PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT THU APR 17 2003 . . . . . . . . SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THE SEASONAL OUTLOOK REFLECTS MAINLY THE PRESENCE OF LONG TERM TRENDS ON U.S. TEMPERATURE AND PRECIPITATION...WITH SOME INPUT FROM SOIL MOISTURE ANOMALIES AND NUMERICAL MODELS DURING THE FIRST SEVERAL SEASONS. EL NINO HAS WEAKENED AND IS FORECAST TO WEAKEN MORE AND IS THOUGHT TO BE A NEGLIGIBLE FACTOR FROM NOW UNTIL ANY SIGNIFICANT CHANGE IN THE EL NINO STATE OCCURS...LEAVING MAINLY THE INFLUENCE OF LONG TERM TRENDS ON THE FORECAST. SOME EL NINO AND OTHER WINTER WEATHER EFFECTS MAY CARRY OVER INTO THE LATE SPRING AND SUMMER INDIRECTLY THROUGH SUCH AGENTS AS SOIL MOISTURE. THE OUTLOOK FOR MAY - JULY 2003 CALLS FOR ABOVE NORMAL TEMPERATURES OVER MUCH OF THE U.S. AND ALASKA...DUE TO RECENT TRENDS REINFORCED OR AUGMENTED IN SOME AREAS BY INDICATIONS FROM NUMERICAL MODELS AND DRY SOIL. ABOVE NORMAL PRECIPITATION IS EXPECTED FOR PORTIONS OF THE PACIFIC NORTHWEST AND SOUTHEASTERN ALASKA BASED ON TRENDS AND NUMERICAL MODELS. EQUATORIAL PACIFIC SEA SURFACE TEMPERATURES IN EARLY APRIL WERE BETWEEN ONE HALF AND ONE DEGREE C OR MORE ABOVE NORMAL OVER THE EQUATORIAL PACIFIC NEAR THE DATE LINE. THE SST ANOMALIES IN THE EASTERN PACIFIC HAVE DECREASED SUBSTANTIALLY AND ARE BELOW NORMAL IN SOME PLACES. NEARLY ALL STATISTICAL AND OCEANIC MODEL PREDICTION TOOLS INDICATE WEAKENING EL NINO CONDITIONS THROUGH THE SUMMER WITH A LACK OF CONSENSUS AS TO WHAT MIGHT HAPPEN LATER IN THE YEAR. POSSIBILITIES FOR NINO 3.4 RANGE FROM A RETURN TO WEAK-TO-MOERATE WARM CONDITIONS TO A STRONG LA NINA...WITH THE OFFICIAL FORECAST FOR NINO 3.4 BEING VERY CLOSE TO NEUTRAL FROM LATE SUMMER THROUGH NEXT SPRING. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). . . . . . . . . BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOK THIS OUTLOOK REFLECTS THE EXPECTED UNITED STATES CLIMATE ANOMALIES BASED ON THE LONG TERM TREND - PRIMARILY FROM OCN - AND STATISTICALLY-BASED RELATIONSHIPS BETWEEN PRESENT OCEANIC AND ATMOSPHERIC CONDITIONS AND U.S. TEMPERATURE AND PRECIPITATION. DYNAMICAL FORECASTS FROM GENERAL CIRCULATION MODELS WERE ALSO CONSIDERED FOR THE FIRST FOUR SEASONS. AT THIS TIME OF YEAR SOIL MOISTURE CONSIDERATION GETS SPECIAL ATTENTION. CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS THE EL NINO OF 2002/03 HAS WEAKENED...WITH THE POSITIVE TEMPERATURE ANOMALIES DECREASING TO LESS THAN ONE DEGREE C OVER THE MOST OF THE CENTRAL PACIFIC. COOLER THAN NORMAL TEMPERATURES BELOW THE SURFACE NOW UNDERCUT THE WARM ANOMALIES NEAR THE SURFACE ACROSS MUCH OF THE EQUATORIAL PACIFIC. THIS IS CONSISTENT WITH A DECLINING EL NINO. OCEANIC AND ATMOSPHERIC INDICATORS ARE STILL CONSISTENT WITH WEAK EL NINO CONDITIONS...WITH ENHANCED CONVECTION IN PLACE SOME OF THE TIME NEAR THE DATELINE IN THE EQUATORIAL PACIFIC. EVEN IF THE ATMOSPHERIC RESPONSE TO EL NINO IN THE TROPICS CONTINUES - ITS IMPACT ON THE MID-LATITUDE WOULD BE SMALL BECAUSE THE SEASONAL WINDOW FOR SUCH TELECONNECTIONS IS CLOSING. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS MOST DYNAMICAL COUPLED OCEAN-ATMOSPHERE MODEL AND STATISTICAL MODEL FORECASTS INDICATE EL NINO CONDITIONS WILL WEAKEN THROUGH SPRING 2003. SOME TOOLS INDICATE POSITIVE ANOMALIES OF BETWEEN .5 AND 1 DEGREE C IN THE NINO 3.4 REGION WILL PERSIST THROUGH THE REMAINDER OF THE YEAR...WHILE OTHERS SHOW A RETURN TO NEAR NORMAL OR BELOW NORMAL SSTS IN THE SAME REGION BY EARLY SUMMER. A CONSOLIDATION FORECAST OF IN HOUSE TOOLS SHOWS TEMPERATURE ANOMALIES IN THE NINO 3.4 SST REGION NEAR ZERO FOR NEXT WINTER AND SPRING 2004. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOK THE STATISTICAL TOOLS - CCA - OCN - SMLR - WERE CONSULTED AT ALL LEAD TIMES. DYNAMICAL MODEL FORECASTS FROM NCEP AND OTHER FORECAST CENTERS WERE EXAMINED FOR THE PERIOD MJJ 2003 - ASO 2003. IN THIS SEASON WE ALSO PAY ATTENTION TO SOIL MOISTURE TOOLS...BOTH THE CAS AND SMT. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - MJJ 2003 TO MJJ 2004 TEMPERATURE: TEMPERATURES FOR MJJ 2003 REFLECT LONG TERM TRENDS OVER THE EASTERN...WESTERN AND GULF COAST STATES...WITH THE COVERAGE OF ABOVE NORMAL EXPANDED TO INCLUDE MUCH OF THE INTERIOR OF THE NATION BASED IN AREAS OF INITIALLY DRY SOIL AND THE OUTPUT FROM SOME STATISTICALLY POST-PROCESSED NUMERICAL MODELS. RECENT TRENDS SUPPORT ABOVE NORMAL TEMPERATURES THROUGHOUT MUCH OF ALASKA...ALTHOUGH SOME NUMERICAL MODELS CALL FOR BELOW NORMAL WHICH CAUSED A REDUCTION IN COVERAGE OF ABOVE FROM THE PREVIOUS MJJ OUTLOOK. RECENT TRENDS INDICATE ABOVE NORMAL TEMPERATURES FOR THE SUMMER OVER MUCH OF THE U.S. EXCEPT FOR THE INTERIOR PORTIONS AND FOR NORTHERN NEW ENGLAND. STATISTICALLY POST-PROCESSED NUMERICAL MODELS ARE QUITE CONSISTENT FOR THE FIRST FOUR SEASONS IN CALLING FOR ABOVE NORMAL OVER MOST OF THE LOWER 48 STATES. CCA ALSO SUPPORTS ABOVE NORMAL IN SOME REGIONS. EVEN WHERE THE STATISTICAL TOOLS OCN AND CCA DO NOT SHOW A PRIORI SKILL...THEY CALL FOR ABOVE NORMAL IN MOST PLACES. THUS WITH NO TOOLS SIGNIFICANTLY OPPOSING ABOVE NORMAL FOR MOST OF THE LOWER 48 STATES...THE TEMPERATURE OUTLOOKS THROUGH ASO 2003 HAVE ABOVE NORMAL OVER MUCH OF THE LOWER 48 STATES. TRENDS GRADUALLY DIMINISH AS THE TRANSITIONAL FALL SEASON APPROACHES AND...COUPLED WITH THE LACK OF AVAILABILITY OF NUMERICAL MODELS AFTER THE FIRST FOUR SEASONS...WHAT REMAINS IN THE OUTLOOK ARE ONLY THE REGIONS OF STRONGEST WARMING TRENDS BY SON 2003. FROM THERE THE FORECAST RAPIDLY TRANSITIONS TO WINTERTIME TEMPERATURE TRENDS...AS INDICATED BY THE DJF OUTLOOK...SHOWING ABOVE NORMAL TEMPERATURES OVER MUCH OF THE COUNTRY EXCEPT FOR THE NORTHWESTERN U.S. INTO THE NORTHERN PLAINS...EASTERN NEW ENGLAND...AND SOUTHERN ALASKA. WARMING TRENDS WEAKEN EAST OF THE ROCKIES AS SPRING APPROACHES LEAVING ABOVE NORMAL TEMPERATURES ONLY IN THE WESTERN U.S. AND PORTIONS OF ALASKA IN OUTLOOKS FOR MAM 2004 AND BEYOND. THE CHANGES MADE IN THE TEMPERATURE FORECASTS FOR CORRESPONDING SEASONS FROM LAST MONTHS OUTLOOK SERIES REFLECT THE CCA. REVISIONS PRIMARILY SHOW INCREASED COVERAGE OF ABOVE NORMAL...WHICH IS CONSISTENT WITH THE TREND EVEN IN REGIONS WHERE IT HAS NO A PRIORI SKILL. CHANGES IN THE FORECASTS FROM JFM THROUGH MAM 2004 ALSO REFLECT THE TREND UPDATE PROVIDED BY NEW DATA THROUGH MARCH 2003. . . . . . . . . PRECIPITATION: THE ABOVE MEDIAN PRECIPITATION FORECAST FOR MJJ 2003 FOR PORTIONS OF THE PACIFIC NORTHWEST IS BASED ON OCN AND STATISTICALLY POST-PROCESSED NUMERICAL MODELS...WHILE THE ABOVE MEDIAN PRECIPITATION FOR SOUTHEASTERN ALASKA IS BASED ONLY ON THE LATTER ALTHOUGH IT IS NOT STRONGLY OPPOSED BY THE STATISTICAL TOOLS. ONLY SLIGHT CHANGES WERE MADE IN THE PRECIPITATION FORECASTS FOR CORRESPONDING SEASONS FROM LAST MONTHS OUTLOOK SERIES...AND THESE ARE BASED ALMOST EXCULSIVELY ON OCN. . . . . . . . . GLOSSARY AND DEFINITIONS: ANALOG (NATURAL ANALOG) - A WEATHER MAP THAT RESEMBLES ANOTHER WEATHER MAP - USUALLY FROM DIFFERENT YEARS BUT THE SAME SEASON IN THE HISTORICAL RECORD. THE CRITERION FOR SELECTING AN ANALOG IS OFTEN THE PATTERN CORRELATION BETWEEN THE MAPS. TWO MAPS WILL JUST BEGIN TO RESEMBLE EACH OTHER TO THE HUMAN EYE AT A PATTERN CORRELATION OF ABOUT 40%. TO BE USEFUL - ANALOGS NEED TO HAVE MUCH HIGHER CORRELATIONS TO THE ORIGINAL MAP THAN THAT - 80% OR MORE. ANALOGS ARE INCREASINGLY DIFFICULT TO FIND AS THE GEOGRAPHIC REGION BEING COMPARED INCREASES IN SIZE. PERFECT ANALOGS TO THE ENTIRE NORTHERN HEMISPHERE SIMPLY DO NOT EXIST - FOR PRACTICAL PURPOSES. THIS IS WHY SIMPLE ANALOG FORECAST METHODS DO NOT WORK VERY WELL. ANNUAL CYCLE - AT MOST LOCATIONS THE CLIMATE STATE VARIABLES - T - P - SST- WIND - AND OTHERS DISPLAY A REGULAR VARIATION WHICH FOLLOWS THAT OF THE ELEVATION OF THE SUN IN THE SKY. A GRAPH OF THE 30 YEAR AVERAGE OF A VARIABLE FOR EACH DAY OF THE YEAR VERSUS DATE SHOWS A WAVE-FORM WHICH - FOR T AT DES MOINES FOR EXAMPLE - RANGES SMOOTHLY FROM LOWEST VALUES IN THE WINTER TO HIGHEST VALUES IN THE SUMMER. ANOMALY - THE ARITHMETIC DIFFERENCE BETWEEN THE VALUE OF A VARIABLE AT A GIVEN PLACE AND TIME AND THE LONG-TERM AVERAGE (USUALLY 30 YEARS) FOR THE LOCATION AND TIME OF YEAR. CA - CONSTRUCTED ANALOG - A LINEAR COMBINATION OF PAST OBSERVED ANOMALY PATTERNS SUCH THAT THE COMBINATION IS AS CLOSE AS DESIRED TO THE INITIAL STATE. A FORECAST IS OBTAINED BY PERSISTING THE WEIGHTS ASSIGNED TO EACH YEAR IN THE HISTORICAL RECORD AND LINEARLY COMBINING THE STATES FOLLOWING THE INITIAL TIME IN THE HISTORICAL YEARS. CAS - CONSTRUCTED ANALOG SOIL MOISTURE PREDICTION TECHNIQUE. CCA - CANONICAL CORRELATION ANALYSIS - A TECHNIQUE WHICH PREDICTS THE STATUS OF U.S. T AND P FOR SOME FUTURE TARGET SEASON USING THE MOST RECENT 4 NON- OVERLAPPING SEASONAL OBSERVATIONS OF TROPICAL PACIFIC SST - CIRCULATION AND U.S. T OR P TO CHARACTERIZE THE RECENT BEHAVIOR OF THE CLIMATE - AND PAST OBSERVATIONS TO PLACE RECENT BEHAVIOR INTO A HISTORICAL CONTEXT. CLIMATOLOGY - THE 30-YEAR AVERAGE OF A VARIABLE - LIKE TEMPERATURE - AT A GIVEN LOCATION AND TIME OF YEAR. . . . . . . . . CONUS - CONTERMINOUS UNITED STATES DYNAMICAL MODEL - A PREDICTION METHOD WHICH USES EQUATIONS DESCRIBING THE PHYSICAL BEHAVIOR OF A SYSTEM AND A COMPREHENSIVE SET OF CURRENT OBSERVATIONS OF THE VALUES OF THE VARIABLES DESCRIBING THE CURRENT STATE OF THE SYSTEM (INITIAL CONDITIONS) TO PREDICT THE VALUES OF THOSE VARIABLES A SHORT TIME-STEP IN THE FUTURE. THOSE VALUES ARE - IN TURN - USED AS THE INITIAL CONDITIONS FOR A SUBSEQUENT PREDICTION - AND SO ON - UNTIL THE DESIRED FUTURE PREDICTION TIME IS REACHED. EASTERLY WIND - WIND BLOWING FROM EAST TO WEST. EC - EQUAL CHANCES - THE PROBABILITY OF THE MOST LIKELY CATEGORY CANNOT BE DETERMINED AND THE EXPECTED LIKELIHOODS OF ABOVE - NORMAL AND BELOW DO NOT DIFFER FROM THEIR CLIMATOLOGICAL ODDS OF 33 1/3% EACH. EC REPLACES CL. EL NINO - THE WARM PHASE OF THE ENSO CYCLE ENSO - ACRONYM FOR EL NINO/SOUTHERN OSCILLATION GCM - GENERAL CIRCULATION MODEL - A GENERIC TERM APPLIED TO GLOBAL DYNAMICAL MODELS. LA NINA - THE COLD PHASE OF THE ENSO CYCLE MJO - MADDEN-JULIAN OSCILLATION - ALSO CALLED TROPICAL INTRA-SEASONAL OSCILLA- TION - A DISTURBANCE IN TROPICAL CONVECTION - PRECIPITATION - WIND AND PRESSURE. MJO PRECIPITATION AND CLOUDINESS ARE ENHANCED ONLY IN REGIONS WHERE SSTS ARE VERY WARM - E.G. INDIAN OCEAN AND WEST PACIFIC. THE PRESSURE AND WIND DISTURBANCE ASSOCIATED WITH MJO IS OBSERVED TO MOVE FROM WEST TO EAST COMPLETELY AROUND THE GLOBAL TROPICS IN ABOUT 30 TO 60 DAYS. NAO - NORTH ATLANTIC OSCILLATION TELECONNECTION PATTERN. NORTHERLY WIND - WIND BLOWING FROM NORTH TO SOUTH. OCN - OPTIMAL CLIMATE NORMALS - A FORECAST BASED ON PERSISTING THE AVERAGE OF THE LAST 10 YEARS FOR TEMPERATURE AND THE LAST 15 YEARS FOR PRECIPITATION. PNA - PACIFIC NORTH AMERICAN TELECONNECTION PATTERN. QBO - QUASI-BIENNIAL OSCILLATION - AN OSCILLATION OF THE WIND IN THE LOWER STRATOSPHERE BETWEEN EASTERLY AND WESTERLY WHICH REVERSES ON A NEARLY- 2 YEAR TIME SCALE. QBO IS ONE OF THE MOST REGULAR OSCILLATIONS KNOWN. SMLR - SCREENING MULTIPLE LINEAR REGRESSION - A TECHNIQUE WHICH SELECTS THE BEST SET OF PREDICTORS - FITTING THEM TO THE OBSERVATIONS TO CREATE EQUATIONS WHICH CAN BE USED TO MAKE PREDICTIONS. SOUTHERLY WIND - WIND BLOWING FROM SOUTH TO NORTH. STATISTICAL PREDICTIONS - PREDICTIONS BASED MAINLY ON LARGE OBSERVATIONAL DATA SETS. CCA - OCN - SMLR - CAS - CA ARE EXAMPLES OF THESE. TELECONNECTIONS - THESE GIVE THE HISTORICAL RELATIONSHIP BETWEEN A GIVEN POINT AND ALL OTHER POINTS OVER A LARGE AREA - LIKE THE NORTHERN HEMISPHERE - FOR A GIVEN TIME OF THE YEAR. THE POINTS ON THE MAP USUALLY CONSIST OF A SET OF MORE OR LESS EVENLY SPACED LOCATIONS CALLED GRID POINTS. TREND - AT A GIVEN LOCATION AND TIME OF YEAR - THE DIFFERENCE BETWEEN THE AVERAGE OF THE MOST RECENT 10 (15) YEARS OF OBSERVATIONS OF T (P) AND THE CLIMATOLOGY. WESTERLY WIND - WIND BLOWING FROM WEST TO EAST. ZONAL FLOW PATTERN - OCCURS WHEN 500-HPA CONTOURS LIE IN AN EAST-WEST DIRECTION PARALLEL TO LATITUDE CIRCLES WITH NEARLY PURE WEST-TO-EAST FLOW. -------------------------------------------------------------------------------- . . . . . . . . FORECASTER: R. MARTIN 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/90DAY/DISC.HTML (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 APRIL 17 2003. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. $$