Weeks in Advance of Others
Weeks in Advance of Others
September 9 - Long Range Summary
Below average temperatures which peaked in intensity across the Midwest, South, and East this past weekend are of increased confidence to represent the final significant cold air outbreak of the next several weeks at a minimum. Not only are recent model forecasts faster to flood nearly all of the Eastern half of the U.S. with midsummer-level heat during the 1st half of this coming week featuring 90s as far north as the northern Plains and 80s across the Great Lakes and Northeast, but this week’s fundamental pattern shift is highly stable and on track to persist well into October according to all longer range models. The main source of day-day volatility to predominantly well above average temperatures east of the Rockies is precipitation including renewed tropical cyclone activity which models are struggling to resolve. Recent European model forecasts have been most consistent in development of an area of disturbed weather currently in the Bay of Campeche to the next named tropical cyclone in the Gulf of Mexico early this week (potentially Francine), followed by landfall near the border of Texas and Louisiana late Wednesday- early Thursday. Subsequent to landfall weakening remnants of this tropical system are forecast to lift northward toward the Great Lakes into next weekend (Sep 14-15) moderating daytime high temperatures along the way. Longer range forecasts of the ECMWF model indicate a similar wet scenario along the mid Atlantic coast by the following weekend (Sep 21-22) as a 2nd potential tropical cyclone makes a close pass along the East Coast. The tropical airmass accompanying either system is far from cold especially at night when overnight low temperatures may reach or exceed 10° above average, but the same clouds and tropical rain represent brief moderation to daytime highs near seasonal levels (mainly 70s). Meanwhile in the West the most recent prolonged period of record heat observed through the 1st week of September is beginning to subside from north-south starting in the Pacific Northwest this present weekend, with continued cooling to slightly below average temperatures forecast across the region by midweek (Sep 11). Farther south near record heat still underway between Southern California and the Desert Southwest will be slowest to moderate closer to seasonal temperatures midweek in a prolonged manner.
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