PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 830 AM EDT THU AUG 16 2007 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THE MAIN FACTORS WHICH USUALLY INFLUENCE THE SEASONAL CLIMATE OUTLOOK INCLUDE: 1) EL NINO AND LA NINA - WHICH COMPRISE EL NINO/SOUTHERN OSCILLATION OR ENSO. 2) TRENDS - APPROXIMATED BY THE DIFFERENCE BETWEEN THE MOST RECENT 10-YEAR MEAN OF TEMPERATURE OR 15-YEAR MEAN OF PRECIPITATION FOR A GIVEN LOCATION AND TIME OF YEAR AND THE 30-YEAR CLIMATOLOGY PERIOD (CURRENTLY 1971-2000). THE OCN TOOL REPRESENTS THE TREND. 3) THE TROPICAL 30-60 DAY OSCILLATION - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS. 4) THE NORTH ATLANTIC OSCILLATION (NAO) AND THE PACIFIC NORTH AMERICAN (PNA) PATTERNS - WHICH AFFECT THE TEMPERATURE ANOMALY PATTERN ESPECIALLY DURING THE COLD SEASONS. THESE PHENOMENA ARE CURRENTLY KNOWN TO BE PREDICTABLE ONLY OVER A WEEK OR SO. 5) PERSISTENTLY DRY OR WET SOILS IN THE SUMMER AND SNOW AND ICE COVER ANOMALIES IN THE WINTER. THESE FACTORS TEND TO PERSIST FOR LONG PERIODS AND ACT AS A KIND OF MEMORY IN THE CLIMATE SYSTEM. 6) STATISTICAL FORECAST TOOLS - CANONICAL CORRELATION ANALYSIS (CCA)... AND SCREENING MULTIPLE LINEAR REGRESSION (SMLR). 7) DYNAMICAL FORECAST MODELS... INCLUDING THE NCEP CLIMATE FORECAST SYSTEM (CFS). 8) AN OBJECTIVE CONSOLIDATION (ABBREVIATED CON IN THE TEXT) OF THE OCN... CCA... SMLR AND CFS FORECASTS IS USED AS A FIRST GUESS IN PREPARING THE FORECAST MAPS. THIS TECHNIQUE MAKES OPTIMUM USE OF THE KNOWN SKILL OF OUR FORECAST TOOLS. EQUATORIAL PACIFIC SEA SURFACE TEMPERATURES (SSTS) ARE CURRENTLY SLIGHTLY ABOVE NORMAL IN THE WESTERN PACIFIC AND BELOW NORMAL EAST OF THE DATE LINE. SSTS IN THE NINO 3.4 REGION (FROM 5N TO 5S AND 170W TO 120W) ARE CONSIDERED A GOOD INDICATOR OF THE STRENGTH OF EL NINO (WARMER THAN NORMAL SSTS) OR LA NINA (COLDER THAN NORMAL SSTS). SSTS IN THE NINO 3.4 REGION HAVE BEEN ABOUT ONE-HALF OF ONE DEGREE C BELOW THE LONG-TERM AVERAGE DURING THE LAST TWO WEEKS SUGGESTING THE POSSIBILITY OF A TRANSITION FROM CURRENT ENSO-NEUTRAL CONDITIONS TO LA NINA CONDITIONS DURING THE NEXT TWO MONTHS. THE NOAA THRESHOLD FOR LA NINA ONSET IS WHEN THE THREE-MONTH MEAN SSTS FOR THE NINO 3.4 REGION ARE MORE THAN ONE-HALF OF ONE DEGREE BELOW THE LONG-TERM AVERAGE. THERE IS A SIGNIFICANT CHANCE THAT THE THRESHOLD FOR LA NINA WILL BE SURPASSED FOR THE SEPTEMBER-OCTOBER-NOVEMBER (SON) SEASON. THOUGH A RAPID TRANSITION OF THE NINO 3.4 REGION SSTS FROM EL NINO TO NEUTRAL CONDITIONS OCCURRED EARLY IN 2007... AND DYNAMICAL MODEL PREDICTIONS AT THAT TIME CALLED FOR AN ONSET OF LA NINA BY THE BEGINNING OF SUMMER 2007... SSTS DID NOT DECREASE AS EARLY OR AS RAPIDLY IN THE CENTRAL PACIFIC AS FORECAST... DUE IN PART TO INTRASEASONAL VARIABILITY. STATISTICAL MODELS... WHICH EARLY IN 2007 HAD FORECAST A CONTINUATION OF ENSO-NEUTRAL SSTS IN THE CENTRAL PACIFIC OR A SLOW DECREASE... ARE NOW IN GREATER AGREEMENT WITH THE DYNAMICAL MODELS ALTHOUGH STILL FORECASTING WARMER CENTRAL PACIFIC SSTS THAN MOST DYNAMICAL MODEL FORECASTS. THREE-MONTH MEAN SSTS IN THE CENTRAL PACIFIC ARE EXPECTED TO BE NEAR OR BELOW THE THRESHOLD FOR LA NINA THROUGH THE DECEMBER-JANUARY-FEBRUARY (DJF) SEASON... AND LA NINA CONDITIONS COULD HAVE SOME INFLUENCE ON THE SEASONAL OUTLOOK INTO THE EARLY PART OF 2008. UNCERTAINTY IN THE PROJECTED PACIFIC SSTS INCREASES BY THE SPRING OF 2008. THE TEMPERATURE OUTLOOK FOR SEPTEMBER-OCTOBER-NOVEMBER (SON) 2007 CALLS FOR ABOVE NORMAL TEMPERATURES OVER MOST OF THE UNITED STATES. THE CHANCES OF ABOVE NORMAL TEMPERATURES ARE SOMEWHAT HIGHER THAN NORMAL FOR THE SOUTHWEST DUE LARGELY TO THE LONG-TERM TRENDS AND ONGOING DROUGHT CONDITIONS. SSTS ALONG THE PACIFIC COAST WHICH ARE NEAR OR BELOW NORMAL SHOULD MODERATE TEMPERATURES THERE. FOR SON 2007 ABOVE MEDIAN PRECIPITATION IS EXPECTED ALONG THE GULF AND ATLANTIC COASTS PARTLY DUE TO AN EXPECTED ACTIVE TROPICAL ATLANTIC STORM SEASON AND ALSO DUE TO THE LONG-TERM TRENDS. THERE IS A GREATER CHANCE OF ABOVE MEDIAN PRECIPITATION FOR THE PACIFIC NORTHWEST AND NORTHERN PLAINS AND A GREATER CHANCE OF BELOW MEDIAN PRECIPITATION IN THE SOUTHWEST DUE TO AN ENHANCED LIKELIHOOD OF LA NINA CONDITIONS AND ALSO THE LONG-TERM TRENDS. BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE: HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/TOOLS/BRIEFING CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS AVERAGE SEA SURFACE TEMPERATURES (SSTS) IN THE EQUATORIAL TROPICAL PACIFIC IN THE LAST THREE MONTHS ARE CONSISTENT WITH ENSO-NEUTRAL CONDITIONS. IN RECENT WEEKS TEMPERATURES HAVE BEEN FROM 0.5 TO 1.5 DEGREES C BELOW NORMAL FROM 170W TO THE SOUTH AMERICAN COAST... AND IN THE LAST TWO WEEKS HAVE BEEN AT LEAST 0.5 DEGREES C BELOW NORMAL IN THE NINO 3.4 REGION. UPPER OCEAN HEAT CONTENT (THE AVERAGE TEMPERATURE IN THE UPPER 300 METERS OF THE OCEAN) WHICH HAS FLUCTUATED IN THE LAST COUPLE OF MONTHS DECREASED IN JULY. CONVECTIVE ACTIVITY HAS BEEN SUPPRESSED OVER MOST OF THE EQUATORIAL PACIFIC AND THE LOW-LEVEL EASTERLIES HAVE BEEN ENHANCED OVER THE CENTRAL PACIFIC CONSISTENT WITH DEVELOPING LA NINA CONDITIONS. SHOULD LA NINA CONDITIONS DEVELOP... IT IS ANTICIPATED THAT THEY WILL PERSIST INTO THE BEGINNING OF 2008. PROGNOSTIC DISCUSSION OF SST FORECASTS STATISTICAL MODELS INDICATE A SLOW PROGRESSION TOWARDS LA NINA. DYNAMICAL MODELS HAVE CONSISTENTLY FORECAST A GREATER AND MORE RAPID DECREASE IN SSTS... THOUGH THE STATISTICAL AND DYNAMICAL MODELS APPEAR MORE CONSISTENT IN RECENT FORECASTS... AND THE CFS INDICATES A SLOWER TRANSITION TO LA NINA THAN IN ITS PREVIOUS FORECASTS. NINO 3.4 SSTS ARE PREDICTED BY THE CFS TO DROP TO BETWEEN 0.5 AND 1 DEGREES C BELOW NORMAL FOR AUGUST AND MORE THAN 1 DEGREE C BELOW NORMAL FOR SEPTEMBER. THE CFS FORECASTS ASO AND SON 2007 SSTS TO BE NEAR 1 DEGREE C BELOW NORMAL FOR NINO 3.4. A NINO 3.4 FORECAST BASED ON THE CONSOLIDATION OF THE CFS... CANONICAL CORRELATION... CONSTRUCTED ANALOGS AND A MARKOV MODEL INDICATES SSTS IN THE RANGE FROM A FEW TENTHS TO SLIGHTLY GREATER THAN 1 DEGREE C BELOW NORMAL ARE MOST LIKELY FOR SON 2007 THROUGH JFM 2008. THE CHANCES OF A WARM EL NINO EVENT ARE NEARLY EXCLUDED OUT TO MAM 2008 WITH PROBABILITIES LESS THAN 3% FOR EACH SEASON. THE LIKELIHOOD OF A RETURN TO ENSO-NEUTRAL SSTS BECOMES GREATER BEGINNING FMA 2008. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS THE OUTLOOK FOR SON 2007 IS BASED ON THE CONSOLIDATION (CON) TOOL... WHICH IS A SKILL-WEIGHTED OBJECTIVE BLEND OF CFS... CCA... SMLR AND OCN. THE OUTLOOK ALSO CONSIDERED TREND-ADJUSTED COMPOSITES BASED ON AN ENHANCED CHANCE OF LA NINA CONDITIONS. THE CON AND LA NINA COMPOSITES ARE NOT AVAILABLE FOR ALASKA... SO THE FORECAST THERE IS BASED LARGELY ON A SUBJECTIVE ANALYSIS OF THE CFS WITH CONSIDERATION OF THE OCN... CCA AND SMLR. THE OUTLOOKS FOR SON 2007 THROUGH JFM 2008... THOUGH BASED LARGELY ON THE CON... ARE ADJUSTED FOR THE INCREASED LIKELIHOOD OF THE DEVELOPMENT OF LA NINA CONDITIONS. FOR THE SPRING AND SUMMER OF 2008... THE SEASONAL OUTLOOKS ARE INCREASINGLY INFLUENCED BY THE LONG-TERM TRENDS. PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2007 TO SON 2008 TEMPERATURE: THE TEMPERATURE OUTLOOK FOR SON 2007 CALLS FOR AN ENHANCED PROBABILITY OF ABOVE NORMAL TEMPERATURES FOR MOST OF THE CONUS. THIS IS BASED LARGELY ON THE CONSOLIDATION AND ITS COMPONENTS WITH SUPPORT FROM THE IRI FORECAST AND TREND-ADJUSTED LA NINA COMPOSITES. NEAR OR BELOW NORMAL SSTS ALONG THE PACIFIC COAST ARE EXPECTED TO MODERATE TEMPERATURES IN COASTAL AREAS. THE SEASONAL OUTLOOKS FOR OND 2007 THROUGH SON 2008 ARE BASED PRIMARILY ON THE CONSOLIDATION. THE TREND DOMINATES THE TEMPERATURE CONSOLIDATION THROUGH MUCH OF THE YEAR AND ESPECIALLY IN WINTER. AN INCREASED PROBABILITY OF LA NINA CONDITIONS LED TO A REDUCTION OF THE AREA OF ABOVE NORMAL TEMPERATURES IN THE NORTHWEST AND A REDUCTION OF THE PROBABILITIES OVER THE NORTHERN PLAINS AND GREAT LAKES REGION FROM OND 2007 TO JFM 2008. PRECIPITATION: THE PRECIPITATION OUTLOOK FOR SON 2007 CALLS FOR AN ENHANCED PROBABILITY OF ABOVE MEDIAN PRECIPITATION ALONG THE GULF COAST AND THE ATLANTIC COAST FROM THE MID-ATLANTIC STATES TO FLORIDA DUE TO THE TREND AND THE LIKELIHOOD OF A MORE ACTIVE THAN NORMAL ATLANTIC TROPICAL SEASON. ABOVE MEDIAN PRECIPITATION IS AGAIN FORECAST FOR THE GULF AND ATLANTIC COASTS FOR ASO AND SON 2008 DUE TO THE TREND AND GREATER ATLANTIC TROPICAL ACTIVITY IN THE LAST DECADE. THE SON 2007 OUTLOOK CALLS FOR BELOW MEDIAN PRECIPITATION IN THE SOUTHWEST AND ABOVE MEDIAN PRECIPITATION IN THE NORTHWEST AND NORTHERN PLAINS SUPPORTED BY THE CONSOLIDATION... AND TREND-ADJUSTED LA NINA COMPOSITES. THE AREA OF ABOVE MEDIAN PRECIPITATION IN THE NORTHERN PLAINS IS LARGELY DUE TO THE TREND AND IS ALSO IN THE ASO AND SON 2008 CONSOLIDATION AND OUTLOOKS. FROM OND 2007 THROUGH JFM 2008 BELOW MEDIAN PRECIPITATION IS EXPECTED ACROSS MOST OF THE SOUTHERN UNITED STATES WITH GREATER PROBABILITIES FOR THE SOUTHWEST AND SOUTHEAST STATES SUPPORTED BY BOTH THE CONSOLIDATION AND BY TREND-ADJUSTED COMPOSITES CONSIDERING THE INCREASED LIKELIHOOD OF LA NINA CONDITIONS. AN ENHANCED LIKELIHOOD OF ABOVE MEDIAN PRECIPITATION IS SHOWN FOR THE PACIFIC NORTHWEST THROUGH DJF 2008 ALSO CONSISTENT WITH POSSIBLE LA NINA CONDITIONS. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). FORECASTER: DAN COLLINS FOR A DESCRIPTION OF OF THE STANDARD FORECAST TOOLS - THEIR SKILL- AND THE FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT HTTP:/WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/DISC.HTML (USE LOWER CASE LETTERS) INFORMATION ON THE FORMATION OF SKILL OF THE CAS FORECASTS MAY BE FOUND AT: HTTP://WWW.CPC.NCEP.NOAA.GOV/SOILMST/FORECASTS.HTML (USE LOWERCASE LETTERS) NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR VALID PERIOD. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM RANGE FORECASTS SHOULD BE CONSULTED. THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT MONTH ON THU SEP 20 2007 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001 FORECAST RELEASE. $$