PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EST FRI DEC 13 2002 6 TO 10 DAY OUTLOOK FOR DEC 19 - 23 2002 . . . . . . . . MODEL COMPARISONS: WHILE THE MODELS AGREE WELL WITH ONE ANOTHER ON THE MAIN FEATURES OF THE 6 TO 10 DAY MEAN 500-HPA CIRCULATION PATTERN OVER MOST OF NORTH AMERICA... INDIVIDUAL ENSEMBLE RUNS SHOW LITTLE AGREEMENT ON POSITION AND INTENSITY OF THE SHORT WAVES ON DAILY FORECASTS... SUGGESTING CONSIDERABLE TIMING DIFFICULTIES. A LOOK AHEAD TO THE 8 TO 14 DAY FORECAST INDICATES THAT THE MODELS ARE PREDICTING A TRANSITION FROM THE CURRENT REGIME CHARACTERIZED BY A TROUGH IN THE WEST AND A RIDGE IN THE EAST... TO A FLOW REGIME SIMILAR TO THE PERSISTENT PATTERN OBSERVED SINCE MID-OCTOBER WITH A WESTERN RIDGE AND EASTERN TROUGH. THE 6 TO 10 DAY PERIOD NOW IS WITHIN THE TRANSITIONAL PERIOD - MAKING THE MEAN SURFACE CONDITIONS DIFFICULT TO PREDICT AND RESULTING IN A HIGH DEGREE OF UNCERTAINTY IN THE FORECAST. THE WEST IS EXPECTED TO CHANGE FROM WET TO SLIGHTLY DRY WHILE THE EASTERN U.S. WILL SEE A RETURN TO COOLER TEMPERATURES WITHIN THE PERIOD. JUST HOW MUCH DRIER IN THE WEST... AND COOLER IN THE EAST WILL DEPEND ON THE STRENGTH OF THE RIDGE FORECAST TO BUILD INTO WESTERN CANADA. THE AMPLITUDE IS CURRENTLY PREDICTED TO BE MUCH LESS THAN THE AVERAGE EARLIER IN THE FALL... WHICH WILL LIMIT THE AMOUNT OF ARCTIC AIR THAT CAN ENTER THE U.S AND KEEP TEMPERATURE ANOMALIES SMALLER IN THE EAST AND ENABLE MORE PRECIPITATION SYSTEMS INTO THE WEST THAN IN THE FALL. AN ACTIVE SOUTHERN JET SHOULD KEEP PRECIPITATION IN THE SOUTH ABOVE THEIR MEDIAN AMOUNTS. FORECAST CONFIDENCE IS BELOW AVERAGE TODAY... 2 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... 30 PERCENT OF THE ECMWF MODEL CENTERED ON DAY 7... 20 PERCENT OF THE 00Z OPERATIONAL GFS CENTERED ON DAY 8... AND 10 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 OVER THE CONUS... BUT DIFFERED IN ALASKA... WITH MOS FORECAST TENDING TO BE COOLER THAN THE KLEIN OR NEURAL NETWORK TOOLS. 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 21 - 27 2002 MODEL COMPARISONS: ALL GFS ENSEMBLE MEMBERS INDICATE A TRANSITION OF 500-HPA FLOW REGIME TO ONE THAT IS SUBSTANTIALLY DIFFERENT FROM THE CURRENT STATE... AND EVEN DIFFERS FROM THE ONE PREDICTED ON THE 6 TO 10 DAY MEAN. THE MODELS PREDICT A VERY BROAD TROUGH THAT EXTENDS FROM THE ROCKIES TO AT LEAST THE MID-ATLANTIC OCEAN. ABOVE NORMAL 500-HPA HEIGHTS AT HIGH LATITUDES MAKE THE FLOW STRONGLY FIT THE NEGATIVE NAO TELECONNECTION PATTERN. THIS SHOULD BRING COOL TEMPERATURES THROUGHOUT MUCH OF THE NATION WITH A STRONG SOUTHERN JET KEEPING THE MAIN STORM TRACK DEPRESSED SOUTHWARD. THE PACIFIC JET REMAINS ACTIVE... HOWEVER... AND STRONG WESTERLY FLOW OVER THE TOP OF THE WEAK RIDGE OVER WESTERN CANADA WILL PUSH PACIFIC AIR INTO CENTRAL NORTH AMERICA AND LIMIT THE SEVERITY OF COLD AIR ENTERING THE BROAD TROUGH. THE PACIFIC FLOW ASSOCIATED WITH A STRONG ALEUTIAN LOW PREDICTED BY THE MODELS IS CONSISTENT WITH THE MODERATE EL NINO CONDITIONS CURRENTLY OBSERVED. THE RIDGE IN WESTERN CANADA WILL HAVE TO BE WATCHED CLOSELY SINCE A STRONGER RIDGE WILL ALLOW A NORTHERLY COMPONENT TO THE FLOW AND ALLOW ARCTIC AIR TO MOVE SOUTHWARD. TODAYS MODELS ARE FASTER TO CHANGE THE FLOW PATTERN THAN YESTERDAYS RUNS... RESULTING IN A FORECAST REVISION IN THE NORTHEASTERN U.S. THAT IS MORE THAN WOULD BE EXPECTED FROM THE ONE DAY PROGRESSION FROM YESTERDAYS FORECAST. ONE MODEL... THE DAVA... EVEN HOLDS ONTO THE EASTERN RIDGE... BUT WAS ONLY LIGHTLY WEIGHTED IN TODAYS BLEND SINCE IT IS AN OUTLIER. CONFIDENCE IN THE WEEK 2 FORECAST IS BELOW AVERAGE...2 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...40 PERCENT OF TODAYS OPERATIONAL GFS CENTERED ON DAY 11...AND 10 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 A SRN CALIF B A IDAHO B B NEVADA B A W MONTANA B B E MONTANA B 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 N N KANSAS N 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 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 N NEW HAMP A N MAINE A N MASS A N 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 A AK N SLOPE A B AK ALEUTIAN A A AK WESTERN A A AK INT BSN A N 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 N N OREGON N B NRN CALIF B B SRN CALIF B N IDAHO N B NEVADA B B W MONTANA N B E MONTANA A B WYOMING N B UTAH B N ARIZONA B A COLORADO B N NEW MEXICO B A N DAKOTA A B S DAKOTA A B NEBRASKA N B KANSAS B N OKLAHOMA B A N TEXAS B A S TEXAS B A W TEXAS B A MINNESOTA A B IOWA A B MISSOURI N N ARKANSAS B A LOUISIANA B A WISCONSIN A B ILLINOIS N B MISSISSIPPI B A MICHIGAN A B INDIANA N B OHIO N B KENTUCKY N N TENNESSEE N N ALABAMA B A NEW YORK N B VERMONT N B NEW HAMP N B MAINE N B MASS N B CONN N B RHODE IS N B PENN N N NEW JERSEY N N W VIRGINIA N N MARYLAND N N DELAWARE N N 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 A N AK ALEUTIAN B A AK WESTERN N A AK INT BSN A N AK S INT A A AK SO COAST A A AK PNHDL A 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