PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EST WED DEC 25 2002 6 TO 10 DAY OUTLOOK FOR DEC 31 2002 - JAN 04 2003 . . . . . . . . MODEL COMPARISONS: FOR THE D+8 PERIOD MOST OF THE MODELS INCLUDING THE GFS INITIALIZATIONS AT THE FOUR 6-HR INTERVALS WITHIN THE PAST 24 HR CONTINUE TO PREDICT A BASICALLY SIMILAR LONG WAVE PATTERN... BUT THE DAVA HAS WEAKLY POSITIVE HEIHGT ANOMALIES OVER THE ENTIRE CONUS WHILE ALL THE OTHER MODELS HAVE TROUGHS OF VARYING AMPLITUDES. THE GFS RUNS INITIALIZED AT THE MOST RECENTLY AVAILABLE 6-HR INTERVALS WERE IN EXCELENT AGREEMENT ON PHASE AND HAD SOME VARIATION IN PREDICTED INTENSIY OF THE TORUGH OVER THE SOUTHERN U.S. THE ECMWF MODEL WAS AGAIN THE MOST INTENSE AND ALSO THE LEAST PROGRESSIVE ON THIS FEATURE. THE ENSEMBLE MEAN WAS WEAKEST AND ALSO THE MOST PROGRESSIVE... SUGGESTING THAT STRONGER TROUGH DEVELOPMENT IS ASSOCIATED WITH MORE DIGGING AND SLOWING OF THE GENERALLY PROGRESSIVE SHORT WAVES IN THE SOUTHERN STREAM. BLOCKING CONTINUES OVER HIGH LATATUDES FROM WESTERN RUSSIA BACK TO NORTHEASTERN CANADA... WHILE THE EL NINO-ENHANCED WESTERLIES CONTINUE TO ROAR ACROSS THE PACIFIC BETWEEN 35N AND 45N. GENERALL BELOW NORMAL HEIGHTS OVER NORTHWESTERN CANADA WILL PREVENT THE DEVELOPMENT OR DEPLOYMENT OF SIGNIFICANT ARCTIC AIR INTO THE CONUS. FORECAST CONFIDENCE IS ABOVE AVERAGE TODAY... 4 ON A SCALE FROM 1 TO 5. THE OFFICIAL 500-HPA HEIGHT FORECAST FOR THE 6 TO 10 DAY PERIOD USES 40 PERCENT OF THE GFS ENSEMBLE MEAN CENTERED ON DAY 8... 15 PERCENT OF THE ECMWF MODEL CENTERED ON DAY 7... 15 PERCENT OF THE 00Z OPERATIONAL GFS CENTERED ON DAY 8... AND 30 PERCENT OF THE DAVA MODEL CENTERED ON DAY 8. WEIGHTS WERE SELECTED NOT ONLY ON THE BASIS OF RECENT SKILL... BUT ALSO WITH THE INTENT OF CORRECTING THE 00Z GFS FORECAST FOR ITS RECENT BIASES. MODEL OF THE DAY: GFS ENSEMBLE MEAN THE TEMPERATURE PROG IS BASED ON SPECIFICATIONS FROM THE KLEIN AND NEURAL NETWORK SPECIFICATIONS FROM THE OFFICIAL 500-HPA PROG... AND THE MOS SPECIFICATIONS FROM THE 00Z GFS RUN... ALL OF WHICH WERE IN VERY GOOD AGREEMENT TODAY. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500-HPA BLEND... CALIBRATED PRECIPITATION FROM THE GFS... AND THE 7- AND 30-DAY BIAS CORRECTED PRECIPITATION FROM THE OPERATIONAL GFS. . . . . . . . . 8 TO 14 DAY OUTLOOK FOR JAN 2 - JAN 8 2003 MODEL COMPARISONS: DURING THE WEEK 2 PERIOD MOST OF THE MODELS SHOW SOME PROGRESSION OF THE TROUGH IN THE SOUTHERN STREAM... WITH THE DAVA THE MOST PROGRESSIVE AND THE INDIVIDUAL GFS RUNS THE LEAST PROGRESSIVE. THE ENSEMBLE MEAN IS A GOOD COMPROMISE AND HAS SCORED NOTICEABLY BETTER THAN THE THE OTHER TOOLS FOR THE PAST TWO MONTHS. WEIGHTS WERE AGAIN SELECTED WITH THE IDEA OF REDUCING THE RECENT BIASES OF THE 00Z GFS MODEL RUNS... WHICH HAVE PUT TOO MUCH TROUGH IN THE MIDDLE OF THE U.S. ... AS WELL AS TO INCLUDE MORE OF THE BETTER-SCORING ENSEMBLE MEAN. THE RESULTANT PATTERN SHOWS SOME PROGRESSION OF FEATURES IN THE SOUTHERN STREAM... WHICH IS REASONALBE GIVEN THE FAST EL NINO SUBTROPICAL WESTERLIES. AT HIGH LATITUDES THE AREA OF BLOCKING IS FORECAST TO REMAIN ABOUT THE SAME. THE PACIFC WESTERLIES ARE PREDICTED TO REMAIN STRONG BUT FOCUS MORE ON THE NORTHERN HALF OF THE U.S. PACIFIC COASXT AS THEY APPROACH THE NORTH AMERICAN CONTINENT. CONFIDENCE IN THE WEEK 2 FORECAST IS ABOVE AVERAGE...4 ON A SCALE FROM 1 TO 5. THE OFFICIAL 500-HPA HEIGHT FORECAST FOR THE 8 TO 14 DAY PERIOD USES 50 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 11... 20 PERCENT OF TODAYS OPERATIONAL GFS CENTERED ON DAY 11... AND 30 PERCENT OF THE DAVA CENTERED ON DAY 11. THE TEMPERATURE PROG IS BASED ON THE NEURAL NETWORK AND KLEIN SPECIFICATIONS FROM THE OFFICIAL FORECAST 500-HPA BLEND... AND THE BIAS CORRECTED 850 HPA TEMPERATURES FROM THE 00Z OPERATIONAL GFS RUN. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500-HPA BLEND AND THE CALIBRATED AND BIAS CORRECTED PRECIPITATION FROM THE OPERATIONAL GFS. FORECASTER: A. J. WAGNER . . . . . . . . NOTES: AUTOMATED FORECASTS ARE ISSUED ON SATURDAY AND SUNDAY. OTHERWISE - FORECASTS INCORPORATE FORECASTER INPUT. THE NOTATION FOR THE CATEGORICAL FORECAST INDICATED ON THE MAPS IS THE SAME AS THAT IN THE TABLES: A-ABOVE N-NEAR NORMAL B-BELOW IN THE SOUTHWEST AND OTHER CLIMATOLOGICALLY DRY REGIONS - THERE WILL BE A GREATER THAN 33.3% CHANCE OF NO PRECIPITATION AND OCCASIONALLY EVEN A NORMAL (I.E. MEDIAN) VALUE OF ZERO - ESPECIALLY DURING THE DRY SEASONS. IN SUCH CASES A FORECAST OF NEAR NORMAL IS EFFECTIVELY A FORECAST OF LITTLE OR NO PRECIPI- TATION. THE NARRATIVE DESCRIPTION OF THE FORECAST PATTERNS FOR TEMPERATURE AND PRECIP- ITATION FOR BOTH THE 6-10 OR 8-14 DAY PERIODS HAS BEEN DISCONTINUED. THE STATE TABLES FOR BOTH THE 6-10 AND 8-14 DAY PERIODS ARE NOW CONTAINED IN THIS MESSAGE ...AVAILABLE AS PMDMRD ON AWIPS. EFFECTIVE THURSDAY MAY 17 2001...THE CLIMATE PREDICTION CENTER HAS SWITCHED TO 1971-2000 BASE PERIOD MEANS FOR TEMPERATURE...PRECIPITATION...AND 500-HPA HEIGHTS AS REFERENCE IN THE CLIMATE OUTLOOKS. THE 1971-2000 BASE PERIOD MEANS HAVE REPLACED THE 1961-1990 BASE PERIOD MEANS. . . . . . . . . GLOSSARY AND DEFINITIONS:------------------------------------------------------ AC - ANOMALY CORRELATION - A MEASURE OF HOW WELL A MODEL FORECASTS THE HEIGHT OR HEIGHT ANOMALY FIELD OBTAINED BY CORRELATING THE IMPLIED GRADIENTS OF THE TWO ANOMALY PATTERNS BEING COMPARED. 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 STUDIED INCREASES IN SIZE. PERFECT ANALOGS TO THE ENTIRE NORTHERN HEMISPHERE SIMPLY DO NO EXIST - FOR PRACTICAL PURPOSES. THIS IS WHY SIMPLE NATURAL ANALOG FORECAST METHODS DO NOT WORK VERY WELL. ANOMALY - THE ARITHMETIC DIFFERENCE BETWEEN THE VALUE OF A VARIABLE AT A GIVEN PLACE AND TIME AND THE LONG-TERM AVERAGE OF THAT VARIABLE AT THAT PLACE AND TIME OF YEAR. AVN - THE RUN OF THE MRF MODEL INITIATED AT 12 UTC (AS OF 07/2002 THE NAME FOR ALL RUNS OF THE NCEP GLOBAL SPECTRAL MODEL). BLEND - A WEIGHTED AVERAGE OF 500 HPA HEIGHT FORECAST MAPS FROM SEVERAL MODELS. WEIGHTS ARE CURRENTLY ASSIGNED SUBJECTIVELY BY THE FORECASTER. THE SUM OF THE WEIGHTS MUST BE 1. WEIGHTS ARE APPLIED BY MULTIPLYING EACH 500 HPA MAP BY ITS WEIGHT AND ADDING ALL OF THE WEIGHTED MAPS TOGETHER TO MAKE THE OFFICIAL 500 HPA FORECAST. CONUS - CONTERMINOUS UNITED STATES. DAVA - DIVERGENT ANOMALY VORTICITY ADVECTION MODEL. THIS IS A BAROTROPIC MODEL WITH DIVERGENCE IN IT TO ALLOW MORE ACCURATE PREDICTION OF LONG WAVES THAN A STANDARD BAROTROPIC MODEL. REFERENCE: QIN J. AND H.M. VAN DEN DOOL - 1996: SIMPLE EXTENSIONS OF AN NWP MODEL. MON. WEA. REV. - VOL 124 - PP 277-287. EL NINO - THE WARM PHASE OF ENSO. ENSO - EL NINO/SOUTHERN OSCILLATION. FLOW PATTERN - THE PATTERN OF WIND INFERRED BY THE 500 HPA CONTOURS - THE WIND TENDS TO BLOW PARALLEL TO THE CONTOURS WITH LOW HEIGHT ON THE LEFT - IN THE NORTHERN HEMISPHERE - THE OPPOSITE IS TRUE IN THE SOUTHERN HEMISPHERE. WIND SPEED IS INVERSELY PROPORTIONAL TO THE SPACING BETWEEN THE CONTOURS. GFS - GLOBAL FORECAST SYSTEM. THIS REFERS TO ANY OF THE GLOBAL MODELS RUN AT NCEP FOUR TIMES A DAY THAT USED TO BE REFERRED TO AS THE MRF AND AVN MODELS. THE MODEL RUN INITIATED AT 00Z (OO GMT) IS THE ONE USED BY CPC IN ITS FORECASTS. 500 HPA HEIGHT IS THE HEIGHT - IN METERS - ABOVE MEAN SEA LEVEL - WHICH ABOUT HALF OF THE MASS OF THE ATMOSPHERE LIES ABOVE AND BELOW - AS MEASURED BY THE PRESSURE. UPPER AIR STORM SYSTEMS TEND TO BE STEERED IN THE DIRECTION OF THE WINDS AT 500 HPA. 500-HPA SYSTEMS CORRELATE STRONGLY WITH SURFACE WEATHER. HPA - HECTO-PASCALS. 1 HPA = 1 MILLIBAR. LA NINA - THE COLD PHASE OF ENSO. MERIDIONAL FLOW PATTERN - OCCURS WHEN 500 HPA CONTOURS EXHIBIT LARGE NORTHWARD AND SOUTHWARD EXCURSIONS WITH EXTENSIVE AREAS OF SOUTHERLY AND NORTHERLY FLOW. MODEL BIAS - THE DIFFERENCE BETWEEN THE MODEL CLIMATOLOGY AND THE OBSERVED CLIMATOLOGY - EXPRESSED AS BIAS = MODEL CLIMO - OBSERVED CLIMO. MODEL OF THE DAY - FOR 6-10 DAYS - IS THE MODEL WHOSE SOLUTION IS CONSIDERED TO BE MORE RELIABLE THAN USUAL - AND MAY BE GIVEN HIGHER THAN TYPICAL WEIGHT IN THE BLEND. NO MODEL OF THE DAY IS CHOSEN FOR 8-14 DAYS. MOS - MODEL OUTPUT STATISTICS - A STATISITCAL TOOL FOR SPECIFYING THE SURFACE TEMPERATURE (AND ITS ANOMALY) FROM MODEL FIELDS - CORRECTING AUTOMATICALLY FOR BOTH BIASES IN THE MODEL FIELDS AND THE SPECIFICATION METHOD. IT IS VALID AS LONG AS A GIVEN CONFIGURATION OF A MODEL IS NOT CHANGED OR MODIFIED. MRF - MEDIUM RANGE FORECAST MODEL (AS OF 07/2002 RENAMED THE AVN) MRF ENSEMBLE - A SET OF MRF (AVN) FORECASTS WHICH ARE ALL VALID AT THE SAME TIME BUT WHOSE STARTING CONDITIONS DIFFER BY SMALL AMOUNTS. THERE ARE CUR- RENTLY 25 MEMBERS IN THE MRF (AVN) ENSEMBLE. THE AVERAGE OF THESE IS THE MRF (AVN) ENSEMBLE MEAN. MJO - MADDEN-JULIAN OSCILLATION - ALSO CALLED TROPICAL INTRA-SEASONAL OSCILLA- TION - A SERIES OF WAVES WITH A PERIOD AVERAGING 50 DAYS THAT MOVES SLOWLY EASTWARD NEAR THE EQUATOR ALTERNATELY ENHANCING AND SUPRESSING PRECIPITATION. NAO - NORTH ATLANTIC OSCILLATION TELECONNECTION PATTERN. PNA - PACIFIC NORTH AMERICAN TELECONNECTION PATTERN. PROG - PROGNOSIS - OR FORECAST. RIDGE - A REGION OF UNUSUALLY HIGH 500 HPA HEIGHT. SHORT WAVES - RELATIVELY LOW-AMPLITUDE - FAST-MOVING DISTURBANCES OF THE 500 HPA FIELD. SOUTHERN STREAM - A FLOW PATTERN WITH UNUSUALLY STRONG FLOW ACROSS THE SOUTH- ERN U.S. - ACCOMPANIED BY UNUSUAL STORMINESS IN THE SOUTH AND SOUTHEAST. SPECIFICATIONS - KLEIN AND NEURAL NETWORK SPECIFICATIONS GIVE THE HISTORICAL RELATIONSHIP BETWEEN 500-HPA HEIGHT ANOMALIES AND SURFACE TEMPERATURE AND PRECIPITATION. KLEIN SPECIFICATIONS TEND TO EMPHASIZE REGIONAL TELECONNEC- TIONS WHILE THOSE FROM THE NEURAL NETWORK WORK FROM GLOBAL TELECONNECTIONS. . . . . . . . . TELECONNECTIONS GIVE THE HISTORICAL RELATIONSHIP BETWEEN THE 500-HPA HEIGHT AT A GIVEN POINT AND ALL OTHER POINTS ON A MAP FOR A GIVEN TIME OF YEAR. WE AVERAGE THE TOP/BOTTOM 10% OF DAILY MAPS FROM 1950-1999 FOR THE SAME TIME OF YEAR HAVING THE HIGHEST/LOWEST 500-HPA HEIGHT AT THE SPECIFIED POINT. TROUGH - A REGION OF UNUSUALLY LOW 500 HPA HEIGHT. UTC - UNIVERSAL TIME COORDINATED - SAME AS GREENWICH MEAN TIME (GMT). WESTERLY WIND - WIND BLOWING FROM WEST TO EAST. EASTERLY WIND - WIND BLOWING FROM EAST TO WEST. NORTHERLY WIND - WIND BLOWING FROM NORTH TO SOUTH SOUTHERLY WIND - WIND BLOWING FROM SOUTH TO NORTH. 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. ------------------------------------------------------------------------------- THE NEXT MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON THURSDAY JANUARY 16 2003. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A A OREGON A A NRN CALIF A A SRN CALIF B B IDAHO N A NEVADA N B W MONTANA A A E MONTANA A N WYOMING N N UTAH N A ARIZONA B B COLORADO N N NEW MEXICO N B N DAKOTA N B S DAKOTA N B NEBRASKA N B KANSAS N N OKLAHOMA N A N TEXAS N A S TEXAS N N W TEXAS N B MINNESOTA A B IOWA A B MISSOURI A N ARKANSAS N A LOUISIANA N A WISCONSIN A B ILLINOIS A N MISSISSIPPI N A MICHIGAN A N INDIANA A N OHIO A A KENTUCKY A A TENNESSEE A A ALABAMA N A NEW YORK A A VERMONT A N NEW HAMP A N MAINE A N MASS A A CONN A A RHODE IS A A PENN A A NEW JERSEY A A W VIRGINIA A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA N A FL PNHDL N A FL PENIN N A AK N SLOPE B B AK ALEUTIAN N N AK WESTERN N N AK INT BSN B N AK S INT N N AK SO COAST N A AK PNHDL A N 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A A OREGON A A NRN CALIF A A SRN CALIF A N IDAHO N A NEVADA A A W MONTANA N A E MONTANA A N WYOMING A A UTAH A N ARIZONA N B COLORADO N N NEW MEXICO N B N DAKOTA A N S DAKOTA A N NEBRASKA A A KANSAS N N OKLAHOMA N B N TEXAS B B S TEXAS B B W TEXAS B B MINNESOTA A B IOWA A B MISSOURI N N ARKANSAS B B LOUISIANA B B WISCONSIN A B ILLINOIS N N MISSISSIPPI B B MICHIGAN A B INDIANA N N OHIO N N KENTUCKY N N TENNESSEE N N ALABAMA B N NEW YORK A A VERMONT A N NEW HAMP A A MAINE A A MASS A A CONN A A RHODE IS A A PENN A A NEW JERSEY A A W VIRGINIA N A MARYLAND A A DELAWARE A A VIRGINIA N A N CAROLINA N A S CAROLINA N A GEORGIA N A FL PNHDL B A FL PENIN N A AK N SLOPE B B AK ALEUTIAN N N AK WESTERN B N AK INT BSN N N AK S INT A N AK SO COAST A A AK PNHDL A A LEGEND TEMPS WITH RESPECT TO NORMAL PCPN WITH RESPECT TO MEDIAN A - ABOVE N - NEAR NORMAL A - ABOVE N - NEAR MEDIAN B - BELOW B - BELOW THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE. FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 - ON AFOS AS NFDPMDMRD. NNNN NNNN