Two faces of summer: Sticky-stormy replaces hot and dry in Virginia — for now

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Miami hasn’t had an official 100-degree high temperature since 1942. Tampa has hit 99 in two summers but never 100 in 134 years of official weather records.

File those surprising weather facts alongside how most locations in our Southwest and Southside Virginia coverage area get more annual average rainfall than Seattle.

The lack of triple-digit temperatures in coastal Florida reflects how it actually takes more solar radiation to warm humid air than it does to warm dry air, like we see in Las Vegas or Phoenix. This can be confusing because extra moisture in the air can make it feel hotter than it is, as bodily sweat less easily evaporates, and that’s where we derive the heat index.

But as a physical property, water heats more slowly than most of the other significant components of the air around us, and there is also a tendency for more heat-restricting clouds and storms to form when it is more humid.

So, while Miami and Tampa commonly have 90s high temperatures 80 or more days a year, and the heat index often runs well above 100 in mid-summer, the triple-digit mark on the thermometer is stunningly elusive.

This contrast between the sticky side of summer and the super-sweltering but drier side of summer is relevant to Virginia’s current late July weather fortunes, and also to what may be happening to our summers overall as global climate continues to warm.

First, let’s look at short- to mid-term weather.

Cooler, wetter pattern

As discussed in this space a week ago , Virginia has entered a new weather pattern from that which dominated most of the latter half of June and the first half of July.

A broad low-pressure trough has settled into the central and eastern U.S. as the “heat-dome” high has repositioned out west. The result has been a southwest flow off the Gulf of Mexico bringing abundant moisture across our region, with a northwest flow over the north-central U.S. depositing cold fronts across the Ohio Valley into the Mid-Atlantic region that stall once they move into the southwest-to-northeast wind flow.

The combination of the moisture, modest daytime heating, terrain effects, the lift along the stalled front, and occasional upper-level disturbances has resulted in frequent periods of showers and thunderstorms since the middle of last week, continuing through at least Friday, focused mostly on the afternoon and early evening hours. Rainfall amounts have been streaky, but most locations in our region have gotten at least a half an inch in the past week, and some have topped 2 inches.

This is what I often call our “sticky-stormy” summer weather pattern.

It’s not been enough to reverse many weeks of regional dryness, but the frequent wetting showers have provided a measure of welcome relief. A few spots have had briefly flooding downpours amid the almost-daily rounds of showers and thunderstorms.

The new pattern has also brought noticeably cooler temperatures, generally near long-term normal highs for mid-to-late July. This would be mid 70s to near-80 highs in the western mountainous areas and 80s in the lower elevations, with lows in the 60s at night. It has been too humid to be “cool” but compared to the searing 90s-near 100 temperatures common in the days before, it feels like a summer reprieve.

This general weather pattern looks to continue into next week, though the next cold front will get enough of a kick to push through late this week and bring drier weather by the weekend. While high temperatures won’t change much, there may be a morning or two with some 50s to lower 60s lows in a large part of the region.

What happens after that is still the subject of some conjecture, but heat looks to be rebuilding underneath broad high pressure across the northern half of the country, and this may portend heat expanding back over us in early August, just as heat gripped the Northeast before it got to us in June. Whether what’s ahead is as extreme as what happened in the first half of July remains to be seen — we’ll revisit down the road.

Sticky-stormy summers more common?

What made this summer’s three-week-plus intermittent heat wave so noteworthy, speaking strictly on a regional level, wasn’t that similar heat waves been happening with increased frequency in recent years, as they have in some other parts of the U.S. Rather, it was especially noteworthy because extreme heat hadn’t happened to any reasonably similar level for our region in 12 years.

Recaps of when the last time it was as hot as it was on certain heat spike days of late June and early July tended to focus on 2012, which really was the last comparable heat wave – Danville’s first 100-degree day since July 8, 2012, Roanoke’s hottest temperature since June 29, 2012, etc.

The intervening years between 2012 and 2024 have mostly featured summers that had near-normal to somewhat above-normal high temperatures across our region, frequently sticky low temperatures above historic norms, fairly frequent periods of showers and thunderstorms including some outright downpours, and virtually no periods of widespread or extreme drought.

Lynchburg, which notably had its driest June on record this year with just 0.04 inch, experienced its wettest July on record just last year (10.39 inches), its fourth wettest July the year before that (9.47 inches), and its fifth wettest August in 2020 (10.96 inches).  Roanoke’s wettest July was in 2013 (12.73 inches), its second-wettest June in 2015 (9.07 inches), and its seventh wettest June in 2020 (7.72 inches). Danville paralleled Roanoke with its wettest July in 2013 (11.50 inches) and its fourth-wettest June in 2015 (8.12 inches), plus its seventh wettest June in 2016 (7.70 inches).

Not far across the state line from Bristol, the Tri-Cities Airport had its wettest and second-wettest Junes in 2013 (8.37 inches) and 2019 (7.67 inches) respectively, and three of its 10 wettest Augusts in 2017 (fourth, 6.28 inches), 2023 (seventh, 6.05) and 2015 (ninth, 6.01). Tri-Cities also curiously had its wettest July in 2012, 12.72 inches.

There is no clear pattern of summer months getting wetter in this data, but it does augment how most summers over the last dozen years have not getting drier across our region, but have often been wet, just as most recent summers also haven’t been having runs of extreme heat in our Southwest and Southside Virginia region — until this one.

Studies of large-scale climate have found that heat waves and droughts are tending to be larger, longer lasting and more extreme, but also that denser moisture is being transported to farther north latitudes resulting in more intense downpours.

It makes sense geographically that our region’s summer weather would have a better chance to trend a little closer to Florida’s than it would to Arizona’s.

Warm ocean water exists 200 to 500 miles east and south of us, with more warm water in the Gulf of Mexico a little farther to our south and southwest. We have a chain of mountains running southwest to northeast roughly parallel to the East Coast. It’s simpler for a variety of weather patterns to sweep moisture off those warm bodies of water and trap it against the mountains, which also provide uplift to condense a good amount of that moisture for rainfall.

With ocean temperatures generally warming and observed dew points increasing inland, it is easier in our terrain and regional position to get sticky and stormy periods than it is to circulate drier air that can heat up more. But that can and does happen from time as heat-dome high pressure systems settle upon us, usually from the west and northwest, adding a downslope component when the center is just to the southwest and the circulation brings west or northwest winds up and over the Appalachians, compressing, drying and heating in the process.

For now, the extremely hot and dry multi-week summer period like we just had remains an exception, rather than a rule, for our particular region. Sticky-stormy summers, more like these couple of weeks we’re having now, have been more frequent in recent years.

We’ll see where it goes from here, both this particular summer and the summers to come.

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.

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