...PENNSYLVANIA WEATHER EMERGENCY PREPAREDNESS WEEK...

THIS IS THE THIRD OF A FIVE PART SERIES ON SEVERE WEATHER SAFETY 
WHICH WILL RUN EACH DAY DURING PENNSYLVANIA/S WEATHER EMERGENCY 
PREPAREDNESS WEEK.
 
...FLASH FLOODS...

THE NUMBER ONE SEVERE WEATHER RELATED KILLER IN THE UNITED STATES IS 
FLOODING. MOST FLOOD-RELATED DEATHS ARE A RESULT OF BEING WASHED 
AWAY WHILE TRYING TO CROSS A FLOODED ROADWAY ON FOOT OR IN AN 
AUTOMOBILE. CURRENTLY...THE NATIONAL WEATHER SERVICE IS ATTEMPTING 
TO RAISE PUBLIC AWARENESS ON THE DANGERS OF FLOODS WITH ITS "TURN 
AROUND DON/T DROWN" CAMPAIGN. WHETHER YOU ARE DRIVING OR 
WALKING...IF YOU COME TO A FLOODED ROAD...TURN AROUND, DON/T 
DROWN!!! YOU WILL NOT KNOW THE DEPTH OF THE WATER NOR WILL YOU KNOW 
THE CONDITION OF THE ROAD UNDER THE WATER.

FLOODS THAT OCCUR ON SMALL STREAMS AND CREEKS WITHIN SIX HOURS OF 
THE CAUSATIVE EVENT ARE KNOWN AS FLASH FLOODS. CAUSATIVE EVENTS CAN 
BE HEAVY RAIN...A DAM BREAK...OR AN ICE JAM FORMATION OR BREAK. 
FLASH FLOODS ARE THE DEADLIEST OF ALL FLOODS AND ARE THE MOST 
DIFFICULT TO FORECAST IN ADVANCE BECAUSE THEY ARE GENERALLY VERY 
LOCALIZED. FOR THIS REASON...WARNING TIME FOR FLASH FLOODS CAN BE 
VERY SHORT. 

SEVERAL FACTORS CONTRIBUTE TO FLASH FLOODING. THE TWO KEY ELEMENTS 
ARE RAINFALL INTENSITY AND DURATION. INTENSITY IS THE RATE OF 
RAINFALL...AND DURATION IS HOW LONG THE RAIN PERSISTS. FLASH FLOODS 
CAN ROLL BOULDERS...TEAR OUT TREES...DESTROY BUILDINGS AND 
BRIDGES...AND SCOUR OUT NEW CHANNELS. RAPIDLY RISING WATER CAN REACH 
HEIGHTS OF 30 FEET OR MORE!!! IN SOME PARTS OF THE COUNTRY...FLASH 
FLOOD-PRODUCING RAINS CAN ALSO TRIGGER CATASTROPHIC MUD SLIDES. 
OFTEN FLASH FLOODING IS CAUSED BY SLOW MOVING 
THUNDERSTORMS...THUNDERSTORMS REPEATEDLY MOVING OVER THE SAME 
AREA...OR RAINS FROM HURRICANES OR TROPICAL STORMS. THESE EVENTS ARE 
ALL WELL FORECAST BY THE NATIONAL WEATHER SERVICE AND THUS WHEN 
THESE INGREDIENTS ARE PRESENT...YOUR SHOULD BE READY TO TAKE QUICK 
ACTION SHOULD FLOODING BEGIN. 

MANY FLOOD RELATED DEATHS OCCUR BECAUSE PEOPLE UNDERESTIMATE THE 
POWER OF WATER. FOR EXAMPLE...ONLY 6 INCHES OF QUICKLY MOVING WATER 
CAN EASILY KNOCK A PERSON OF THEIR FEET. ONLY TWO FEET OF WATER...AN 
AMOUNT THAT SOME TIRES ARE EVENT LARGER THAN...CAN EASILY PICK UP 
MOST VEHICLES AND MOVE THEM AT WILL. 

HEAVY RAINS FROM THE REMNANTS OF HURRICANE JEANNE DUMPED 4 TO 9 
INCHES OF RAIN OVER SOUTHEASTERN PENNSYLVANIA IN JUST A FEW HOURS ON 
SEPTEMBER 28, 2004. A PHILADELPHIA RESIDENT DROWNED WHEN SHE WAS 
SWEPT OFF HER FEET WHILE WAITING FOR A BUS AS URBAN RUNOFF MOVED IN 
HER DIRECTION. HEAVY RAIN FROM THE REMNANTS OF HURRICANE IVAN 
PRODUCED FLASH FLOODING IN THE HILLY TERRAIN OF THE LEHIGH VALLEY 
AND POCONO MOUNTAINS OF PENNSYLVANIA ON SEPTEMBER 18, 2004 RESULTING 
IN MASSIVE PROPERTY DAMAGE.

EVEN IN THE ABSENCE OF TROPICAL SYSTEMS, HEAVY RAINS FROM SLOW 
MOVING THUNDERSTORMS CAN PRODUCE FLASH FLOODING AS WELL. SUCH WAS 
THE CASE IN BURLINGTON COUNTY NEW JERSEY ON JULY 12, 2004 WHEN SLOW 
MOVING THUNDERSTORMS DUMPED UP TO 13 INCHES OF RAIN IN LESS THAN 12 
HOURS OVER PARTS OF THE RANCOCAS CREEK WATERSHED. MASSIVE FLOODING 
ENSUED, AND APPROXIMATELY 44 DAMS WERE EITHER COMPROMISED OR 
DESTROYED. PRESIDENT BUSH DECLARED PARTS OF BURLINGTON AND CAMDEN 
COUNTIES A DISASTER AREA AS A RESULT OF THIS FLOODING.

...WHAT DOES A FLASH FLOOD WATCH MEAN?
A FLASH FLOOD WATCH MEANS THAT CONDITIONS ARE FAVORABLE FOR FLASH 
FLOODING TO DEVELOP SOMEWHERE IN THE WATCH AREA. A FLASH FLOOD WATCH 
IS USUALLY ISSUED FOR SEVERAL COUNTIES AT A TIME. UNDER IDEAL 
CONDITIONS, A FLASH FLOOD WATCH IS ISSUED EVEN BEFORE HEAVY RAIN 
MOVES INTO THE AREA. A FLASH FLOOD WATCH PROVIDES SITUATIONAL 
AWARENESS BY ALERTING RESIDENTS FLASH FLOODING IS A POSSIBILITY AND 
THAT CONDITIONS NEED TO BE WATCHED.

...WHAT DOES A FLASH FLOOD WARNING MEAN?
A FLASH FLOOD WARNING MEANS FLOODING HAS BEEN REPORTED...OR THAT 
FLOODING IS VERY PROBABLE BASED ON RAINFALL ESTIMATES INDICATED BY 
NWS DOPPLER RADAR. MOVE TO HIGHER GROUND IMMEDIATELY TO GET OUT OF 
THE DANGER AREA. NEVER DRIVE ACROSS BRIDGES COVERED WITH WATER OR 
THROUGH WATER-COVERED ROADWAYS. BE ESPECIALLY CAREFUL AT NIGHT WHEN 
FLOODED AREAS ARE HARDER TO SEE.


MARCH 10 TO MARCH 14 IS NATIONAL FLOOD SAFETY AWARENESS WEEK.  FOR 
MORE INFORMATION ON FLOOD SAFETY...INCLUDING THE NWS "TURN AROUND 
DON'T DROWN" CAMPAIGN, PLEASE VISIT THE NWS FLOOD AWARENESS WEBSITE 
AT WWW.FLOODSAFETY.NOAA.GOV.
 
$$