Post by tornado on Aug 12, 2019 14:48:23 GMT -5
From the Washington Post:
A Pair of Microbursts Hit Boston's Logan Airport
I'm wondering of this will be counted in the Bad Weather Operations Score for BOS?
Story here, but link has photos/video.
A Pair of Microbursts Hit Boston's Logan Airport
I'm wondering of this will be counted in the Bad Weather Operations Score for BOS?
Story here, but link has photos/video.
Capital Weather Gang• Analysis
Here’s how a pair of microbursts hit Boston’s Logan Airport
Winds up to 73 mph halted airport operations for 90 minutes.
Matthew Cappucci
Meteorologist, Capital Weather Gang
August 1
It was sunny, with a few rumbles of thunder amid an impending thunderstorm. Then a wall of water and damaging winds hit.
Travelers at Boston’s Logan International Airport were in for quite a surprise Wednesday afternoon. Storms approached the airport around 3:20 p.m. At 3:30 p.m., the automated anemometer at the airport registered a 68 mph wind gust.
By 3:34 p.m., all air traffic into Logan had been halted, according to the National Weather Service’s Boston Center Weather Service Unit. It works with Logan Airport to assist operations and provide weather support for decision-makers. “We work closely with traffic management and coordinate with the approach control tower,” said Brian Seeley, a meteorologist at the center.
The last flight into the airport, a flight arriving from Zurich, had managed to touch down at 3:15 p.m. An aviation photographer on the scene reported that two other flights attempted to land, but were forced to go around. All other flights were diverted or placed in a holding pattern.
All air traffic halted into Boston Logan Airport, Microburst over field, wind gust to 59kt just reported.
— NWS CWSU BOSTON (@nwscwsuzbw) July 31, 2019
At 3:41 p.m., a severe thunderstorm warning was issued for Logan Airport, and it was just in time. “There was a second microburst at 3:53 p.m.,” said Glenn Field, warning coordination meteorologist at the National Weather Service in Boston. “That one was stronger. Logan saw winds gust to 73 mph.”
Field explained how the storm had “backbuilt” to the west, growing and posing the risk of producing another microburst. “We had a warning up for that one,” he said.
How it happened
The National Weather Service in Boston had highlighted the potential for “locally strong to damaging wind gusts” in its morning forecast discussion. It described steep low-level lapse rates, and a temperature and moisture structure in the atmosphere conducive to damaging winds.
What does all that mean?
Essentially, the atmosphere cooled off quickly just above the ground, lending some extra support for storms. There was also plentiful dry air near the surface. That meant any pockets of sinking air would dry up, any moisture evaporating as the pockets approached the ground. This would, in turn, cool that air pocket, making it denser and enhancing its downward momentum. This is exactly what happened not once, but twice.
The second instance proved to be more intense at the airport. The 3:45 p.m. radar scan (below) shows a core of heavy rain and hail over downtown Boston. The bulk of the precipitation was concentrated between 10,000 and 20,000 feet.
By 3:51 p.m., it’s apparent that the core is dropping fast. Note the radar scan at that time (shown above) — it depicts the precipitation core collapsing below 13,000 feet. As the core of precipitation continues to descend, some of the moisture dries up. That cools descending air, accelerating it toward the ground even faster.
At 3:52 p.m., it hits the ground. The effect is similar to throwing a water balloon smack dab at the ground. The fluid would “splat” outward. That’s essentially how a microburst behaves. Because the air can’t go through the ground, it spreads out in all directions. The damage caused by microbursts often resembles a “starburst” pattern. This microburst, the second to strike Logan Airport in 25 minutes, brought winds to 73 mph.
By 3:57 p.m., the microburst is essentially over. Notice not only how the core has fully dropped in barely 10 minutes, but also how much drier the column is. That’s partially because of the evaporative cooling that occurred. The heat content of the air, “lost” in evaporation (called latent heat), was transformed into the kinetic energy of the microburst’s furious wind.
A number of photographers captured the microburst in progress. Ryan Boehm snapped an impressive photo of lightning striking Boston’s 200 Clarendon at the same time that the tail end of the microburst was over Logan.
Notice the “rain foot” on the microburst, indicating strong winds at ground level where the pocket of air flattens and rushes outward. There’s even an “outflow front” — pay attention to that area of rain that seems to curve up and back a little bit. That’s where a subtle horizontal vortex ring around the microburst has formed since the winds are so strong just above the ground. Maximum winds are likely to be found about 75 to 100 feet above the surface.
A number of other photographers captured similar views.
The photo below appears to show the microburst at Logan Airport. Notice the precipitation fanning out as it approaches the ground, carried in the wedge of cooler air outrunning the downdraft that gave rise to it.
Video taken by a webcam at the Eastern Yacht Club in Marblehead (shown below), about seven miles northeast of the airport, shows a different downburst — with winds probably topping 60 mph. Notice how the “foot” of rain and wind arrives first, followed by exceptional winds (enough to shake the flagpole), and then a total reversal of the winds as the microburst exits.
Here’s how a pair of microbursts hit Boston’s Logan Airport
Winds up to 73 mph halted airport operations for 90 minutes.
Matthew Cappucci
Meteorologist, Capital Weather Gang
August 1
It was sunny, with a few rumbles of thunder amid an impending thunderstorm. Then a wall of water and damaging winds hit.
Travelers at Boston’s Logan International Airport were in for quite a surprise Wednesday afternoon. Storms approached the airport around 3:20 p.m. At 3:30 p.m., the automated anemometer at the airport registered a 68 mph wind gust.
By 3:34 p.m., all air traffic into Logan had been halted, according to the National Weather Service’s Boston Center Weather Service Unit. It works with Logan Airport to assist operations and provide weather support for decision-makers. “We work closely with traffic management and coordinate with the approach control tower,” said Brian Seeley, a meteorologist at the center.
The last flight into the airport, a flight arriving from Zurich, had managed to touch down at 3:15 p.m. An aviation photographer on the scene reported that two other flights attempted to land, but were forced to go around. All other flights were diverted or placed in a holding pattern.
All air traffic halted into Boston Logan Airport, Microburst over field, wind gust to 59kt just reported.
— NWS CWSU BOSTON (@nwscwsuzbw) July 31, 2019
At 3:41 p.m., a severe thunderstorm warning was issued for Logan Airport, and it was just in time. “There was a second microburst at 3:53 p.m.,” said Glenn Field, warning coordination meteorologist at the National Weather Service in Boston. “That one was stronger. Logan saw winds gust to 73 mph.”
Field explained how the storm had “backbuilt” to the west, growing and posing the risk of producing another microburst. “We had a warning up for that one,” he said.
How it happened
The National Weather Service in Boston had highlighted the potential for “locally strong to damaging wind gusts” in its morning forecast discussion. It described steep low-level lapse rates, and a temperature and moisture structure in the atmosphere conducive to damaging winds.
What does all that mean?
Essentially, the atmosphere cooled off quickly just above the ground, lending some extra support for storms. There was also plentiful dry air near the surface. That meant any pockets of sinking air would dry up, any moisture evaporating as the pockets approached the ground. This would, in turn, cool that air pocket, making it denser and enhancing its downward momentum. This is exactly what happened not once, but twice.
The second instance proved to be more intense at the airport. The 3:45 p.m. radar scan (below) shows a core of heavy rain and hail over downtown Boston. The bulk of the precipitation was concentrated between 10,000 and 20,000 feet.
By 3:51 p.m., it’s apparent that the core is dropping fast. Note the radar scan at that time (shown above) — it depicts the precipitation core collapsing below 13,000 feet. As the core of precipitation continues to descend, some of the moisture dries up. That cools descending air, accelerating it toward the ground even faster.
At 3:52 p.m., it hits the ground. The effect is similar to throwing a water balloon smack dab at the ground. The fluid would “splat” outward. That’s essentially how a microburst behaves. Because the air can’t go through the ground, it spreads out in all directions. The damage caused by microbursts often resembles a “starburst” pattern. This microburst, the second to strike Logan Airport in 25 minutes, brought winds to 73 mph.
By 3:57 p.m., the microburst is essentially over. Notice not only how the core has fully dropped in barely 10 minutes, but also how much drier the column is. That’s partially because of the evaporative cooling that occurred. The heat content of the air, “lost” in evaporation (called latent heat), was transformed into the kinetic energy of the microburst’s furious wind.
A number of photographers captured the microburst in progress. Ryan Boehm snapped an impressive photo of lightning striking Boston’s 200 Clarendon at the same time that the tail end of the microburst was over Logan.
Notice the “rain foot” on the microburst, indicating strong winds at ground level where the pocket of air flattens and rushes outward. There’s even an “outflow front” — pay attention to that area of rain that seems to curve up and back a little bit. That’s where a subtle horizontal vortex ring around the microburst has formed since the winds are so strong just above the ground. Maximum winds are likely to be found about 75 to 100 feet above the surface.
A number of other photographers captured similar views.
The photo below appears to show the microburst at Logan Airport. Notice the precipitation fanning out as it approaches the ground, carried in the wedge of cooler air outrunning the downdraft that gave rise to it.
Video taken by a webcam at the Eastern Yacht Club in Marblehead (shown below), about seven miles northeast of the airport, shows a different downburst — with winds probably topping 60 mph. Notice how the “foot” of rain and wind arrives first, followed by exceptional winds (enough to shake the flagpole), and then a total reversal of the winds as the microburst exits.
