Fall has finally dropped a hint, but only that, and it may be a while before it does much more.
Monday and Tuesday brought the coolest mornings Cardinal News’ Southwest and Southside Virginia coverage area have seen in two months, with many upper 40s to mid 50s lows across the region, and some even cooler — Tazewell County icebox Burke’s Garden fell to 42 on Tuesday morning.
The cool mornings punctuated a roughly 60-hour period when a sticky summer seemed to be in remission, losing the persistent stickiness that has made August one of the warmest on record for many locations in our region, perhaps surprisingly given infrequent high afternoon heat,
The recent coolness was not only a contrast to a hot and sticky summer, but a reminder of last August, one of the coolest on record for many locations in our region, with a late August cool snap bringing 40s lows to most locations in our region and mid 30s in the chilliest valleys.
We didn’t quite have that kind of late August chill this go-round, nor is there any of that on the horizon looking into early September. Quite the opposite, in fact.
Not the heat, but the humidity
This has not been a blazing hot August in Southwest and Southside Virginia. There’s just been too many stormy periods around interrupting the heat and unevenly spreading still-needed rainfall.
But it has been a persistently sticky month that has managed to sneak the August amid relatively sparse company as one of the warmest on record for multiple locations in our region.
Through Monday, with one week remaining in the month, August through its first 24 days would have ranked as sixth warmest on record at Roanoke (77.9 degrees average temperature), tied for seventh warmest at Blacksburg (73.4), 10th warmest at Danville (79.7), tied for 11th warmest at Wytheville (72.9), tied for 15th warmest at Burke’s Garden (68.7), and 19th warmest at Lynchburg (77.3). These are locations with a century or more of continuous weather records, aside from Wytheville which has 96 years.
It may seem strange that August has rated so highly in warmth when neither Wytheville nor Blacksburg (nor Burke’s Garden, but that’s generally expected) have hit 90 degrees all month, and when Roanoke has gotten no higher than 92, the second coolest August maximum temperature in the last decade. (It only made it as high as 91 last August.)
It makes a little more sense for Danville, where five August days have topped 95, peaking at 97 on Aug. 20. Southside Virginia edged into the mid-month heat wave that encompassed the Carolinas — the John H. Kerr Dam in Mecklenburg County scraped 100 on Aug. 15.
But when it comes to average temperatures over several weeks or a month, there are two ends to the thermometer.
That may be a less apt metaphor in this day of digital equipment instead of mercury tubes, but the truth is that average temperatures are the mean between a day’s high and low temperatures, added together and divided by the number of days. So the morning’s coolest temperature counts as much as the afternoon’s hottest temperature.
Roanoke, for instance, has had an average low temperature of 68.5 degrees through Monday, which would be the sixth warmest for August were it the end of the month. Tuesday’s low of 54 might edge that average down a tiny bit, but warmer days ahead won’t.
Blanket of moisture
Temperatures don’t fall as much at night when there is a blanket of humidity in the air. As a result, excluding the past couple of days when a cooler, drier air mass sliding in from the northwest finally cleared our area of the stickiness, low temperature have tended to average above our long-term norms more often and more extremely than our daily high temperatures have during this particular August.
While here we are talking about the weather of this particular month, when high pressure setting up to our east has tended to bring abundant atmospheric moisture north and northwest from warm seas, there is a broader application for large-scale climate.
Many of those record-warm global and continental temperatures you often hear about — such as July being the warmest month on record globally — reflect warmer low temperatures as much or more than they do extreme high temperatures. Moisture transport off warmer oceans has tended to raise overnight low temperatures at many locations around the globe, even in some weather patterns that keep daytime temperatures below extremes.
For our region’s particular short-term weather, stickiness and heat are both building back over the next several days.
We’ll see a renewal of showers and thunderstorms the next few days, then drier, but hotter, weather into next week as high pressure aloft builds in from the west.
We’re not through with summer, or at least summerlike weather, even though the meteorological calendar flip to fall happens Tuesday with the start of September and the cultural end of summer follows with Labor Day less than a week later — not to mention, the start of college football season.
We’ll have to wait a little longer for this week’s brief nip in the air to fully manifest its pumpkin spice glory.
