PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EST THU DEC 12 2002 6 TO 10 DAY OUTLOOK FOR DEC 18 - 22 2002 . . . . . . . . MODEL COMPARISONS: THE MODELS CONTINUE IN GOOD AGREEMENT ON THE MAIN FEATURES OF THE 6 TO 10 DAY MEAN 500-HPA CIRCULATION PATTERN OVER NORTH AMERICA. THERE ARE ONLY SLIGHT DIFFERENCES IN THE WESTERN U.S. BETWEEN THE OPERATIONAL GFS... GFS ENSEMBLE MEAN... DAVA AND ECMWF SOLUTIONS. A WELL DEFINED FRONTAL BOUNDARY PRECEEDED BY WARM AIR AND AN OPEN MOISTURE SOURCE FROM THE GULF OF MEXICO IS EXPECTED TO MOVE THROUGH THE PLAINS AND INTO THE EASTERN STATES WITHIN THE PERIOD... HOWEVER WESTERLY AND SOUTHWESTERLY FLOW OVER MUCH OF CANADA WILL PREVENT ARCTIC AIR FROM ENTERING THE CONUS AND LIMIT THE SEVERITY OF THE COLD AIR BEHIND THE SYSTEM. THIS FRONT WILL PUT A LARGE AREA AT RISK OF SIGNIFICANT PRECIPITATION IN THE EASTERN U.S. THE TEMPERATURES AND PRECIPITATION IN MUCH OF THE CENTRAL PART OF THE COUNTRY WILL DEPEND ON THE SPEED OF THIS FRONTAL SYSTEM. ONE MAJOR DIFFERENCE BETWEEN MODELS IS THE TREATMENT OF A TROUGH IN THE EASTERN ATLANTIC. THE ECMWF MODEL DEEPENS A TROUGH IN THE EASTERN ATLANTIC TO SUCH AN EXTENT THAT IT CUTS OFF FROM THE MAIN 500-HPA FLOW... FORCING THE POLAR JET NORTHWARD AND SLOWING THE PROGRESS OF THE FRONTAL SYSTEM IN THE MIDWEST... WHILE THE OTHER MODELS KEEP THE TROUGH WITHIN THE MAIN STREAM OF THE WESTERLIES... ALLOWING THE FRONT TO PROGRESS EASTWARD. THE BLENDED 500-HPA HEIGHT FORECAST PRODUCES A COMPROMISE BETWEEN THE TWO SOLUTIONS. TODAYS PRECIPITATION FORECAST FOR THE WEST IS MUCH DRIER THAN INDICATED YESTERDAY DUE TO THE EASTWARD PROGRESSION OF THE WESTERN TROUGH - HOWEVER STRONG WESTERLIES ARE DISPLACED WELL SOUTH OF USUAL FOR THIS TIME OF YEAR AND WILL KEEP THE LIKELIHOOD OF SIGNIFICANT PRECIPITATION IN THE SOUTHWESTERN U.S. HIGH. 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 35 PERCENT OF THE GFS ENSEMBLE MEAN CENTERED ON DAY 8...30 PERCENT OF THE ECMWF MODEL CENTERED ON DAY 7...20 PERCENT OF THE 00Z OPERATIONAL GFS CENTERED ON DAY 8... AND 15 PERCENT OF THE DAVA MODEL CENTERED ON DAY 8. MODEL OF THE DAY: GFS ENSEMBLE MEAN THE TEMPERATURE PROG IS BASED ON MOS TEMPERATURES FROM THE GFS ENSEMBLE MEMBERS AND SPECIFICATIONS FROM KLEIN AND NEURAL NETWORK EQUATIONS. THESE TOOLS WERE IN GOOD AGREEMENT TODAY. 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...AND ANALOGS FROM THE VARIOUS MODELS. . . . . . . . . 8 TO 14 DAY OUTLOOK FOR DEC 20 - 26 2002 MODEL COMPARISONS: THE VARIOUS MODELS REMAIN CONSISTENT WITH YESTERDAYS FORECAST -- WITH THE GFS ENSEMBLE MEMBERS SLOWLY BUILDING A RIDGE IN WESTERN CANADA AS A MID-LATITUDE TROUGH AMPLIFIES INTO THE SOUTHERN ROCKIES. THE DAVA REMAINS CONSISTENT WITH ITS EARLIER RUN AND KEEPS THE FLOW SIMILAR TO ITS 6 TO 10 DAY SOLUTION. THE GFS ENSEMBLE IS THE FAVORED SOLUTION SINCE YESTERDAYS AND TODAYS 6 TO 10 DAY MODELS SOLUTIONS APPEAR TO BE TRENDING TOWARD THE GFS 8 TO 14 DAY SOLUTION. AMPLE PRECIPITATION IS EXPECTED OVER MUCH OF THE U.S. IN RESPONSE TO THE ACTIVE JET EXTENDING FROM COAST TO COAST OVER THE U.S. MOST TOOLS NOW PREDICT MOSTLY LIGHT PRECIPITATION FOR THE PACIFIC NORTHWEST FOR 8 TO 14 DAY PERIOD IN RESPONSE TO THE BUILDING RIDGE IN WESTERN 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 50 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 11...30 PERCENT OF TODAYS OPERATIONAL GFS CENTERED ON DAY 11...AND 20 PERCENT OF THE DAVA CENTERED ON DAY 11. THE TEMPERATURE PROG IS BASED ON THE KLEIN AND NEURAL NETWORK SPECIFICATIONS FROM THE OFFICIAL FORECAST 500-HPA BLEND WHICH WERE IN GOOD AGREEMENT WITH EACH OTHER AND WITH THE ANALOGS FROM THE MODELS. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500-HPA BLEND...ANALOGS FROM THE VARIOUS MODELS... AND THE CALIBRATED PRECIPITATION FROM THE OPERATIONAL GFS. FORECASTER: D. UNGER . . . . . . . . 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 B B OREGON B N NRN CALIF B N SRN CALIF B A IDAHO B N NEVADA B N W MONTANA N B E MONTANA N B WYOMING N N UTAH B A ARIZONA B A COLORADO B A NEW MEXICO B A N DAKOTA N B S DAKOTA N B NEBRASKA N N KANSAS N A OKLAHOMA N A N TEXAS N A S TEXAS N N W TEXAS N A MINNESOTA A B IOWA A A MISSOURI A A ARKANSAS A A LOUISIANA A A WISCONSIN A A ILLINOIS A A MISSISSIPPI A A MICHIGAN A A INDIANA A A OHIO A A KENTUCKY A A TENNESSEE A A ALABAMA A A NEW YORK A A VERMONT A A 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 A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA A A FL PNHDL A A FL PENIN A N AK N SLOPE A B AK ALEUTIAN A A AK WESTERN A A AK INT BSN A B AK S INT A A AK SO COAST A A AK PNHDL N B 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 B UTAH B A ARIZONA B A COLORADO B A NEW MEXICO B A N DAKOTA N B S DAKOTA N B NEBRASKA B N KANSAS B A OKLAHOMA B A N TEXAS B A S TEXAS B A W TEXAS B A MINNESOTA A N IOWA N A MISSOURI N A ARKANSAS N A LOUISIANA N A WISCONSIN A N ILLINOIS N A MISSISSIPPI N A MICHIGAN A N INDIANA A A OHIO A A KENTUCKY A A TENNESSEE A A ALABAMA N A NEW YORK A A VERMONT A A 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 A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA A A FL PNHDL A A FL PENIN A B AK N SLOPE A B AK ALEUTIAN A A AK WESTERN A A AK INT BSN A B AK S INT A A AK SO COAST A A AK PNHDL A B 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