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Public Information Statement
Issued by NWS Portland, ME
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PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE GRAY ME
900 AM EDT THU MAY 2 2013

THE NATIONAL WEATHER SERVICE HAS DECLARED THE WEEK OF
APRIL 29TH  THROUGH MAY 4TH, SEVERE WEATHER AWARENESS
WEEK IN NEW ENGLAND.  THIS IS THE THIRD IN A SERIES OF
FIVE PUBLIC INFORMATION STATEMENTS ON VARIOUS TOPICS
RELATED TO SEVERE WEATHER AWARENESS.


...SEVERE WEATHER AWARENESS - SEVERE THUNDERSTORMS -
DOWNBURSTS, MICROBURSTS, MESO-CYCLONES, AND HAIL...

BY DEFINITION, A SEVERE THUNDERSTORM IS ONE WHICH
PRODUCES WIND GUSTS OF 58 MPH OR MORE, OR HAIL 1 INCH IN
DIAMETER OR GREATER. SEVERE THUNDERSTORMS CAN ALSO
PRODUCE TORNADOES.

IN NEW ENGLAND, SEVERE THUNDERSTORMS ARE NOT UNCOMMON
DURING THE SUMMER.  EVERY YEAR, THE NATIONAL WEATHER
SERVICE GETS NUMEROUS REPORTS OF WIND AND HAIL DAMAGE
THROUGHOUT MAINE AND NEW HAMPSHIRE.  SEVERE THUNDERSTORM
WINDS DOWN TREES AND BRANCHES ONTO HOMES, BUILDINGS,
VEHICLES, AND POWER LINES.  SCATTERED POWER OUTAGES ARE
OFTEN THE RESULT OF LIGHTNING OR WIND-FALLEN TREES AND
BRANCHES.  ALSO, WIND-DRIVEN HAIL FROM THUNDERSTORMS
FLATTENS AND/OR DAMAGES CROPS IN THE STATES.  ON RARE
OCCASIONS, LARGE HAILSTONES DAMAGE HOMES, BUILDINGS, AND
VEHICLES.  IN ADDITION TO THE LIGHTNING, FALLING TREES
AND LARGE HAIL ALSO POSE A SIGNIFICANT THREAT TO PEOPLE,
AS WELL.


THUNDERSTORM WINDS, DOWNDRAFTS, DOWNBURSTS, AND
MICROBURSTS

DURING THE DEVELOPMENT OF A THUNDERSTORM, WARM AIR RISES
UPWARD IN THE ATMOSPHERE (AN UPDRAFT) CAUSING THE
FORMATION OF CLOUDS AND PRECIPITATION.  AS A THUNDERSTORM
MATURES, COOL, PRECIPITATION-LADEN AIR SINKS DOWNWARD
THROUGH THE ATMOSPHERE (A DOWNDRAFT).  WHEN A DOWNDRAFT
REACHES THE GROUND IT SPREADS OUT CAUSING THE COOL, GUSTY
WIND THAT OFTEN ACCOMPANIES A THUNDERSTORM.

IN SOME THUNDERSTORMS, INTENSE DOWNDRAFTS DEVELOP.  WHEN
THESE DOWNDRAFTS REACH THE GROUND, THEY SPREAD OUT VERY
QUICKLY CAUSING STRONG AND OFTEN DAMAGING WINDS AT THE
GROUND.  THESE INTENSE DOWNDRAFTS ARE CALLED DOWNBURSTS
AND CAN CAUSE SIGNIFICANT WIND DAMAGE OVER LARGE AREAS.
IN THE CASE OF DOWNBURSTS, THE DAMAGE IS GENERALLY
REFERRED TO AS STRAIGHT-LINE WIND DAMAGE SINCE FALLEN
TREES GENERALLY LINE UP IN THE SAME DIRECTION.  IN MAINE
AND NEW HAMPSHIRE, MOST THUNDERSTORM WIND DAMAGE IS
CAUSED BY DOWNBURSTS.

A SPECIAL TYPE OF DOWNBURST IS THE MICROBURST.
MICROBURSTS GET THEIR NAME BECAUSE THEY GENERALLY AFFECT
A MUCH SMALLER GEOGRAPHICAL AREA, BUT THE WINDS IN A
MICROBURST CAN BE VERY INTENSE.  LIKE THE GENERAL
DOWNBURST, MOST OF THE DAMAGE WITH MICROBURSTS LINES UP
IN ONE DIRECTION, ALTHOUGH, THERE MAY BE A TENDENCY FOR
THE DAMAGE TO RADIATE OUTWARD.  MICROBURSTS ARE USUALLY
ACCOMPANIED BY HEAVY RAIN AND/OR HAIL AND CAN HAVE WINDS
AS STRONG AS THOSE IN A SMALL TORNADO.

UNDER CERTAIN ATMOSPHERIC CONDITIONS, THUNDERSTORMS CAN
BEGIN TO DEVELOP A CIRCULATION WITHIN THE THUNDERSTORM
CLOUD.  THESE STORMS ARE OFTEN CALLED MESO-CYCLONES
BECAUSE OF THE COUNTER-CLOCKWISE CIRCULATION THAT
DEVELOPS WITHIN THE STORM.  THE UPDRAFTS AND DOWNDRAFTS
IN THESE STORMS CAN PERSIST FOR HOURS AS THE STORM MOVES
ALONG ITS PATH.  SEVERE WINDS AND HAIL ARE ALSO MORE
LIKELY WITH MESO-CYCLONES, AND IF THE ROTATION WITHIN THE
STORM BECOMES MORE INTENSE, THERE IS AN INCREASING
POSSIBILITY THAT THE STORM MIGHT PRODUCE A TORNADO.
NATIONAL WEATHER SERVICE DOPPLER RADAR ALLOWS
METEOROLOGISTS TO MONITOR AIR MOVEMENT WITHIN THESE
STORMS AND TO SEE THE DEVELOPMENT AND STRENGTH OF ANY
CIRCULATION WITHIN THE STORM.

DURING THE SUMMER OF 2011, MAINE AND NEW HAMPSHIRE HAD
NUMEROUS THUNDERSTORMS THAT PRODUCED DAMAGING STRAIGHT-
LINE WINDS.  FORTUNATELY, NO ONE WAS KILLED BY ANY OF THE
FALLING TREES CAUSED BY THESE WINDS.


HAIL

THE CIRCULATION THAT ACCOMPANIES A MESO-CYCLONE IS ALSO A
FACTOR IN HAIL FORMATION.  HAIL INITIALLY FORMS WHEN
LIQUID WATER DROPLETS ARE CARRIED UPWARD BY THE UPDRAFT
TO A LEVEL WHERE THE DROPLETS FREEZE.  EVENTUALLY, THE
SMALL HAIL STONE MAY BEGIN TO FALL DOWNWARD, ONLY TO BE
CAUGHT ONCE AGAIN BY THE PERSISTENT UPDRAFT OF A MESO-
CYCLONE.  EACH TIME THE HAILSTONE GOES THROUGH THIS
PROCESS, IT GETS LARGER AND HEAVIER.  EVENTUALLY, THE
HAILSTONE WILL BE BLOWN AWAY FROM THE UPDRAFT OR WILL
BECOME TOO HEAVY FOR THE UPDRAFT TO SUPPORT AND THE
HAILSTONE WILL FALL TO THE GROUND.

IN MAINE AND NEW HAMPSHIRE, HAIL IS FAIRLY COMMON DURING
WELL- DEVELOPED SUMMERTIME THUNDERSTORMS.  ALTHOUGH MOST
HAIL THAT REACHES THE GROUND IN NORTHERN NEW ENGLAND IS
AN INCH OR LESS IN DIAMETER, OCCASIONALLY HAILSTONES OVER
2 INCHES IN DIAMETER WILL FALL.  LARGE HAILSTONES CAN
FALL AT SPEEDS FASTER THAN 100 MPH AND CAN DO
CONSIDERABLE DAMAGE TO CARS, HOMES, AND BUILDINGS, AND
CAN BE A SIGNIFICANT THREAT TO PEOPLE, AS WELL.

DURING 2012 IN NEW HAMPSHIRE, THE MOST SIGNIFICANT HAIL
REPORT WAS 2.00 INCHES IN WESTMORELAND IN CHESHIRE
COUNTY. IN MAINE IN 2012, THERE WERE NO REPORTS OF HAIL 2
INCHES OR GREATER.

HERE ARE SOME OF THE LARGER HAILSTONES REPORTED IN
NORTHERN NEW ENGLAND SINCE 1995.

3.00 INCHES
     JUN 19 1995  SPRINGFIELD, MAINE
     JUN 22 2008  MT. CARDIGAN, NEW HAMPSHIRE

2.75 INCHES
     AUG 24 1998  TAMWORTH/FREEDOM, NEW HAMPSHIRE
     JUN  1 2011  KINGFIELD, MAINE

2.50 INCHES
     AUG  4 2007  FT. KENT, MAINE
     MAY 27 2011  BINGHAM, MAINE

2.00 INCHES
     AUG 18 1996  LINCOLNVILLE, MAINE
     JUL 11 2006  EXETER, NEW HAMPSHIRE
     JUL 11 2006  HAMPTON FALLS, NEW HAMPSHIRE
     JUL  9 2007  CONCORD, NEW HAMPSHIRE
     AUG  4 2007  GRAND ISLE, MAINE
     AUG  4 2007  CARIBOU, MAINE
     AUG 30 2007  ROME, MAINE
     JUL 18 2008  STRAFFORD, NEW HAMPSHIRE
     JUN  5 2010  SOUTH PARIS, MAINE
     MAY 29 2012  WESTMORELAND, NEW HAMPSHIRE

FOR BOTH SEVERE WINDS (58 MPH OR GREATER) AND LARGE HAIL
(1 INCH OR GREATER IN DIAMETER), THE NATIONAL WEATHER
SERVICE ISSUES SEVERE THUNDERSTORM WATCHES AND WARNINGS.
 A WATCH INDICATES THAT THE ATMOSPHERIC CONDITIONS ARE
FAVORABLE FOR SEVERE WEATHER TO DEVELOP.  A WARNING
INDICATES THAT SEVERE WEATHER IS IMMINENT OR IS ALREADY
OCCURRING.  IF YOU HEAR A WARNING FOR YOUR AREA, BE
PREPARED TO SEEK A SAFE SHELTER IF YOU ARE IN THE PATH OF
THE STORM.

HERE IS A LIST OF THE OTHER TOPICS THAT WILL BE COVERED
IN PUBLIC INFORMATION STATEMENTS ISSUED BY THE NATIONAL
WEATHER SERVICE THIS WEEK.

THURSDAY....TORNADOES
FRIDAY......FLASH FLOODS

$$

JENSENIUS
NATIONAL WEATHER SERVICE
GRAY, MAINE

NNNN
National Weather Service National Headquarters
