Watches Issued: Widespread Damaging Wind Gusts Wind Down in the Northeast and Mid-Atlantic following Monday's Low-End Derecho

Jonathan Erdman and Brian Donegan
Published: May 16, 2018

Another active day of severe thunderstorms is in store Tuesday in the Northeast after a low-end derecho swept through the mid-Atlantic states Monday, producing damaging winds and strong wind gusts from Ohio to Virginia, including the Washington D.C. metro.

We have more about Monday's derecho below. First, let's outline Tuesday's severe threat.

An line of severe thunderstorms is quickly marching eastward through southeastern Pennsylvania, northern Maryland and southern New Jersey. 

NOAA's Storm Prediction Center has issued the following severe weather watches: 

  • A severe thunderstorm watch valid until 11 p.m. EDT for southeastern Pennsylvania, southern New Jersey, northeastern Maryland and Delaware. This includes the Philadelphia metro area. 
  • A severe thunderstorm watch valid until 11 p.m. EDT for Washington, D.C., central Maryland and northern Virginia. This watch area also includes Baltimore

These areas can expect to see destructive wind gusts up to 80 mph and a few tornadoes. 


Current Radar, Watches and Warnings.

One person was killed in a car by a falling tree Tuesday afternoon near the town of Effort, Pennsylvania. Straight-line winds likely pushed the tree over. 

At least three injuries resulted from straight-line wind damage on Tuesday: 

  • A falling tree struck a person in Washington Township, New Jersey
  • A falling tree limb struck another person in West Hudson Park in Hudson, New Jersey
  • Flying debris from a wind-blown scaffolding struck a third person on Manhattan Island in New York City

There are numerous reports of downed trees from straight-line winds from eastern Ohio to central Pennsylvania. At least one tree fell on a house near Muncy, Pennsylvania, or about 15 miles east-southeast of Williamsport, as the squall line moved through. 

Hail as large baseballs fell near the Catskill Mountains and mid-Hudson Valley, as leading thunderstorms punched through southeastern New York. 

Large hail broke windows on a home and in a car near Elizaville, New York Tuesday afternoon. 

A severe thunderstorm with damaging gusts and a possible tornado struck around 3:30 p.m. EDT near Yulan, New York, or about 40 miles east-northeast of Scranton, Pennsylvania. Multiple people were trapped in vehicles and houses. 

Newburgh, New York took quite a beating by storms as they moved across the Hudson River. Several buildings lost portions of their roofs, including the Hotel Imperial. Several trees also crashed onto cars and streets in Newburgh Tuesday evening.  

Roughly 600,000 people were without power at the time of peak outages in Pennsylvania, Connecticut, Virginia, New Jersey and New York following the squall line, according to poweroutage.us

Roughly 80,000 of those outages come from the Stroudsburg, Pennsylvania area where wind toppled numerous trees onto vehicles, houses, power lines and roads. 

Further south along the Hudson, winds pushed over trees near Grand Central Station, stalling traffic at the busy station. 

(MORE: Tornado Central)

Severe Weather Forecast

On Tuesday, a jet stream disturbance will surge from the Ohio Valley into the Northeast, as warm and humid air spreads as far north as southern New England ahead of an arriving cold front.

All of these factors will combine to fire up another round of severe thunderstorms in the Northeast. Here are the forecast details.

Tuesday

  • Northeast: A line of severe thunderstorms will quickly move southward across the mid-Atlantic. Widespread damaging straight-line winds are the main threat, but a few tornadoes and hail are also possible.
  • Cities: Boston | Hartford | Albany | NYC | Philadelphia | Baltimore


Tuesday's Severe Weather Forecast

  • Plains: Scattered severe storms are once again possible this evening in parts of the southern Plains, from western Texas to western Oklahoma and northeastern New Mexico. Large hail, high wind gusts and perhaps a tornado/gustnado or two are possible.

Monday's Derecho

On Monday, a line of severe thunderstorms tracked over 400 miles, producing high winds or wind damage from Ohio to the Virginia Tidewater over roughly eight hours.

Radar and thunderstorm wind/wind damage reports (blue dots) from the low-end derecho on May 14, 2018. The radar loop was roughly from noon through 10 p.m. EDT.

The line first produced severe weather in the Columbus, Ohio, metro area just before 1 p.m. EDT, including a 59-mph gust at The Ohio State University Airport and downed trees near Galena.

The early-afternoon line of storms produced wind damage in parts of southeastern Ohio and southwestern Pennsylvania, then accelerated into the Appalachians of West Virginia, where widespread trees were downed in Pendleton and Randolph counties.

By early evening, the squall line raced southeastward through the Washington D.C. metro and much of Virginia before fizzling Monday night off the Virginia Tidewater.

Using the criteria from a 2005 study by Walker Ashley and Thomas Mote, this squall line appeared to have been a low-end derecho, a term meteorologists use for a widespread straight-line damaging wind event produced by thunderstorms. 

(MORE: Summer Derechos Have a Favored Corridor)

Working through Ashley and Mote's (hereafter, A&M) criteria, here's how we arrived at this conclusion:

  • Length: The swath of high winds/wind damage was roughly 430 miles – roughly 692 kilometers – long, easily satisfying the 400-kilometer criterion from A&M. (Note: a proposed change to the derecho criteria from NOAA's Storm Prediction Center would raise the length requirement to 650 kilometers)
  • Chronological progression: The wind reports flowed forward logically with time (see the radar/reports loop above).
  • No large time/space gap between reports: There were no time gaps of over 2.5 hours or spatial gaps of greater than 2 degrees of latitude or longitude between successive wind reports. While the wind damage reports were more concentrated from eastern West Virginia to Virginia, given the time/space gap didn't exceed thresholds, we include the Ohio and Pennsylvania reports in the overall length of the squall line.
  • Origin of wind swath: Damage swaths were all part of the same system, which included some severe thunderstorms ahead of the main squall line in western Virginia.
  • Continuity: Again, the line of thunderstorms responsible for the high winds and wind damage was an easily tracked entity via radar.

As there is an intensity spectrum of tornadoes, tropical storms and hurricanes, such is also the case with derechos.

We would categorize this as a low-end derecho.

The high wind swath wasn't particularly long, there weren't a particularly large number of reports, and, while not one of the A&M derecho criteria, there appear to have been no "higher-end" wind gusts – say, 75 mph or higher.

So, you can think of this derecho as the analog of an EF0 tornado or a 40-mph tropical storm (recognizing EF0 tornadoes and low-end tropical storms can still be dangerous).

The infamous late-June 2012 mid-Atlantic derecho would, therefore, be like an EF5 tornado or a Category 5 hurricane if there was a derecho intensity scale.

The length of the wind damage, high wind report (blue dots) swath from the May 14, 2018, low-end derecho. To be classified as a derecho, Ashley & Mote ('05) require a swath length of at least 400 kilometers (roughly 248 miles).
(Reports: NOAA/NWS/SPC)

Washington D.C. Impact

Washington's Dulles Airport issued a temporary ground stop early Monday evening as a line of severe thunderstorms approached the area. Runways reopened and ground operations resumed about an hour later.

These storms prompted a tornado warning just west of Washington D.C., including the area around Dulles Airport, as rotation was indicated on Doppler radar imagery. For safety, all passengers at the airport were sent underground to the train tunnel.

A National Weather Service employee spotted a funnel cloud in Ashburn, Virginia, just northwest of Dulles Airport, but there were no reports of it touching down.

In addition, golf ball-size hail – 1.75 inches in diameter – was reported in Reston, Virginia, with this line of severe storms. Wind damage was also observed there, with at least one large tree uprooted onto a garage.

Many people across the Washington D.C. metro area captured stunning photos of a shelf cloud as the thunderstorms moved in.

 


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