National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
NOUS41 KBOX 021417
PNSBOX
CTZ002>004-MAZ002>024-026-NHZ011-012-015-RIZ001>008-031400-

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE TAUNTON MA
1015 AM EDT THU MAY 2 2013

...SEVERE WEATHER PREPAREDNESS WEEK CONTINUES -- DOWNBURST WINDS
FROM SEVERE THUNDERSTORMS CAN BE POWERFUL...

THE NATIONAL WEATHER SERVICE HAS DECLARED THE WEEK OF APRIL 29 TO
MAY 3 AS SEVERE WEATHER PREPAREDNESS WEEK FOR SOUTHERN NEW ENGLAND.
THE FOLLOWING IS THE FOURTH 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 AND RELATIVELY SMALL AREA OF RAPIDLY
DESCENDING AIR BENEATH A THUNDERSTORM. IT CAN RESULT FROM STRONGER
JET STREAM WINDS 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 A COMMON THUNDERSTORM DOWNDRAFT BECAUSE THE
WINDS IT PRODUCES HAVE THE POTENTIAL TO CAUSE DAMAGE ON OR NEAR THE
GROUND.  SURFACE DAMAGE PATTERNS HAVE SHOWN THAT WHETHER THE WINDS
ARE STRAIGHT OR 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.

$$

EVT

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