PROGNOSTIC DISCUSSION FOR LONG-LEAD OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMPS SPRINGS MD 300 PM EST THU FEB 20 2003 . . . . . . . . SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THE SEASONAL OUTLOOK REFLECTS THE INFLUENCE OF EL NINO AND LONG TERM TRENDS ON U.S. TEMPERATURE AND PRECIPITATION IN THE SPRING. EL NINO IS FORECAST TO WEAKEN AND BECOME A NEGLIGIBLE FACTOR AFTER ABOUT MAY - LEAVING ONLY THE INFLUENCE OF LONG TERM TRENDS ON THE FORECASTS BEYOND APRIL - JUNE. THE OUTLOOK FOR MARCH - MAY 2003 CALLS FOR ABOVE NORMAL TEMPERATURES OVER MUCH OF THE WESTERN U.S. AND ALASKA - DUE PRIMARILY TO RECENT TRENDS WITH SOME ADDITIONAL HELP FROM EL NINO ALONG THE IMMEDIATE PACIFIC COAST AND IN THE PACIFIC NORTHWEST. BELOW NORMAL TEMPERATURES ARE EXPECTED OVER THE SOUTHEAST FROM TEXAS TO FLORIDA - DUE TO EL NINO. PRECIPITATION IS EXPECTED TO BE BELOW NORMAL IN THE PACIFIC NORTHWEST AND MONTANA - AND AROUND THE GREAT LAKES - THE OHIO RIVER VALLEY AND NORTHERN NEW ENGLAND DUE TO EL NINO. EL NINO INCREASES STORM ACTIVITY IN THE SOUTHERN STORM TRACK IN SPRINGTIME ELEVATING THE CHANCES OF ABOVE NORMAL PRECIPITATION FOR MUCH OF THE SOUTHERN U.S. FROM CALIFORNIA - ACROSS THE SOUTHWEST AND THE SOUTHERN ROCKIES TO TEXAS AND ONTO THE GULF COAST AND FLORIDA. EQUATORIAL PACIFIC SEA SURFACE TEMPERATURES IN JANUARY WERE BETWEEN ONE HALF AND ONE DEGREE C ABOVE NORMAL OVER THE EQUATORIAL PACIFIC EAST OF ABOUT 120W AND OVER TWO DEGREES JUST EAST OF THE DATE LINE. THE SST ANOMALIES IN THE EASTERN PACIFIC HAVE DECREASED SUBSTANTIALLY IN EARLY FEBRUARY AND NOW ARE ONLY MARGIN- ALLY ABOVE NORMAL. SSTS IN THE CENTRAL PACIFIC HAVE WEAKENED IN RECENT WEEKS AS WELL - BUT REMAIN MORE THAN ONE DEGREE C ABOVE NORMAL BETWEEN 170E AND 150W LONGITUDE. NEARLY ALL STATISTICAL AND OCEANIC MODEL PREDICTION TOOLS FOR THE EQUATORIAL PACIFIC INDICATE WEAKENING EL NINO CONDITIONS THROUGH THE SPRING WITH A CONSENSUS OF TOOLS INDICATING A RETURN TO NORMAL CONDITIONS BY THE SUMMER. 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. EL NINO COMPOSITES HEAVILY INFLUENCED THE MAM 2003 FORECAST - AND WERE USED TO A LESSER EXTENT FOR AMJ. CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS MODERATE WARM EPISODE (EL NINO) CONDITIONS PREVAILED DURING JANUARY 2003 WITH AVERAGE SST ANOMALIES IN THE EASTERN EQUATORIAL PACIFIC AVERAGING ABOUT .5 DEGREE C FROM ABOUT 120W TO THE SOUTH AMERICAN COAST. SSTS ANOMALIES IN THE CENTRAL PACIFIC ARE STRONGER - AVERAGING OVER 1 DEGREE C FROM 170E TO 150W AND OVER 2 DEGREES C JUST EAST OF THE DATE LINE. THE EL NINO IS SHOWING SIGNS OF WEAKENING IN RECENT WEEKS - WITH THE POSITIVE TEMPERATURE ANOMALIES DECREASING BY ABOUT .5 TO 1 DEGREE C OVER MUCH OF THE CENTRAL AND EASTERN PACIFIC IN THE FIRST HALF OF FEBRUARY. IN ADDITION - COOLER THAN NORMAL TEMPERATURES BELOW THE SURFACE HAVE BEEN STEADILY MOVING EASTWARD AND ARE UNDERCUTTING THE WARM ANOMALIES NEAR THE SURFACE. THIS IS CONSISTENT WITH A MATURE EL NINO AND INDICATES THAT THE EVENT HAS PEAKED AND HAS NOW ENTERED A WEAKENING PHASE. OCEANIC AND ATMOSPHERIC INDICATORS IN JANUARY WERE STILL CONSISTENT WITH MODERATE EL NINO CONDITIONS AND WITH WARMER THAN NORMAL SSTS AND ENHANCED CONVECTION EXTENDING TO JUST EAST OF THE DATELINE IN THE EQUATORIAL PACIFIC... THE ATMOSPHERIC RESPONSE TO EL NINO IS EXPECTED TO CONTINUE FOR THE NEXT FEW MONTHS. THE MADDEN JULIAN OSCILLATION (MJO) WAS A MAJOR SOURCE OF WEEK-TO-WEEK VARIABILITY IN THE ATMOSPHERIC CIRCULATION OF THE TROPICS EARLY IN JANUARY BUT HAS SUBSIDED SINCE THEN WITH VERY LITTLE ACTIVITY IN RECENT WEEKS. . . . . . . . . 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 EVEN BELOW NORMAL SSTS IN THE SAME REGION BY EARLY SUMMER. A CONSENSUS OF BOTH STATISTICAL AND DYNAMICAL FORECASTING METHODS INDICATES THAT SST ANOMALIES IN THE NINO 3.4 REGION WILL RETURN TO NEAR ZERO BY LATE SUMMER. THIS FORECAST AGREES WITH THE TYPICAL EVOLUTION IN SPRINGTIME SSTS FOLLOWING A MATURE EL NINO. THERE ARE FEW RELIABLE INDICATIONS OF EQUATORIAL PACIFIC SSTS BEYOND THE SUMMER AND INTO NEXT WINTER - WITH A CONSENSUS FORECAST OF SEVERAL STATISTICAL TOOLS INDICATING 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 MAM 2003 - JJA 2003. THE LARGE-SCALE CIRCULATION PATTERNS ARE EXPECTED TO REFLECT WARM EPISODE (EL NINO) CONDITIONS THROUGH SPRING - SO WARM EPISODE COMPOSITES WERE USED FOR MAM AND AMJ 2003. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - MAM 2003 TO MAM 2004 TEMPERATURE: TEMPERATURES FOR 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 NORTHWESTERN PORTION OF THE U.S. AND COASTAL ALASKA FOR MAM. RECENT TRENDS SUPPORT ABOVE NORMAL TEMPERATURES THROUGHOUT MUCH OF THE WEST AND ALASKA - ALTHOUGH THEIR RELIABILITY IN THE SOUTHWEST IS LESSENED BY THE INFLUENCE OF EL NINO. BELOW NORMAL TEMPERATURES ACROSS MUCH OF THE SOUTH IN MAM 2003 ARE CONSISTENT WITH THE EL NINO SIGNAL - AND HAVE SUPPORT FROM SMLR AND A CONSENSUS OF GCM FORECASTS. EL NINO IS EXPECTED TO WEAKEN IN THE SPRING AND SHOULD HAVE LITTLE EFFECT ON U.S. TEMPERATURES PAST AMJ 2003 - LEAVING ONLY LONG TERM TRENDS TO INFLUENCE THE FORECAST BEYOND THEN. 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. THERE IS SUPPORT FOR ABOVE NORMAL TEMPERATURES IN JJA FROM OTHER TOOLS AS WELL - WITH BOTH CCA AND SMLR INDICATING WARMER THAN NORMAL TEMPERA- TURES IN THE SOUTHEAST AND EAST COASTS. TRENDS GRADUALLY DIMINISH AS THE TRANSITIONAL FALL SEASON APPROACHES - LEAVING ONLY THE REGIONS OF STRONGEST WARMING TRENDS BY OND 2003. FROM THERE THE FORECAST RAPIDLY TRANSITIONS TO WINTERTIME TEMPERATURE TRENDS - INDICATED BY THE DJF OUTLOOK - SHOWING ABOVE NORMAL TEMPERATURES OVER MUCH OF THE COUNTRY EXCEPT FOR THE NORTHWESTERN U.S. INTO THE NORTHERN PLAINS - NORTHERN 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 FMA 2004 AND BEYOND. THE SLIGHT CHANGES MADE IN THE TEMPERATURE FORECASTS FOR CORRESPONDING SEASONS FROM LAST MONTHS OUTLOOK SERIES REFLECT SOME CHANGES IN THE CCA AND SMLR PREDICTIONS - AND THE FORECASTS FROM AN NEW COMPOSITING TOOL BASED ON THE NINO 3.4 CONSOLIDATION FORECAST. WITH NEAR NEUTRAL ENSO CONDITIONS ANTICIPATED THROUGH MUCH OF THIS FORECAST PERIOD - THE NEW COMPOSITING TOOL PROVIDED AN ESTIMATE OF TEMPERATURE TRENDS TO COMPLEMENT OCN. REVISIONS PRIMARILY SHOW SLIGHTLY INCREASED CONFIDENCE IN THE TREND SIGNALS. CHANGES IN THE FORECASTS FROM NDJ 2003 THROUGH JFM 2004 REFLECT THE TREND UPDATE PROVIDED BY NEW DATA THROUGH JANUARY 2003 - AND CONSISTENCY ADJUSTMENTS IN ADJACENT SEASONS. . . . . . . . . PRECIPITATION: BELOW MEDIAN PRECIPITATION IS EXPECTED IN MAM 2003 FOR EASTERN SECTIONS OF THE PACIFIC NORTHWEST AND MONTANA. DRIER THAN NORMAL CONDITIONS ARE ALSO EXPECTED OVER THE TENNESSEE VALLEY NORTHWARD TO THE GREAT LAKES AND EXTENDING ALONG THE NORTHERN U.S. BORDER TO NORTHERN NEW ENGLAND - BASED ON ENSO COMPOSITES WITH SUPPORT FROM GCM PREDICTIONS AND SMLR. ABOVE MEDIAN PRECIPITATION IS FORECAST FOR THE SOUTHWEST - THE SOUTHERN ROCKIES - THE GULF COAST AND FLORIDA IN MAM 2003 - BASED ON ENSO COMPOSITES. ABOVE MEDIAN PRECIPITATION CONTINUES IN THE SOUTHWEST INTO AMJ SUPPORTED BY EL NINO COMPOSITES AND EL NINO LAGGED COMPOSITES RELATIVE TO JFM. WITH THE EL NINO WEAKENING A BIT FASTER THAN ANTICIPATED ON LAST MONTHS FORECAST THE MJJ FORECAST WAS REVISED SLIGHTLY TO SHOW SOME OF THE ABOVE NORMAL PRECIPITATION TRENDS IN THE PACIFIC NORTHWEST THAT HAD BEEN MASKED IN LAST MONTHS FORECAST BY THE WEAK ENSO SIGNAL FOR BELOW MEDIAN SPRINGTIME PRECIPITATION IN THAT REGION. BELOW MEDIAN PRECIPITATION FOR PORTIONS OF THE GREAT BASIN IS INDICATED BY OCN WITH SOME SUPPORT FROM SMLR DURING JJA AND JAS 2003. ONLY SLIGHT CHANGES WERE MADE IN THE PRECIPITATION FORECASTS FOR CORRESPONDING SEASONS FROM LAST MONTHS OUTLOOK SERIES. THE CONFIDENCE IN THE PRECIPITATION FORECAST FOR MAM 2003 WAS REDUCED SLIGHTLY TO REFLECT THE WEAKENING EL NINO - AND THE TREND SIGNAL FOR ABOVE MEDIAN PRECIPITATION WAS RESTORED IN MJJ 2003 IN THE PACIFIC NORTHWEST FOR REASONS EXPLAINED EARLIER. . . . . . . . . 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: D. UNGER 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 MARCH 20 2003. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. $$