Adirondack Derecho of July 1995


Reflectivity image of derecho entering nw NY

During the early morning hours of July 15, 1995 a series of severe thunderstorms crossed the Adirondacks and much of eastern New York. The meteorological phenomena which struck the region can be identified using the Spanish term "Derecho." A Derecho event stems from a larger family of storms called the Mesoscale Convective System (MCS).

   
   

 

 


PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE ALBANY, NY
700 AM EDT FRI JUL 15 2005


...10TH ANNIVERSARY OF THE ADIRONDACK DERECHO (WINDSTORM)...


TODAY MARKS THE 10TH ANNIVERSARY OF THE JULY 15 1995 DERECHO THAT RAVAGED MUCH
OF EASTERN NEW YORK AND WESTERN NEW ENGLAND.  A DERECHO IS A WIDESPREAD AND LONG
LIVED WINDSTORM THAT IS ASSOCIATED WITH A BAND OF RAPIDLY MOVING THUNDERSTORMS.

IN 1995...A LINE OF DAMAGING THUNDERSTORMS DEVELOPED IN THE NORTHERN GREAT LAKES
DURING THE NIGHT OF JULY 14 AND QUICKLY STRENGTHENED AS IT MOVED INTO NORTHERN 
NEW YORK BY 4 AM ON JULY 15...AND THEN INTO SOUTHERN NEW ENGLAND BY 8 AM. ESTIMATED 
PEAK WIND SPEEDS IN EXCESS OF 100 MPH OCCURRED IN THE ADIRONDACKS AND THE STORMS 
THEMSELVES COVERED OVER 800 MILES (FROM ONTARIO PROVINCE TO CAPE COD) IN LESS THAN 
12 HOURS...MOVING AT AN AVERAGE FORWARD SPEED OF 67 MPH. 

THIS DERECHO RESULTED IN FIVE DEATHS AND 11 INJURIES AND CAUSED DAMAGE TO NEARLY 
ONE MILLION ACRES OF TREES IN THE ADIRONDACKS. ALSO…IT WAS ONE OF THE COSTLIEST 
WINDSTORMS IN EASTERN NORTH AMERICA...WITH NEARLY A HALF BILLION DOLLARS IN DAMAGES. 

THE REGION HAS EXPERIENCED OTHER DERECHO EVENTS SINCE...INCLUDING MAY 29 AND 
SEPTEMBER 6 1998.

DERECHOS ARE AN INFREQUENT AND EXTREME EVENT IN OUR AREA. HOWEVER...STRAIGHT-LINE
WINDS...SUCH AS FROM A MICROBURST...ARE RESPONSIBLE FOR MOST THUNDERSTORM DAMAGE 
ACROSS THE COUNTRY. BOTH OF THESE PHENOMENA ILLUSTRATE THAT SEVERE THUNDERSTORMS 
PRODUCING DAMAGING WINDS ARE JUST AS DESTRUCTIVE AND POTENTIALLY DEADLY AS TORNADOES.   

CLIMATOLOGY SHOWS THAT TORNADO OCCURRENCES IN EASTERN NEW YORK AND WESTERN NEW 
ENGLAND ARE AROUND ONE TO THREE PER YEAR. WIND SPEEDS IN THESE TORNADOES ARE 
TYPICALLY LESS THAN 110 MPH...BUT ON OCCASION CAN EXCEED 125 MPH. MEANWHILE...
OVER 100 SEVERE THUNDERSTORMS CONTAINING STRONG DAMAGING WINDS AND OR LARGE 
HAIL OCCUR ACROSS EASTERN NEW YORK AND WESTERN NEW ENGLAND EACH YEAR. WIND SPEEDS 
IN THESE SEVERE THUNDERSTORMS CAN EQUAL THOSE OF AN F0 OR F1 TORNADO. MOREOVER...
SEVERE THUNDERSTORMS ARE MORE WIDESPREAD IN COVERAGE AND LAST LONGER THAN TORNADOES.

THEREFORE...IT IS ESSENTIAL TO HEED SEVERE THUNDERSTORM WATCHES AND WARNINGS WITH 
THE VIGILANCE OF A TORNADO WATCH OR WARNING. 

A SEVERE THUNDERSTORM WATCH IS ISSUED WHEN CONDITIONS ARE FAVORABLE FOR THE DEVELOPMENT
OF THUNDERSTORMS THAT COULD PRODUCE SEVERE WEATHER. THESE WATCHES ARE ISSUED FOR LARGE
GEOGRAPHICAL AREAS SUCH AS MULTIPLE COUNTIES OR STATES FOR A DURATION OF SEVERAL HOURS. 
AT THIS POINT...YOU SHOULD HAVE A PLAN OF ACTION AND STAY TUNED TO NOAA WEATHER RADIO 
ALL HAZARDS FOR THE LATEST WEATHER INFORMATION.

SEVERE THUNDERSTORM WARNINGS ARE ISSUED WHEN SEVERE WEATHER HAS BEEN 
INDICATED BY NATIONAL WEATHER SERVICE DOPPLER RADAR OR OBSERVED BY THE PUBLIC. 
THEY ARE ISSUED BY COUNTY WITH A DURATION OF GENERALLY AN HOUR OR LESS. WHEN
A WARNING IS ISSUED...YOU SHOULD TAKE ACTION...INCLUDING POSSIBLE EVACUATION...
MOVING INTO A BASEMENT OR INTERIOR HALLWAY AND AWAY FROM WINDOWS AND DOORS.

AGAIN...SEVERE THUNDERSTORMS CAN BE JUST AS DANGEROUS AS TORNADOES... AND 
DESERVE THE SAME RESPECT...PRECAUTIONS AND ACTIONS.

FOR MORE INFORMATION ON DERECHOS...INCLUDING THE JULY 1995 ADIRONDACK 
DERECHO...PLEASE GO TO OUR WEB PAGE AT WEATHER.GOV...THEN CLICK ON EASTERN 
NEW YORK OR WESTERN NEW ENGLAND AND LOOK FOR THE DERECHO LINK ON THE TOP 
OF THE PAGE.

$$

OKEEFE


 

 

 

 

 

Analysis of the Derecho that struck the Adirondacks in July of 1995



Reflectivity Lloop from KRMX radar
Radar loop of reflectivity images taken at an elevation angles of 1.4 degrees from the KRMX 88-D Doppler Radar. The loop begins at 0814 UTC and ends in 0906 UTC on 07/15/95.



KRMX reflectivity at 0732z KRMX reflectivity at 0750z KRMX reflectivity at 0807z
3:32 am EDT 3:50 am EDT 4:07 am EDT
KRMX reflectivity at 0836z KRMX reflectivity at 0848z KRMX reflectivity at 0906z
4:36 am EDT 4:48 am EDT 5:06 am EDT


As water vapor rises and cools, thunderstorms physically release warm air (latent heat) into the atmosphere by a process called condensation (as opposed to evaporation which is a cooling process). Warm, moist air is lighter than cool air. Therefore, this column of moist air becomes an area of low pressure relative to its surroundings. Cooler air, which is heavier (high pressure), rushes towards the MCS center from all directions, creating an environment in which winds converge much like approaching automobiles into a toll booth. Since air cannot be forced into the ground, it is reflected upward, thereby causing more air to rise, cool and condense (releasing more latent heat) within the MCS. The self sustaining process is actually similar to the processes within a hurricane.


Bow echo evolution
Schematic of radar view of a Bow echo squall line.


Once a MCS has developed, bow shaped lines of convection (thunderstorms) may form. This is referred to as a bow echo. Inside of the of the bow, faster winds from mid levels of the atmosphere are transported towards the surface. The updrafts and downdrafts within the thunderstorm complex provide a conveyor belt mechanism of transporting high velocity winds to the surface. The system is labeled a Derecho if a bow echo is followed by an extended area of damaging winds. The following two radar images depict the bow echo signature along with a vast area of damaging winds.

Distinguished shape and pattern associated with a Bow Echo. Composite Reflectivity image is from the KRMX 88-D Doppler Radar at 0906 UTC on 07/15/95.
Distinguished shape and pattern associated with a Bow Echo. Composite Reflectivity image is from the KRMX 88-D Doppler Radar at 0906 UTC on 07/15/95.



 Base Velocity image is from the KRMX 88-D Doppler Radar at 0906 UTC on 07/15/95.
Very large area of damaging winds across extreme eastern Lake Ontario and Jefferson County NY. Pale green color is indicative of northwest winds in excess of 63 Kts. Base Velocity image is from the KRMX 88-D Doppler Radar at 0906 UTC on 07/15/95.



On July 15th, a MCS developed over Ontario Province. Doppler Weather Surveillance Radar (WSR- 88D), then identified the formation of a Bow Echo east of Kingston. In addition, the WSR-88D archived color information displaying wind motion. This "Velocity Imagery" indicated the presence of a Derecho, as high velocity winds were contained over a large area inside the bow shape. In essence, strong jet stream winds were transported to ground level as the Derecho passed.

These storms continued moving southeast, reaching Thousand Island Park shortly after 4:00 am with wind estimates exceeding 60 knots (69 mph). During this period a Lightning Detection System (LDS) displayed flash rates of 3000 strokes per hour.
Lightning graph
Graph shows that over 600 lightning strikes were observed in a 10 minute period during the storms peak intensity. 600 lightning strikes in 10 minutes translates into 60 strikes a minute or one strike every second.

Satellite photography depicted expanding cloud tops to 75,000 feet. The Derecho had a width of 50 to 100 miles and a nearly continuous path until reaching southern New England by 8:00 am.

Bow echo path
Path of "Bow Echo" as it crossed southern Ontario, New York And western New England. Time in UTC.


The unmodified Skew-T atmospheric sounding taken at Sault Ste. Marie, MI, where the derecho originated and developed illustrate how unstable the atmosphere was. The lifted index was -8 and the CAPE near 3000 J/Kg. The Hodograph shows there was a large amount of turning directional shear.



SKEWT from station Y62 Skew-T atmospheric sounding taken at Sault Ste. Marie, MI where the derecho originated) at 00 UTC on 07/15/95.


Y62 hodograph
Hodograph from atmospheric sounding taken at Sault Ste. Marie, MI (where the derecho originated) at 00 UTC on 07/15/95.





Various images were taken from the WATADS software package. WATADS(WSR-88D Algorithm Testing And Display System).

Bow Echo diagram from Storm Spotters Guide -- Guide to Meteorology (UIUC)


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