Extreme Cold-Season Precipitation Regimes in Eastern North America: Dynamic-Thermodynamic Analysis
Abstract
Extreme precipitation is often challenging to predict but can have substantial impacts through flooding and loss of life and property, especially when it is persistent and affects a large region. We define extreme precipitation regimes during the southeastern North American winter (December to February) based on extreme amount, persistence, and areal coverage of precipitation, using the ECMWF Reanalysis-5 (ERA5) precipitation data from 1979 to 2020. These regimes are generally associated with an upper-level trough/ridge pattern in western/eastern North America that slowly moves eastward as the regime progresses, favoring intrusions of moist, tropical air associated with nearly moist-neutral, saturated stratification. Precipitation is associated with a series of surface cyclones traveling along a strong baroclinic zone from the central U.S. eastward into Atlantic Canada, often with short-lived breaks behind each cyclone with dry northerly low-level flow penetrating into the northern U.S. Surface stations to the south of the storm track observe brief but heavy showers and thunderstorms ahead of cold fronts with weak quasi-geostrophic (QG) forcing for ascent, while those north of the storm track observe lighter but steadier precipitation and strong QG forcing for ascent. Though these synoptic-scale features are the main drivers of regimes, mesoscale features are important modulators locally. Idealized condensation computations are similar to the observed precipitation amounts, reinforcing the utility of using the thermodynamic and dynamic variables examined. The evolutions of a few example regimes with different durations and different parts of the quadrant having the heaviest precipitation are examined in order to focus in more detail on pertinent synoptic and mesoscale contributors to these regimes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA042.0007L
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3354 Precipitation;
- ATMOSPHERIC PROCESSES;
- 1854 Precipitation;
- HYDROLOGY;
- 4313 Extreme events;
- NATURAL HAZARDS