PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 830 AM EST THU APRIL 21 2005 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS CURRENT OBSERVATIONS INDICATE THAT THE WEAK WARM EPISODE CONDITIONS (EL NINO) THAT HAVE PREVAILED OVER THE EQUATORIAL PACIFIC SINCE JJA 2004 HAVE CONTINUED TO WEAKEN. THE LARGE AREA OF ABOVE NORMAL SSTS NEAR THE DATE LINE HAS DIMINISHED IN BOTH SIZE AND INTENSITY... WITH MAXIMUM DEPARTURES BETWEEN 0.5 AND 1.0 DEGREE CELSIUS OBSERVED OVER PARTS OF THE WESTERN AND WEST CENTRAL PACIFIC. A KELVIN WAVE WHICH WAS GENERATED BY A STRONG LOW-LEVEL WIND BURST IN THE WESTERN TROPICAL PACIFIC IN EARLY MARCH HAS TRAVELED ACROSS THE PACIFIC WARMING THE WATERS OF THE EASTERN PACIFIC TO BETWEEN 0.5 AND 1.5 DEGREES CELSIUS ABOVE NORMAL. A CONSENSUS OF SEA SURFACE TEMPERATURE (SST) PREDICTION TOOLS INDICATE THAT ENSO-NEUTRAL CONDITIONS WILL PREVAIL THROUGH THE SUMMER. THEREFORE ENSO COMPOSITES WERE NOT USED FOR ANY OF THE OUTLOOKS PRESENTED HERE. . . . . . . . . THE OUTLOOK FOR MJJ 2005 THROUGH ASO 2005 IS BASED ON A WIDE ARRAY OF FORECAST TOOLS INCLUDING DYNAMICAL AND STATISTICAL TOOLS. FOR THE SECOND CONSECUTIVE MONTH... ONLY MINIMAL CONSIDERATION WAS GIVEN TO THE CFS... SINCE IT APPEARS TO BE TOO COOL AND WET DURING THE SUMMER AND FALL SEASONS. THE AVAILABLE DYNAMICAL MODELS INCLUDE THE IRI MULTI-MODEL ENSEMBLE... THE CDC STATISTICAL ENSEMBLE RENDERING OF THE RESPONSE OF SIX MODELS TO SST FORECASTS AND THE SCRIPPS COUPLED MODEL FORECAST. ALL OF THESE MODELS PREDICT A REGION OF ABOVE NORMAL PRECIPITATION IN PARTS OF THE NORTHERN PLAINS... AND RELATIVELY DRY CONDITIONS IN THE SOUTHEAST DURING MJJ. SEVERAL OF THE STATISTICAL TOOLS INCLUDING THE CONSTRUCTED ANALOG BASED ON SOIL MOISTURE AND CIRCULATION... THE OCN... AND THE ENSEMBLE CCA... ARE CONSISTENT WITH THESE FEATURES. THERE IS A CONSENSUS AMONG THE DYNAMICAL MODEL FORECASTS FOR THE PLAINS WET AREA TO SHIFT WESTWARD DURING JJA AND FOR DRYNESS TO PERSIST IN THE SOUTHEAST. . . . . . . . . BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOK 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 SST ANOMALIES ALONG THE EQUATOR IN THE PACIFIC HAVE DECREASED SINCE THE BEGINNING OF THE YEAR... WITH DEPARTURES OF 0.5 DEGREES C ABOVE NORMAL OBSERVED ONLY BETWEEN 155E AND 175W AND BETWEEN 120W AND 100W BY THE MIDDLE OF APRIL. SINCE THE BEGINNING OF THE YEAR THE ENSO INDICES HAVE DECREASED ACROSS THE PACIFIC... WITH VALUES IN NINO 4... NINO 3.4... AND NINO 3 ALL WITHIN 0.5 DEGREES CELSIUS OF NORMAL BY THE MIDDLE OF APRIL. CONVECTIVE ACTIVITY OVER THE INDIAN OCEAN AND WESTERN PACIFIC DURING APRIL HAS BEEN DOMINATED BY INTRASEASONAL ACTIVITY... WITH THE REGION OF CONVECTION COVERING INDONESIA AND THE WESTERN PACIFIC BY THE MIDDLE OF APRIL. EXPECTATIONS ARE THAT THIS ENSO WARM EPISODE IS ENDING WITH NEAR-NEUTRAL ENSO CONDITIONS EXPECTED TO PERSIST THROUGH THE NORTHERN HEMISPHERE SUMMER. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS THE CFS PREDICTS SEASONAL MEAN NINO 3.4 SST ANOMALIES WILL DECLINE FROM THE CURRENT (DJF) AVERAGE OF ABOUT +0.3 C TO ZERO FOR MJJ... BECOMING SLIGHTLY NEGATIVE BY LATE SUMMER 2005. STATISTICAL PREDICTIONS FROM CCA... CA... AND THE MARKOV MODEL KEEP NINO 3.4 SST ANOMALIES ABOVE ZERO... WITH CCA THE WARMEST TOOL... PREDICTING SSTS TO INCREASE SLIGHTLY TO JUST OVER 1 DEG C BY LATE FALL 2005. THE CA TOOL PREDICTS SST ANOMALIES TO DECREASE SLOWLY TO +0.1 C BY EARLY SUMMER... FOLLOWED BY A GRADUAL INCREASE WHICH PEAKS JUST BELOW +1.0 C IN LATE WINTER 2005-06. THE MARKOV TOOL GRADUALLY INCREASES THE NINO 3.4 SST ANOMALY TO +0.75 C BY LATE FALL. THE SKILL-WEIGHTED CONSOLIDATION OF THESE TOOLS INDICATES THE NINO 3.4 SST ANOMALIES WILL REMAIN STEADY THROUGH SPRING... THEN RISE SLOWLY FROM EARLY SUMMER THROUGH MID-WINTER... PEAKING AT ABOUT 0.8 C IN DJF AND THEN DECLINE TO NEAR ZERO BY MJJ 2006. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOK THE OUTLOOK FOR MJJ 2005 THROUGH ASO 2005 IS BASED ON THE MULTI-MODEL ENSEMBLE FROM IRI... THE SCRIPPS MODEL AND STATISTICAL TOOLS... INCLUDING CCA... SMLR AND OCN. CAS AND ECCA WERE ALSO USED FOR MJJ. OCN AND CCA ARE THE PRIMARY TOOLS USED FOR SON 2005 THROUGH MJJ 2006. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - MJJ 2005 TO MJJ 2006 TEMPERATURE: FOR MJJ THERE IS A STRONG CONSENSUS AMONG TOOLS FOR BELOW NORMAL TEMPERATURES IN A REGION CENTERED ON MINNESOTA AND IOWA... AND FOR WARM ANOMALIES IN THE SOUTHWEST... THE PACIFIC NORTHWEST AND IN SECTIONS OF THE SOUTHEAST. THE COOL ANOMALY IN THE NORTH IS EXPECTED TO DRIFT WESTWARD DURING JJA AND DISAPPEAR BY JAS. WARM ANOMALIES ARE PREDICTED FOR MUCH OF ALASKA AND THE WEST AND ALSO IN SECTIONS OF THE SOUTHEAST DURING MJJ AND JJA BY MOST OF THE TOOLS ... ANCHORED BY THE VERY CONSISTENTLY STRONG TRENDS IN THE SOUTHWEST. WARM ANOMALIES FORECAST IN THE EAST IN JAS AND ASO ARE PUSHED FURTHER SOUTH DUE TO A WEAKER CONSENSUS AMONG THE TOOLS. FROM SON 2005 THROUGH MJJ 2006 OCN AND CCA ARE THE MAIN FORECAST TOOLS AND REFLECT PRIMARILY THE INFLUENCE OF TRENDS. NOTABLY... ALASKA IS PREDICTED TO HAVE WARM ANOMALIES FROM DJF 2005-2006 THROUGH MJJ 2006. . . . . . . . . PRECIPITATION: FOR MJJ THERE IS A VERY STRONG CONSENSUS AMONG TOOLS FOR ABOVE NORMAL PRECIPITATION IN THE WESTERN GREAT LAKES UPPER MIDWEST REGION AND BELOW NORMAL PRECIPITATION IN FLORIDA AND THE EXTREME SOUTHEAST. THE WET ANOMALY IN THE NORTH IS EXPECTED TO DRIFT WESTWARD DURING JJA AND DISAPPEAR BY JAS. BELOW NORMAL PRECIPITATION IS ALSO EXPECTED IN THE SOUTH ALONG THE GULF COAST DURING JJA. WET ANOMALIES APPEAR IN THE SOUTHEAST ALONG THE ATLANTIC COAST DURING JAS - SON COURTESY OF THE EXPECTED CONTINUATION OF ENHANCED TROPICAL ACTIVITY WHICH WE UNDERSTAND TO BE PART OF A LONG TERM TREND. CCA AND OCN ARE THE ONLY INPUTS TO THE FORECASTS FOR OND 2005-MJJ 2006. FROM JFM - MJJ 2006 NO STRONG TRENDS ARE EVIDENT ANYWHERE ACROSS THE COUNTRY. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). . . . . . . . . FORECASTER: M. HALPERT 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. AO - ARCTIC OSCILLATION - A MEASURE OF THE DIFFERENCE IN PRESSURE (AT SEA LEVEL) OR 500-HPA HEIGHT (IN THE MIDDLE TROPOSPHERE) BETWEEN THE NORTHERN POLAR REGION AND MIDDLE LATITUDES. WHEN PRESSURES AND HEIGHTS ARE ABOVE (BELOW) NORMAL AT HIGH LATITUDES AND BELOW (ABOVE) NORMAL AT MIDDLE LATITUDES - THE AO IS DEFINED AS NEGATIVE (POSITIVE) AND IS ASSOCIATED WITH BELOW (ABOVE) NORMAL TEMPERATURES OVER MIDDLE LATITUDES - INCLUDING THE CONUS. 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. CFS - CLIMATE FORECAST SYSTEM - A FULLY-COUPLED OCEAN-ATMOSPHERE FORECAST SYSTEM WHICH USES NO ADJUSTMENTS TO OCEAN-ATMOSPHERE FLUXES IN POST- PROCESSING (A ONE-TIER SYSTEM) DEVELOPED AT THE NATIONAL CENTERS FOR ENVIRONMENTAL PREDICTION. 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. ECCA - ENSEMBLE CCA. A MULTI-VARIATE STATISTICAL FORECAST BASED ON THE PAST PERFORMANCE OF THE CFS MODEL FORECAST USING THE MOST RECENT FORECAST AS THE PREDICTOR. 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. ITCZ - INTERTROPICAL CONVERGENCE ZONE - A LINE WHERE THE SOUTHEASTERLY AND NORTHEASTERLY TRADE WINDS CONVERGE - CHARACTERIZED BY ENHANCED CONVECTION. IT MAY BE IN EITHER THE NORTHERN OR SOUTHERN HEMISPHERE - AND OCCASIONALLY A DOUBLE ITCZ MAY BE SEEN IN BOTH HEMISPHERES NOT FAR FROM THE EQUATOR. LA NINA - THE COLD PHASE OF THE ENSO CYCLE MJO - MADDEN-JULIAN OSCILLATION - ALSO CALLED TROPICAL INTRA-SEASONAL OSCILLATION - 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 - WHICH MAY BE CONSIDERED AS THE ATLANTIC HALF OF THE AO. NOTE THAT THE STATUS OF THE AO/NAO AND OTHER SLOWLY VARYING CIRCULATION MODES - WHILE VERY IMPORTANT IN DETERMINING THE TEMPERATURE AND PRECIPITATION REGIMES OVER THE U.S. - ARE UNPREDICTABLE BEYOND A WEEK OR TWO AHEAD AT BEST BY CURRENT TECHNOLOGY AND ARE NOT EXPLICITLY INCLUDED IN OUR FORECAST PROCESS AS RELIABLE PREDICTORS. 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. -------------------------------------------------------------------------------- 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 MAY 19 2005. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. $$