Public Information Statement
Issued by NWS Portland, ME

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MEZ007>009-012>014-018>022-023>028-NHZ001>015-301200


PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE GRAY ME
720 AM EDT WED APR 29 2015

THE NATIONAL WEATHER SERVICE HAS DECLARED THE WEEK OF
APRIL 27TH  THROUGH MAY 1ST, 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 2014, MAINE AND NEW HAMPSHIRE HAD NUMEROUS
THUNDERSTORMS THAT PRODUCED DAMAGING STRAIGHT-LINE WINDS.  ON JULY
15TH, A MICROBURST HIT THE TOWN OF YORK, MAINE, WITH ESTIMATED WINDS
OF 80 MPH.  THE MICROBURST SNAPPED AND UPROOTED TREES IN AN AREA
ABOUT 1.5 MILES WIDE AND 1 MILE LONG, AND DAMED HOMES AND VEHICLES.
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 2014 IN NEW HAMPSHIRE, THE MOST SIGNIFICANT HAIL REPORT WAS
2.00 INCHES IN STATHAM. IN MAINE, THERE WERE NO REPORTS OF HAIL 2
INCHES OR GREATER IN 2014.

HERE ARE SOME OF THE LARGER HAILSTONES REPORTED IN MAINE AND NEW
HAMPSHIRE 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
     JUN 29 2013  ANDOVER, MAINE
     SEP 11 2013  WINDHAM, MAINE
     SEP 12 2013  UPTON, MAINE
     JUL  3 2014  STATHAM, 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

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