PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT THU JUNE 19 2003 CORRECTED JUNE 20 2003 . . . . . . . . SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THE SEASONAL OUTLOOK REFLECTS THE PRESENCE OF LONG TERM TRENDS ON U.S. TEMPERATURE AND PRECIPITATION...STATISTICAL FORECAST TOOLS ...WITH SOME INPUT FROM NUMERICAL MODELS DURING THE FIRST SEVERAL SEASONS AND - FINALLY - THE POSSIBILITY A LA NINA WILL DEVELOP BY OR BEFORE THE JULY-AUGUST- SEPTEMBER SEASON - THOUGH UNCERTAINTY ABOUT THIS TRANSITION IS HIGHER THAN IT WAS LAST MONTH DUE TO RECENT INCREASES IN THE HEAT CONTENT OF THE EASTERN TROPICAL PACIFIC OCEAN. THE RAPID TRANSITION AWAY FROM EL NINO TOWARD LA NINA EARLIER THIS YEAR - FOLLOWED - IN MAY AND JUNE - BY AN APPARENT SLOWING - POSSIBLY EVEN REVERSAL - IN THIS TRANSITION INCREASES THE UNCERTAINTY ASSOCIATED WITH FORECASTS. THEREFORE BOTH PROBABILITIES AND AREA COVERED BY NON-EC PROBABILITIES WILL BE RELATIVELY LOW IN THIS SET OF FORECASTS. THE FORECASTS REFLECT A TRANSITION TO SOMETHING APPROXIMATING AN AVERAGE OF WEAK LA NINA CONDITIONS AND ENSO-NEUTRAL CONDITIONS. LA NINA CONTRIBUTIONS CEASE AFTER JFM - AFTER WHICH TIME MAINLY TREND IS USED FOR THE FORECAST. THE OUTLOOK FOR JULY THROUGH SEPTEMBER 2003 CALLS FOR ABOVE NORMAL TEMPERATURES OVER THE SOUTHWEST - SOUTHERN TEXAS AND SECTIONS OF THE SOUTHEAST. JAS PRECIPITATION IS EXPECTED TO BE ABOVE NORMAL IN THE SOUTHWEST WHERE AN ENHANCED MONSOON IS POSSIBLE - THOUGH HIGHLY UNCERTAIN. . . . . . . . . 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 EASTERLY WINDS - WHICH WERE STRONGER THAN NORMAL OVER THE CENTRAL AND WEST- CENTRAL EQUATORICAL PACIFIC DURING MARCH AND APRIL - HAVE RECENTLY GIVEN WAY TO MODEST WESTERLY ANOMALIES OVER MUCH OF THE PACIFIC. WINDS ARE LIKELY TO RETURN TO NORMAL OR EVEN ENHANCED EASTERLY - AT LEAST IN THE EAST. THE TRADITIONAL TAHITI-MINUS-DARWIN-BASED SOI WAS -0.6 IN MAY. EQUATORIAL PACIFIC SEA SURFACE TEMPERATURES REMAIN COOLER THAN NORMAL EAST OF 150W. TEMPERATURES ARE ABOUT 0.5 TO 1 DEGREE ABOVE NORMAL BETWEEN 165W AND 165E. SUB-SURFACE WATERS HAVE WARMED IN RESPONSE TO A STRONG INTRASEASONAL OSCILLATION WHICH IS PASSING THROUGH THE EASTERN TROPICAL PACIFIC NOW. HEAT CONTENT OF THE WATERS IN THE EAST HAS RISEN - BRINGING INTO QUESTION THE STRENGTH AND DURATION OF ANY LA NINA WHICH MAY DEVELOP. ON THE OTHER HAND IN A NUMBER OF REGIONS THE ATMOSPHERE IS DISPLAYING BEHAVIOR WHICH IS CONSISTENT WITH COLD EVENT IMPACTS. FOR EXAMPLE - THE MONSOON IS CURRENTLY ENHANCED OVER MEXICO. ALSO - SIGNS OF ENHANCEMENT OF THE CENTRAL AMERICAN MONSOON HAVE APPEARED IN LOW-LEVEL WINDS IN THE EASTERN TROPICAL AND SUBTROPICAL PACIFIC. THIS TREND IS EXPECTED TO CONTINUE INTO THE SUMMER AND THE MONSOON NOW SEEMS LIKELY TO BE AT LEAST SLIGHTLY ENHANCED IN THE SOUTHWEST US. FINALLY - 200 HPA HEIGHTS HAVE FALLEN OVER THE TROPICAL PACIFIC BASIN - INDICATING COOLING IN THE REGION - ANOTHER FEATURE CONSISTENT WITH LA NINA IMPACTS. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS FORECASTS FROM MULTIPLE MODELS GIVE A WIDE ARRAY OF POSSIBLE FUTURE SST PATTERNS IN THE TROPICAL PACIFIC - INDICATING CONSIDERABLE UNCERTAINTY. AN AVERAGE OVER ALL MODELS INDICATES WEAK LA NINA CONDITIONS DEVELOPING DURING THE SUMMER WITH LARGEST SST ANOMALIES OF ABOUT -0.4 DEGREES C DURING THE EVENT DURING FALL AND EARLY WINTER. TO SEE THESE FORECASTS PLEASE SEE: http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/plume.gif A CONSOLIDATION FORECAST OF IN-HOUSE TOOLS SHOWS TEMPERATURE ANOMALIES IN THE NINO 3.4 SST REGION PREDICTS WEAK LA NINA CONDITIONS DURING THE SUMMER. NINO 3.4 SST ANOMALIES ARE PREDICTED TO STRENGTHEN TO ABOUT -0.9 BY SON. CONFIDENCE IN THE FORECAST DROPS SHARPLY AFTER SON WHILE THE SST ANOMALY ALSO DECLINES DURING THE WINTER IN THE CONSOLIDATION. 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 JAS 2003 - OND 2003. IN JAS WE ALSO PAY ATTENTION TO THE SOIL MOISTURE TOOL CAS. INITIAL SOIL MOISTURE ANOMALIES ARE UNUSUALLY WET IN THE SOUTHEAST - THE TENNESSEE VALLEY - THE MIDDLE ATLANTIC THROUGH SOUTHERN NEW ENGLAND AND DRY IN SECTIONS OF THE CENTRAL GREAT PLAINS - THE SOUTHWEST AND THE ROCKIES. CAS TEMPERATURE HAS SIGNIFICANT SKILL IN NEW ENGLAND - THE MIDWEST - THE GREAT LAKES - SOUTHERN FLORIDA - TEXAS THROUGH OKLAHOMA - THE CENTRAL AND SOUTHERN ROCKIES AND CALIFORNIA. THE DYNAMICAL MODELS ARE CONSISTENT IN PREDICTING ABNORMAL WARMTH OVER MUCH OF THE CONTIGUOUS US AND ABNORMAL COLD AND WETNESS OVER ALASKA. THESE TOOLS FORECASTS REPRESENT A CONSISTENT RESPONSE TO A PREDICTED CONTINUED EVOLUTION TOWARD COLD EVENT CONDITIONS. HOWEVER - RECENT CHANGES IN THE HEAT CONTENT OF THE EASTERN TROPICAL PACIFIC OCEAN HAVE REDUCED THE LIKELIHOOD LA NINA WILL DEVELOP WITH THE STRENGTH AND PERSISTANCE ANTICIPATED LAST MONTH AND BY THE SST FORECASTS THIS MONTH. FOR THESE REASONS - THE DYNAMICAL MODEL FORECASTS ARE DE-EMPHASIZED IN THIS FORECAST. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2003 TO JAS 2004 TEMPERATURE: THE TEMPERATURE FORECAST FOR JAS IS BASED UPON A TREND-ADJUSTED COMPOSITE OF 27 CASES FROM THE HISTORICAL RECORD WHICH WERE CHARACTERIZED BY ENSO-NEUTRAL TROPICAL PACIFC OCEAN SURFACE TEMPERATURES - A SIMILAR SET OF 13 LA NINA COMPOSITES ALONG WITH INDICATIONS FROM CCA - OCN AND DYNAMICAL MODELS. TEMPERATURES ARE EXPECTED TO REMAIN ABOVE NORMAL IN SOUTHERN AND FAR WESTERN ALASKA DURING JAS DUE TO CCA - OCN AND CONTINUED ABNORMALLY WARM SSTS IN THE BERING SEA. IN THE CONTINENTAL US THE TREND REQUIRES WARM ANOMALIES CENTERED OVER THE SOUTHWEST AND FLORIDA. THESE CONSIDERATIONS CONTINUE THROUGH JFM. WARM ANOMALIES IN THE SOUTHWEST ARE TEMPERED SOMEWHAT BY THE EXPECTATION OF ENHANCED MONSOON CONDITIONS THERE. THIS IS INDICATED BY LOWER PROBABILITY ANOMALIES IN THE REGION IN COMPARISON WITH LAST MONTHS JAS FORECAST. FROM OND THROUGH JFM TEMPERATURE FORECASTS ARE BASED PRIMARILY UPON COMPOSITES CONDITIONAL UPON ENSO-NEUTRAL TO WEAK LA NINA CONDITIONS ALONG WITH INDICATIONS FROM CCA AND TREND. WARMER THAN NORMAL TEMPERATURES ARE PREDICTED IN ALASKA THROUGHOUT THIS PERIOD DUE TO OCN AND EXPECTED ABNORMALLY WARM OCEANS. LARGE REDUCTIONS IN THE AREA COVERED BY NON-ZERO PROBABILITY ANOMALIES - PARTICULARLY IN THE EASTERN US ARE DUE TO AN INCREASE IN UNCERTAINTY IN THIS MONTHS FORECAST TOOLS. THOUGH OCN IS THE PRIMARY TOOL USED IN THAT REGION - THIS MONTH AND LAST - THE LATEST FORECAST EMPHASIZES ONLY THE STRONGEST - MOST CONFIDENT INDICATION FROM THAT TOOL. THOSE ARE FOUND MAINLY IN THE SOUTH AND SOUTHWEST DURING WINTER AND IN THE SOUTHWEST IN SUMMER. FORECASTS AFTER JFM ARE BASED ON TREND-ADJUSTED ENSO-NEUTRAL COMPOSITES - OCN AND CCA. . . . . . . . . PRECIPITATION: DURING JAS ENHANCED MONSOON CONDITIONS ARE CURRENTLY CONSIDERED TO BE SLIGHTLY MORE LIKELY - ABOUT 5 PERCENT MORE LIKELY - THAN EC IN THE SOUTHWESTERN US AND ABOVE-MEDIAN RAINFALL IS PREDICTED THERE. FOR ASO THROUGH SON - TREND-ADJUSTED ENSO COMPOSITES AND DYNAMICAL MODELS ALL INDICATE ABOVE NORMAL PRECIPITATION IN FLORIDA. DRY REGIONS IN THE WESTERN US FROM JAS THROUGH OND ARE INDICATED BY TREND-ADJUSTED ENSO COMPOSITES - AS IS THE WET ANOMALY IN THE NORTHWEST US FROM OND THROUGH NDJ - THE WET ANOMALIES IN THE CENTRAL US IN DJF AND JFM AND THE DRY ANOMALY IN SOUTHERN TEXAS IN NDJ. TREND-ADJUSTED ENSO-NEUTRAL COMPOSITES AND CCA ARE USED FOR FORECASTS FROM FMA THROUGH JJA 2004. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). . . . . . . . . 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. 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 US - ARE UNPREDICTABLE BY CURRENT TECHNOLOGY AND ARE NOT EXPLICITLY INCLUDED IN OUR FORECAST PROCESS. 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: E. OLENIC 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 JULY 17 2003. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. $$