PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EST THU DECEMBER 18 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 THE LIKELY CONTINUATION OF ENSO NEUTRAL OR WEAK WARM EVENT CONDITIONS IN THE TROPICAL PACIFIC DURING THE NEXT SEVERAL MONTHS. A WEAK WARM EVENT - SHOULD IT DEVELOP - IS NOT LIKELY TO HAVE A MAJOR IMPACT ON US CLIMATE THIS WINTER. ALTHOUGH THEY ARE NOT VERY PREDICTABLE BEYOND A WEEK OR TWO - THE ARCTIC AND ESPECIALLY THE NORTH ATLANTIC OSCILLATIONS HAVE BEEN GIVING INDICATIONS OF GOING MORE TOWRDS THE NEGATIVE THAN POSITIVE SIDE IN RECENT MODEL FORECASTS - WHICH COULD FAVOR PERIODS OF COLD WEATHER OVER THE EASTERN U.S. SHOULD THIS CONTINUE. THE RAPID COOLING TREND TOWARDS LA NINA IN THE EQUATORIAL PACIFIC DURING LAST JANUARY THROUGH MAY WAS FOLLOWED BY WARMING DURING JUNE AND EARLY JULY - AND CONDITIONS HAVE REMAINED WITHIN THE WARM HALF OF THE NEUTRAL RANGE SINCE THEN. AS OF MID-DECEMBER - SURFACE AND SUBSURFACE TEMPERATURES IN THE EQUATORIAL PACIFIC CONTINUE TO BE SLIGHTLY ABOVE THE LONG TERM AVERAGE. A WEAK WARM EVENT IS POSSIBLE EARLY IN 2004 BUT FOR NOW WE ASSUME NEUTRAL CONDITIONS. THE OUTLOOK FOR JANUARY THROUGH MARCH 2004 CALLS FOR BETTER THAN AVERAGE ODDS OF ABOVE NORMAL TEMPERATURES OVER MOST OF THE WESTERN HALF OF THE NATION - EXTENDING ACROSS THE UPPER MISSISSIPPI VALLEY TO THE WESTERN GREAT LAKES REGION. BELOW-NORMAL TEMPERATURES ARE EXPECTED TO BE THE MOST LIKELY OUTCOME ON THE AVERAGE FROM EASTERN TEXAS ACROSS THE GULF COAST STATES TO THE SOUTHERN APPALACHIANS AND THE CAROLINAS INDLUDING ALL OF FLORIDA EXCEPT FOR THE EXTREME SOUTHERN PENINSULA. THE CHANCE FOR BELOW-MEDIAN PRECIPITATION IS MORE LIKELY THAN AVERAGE OVER THE INTERIOR SOUTHWEST - PORTIONS OF THE CENTRAL GREAT PLAINS - AND FLORIDA INCLUDING THE IMMEDIATE CENTRAL GULF COAST. ABOVE-MEDIAN PRECIPITATION HAS ENHANCED LIKELIHOOD OVER MUCH OF SOUTHERN AND WESTERN TEXAS AS WELL AS OVER THE PACIFIC NORTHWEST EXTENDING AS FAR EAST AS NORTHWESTERN MONTANA. . . . . . . . . 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-DECEMBER WEEKLY AVERAGES OF SST SHOW POSITIVE ANOMALIES ALONG THE EQUATOR IN THE PACIFIC FROM A FEW TENTHS TO SLIGHTLY MORE THAN ONE DEGREE C. THE MOST CONSISTENTLY WARM AND UNTIL RECENTLY GROWING REGION OF ABNORMALLY WARM SURFACE WATER LIES ALONG AND ON BOTH SIDES OF THE EQUATOR BETWEEN 175W AND 160E. NEVERTHELESS - MUCH OF THIS REGION SUB-NORMAL CONVECTION - WITH THE NOVEMBER EQUITORIAL OLR INDEX NEAR THE DATELINE MODERATELY POSITIVE. AS OF MID-DECEMBER - THE TAO TEMPERATURE AND CPC OLR OBSERVATIONS STILL DID NOT SHOW ANY IDICATION OF AN EL NINO - BUT THE OLR PATTERN IS ASYMMETRIC WITH RESPECT TO THE EQUATOR - SUGGESTING INSTEAD AN ENHANCED NORTHERN HEMISPHERE ITCZ. THESE OBSERVATIONS SUPPORT THE ASSUMPTION OF ENSO-NEUTRAL CONDITIONS AT LEAST DURING THE FIRST FEW SEASONS OF THIS OUTLOOK. THIS ASSUMMPTION IS FURTHER SUPPORTED BY A RECENT INCREASE IN THE EQUATORIAL TRADE WINDS NEAR AND JUST WEST OF THE DATELINE - RESULTING IN A SLIGHT DECREASE OF SSTS IN THAT AREA. THE TRADE WINDS ARE CLOSE TO SEASONAL AVERAGE VALUES OVER MOST OF THE TROPICAL PACIFIC - AND ARE WEAKER THAN NORMAL ONLY NEAR THE SOUTH AMERCIAN COAST. THE NINO3.4 TEMPERATURE ANOMALY IS CLOSE TO WHAT IT WAS ONE MONTH AGO AND IS ABOUT +0.5 C. WHILE WE ARE - TECHNICALLY - NEARING A WEAK EL NINO - TYPICAL EL NINO IMPACTS ON THE TROPICAL ATMOSPHERE AND ELSEWHERE ARE NOT EVIDENT. . . . . . . . . PROGNOSTIC DISCUSSION OF SST FORECASTS FORECASTS FROM MULTIPLE MODELS GIVE A RANGE OF POSSIBLE FUTURE SST PATTERNS IN THE TROPICAL PACIFIC WITH THE NINO 3.4 SST ANOMALY WITHIN THE LIKELY RANGE OF -0.1 TO +0.7 C FOR THE NEXT FEW SEASONS. BEGINNING WITH THE UPCOMING SUMMER THERE IS MORE UNCERTAINTY BUT THE CONSENSUS OF THE AVAILABLE PROJECTIONS STILL FALLS WITHIN THE ENSO-NEUTRAL TO VERY WEAK EL NINO RANGE FROM THEN THROUGH NEXT FALL. 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 REMAIN SLIGHTLY ABOVE ZERO THROUGH SPRING 2004 - WITH THE ODDS FOR NEUTRAL CONDITIONS REACHING 79% IN JFM AND DECLINING SLOWLY THEREAFTER. FROM AMJ THROUGH SON 2004 THE PROBABILITIES OF NEUTRAL AND WEAK EL NINO CONDITIONS ARE ABOUT EQUAL - WHILE THERE IS LITTLE CHANCE FOR LA NINA. BY NEXT WINTER - THE CONSENSUS IS STILL WITHIN THE NEUTRAL RANGE - BUT THERE IS AN INCREASED SPREAD WHICH ALLOWS A NON-TRIVIAL CHANCE FOR EITHER EL NINO OR LA NINA TO DEVELOP - ALTHOUGH A NEUTRAL ENSO CONDITION IS STILL THE MOST PROBABLE OUTCOME. SSTA FORECASTS FOR THE NINO 3.4 REGION BY MODELS RUN IN OTHER CENTERS GENERALLY FALL IN THE ENSO-NEUTRAL RANGE AS WELL - BUT DO NOT RULE OUT A WEAK WARM EVENT. NEVERTHELESS - THE SEASONAL AVERAGE EFFECT ON THE ATMOSPHERE WOULD NOT BE MUCH DIFFERENT THAN WITH NEUTRAL CONDITIONS - AND WE EXPECT THAT TRANSIENT ATMOSPHERIC CIRCULATION PATTERNS WILL BE FORCED PRIMARILY BY VARYING PHASES OF THE MJO. 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 - IRI AND CDC- WERE EXAMINED FOR THE PERIOD JFM 2003 THROUGH AMJ 2004 AND A CONSENSUS OF THESE WAS USED IN PREPARING THE FORECASTS FOR THESE SEASONS. 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. ALSO - SOME CONSIDERATION OF COMPOSITE OBSERVED TEMPERATURE AND PRECIPITATION ANOMALY PATTERNS OVER THE CONUS FOR PAST CASES OF NEUTRAL AND NEGATIVE AO REGIMES STRATIFIED WITH NEUTRAL OR EL NINO SST PATTERNS OVER THE EQUATORIAL PACIFIC WERE CONSIDERED IN PREPARING THE FORECASTS FOR THE FIRST FEW LEADS. THE PRIMARY TOOLS USED IN THE JFM THROUGH AMJ FORECASTS WERE OCN AND CCA - TWO-TIER FORECASTS FROM SIX MODELS PROVIDED BY CDC - DYNAMICAL MULTI-MODEL ENSEMBLES FROM IRI AND DYNAMICAL MODEL FORECASTS FROM NCEPS ENVIRONMENTAL MODELING CENTER. THE IMPACT OF OCN AND CCA IS VISIBLE IN THE SOUTHERN AND WESTERN US AND IN ALASKA JFM THROUGH AMJ TEMPERATURE FORECASTS AND TO A LESSER EXTENT IN THE PRECIPITATION FORECASTS FOR THESE SAME SEASONS. THERE WAS QUITE GOOD AGREEMENT AMONG NCEP - CDC AND IRI DYNAMICAL MODELS ON THE UPPER AIR HEIGHT PATTERN DURING THE LATE WINTER INTO EARLY SPRING - AN AMPLIFIED PATTERN WITH A DEEP ANOMALOUS TROUGH SOUTH OF THE ALEUTIANS OR OVER THE EASTERN PACIFIC - A POSITIVE HEIGHT ANOMALY OVER WESTERN OR CENTRAL NORTH AMERICA - AND A NEGATIVE ANOMALY AND TROUGH CENTERED SOMEWHERE NEAR OF JUST OFF THE EAST COAST OF THE U.S. - SOME WITH AN EXTENSION BACK TOWARDS OR OVER THE SOUTHEASTERN U.S. THE PATTERN SUGGESTED BY THESE FORECASTS IS RELATED TO ABNORMAL WARMTH IN THE FAR WEST - SOME ABNORMAL WARMTH IN THE GREAT PLAINS OR NORTH-CENTRAL STATES DURING JFM 2004 AND BELOW NORMAL TEMPERATURES OVER THE GULF COAST AND SOUTH ATLANTIC STATES. DRIER THAN AVERAGE CONDITIONS ARE INDICATED FOR THE SOUTHWEST - FLORIDA - AND OVER THE CENTRAL GREAT PLAINS - WHILE WETTER THAN AVERAGE CONDITIONS ARE EXPECTED IN THE NORTHWEST AND IN PARTS OF TEXAS. THE DRYNESS FORECAST BY THE MODELS FOR CALIFORNIA WAS CONSIDRED RISKY DUE TO THE POSSIBILITY OF A WET REGIME IN COASTAL AREAS BEING FORCED AT TIMES BY THE ABOVE NORMAL SSTS NEAR THE DATELINE - SO EC WAS FORECAST IN CALIFORNIA ALTHOUGH DRYNESS WAS LEFT OVER INLAND AREAS WHICH ARE LESS SENSITIVE TO SST ANOMALIES OVER THE WESTERN AND CENTRAL PACIFIC WITH WEAK EL NINOS. . . . . . . . . PROGNOSTIC DISCUSSION OF OUTLOOKS - JFM 2004 TO JFM 2005 TEMPERATURE: FOR JFM 2004 WE CONSIDERED NEGATIVE ANOMALIES FOR THE NORTHEAST WHICH IS A POSSIBILITY IF CONVECTION WERE TO BECOME ESTABLISHED CLOSE TO THE EQUATOR NEAR OR WEST OF THE DATELINE AND A POSITIVE PNA ESTABLISHED - BUT GIVEN TRENDS FOR ABNORMAL WARMTH - EC IS ASSIGNED TO MUCH OF THE EAST FROM VIRGINIA NORTHWARD. FOR JFM THE TREND ALSO FAVORS POSITIVE ANOMALIES CENTERED OVER PARTS OF THE SOUTHWEST - INTERIOR ALASKA - AND FLORIDA - BUT IS OPPOSED BY MOST MODEL FORECASTS OVER THE LATTER AREA. IN MANY AREAS THE INDICATIONS FOR WARMTH ARE SUPPORTED BY CCA. POSITIVE TEMPERATURE ANOMALIES OVER THE GREAT PLAINS AND UPPER MIDWEST ARE FROM A CONSENSUS OF THE DYNAMICAL MODELS WITH SUPPORT FROM TRENDS - BUT WERE OPPOSED BY STRATIFIED CLIMATOLOGY OF ENSO-NEUTRAL CASES WITH NEUTRAL OR NEGATIVE AO - REULTING IN LOWER CONFIDENCE AS REFLECTED IN THE PROBABILITIES. FROM FMA THROUGH MAM TEMPERATURE FORECASTS ARE BASED PRIMARILY UPON CCA... OCN... AND DYNAMICAL MODELS WITH SOME INPUT FROM A COMPOSITE OF PAST CASES FOR TREND-ADJUSTED ENSO-NEUTRAL CONDITIONS. WARMER THAN AVERAGE TEMPERATURES ARE PREDICTED IN ALASKA LASTING THROUGH SUMMER 2004 DUE TO OCN - CCA AND DYNAMICAL MODELS. OVER THE CONUS THE STRONGEST MOST CONFIDENT INDICATIONS - ALL WARM - ARE FOUND MAINLY OVER THE SOUTHWEST DURING WINTER...IN THE SOUTHWEST AND WEST IN SPRING... AND IN THE SOUTH AND SOUTHWEST AGAIN IN SUMMER. TRENDS ALONE... AS WELL AS CCA...WOULD FAVOR MUCH OF THE EASTERN HALF OF THE NATION TO HAVE ABOVE NORMAL TEMPERATURES DURING THE WINTER SEASONS... BUT THE ENSO-NEUTRAL COMPOSITES AND UNCERTAINTY IN THE AO AND NAO CAUSED US TO PUT EC IN SOME OF THOSE REGIONS. AS THE TREND SIGNAL FOR WARMTH OVER THE NORTHERN GREAT PLAINS REVERSED TO A NEGATIVE (INDICATING BELOW NORMAL) VALUE GOING INTO SPRING - AND STRATIFIED CLIMATOLOGY OF PAST CASES WITH ENSO-NEUTRAL AND NEUTRAL OR NEGATIVE AO AGREED ON BELOW NORMAL TEMPERATURES - THIS WAS FORECAST OVER THE NORTHERN PLAINS FOR MAM AND AMJ. FORECASTS BEGINNING WITH AMJ ARE BASED LARGELY ON OCN AND CCA INDICATIONS - AND FOR THE SUMMER 2004 SEASONS INDICATE WARMTH OVER THE SOUTHWEST - SOUTHEAST - AND PACIFIC COAST FROM OCN WITH SOME SUPPORT FROM CCA. THE WARMTH PREDICTED IN THE LAST SET OF FORECASTS FOR PORTIONS OF THE MIDDLE ATLANIC STATES DURING MJJ WAS TRIMMED BACK DUE TO THE EXTREMELY WET GROUND IN THIS AREA MAKING IT LESS LIKELY THAT SIGNIFICANTLY ABOVE NORMAL TEMPERATURES COULD DEVELOP THAT EARLY IN THE WARM SEASON. . . . . . . . . PRECIPITATION: ABOVE-MEDIAN PRECIPITATION IS FORECAST FOR JFM IN PORTIONS OF THE SOUTHERN GREAT PLAINS AND LOWER MISSISSIPPI VALLEY BASED ON OCN AND DYNAMICAL MODELS. INDICATIONS FOR BELOW-MEDIAN PRECIPITATION OVER PORTIONS OF THE SOUTHWEST WERE ALSO BASED ON OCN - DYNAMICAL MODELS AND TREND-ADJUSTED ENSO-NEUTRAL CONDITIONS. BELOW-MEDIAN PRECIPITATION FOR FLORIDA AND SOUTHERN GEORGIA IS SUPPORTED NOT ONLY BY TRENDS BUT ALSO BY DYNAMICAL MODELS. ACCORDING TO DYNAMICAL MODEL STUDIES - THIS HAPPENS IF CONVECTION STAYS FAR ENOUGH WEST OF THE DATE LINE. IF CONVECTION DEVELOPS OVER THE EASTERN PACIFIC - SIGNIFIANT COLD-SEASON PRECIPITATION CAN MOVE INTO SOUTHERN CALIFORNIA - BUT IS UNLIIKELY TO PUSH INTO THE INTERIOR SOUTHWEST UNLESS A STRONG EL NINO DEVELOPS - WHICH IS JUDGED HIGHLY UNLIKELY AT THIS TIME. THEREFORE THE AREA OF BELOW MEDIAN PRECIPITATION FORECAST FOR THER SOUTHWEST WAS TRIMMED TO THE INTERIOR ONLY. AN AREA OF ABOVE-MEDIAN PRECIPITATION IS FORECAST FOR THE PACIFIC NORTHWEST DURING JFM AND FMA BASED ON THE MODEL CONSENSUS - AND WAS FAVORED TO BE CENTERED FARTHER SOUTH OVER CENTRAL CALIFORNIA DURING MAM FROM THE MODEL CONSENSUS. THE AREA OF ABOVE-MEDIAN PRECIPITATION IS PREDICTED BACK OVER THE PACIFIC NORTHWEST DURING AMJ AND MJJ BUT THEN IS BASED ON OCN WITH SOME SUPPORT FROM CCA. THERE WERE FEW RELIABLE PRECIPITATION SIGNALS FOR JJA THROUGH SON 2004 - WITH THE EXCEPTION OF DRYNESS IN PORTIONS OF THE FAR WEST DURING JAS AND ASO AND WETNESS CENTERED OVER WESTERN NEBRASKA IN ASO AND SON INDICATED BY THE TREND-ADJUSTED ENSO-NEUTRAL COMPOSITES WITH SOME SUPPORT FROM OCN. FROM SON THROUGH NDJ 2004 SOME OF THE TRENDS FOR WET RETURN TO THE SOUTHERN PLAINS. FORECAST INDICATIONS FOR PRECIPITATION ARE TYPICALLY UNCERTAIN IN MOST OF ALASKA...AND WITH THE EXCEPTION OF STRONGLY-FORCED COLD SEASON PATTERNS DURING EL NINO EVENTS USUALLY HAVE RATHER LOW SKILL ESPECIALLY IN THE WARM SEASONS. THEREFORE THE ENTIRE STATE WAS LEFT EC FOR PRECIPITATION AT ALL LEADS. 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. 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. -------------------------------------------------------------------------------- . . . . . . . . FORECASTER: A. J. WAGNER 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 JAN 15 2004. 1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001 FORECAST RELEASE. $$