A lightning strike injured a Cecil County zookeeper, half-dollar-sized hail fell in several counties and tornado sightings sent people scurrying for shelter from Rockville to Baltimore-Washington International Thurgood Marshall Airport.
Yet the worst fears of weather forecasters didn't materialize Thursday.
The National Weather Service's Storm Prediction Center called the first of two systems that darkened skies and dumped rain Thursday a "low-end" derecho, known for powerful winds that travel in a straight line over hundreds of miles. The morning storm was a weak cousin of the June 2012 derecho that killed three and left 760,000 without power in Maryland.
In an afternoon bout, emergency officials confirmed by sight a tornado in Montgomery Countythat prompted warnings in Howard and Anne Arundel counties. BWI officials advised travelers and employees to take shelter in lower-level terminal bathrooms as a funnel cloud was seen approaching, though it is not confirmed to have touched down there. The Bay Bridge was closed for a period while the storm passed.
UPDATE: The National Weather Service confirmed Friday night that two tornadoes touched down in Maryland.
The first occurred in Montgomery County Thursday afternoon about 3:40 p.m. A preliminary investigation revealed that it traveled from North Potomac to Burtonsville, leaving a 17.3 mile path of damage behind. Its winds reached 75 miles per hour, and the tornado had a maximum width of 150 yards. Numerous homes were damaged by uprooted trees, the weather service said.
The second tornado occurred in St. Mary's County. Details won't be available until Monday.
There were no reports of significant damage in the Baltimore region. Over the course of the day, more than 39,000 Baltimore Gas and Electric Co.customers lost power, according to the utility. As of 10 p.m., power had been restored to nearly 34,000 of those customers, BGE said. By 10 a.m. Friday, nearly 2,000 customers remained without electricity.
The storms finished off a chaotic week of Maryland weather — first with heavy rains from Tropical Storm Andrea late last week, then four confirmed tornadoes and more heavy rain across the state Monday. Forecasters and media focused for days on the potential for dangerous severe weather Thursday, in part because of memories of the June 2012 derecho, which came with little advance warning.
Maryland Emergency Management Agency officials said after scares like the derecho, which took much of the region by surprise, they pushed to get a message of preparation out well in advance this time, though they recognized by midday that Thursday's storms wouldn't rival last year's derecho.
"One of the mottoes we use is, we prepare for the worst and hope for the best," said Edward McDonough, a MEMA spokesman. "The worst-case scenario would have been a repeat of last June 29."
While such clusters of severe weather don't seem to occur often, one forecaster said they aren't that unusual for the region.
"We haven't had it happen this often for a couple of years," said Aaron Salter, spokesman for meteorology company Foot's Forecast. "In the weather world, people tend to forget what happens after a few years."
Nine tornadoes were confirmed to have touched down across the state last year on June 1. In 2002, outbreaks of tornadoes included one that crossed southern Maryland, the strongest in state history reaching F-4 on the Fujita scale.
"If you do a plot of our climatological peak for severe weather season, you would see a peak around June 15," said Jim Lee, meteorologist in charge at the National Weather Service's Baltimore/Washington forecast office, in Sterling, Va. "This is right at the right time of year."
The derecho storm complex traveled over 600 miles in 12 hours, from Indiana late Wednesday night to the Baltimore area about 9 a.m.
The storms came from the Midwest, with 65-mph-plus wind gusts and nearly two dozen tornado reported around the southern shores of the Great Lakes. A clash between cold Canadian air pushing south and moist, warm air from the Gulf of Mexico raised concerns of a potential derecho overnight Wednesday into Thursday.
It did not strengthen enough to pack the winds of 60 mph or more that would have classified it as a typical derecho, but the storm behaved like one in other respects.
A 19-year-old woman working at the Plumpton Park Zoo in Rising Sun was hospitalized after being hurt when lightning damaged a nearby tree Thursday morning. She had to be resuscitated at least twice, and her condition was not known, said Cecil County Emergency Services Director Richard Brooks.
Weather spotters in Carroll Countyreported hail as much as 1.5 inches in diameter, while the quick burst of heavy rain flooded roads from Carroll to Harford counties. The storm also was reported to have spawned a waterspout on the Chesapeake Bay near the Bay Bridge, according to the Weather Service.
After that line of storms passed, the sun peeked through the clouds, but forecasters continued to warn that the day's biggest severe weather risk was to come in the afternoon.
Maryland had been included in an area with a heightened risks for dangerous winds, potentially of 70 mph or greater, as well as hail and tornadoes, but storm forecasters later shifted that area farther south to Tidewater Virginia and North Carolina.
As the storms hit about 4 p.m., MEMA urged workers to remain at work instead of venturing home on the roads. Earlier, Anne Arundel County sent children in their last days of the school year home ahead of the storm, canceling after-school activities.
The afternoon storms spawned multiple tornado warnings, including one after Montgomery Countyfire officials spotted a tornado that damaged the Rockville Ice Arena, said Chris Strong, a Weather Service meteorologist. About 12,000 power outages reported in Montgomery County, the bulk of those reported to Washington-area utility Pepco, according to the utility.
The weather service typically does not consider a tornado confirmed until its staff surveys and evaluates damage, but it will make such a call when a report comes from a reputable source, said the Weather Service's Lee.
The service said Friday it is inspecting potential tornado damage in Howard and Anne Arundel counties, as well as part of St. Mary's County and several areas of Virginia. A report on the damage and any confirmed tornadoes is expected as early as Friday afternoon, or by Monday at the latest, according to a weather service statement.
In Southern Maryland, the Coltons Point area of St. Mary's — where a tornado was confirmed to have touched down Monday — suffered more damage as the storm downed multiple trees. Nearby, baseball-sized hail was reported.
Flooding was also widespread, with 1.3 inches measured at BWI and 1.06 inches at the Inner Harbor. That brings to 5.35 inches the rainfall total at the airport in the week ending Thursday; about 3.5 inches falls in a normal June there.
While summer severe weather outbreaks are common in the region, Lee acknowledged tornado warnings do tend to be issued more often than in years past because of improved technology. The Weather Service's Sterling office has its own state-of-the-art radar system as well as access to Federal Aviation Administrationradar at BWI, Andrews Air Force base and the two Washington-area airports.
After such an active week, the weather is forecast to quiet over the coming days. The cold front that helped spark the storms will bring low temperatures and low humidity for the weekend, with highs in the lower- to mid-80s.
Reuters contributed to this article.
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