30
Day

Canadian air which surged into the Northeast early this past weekend in a more intense form (10°-15° below average) than models forecast is strong indication additional lobes of cold air poised to frequently drain down the Eastern Seaboard in stagnant flow into mid June will also be colder than computer generated forecasts. At least general timing of cold air reinforcement through the Northeast into the mid Atlantic region is of improved consensus in recent model runs; with Wednesday-Thursday marking the next noticeable double-digit below average temperature drop, followed by another early next week (Jun 12-13) that could be the coldest of the June series. While far less of this unseasonably cold air will reach the Midwest last week’s hot 90s in Chicago are unlikely to return. The western extent of cold air outbreaks focusing east of the Appalachians will interrupt brief intervals of seasonably warm low-mid 80s across the Midwest with 2-3 day periods of slightly below average mid 70s, to average out near seasonal temperatures over several day time scales through mid June. Meanwhile the Southwest is the next coolest region relative to climatology until stagnant amplified flow can breakdown at some point during the 11-15 day period. As with all major pattern shifts models are highly uncertain with important aspects of change leading to volatile 11-15 day forecasts, but lower amplitude flow in itself almost ensures the core of greatest heat currently locked between the Pacific Northwest and northern Plains (mainly 11°-15° above average) will spread eastward in a modifying (weakening) form mid-late June. Modestly dry surface conditions which developed between the Midwest and mid Atlantic region in late spring set the stage for sustained slightly above average mid-upper 80s during the latter half of June in these areas, but wetter conditions already developing across most of the Northeast are a cooler (near seasonal) Eastern Seaboard signal into the start of July according to 30-day MWA ensemble forecasts.