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NOUS41 KBOX 291300  
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CTZ002>004-MAZ002>024-026-RIZ001>008-301300-  
 
PUBLIC INFORMATION STATEMENT  
NATIONAL WEATHER SERVICE TAUNTON MA  
900 AM EDT FRI APR 29 2016  
 
...SEVERE WEATHER PREPAREDNESS WEEK CONTINUES -- DOWNBURST WINDS  
FROM SEVERE THUNDERSTORMS CAN BE POWERFUL...  
 
THE NATIONAL WEATHER SERVICE HAS DECLARED THE WEEK OF APRIL 25 TO  
APRIL 29 AS SEVERE WEATHER PREPAREDNESS WEEK FOR SOUTHERN NEW  
ENGLAND. THE FOLLOWING IS THE FIFTH IN A SERIES OF FIVE  
INFORMATIONAL STATEMENTS ABOUT SEVERE WEATHER.  
 
WHILE NOT AS NOTORIOUS...OR PERHAPS AS SPECTACULAR TO WITNESS AS  
A TORNADO...STRAIGHT-LINE WINDS ARE RESPONSIBLE FOR MOST  
THUNDERSTORM WIND DAMAGE...ESPECIALLY ACROSS SOUTHERN NEW  
ENGLAND.  
 
A DOWNBURST IS A STRONG...RELATIVELY SMALL...AREA OF RAPIDLY  
DESCENDING AIR BENEATH A THUNDERSTORM. IT CAN RESULT FROM  
STRONGER WINDS ALOFT BEING TRANSPORTED DOWNWARD TO THE SURFACE...  
OR IT CAN RESULT AS AIR WITHIN THE DOWNBURST IS COOLED  
SIGNIFICANTLY AS RAIN EVAPORATES INTO INITIALLY DRIER AIR. THIS  
COOL...THUS DENSE...AIR SINKS RAPIDLY TO THE SURFACE. A DOWNBURST  
IS DIFFERENTIATED FROM COMMON THUNDERSTORM WINDS BECAUSE THE  
DOWNBURST WINDS HAVE THE POTENTIAL TO CAUSE DAMAGE NEAR THE  
GROUND. SURFACE DAMAGE PATTERNS HAVE SHOWN THAT WHETHER THE  
WINDS ARE STRAIGHT OR EVEN A LITTLE BIT CURVED...THEY TEND TO  
SPREAD OUT...OR DIVERGE...CONSIDERABLY AS THEY REACH THE SURFACE.  
CONVERSELY...DAMAGE PATTERNS RESULTING FROM A TORNADO GENERALLY  
CONVERGE TOWARD A NARROW CENTRAL TRACK.  
 
INTENSE DOWNBURSTS CAN BE PHENOMENAL. SPEEDS HAVE BEEN CLOCKED AS  
HIGH AS 175 MPH NEAR MOREHEAD CITY NORTH CAROLINA AND AT 158 MPH  
AT ANDREWS AIR FORCE BASE IN MARYLAND. CLOSER TO HOME...104 MPH  
DOWNBURST WINDS WERE MEASURED AT BOTH WORCESTER MASSACHUSETTS ON  
MAY 31 1998 AND WHITMAN MASSACHUSETTS ON MAY 21 1996. STRONG  
DOWNBURSTS WILL DEFINITELY CAUSE ROARING SOUNDS AND PEOPLE MAY  
OFTEN REFER TO A SOUND LIKE A FREIGHT TRAIN...TERMS TYPICALLY  
ASSOCIATED WITH TORNADOES. ALTHOUGH DOWNBURSTS ARE NOT  
TORNADOES...THEY CAN CAUSE DAMAGE EQUIVALENT TO THAT OF A SMALL  
TO MEDIUM TORNADO. AFTER ALL...WIND IS WIND.  
 
DOWNBURSTS ARE CLASSIFIED AS EITHER MACROBURSTS OR MICROBURSTS...  
DEPENDING ON THE AREAL EXTENT OF THE DAMAGING WIND SWATH. A  
MACROBURST/S DAMAGE EXTENDS HORIZONTALLY FOR MORE THAN 2.5 MILES.  
A MICROBURST IS A SMALL DOWNBURST WITH ITS DAMAGING WINDS  
EXTENDING 2.5 MILES OR LESS. THE SMALL HORIZONTAL SCALE AND  
SHORT TIME SPAN OF A MICROBURST MAKES IT PARTICULARLY HAZARDOUS  
TO AVIATION.  
 
THE NATIONAL WEATHER SERVICE ISSUES SEVERE THUNDERSTORM WARNINGS  
FOR THUNDERSTORMS THAT ARE EXPECTED TO PRODUCE DAMAGING WIND  
GUSTS OF 58 MPH OR GREATER...OR HAIL THAT IS ONE INCH OR GREATER  
IN DIAMETER.  
 

 
 
FOR THE LATEST UPDATES...PLEASE VISIT OUR WEBPAGE AT  
WWW.WEATHER.GOV/BOSTON  
 
YOU CAN FOLLOW US ON FACEBOOK AT  
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.BOSTON.GOV  
 
YOU CAN FOLLOW US ON TWITTER AT  
@NWSBOSTON  
 
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