May 18 - Long Range Summary
Large scale pattern change ensures a significantly warmer latter half of May compared to its cold start across the Eastern half of the country. The Northeast is already warming near seasonal temperatures faster than models previously forecast and will warm above average after Tropical Storm Arthur shifts farther away from the North Carolina coast by Tuesday, and wet Midwestern disturbance bypasses the Northeast by swinging southward through the Tennessee Valley and mid Atlantic region through Friday. Moderate cooling focusing into the interior West this week will not last through the 6-10 day period before well above average heat resumes from the West Coast to central and southern Rockies to predominate the end of May and June. Meanwhile the hottest airmass of the year certain to build between the Rockies and northern-central Plains this week near 20° above average is forecast to shift farther east at near 15° above average strength, peaking temperatures into the mid 80s across the Upper Midwest next weekend (May 23-24) and the Northeast early next week (May 25-26). This surge of midsummer-level heat in the Great Lakes and Northeast will not persist through the end of May. However, extended range models are far weaker with subsequent Eastern cooling and aligning with prior MWA forecasts contracting minor cooling (mainly seasonal) into portions of the central U.S. leaving a warm-biased early summer pattern in place across the West and East through most if not all of June.
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