May 25 - July 30
Verifying Model Forecasts of Arctic Fronts in Advance of Winter Storms in the Southern Plains
Willliam E. Leatham, IV, Patrick Burke, and Andrew Taylor
What is already known:
- Models consistently misplace the cold front and freezing line position to the north.
- This northerly tendency needs to be quantified and corrected.
- Increased forecasted confiednce in providing the public with warnings in advance of winter storms.
What this study adds:
- Little previous work found on operational model verification of a southward progressing arctic front and freezing line associated with winter storms.
- Quantification of forecast error in operational models during these situations.
- Raises concerns about the diversity and possible biases in ensemble systems.
- Makes forecasters aware of the range of error and average error, allowing them to account for this in the future.
Abstract:
Arctic fronts and associated freezing line positions are of concern in winter storm forecasting. In the southern Great Plains of the United States the arrival of shallow arctic air plays a major role in the development of severe ice storms. At other times, the cold air becomes deep enough to support snowstorms and even blizzard conditions. Forecasters' providing at least twelve to twenty-four hour advanced warning allows the public and other groups time to prepare for these potentially dangerous events. Therefore, determining how operational forecast models perform in these situations is crucial to improving forecast accuracy and increasing our understanding of shallow cold air. This paper compares the observed surface freezing line and cold front location with model forecasts of both these features during the twenty-four hour period leading up to the onset of four winter storms. The model forecasts tend to move arctic fronts southward much too slowly. This has strong implications for the southward extent of winter storm warnings based on model forecasts, and their associated lead time.