NOUS42 KTBW 171000 PNSTBW FLZ039-042-043-048>052-055>057-060>062-065-181200- PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL 600 AM EDT WED OCT 17 2007 ...LA NINA HAS RETURNED... THE OUTLOOK FROM THE CLIMATE PREDICTION CENTER FOR THE UPCOMING WINTER OF 2007-2008 IS CALLING FOR A CONTINUATION OF WEAK TO MODERATE LA NINA CONDITIONS OVER THE PACIFIC OCEAN. LA NINA IS CHARACTERIZED BY A COOLING OF EQUATORIAL PACIFIC WATERS WHICH AFFECTS LARGE SCALE WEATHER SYSTEMS AROUND THE GLOBE. OVER THE UNITED STATES THIS USUALLY MEANS THAT THE JET STREAM IS FARTHER NORTH BUT MORE VARIABLE IN STRENGTH AND POSITION. THIS LEADS TO LESS STORMY CONDITIONS ACROSS THE FLORIDA PENINSULA. COLD FRONTS WILL MOVE ACROSS THE REGION...BUT SINCE THE MID/UPPER LEVEL ENERGY USUALLY REMAINS WELL NORTH OF THE AREA...RAINFALL IS LIMITED AND WILL LIKELY BE BELOW NORMAL. THE LINK BETWEEN LA NINA AND WINTERTIME TEMPERATURES IS A LITTLE BIT WEAKER. WITH THE AVERAGE STORM TRACK FARTHER NORTH DURING LA NINA WE USUALLY SEE DRIER AIR OVER THE STATE WITH MORE FAIR WEATHER DAYS. THE DRIER AIR LEADS TO WARMER DAYTIME AND SLIGHTLY COOLER NIGHTTIME TEMPERATURES THAT RESULT IN SLIGHTLY ABOVE AVERAGE TEMPERATURES ACROSS THE AREA. DURING LA NINA...FREEZES ARE POSSIBLE INTO CENTRAL AND SOUTH FLORIDA. HOWEVER...THE IMPACT OF THE NORTH ATLANTIC OSCILLATION (NAO) AND ARCTIC OSCILLATION (AO) PLAY A LARGE ROLE IN CONTROLLING TEMPERATURES ACROSS FLORIDA DURING THE WINTER AND EARLY SPRING. THESE OSCILLATIONS SHIFT ON A MONTHLY AND SOMETIMES WEEKLY BASIS AND TYPICALLY ARE NOT INCLUDED IN LONG TERM FORECASTS. DURING LA NINA CONDITIONS THE LIKELY CAUSE OF FREEZING TEMPERATURES IS RADIATIONAL COOLING UNDER CLEAR SKIES AND CALM WINDS. THIS IS UNLIKE EL NINO WITH ADVECTIVE FREEZES WHERE COLD AIR IS DRAGGED SOUTHWARD BEHIND LOW PRESSURE SYSTEMS THAT PASS ACROSS THE STATE. LONG TERM AVERAGES INDICATE TWO TO FOUR DAYS OF FREEZING TEMPERATURES EACH WINTER ACROSS INLAND PORTIONS OF CENTRAL FLORIDA WITH ONLY ABOUT ONE FREEZE OVER SOUTHWEST FLORIDA. FARTHER NORTH ACROSS THE NATURE COAST MANY MORE DAYS OCCUR WITH FREEZING TEMPERATURES. SOME LOCATIONS SUCH AS INVERNESS AND BUSHNELL HAVE ON AVERAGE AROUND 10 DAYS...WHILE FURTHER NORTH NEAR CHIEFLAND THERE ARE AS MANY AS 20 DAYS WITH TEMPERATURES FALLING TO OR BELOW FREEZING EACH WINTER. THE LAST LA NINA TO AFFECT THE REGION WAS DURING THE WINTER OF 2005- 2006. ALTHOUGH THIS LA NINA WAS RATHER WEAK...RAINFALL DURING THIS WINTER WAS GENERALLY BELOW NORMAL. HOWEVER...THERE WERE A COUPLE OF DAYS...SUCH AS JANUARY 1 2006 AT SARASOTA-BRADENTON AND FEBRUARY 3 2006 ACROSS THE TAMPA BAY AREA...THAT HAD EXTRAORDINARY RAINFALL AMOUNTS. BEFORE THIS THE LAST LA NINA WAS A PROLONGED EPISODE THAT LASTED FROM THE FALL OF 1998 TO SPRING 2001. DURING THESE THREE WINTERS RAINFALL ACROSS MUCH OF THE AREA WAS BELOW NORMAL WITH MOST AREAS RECEIVING ONLY ABOUT 50 PERCENT OF THE NORMAL RAINFALL. THE CURRENT LA NINA IS NOT EXPECTED TO APPROACH THE MAGNITUDE OF THE 1998-2001 EVENT...BUT AFTER A RATHER DRY WINTER EARLIER THIS YEAR FOLLOWED BY NEAR TO BELOW AVERAGE RAINFALL THIS PAST SPRING AND SUMMER...THE OUTLOOK OF BELOW NORMAL RAINFALL FOR THE UPCOMING WINTER WILL LIKELY LEAD TO CONTINUED WATER RESTRICTIONS ACROSS PORTIONS OF WEST CENTRAL AND SOUTHWEST FLORIDA . RESIDENTS OF WEST CENTRAL AND SOUTHWEST FLORIDA SHOULD REMAIN INFORMED OF POTENTIAL WEATHER EVENTS THIS UPCOMING WINTER AND EARLY SPRING. STAY TUNED TO LOCAL MEDIA OUTLETS AND NOAA WEATHER RADIO FOR THE LATEST WEATHER INFORMATION. FOR MORE INFORMATION ON LA NINA INCLUDING GRAPHICS...PLEASE VISIT THE NATIONAL WEATHER SERVICE TAMPA BAY PAGE AT WWW.WEATHER.GOV/TAMPABAY OR THE CLIMATE PREDICTION CENTER AT WWW.CPC.NOAA.GOV $$ PRC/CP