PROGNOSTIC DISCUSSION FOR LONG-LEAD OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EDT THURSDAY AUGUST 16 2001 BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOK . . . . . . . . THESE OUTLOOKS PRIMARILY REFLECT THE EXPECTED U.S. CLIMATE ANOMALIES FOR ENSO- NEUTRAL CONDITIONS ... AND THE LONG-TERM TREND AS ESTIMATED BY OCN. SOIL MOISTURE CONDITIONS FACTOR INTO THE OUTLOOK FOR SON. EQUATORIAL PACIFIC SSTS ARE NOW SLIGHTLY ABOVE NORMAL IN THE WEST AND CENTRAL PACIFIC AND SLIGHTLY BELOW NORMAL NEAR SOUTH AMERICA. SOME STATISTICAL AND DYNAMIC PREDICTIONS OF NINO 3.4 SSTS INDICATE WEAK WARM EPISODE (EL NINO) CONDITIONS BY THE END OF THE YEAR - WHILE OTHERS PREDICT ANOMALIES VERY NEAR ZERO THROUGHOUT THE UPCOMING COOL SEASON. WHILE IT IS LIKELY THAT EQUATORIAL PACIFIC SSTS WILL BE ABOVE AVERAGE - THE ANOMALIES ARE WEAK AND NOT LIKELY TO PRODUCE THE LARGE-SCALE ATMOSPHERIC EFFECTS ASSOCIATED WITH STRONG EL NINO EVENTS THIS COOL SEASON. CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS NEAR-NORMAL ATMOSPHERIC AND OCEANIC CONDITIONS CONTINUE TO PREVAIL IN THE TROPICAL PACIFIC IN JULY. SST ANOMALIES ALONG THE EQUATOR CURRENTLY ARE JUST OVER 0.5 DEG C IN THE CENTRAL PACIFIC AND ARE STILL AROUND -1 DEG C NEAR THE SOUTH AMERICAN COAST. THE ABOVE NORMAL OCEAN TEMPERATURE EXTEND FROM THE SURFACE TO OVER 200 M DEPTH OVER MOST OF THE CENTRAL PACIFIC OCEAN AND THIS AREA OF POSITIVE SUB-SURFACE TEMPERATURE ANOMALIES CONTINUES TO MOVE EASTWARD. THE ATMOSPHERIC CIRCULATION IN THE TROPICAL PACIFIC HAS BEEN VERY CLOSE TO NORMAL FOR SEVERAL MONTHS NOW. TAKEN TOGETHER - THESE OBSERVATIONS SIGNIFY AN END TO THE COLD EVENT CONDITIONS THAT HAVE PREVAILED FOR OVER 3 YEARS. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS WEAK WARM ENSO CONDITIONS ARE PREDICTED TO SLOWLY DEVELOP OVER THE NEXT SEVERAL SEASONS. MOST DYNAMIC MODELS (NCEP - ECMWF - SCRIPPS) GRADUALLY INCREASE NINO 3.4 SSTS TO BETWEEN 0.5 AND 1 DEG C ABOVE NORMAL BY YEARS END. ON THE OTHER HAND - MANY STATISTICAL MODELS (CONSTRUCTED ANALOG - MARKOV MODEL - LINEAR INVERSE MODELING) PREDICT NEUTRAL OR COOL NINO 3.4 SSTS FOR THIS COOL SEASON - ALTHOUGH THE CCA PREDICTION IS FOR ABOVE NORMAL SSTS. NONE OF THE MODELS PREDICT STRONG ANOMALIES FOR THE EQUATORIAL PACIFIC IN THE NEXT FEW SEASONS. A CONSOLIDATION OF THREE NCEP TOOLS BASED ON THEIR PAST PERFORMANCE INDICATES NEAR NORMAL CONDITIONS WILL PREVAIL THROUGH THE WINTER - WITH GRADUALLY INCREASING ANOMALIES THAT REACH AROUND 0.5 DEGREES BY LATE NEXT SPRING. CONSIDERING THAT TEMPERATURES ANOMALIES ARE ALREADY POSITIVE - NINO 3.4 SEA SURFACE TEMPERATURES ARE EXPECTED TO REMAIN POSITIVE FOR THE REMAINDER OF THE YEAR - GRADUALLY INCREASING TO MARGINALLY WARM ENSO CONDITIONS BY LATE IN THE WINTER. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOK THE STATISTICAL TOOLS ... CCA - OCN AND SMLR ... WERE CONSULTED AT ALL LEAD TIMES. THE CONSTRUCTED ANALOG SOIL MOISTURE-BASED FORECAST TOOL (CAS) WAS USED ONLY FOR THE FIRST LEAD. BECAUSE THE INITIAL ENSO STATE IS NEAR ZERO AND IS FORECAST TO BE WEAK - THE NCEP COUPLED MODEL WAS CONSIDERED ONLY WHERE IT AGREED WITH A CONSENSUS OF OTHER GENERAL CIRCULATION MODELS RUN AT OTHER CENTERS FOR CLIMATE PREDICTION. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2001 TO SON 2002 TEMPERATURE: MOST FORECAST TOOLS INDICATE WARMER-THAN-NORMAL TEMPERATURES FOR SON 2001 - DJF 2001 IN THE SOUTHWEST U.S.. DRY INITIAL SOIL MOISTURE CONDITIONS IN TEXAS EXTENDS THIS AREA OF ABOVE NORMAL TEMPERATURES INTO MOST OF TEXAS FOR SON. OCN - CCA - AND SMLR PREDICT ABOVE NORMAL TEMPERATURES FOR SOUTHERN FLORIDA THROUGH OND. CCA GIVES STRONG INDICATIONS FOR BELOW NORMAL TEMPERATURES IN WESTERN ALASKA IN THE FALL. EQUATORIAL PACIFIC SSTS ARE WARMER THAN ANTICIPATED IN LAST MONTHS FORECAST. THIS SKEWS THE EXPECTED SEASONAL CLIMATE RESPONSE SLIGHTLY FROM NEUTRAL TOWARD WARM ENSO EVENT COMPOSITES (ALTHOUGH THE OUTLOOK STILL PRIMARILY REFLECTS NEUTRAL EVENTS) AND RESULTS IN A CHANGE IN THE OUTLOOK FOR THE UPPER MIDWEST FROM THE BELOW NORMAL TEMPERATURES ISSUED LAST MONTH TO CLIMATOLOGY ON THE CURRENT OUTLOOK. WITH WEAK ENSO FORCING THE PRIMARY FACTOR INFLUENCING THE SEASONAL CLIMATE ANOMALIES OVER THE EASTERN U.S. THIS WINTER WILL BE THE PHASE OF THE ARCTIC OSCILLATION (AO). THE AO IS NOT PREDICTABLE BEYOND THE LIMITS OF WEATHER PREDICTION MODELS - BUT RECENT TRENDS SUGGEST THAT THE SEASONAL FREQUENCY OF THE AO NEGATIVE PHASE IS GREATER THAN IT WAS IN THE EARLY AND MID 1990S. SINCE THE NEGATIVE AO PHASE IS ASSOCIATED WITH COOLER THAN NORMAL CONDITIONS THROUGHOUT THE EAST - THE AO TREND COUNTERACTS RECENT TRENDS TOWARD WARMER-THAN-NORMAL WINTER TEMPERATURES OVER MUCH OF THE EASTERN U.S. IN FAVOR OF CLIMATOLOGICAL ODDS. THE AO HAS LITTLE INFLUENCE IN THE WESTERN U.S. AND THEREFORE TEMPERATURE TRENDS ACCOUNT FOR THE LARGE AREA OF ABOVE NORMAL TEMPERATURES PREDICTED IN THE WESTERN U.S. FROM JFM THROUGH AMJ. THE TEMPERATURE OUTLOOK FOR NEXT SUMMER AND FALL IS BASED ON OCN. THE RECENT COOL SUMMERS IN THE EASTERN U.S. AND WARM SUMMERS IN THE MIDWEST ARE OPPOSITE THE DECADAL TRENDS IN BOTH AREAS AND REDUCE THE PROBABILITY ANOMALIES IN EACH OF THOSE AREAS TOWARD CLIMATOLOGY WHEN COMPARED TO LAST MONTHS FORECAST. NOTE: THE CHANGE IN NORMALS IMPLEMENTED IN MAY 2001 HAS NOT RESULTED IN ANY MAJOR CHANGES IN THE OUTLOOK PATTERNS... ALTHOUGH SLIGHT WEAKENING IS SHOWN IN SOME OF THE TRENDS FOR WARMTH... AS MIGHT BE EXPECTED. . . . . . . . . PRECIPITATION: ABOVE MEDIAN PRECIPITATION OVER PORTIONS OF THE SOUTHEAST IN SON IS INDICATED BY OCN AND WILL BE AIDED BY INITIALLY WET SOIL CONDITIONS SUPPORTING THE RECYCLING MOISTURE LOCALLY. THE PRECIPITATION OUTLOOK FOR OND 2001 THROUGH JFM 2002 INCLUDES A REGION OF ABOVE MEDIAN PRECIPITATION IN THE SOUTH-CENTRAL U.S. WHICH COMES FROM OCN. CCA - SMLR - AND CMP INDICATE BELOW MEDIAN PRECIPITATION IN THE DESERT SOUTHWEST FOR NDJ AND DJF 2001. OCN INDICATES ABOVE MEDIAN PRECIPITATION IN THE PACIFIC NORTHWEST FOR AMJ AND MJJ 2002 - HOWEVER THE SIGNAL IS WEAKER THAN LAST MONTHS FORECAST BECAUSE OF THE DRY CONDITIONS EXPERIENCED THERE IN SPRING 2001. ABOVE MEDIAN PRECIPITATION OVER THE NORTHERN PLAINS IN JJA AND JAS 2002 IS BASED ON OCN. FOR A DESCRIPTION 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/MULTI-SEASON/ 13_SEASONAL_OUTLOOKS/TOOLS (USE LOWER CASE LETTERS) INFORMATION ON THE FORMULATION AND SKILL OF THE CAS FORECASTS MAY BE FOUND AT: HTTP://WWW.CPC.NCEP.NOAA.GOV/SOILMST/FORECASTS.HTML (USE LOWER CASE LETTERS) NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR VALID PERIODS. 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 THURSDAY SEPTEMBER 13 2001. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. NNNN NNNN