By Saturday morning, a Canadian cold front will push through western Virginia, introducing the leading edge of an air mass that orginated in the Arctic Circle earlier this week and got squeezed southward by high pressure systems over the western U.S. and over Greenland. It’s the way cold air is frequently delivered to us in winter, but of course then, it is traversing thousands of miles of snow-covered terrain or at least cold ground on its way. Not in August. Also related to the typical course of air masses in August, the front will stall just south of our region across the Carolinas the next couple or three days. As disturbances slide southeastward in the northwest flow, a wave or two of low pressure may develop along the front and fling some moisture back across us for clouds and showers. These impulses are difficult to time, but perhaps late Sunday into Monday may be a period for at least a somewhat enhanced chance of rain. One effect of the clouds and showers will probably be that we will not see the kind of especially cool low temperatures we might have with clear, crisp, calm nights. There may be some degree of cooling into Sunday morning, and perhaps again Tuesday and Wednesday morning, that would allow many spots to dip into the 50s. But the clouds will also prevent daytime warming, and with limited sun into an air mass from Canada, it’s quite possible highs will not reach 80 on one or both days this weekend, even in Roanoke. The Hydrometeorological Prediction Center goes even further on Monday, projecting a high of just 74 for Roanoke (inset map at left), which would be 12 degrees below normal. While we may not challenge upper 40s/low 50s record lows in Roanoke or mostly mid-upper 40s record lows for Blacksburg with this cool air mass, there is no sign of a significant warmup anytime soon, and the air mass may even be reinforced again later this week. A prolonged period of below-normal high temperatures, with below-normal low temperatures on some mornings (normal high/low is 86/65 for Roanoke, 82/59 for Blacksburg) appears to be on tap for Southwest Virginia, shaving decimal points off what may not end up as even a top 10 hot summer that was so extreme at its peak.