Northwest winds, rotating around central U.S. high pressure with air originating from the Desert Southwest, and then drying and out heating up as they compressed blowing down the east side of the Appalachians, brought in the late June-early July heat wave. Northwest winds gusting above 80 mph on the evening of June 29 knocked out power for millions in the Virginias and nearby states, making the stifling heat unbearably worse. Northwest winds on this September Saturday — outflow from a poorly organized squall line that, and then breezes behind a Canadian cold front — are ushering in fall. With lows expected to drop into the mid 40s to low 50s by Monday and Tuesday morning over much of Southwest Virginia, and highs not expected to top 80 for a few days, behind a front that will drop as far south as Cuba, there can be little doubt that the tundra has made its first major autumn incursion into the eastern half of the United States. Temperatures late this week will moderate back into some low and maybe even mid 80s highs and lows floating around 60. Keep in mind, though, that is still very much normal for the first half of September — Roanoke’s normal high doesn’t get below 80 until Sept. 14, and Blacksburg’s doesn’t get as low as 75 until Sept. 16. What makes this even more likely to be truly the start of fall-like weather is that there are major indications that another, and possibly even cooler, air mass will drop down from the Arctic tundra next weekend or early the following week (10-day Euro model temperature anomaly map linked). One drawback to these serial Canadian air masses is that they are very dry, so folks who want rain and need rain, are not likely to get any. The Hydrometeorological Prediction Center calls for zero rain in western Virginia over the next 5 days (and what is colored in for eastern Virginia is with tonight’s cold front). Temperatures will be cool to normal for the next couple of weeks, and it has a chance to go most or all of that time without measurable rain, too.