of the subtropical high that then intersected a quasi-stationary baroclinic zone, thereby supporting the development of frequent mesoscale convective systems (MCSs). Frequent low pressure waves along the front, as well as the presence of a nearby exit or entrance region of an upper tropospheric jet streak, enhanced synoptic scale ascent. Early detection of these extreme events might be possible by both medium and short range forecasters using ensemble guidance to ascertain the potential likelihood of similar patterns and features to the aforementioned 13-day periods. On the global climate scale, the late winter and spring season preceding both summer floods featured anomalously wet conditions over the central United States, which contributed to high antecedent soil moisture conditions. Despite the anomalously wet pre-flood periods, there were no similarities in pre-flood monthly El nino Southern Oscillation (ENSO) anomalies, yet both years did feature a negative North Atlantic Oscillation (NAO) signal two months prior to and during the floods. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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