Weatherwatch: may 2004

摘要

A remarkably persistent pattern of cool air lurked near the U.S./ Canadian border, leaving many areas from the Plains to the East Coast under the influence of a warm, humid airmass for most of the month, with the exception of the first week. In fact, the battleground between cool air. and warm, humid conditions sparked torrential rainfall across the Midwest and contributed to one of the most prolific periods of severe thunderstorm activity on record. Widespread showers also fell across the Northwest, but regions missing out on most of the rainfall included the southern Atlantic states, High Plains, and Southwest. Warmth was most pronounced in the mid-Atlantic states, where monthly temperatures approached or reached May-record levels and averaged as much as 8°F above normal. Unusually warm weather was also observed on the central and southern Plains. In sharp contrast, below-normal temperatures were the rule from Montana to the upper Great Lakes states. Monthly readings averaged as much as 8°F below normal in eastern North Dakota and northern Minnesota.