PROGNOSTIC DISCUSSION FOR LONG-LEAD OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EDT THURSDAY DECEMBER 19 2002 . . . . . . . . SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THIS SET OF OUTLOOKS IS INFLUENCED BY TWO MAIN FACTORS - EL NINO AND TREND. THE OUTLOOK FOR JANUARY-MARCH 2003 CALLS FOR ABOVE NORMAL TEMPERATURES OVER MUCH OF THE NORTHERN U.S. DUE TO EL NINO ENHANCED BY TREND. BELOW NORMAL TEMPERATURES ARE EXPECTED OVER THE SOUTHEAST FROM TEXAS TO FLORIDA - ALSO DUE TO EL NINO. PRECIPITATION IS EXPECTED TO BE BELOW NORMAL IN THE PACIFIC NORTHWEST - THE NORTHERN ROCKIES - AND IN THE OHIO VALLEY - DUE MAINLY TO EL NINO. FOR THE SAME REASONS - PRECIPITATION IS EXPECTED TO BE ABOVE NORMAL FOR MUCH OF THE SOUTHERN U.S. FROM CALIFORNIA - ACROSS THE SOUTHWEST - THE SOUTHERN PLAINS AND THE SOUTHEAST. PRECIPITATION IS ALSO EXPECTED TO BE ABOVE NORMAL IN THE CENTRAL PLAINS - AND WET CONDITIONS ALSO HAVE ADDITIONAL SUPPORT FROM THE TREND OVER TEXAS AND OKLAHOMA. THE TEMPERATURE OUTLOOK FOR ALASKA DURING JANUARY-MARCH 2003 CALLS FOR ABOVE NORMAL TEMPERATURES OVER CENTRAL AND EASTERN PARTS OF THE STATE WITH EQUAL CHANCES (CLIMATOLOGICAL PROBABILITIES) FORECAST FOR PRECIPITATION OVER ALL BUT THE SOUTHERN SECTIONS - WHERE WETTER THAN NORMAL CONDITIONS ARE INDICATED. EQUATORIAL PACIFIC OCEAN SURFACE TEMPERATURES DURING NOVEMBER REMAINED AT OR ABOVE TWO DEGREES C ABOVE NORMAL OVER MUCH OF THE REGION FROM 175W TO 100W. THE MAGNITUDE OF THE ANOMALIES HAS INCREASED STEADILY OVER THE PAST FEW MONTHS. CURRENT CONDITIONS ARE INDICATIVE OF A MODERATE EL NINO EPISODE. THE U.S. OUTLOOKS FOR JANUARY-MARCH REFLECT THIS - SHOWING ABNORMALLY WARM CONDITIONS OVER THE NORTHERN CONTINENTAL U.S. WITH BELOW NORMAL TEMPERATURES IN THE SOUTHEAST. DRIER THAN NORMAL CONDITIONS OVER SECTIONS OF THE NORTHWEST - THE ROCKIES - AND THE GREAT LAKES-OHIO VALLEY REGION AND WETTER THAN NORMAL CONDITIONS ACROSS MUCH OF THE SOUTHERN TIER OF THE U.S. ARE ALSO CONSISTENT WITH MODERATE EL NINO CONDITIONS. THIS BASIC PATTERN IS FORECAST TO PERSIST 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 AND CONTINUES THROUGHOUT THE REMAINDER OF 2003 INTO JANUARY-MARCH 2004 AS THE STATUS OF EL NINO IS UNCERTAIN BEYOND MAM 2003. 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 - AS ESTIMATED BY 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. DURING THE JANUARY-MARCH TO MARCH-MAY SEASONS- EL NINO COMPOSITES WERE USED EXTENSIVELY. THUS THE OUTLOOKS FOR JFM THROUGH MAM 2003 REFLECT EXPECTED MODERATE EL NINO CONDITIONS. CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS MODERATE WARM EPISODE (EL NINO) CONDITIONS PREVAILED DURING NOVEMBER 2002 AS AVERAGE SST ANOMALIES INCREASED ACROSS THE EQUATORIAL PACIFIC TO MORE THAN +2.0 DEGREE C ABOVE NORMAL ALONG THE EQUATOR FROM THE DATE LINE TO 110W. ATMOSPHERIC INDICATORS OF A WARM EPISODE INCLUDE NEGATIVE VALUES OF THE SOUTHERN OSCILLATION INDEX (SOI) - SINCE MARCH 2002 - AND GENERALLY WEAKER THAN AVERAGE LOW-LEVEL EASTERLY WINDS DURING MAY-NOVEMBER 2002 THROUGHOUT THE EQUATORIAL PACIFIC - ESPECIALLY IN THE WESTERN AND CENTRAL PACIFIC. THE MADDEN JULIAN OSCILLATION (MJO) WAS A MAJOR SOURCE OF WEEK-TO-WEEK AND MONTH-TO-MONTH VARIABILITY IN THE ATMOSPHERIC CIRCULATION OF THE TROPICS AND SUBTROPICS EARLIER THIS YEAR BUT IT HAS WEAKENED AS EL NINO CONDITIONS HAVE BECOME SOLIDLY ESTABLISHED - WITH CONVECTION LOCKED-IN NEAR THE DATELINE. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS THE OCEANIC AND ATMOSPHERIC VARIABLES DISCUSSED ABOVE REFLECT THE PRESENCE OF MODERATE EL NINO CONDITIONS. MOST DYNAMICAL COUPLED OCEAN-ATMOSPHERE MODEL AND STATISTICAL MODEL FORECASTS INDICATE EL NINO CONDITIONS ARE LIKELY TO CONTINUE THROUGH SPRING 2003. THE LATEST OBSERVED SEASONAL AVERAGE - SON - FOR NINO 3.4 IS A +1.5 DEGREE C ANOMALY. THE CONSENSUS OF VARIOUS FORECAST METHODS IS FOR SSTS TO REMAIN MORE THAN 1.0 DEGREES C ABOVE NORMAL UNTIL FMA. THIS MAY BE A BIT CONSERVATIVE GIVEN THAT RECENT WEEKLY AVERAGES HAVE BEEN ABOVE 1.5 DEGREES AND WARM EVENTS TYPICALLY MATURE DURING THE WINTER. NEVERTHELESS THE CURRENT EVENT IS EXPECTED TO BE WEAKER THAN 97/98 WHICH FEATURED 2.5 DEGREE ANOMALIES FOR NINO 3.4. NOTE THAT THE GLOBAL IMPACTS OF THIS WARM EPISODE ON THE AVERAGE SHOULD BE CORRESPONDINGLY WEAKER THAN THOSE OBSERVED DURING THE VERY STRONG 1997 - 98 EL NINO. MOST TOOLS ARE LESS CLEAR ABOUT WHAT WILL HAPPEN WITH EL NINO BEYOND AMJ 2003. 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 JFM 2003 - AMJ 2003. THE LARGE-SCALE CIRCULATION PATTERNS ARE EXPECTED TO REFLECT WARM EPISODE (EL NINO) CONDITIONS DURING THE REMAINDER OF THE WINTER WINTER AND EARLY SPRING - SO WARM EPISODE COMPOSITES WERE USED PROMINENTLY FOR SEASONS FROM JFM THROUGH MAM 2003. A NEW RENDERING OF SUCH COMPOSITES BASED ON OFFICIAL NOAA 0.5 DEGREE ANOMALY THRESHOLD HAS 12 CASES FOR JFM - 11 CASES FOR FMA - AND ONLY 8 CASES FOR MAM. BOTH A HIGH FREQUENCY (NO TREND) VERSION AND A TREND-ADJUSTED VERSION OF THESE COMPOSITES HAVE BEEN CONSULTED BY THE FORECASTERS. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - JFM 2003 TO JFM 2004 TEMPERATURE: TEMPERATURES FOR JFM THROUGH MAM 2003 REFLECT THE COMBINED INFLUENCE OF LONG TERM TRENDS AND A MATURE MODERATE STRENGTH EL NINO. EL NINO COMPOSITES SUPPORT WARMER THAN NORMAL TEMPERATURES ACROSS THE NORTHERN TIER OF STATES FOR JFM THROUGH FMA - AND IN MOST OF THE WEST DURING MAM. BELOW NORMAL TEMPERATURES ACROSS MUCH OF THE SOUTH FROM JFM THROUGH MAM 2003 ARE CONSISTENT WITH THE EL NINO SIGNAL - WITH SUPPORT FROM THE SCREENING MULTIPLE LINEAR REGRESSION TOOL FOR JFM. OCN - WITH VARYING AMOUNTS OF SUPPORT FROM CCA - INDICATES WARMER THAN NORMAL TEMPERATURES FOR MOST OF THE REMAINING SEASONS IN THE SOUTHWEST - AND THROUGHOUT MUCH OF THE SOUTH AND EAST AND WEST COASTS DURING THE SUMMER MONTHS - AND ACROSS MUCH OF THE EAST AND WEST COAST DURING NEXT WINTER. THE EXPECTED EL NINO SIGNAL - WITH SOME SUPPORT FROM TRENDS - FAVORS ABOVE NORMAL TEMPERATURES OVER AT LEAST THE SOUTHEASTERN PORTION OF ALASKA DURING JFM. THIS ABOVE NORMAL IS FORECAST TO EXPAND OVER MUCH OF THE STATE THROUGH MJJ 2003 - BASED ON OCN - AND THEN WANE. . . . . . . . . PRECIPITATION: BELOW MEDIAN PRECIPITATION IS EXPECTED DURING JFM 2003 FROM EASTERN SECTIONS OF THE PACIFIC NORTHWEST EASTWARD THROUGH MONTANA. MUCH OF THIS AREA IS ALSO EXPECTED TO EXPERIENCE BELOW NORMAL PRECIPITATION DURING THE NEXT TWO SEASONS. DRIER THAN NORMAL CONDITIONS ARE ALSO EXPECTED OVER THE OHIO VALLEY AND THE GREAT LAKES DURING JFM 2003 - PERSISTING THROUGH MAM 2003 - BASED ON ENSO COMPOSITES. ABOVE NORMAL PRECIPITATION IS FORECAST IN THE SOUTHWEST - THE SOUTH CENTRAL - AND THE SOUTHEASTERN U.S. FROM JFM 2003 THROUGH MAM 2003 - BASED ON ENSO COMPOSITES - TRENDS AND NEARLY ALL FORECAST TOOLS. ABOVE MEDIAN PRECIPITATION IS MAINTAINED IN THE SOUTHWEST DURING AMJ SUPPORTED BY EL NINO COMPOSITES AND EL NINO LAGGED COMPOSITES RELATIVE TO DJF. BELOW-MEDIAN PRECIPITATION FOR PORTIONS OF THE GREAT BASIN IS INDICATED BY OCN WITH SOME SUPPORT FROM SMLR DURING JJA AND JAS 2003. THERE ARE NO RELIABLE FORECAST INDICATIONS FOR ALASKA PRECIPITATION AT ANY LEAD BY THE TOOLS WE HAVE. NEVERTHELESS SYNOPTIC REASONING WOULD SUGGEST ON-SHORE FLOW AROUND THE DEEPER THAN NORMAL ALEUTIAN LOW. HENCE WE FORECAST ABOVE-MEDIAN PRECIPITATION FOR THE SE PART OF THE STATE FOR JFM AND FMA 2003. . . . . . . . . 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. -------------------------------------------------------------------------------- . . . . . . . . FORECASTERS: A. J. WAGNER AND M. HALPERT 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 JANUARY 16 2003. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. NNNN NNNN