If you live in or near the Roanoke or New River valleys and think the first half of this September was the hottest you can remember, there’s a good chance you’re exactly right.
For Blacksburg, it was the hottest first 15 days of September dating to the start of its official weather records in 1952, based both on average overall temperature and average daily high temperature. Blacksburg averaged 72.8 degrees Sept. 1-15, beating out 72.3 from the same stretch in 1961, with daily high temperatures averaging 86.4, beating out 85.3 from 1983.
It wasn’t the hottest first half of September for Roanoke since the start of official records in 1912, but it was the hottest in the living memory of anyone who is about 60 or younger.
Roanoke’s first half of September ranked fifth in the past 107 years for average temperature at 76.9 degrees, but the last one that was hotter was 58 years ago in 1961, at 77.7 degrees. The first half of September in 1925 tops the list, averaging 78.1 degrees.
Perhaps somewhat surprisingly, afternoon high temperatures over the first half of September ranked no higher than 13th since 1912 for Roanoke. However, echoing a theme often repeated in recent years in this space, the overnight lows have been historically warm for early September, averaging 66.3 degrees. Only two years have had warmer lows in the first half of September: 1961 at 66.7, and last September, in 2018, atop the list at 67.6.
The early September heat reached a crescendo last week with impressive daily records set on consecutive days at each of the aforementioned major climate stations, located at the National Weather Service office in Blacksburg and the Roanoke-Blacksburg Regional Airport in northwest Roanoke.
On Wednesday, Blacksburg vaulted to 94 degrees. That was not only the hottest Sept. 11 on record, beating 93 from 1983, but it was the hottest day at any time of year Blacksburg has experienced in seven years, since it was 95 on July 1, 2012, two days after the infamous derecho. It was also the hottest it has been in September in 36 years and the second latest on the calendar it has been as high as 94, both of those points going back to a 94-degree high on Sept. 12, 1983.
Not to be outdone, Roanoke topped out at 97 on Thursday, a daily record for Sept. 12, topping 96 from 1933, but also the hottest it has been that late on the calendar since it was also 97 on Sept. 16, 1991. Only nine dates later than Sept. 12 since 1912 have been at or above 97 degrees for Roanoke.
Last week’s heat was curbed quickly by a “wedge” pattern of cool, damp air banked against the mountains for a cloudy, drizzly Friday when temperatures stalled in the upper 60s to mid 70s, then only gradual recovery of warmth over the weekend.
The second half of September began with a hot day on Monday, when Roanoke reached 92, its 57th day at or above 90 in 2019, the most since 1953 and in 10th place overall since 1912. Blacksburg tied a 21-year-old record for Sept. 16 with a high of 91.
However, there is a break from the extended summerlike temperatures over the next three days, as the backside rotation of Hurricane Humberto, well out in the Atlantic and no threat to the U.S., circulates cooler, drier air in from the northeast into our region. Morning lows may dip into the 40s in some spots Thursday and Friday mornings, no higher than the lower to mid 50s even in the urban parts of the Roanoke Valley, with highs mostly staying below 80 Wednesday and Thursday, then some low-humidity lower 80s by Friday.
Unfortunately for those yearning for fall to arrive with its designated astronomical start on the calendar Monday, the heat is likely to return over the weekend and next week.
High pressure remains firmly anchored at the surface and aloft over a big chunk of the central and eastern U.S., and there is no clear sign of it being forced out in bulk over the next 10 days or so. Arctic air may start chewing into it over the north-central U.S. late in the month, a trend worth watching to see if it can bring autumn chill to our region by early October.
There will probably be some more days with highs in the 90s and possibly some record-challenging days next week. September as a whole, with the heat we’ve already had and likely to yet have, is well positioned to make a run at being the hottest on record for both Roanoke and Blacksburg.
Two of the last three Septembers, in 2016 and 2018, rank among Roanoke’s 10 warmest on record, in fifth and seventh place, respectively. Reversing the order, those two Septembers rank first and second since 1912 in average daily low temperature.
Three warm Septembers in four years doesn’t yet establish a climatic trend in our backyard, but it does raise yellow flags about whether the “shoulder season” between summer and fall is changing locally, in correlation with global climate trends. The trend toward consistently warmer daily low temperatures locally in summer over the past 20 to 30 years is well established and appears to be expanding into both May and September.
The odd month out of the four most recent Septembers illustrates how chaotic short- and mid-term weather patterns can be.
The first 15 days of September 2017 were Roanoke’s second coolest such stretch on record, and coolest for average high temperature, only 74.1 degrees, more than 13 degrees cooler on average that the first half of this September has been.
September 2017 didn’t end that way — the month as a whole is only middle of the pack for average temperatures — but it started unseasonably cool.
This first half of September is indeed the hottest many of us can remember. But a truly fall-like start to September isn’t a distant memory, either.
Weather Journal appears on Wednesdays.