PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EST TUE DEC 17 2002 6 TO 10 DAY OUTLOOK FOR DEC 23 - 27 2002 . . . . . . . . MODEL COMPARISONS: MODELS AT DAY 5 ARE IN VERY GOOD AGREEMENT WITH REGARD TO OVERALL SPLIT FLOW PATTERN WITH A VERY ACTIVE SOUTHERN JETSTREAM. IN THE NORTHERN STREAM A CLOSED-OFF TROUGH DOMINATES EASTERN CANADA WHILE A HIGHLY AMPLIFIED RIDGE DOMINATES WESTERN CANADA. NOGAPS IS A BIT OF AN OUTLIER AS IT FORMS A STRONG REX-TYPE BLOCK IN EAST/CENTRAL CANADA. 0Z UKMET LIFTS OUT THE TROUGH IN EASTERN CANADA TO THE NORTHEAST THE FASTEST. IN THE SOUTHERN STREAM THE MODELS DIFFER A BIT IN THE TIMING AND STRENGTH OF INDIVIDUAL SHORTWAVES. THE 6Z GFS...ECMWF AND CANADIAN MODELS ARE A BIT SLOWER AND MORE AMPLIFIED WITH A SHORTWAVE APPROACHING THE OHIO VALLEY AND THE ECMWF...CANADIAN AND NOGAPS ARE FASTER BRINGING A SHORTWAVE INTO THE SOUTHWEST U.S. BY THE D+8 PERIOD 0Z GFS DEPICTS A VERY STRONG ZONAL FLOW ACROSS THE SOUTHERN CONUS...A RIDGE IN THE EASTERN PACIFIC AND A TROUGH JUST INLAND OF THE PACIFIC NORTHWEST. THE ECMWF...AS HAS BEEN TRUE THE LAST FEW DAYS...DEPICTS HIGHER HEIGHTS IN THE SOUTHEAST U.S. COMPARED TO THE OPERATIONAL GFS. THE ECMWF ALSO HAS MORE PHASING WITH RESPECT TO THE RIDGE IN THE WESTERN U.S./CANADIAN REGION WHICH ALLOWS A STRONG FLOW FROM THE ARCTIC TO PLUNGE COLD AIR INTO THE NORTH-CENTRAL CONUS. GFS ENSEMBLE MEAN AND DAVA SEEM TO SUPPORT THE ECMWF IDEA OF A MORE PHASED AND AMPLIFIED RIDGE IN THE WEST. IN TERMS OF HEIGHT ANOMALIES THE MODELS AGREE THAT THE CONUS WILL BE DOMINATED BY BELOW NORMAL HEIGHTS... THOUGH THE DAVA AND ESPECIALLY THE ECMWF DEPICT POSITIVE HEIGHT ANOMALIES IN THE EXTREME SOUTHEASTERN U.S. FORECAST CONFIDENCE IS ABOUT AVERAGE TODAY... 3 ON A SCALE FROM 1 TO 5. THE OFFICIAL 500-HPA HEIGHT FORECAST FOR THE 6 TO 10 DAY PERIOD USES 30 PERCENT OF THE GFS ENSEMBLE MEAN CENTERED ON DAY 8... 35 PERCENT OF THE ECMWF MODEL CENTERED ON DAY 7... 15 PERCENT OF THE 00Z OPERATIONAL GFS CENTERED ON DAY 8... AND 20 PERCENT OF THE DAVA MODEL CENTERED ON DAY 8. MODEL OF THE DAY: ECMWF THE TEMPERATURE PROG IS BASED ON MOS TEMPERATURES FROM THE GFS ENSEMBLE MEMBERS ... SPECIFICATIONS FROM KLEIN AND NEURAL NETWORK EQUATIONS...THE ANALOG FROM THE BLENDED HEIGHT FIELD...TELECONNECTIONS ON THE NEGATIVE HEIGHT CENTER LOCATED AT 35N 115W. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500-HPA BLEND... CALIBRATED PRECIPITATION FROM THE GFS... ACCUMULATED PRECIPITATION FROM THE RECENT GFS OPERATIONAL RUNS... ANALOGS FROM THE VARIOUS MODELS...TELECONNECTIONS ON THE NEGATIVE HEIGHT CENTER LOCATED AT 35N AND 115W AND THE BIAS CORRECTED PRECIPITATION FROM THE OPERATIONAL GFS. . . . . . . . . 8 TO 14 DAY OUTLOOK FOR DEC 25 - 31 2002 MODEL COMPARISONS: DURING THE WEEK 2 PERIOD THE OVERALL PATTERN CHANGES VERY LITTLE...THOUGH THE TROUGH FORECAST TO BE ALONG THE WEST COAST DOES PROGRESS A BIT TO THE EAST. NEGATIVE HEIGHT ANOMALIES ARE FORECAST TO DOMINATE COAST TO COAST OVER THE CONUS WHILE POSITIVE HEIGHT ANOMALIES ARE FORECAST IN EASTERN CANADA. CONFIDENCE IN THE WEEK 2 FORECAST IS ABOUT AVERAGE...3 ON A SCALE FROM 1 TO 5. THE OFFICIAL 500-HPA HEIGHT FORECAST FOR THE 8 TO 14 DAY PERIOD USES 40 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 11...20 PERCENT OF TODAYS OPERATIONAL GFS CENTERED ON DAY 11... 30 PERCENT OF THE DAVA CENTERED ON DAY 11... AND 10 PERCENT OF THE ECMWF CENTERED ON DAY 7. THE TEMPERATURE PROG IS BASED ON THE KLEIN AND NEURAL NETWORK SPECIFICATIONS FROM THE OFFICIAL FORECAST 500-HPA BLEND...THE ANALOGS FROM THE MODELS AND OFFICIAL HEIGHT BLEND AND THE BIAS CORRECTED 850 HPA TEMPERATURES FROM THE OPERATIONAL GFS. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500-HPA BLEND...ANALOGS FROM THE VARIOUS MODELS... AND THE CALIBRATED AND BIAS CORRECTED PRECIPITATION FROM THE OPERATIONAL GFS. FORECASTER: R. SCHECHTER . . . . . . . . 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 THURSDAY DECEMBER 19 2002. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N B OREGON B B NRN CALIF B N SRN CALIF B A IDAHO B N NEVADA B N W MONTANA B B E MONTANA B N WYOMING B N UTAH B N ARIZONA B A COLORADO B A NEW MEXICO B A N DAKOTA B B S DAKOTA B N NEBRASKA B A KANSAS B A OKLAHOMA N A N TEXAS N A S TEXAS N A W TEXAS B A MINNESOTA N B IOWA N A MISSOURI N A ARKANSAS N A LOUISIANA N A WISCONSIN N N ILLINOIS N N MISSISSIPPI N A MICHIGAN N N INDIANA N N OHIO N A KENTUCKY N A TENNESSEE N A ALABAMA N A NEW YORK N N VERMONT N N NEW HAMP N N MAINE N N MASS N N CONN N N RHODE IS N N PENN N A NEW JERSEY N N W VIRGINIA N A MARYLAND N A DELAWARE N N VIRGINIA N A N CAROLINA N A S CAROLINA N A GEORGIA A N FL PNHDL A N FL PENIN A N AK N SLOPE A N AK ALEUTIAN A A AK WESTERN A A AK INT BSN A N AK S INT A N AK SO COAST A A AK PNHDL A N 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON B B OREGON B B NRN CALIF B N SRN CALIF B A IDAHO B B NEVADA B N W MONTANA B B E MONTANA N B WYOMING B N UTAH B N ARIZONA B A COLORADO B N NEW MEXICO B A N DAKOTA N B S DAKOTA N N NEBRASKA B N KANSAS B N OKLAHOMA B A N TEXAS N A S TEXAS N A W TEXAS B A MINNESOTA A N IOWA N A MISSOURI N N ARKANSAS N A LOUISIANA N A WISCONSIN A A ILLINOIS N N MISSISSIPPI N A MICHIGAN N N INDIANA N N OHIO N N KENTUCKY B A TENNESSEE B A ALABAMA N A NEW YORK N N VERMONT N B NEW HAMP N B MAINE N B MASS N N CONN N N RHODE IS N N PENN N N NEW JERSEY N N W VIRGINIA B A MARYLAND B A DELAWARE B A VIRGINIA B A N CAROLINA B A S CAROLINA N A GEORGIA N A FL PNHDL N A FL PENIN N N AK N SLOPE N N AK ALEUTIAN N A AK WESTERN A A AK INT BSN N N AK S INT A A AK SO COAST A A AK PNHDL N N 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