0PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EDT WED SEP 11 2002 6 TO 10 DAY OUTLOOK FOR SEP 17 - 21 2002 . . . . . . . . MODEL COMPARISONS: ALTHOUGH DIFFERENCES IN DETAIL REMAIN... THE MODELS ARE IN MUCH BETTER AGREEMENT TODAY THAN THEY HAVE BEEN RECENTLY IN THEIR MEAN 500 HPA PATTERN AND ANOMALY DEPICTIONS FOR THE 6 TO 10 DAY PERIOD. THE DAVA... ENSEMBLE MEAN... AND OPERATIONAL MRF ALL INDICATE AN AMPLIFIED PATTERN ACROSS THE HIGHER LATITUDES OF NORTH AMERICA. CONSENSUS FEATURES INCLUDE /1/ A MODERATE CENTRAL PACIFIC OCEAN RIDGE AND POSITIVE 500 HPA ANOMALY CENTER... /2/ A BROAD AREA OF AMPLIFIED NEGATIVE 500 HPA HEIGHT ANOMALIES EXTENDING FROM CENTRAL SIBERIA THROUGH THE NORTHEAST SIBERIAN ARCTIC COAST... ALASKA... WESTERN CANADA... AND ADJACENT PORTIONS OF THE PACIFIC OCEAN AND NORTH AMERICA... AND /3/ A LARGE AMPLIFIED AREA OF ABOVE-NORMAL 500 HPA HEIGHTS FROM NORTHERN EUROPE NORTH- WESTWARD ACROSS NORTHERN GREENLAND THEN SOUTHWESTWARD THROUGH THE HUDSON BAY TO THE GREAT LAKES REGION. THE ECMWF REMAINS IN DISAGREEMENT WITH THE OTHER MODELS AND IS INCONSISTENT WITH ITS PREVIOUS RUN... HISTORICAL ANALOGS... AND MAIN FEATURE TELECONNECTIONS... AND THEREFORE HAS BEEN DISREGARDED. DESPITE THE HIGH-LATITUDE 500 HPA ANOMALY AMPLITUDES... THE FORECAST PATTERN STILL LEAVES WEAK MID-LEVEL FLOW AND LOW-GRADIENT ANOMALY FIELDS ACROSS THE UNITED STATES IN THE MEAN. THEREFORE... CONFIDENCE IN THE PARTICULARS OF SEN- SIBLE WEATHER FOR THE 6 TO 10 DAY PERIOD REMAINS LOW RELATIVE TO THE DEGREE OF MODEL AGREEMENT. ALSO... QUESTIONS REMAIN REGARDING /1/ THE AMPLITUDE AND EXTENT OF SLIGHTLY BELOW-NORMAL 500 HPA HEIGHTS ACROSS THE SOUTHEAST AND MID-ATLANTIC STATES... /2/ THE STRENGTH OF THE 500 HPA JET STREAM ENTERING THE PACIFIC NORTH- WEST SOUTH OF THE NEGATIVE 500 HPA HEIGHT ANOMALY CENTER NEAR THE WEST CANDA COAST... AND /3/ THE AMPLITUDE AND SOUTHWESTWARD EXTENT OF ABOVE-NORMAL 500 HPA HEIGHTS REACHING SOUTHWARD FROM THE HUDSON BAY POSITIVE ANOMALY CENTER ACROSS THE CENTRAL AND SOUTHWEST UNITED STATES. RECENT OPERATIONAL MRF BIASES INDICATE THAT THIS MODEL MAY BE TOO BULLISH IN BRINGING A RATHER STRONG SHORTWAVE AND CUTOFF 500 HPA LOW THROUGH THE NORTHERN PLAINS TO THE SOUTH OF THE HUDSON BAY POSITIVE ANOMALY... AND IN KEEPING BELOW-NORMAL MEAN 500 HPA HEIGHTS ACROSS THE SOUTHEAST AND MID-ATLANTIC REGIONS. ON THE OTHER HAND... BOTH THE ENSEMBLE MEAN AND DAVA... WHILE MORE AMPLIFIED THAN THEY HAVE BEEN RECENTLY... STILL SEEM TOO WEAK WITH MOST OF THEIR ANOMALY AMPLITUDES EVEN THOUGH WE THINK THEY HAVE A BETTERN HANDLE ON FEATURE PLACEMENT. AS A RESULT... THE OFFICIAL 500 HPA PROG IS A BLEND OF THESE THREE MODELS. FORECAST CONFIDENCE IS RATED AS AVERAGE... 3 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 ENSEMBLE MEAN FOR DAYS 6 TO 10... 40 PERCENT OF THE OPERATIONAL MRF FOR DAYS 6 TO 10... AND 20 PERCENT OF THE DAVA FOR DAYS 6 TO 10. MODEL OF THE DAY: THE MRF ENSEMBLE MEAN AND OPERATIONAL MRF ARE EVENLY WEIGHTED THE TEMPERATURE PROG IS BASED MAINLY ON AN AVERAGE OF THE KLEIN AND NEURAL NET SPECIFICATIONS FROM THE OFFICIAL BLEND... HISTORIC ANALOGS... BIAS-CORRECTED OPERATIONAL MRF 850 MB TEMPERATURE ANOMALIES... THE EXPERIMENTAL ENSEMBLE MEAN MOS... AND THE KLEIN SPECIFICATIONS FOR THE INDIVIDUAL ENSEMBLE MEMBERS. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FOR THE 500 HPA BLEND... HISTORIC ANALOGS... BIAS-CORRECTED OPERATIONAL MRF OUTPUT... CALIBRATED OPERATIONAL MRF OUTPUT... AND THE DISTRIBUTION OF NEURAL NET SPECIFICATIONS FOR THE INDIVIDUAL ENSEMBLE MEMBERS. . . . . . . . . 8 TO 14 DAY OUTLOOK FOR SEP 19 - 25 2002 MODEL COMPARISONS: THE DAVA... ENSEMBLE MEAN... AND OPERATIONAL MRF ALL AGREE THAT AN AMPLIFIED POSITIVE 500 HPA HEIGHT ANOMALY SHOULD PERSIST IN THE MEAN THROUGH THIS PERIOD ACROSS NORTHERN GREENLAND... NORTH-CENTRAL CANADA... AND EASTER CANADA WHILE A MODERATE CENTRAL PACIFIC RIDGE ALSO REMAINS IN PLACE. BETWEEN THESE FEATURES... THE OPERATIONAL MRF KEEPS A LARGE AREA OF NEGATIVE 500 HPA HEIGHT ANOMALIES CENTERED NEAR ALASKA AND EXTENDING WESTWARD BACK THROUGH MUCH OF SIBERIA... AND TO A LESSER EXTENT SOUTHEASTWARD ALONG THE WEST CANADIAN COAST. HOWEVER... THE EARLIER WEST-CANADIAN NEGATIVE 500 HPA HEIGHT ANOMALY CENTER IS NO LONGER EVIDENT IN THE MEAN... AND THE OPERATIONAL MRF INSTEAD DEVELOPS A SLOWLY-MOVING AMPLIFIED 500 HPA TROUGH THAT CREEPS THROUGH THE MIDDLE AND EASTERN UNITED STATES OVER THE COURSE OF DAYS 8 TO 14... SIMILAR TO ITS EAR- LIER TROUGH DEPICTION SOUTH OF THE EAST CANADIAN POSITIVE 500 HPA ANOMALY CENTER BUT CONSIDERABLY MORE AMPLIFIED THIS TIME AROUND. THE OTHER MODELS AND RECENTLY- OBSERVED OPERATIONAL MRF BIASES ARGUE AGAINST THIS DEVELOPMENT... AT LEAST TO THE EXTENT DEPICTED BY THE OPERATIONAL MRF... SO THE OTHER MODELS WERE GIVEN MORE WEIGHT IN THE OFFICIAL 500 HPA BLENDED FORECAST HEIGHT FIELD. IN ADDITION THE ENSEMBLE MEAN AND DAVA BOTH ARE TRANSITIONING AWAY FROM BELOW-NORMAL 500 HPA HEIGHTS IN ALASKA... AND TOWARD BRIDGING THE GAP BETWEEN THE STRONG POSITIVE 500 HPA HEIGHT ANOMALIES ACROSS THE NORTH POLE AND NORTHERN/EASTERN CANADA WITH THE PERSISTENT MODERATELY-AMPLIFIED CENTRAL PACIFIC OCEAN RIDGE. THIS ALSO SEEMS MORE LIKELY IN LIGHT OF RECENT OPERATIONAL MRF BIASES WHICH HAVE HELD 500 HPA HEIGHTS TOO LOW FOR TOO LONG OVER AND NEAR ALASKA. FORECAST CONFIDENCE IS RATED AS ABOUT AVERAGE... 3 ON A SCALE FROM 1 TO 5. THE OFFICIAL 500-HPA HEIGHT FORECAST FOR THE 8 TO 14 DAY PERIOD USES 45 PERCENT OF THE DAVA FILED FOR DAYS 8 TO 14... 35 PERCENT OF THE ENSEMBLE MEAN FIELD FOR DAYS 8 TO 14... AND 20 PERCENT OF THE OPERATIONAL MRF FIELD FOR DAYS 8 TO 14. THE TEMPERATURE PROG IS A CONSENSUS OF THE KLEIN AND NEURAL NET TEMPERATURE SPECIFICATIONS FROM THE OFFICIAL BLEND AND THE KLEIN SPECIFICATIONS FOR INDIVIDUAL ENSEMBLE MEMBERS. THE PRECIPITATION PROG IS A CONSENSUS OF THE CALIBRATED AND BIAS-CORRECTED MRF OUTPUT AND THE DISTRIBUTION OF NEURAL NET SPECIFICATIONS FOR THE INDIVIDUAL ENSEMBLE MEMBERS. FORECASTER: R. TINKER . . . . . . . . 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. 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 SEPTEMBER 19 2002. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON B A OREGON N A NRN CALIF A B SRN CALIF A B IDAHO N N NEVADA A B W MONTANA N N E MONTANA A N WYOMING A B UTAH A B ARIZONA A B COLORADO A B NEW MEXICO A B N DAKOTA A N S DAKOTA A N NEBRASKA A N KANSAS A N OKLAHOMA N N N TEXAS N N S TEXAS N N W TEXAS A B MINNESOTA A N IOWA A N MISSOURI A N ARKANSAS N N LOUISIANA N B WISCONSIN A N ILLINOIS A B MISSISSIPPI B B MICHIGAN A B INDIANA N B OHIO N B KENTUCKY N B TENNESSEE N B ALABAMA B B NEW YORK N N VERMONT N A NEW HAMP N A MAINE N A MASS N A CONN N N RHODE IS N N PENN N N NEW JERSEY N N W VIRGINIA N B MARYLAND B N DELAWARE B N VIRGINIA B B N CAROLINA B B S CAROLINA B N GEORGIA B N FL PNHDL B N FL PENIN B N AK N SLOPE N N AK ALEUTIAN B N AK WESTERN B N AK INT BSN B N AK S INT B B AK SO COAST B B AK PNHDL N A 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N A OREGON N B NRN CALIF N B SRN CALIF N B IDAHO N N NEVADA N B W MONTANA N N E MONTANA A N WYOMING A B UTAH A B ARIZONA N N COLORADO A N NEW MEXICO A N N DAKOTA A B S DAKOTA A A NEBRASKA A A KANSAS A A OKLAHOMA A N N TEXAS N B S TEXAS N B W TEXAS A N MINNESOTA A N IOWA A N MISSOURI A B ARKANSAS N B LOUISIANA N B WISCONSIN A B ILLINOIS A B MISSISSIPPI B B MICHIGAN A B INDIANA A B OHIO A B KENTUCKY N B TENNESSEE N B ALABAMA B N NEW YORK A B VERMONT A B NEW HAMP A B MAINE A B MASS N B CONN N B RHODE IS N B PENN N B NEW JERSEY N B W VIRGINIA N B MARYLAND N B DELAWARE N B VIRGINIA N B N CAROLINA N B S CAROLINA N N GEORGIA B N FL PNHDL B N FL PENIN B N AK N SLOPE N N AK ALEUTIAN B N AK WESTERN B A AK INT BSN B A AK S INT B A AK SO COAST B 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