PROGNOSTIC DISCUSSION FOR LONG-LEAD OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EDT THURSDAY SEPTEMBER 19 2002 . . . . . . . . SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THIS SET OF OUTLOOKS IS AFFECTED BY TWO MAIN FACTORS - EL NINO AND TREND. THE OUTLOOK FOR OCTOBER-NOVEMBER-DECEMBER 2002 CALLS FOR ABOVE NORMAL TEMPERATURES OVER MUCH OF THE NORTHERN U.S. DUE TO EL NINO. PRECIPITATION IS EXPECTED TO BE BELOW NORMAL IN THE PACIFIC NORTHWEST AND MONTANA - PRIMARILY DUE TO EL NINO - AND BELOW NORMAL IN THE MID-ATLANTIC - EXTREME SOUTHERN NEW ENGLAND - AND MUCH OF THE OHIO VALLEY ALSO DUE TO EL NINO. PRECIPITATION IS EXPECTED TO BE ABOVE NORMAL FOR PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY AND OVER THE FLORIDA PENINSULA - ALSO DUE TO EL NINO WITH SUPPORT FROM THE TREND. THE TEMPERATURE OUTLOOK FOR ALASKA DURING OCTOBER-NOVEMBER-DECEMBER 2002 CALLS FOR BELOW NORMAL TEMPERATURES OVER WESTERN PORTIONS OF THE STATE WITH CLIMATOLOGICAL PROBABILITIES (EQUAL CHANCES) FORECAST FOR PRECIPITATION. THE EQUATORIAL PACIFIC OCEAN SURFACE TEMPERATURES REMAIN AT OR ABOVE ONE DEGREE C ABOVE NORMAL IN THE REGION FROM 175E TO 130W. THE STRENGTH OF THE ANOMALIES HAS REMAINED CONSISTENT FOR THE PAST FEW MONTHS. AT PRESENT THE CONDITIONS ARE INDICATIVE OF A MODERATE EL NINO EPISODE. THE OUTLOOKS FOR THE COLD SEASON REFLECT THIS - SHOWING ABNORMALLY WARM CONDITIONS FOR THE NORTHERN CONTINENTAL U.S. WITH DRIER THAN NORMAL CONDITIONS OVER THE NORTHWEST - PORTIONS OF THE NORTHERN PLAINS - AND OHIO VALLEY. ABNORMALLY WET - AND IN SOME AREAS COOL - CONDITIONS ARE EXPECTED ACROSS MUCH OF THE SOUTHERN TIER OF THE U.S. DURING THE WINTER AND INTO THE SPRING. THE FORECAST REVERTS TO THE TREND - MAINLY WARMER THAN NORMAL TEMPERATURES IN THE SOUTHWEST AND THE SOUTHEAST - BY LATE SPRING AND SUMMER 2003. . . . . . . . . BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOK THIS OUTLOOK REFLECTS THE EXPECTED UNITED STATES CLIMATE ANOMALIES BASED ON THE LONG TERM TREND - AS ESTIMATED BY OCN - AND STATISTICALLY BASED RELATIONSHIPS BETWEEN PRESENT OCEANIC AND ATMOSPHERIC CONDITIONS AND U.S. TEMPERATURE AND PRECIPITATION FROM THE CANONICAL CORRELATION ANALYSIS MODEL. DYNAMICAL FORECASTS FROM GENERAL CIRCULATION MODELS WERE ALSO CONSIDERED FOR THE FIRST FOUR SEASONS. DURING THE COLD SEASON EL NINO COMPOSITES WERE ALSO USED. THUS THE OUTLOOKS FOR OND 2002 THROUGH MAM 2003 REFLECT EXPECTED MODERATE EL NINO CONDITIONS DURING THAT PERIOD. CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS WARM EPISODE (EL NINO) CONDITIONS PREVAILED DURING AUGUST 2002 AS SST ANOMALIES REMAINED ABOVE 1 DEGREE C ABOVE NORMAL ALONG THE EQUATOR FROM 175E TO 130W. ATMOSPHERIC INDICATORS OF A WARM EPISODE INCLUDE CONSISTENTLY NEGATIVE VALUES OF THE SOUTHERN OSCILLATION INDEX (SOI) - SINCE MARCH 2002 - AND WEAKER THAN AVERAGE LOW-LEVEL EASTERLY WINDS DURING MAY-AUGUST 2002 THROUGHOUT THE EQUATORIAL PACIFIC. THE MADDEN JULIAN OSCILLATION (MJO) HAS BEEN A MAJOR SOURCE OF WEEK-TO-WEEK AND MONTH-TO-MONTH VARIABILITY IN THE ATMOSPHERIC CIRCULATION OF THE TROPICS AND SUBTROPICS IN RECENT MONTHS BUT IT APPEARS TO BE WEAKENING AS EL NINO CONDITIONS BECOME MORE FIRMLY ESTABLISHED. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS THE OCEANIC AND ATMOSPHERIC VARIABLES DISCUSSED ABOVE REFLECT THE PRESENCE OF MODERATE EL NINO CONDITIONS. THIS ASSESSMENT IS CONSISTENT WITH MOST COUPLED MODEL AND STATISTICAL MODEL FORECASTS - WHICH INDICATE THAT EL NINO CONDITIONS ARE LIKELY TO CONTINUE THROUGH THE END OF 2002 AND INTO EARLY 2003. ALTHOUGH THERE IS UNCERTAINTY IN THE FORECASTS ABOUT THE TIMING AND INTENSITY OF THE PEAK OF THIS WARM EPISODE - ALL OF THE FORECASTS INDICATE THAT IT WILL BE MUCH WEAKER THAN THE 1997 - 98 EL NINO. IT IS IMPORTANT TO ADD THAT THE GLOBAL IMPACTS OF THIS WARM EPISODE SHOULD BE CORRESPONDINGLY WEAKER THAN THOSE OBSERVED DURING THE VERY STRONG 1997 - 98 EL NINO. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOK THE STATISTICAL TOOLS - CCA - OCN - SMT - WERE CONSULTED AT ALL LEAD TIMES. DYNAMICAL MODEL FORECASTS FROM NCEP AND OTHER FORECAST CENTERS WERE CONSULTED FOR THE PERIOD OND 2002 - JFM 2003. THE LARGE-SCALE CIRCULATION PATTERNS ARE EXPECTED TO REFLECT WARM EPISODE (EL NINO) CONDITIONS DURING THE LATE FALL - WINTER AND EARLY SPRING - SO WARM EPISODE COMPOSITES FOR A MODERATE WARM EPISODE WERE CONSIDERED FOR SEASONS FROM OND 2002 THROUGH MAM 2003. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - OND 2002 TO OND 2003 TEMPERATURE: TEMPERATURES FOR OND 2002 THROUGH MAM 2003 REFLECT THE COMBINED INFLUENCE OF LONG TERM TRENDS AND A MATURE EL NINO OF MODERATE STRENGTH. EL NINO COMPOSITES SUPPORT WARMER THAN NORMAL TEMPERATURES ACROSS THE NORTHERN TIER OF STATES FOR FALL THROUGH EARLY SPRING. THE WARMING TREND ACROSS MUCH OF THE SOUTH MODERATES THE EL NINO SIGNAL FOR BELOW NORMAL TEMPERATURES THERE. AS A CONSEQUENCE CLIMATOLOGICAL PROBABILITIES (EQUAL CHANCES) ARE FORECAST DURING THE LATE FALL AND EARLY WINTER LEADS ACROSS MUCH OF THE REGION. THE EL NINO SIGNAL FOR BELOW NORMAL TEMPERATURES DOMINATES THE TREND SIGNAL TO FAVOR BELOW NORMAL TEMPERATURES OVER FLORIDA AND THE LOWER RIO GRANDE VALLEY DURING THE LATE WINTER AND SPRING. INABILITY TO FORECAST THE SEASONAL PHASE OF THE NAO PREVENTS A CATEGORICAL FORECAST ACROSS MUCH OF THE SOUTH AND ALONG THE EASTERN SEABOARD - LEAVING THE ODDS CLOSE TO CLIMATOLOGICAL IN MUCH OF THIS REGION DURING NDJ 2002-03 AND DJF 2002-03. OCN - WITH VARYING AMOUNTS OF SUPPORT FROM CCA - INDICATES WARMER THAN NORMAL TEMPERATURES FOR MOST OF THE REMAINING SEASONS IN THE SOUTHWEST. CONFLICTING OR WEAK SIGNALS FROM THE VARIOUS TEMPERATURE FORECAST TOOLS REQUIRE THAT CLIMATOLOGICAL PROBABILITIES (EQUAL CHANCES) BE FORECAST FOR ALASKA FOR NDJ 2002-03. BEGINNING IN DJF 2002-03 THE EXPECTED EL NINO - WITH SOME SUPPORT FROM TRENDS - FAVORS ABOVE NORMAL TEMPERATURES OVER AT LEAST THE SOUTHEASTERN PORTION OF THE STATE. THIS ABOVE NORMAL IS FORECAST TO EXPAND OVER MUCH OF THE STATE THROUGH MJJ 2003 - BASED ON OCN - AND THEN WANE. . . . . . . . . PRECIPITATION: FOR NDJ 2002-03 WE INDICATE BELOW MEDIAN PRECIPITATION FROM MUCH OF THE PACIFIC NORTHWEST EASTWARD THROUGH MONTANA AND MOST OF WYOMING. IN SUBSEQUENT SEASONS THIS AREA OF BELOW MEDIAN CONTINUES WITH SOME VARIATIONS IN COVERAGE AND INTENSITY THROUGH MAM 2003. DRIER THAN NORMAL CONDITIONS ARE EXPECTED TO DEVELOP OVER THE OHIO VALLEY DURING NDJ 2002-03 AND PERSIST THROUGH MAM 2003 - BASED ON ENSO COMPOSITES. ABOVE NORMAL PRECIPITATION IS FORECAST IN THE SOUTH CENTRAL AND SOUTHEASTERN U.S. FROM NDJ 2002-03 THROUGH FMA 2003 - BASED ON ENSO COMPOSITES. ABOVE NORMAL PRECIPITATION IS ALSO FORECAST OVER PORTIONS OF THE SOUTHWEST DURING THE LATE WINTER AND EARLY SPRING FROM DJF 2002-03 THROUGH FMA 2003 - ALSO FROM ENSO COMPOSITES. ABOVE MEDIAN PRECIPITATION IS GIVEN FOR PORTIONS OF THE WEST COAST STATES DURING MJJ 2003 BY OCN WITH SUPPORT FROM CCA. BELOW MEDIAN PRECIPITATION FOR PORTIONS OF THE GREAT BASIN IS INDICATED BY OCN WITH SOME SUPPORT FROM SMT DURING JJA AND JAS 2003. THERE ARE NO RELIABLE FORCAST INDICATIONS FOR ALASKA PRECIPITATION AT ANY LEAD - SO CLIMATOLOGICAL PROBABILITIES ARE FORECAST. . . . . . . . . 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. CLIMATOLOGICAL PROBABILITIES - CL - OCCUR WHEN THE EXPECTED LIKELIHOODS OF ABOVE - NORMAL AND BELOW DO NOT DIFFER FROM THEIR CLIMATOLOGICAL ODDS OF 33 1/3% EACH. . . . . . . . . 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. 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. -------------------------------------------------------------------------------- . . . . . . . . FORECASTERS: R. MARTIN AND H. VAN DEN DOOL 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 THURSDAY OCTOBER 17 2002. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. NNNN NNNN