Temperatures are slowly moderating in Southwest Virginia after this past weekend’s cold front. Roanoke topped 80 (high of 81) and Blacksburg almost did (79) on Wednesday, after morning lows that were in most places about 5 degrees warmer than Tuesday morning’s chill. Lows may again be a bit warmer on Thursday and Friday, more 50s than 40s across the region, with highs similar to what they were today, if not creeping another degree or two upward on one or both days. But long term, there is still a lot of cool air in the tank, and strong indications that the weather pattern will set up to pour that tank of Canadian chill right into the central and eastern U.S. over the next couple of weeks. It will probably about another week until we get the next major installment of cool air, though a weak cold front over the weekend and early next week may somewhat reinforce the general temperature regime we have now. But, after that, areas of high pressure building over Greenland and the western United States are expected to funnel a shot or two of genuinely cold air from the Canadian tundra southward. The 10-day European model picks up on this pattern well — it’s what would be a classic pattern in midwinter for Arctic air shots and possibly a winter storm or two. You can see the circled blue H’s over Greenland at the top of the screen and farther south over the north Atlantic — this signals the “negative phase” of the North Atlantic Oscillation, which will have increasing impact the deeper we get into fall in bringing cold air southward from the North Pole through Canada into the U.S. The blue/green colors show lower atmospheric heights building southward, with cold air filling in, and several low-pressure centers over Canada and the Great Lakes. Forecast models are in close agreement on the general nature of this pattern, though not all the specifics. This pattern will continue to bring occasional shots of cold air southward — such as this one (blue colors) depicted by the Euro moving into the U.S. on Sept. 22. If this all transpires as it looks now, I would not at all be surprised to see the first lake effect snow develop along some of the Great Lakes (probably the more northern parts) during the next two weeks, and probably more widespread 30s in our region at some point rather than just Burkes Garden’s lonely 36 on Tuesday. Exact low temperatures are of course impossible to forecast this far in advance, but suffice it to say that it’s unlikely that this week’s cool mornings will be the coldest of the month . But then, it’s rare in any September for the first 10 days to be the coolest.
For those looking for rain, the front stubbornly edging in over the weekend and early next week may be able to squeeze out some moisture, but it doesn’t look like there will be a lot to work with. A storm system may develop in the central U.S. and head toward the Great Lakes, again not a great storm path for rainfall in our neck of the woods. We should keep an eye out though for possible storm systems spinning farther south with this pattern that could bring more widespread rain just before one of the new cold air intrusions, but there’s nothing firm on the horizon just yet.