PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EDT WED OCT 16 2002 6 TO 10 DAY OUTLOOK FOR OCT 22 - 26 2002 NOTE: THE MODEL THAT USED TO BE REFERRED TO AS THE MRF AND AVN IS NOW KNOWN AS THE GFS (GLOBAL FORECAST SYSTEM) MODEL. SEE GLOSSARY FOR DETAILS. . . . . . . . . MODEL COMPARISONS: THE AVAILABLE MODELS ARE IN VERY GOOD AGREEMENT ON THE MAJOR FEATURES OF THE 6 TO 10 DAY MEAN 500-HPA CIRCULATION OVER NORTH AMERICA. DUE TO NETWORK PROBLEMS THE ECMWF WAS NOT AVAILABLE TODAY. THE GFS... GFS ENSEMBLE AND DAVA MODELS CONTINUE TO PREDICT A NEGATIVE ARCTIC OSCILLATION TELECONNECTION PATTERN FEATURING ABOVE NORMAL 500-HPA HEIGHTS OVER THE POLAR REGION AND BELOW NORMAL HEIGHTS OVER MOST OF THE MID-LATITUDES. A TROUGH OVER THE ALEUTIANS IS FORECAST FURTHER EAST THAN YESTERDAYS FORECAST POSITION... BRINGING BELOW NORMAL 500-HPA HEIGHTS TO WESTERN AND CENTRAL ALASKA AND FORCING A SHARPER RIDGE OVER WESTERN CANADA. THE GFS ENSEMBLES INDICATE UNCERTAINTY OVER THE EASTERN NORTH PACIFIC... WITH THE MAJORITY OF MODEL RUNS MOVING SHORT WAVES EMBEDDED IN A STRONG NORTH PACIFIC JET NORTHWARD INTO THE GULF OF ALASKA ... WHILE A FEW MEMBERS MOVE SHORT WAVES INTO THE PACIFIC NORTHWEST. THERE IS VERY GOOD AGREEMENT THAT THE EASTERN U.S. WILL BE UNDER THE INFLUENCE OF A BROAD TROUGH FEATURING SHORT WAVES MOVING RAPIDLY SOUTHEASTWARD OVER THE NORTHERN PLAINS AND OFF THE EAST COAST. PRECIPITATION IS EXPECTED TO BE ON THE LIGHT SIDE IN THE NORTHERN U.S.. ANY SIGNIFICANT PRECIPITATION AMOUNTS WILL DEPEND ON DISTRUBANCES IN THE SOUTHERN JET. THE GUIDANCE RESTRICTS ABOVE MEDIAN PRECIPITAION AMOUNTS TO THE SOUTHERN U.S. - HOWEVER SIGNIFICANT PRECIPITATION CAN SPREAD INTO THE NORTH CENTRAL AND NORTHEASTERN U.S. IF SHORT WAVES IN THE NORTHERN AND SOUTHERN JET PHASE TOGETHER. 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 45 PERCENT OF THE GFS-BASED ENSEMBLE MEAN CENTERED ON DAY 8... 35 PERCENT OF THE HIGH RESOLUTION OPERATIONAL GFS CENTERED ON DAY 8... AND 20 PERCENT OF THE DAVA MEAN CENTERED ON DAY 8. MODEL OF THE DAY: GFS-BASED ENSEMBLE MEAN. THE TEMPERATURE PROG IS BASED MAINLY ON THE MOS SPECIFICATION BASED ON INDIVIDUAL GFS ENSEMBLE MEMBERS... WHICH AGREE WELL WITH THE OTHER TOOLS. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500- HPA BLEND... ANALOGS FROM THE VARIOUS MODELS... AND THE BIAS CORRECTED AND CALIBRATED ACCUMULATED PRECIPITATION FROM THE GFS. . . . . . . . . 8 TO 14 DAY OUTLOOK FOR OCT 24 - 30 2002 MODEL COMPARISONS: THE MODEL SOLUTIONS FOR THE 8-14 DAY MEAN 500-HPA HEIGHTS ARE VERY SIMILAR TO THEIR 6-10 DAY MEAN COUNTERPARTS... THUS THE TEMPERATURE AND PRECIPITATION FORECASTS FOR THE TWO PERIODS ARE SIMILAR. 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 THE GFS ENSEMBLE MEAN CENTERED ON DAY 11... 40 PERCENT OF THE GFS MEAN CENTERED ON DAY 11... AND 10 PERCENT OF THE DAVA CENTERED ON DAY 11. THE TEMPERATURE PROG IS BASED MAINLY ON THE KLEIN AND NEURAL NETWORK SPECIFICATIONS FROM THE OFFICIAL FORECAST 500-HPA BLEND... AND ON ANALOGS FROM THE VARIOUS MODELS. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500- HPA BLEND... ANALOGS FROM THE VARIOUS MODELS... AND THE CALIBRATED ACCUMULATED PRECIPITATION FROM THE 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 TOMORROW... THURSDAY OCTOBER 17 2002. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A B OREGON A B NRN CALIF A B SRN CALIF N N IDAHO A B NEVADA A B W MONTANA A B E MONTANA N B WYOMING B N UTAH N N ARIZONA N N COLORADO B N NEW MEXICO B A N DAKOTA B B S DAKOTA B B NEBRASKA B N KANSAS B N OKLAHOMA B A N TEXAS B A S TEXAS B A W TEXAS B A MINNESOTA B B IOWA B B MISSOURI B N ARKANSAS B A LOUISIANA B A WISCONSIN B B ILLINOIS B B MISSISSIPPI B A MICHIGAN B B INDIANA B B OHIO B B KENTUCKY B N TENNESSEE B N ALABAMA B A NEW YORK B N VERMONT B N NEW HAMP B N MAINE B N MASS B N CONN B N RHODE IS B N PENN B N NEW JERSEY B N W VIRGINIA B N MARYLAND B A DELAWARE B A VIRGINIA B A N CAROLINA B A S CAROLINA B A GEORGIA B A FL PNHDL B A FL PENIN B B AK N SLOPE A A AK ALEUTIAN N N AK WESTERN N N AK INT BSN A A AK S INT A A AK SO COAST A A AK PNHDL A A 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A N OREGON A B NRN CALIF A B SRN CALIF N A IDAHO N B NEVADA A B W MONTANA N B E MONTANA N N WYOMING N N UTAH N N ARIZONA B A COLORADO B N NEW MEXICO B A N DAKOTA B B S DAKOTA B B NEBRASKA B B KANSAS B N OKLAHOMA B A N TEXAS B A S TEXAS B A W TEXAS B A MINNESOTA B B IOWA B B MISSOURI B N ARKANSAS B A LOUISIANA B A WISCONSIN B B ILLINOIS B B MISSISSIPPI B A MICHIGAN B B INDIANA B B OHIO B B KENTUCKY B N TENNESSEE B A ALABAMA B A NEW YORK B B VERMONT B B NEW HAMP B B MAINE B B MASS B N CONN B N RHODE IS B N PENN B N NEW JERSEY B N W VIRGINIA B N MARYLAND B A DELAWARE B A VIRGINIA B A N CAROLINA B A S CAROLINA B A GEORGIA B A FL PNHDL B A FL PENIN B N AK N SLOPE A N AK ALEUTIAN N N AK WESTERN A A AK INT BSN A A AK S INT A A 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