Tornadoes confirmed in Howard and Frederick counties on Thursday were the fourth and fifth in Maryland this year, two more signs that this is one of the most active severe weather seasons in years, both locally and nationally.
Already, this year is Maryland’s most active for tornadoes since 2013 — the last in a string of three years in which the tornado tally hit double digits, with as many as 18 in 2011.
Across the country, there have been more than 1,000 tornadoes so far in 2019 — third-most since 2005, behind only 2008 and 2011, according to the Storm Prediction Center.
May was a particularly active month, and potentially record-setting. There were at least eight confirmed tornadoes across the country every day for 13 consecutive days, according to AccuWeather.com, one of the longest such streaks of severe weather on record. And there were more than 500 preliminary tornado reports during the month. After each is investigated, the final count for the month could surpass a record of 414 set in May 2015, AccuWeather meteorologists said.
Meteorologists say the flurry of cyclones is the result of an active weather pattern in which the jet stream buckles over the United States, creating what they call ridges of high pressure and troughs of low pressure. The jet stream is like a highway of air in the atmosphere, steering weather from west to east across the country. But when it weakens and bends — potentially a consequence of warming in the Arctic, scientists say — those pressure differences clash, often spawning severe storms.
That pattern was unusually persistent throughout the second half of May, contributing not just to the spate of tornadoes but severe flooding across the Midwest, AccuWeather meteorologist Alyson Hoegg said. Low pressure systems repeatedly came out of the Rocky Mountains and bumped up against areas of unusually hot and humid weather in the East, triggering storms along frontal boundaries from the Midwest to the Southeast to the Mid-Atlantic, Hoegg said.
“The pattern has been so active it’s just been day after day of severe weather,” she said.
Maryland may not typically see the intense and violent tornadoes more common in the Midwest, but it is one of the most active tornado states for its size. The state sees about 10 tornadoes per 10,000 square miles each year (Maryland is 12,407 square miles, in all), compared to about 12 per 10,000 square miles in Florida and Kansas.
May is often when the season for severe storms and tornadoes peaks, though they are possible any time of year. Last year in East Baltimore, two men died when a tornado hit an Amazon warehouse in November.
Though some storms are possible around Maryland on Sunday, meteorologists expect more tranquil weather for the early part of June.