PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 830 AM EDT THU SEP 20 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. LA NINA CONDITIONS HAVE DEVELOPED ACROSS THE EQUATORIAL PACIFIC OCEAN DURING THE PAST FEW MONTHS... WITH BELOW AVERAGE SEA SURFACE TEMPERATURES (SSTS) OBSERVED BETWEEN 170E AND THE COAST OF SOUTH AMERICA BY THE MIDDLE OF SEPTEMBER. 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 DECREASED CONSISTENTLY SINCE EARLY JULY... REACHING -0.9 LAST WEEK. 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. IT IS NOW EXPECTED THAT THIS THRESHOLD WILL BE REACHED FOR THE JULY - SEPTEMBER (JAS) SEASON. MANY DYNAMICAL MODEL PREDICTIONS HAVE BEEN PREDICTING A MORE RAPID ONSET OF LA NINA THAN HAS ACTUALLY OCCURRED... AS SSTS DID NOT DECREASE AS EARLY OR AS RAPIDLY IN THE CENTRAL PACIFIC AS FORECAST... DUE IN PART TO INTRASEASONAL VARIABILITY. MANY 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. SEASONAL SSTS IN THE CENTRAL PACIFIC ARE EXPECTED TO BE BELOW THE LA NINA THRESHOLD THROUGH THE JANUARY-MARCH (JFM) SEASON... AND LA NINA CONDITIONS ARE ANTICIPATED TO HAVE SOME INFLUENCE ON THE GLOBAL CLIMATE INTO THROUGH THE EARLY PART OF 2008. UNCERTAINTY IN THE PROJECTED PACIFIC SSTS INCREASES BY THE SPRING OF 2008. THE TEMPERATURE OUTLOOK FOR OCTOBER-NOVEMBER-DECEMBER (OND) 2007 CALLS FOR AN INCREASED CHANCE OF ABOVE NORMAL TEMPERATURES OVER MOST OF THE UNITED STATES. THE ONLY EXCEPTIONS ARE ALONG THE CANADIAN BORDER FROM MONTANA WESTWARD AND IN THE SOUTHEAST ALONG THE SOUTH ATLANTIC COAST. HISTORICALLY BOTH OF THESE REGIONS EXPERIENCE NEAR OR BELOW AVERAGE TEMPERATURES ASSOCIATED WITH LA NINA. 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 OND 2007 ABOVE MEDIAN PRECIPITATION IS EXPECTED IN THE PACIFIC NORTHWEST AND A GREATER CHANCE OF BELOW MEDIAN PRECIPITATION IN THE SOUTHWEST AND PARTS OF THE SOUTHERN PLAINS DUE TO AN ENHANCED LIKELIHOOD OF LA NINA CONDITIONS AND ALSO THE LONG-TERM TRENDS. THE CHANCE OF ABOVE MEDIAN PRECIPITATION HAS BEEN SHIFTED INTO NORTHERN CALIFORNIA DUE TO THE MORE RAPID AND POTENTIALLY STRONGER DEVELOPMENT OF LA NINA CONDITIONS. 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 BELOW AVERAGE SEA SURFACE TEMPERATURES (SSTS) IN THE EASTERN EQUATORIAL TROPICAL PACIFIC EXPANDED WESTWARD DURING AUGUST AND SEPTEMBER AND NOW EXTEND FROM 170 DEG E TO THE WEST COAST OF SOUTH AMERICA. IN RECENT WEEKS TEMPERATURES HAVE GENERALLY BEEN MORE THAN 0.5 DEGREES C BELOW NORMAL FROM THE DATE LINE TO THE SOUTH AMERICAN COAST... WITH DEPARTURES MORE THAN 1.0 DEGREES C OBSERVED IN MOST REGIONS EAST OF 160 DEG W. CONSISTENT WITH THIS PATTERN... ALL FOUR NINO REGIONS HAVE BECOME NEGATIVE... WITH NINO 4 BECOMING NEGATIVE FOR THE FIRST TIME SINCE FEBRUARY 2006 AND NINO 3.4 REACHING -0.9. UPPER OCEAN HEAT CONTENT (THE AVERAGE TEMPERATURE IN THE UPPER 300 METERS OF THE OCEAN) CONTINUED TO BE BELOW AVERAGE WITH TEMPERATURES AT THERMOCLINE DEPTH 1 DEG C TO 4 DEG C BELOW AVERAGE. RECENTLY CONVECTION HAS BEEN SUPPRESSED OVER MOST OF THE EQUATORIAL PACIFIC AND ENHANCED OVER THE MARITIME CONTINENT AND THE LOW-LEVEL EASTERLIES HAVE BEEN ENHANCED OVER THE CENTRAL PACIFIC. AT UPPER LEVELS... EQUATORIAL WESTERLY WIND ANOMALIES WERE OBSERVED OVER THE CENTRAL PACIFIC... FLANKED BY A WEAK ANOMALOUS CYCLONIC COUPLET. THESE FEATURES ARE ALSO CONSISTENT WITH LA NINA CONDITIONS. PROGNOSTIC DISCUSSION OF SST FORECASTS MANY STATISTICAL MODELS INDICATE WEAK LA NINA CONDITIONS PERSISTING THROUGH THE WINTER... WHILE MOST DYNAMICAL MODELS PREDICT A GREATER AND MORE RAPID DECREASE IN SSTS. THE CFS INDICATES A CONTINUED DECREASE IN SSTS THROUGH OND 2007... WITH SSTS DEPARTURES REMAINING BELOW -1.0 DEG C THROUGH JFM 2008. A NINO 3.4 FORECAST BASED ON THE CONSOLIDATION OF THE CFS... CANONICAL CORRELATION... CONSTRUCTED ANALOGS AND A MARKOV MODEL INDICATES SSTS ANOMALIES DECREASE TO NEAR -1.0 DEG C FOR OND... REMAIN NEAR -1.0 THROUGH DJF... BEFORE RETURNING TO ENSO NEUTRAL CONDITIONS DURING MAM 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 IN FMA 2008. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS THE OUTLOOK FOR OND 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 LA NINA CONDITIONS. THE CON IS NOT AVAILABLE FOR ALASKA... SO THE FORECAST THERE IS BASED LARGELY ON ANALYSIS OF THE CFS WITH CONSIDERATION OF THE OCN... CCA AND SMLR. THE OUTLOOKS FOR OND 2007 THROUGH FMA 2008... ARE BASED ON A SUBJECTIVE BLENDING OF LA NINA COMPOSITES WITH THE CON. FOR MAM THROUGH OND 2008 THE SEASONAL OUTLOOKS ARE INCREASINGLY INFLUENCED BY THE LONG-TERM TRENDS. PROGNOSTIC DISCUSSION OF OUTLOOKS - OND 2007 TO OND 2008 TEMPERATURE: THE TEMPERATURE OUTLOOK FOR OND 2007 CALLS FOR AN ENHANCED PROBABILITY OF ABOVE NORMAL TEMPERATURES FOR LARGE PARTS OF THE CONUS. THIS IS BASED LARGELY ON THE CONSOLIDATION AND ITS COMPONENTS WITH SUPPORT FROM THE IRI FORECAST .. WITH MODIFICATIONS FROM LA NINA COMPOSITES. NEAR OR BELOW NORMAL SSTS ALONG THE PACIFIC COAST ARE EXPECTED TO MODERATE TEMPERATURES IN COASTAL AREAS. THE SEASONAL OUTLOOKS FOR NDJ 2007 THROUGH FMA 2008 ARE BASED PRIMARILY ON A SUBJECTIVE BLENDING OF LA NINA COMPOSITES WITH THE CONSOLIDATION TOOL. THE TREND DOMINATES THE TEMPERATURE CONSOLIDATION THROUGH MUCH OF THE YEAR AND ESPECIALLY IN WINTER. THE DEVELOPING LA NINA LED TO A REDUCTION OF THE AREA OF ABOVE NORMAL TEMPERATURES IN THE NORTHWEST AND IN THE SOUTHEAST DURING OND AND NDJ 2007. THE REGION OF ABOVE NORMAL TEMPERATURES WAS REDUCED ACROSS THE NORTHWEST AND NORTHERN PLAINS DURING DJF 2007 AND FMA 2008... WITH NEAR NORMAL TEMPERATURES FAVORED ACROSS PARTS OF THIS REGION DURING JFM 2008... AS THE TRENDS FOR ABOVE AVERAGE TEMPERATURES IN THIS REGION ARE OFFSET BY THE DEVELOPING LA NINA EVENT WHICH HISTORICALLY HAS FAVORED BELOW AVERAGE TEMPERATURES. PRECIPITATION: THE PRECIPITATION OUTLOOK FOR OND 2007 CALLS FOR AN ENHANCED PROBABILITY OF ABOVE MEDIAN PRECIPITATION IN THE PACIFIC NORTHWEST AND FOR BELOW MEDIAN PRECIPITATION IN THE SOUTHWEST. BOTH OF THESE FEATURES ARE FAVORED BY TREND-ADJUSTED LA NINA COMPOSITES AND ARE ALSO CONSISTENT WITH THE CONSOLIDATION TOOL. FROM NDJ 2007 THROUGH FMA 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 2007 ALSO CONSISTENT WITH LA NINA CONDITIONS. ABOVE MEDIAN PRECIPITATION IS ALSO FAVORED IN THE OHIO AND TENNESSEE VALLEYS FROM DJF 2007 THROUGH FMA 2008. THIS OUTLOOK IS ALSO CONSISTENT WITH TREND-ADJUSTED LA NINA COMPOSITES. ALL FORECASTS FROM JJA THROUGH OND 2008 ARE BASED ON LONG TERM TRENDS AND THE CONSOLIDATION TOOL... WITH THE LIKELIHOOD OF ABOVE NORMAL PRECIPITATION INCREASED ALONG PARTS OF THE GULF COAST DURING THE PEAK OF NEXT YEARS HURRICANE SEASON. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). FORECASTER: MIKE HALPERT 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 OCT 18 2007 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001 FORECAST RELEASE. $$