ZCZC NYCWRKPS5 000
  TTAA00 KNYC 161833
  CTZ005>012-NJZ002>006-011-NYZ067>081-301000-
  
  PUBLIC INFORMATION STATEMENT
  NATIONAL WEATHER SERVICE UPTON NY
  600 AM EDT THU OCT 29 2009
  
  ...THIS IS WINTER WEATHER AWARENESS WEEK... 
  
  PLEASE JOIN THE NATIONAL WEATHER SERVICE AND THE NEW YORK STATE 
  DISASTER PREPAREDNESS COMMISSION IN PROMOTING WINTER WEATHER 
  EDUCATION INCLUDING SAFETY.
  
  TODAY'S THEME IS WINTER FLOODS.
  
  COASTAL STORMS CAN CAUSE HEAVY RAIN AND HIGH WINDS THAT LAST MORE 
  THAN 12 HOURS.
  
  HEAVY RAIN CAN RESULT IN FLOODING OF RIVERS...STREAMS AND LOW LYING 
  POOR DRAINAGE AREAS. FOLLOWING THE BLIZZARD OF JANUARY 7TH AND 8TH 
  OF 1996...STRONG SOUTH WINDS...MILD TEMPERATURES...A RIPE SNOWPACK 
  AND HEAVY RAIN RESULTED IN WIDESPREAD SEVERE URBAN...RIVER AND 
  SMALL STREAM FLOODING INCLUDING MANY ROOF COLLAPSES ACROSS THE REGION.
  
  HIGH WINDS COMBINED WITH HIGH ASTRONOMICAL TIDES CAN PRODUCE COASTAL 
  OR TIDAL FLOODING. 
  
  WHAT CAUSES TIDAL FLOODING?
  
  PROLONGED ONSHORE OR EAST TO NORTHEAST WINDS OVER A LONG DISTANCE AND 
  CONSTANT SPEED CAUSE WATER TO PILE ALONG THE COAST. THIS PROCESS IS 
  KNOWN AS TIDAL PILING. THE ONSHORE WINDS ARE USUALLY PRODUCED BY A 
  COMBINATION OF HIGH PRESSURE NORTH OF THE AREA AND LOW PRESSURE 
  ALONG THE COAST...SOUTH OF THE AREA. THE DURATION AND STRENGTH OF 
  THE ONSHORE WINDS AND THE RATE AND MAGNITUDE OF PRESSURE FALLS 
  TOGETHER WITH THE HEIGHT OF ASTRONOMICAL TIDES WILL DETERMINE THE 
  MAGNITUDE AND AREAL EXTENT OF FLOODING.
  
  TIDAL PILING WILL CAUSE ABOVE NORMAL TIDES...ESPECIALLY AROUND THE 
  TIMES OF HIGH TIDE. HOWEVER...TIDAL PILING WILL ALSO PREVENT THE HIGH 
  TIDE FROM RECEDING. THIS WATER WILL STILL BE ALONG THE COAST FOR THE 
  NEXT HIGH TIDE...AGGRAVATING THE PROBLEM. IN THIS CASE...TIDAL 
  FLOODING WILL BE WORSE WITH EACH PASSING HIGH TIDE. THE COMBINATION 
  OF A SLOW MOVING STORM AND STRONG HIGH PRESSURE CAUSES A PROLONGED 
  ONSHORE WIND...WHICH CAN AFFECT SEVERAL TIDAL CYCLES. DURING THE 
  DECEMBER 1992 NOREASTER...SIGNIFICANT FLOODING OCCURRED ON 4 
  CONSECUTIVE DAYS.
  
  ALTHOUGH RAINFALL CAN COMPOUND TIDAL FLOODING PROBLEMS...IT IS NOT A 
  CAUSE OF TIDAL FLOODING. DURING THE HALLOWEEN NOR'EASTER OF 
  1991...WIDESPREAD SIGNIFICANT TIDAL FLOODING OCCURRED UNDER PARTLY 
  SUNNY SKIES.
  
  ANOTHER WINTER PROBLEM FOR LOCATIONS TO THE NORTH AND WEST OF NEW 
  YORK CITY IS FLOODING CAUSED BY ICE JAMS IN THE RIVERS.
  
  AS RIVER FLOW INCREASES...WATER LEVELS RISE. SINCE ICE THAT COVERS 
  THE RIVERS IS LIGHTER THAN WATER IT WILL TEND TO FLOAT. UNDER THE 
  PRESSURE IT WILL BREAK UP AND THEN MOVE DOWNSTREAM IN THE CURRENT 
  UNTIL IT RUNS INTO AN OBSTRUCTION SUCH AS A BEND...ISLAND...OR WIDE 
  SHALLOW AREA. WHEN THIS HAPPENS THE ICE WILL OFTEN STOP AND PILE UP 
  INTO A JAM. THIS IN TURN BLOCKS THE FLOW OF THE RIVER AND CAN RESULT 
  IN WATER OVERFLOWING THE BANKS AND FLOODING AREAS ADJACENT TO THE 
  RIVER. IN ADDITION...AS THE WATER RISES THE PRESSURE CAN BREAK THE 
  ICE JAM AND RELEASE A SUDDEN SURGE OF WATER AND ICE DOWN THE RIVER.
  
  WHILE ICE JAMS ARE NOT UNUSUAL...IT IS NEARLY IMPOSSIBLE TO PREDICT 
  EXACTLY WHEN OR WHERE A JAM WILL FORM...OR IF AND WHEN ONE WILL 
  BREAK. 
  
  FRIDAY'S STATEMENT COVERS WATCHES...WARNINGS AND ADVISORIES.
  
  $$