Monday, June 11, 2012

What is it with Memorial Day and Severe Weather in the Northeast

Hi Rebecca here again, This post will be about severe weather in the Northeast. It will focus on the weeks around the end of May and first of June. Over the last week and a half the Northeast and areas close to the Northeast have see quite a bit of severe weather. We can all remember the severe outbreak on the 29th of May. Then on June 1st Maryland was hit by another severe outbreak; when it was over 10 tornadoes were confirmed by the NWS. This post will go into a little detail on these two events. It will also touch on some of the other outbreaks of note during this time of year in the Northeast. Severe weather is common enough around the 31st of May It's often called the infamous May 31 severe window.

 The Northeast historically sees a jump in severe weather events around the end of May into first part of June. Over the decades, the time around Memorial Day weekend has marked a sudden increase in widespread severe weather outbreaks. The meteorological conditions at this time of year; along with people coming out in droves for the usually nice weather  creates a perfect storm for disaster in the northeast.   

 The May 29th and June 1 2012 outbreaks.

On May 29, we had a very warm, humid, and unstable air mass was overhead.  The surface temps were in the 80's and dewpoints were in the 60's. Also,  CAPE  values were between 2000 and 3500 J/kg, mid level lapse rates were around 7 Celsius per kilometer with a 35 to 40 kt unidirectional wind shear. This was a recipe for potential severe weather all that was needed was a trigger and that trigger was a strong cold front approaching from the west.  Between 11:00 am and Noon  a few broken lines of thunderstorms developed in Western NYS.  As the frontal boundary ahead of the cold front pushed into the unstable air mass,  the storms quickly went severe.  By the time the lines made it into Central and Eastern NYS the atmosphere was prime for a widespread severe event.

In the storms wake there were over 200 severe reports in our neck of the woods.  Most of the damage occurred in New York (114 reports) and Pennsylvania (77 reports). Vermont and Western New England (over 50 reports). Of these  dozens were damaging hail reports; hail in North Bolton, NY was measured at three and a half inches in diameter, and baseball-size hail was reported in the Fulton County town of Stratford.  The storms caused widespread wind damage, some winds were clocked at over 70 mph, which resulted  in many  reports of trees down.  In addition to all of this, the NWS issued several  doppler indicated tornado warnings.  One of these warnings resulted in a EF-0 tornado that hit the village of West Glover in Orleans County Vermont. This is the first  tornado Vermont has seen in two yeasr.

                                 Picture taken by Terri Fike Dinitto showing a funnel cloud near Marcy, N.Y.

              Picture taken by Brandi LaRoe showing  a possible funnel cloud and hail shaft near Whitehall

The June 1st 2012 event.
A few days later on June 1st severe weather stuck again. This time in Maryland and Virginia. New York State and Western New England  dodged a bullet  if the system had been just a little more to the east, we would have seen this too. The NWS has filed 58 wind damage (mostly downed trees) and 28 flash flooding reports from northern Virginia, central Maryland, and the District of Columba. Maryland saw the worst of it. The NWS has confirmed 11 tornadoes  in Maryland on this Friday.  Harford County MD  saw the worst of it with over $1,000,000 dollars in damage.
 You may be surprised to learn that after  the record setting  pace for tornadoes at the beginning of 2012 things of slowed down.  As of this writing there have been 805 tornadoes reported. This may seem like a lot but the average number reported by this time is normally 886. In fact last month only saw 117 preliminary tornado reports . This is the least amount of  May tornadoes reported since May, 1979.  May, 1979 has the distinction of having the  fewest May tornadoes  since records have been kept.  The number of tornadoes in  May 1979 was 112 tornadoes.  May 10th thru the 20th marks the peak of severe weather season in the Northeast.
End of May first of June severe events in the past
 I will briefly outline a few noteworthy   Northeast severe weather outbreaks that have occurred around Memorial Day.
May 26, 2011
This event was the first significant severe weather outbreak of the season. The storms affected most of northern New York and Vermont. The air mass had surface temps in the 80's and dewpoints in the 60's.  The high instability values along with moderate deep shear produced an environment extremely favorable for thunderstorm development during the afternoon and evening hours on 26 May 2011 Thunderstorms developed when  the shortwave moving off the Great Lakes interacted with the enormously unstable air. Now throw in a stationary boundary working with the available moisture and a vigorous upper level jet; it didn't take long for the storms to go severe. Many of these cells developed into supercells.  These long track supercells  developed across the Saint Lawrence Valley and northern Adirondack Mountains, and then tracked east into the Champlain Valley, then into central and northern Vermont.  There were dozens of large hail reports, with baseball size hail reported near South Duxbury, Vermont.  The storms also produced several wind damage reports, many clocked winds between 60 and 70 mph. The conditions allowed for several rounds of thunderstorms. These storms trained over the same areas for hours. Because of this between three and seven inches of rain fell. During the overnight hours, the rain caused tremendous flash floods in the Adirondacks, Champlain Valley, and  northern and central Vermont. Two EF1 tornadoes formed in Pennsylvania close to the New York border. The storms also impacted New Hampshire and Maine.
June 1, 2011
The Westfield to Charlton Tornado.
As most of us will remember, last year the most powerful tornado in years struck Massachusetts. The tornado formed near Westfield, MA. It later moved through Springfield, MA; where it caused extensive damage and unfortunately resulted in the deaths of 4 people. The Tornado traveled for 39 miles when it lifted in southwest Charlton, MA. The same storm system produced three other tornadoes in Wilbraham, North Brimfield, and Sturbridge. There were also dozens of hail reports, including hail that was almost four inches in diameter in Windsor, MA.  

May 31, 2002
This event produced over 200  severe weather reports. The reports consisted mainly of straight line wind damage with some hail reports as well. This severe outbreak resulted in tornadoes in Maine, Connecticut, Canada, and in  New York State.  The four tornadoes in New  York were in the southern tier of the state.  A broken line of thunderstorms formed during the early afternoon producing spotty, light straight-line wind damage. However, a second round of thunderstorms developed behind the first line later in the afternoon and this is the one that produced the four tornadoes. This outbreak had a very similar setup to the May 29, 2012 event. The temps were hot, dewpoints in the 60's, and high CAPE values. The trigger for this event was also a cold front. The event in 2002 had an upper level northwest flow and a strong low level southwest flow. This type of flow pattern is seen in severe weather outbreaks quite often in the northeast. This is most likely because the southwest flow helps by warming and moistening  the low-levels; while the northwest flow cools and dries the air aloft; this veering wind profile leads to massive destabilization in the atmosphere. The metrological term for this is differential theta-e advection (for those who have to know).  

May 31, 1998

This outbreak was a very significant one. It was caused by a super long lived derecho that started in southeast Montana during the  afternoon of May 30 and  extending throughout May 31. The NWS has stated that the derecho was the most violent line of thunderstorms on earth during the 1998 calendar year. The derecho had produced several tornadoes before it reached the Northeast. In the northeast straight line winds caused tremendous damage. One wind report out of Worcester, MA, told of a 104mph gust. A total of  41 tornadoes were produced in the Northeast, mostly in New York and Pennsylvania. In the afternoon CAPE values were around 2500 J/kg out ahead of the line. As the derecho dissipated an outflow boundary moved into the warm and unstable air mass. Severe thunderstorms quickly developed along this line. One of the storms formed the most destructive and long lived tornado of the day. This tornado  ripped through the Saratoga County Communities of Stillwater, NY and Mechanicville, NY , where it caused massive damage but fortunatel no fatalities. After chewing up Mechanicville it  moved into the Rensselear County town of Schaghticoke. The tornado continued east across Hoosic Falls, NY into the Washington County town of White Creek and into Bennington County Vermont.  New Hampshire and Connecticut also saw one tornado each. When all was said and done the storms caused an estimated $83 million in damage, 109 injuries and 1 fatality in Pennsylvania.
Detailed information from NWS Albany on the Stillwater and Mechanicville tornado can be found here.

A paper by Andrew Gregorio that goes into the meteorology of the storm can be found here.

June 2, 1998

The area had just started to assess the impact of the severe weather from the 31st; when yet another massive outbreak occurred. This outbreak has been dubbed the 1998 Eastern Tornado outbreak. it was one of the most significant tornado outbreaks in history of the East Coast. The event produced 50 tornadoes from the Northeast  to South Carolina. The vast majority of them were in New York, Pennsylvania, and New Jersey. This outbreak caused an estimated 42 million dollars in damage and caused 80 injuries and 2 fatalities.  One thing that will always make this outbreak standout was the uncommonly high number of supercell thunderstorms; which produced high number of wind and hail damage reports over the central Appalachian Mountain area.

May 29, 1995

During the afternoon a thunderstorm developed over Central New York. Over the next several hours the storm moved east. The atmosphere over the Hudson Valley was favorable for severe weather. There was also a low level southerly flow over the Hudson Valley. This flow increased the rotation in the lower atmosphere. At the same time there was a Northeast flow that was diving dewpoints into the 60's (terrain channeling is one of the reasons the Hudson Valley has a greater risk of tornadoes then most places in the Northeast).   Because of this, the storm rapidly strengthened over the valley. The Storm produced scattered damage reports. As the shear increased the thunderstorm grew even stronger. Then at 6:40 pm  a F2 tornado formed and moved across  Columbia County, New York. The tornado dissipated at 7:00 pm as it approached the Massachusetts border. Soon the storm re-intensified. Then at 7:06 pm the  storm formed another  tornado in North Egremont Massachusetts, near Prospect Lake.  The tornado moved east into Monterey, MA ( Great Barrington).  I've seen reports that placed this as an F3 or an F4. (based on damage pictures and reports  I've seen, I believe it was an F4). This tornado caused considerable damage across Berkshire County. The tornado injured 24 people; sadly, three people were killed when their car was lifted and thrown into the woods. The tornado cause about 24 million dollars in damage.  there were two other northeast tornadoes. An F0 between Walden, NY and Newburgh, NY and an F1 that moved across South Britain and Southbury Connecticut.

May 31, 1985

This severe outbreak occurred in Ohio New York,  Pennsylvania, and Ontario Canada.  Afternoon temps were in the low to upper 80's with dewpoints in the 60's. Capes were 1500 -2500 J/kg. The Lifted Indexes were in the -4 to -7 range and a Showalter Index –8C. Moderate wind shear was also present along with upper level Jet support. There was also a midlevel cap in place. The conditions were ripe for severe weather, all that was needed was a trigger to light the match. That trigger was a low pressure system trailing a cold front.  The cap blew at just the right time. So, once the cold front touched the highly unstable air everything exploded. The cold front began crossing Great Lakes late morning / early afternoon,   several thunderstorms developed shortly after 1:30 pm. later in the afternoon along the cold front lines of severe thunderstorms with supercells rapidly developed  in  northeast Ohio and northwest Pennsylvania.  within half an hour, damaging hail and wind reports started coming in.  Baseball size hail was reported Between St Catharine's CA and Lockport, NY, especially hard hit was Niagara-on-the-Lake. The storm produced 41 tornadoes, Two  of these tornadoes crossed into New York, affecting southern Chautauqua and Cattaraugus counties.
A link can be found here that shows a few pictures from the 1985 event.


Other events around this time of year, one was the Johnstown flood, over 24 hours of heavy rain fell in southern tier of New York, Ohio, northern West Virginia, and especially Pennsylvania. At around 3:10 pm, the South Fork Dam above Johnstown failed. Lake Conemaugh was empted in short order,  A wall of water  over 80 feet high sweep over the valley and destroyed Johnstown. The flood killed 2,209 people. Another event happened on June 9, 1953. The deadliest tornado in the Northeast, an F4, killed 94 people in Worcester, Massachusetts.

Well that's it for this installment. As you can see the time around Memorial Day is no stranger to severe weather outbreaks.