PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 830 AM EDT THU MAY 20 2004 . . . . . . . . SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THE SEASONAL OUTLOOK REFLECTS PRIMARILY THE PRESENCE OF LONG TERM TRENDS ON U.S. TEMPERATURE AND PRECIPITATION... STATISTICAL FORECAST TOOLS... AND SOME INPUT FROM NUMERICAL MODELS DURING THE FIRST SEVERAL SEASONS... ALL WITHIN THE CONTEXT OF THE LIKELY CONTINUATION OF ENSO-NEUTRAL CONDITIONS IN THE TROPICAL PACIFIC DURING THE NEXT SEVERAL MONTHS. SSTS IN THE TROPICAL PACIFIC REMAIN BELOW THE THRESHOLD REQUIRED TO PRODUCE ENSO IMPACTS ON THE US CLIMATE. IN FACT - SSTS IN THE ENSO-RELEVANT REGION HAVE MOVED EVEN CLOSER TO NORMAL IN THE PAST TWO MONTHS... AND BELOW NORMAL SSTS OVER THE EASTERN EQUATORIAL PACIFIC HAVE STRENGTHENED SOMEWHAT. CLIMATE MODELS FROM NCEP - CDC - IRI AND ECMWF ARE CURRENTLY DIVIDED INTO TWO MAIN GROUPS. ONE GROUP INDICATES CONTINUATION OF NEAR-NEUTRAL TROPICAL SSTS AT LEAST THROUGH THE SUMMER WITH A FEW MODELS CONTINUING NEAR-NEUTRAL CONDITIONS AT LEAST THROUGH THE END OF THE YEAR. OTHER MODELS HOWEVER ARE INDICATING THE DEVLOPMENT OF EL NINO CONDITIONS... SOME AS EARLY AS THE END OF THE SUMMER. WE ARE SOMEWHAT SKEPTICAL OF THE SCENARIOS PREDICTED BY THIS LATTER GROUP OF MODELS AS ONLY THE VERY STRONGEST EL NINOS HAVE BEEN ABLE TO START IN THE BOREAL SUMMER DUE TO NORMALLY SEASONALLY LOWERING SSTS ALONG THE EQUATOR THAT MAKE IT INCREASINGLY DIFFICULT TO INITIATE CONVECTION UNLESS SSTS GO WELL ABOVE NORMAL. THE FORECASTS FOR THE FIRST FEW SEASONS THROUGH ASO 2004 ARE SHOWING ABOVE NORMAL TEMPERATURES OVER MUCH OF THE WEST AND SOUTHWEST THROUGHOUT... AND AN AREA OF RELATIVE WAMRTH IN THE EAST THAT TENDSS TO SHIFT NORTHWARD AND WEAKEN WITH TIME. A REGION OF ABNORMAL DRYNESS IS LIKELY OVER THE NORTHWEST U.S. BEGINNING OVER WASHINGTON AND OREGON DURING JJA AND EXPANDING TO INCLUDE MOST OF THE GREAT BASIN AND PARTS OF THE NORTHERN ROCKIES DURING JAS AND ASO. SOME PREFERENCE FOR ABOVE NORMAL TEMPERATURES IS INDICATED FOR PARTS OF THE SOUTH COAST OF ALASKA DURING JJA... BUT AFTER THAT EQUAL CHANCES ARE GIVEN FOR THE THREE POSSIBLE CATEGORIES FOR BOTH PRECIPITATION AND TEMPERATURE (ABOVE - NEAR MEDIAN OR NEAR NORMAL - BELOW) OVER ALASKA. THE AUTUMN SEASONS OF SON AND OND HAVE THE WEAKEST SIGNALS FOR TEMPERATURE OF THE ENTIRE YEAR OVER THE CONUS ALTHOUGH THERE IS AN INDICATION FOR ABOVE MEDIAN PRECIPITATION OVER PART OF THE SOUTH-CENTRAL STATES. DURING THE COMING WINTER AND FOLLOWING SPRING LONG-TERM TRENDS FAVOR ABOVE NORMAL TEMPERATURES CENTERED OVER THE MIDWEST DURING THE WINTER... REACHING MAXIMUM AREA COVERAGE OF MUCH OF THE COUNTRY DURING JFM AND SETTLING INTO THE WEST AND SOUTHWEST FOR THE REMAINING SEASONS. MOST OF THESE SEASONS HAVE NO RELIABLE SIGNALS FOR PRECIPITATION. . . . . . . . . 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 AS OF MID-MAY WEEKLY AVERAGES OF SST SHOW TEMPERATURE ANOMLIES IN THE NEAR NORMAL RANGE (WITHIN +/- 0.5C) ACROSS MUCH OF THE TROPICAL PACIFIC. EXCEPTIONS INCLUDE SMALL REGIONS OF 0.5 TO 1.0 DEGREE ANOMALIES JUST WEST OF THE DATELINE AND NEAR INDONESIA - AND AN AREA OF -0.5 TO -1.5 DEGREE ANOMALIES EXTENDING FROM THE COAST OF PERU WEST-NORTHWESTWARD TO ABOUT 125W. RECENT 5-DAY MEAN TOGA-TAO DEPTH-LONGITUDE CROSS-SECTIONS SHOW ABNORMALLY WARM WATER - WITH ANOMALIES OF UP TO 1.5 TO 2.0 C - CENTERED ABOUT 125 METERS BELOW THE SURFACE OF THE CENTRAL PACIFIC MOVING EAST WITH TIME AND A REGION OF ABNORMALLY COLD WATER IN THE EASTERN PART OF THE OCEAN SLOPING UP TOWARDS THE SURFACE BETWEEN 120W AND THE SOUTH AMERICAN COAST. THIS ARRANGEMENT OF ANOMALIES MAKES FOR A LARGER-THAN-AVERAGE TILT IN THE THERMOCLINE - FROM DEEPER THAN NORMAL IN THE WEST TO SHALLOWER THAN NORMAL IN THE EAST. THE QUANTITY OF EXCESS HEAT STORED IN THE AREA OF WARMER THAN NORMAL WATER IS CONSIDERED TO BE INSUFFICIENT TO INITIATE AN EL NINO WHEN IT SHOALS OVER THE EASTERN PACIFIC LATER IN THE SPRING OR EARLY SUMMER. THE TRADE WINDS HAVE BEEN MOSTLY STRONGER THAN NORMAL DURING THE PAST MONTH OVER THE CENTRAL PACIFIC... WHICH HAS LED TO THE GRADUAL COOLING OF SURFACE WATERS ALONG AND NEAR THE EQUATOR. A BURST OF WESTERLY WINDS THAT OCCURRRED OVER THE FAR WESTERN TROPICAL PACIFIC DURING EARLY APRIL IS PROBABLY THE CAUSE OF THE ABOVE-MENTIONED WARM WATER AT DEPTH OVER THE CENTRAL PACIFIC... NOW MOVING EASTWARD AS A KELVIN WAVE. OUTGOING LONG-WAVE RADIAION (OLR) MAPS FROM SATELLITE OBSERVATIONS SHOW THAT MOST ACTIVE CONVECTION HAS BEEN OVER THE WESTERN PACIFIC NEAR THE EQUATOR AND WELL TO THE NORTH OF THE EQUATOR OVER THE EASTERN PACIFIC WHERE IT MAY BE RELATED TO THE START OF THE EASTERN PACIFIC HURRICANE SEASON. ELSEWHERE IN THE TROPICAL PACIFIC OLR IS SUB-NORMAL. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS FORECASTS FROM MULTIPLE MODELS GIVE A RANGE OF POSSIBLE FUTURE SST ANOMALIES IN NINO 3.4 OF -0.4 TO +1.5 C THROUGH SON... ALTHOUGH MOST ARE IN THE VICINITY OF AROUND 0.5C... THE BOUNDARY BETWEEN NEUTRAL AND A WEAK WARM EVENT. THE CONSENSUS OF THE MODEL SST FORECASTS FALLS REMAINS WITHIN THE ENSO-NEUTRAL RANGE FROM THEREAFTER ALTHOUGH WITH INCREASED SPREAD AND UNCERATINTY. TO SEE THESE FORECASTS GO TO: http:// www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/index.pri.html A CONSOLIDATION FORECAST OF IN-HOUSE TOOLS INDICATES THAT NINO 3.4 SST ANOMALIES WILL RISE FROM ITS CURRENT NEAR ZERO STATE TO SLIGHTLY ABOVE THE +0.5C THRESHOLD FROM SON THROUGH DJF AND THEN DECLINE SLOWLY THEREAFTER. THE PROBABILITY SPREAD FOR COLD - NERUTRAL - OR WARM ENSO CONDITIONS INCREASES WITH THE GREATEST LIKELIHOOD SHIFTING FROM NEAR NORMAL IN SUMMER TO ABOUT EQUAL CHANCES FOR NETURAL OR WARM ENSO CONDITIONS BY FALL. THERE IS LITTLE CHANCE FOR A COLD EVENT TO DEVELOP. BEGINNING NEXT WINTER - THE CONSENSUS IS NEAR THE NEUTRAL/WARM EVENT BORDER BUT THEN DECLINES SLOWLY. SINCE WEAK WARM EVENTS DO NOT EXERT STRONG FORCING ON THE ATMOSPHERE... SHOULD ONE DEVELOP... WE EXPECT THAT TRANSIENT ATMOSPHERIC CIRCULATION PATTERNS WILL CONTINUE TO BE FORCED PRIMARILY BY INTRA-SEASONALLY VARYING PHASES OF THE MJO... AND THE HIGHER LATITUDE PATTERNS WILL BE DETERMINED BY VARYING PHASES OF THE AO AND NAO THAT ARE NOT CURRENTLY PREDICTABLE AT SEASONAL RANGES. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOK THE PRIMARY TOOLS USED IN THE JJA THROUGH ASO FORECASTS WERE OCN AND CCA. CONSULTED - BUT NOT USED SIGNIFICANTLY - WERE TWO-TIER FORECASTS FROM SIX MODELS PROVIDED BY CDC - DYNAMICAL MULTI-MODEL ENSEMBLES FROM IRI AND DYNAMICAL MODEL FORECASTS FROM NCEPS ENVIRONMENTAL MODELING CENTER... SINCE THE MODELS GAVE A WIDE RANGE OF OFTEN CONFLICTING INDICATIONS... AND HAVE LITTLE A PRIORI SKILL DURING ENSO NETURAL CONDITIONS. CCA AND OCN TEMPERATURE FORECASTS WERE OFTEN CONSIDERED TOGETHER AS A CONSOLIDATION OF THESE TWO TOOLS AND WERE USED FOR THOSE AREAS AND PROJECTION TIMES WHERE THEY HAD USEFUL STATISTICAL SIGNIFICANCE. THE CONSTRUCTED ANALOG TECHNIQUE USING SOIL MOISTURE (CAS) WAS CONSDIERED AS IT DOES BEST DURING THE WARM SEASONS. IT CONFIRMED... ENLARGED AND EXTENDED IN TIME THE AREAS OF DRYNESS PREDICTED FOR THE NORTHWEST FROM OCN. AREAS OF ABOVE MEDIAN RAINFALL INDICATED BY CAS OVER THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY - EVEN THOUGH THEY HAD A STRONG SIGNAL - HAD NO USEFUL A PRIORI SKILL... SO WERE NOT SHOWN ON THE OFFICIAL FORECAST MAPS. ALSO - SOME CONSIDERATION WAS GIVEN TO COMPOSITE OBSERVED TEMPERATURE AND PRECIPITATION ANOMALY PATTERNS OVER THE CONUS FOR PAST CASES OF NEUTRAL SST PATTERNS OVER THE EQUATORIAL PACIFIC... WITH A SLIGHT TILT TOWARDS WARM ENSO COMPOSITE PATTERNS. THE IMPACT OF OCN AND CCA IS VISIBLE IN THE WARMTH PREDICTED OVER THE SOUTHERN AND WESTERN U.S. FROM JFM THROUGH JJA 2005 FOR THE TEMPERATURE FORECASTS. CCA AND OCN ARE THE ONLY TOOLS USED BEYOND THE FOURTH LEAD. THERE WERE FEW SIGNIFICANT INDICATIONS FOR MAKING OTHER THAN AN EQUAL CHANCES FORECAST FOR PRECIPITATION AT THE LONGER LEADS. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - JJA 2004 TO JJA 2005 TEMPERATURE: CCA AND OCN ARE THE MAIN TOOLS USED HERE. FOR JJA 2004 CCA AND OCN INDICATE ABOVE NORMAL TEMPERATURES FOR PART OF THE SOUTH COAST AND PANHANDLE OF ALASKA - THE PACIFIC NORTHWEST AND MUCH OF THE SOUTHWESTERN U.S. FROM CALIFORNIA TO THE SOUTHERN GREAT PLAINS. ALTHOUGH THESE TOOLS ALSO INDICATED ABOVE NORMAL TEMPERATURES FOR MOST OF TEXAS AND GULF COAST AREAS - EC WAS PREDICTED THERE BECAUSE OF A STRONG OPPOSING SIGNAL FOR BELOW NORMAL TEMPERATURES FROM CAS DUE TO RECENT HEAVY PRECIPITATION. EAST OF THE MISSISSIPPI RIVER MOST AREAS ALSO HAD INDICATIONS FOR WARMTH FROM CCA AND/OR OCN - AND SINCE THERE WAS NO OPPOSING SIGNAL FROM CAS ABOVE NORMAL TEMPERATURES WERE PREDICTED OVER MUCH OF THE EAST. THIS OVERALL WARM - AND LARGELY TREND - SIGNAL FADES FROM ALASKA IN JJA 2004 THROUGH AMJ 2005 BUT RETURNS IN MJJ 2005. OVER THE CONUS THE EXCESS WARMTH REMAINS IN PLACE OVER ALL OF THE SOUTHWEST - BUT FADES FROM THE NORTHWEST GOING FROM JJA THROUGH ASO. THE AREA OF ABOVE NORMAL TEMPERATURES PREDICTED OVER THE EAST WEAKENS AND SHIFTS NORTHWARD DURING THESE SEASONS. BY SON THE TREND FOR ABNORMAL WARMTH RETREATS TO A SMALL SECTION OF THE INTERIOR SOUTHWEST CENTERED ON ARIZONA - WHILE SOUTHERN FLORIDA REMAINS IN THE ABOVE NORMAL CLASS. THE CCA-OCN SIGNAL FADES TO EC EVERYWHERE BY OND WHEN THE SKILL OF CCA AND OCN ARE AT THEIR ANNUAL MINIMUM. THE SIGNAL BEGINS TO REBOUND IN NDJ IN THE CORE OF THE SOUTHWEST - AND BY DJF THIS REGION GETS COMPANY FROM THE NORTHEAST - THE GREAT LAKES - THE OHIO VALLEY AND TENNESSEE AND EASTERN SECTIONS OF THE NORTHERN AND CENTRAL GREAT PLAINS. THE CCA-OCN SIGNAL PEAKS IN JFM 2005 - WHEN MORE OF THE NATION IS LIKELY TO HAVE ABOVE NORMAL TEMPERATURES THAN IN ANY OTHER SEASON. CCA-OCN INDICATES ABNORMAL WARMTH ONLY IN THE WEST FROM FMA THROUGH AMJ BUT BY THE FINAL TWO LEADS - MJJ AND JJA 2005 - THE CCA-OCN COMBINED TOOL AGAIN INDICATES ENHANCED LIKELIHOOD FOR ABNORMAL WARMTH IN THE SOUTHEAST - SOUTHERN TEXAS - AND DURING MJJ IN SOUTHERN ALASKA. . . . . . . . . PRECIPITATION: THERE IS A LIKELIHOOD OF SUB-MEDIAN PRECIPITATION FROM JJA THROUGH ASO FROM OCN AND CCA FOR VARIOUS PARTS OF THE NORTHWEST AND THE GREAT BASIN - WITH A BRIEF APPEARNACE OF SUB-MEDIAN ALSO OVER NORTHERN NEW YORK AND NEW ENGLAND DURING JAS. AN ENHANCED LIKELIHOOD OF ABOVE MEDIAN PRECIPITATION IS EXPECTED IN PARTS OF THE SOUTH-CENTRAL U.S. FOR SOME OF THE FALL AND WINTER SEASONS - ALONG WITH INDICATIONS FOR SUB-MEDIAN PRECIPITATION OVER PART OF THE CENTRAL PLAINS DURING NDJ. ELSEWHERE AND FOR OTHER SEASONS NOT MENTIONED EC IS INDICATED DUE TO LACK OF ANY SIGNIFICANT SIGNALS. NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES). . . . . . . . . FORECASTER: A. J. WAGNER 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. 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. 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 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 - 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 JUN 17 2004. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. $$