104. 105. 104.
Those were the high temperatures at Roanoke on back-to-back days 38 years ago this past weekend, on Aug. 20-22, 1983, the hottest three consecutive days in Roanoke weather history and a quarter of the dozen days 104 or higher that have happened since 1912.
This is going to be a hot week in our region, but not nearly that hot. Highs in the mid 90s are expected in the Roanoke area most days this week, with closer to 90 in the New River Valley. A day or two in the upper 90s can’t be ruled out for Roanoke, with an outside shot at 100, but 104 or 105 very unlikely.
Articles in The Roanoke Times & World-News over those three days in August 1983 tell of people being taken to hospitals with heat exhaustion and high school football practices curtailed to limit the heat’s effects.
In Lynchburg, the heat put so much pressure on a propane tank that it exploded into an inferno, damaging 12 apartment units.
It all ended with a round of thunderstorms late Aug. 22 that resulted in multiple people in our region being struck by lightning.
“Temperature of 104 ties all-time mark” the Roanoke Times blared across its front page on Aug. 21, 1983, referring to the previous day.
Two things make that headline a bit quaint.
First, weather records prior to 1947, going back to 1912, have been restored to the official data for Roanoke, and those include a couple of 105-degree days in the 1930s. So, based on the expanded list, August 20, 1983, wouldn’t have quite tied the all-time record.
Second, that very day, Roanoke would beat the 104 of Aug. 20, with a high of 105 on Aug. 21, 1983, becoming the third such day in Roanoke’s weather history with the restored data. It had not been that hot in the Star City for 47 years previously, and it hasn’t been that hot since.
Weather extremes rarely come in regularly spaced intervals, but curiously, the 104-degree highs on Aug. 20 and Aug 22 of 1983 came 29 years after the last occurrence of 104 in 1954 and 29 years before the next occurrence on June 29, 2012, what we remember as the day of the derecho.
Heat waves are not creative in how they develop. There is basically one way they happen.
High pressure at both the surface and aloft creates a mound of stagnant, slowly sinking and compressing air overhead, heating and drying underneath. The deeper this mound of air and the longer it sticks around, the hotter and more persistently hot it will be.
Locally, our hottest days tend to be underneath such high pressure centered just southwest of us in such a way as to circulate light westerly winds over the Appalachians, compressing and drying as they reach the Roanoke Valley and points eastward.
The 1983 heat wave built over us from the northwest, first enveloping the Midwest and Great Lakes and even southern Canada, and then expanded toward us, with high pressure centered slightly to the southwest.
Modern climate science projects that “heat dome” high pressure patterns similar to the one our region experienced in 1983 are becoming more frequent, more persistent and more intense across the globe, attributed to heat trapped by greenhouse gases due to human industrial activities.
The Pacific Northwest experienced a searing heat wave earlier this summer that sent the mercury to 116 at Portland, Oregon, and 121 at Lytton, British Columbia, Canada’s hottest temperature on record in a community that mostly burned to the ground in a wildfire a couple days later. Scientists have estimated that heat wave was made about 4 degrees hotter than it otherwise would have been by global warming.
Specific to the Roanoke area, summers have indeed been getting warmer in recent years, with this current one set to join the top five or 10 summers on record since 1912 for warmest average temperature, but there has been no significant trend to more extreme daily high temperatures.
A temperature as high as 104 has only happened once since Aug. 22, 1983. There have been just 11 days at or above 100 since 2000, the same number as happened in the previous 20 years, which is fewer than the singular decade of the 1950s (15) or the year 1930 by itself (21).
But, yet, 10 of Roanoke’s 20 warmest summers on record since 1912, based on average temperature, or the mean between daily highs and lows, have occurred since 2000.
That includes this one, which through Monday averages 77.3 degrees, which would be tied for fifth warmest were it complete, which it will be next Tuesday. For weather data, summer runs June 1 to Aug. 31.
Roanoke’s highest temperature to date this summer has been 96. Highs have been warmer than normal, likely to finish in the top 20 for average high temperature (88 through Monday) and in the top third for number of 90+ days (35 through Monday), but this summer hasn’t had runs of upper 90s or over-100 temperatures.
Widely observed higher dew points, swept in from warmer oceans, plays a significant role in warmer overnight low temperatures.
While more moisture in the air makes daily heat feel worse to the body, it can also somewhat insulate from the highest daytime temperature readings. There is a reason Miami often tops 90 but hasn’t had an official 100-degree high temperature since 1942.
Urban growth around the climate station site at the airport may also play a role.
A recent Climate Central study estimated that the urban heat island may raise temperatures almost 6 degrees near Roanoke’s city center. It would probably be less than that near the temperature station site at the airport, but still significant in a location with surroundings that changed from pastures to concrete in the last 40 years.
The question is, if an atmospheric setup like 1983 happened again in the near future, would a warmer world allow for a new all-time record high temperature above 105, or would extreme highs be mitigated some by the greater humidity from the oceans trapped against the mountains, and be a little less hot in the day but warmer and stickier at night than the low-mid 70s lows of the 1983 heat wave?
Time will tell.
Weather Journal appears on Wednesdays.