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PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 830 AM EDT THU AUG 21 2008 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 OCN TOOL AS 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). 3) THE TROPICAL 30-60 DAY OSCILLATION - SOMETIMES CALLED MADDEN JULIAN OSCILLATION (MJO) - 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) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE VARIABILITY AFFECTING BOTH THE TROPICS AND THE NORTH PACIFIC AND NORTH AMERICAN REGIONS, BUT WHICH VARIES ON A MUCH LONGER TIME-SCALE THAN ENSO. 6) 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. THE MAIN FORECAST TOOLS ARE AS FOLLOWS: 7) STATISTICAL FORECAST TOOLS - CANONICAL CORRELATION ANALYSIS (CCA), SCREENING MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOGUE (CA) AND ENSEMBLE CCA (ECCA). 8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM (CFS). 9) AN OBJECTIVE CONSOLIDATION (ABBREVIATED CON IN THE TEXT) OF THE OCN, CCA, SMLR, ECCA, 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. THE EQUATORIAL PACIFIC RETURNED TO ENSO NEUTRAL CONDITIONS DURING JUNE 2008, AND STAYED THERE DURING JULY. AS WITH PREVIOUS TRANSITIONS FROM A LA NINA TO AN ENSO NEUTRAL STATE, A WEAK LA NINA ATMOSPHERIC CIRCULATION CONTINUES OVER THE TROPICS. ABOVE NORMAL SSTS EXTEND WESTWARD FROM NEAR THE SOUTH AMERICAN COAST TO CURRENTLY AROUND 140 W LONGITUDE. BELOW NORMAL SUBSURFACE WATER TEMPERATURES IN THE CENTRAL EQUATORIAL PACIFIC HAVE WAXED AND WANED IN AREA, DEPTH AND MAGNITUDE IN RESPONSE TO PERIODS OF STRONGER AND WEAKER TRADES. THERE IS GOOD AGREEMENT IN THE FORECAST FOR NINO 3.4 SST ANOMALIES IN THE NEXT FEW MONTHS. A CONSENSUS OF THE FORECASTS MAINTAINS ENSO NEUTRAL CONDITIONS, WITH NINO 3.4 SST ANOMALIES SLIGHTLY BELOW ZERO INTO THE BEGINNING OF NEXT YEAR. THE TEMPERATURE OUTLOOK FOR SON 2008 CALLS FOR ABOVE NORMAL TEMPERATURES ACROSS A BROAD SWATH OF THE U.S., FROM THE SOUTHWEST DESERT AND CENTRAL SOUTHERN STATES INTO THE NORTHEAST. THESE EXPECTED AREAS OF ABOVE ARE DUE PRIMARILY TO RECENT TEMPERATURE TRENDS AND FOLLOW CLOSELY THE RECENT OBJECTIVE CONSOLIDATION FORECAST, WHICH INCLUDES THE STATISTICAL FORECAST TOOLS AND THE CFS FORECAST. THERE IS AN ENHANCED LIKELIHOOD OF ABOVE MEDIAN PRECIPITATION FOR SON 2008 FOR THE NORTHEAST AND PARTS OF THE HIGH AND CENTRAL PLAINS AS INDICATED BY THE OBJECTIVE CONSOLIDATION DUE SOMEWHAT TO RECENT TRENDS. THE INCREASED LIKELIHOOD OF ABOVE MEDIAN RAINFALL FOR THE GULF AND SOUTHERN ATLANTIC COASTS IS DUE TO RECENT TRENDS RESULTING FROM GREATER THAN NORMAL CLIMATOLOGICAL TROPICAL ACTIVITY. 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 LA NINA CONDITIONS WERE REPLACED BY ENSO NEUTRAL CONDITIONS DURING JUNE 2008, AS INDICATED BY SEA SURFACE TEMPERATURES (SSTS) ACROSS THE EQUATORIAL PACIFIC OCEAN. SSTS IN THE EAST-CENTRAL PACIFIC OCEAN ARE NOW LESS THAN ONE HALF OF ONE DEGREE CELSIUS BELOW ZERO. CONVECTION CONTINUES TO BE SLIGHTLY SUPPRESSED HOWEVER IN THE CENTRAL EQUATORIAL PACIFIC OCEAN, WHILE LOW LEVEL EASTERLY WINDS AND UPPER LEVEL WESTERLIES REMAIN ENHANCED OVER THE TROPICAL PACIFIC REGION, REFLECTING THE RESIDUAL INFLUENCE OF THE PAST LA NINA. SSTS ALONG THE EQUATOR ARE ABOVE NORMAL FROM ABOUT 140 W TO NEAR THE SOUTH AMERICAN COAST. SST ANOMALIES IN EARLY AUGUST WERE VERY NEAR ZERO IN THE NINO 3.4 REGION, FROM 170 W TO 120 W LONGITUDE AND 5 S TO 5 N LATITUDE. WATER TEMPERATURES IN THE UPPER 300 M OF THE EQUATORIAL PACIFIC HAVE INCREASED FROM FEBRUARY TO JUNE AND HAVE NOW STABILIZED SOMEWHAT ABOVE NORMAL FOR MUCH OF THE BASIN. BELOW NORMAL SUBSURFACE WATER TEMPERATURES AT GREATER DEPTH IN THE CENTRAL EQUATORIAL PACIFIC HAVE WAXED AND WANED IN AREA, DEPTH AND MAGNITUDE IN RESPONSE TO PERIODS OF STRONGER AND WEAKER TRADES. THE CURRENT STATE OF THE TROPICAL PACIFIC OCEAN AND ATMOSPHERE IS REPRESENTATIVE OF ENSO NEUTRAL CONDITIONS. PROGNOSTIC DISCUSSION OF SST FORECASTS MOST DYNAMICAL AND STATISTICAL SST FORECASTS FOR THE NINO 3.4 REGION PREDICT SSTS IN THE RANGE BETWEEN -0.5 AND +0.5 C, INDICATING ENSO-NEUTRAL CONDITIONS, THROUGH AUTUMN AND INTO NEXT YEAR. COMPARED TO LAST MONTHS FORECAST THE AGREEMENT AMONG TOOLS HAS MUCH INCREASED. ALL NCEP SST FORECASTS MAINTAIN SLIGHTLY NEGATIVE NINO 3.4 SST ANOMALIES THROUGH 2008 INTO 2009. A CONSOLIDATION OF NCEP FORECASTS SUGGESTS THAT NINO 3.4 SST ANOMALIES ARE MOST LIKELY TO REMAIN SLIGHTLY BELOW ZERO THROUGH THE SPRING OF 2009. CONSIDERING CURRENT OBSERVATIONS AND SST FORECASTS FROM STATISTICAL AND DYNAMICAL MODELS FROM NCEP AND FROM OTHER CENTERS NOT INCLUDED IN THE CONSOLIDATION FORECAST, ENSO NEUTRAL CONDITIONS ARE MOST LIKELY INTO EARLY NEXT YEAR WITH NINO 3.4 SST ANOMALIES EXPECTED TO BE WITHIN ONE HALF OF ONE DEGREE CELSIUS OF ZERO. ATMOSPHERIC CONDITIONS RELATED TO LA NINA OFTEN PERSIST FOR A FEW MONTHS AFTER SSTS RETURN TO ENSO NEUTRAL CONDITIONS - AND THIS YEAR IS NO EXCEPTION. RESIDUAL LA NINA ATMOSPHERIC CONDITIONS MAY SLIGHTLY ENHANCE TROPICAL ACTIVITY IN THE ATLANTIC AND SLIGHTLY SUPPRESS TROPICAL ACTIVITY IN THE EASTERN PACIFIC IN THE LATE SUMMER AND OR FALL.(SEE THE NOAA 2008 HURRICANE SEASON OUTLOOK DISCUSSION FOR MORE INFORMATION). PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR ALL LEAD TIMES ARE BASED ON THE CONSOLIDATION (CON), A SKILL-WEIGHTED AND CALIBRATED OBJECTIVE BLEND OF THE CFS, CCA, SMLR, OCN, AND ECCA FORECAST TOOLS. OTHER TOOLS - IRI EPCP AND CAS -ARE CONSIDERED AND USED FOR EXPERT ADJUSTMENT OF THE FORECAST. THE CON FORECAST IS NOT AVAILABLE FOR ALASKA, SO THE FORECAST THERE IS BASED ON THE FORECASTERS COMBINING OCN, CCA, SMLR AND THE CFS FORECASTS. THE ENSO STATE IS NOT EXPECTED TO HAVE AN IMPACT ON THE COMING SEASONAL TEMPERATURE AND PRECIPITATION OUTLOOKS, WITH THE EXCEPTION OF RESIDUAL INDIRECT EFFECTS OF THIS PAST WINTERS LA NINA. THE TEMPERATURE AND PRECIPITATION OUTLOOKS FROM SON 2008 TO SON 2009 CLOSELY FOLLOW THE CON FORECAST - THIS IS MORE OBVIOUS FOR TEMPERATURE THAN FOR PRECIPITATION BECAUSE THE LATTER HAS LITTLE SKILL. THE CFS FORECAST IS ONLY AVAILABLE AND PART OF THE CONSOLIDATION THROUGH FMA 2009. PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2008 TO SON 2009 TEMPERATURE: THE OUTLOOK FOR SON 2008 INDICATES ENHANCED PROBABILITIES OF ABOVE NORMAL TEMPERATURES FOR A BROAD SWATH EXTENDING FROM THE DESERT SOUTHWEST EXTENDING EASTWARD ACROSS TEXAS TO THE NORTHEAST U.S. WITH CURRENT ENSO NEUTRAL CONDITIONS EXPECTED ABOVE NORMAL TEMPERATURES IN THE SON 2008 SEASON ARE LARGELY DUE TO RECENT TEMPERATURE TRENDS. ABOVE NORMAL TEMPERATURES IN THE NORTHEASTERN U.S. ARE BASED ON THE CONSOLIDATION FORECAST. TEMPERATURE FORECASTS AFTER SON 2008 CLOSELY FOLLOW THE CONSOLIDATION FORECAST DERIVED FROM THE CFS, OCN, CCA, ECCA AND SMLR. CURRENT ENSO NEUTRAL CONDITIONS AND UNCERTAINTY IN THE FUTURE ENSO STATE MEAN THAT ALL SEASONAL TEMPERATURE FORECASTS ARE LARGELY IMPACTED BY TEMPERATURE TRENDS. THE AREA OF ENHANCED CHANCES OF ABOVE NORMAL TEMPERATURES EXPANDS TO INCLUDE MOST OF THE U.S. EXCEPT FOR THE AREA WEST OF THE ROCKY MOUNTAINS FOR THE NDJ 2008-2009 THROUGH JFM 2009 SEASONS. THE AREAS OF GREATER THAN CLIMATOLOGICAL PROBABILITIES OF ABOVE NORMAL TEMPERATURES DECREASE SUBSTANTIALLY THROUGH THE NEXT FEW THREE-MONTH PERIODS BEFORE EXPANDING TO COVER MOST OF THE WESTERN U.S. IN NEXT SUMMERS JAS 2009 OUTLOOK. THE OUTLOOK FOR SON 2009 LOOKS SOMEWHAT SIMILAR TO THE FIRST SEASONAL OUTLOOK FOR SON 2008, DUE TO THE IMPORTANT INFLUENCE OF THE TEMPERATURE TRENDS BUT DIFFERENCES MAY BE NOTED DUE TO SMLR AND ECCA THE OUTLOOKS FOR ALASKA ARE DERIVED MAINLY FROM THE RECENT TEMPERATURE TRENDS WITH SECONDARY SUPPORT FROM OTHER TOOLS. PRECIPITATION: ELEVATED PROBABILITIES FOR ABOVE MEDIAN PRECIPITATION IN THE SON 2008 OUTLOOKS FOR FLORIDA AND PARTS OF THE GULF AND ATLANTIC COASTS, THE NORTHEAST, AND PARTS OF THE CENTRAL PLAINS ARE DERIVED FROM THE CONSOLIDATION FORECAST. MOST OF THE PRECIPITATION FORECASTS FOR SON 2008 ARE SUPPORTED BY RECENT PRECIPITATION TRENDS. THE ABOVE MEDIAN PRECIPITATION FORECAST FOR COASTAL AREAS IN THE SOUTHEAST IN SON 2008 ARE RELATED TO INCREASED TROPICAL ACTIVITY DURING RECENT YEARS AND ARE AGAIN INCLUDED IN THE JAS AND ASO 2009 OUTLOOKS. AREAS OF BELOW MEDIAN PRECIPITATION ARE FORECAST FOR PARTS OF THE DESERT SOUTHWEST FROM OND 2008 TO DJF 2008-2009 AND FOR MUCH OF THE SOUTHEAST FROM NDJ 2008-2009 TO MAM 2009 RESULTING FROM RECENT PREDICTABLE PRECIPITATION TRENDS AS INDICATED BY THE CONSOLIDATION. AREAS OF INCREASED PROBABILITY FOR ABOVE MEDIAN PRECIPITATION CENTERED AROUND THE TEXAS PANHANDLE FROM DJF 2008-2009 TO FMA 2009 ALSO REPRESENT RECENT TRENDS AS INDICATED BY THE CONSOLIDATION. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). FORECASTER: HUUG VAN DEN DOOL 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 18 2008 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001 FORECAST RELEASE. $$
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