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Several locations in our region dropped to the freezing mark or below on Tuesday morning. But summer heat is right around the corner.
Most of Virginia is already considered in minor heat risk as soon as Monday — 80s highs, mostly — in the National Weather Service’s new “HeatRisk” application, something we’ll revisit in more detail in weeks ahead. The weekend into next week is likely the start of a prolonged trend toward warmer temperatures entering May. (Looking mostly dry for several days, also, something else that may be worth a revisit soon.)
Based on recent trends to extremely hot summers nationally, an ongoing run of 10 months that have been the hottest on record globally, some extremely warm sea surface temperatures in multiple oceans, and the expected switch from a recently expired El Niño to a developing La Niña in the equatorial Pacific Ocean, there is already much educated speculation that the summer ahead could be the hottest or nearly the hottest on record for the United States.
But heat on a national level does not always translate in parallel to a smaller region, as last summer’s rampant and well-publicized heat waves largely missed Southwest and Southside Virginia. It was generally a warmer summer than normal but not extraordinary in our backyard. In fact, it was the coolest summer in six to 20 years at many locations across our region.
It may seem contrary to logic, but La Niña, with cooler sea surface temperatures, has some tendency to lead to hotter summer patterns over much of the U.S. than does El Niño, with warmer sea surface temperatures in a stripe of the Pacific Ocean near the equator. Stagnant patterns favoring a large central and/or eastern U.S. heat-dome high tend to be more common during La Niña than in El Niño, when there can be more dynamic jet stream flow.
Summer signals with either La Niña or El Niño tend to be weaker than in fall and winter. Of course, these oscillations don’t happen in a vacuum, but in concert with scores of other short, middle and long-term weather patterns and climate oscillations globally. For now, let’s leave La Niña impacts on hurricane season (typically more active in Atlantic), and next winter (tilt to milder, drier historically in our region), for the future, and focus on this summer specifically in Southwest and Southside Virginia, the coverage area of Cardinal News.
Furthermore, let’s narrow the consideration specifically to summers when El Niño transitioned to La Niña, as is projected to occur this summer. There are 10 examples in the past 70 years — 1954, 1964, 1973, 1983, 1988, 1995, 1998, 2007, 2010 and 2016. That’s not a sample size big enough to prove anything, but it is just large enough to perhaps tease out some hints at tendencies to be looking out for.
Recurring heat waves
While there certainly seems to be some propensity for summers as a whole in the El Niño-La Niña nexus to tilt to the warmer end of average temperatures, the most interesting recurring tendency in these summers has been for shorter-term spikes of heat toward the upper extreme of what our region has experienced historically.
That 1983 is one of these El Niño-La Niña transition summers may already raise a red alert for summer heat to those who remember the brutal August 20-22 stretch that summer that saw many readings well over 100 degrees in the lower elevations of our region and mid-upper 90s common even in some higher elevations. Roanoke reached 104, 105 and 104 on consecutive days in 1983.
A disproportionate number of triple-digit days over the past 70 years have occurred at Roanoke, Lynchburg and Danville among those summers we just listed as being in transition from El Niño to La Niña.
More than half of Lynchburg’s days reaching 100 degrees or higher — nine of 16 — occurred in just four of those El Niño-to-La Niña transition summers. In other words, just over 56% of Lynchburg’s days reaching 100 or higher have occurred in about 6% of the Hill City’s summers over the past 70 years, those four summers being in the bridge between El Niño and La Niña.
For Roanoke, 17 of 45 100-plus days have occurred in just seven of the 10 El Niño-to-La Niña transition summers, while at Danville, 37 of 90 100-plus days have occurred in the same seven summers. In each case, a tenth of the summers account for more than a third of triple-digit days.
Elsewhere in the region, El Niño-to-La Niña transition summers have accounted for each of the following heat superlatives over the past 70 years.
· Blacksburg: Five of the nine summers that have had at least one day of temperatures of 95 or higher.
· Wytheville: Two of the three 98-degree readings on record, in 1988 and 2010.
· Martinsville: Five of the eight summers that have reached 100 degrees or higher.
· Appomattox: Three of the four highest temperatures — 103 in 1983, 101 in 2007 and 101 in 2010. (Other was 103 in 1977.)
· Burke’s Garden: Three of the four days 92 or higher (94 in 1983, 93 in 1988, 92 in 2007). The other was 92 in 2012.
· Lexington: Hottest temperature of the past 70 years — 103 — occurred in 2007.
· Abingdon: Only 100-degree reading; it occurred in 1988. One of its two 99-degree highs happened in 1983. (The other was 2012.)
· Wise: Four of last five times it reached at least 92 were in 1983 (92), 1988 (94), 1995 (93), and 2007 (92). A 95-degree high was recorded in 2012.
· John H. Kerr Dam: Often-hottest sensor in our region soared to 108 in 2007, 106 in 2010 and 105 in 1988, half of the summers that reached at least 105.
The idea that these El Niño-La Niña summers have a greater propensity for at least a few days of extreme heat appears to have some legs across virtually all of Cardinal News territory.
Warm nights, few 100-degree days
Were this coming summer to join the list, such an occurrence would be quite novel over recent years, as our region really hasn’t had a substantial run of extreme heat since the June 28-July 9 period of 2012 that included the infamous derecho. Collectively, Roanoke, Lynchburg and Danville have combined for just one triple-digit day since 2012 — a 100-degree high at Roanoke on July 20, 2020. The present streak of 11 years without a 100-degree or higher temperature is the longest such streak in Danville weather history going back to the beginning of its official records in 1917.
Multiple recent summers have ranked among the top few on record at many sites in our region based on average temperature, the mean of high and low temperatures over the entire 91 days of meteorological summer from June 1 to Aug. 31. That is generally consistent with what has been observed nationally and globally, but in our region it has been warmer overnight low temperatures that have driven that trend more than frequent extremely hot daytime high temperatures. (Higher dew points from warmer oceans are the likely culprit.)
Having a run of extreme heat in the summer ahead is no lock, of course. We could get caught on the downwind side of a strong central U.S. heat dome with frequent cold fronts and have a not terribly hot summer. We could again trend more toward the sticky nights rather than sizzling days even if it is a warmer-than-normal summer. Some El Niño-La Niña transition summers like 1964 and, most recently, 2016 did not manifest with extraordinary summer heat in our region. And there is also still at least some chance that the El Niño to La Niña shift doesn’t occur as projected, with equatorial sea surface temperatures getting stuck in neutral.
For now, we’ll file this little tidbit of loose historical correlation away as something to be on the lookout for moving into summer, not something that’s etched in stone to happen.
Freezing Tuesday morning
Tuesday morning was quite chilly at many locations across our region, with nearly every location dropping into the 30s and several dipping to the freezing mark or below.
32 degrees: Abingdon, Blacksburg, Danville, Lexington, Martinsville, Rocky Mount.
31 degrees: Chatham, Galax, Pulaski.
30 degrees: Brookneal, Covington, Radford, Saltville, Wytheville.
29 degrees: Pearisburg, Richlands.
27 degrees: Copper Hill
23 degrees: Burke’s Garden
It’s a reminder that we’re not necessarily quite past the potential for frosts or near-freezing temperatures, especially in outlying areas west of the Blue Ridge, where many locations don’t have last freezes on average until early May.
There may be a few isolated frosty lows Thursday and Friday morning, while most are in the upper 30s to mid 40s, before a significant warmup into next week that will bring on highs in the 80s and lows in the 50s and 60s.
Journalist Kevin Myatt has been writing about weather for 20 years. His weekly column, appearing on Wednesdays, is sponsored by Oakey’s, a family-run, locally owned funeral home with locations throughout the Roanoke Valley.