Craig Koplien: Weather or Not

Tornadoes & Severe Thunderstorms

Story Created: Apr 23, 2008

Story Updated: Apr 23, 2008

Tornadoes & Severe Thunderstorms

Craig Koplien

email:  ckoplien@todaystmj4.com

Today is the Day 3 of Tornado and Severe Weather Awareness Week in Wisconsin.  All week I'll be posting important information here on the blog that you can use to help keep your family safe.




...TORNADO AND SEVERE WEATHER AWARENESS WEEK IS APRIL 21-25...


-------------------------------------------------------------------
... SEVERE THUNDERSTORMS...
-------------------------------------------------------------------

SEVERE THUNDERSTORMS CONTAIN MULTIPLE DANGERS THAT CAN THREATEN
YOUR SAFETY AND PERSONAL PROPERTY IN ANY PART OF THE COUNTRY AND AT
ANY TIME OF THE YEAR. ALTHOUGH THESE STORMS CAN BE FAIRLY SMALL AND
BRIEF...AVERAGING AROUND 10 TO 15 MILES IN DIAMETER AND HAVE AN
AVERAGE LIFETIME OF 20 TO 30 MINUTES...THEY CAN CAUSE A TREMENDOUS
AMOUNT OF DAMAGE IN THIS SHORT TIME FRAME. SOME SUPERCELL
THUNDERSTORMS CAN HAVE A LIFESPAN OF 1 HOUR OR MORE.

SEVERE THUNDERSTORMS ARE DEFINED AS HAVING ONE OR MORE OF THE
FOLLOWING:

...A TORNADO

...PEAK WINDS IN EXCESS OF 58 MILES PER HOUR /50 KNOTS/

...HAIL AT LEAST 3/4 OF AN INCH IN DIAMETER /APPROXIMATELY THE
   SIZE OF A PENNY/

AS IN ANY THUNDERSTORM...SEVERE THUNDERSTORMS ALSO FREQUENTLY
CONTAIN DANGEROUS LIGHTNING.

WISCONSIN SEES AN AVERAGE OF 30 TO 40 DAYS A YEAR WITH
THUNDERSTORMS. HERE'S THE BREAKDOWN ON SHORT-LIVED SEVERE WEATHER
EVENTS IN WISCONSIN...

   ***ROUGHLY 52 PERCENT OF ALL SEVERE EVENTS IN THE STATE ARE
      STRAIGHT LINE WIND EVENTS /WIND SPEEDS 58 MPH OR HIGHER/

   ***31 PERCENT ARE HAIL EVENTS WITH HAIL-STONES THAT ARE AT
      LEAST 3/4 INCH IN DIAMETER

   ***7 PERCENT ARE TORNADO EVENTS

HERE ARE SOME MORE INTERESTING FACTS ABOUT SEVERE THUNDERSTORMS IN
THE STATE OF WISCONSIN...

...HAIL CAN OCCUR IN ANY COUNTY.  HOWEVER...THE SOUTHERN HALF OF
   WISCONSIN HAS A GREATER NUMBER OF RECORDED HAIL EVENTS.

...EACH SUMMER THERE ARE ABOUT 15 SEVERE THUNDERSTORMS IN WISCONSIN
   WHICH PRODUCE HAIL 1.5 INCHES IN DIAMETER /PING PONG BALL SIZE/ OR
   LARGER.

...THE LARGEST HAILSTONE IN WISCONSIN WAS ABOUT 5.7 INCHES IN
   DIAMETER. THIS LARGE HAILSTONE FELL ON MAY 22 IN 1921 ON THE
   NORTH SIDE OF WAUSAU.

...SEVERE THUNDERSTORMS CAN OCCUR AT ANY TIME OF THE DAY AND AT ANY
   TIME OF THE YEAR.  THE PEAK SEASON FOR SEVERE THUNDERSTORMS IS
   BETWEEN APRIL AND SEPTEMBER AND MOST LIKELY TO OCCUR IN THE LATE
   AFTERNOON OR EVENING HOURS.

...ON SUNDAY MAY 31 1998 HURRICANE-FORCE WINDS IN EXCESS OF 100 MPH
   RAKED SEVERAL COUNTIES IN SOUTH-CENTRAL AND SOUTHEAST WISCONSIN.
   A PEAK GUST OF 128 MPH WAS MEASURED IN SOUTHERN DODGE COUNTY. ONE
   PERSON IN SOUTHERN WASHINGTON COUNTY WAS CRUSHED TO DEATH WHILE
   SLEEPING DURING THE POWERFUL STORM WHEN A TREE FELL ON THEIR
   HOME.  HURRICANE WINDS START AT 74 MPH.

...FROM 1970 TO 2007...WISCONSIN HAS HAD 22 DAYS WITH DOCUMENTED
   STRAIGHT-LINE THUNDERSTORM DOWN-BURST WINDS OF 100 MPH OR HIGHER.

...ON JULY 4TH IN 1977...A POWERFUL THUNDERSTORM SYSTEM GENERATED
   WIND GUSTS OF OVER 100...WITH SOME GUSTS ESTIMATED AS HIGH AS 150
   TO 155 MPH.  SEVERE TREE DAMAGE OCCURRED OVER A DISTANCE OF 166
   MILES.

...SEVERE THUNDERSTORM WATCHES AND WARNINGS...
IT IS IMPORTANT TO KNOW THE DIFFERENCE BETWEEN A SEVERE THUNDERSTORM
WATCH AND A WARNING. WHEN A SEVERE THUNDERSTORM WATCH IS ISSUED BY
THE STORM PREDICTION CENTER...IT MEANS THAT SEVERE THUNDERSTORMS ARE
POSSIBLE IN AND CLOSE TO THE WATCH AREA. WHEN A SEVERE THUNDERSTORM
WARNING IS ISSUED BY LOCAL NATIONAL WEATHER SERVICE OFFICES...IT
MEANS THAT SEVERE THUNDERSTORMS ARE IMMINENT OR OCCURRING IN YOUR
AREA.

ALWAYS MAKE SURE THAT YOU KNOW THE NAME OF THE COUNTY IN WHICH YOU
RESIDE. WATCHES AND WARNINGS ARE ISSUED ON A COUNTY BASIS.  IF
SEVERE THUNDERSTORMS ARE A POSSIBILITY IN YOUR AREA...MONITOR NOAA
ALL HAZARDS WEATHER RADIO...OR LOCAL TV OR RADIO STATIONS FOR THE
LATEST SEVERE THUNDERSTORM WATCHES AND WARNINGS IN YOUR AREA.

DURING ANY TYPE OF THUNDERSTORM...ESPECIALLY SEVERE THUNDERSTORMS...
YOU NEED TO TAKE ACTION TO PROTECT YOURSELF. MOVE TO A STURDY
BUILDING AND STAY AWAY FROM WINDOWS. DO NOT USE CORDED TELEPHONES
UNTIL THE STORM HAS PASSED YOUR AREA. IN CASE OF AN EMERGENCY...
USE A CELL PHONE. IT HAS BEEN PROVEN SAFE TO USE CELL PHONES DURING
A THUNDERSTORM BECAUSE THEY DO NOT HAVE A PHYSICAL CONNECTION TO
THE OUTSIDE. ALWAYS REMEMBER THAT THUNDERSTORMS CAN AND DO PRODUCE
TORNADOES WITH LITTLE OR NO ADVANCE WARNING. REMEMBER...IF YOU CAN
HEAR THUNDER...YOU ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING.


-------------------------------------------------------------------
STRAIGHT-LINE THUNDERSTORM WINDS...
-------------------------------------------------------------------

...SIGNATURE OF STRAIGHT-LINE WINDS...
STRAIGHT-LINE WINDS ARE OFTEN RESPONSIBLE FOR MOST OF THE WIND DAMAGE
ASSOCIATED WITH A THUNDERSTORM. THESE WINDS ARE OFTEN CONFUSED WITH
TORNADOES BECAUSE OF SIMILAR TYPES OF DAMAGE AND WIND SPEEDS. HOWEVER
THE STRONG DAMAGING WINDS ASSOCIATED WITH STRAIGHT-LINE WINDS ARE
UNLIKE THE ROTATING WINDS OF A TORNADO. IF YOU WERE TO SURVEY THE
DAMAGE PATTERN LEFT BY STRAIGHT-LINE WINDS...YOU WOULD SEE DEBRIS...
SUCH AS UPROOTED TREES...LAID OUT IN NEARLY PARALLEL ROWS.

...DOWN-BURST BASICS...
DOWN-BURSTS ARE ONE EXAMPLE OF DAMAGING STRAIGHT LINE WINDS. A
DOWN-BURST IS A SMALL AREA OF RAPIDLY DESCENDING RAIN AND RAIN-COOLED
AIR BENEATH A THUNDERSTORM. WIND SPEEDS IN SOME OF THE STRONGER
DOWN-BURSTS CAN REACH 100 TO 150 MILES PER HOUR WHICH IS SIMILAR TO
THAT OF A STRONG TORNADO. THE WINDS PRODUCED FROM A DOWN-BURST OFTEN
TRAVEL IN ONE DIRECTION...AND THE WORST DAMAGE IS USUALLY ON THE
FORWARD SIDE OF THE DOWN-BURST. HOWEVER...SOMETIMES THEY WILL HIT
THE GROUND AND SPREAD OUT IN ALL DIRECTIONS. IN THAT CASE...DAMAGE
WILL TEND TO FAN OUT FROM A LARGE CENTER POINT.

...DERECHOS...
ANOTHER CATEGORY OF STRAIGHT-LINE WINDS COMMON TO THE MIDWEST ARE
KNOWN AS DERECHOS. DERECHOS USUALLY OCCUR IN THE MIDWESTERN STATES
IN THE LATE SPRING AND SUMMER. DERECHOS ARE CREATED BY THE MERGING OF
MANY THUNDERSTORM CELLS...PARTICULARLY JUST NORTH OF A WARM
FRONT...INTO A LARGE CLUSTER OR A SOLID SQUALL LINE EXTENDING FOR
MANY MILES PERPENDICULAR TO THE WARM FRONT. THE WIDTH OF SUCH A
CLUSTER CAN RANGE FROM 20 TO 65 MILES AND THE WIDTH OF THE SQUALL
LINE CAN RANGE FROM 10 TO 20 MILES. THE LENGTH OF THE LINE CAN REACH
100 MILES OR MORE.

IN EXTREME CASES...THESE STORMS CAN CREATE MAXIMUM WIND GUSTS OF 150
MPH. NOT ONLY CAN A DERECHO CONTAIN INCREDIBLY STRONG STRAIGHT-LINE
WINDS...IT IS ALSO CAPABLE OF PRODUCING SMALL TORNADOES ON THE
NORTHERN HOOK-END OF THE LINE AS WELL AS IN INDIVIDUAL SUPERCELLS
EMBEDDED WITHIN THE SQUALL LINE. AS A RESULT...THESE TYPES OF SYSTEMS
CAN BE EXTREMELY DANGEROUS AND PRODUCE WIDESPREAD INCREDIBLE DAMAGE.

...HURRICANE-FORCE THUNDERSTORM WIND FREQUENCY...
ON AVERAGE...WISCONSIN EXPERIENCES HURRICANE-FORCE WIND GUSTS OF 74
MPH OR HIGHER ON 5 DAYS PER YEAR. ON AVERAGE... WISCONSIN
EXPERIENCES A THUNDERSTORM WIND GUST OF 100 MPH OR MORE ON ONE DAY
EVERY OTHER YEAR.

...EXAMPLES OF POWERFUL DOWNBURSTS...
ON AUGUST 21 2002...NUMEROUS OCCURRENCES OF THUNDERSTORM WINDS BLEW
THROUGH PRIMARILY SOUTHEAST WISCONSIN...INCLUDING A POWERFUL 100 MPH
MACRO-BURST THAT TORE THROUGH BROOKFIELD WISCONSIN. MANY LARGE TREES
AND STREET SIGNS WERE TOPPLED. IN NEARBY MILWAUKEE WISCONSIN...AN 80
MPH GUST RIPPED A 100 FOOT LONG BLIMP FROM IT/S MOORING AND BLEW IT
SIX BLOCKS THROUGH THE DOWNTOWN AREA. DAMAGE TOTALED IN THE MILLIONS
OF DOLLARS. THANKFULLY...NO ONE WAS INJURED OR KILLED IN THESE
EVENTS.

ALWAYS KEEP IN MIND THAT MAJOR DAMAGE TO A HOME...BUILDING OR ANY
PERSONAL PROPERTY CAN BE CAUSED BY A VARIETY OF DIFFERENT STRAIGHT-
LINE WIND EVENTS. ALWAYS TAKE COVER WHEN STRONG THUNDERSTORM WINDS
THREATEN.

AS WITH ANY SEVERE WEATHER...STAY TUNED TO NOAA ALL HAZARDS WEATHER
RADIO OR YOUR LOCAL TV OR RADIO STATIONS FOR THE LATEST FORECAST AND
ANY SEVERE WEATHER WATCHES OR WARNINGS.

FOR ADDITIONAL SEVERE WEATHER INFORMATION...UP TO DATE FORECASTS...
AND ANY WATCHES/WARNINGS/ADVISORIES PLEASE VISIT OUR WEB SITE AT...

HTTP://WWW.WEATHER.GOV/MKX/                 /ALL LOWER CASE/

On Demand