Amid all of the hot air around Washington this year, warnings for severe storms have sounded more frequently here than anywhere in the nation.Severe thunderstorm warning count by National Weather Service office in 2021. (Iowa Mesonet)
The nation’s capital and its surroundings have traded places with the Central and Southern United States as the epicenter of severe thunderstorm warnings in 2021. Weather patterns have conspired to focus unrelenting thunderstorm activity in the Mid-Atlantic and Northeast, while subduing it in the places where it’s most common.
The National Weather Service office serving the Washington-Baltimore region has issued a whopping 528 severe thunderstorm warnings for its zone of responsibility from eastern West Virginia to the Chesapeake Bay. That number surpasses the warning count for the area around storm-prone Norman, Okla., which has received a second-most 489 warnings.
If we account for the fact that the regions served by the various Weather Service offices vary in size, the Washington-Baltimore office, based in Sterling, Va., still comes out on top. The office has issued 275 warnings for every 10,000 square miles. The office serving the area around Philadelphia comes in second place with 199 warnings per 10,000 square miles. The other three offices among the top five are all in the Mid-Atlantic and Northeast, serving the regions around Pittsburgh, Binghamton, N.Y., and Richmond-Norfolk.Alerts for destructive thunderstorms to appear on your phone
On the map that shows the difference in the number of warnings issued compared to average (below), the Washington-Baltimore region stands out like a sore thumb; it has received 223 more storm warnings than normal.The difference from average in the number of severe thunderstorm warnings issued in 2021. (Iowa Mesonet)
This same map makes clear how much of the typical severe weather territory, stretching from the South into the Plains, has had a relatively quiet year, with most offices having issued at least 100 fewer warnings than average.
The number of warnings in the Washington-Baltimore region has generally been validated by the number of reports of damaging winds received by the Weather Service in the wake of storms. These reports, mostly indicating downed trees and wires, come into the Weather Service from the media, emergency managers, storm spotters and social media.
The Washington-Baltimore office has tallied an unsurpassed 1,406 damage reports while the office serving Philadelphia has recorded 1,239, the second-most. The office serving the area around Rapid City, S.D., has received the third-most reports with 635.Number of storm damage reports by National Weather Service office. (Iowa Mesonet)
So far this year, 73.1 percent of the warnings issued by the Washington-Baltimore office have had associated damage reports to validate them.
Chris Strong, warning coordination meteorologist at the Washington-Baltimore office, said in an interview that the damage reports “are bearing out” the high number of warnings. The percentage of warnings validated this year is somewhat above the average of 70.9 percent over the last decade.
As shown in the chart below, an increase in the rate at which the Weather Service is issuing warnings does appear to be outpacing a long-term increase in the number of days with thunderstorms in the Washington area. This could suggest an increase in false alarms.Storm warnings are growing considerably faster than thunder days.
Strong stressed his office doesn’t want to issue warnings when they’re unnecessary. “We are concerned about over-warning too, and try to find the balance with public safety,” he said.For those afraid of storms, summer is the worst season
Days of thunder
Considering all of the storm warnings issued, it doesn’t come as a surprise that the region has had a large number of days with thunder this year. In the District, there have been 42 days with thunder observed this year, compared to the long-term average of 34 for an entire year. The above-average number fits into the trend toward more such days in recent decades (as apparent in the above chart).
In August alone, there were more than a dozen days with thunder observed in the District for the sixth year in a row, topping the average of eight.
Even so, the 42 days of thunder this year is slightly down from record seasons in 2018 and 2019, when there were 62 and 63. That said, 2021 isn’t over and could still gain some ground on those two years.
The weather pattern behind the storminessThe summer (June-August) weather pattern was dominated by high pressure heat domes out West, indicated by the red shaded area over the Four Corners region, and occasional dips in the jet stream in the East, indicated by the sinking color contours. (National Weather Service)
A favorable large-scale atmospheric environment has served as the breeding ground for the swarms of storms this year.
Between May and mid-July, the storms erupted in association with cold fronts and low pressure systems transiting the region. A persistent dip in the jet stream near the Great Lakes (shown in the map above) set up relatively frequent and fast flow from the northwest, which is a well-known setup for severe weather in the Mid-Atlantic and Northeast. It facilitates a collision between cool air from the northwest with muggy air from the south.
In the second half of August, a very active stormy period coincided with an unstable air mass fueled by steamy air pumped in from the south even in the absence of a nearby front. Then, the stormy remnants of Hurricane Ida came through to close the month which not only spurred a slew of severe storms warnings but also spawned the destructive Annapolis tornado.
Jason Samenow contributed to this report.
Source : https://www.msn.com/en-us/weather/topstories/why-washington-is-the-nation-e2-80-99s-hot-spot-for-severe-storm-warnings-this-year/ar-AAOMTLG1664