If you ask an astronomer when summer ends, they'll tell you "September 23." That is the date of the autumnal equinox, the date when the day and night are approximately equal in length (the day is always a couple minutes longer because the sun does not set all at once and therefore radiates light until the very last part of it has set below the horizon). Ask a meteorologist though, and they'll tell you that autumn begins September 1, as that is the beginning of 'meteorological autumn,' which goes until November 30. During this time period, our nights get longer while our days get shorter, our daytime and nighttime temperatures plummet, stronger storms start to enter the region, and people become more and more obsessed with the Seahawks. Our earliest lowland snows have generally appeared the last two weeks of November, and our stormiest week is Thanksgiving week. I will have an exclusive winter 2015-2016 forecast on WeatherOn that will be released November 1, so be on the lookout for that. For now, I thought I'd give a more informal autumn forecast.

This has been one of the more abrupt summer-to-fall transitions that I can remember. June and July both broke their respective all-time average temperature records and were extremely dry as well, while August was our 4th wettest month on record and was capped off by a historic windstorm at the end of the month.  Now, it's mid-September, and we are still seeing cooler temps and showers.

We've gone from a pattern of persistent ridging directly over our area to one of persistent troughing, with the ridge having retrograded much further west. Now, storm systems and "shortwave troughs" are undulating on the east side of this ridge and sliding down from the northwest into our area, giving us cooler temperatures and precipitation than anything we experienced during June, July, and even much of August.

http://www.weatheron.net/#!El-Ni%C3%B1o-Strengthens-As-Fall-Arrives/cmbz/55fb7c280cf25fa7fe0f9548