30
Day

In stark contrast to early September cold air has been fully scoured out of North America, leaving clouds and precipitation as only sources of modestly cool temperatures (near seasonal) through the next 10-days at a minimum. Extended range precipitation details are volatile amongst models but consensus in near term forecasts valid this week focus greatest rainfall into the mid Atlantic region, Florida, the Southwest, and north central U.S. where near seasonal mean temperatures are most likely, in an otherwise warm and dry pattern in place across the majority of the U.S. Notable temperature changes are moderation of summerlike mid 90° heat lingering between the Deep South and portions of the Midwest during the latter half of this week, and warmer low 80s forecast across the majority of the Northeast each day through the workweek (5°-8° above average). Mild late week temperatures devoid of extremes are related to large scale pattern de-amplification aloft to faster (unblocked) flow which is also an inherent source of model volatility in longer range forecasts. In this case ensemble mean and operational model forecasts valid during the 11-15 day period diverge greatly with the latter fast to establish cooler pattern change across the Midwest and East. In contrast ensemble mean forecasts maintain the status quo of widespread mild temperatures through the end of September with exception of cooler (seasonal) temperatures in the Northwest. Modest Northwestern cooling may be related to early stages of La Niña development that also support predominance of mild temperatures by fall standards across most of the rest of the U.S. which longer range 30-day MWA ensemble forecasts maintain through mid October. Meanwhile the rare prolonged lull in tropical cyclone activity still underway is likely to end as most models forecast tropical development in the central Atlantic within the next week. While models also deflect this next potential tropical cyclone well off the East Coast sparing the U.S. from landfall, it is likely to mark onset of an active end to the hurricane season which is yet another mild temperature signal across the majority of the Eastern U.S. through mid fall.