Adirondack Derecho of July 1995
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.
Analysis of the Derecho that
struck the Adirondacks in July of 1995
|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.
|3:32 am EDT
||3:50 am EDT
||4:07 am EDT
|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
|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.
|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.
|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.
|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
Skew-T atmospheric sounding taken at Sault Ste. Marie, MI where the derecho originated) at 00 UTC on 07/15/95.
|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.
Testing And Display System).
Bow Echo diagram from Storm Spotters Guide -- Guide to Meteorology (UIUC)
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