PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EDT MON SEP 02 2002 6 TO 10 DAY OUTLOOK FOR SEP 8 - 12 2002 . . . . . . . . MODEL COMPARISONS: THE ECMWF... AVN ENSEMBLE MEAN... AND DAVA MODELS AGREE ON THE LARGE-SCALE FEATURES OF THE 500-HPA CIRCULATION PREDICTED FOR THE 6 TO 10 DAY PERIOD OVER NORTH AMERICA... BUT THE HIGH RESOLUTION AVN MODEL IS AGAIN SOMEWHAT OF AN OUTLIER... ESPECIALLY ON SOME INDIVIDUAL FEATURES OVER THE EASTERN PACIFIC AND THE WESTERN ATLANTIC. ITS AGREEMENT WITH THE OTHER MODELS IS NOT TOO BAD OVER THE LOWER 48 U.S. HOWEVER. IN GENERAL... THE MODELS AGREE ON CONTINUING TO PREDICT A DEEP TROUGH NEAR OF JUST OFF THE WEST COAST AND A STRONG RIDGE IN THE NORTH PACIFIC JUST SOUTH OF THE WESTERN ALEUTIANS. AN AMPLIFIED RIDGE ALSO IS PREDICTED OVER THE MISSISSIPPI VALLEY EXTENDING NORTHEASTWARD THROUGH THE GREAT LAKES REGION INTO QUEBEC... WITH THE ECMWF AS USUAL HAVING A STRONGER RIDGE THAN ANY OF THE OTHER MODELS. THE POSITIVE ANOMALY CENTER ASSOCIATED WITH THE RIDGE IS PLACED BY MOST OF THE MODELS NEAR THE GREAT LAKES OR OVER SOUTHERN QUEBEC. SOME OF THE DIFFERENCES IN THE AVN MODEL OVER THE PACIFIC MAY BE RELATED TO UNCERTAINTIES IN JUST WHERE TYPHOONS OVER THE WESTERN PACIFIC WILL INJECT ENERGY INTO THE WESTERLIES. THE ATLANTIC REMAINS RELATIVELY QUIET FOR THIS TIME OF YEAR... WITH TWO RELATIVELY WEAK TROPICAL STORMS - ONE IN THE CENTRAL ATLANTIC AND ONE THAT RECENTLY FORMED IN AN AREA OF CONVECTION OFF THE SOUTHEAST COAST. NEITHER IS EXPECTED TO AFFECT THE U.S. MAINLAND DURING THE 6-10 DAY PERIOD. CONFIDENCE IN TODAYS FORECAST IS RATED AS ABOVE AVERAGE DUE TO RELATIVELY GOOD MODEL AGREEMENT... 4 ON A SCALE OF 1 TO 5. THE OFFICIAL 500-HPA HEIGHT FORECAST FOR THE 6 TO 10 DAY PERIOD USES ... 40 PERCENT OF THE AVN ENSEMBLE MEAN CENTERED ON DAY 8... 20 PERCENT OF THE MOST RECENT ECMWF CENTERED ON DAY 7... 30 PERCENT OF TODAYS DAVA CENTERED ON DAY 8... AND 10 PERCENT OF TODAYS OPERATIONAL AVN CENTERED ON DAY 8. MODEL OF THE DAY: AVN ENSEMBLE MEAN THE TEMPERATURE PROG IS BASED MAINLY ON AN AVERAGE OF THE KLEIN AND NEURAL NET SPECIFICATIONS FROM THE OFFICIAL BLEND... WHICH WERE IN GOOD OVERALL AGREEMENT. THE CALIBRATED MOS FORECAST FROM THE AVN ENSEMBLES WAS NOT AVAILABLE TODAY. THE AREA OF ABOVE NORMAL TEMPERATURE ANOMALIES WAS SUBJECTIVELY CUT BACK SOMEWHAT OVER THE SOUTHEAST AND MIDDLE ATLANTIC DUE TO SATURATED TOPSOILS IN AREAS WITH RECENT HEAVY PRECIPITATION. THIS WAS ALSO MORE IN AGREEMENT WITH A CONSENSUS OF THE BEST ANALOGS TO THE VARIOUS MODELS... WHICH FOR THE MOST PART SHOWED LESS EXTENSIVE AREAS OF ABOVE NORMAL THAN EITHER THE KLEIN OR THE NEURAL NETR SPEICIFICAITONS ON THE OFFICIAL BLEND. THE PRECIPITATION PROG IS BASED ON PRECIPITATION ASSOCIATED WITH ANALOGS TO THE FORECAST 500-HPA CIRCULATION PATTERNS FROM THE VARIOUS MODELS... NEURAL NET SPECIFICATIONS... AND CALIBRATED AND BIAS-CORRECTED PRECIPITATION FROM THE OPERATIONAL AVN. . . . . . . . . 8 TO 14 DAY OUTLOOK FOR SEP 10 - 16 2002 MODEL COMPARISONS: THE AVN ENSEMBLE MEAN AND DAVA PREDICT A SIMILAR PHASE PATTERN BUT WITH LESS AMPLITUDE THAN THE 6 TO 10 PERIOD FOR THE 8 TO 14 DAY PERIOD... RESULTING IN A 500-HPA CIRCULATION THAT IS VERY SIMILAR FOR THE TWO PERIODS... BUT SOMEWHAT WEAKER. THE OPERATIONAL AVN IS AGAIN THE OUTLIER - WITH LITTLE AMPLITUDE AND FAST ZONAL FLOW NEAR THE U.S. / CANADIAN BORDER AND THE RMENANTS OF THE CENTRAL U.S. RIDGE RETROGRADING TO THE GREAT BASIN. THIS SOLUTION HAS BEEN LARGELY DISCOUNTED IN THE WEEK TWO BLEND AS WELL. CONFIDENCE IN TODAYS SOLUTION IS ABOUT AVERAGE... 3 ON A SCALE OF 1-5. THE BLENDED 500-MB HEIGHT PATTERN USES 40 PERCENT OF TODAYS AVN ENSEMBLE MEAN CENTERED ON DAY 11... 10 PERCENT OF TODAYS ENSEMBLE MEAN CENTERED ON DAY 7... 20 PERCENT OF TODAYS DAVA CENTERED ON DAY 11... 10 PERCENT OF TODAYS DAVA CENTERED ON DAY 7... 10 PERCENT OF TODAYS ECMWF CENTERED ON DAY 7... AND 10 PERCENT OF TODAYS AVN HIGH RESOLUTION MODEL CENTERED ON DAY 11. THE TEMPERATURE PROG IS A CONSENSUS OF THE KLEIN AND NEURAL NET TEMPERATURE SPECIFICATIONS FROM THE OFFICIAL BLEND... AND ANALOGS TO THE MODELS. THE PRECIPITATION PROG IS A CONSENSUS OF THE CALIBRATED AND BIAS-CORRECTED MRF OUTPUT... AND ANALOGS TO THE MODEL SOLUTIONS. FORECASTER: A. J. WAGNER . . . . . . . . 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 B N NRN CALIF B N SRN CALIF B N IDAHO N A NEVADA N A W MONTANA N A E MONTANA A A WYOMING A N UTAH A A ARIZONA A B COLORADO A B NEW MEXICO A B N DAKOTA A A S DAKOTA A B NEBRASKA A B KANSAS A B OKLAHOMA A B N TEXAS A B S TEXAS N N W TEXAS A B MINNESOTA A A IOWA A N MISSOURI A N ARKANSAS A B LOUISIANA N B WISCONSIN A A ILLINOIS A A MISSISSIPPI N N MICHIGAN A A INDIANA A N OHIO A N KENTUCKY A N TENNESSEE A B ALABAMA N N NEW YORK A B VERMONT A B NEW HAMP A B MAINE A B MASS A B CONN A B RHODE IS A B PENN A B NEW JERSEY A B W VIRGINIA A B MARYLAND A B DELAWARE A B VIRGINIA A B N CAROLINA N N S CAROLINA N N GEORGIA N B FL PNHDL B A FL PENIN B A AK N SLOPE N N AK ALEUTIAN N B AK WESTERN B N AK INT BSN B B AK S INT B N AK SO COAST B B AK PNHDL B N 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON B A OREGON B A NRN CALIF N N SRN CALIF B N IDAHO A N NEVADA A N W MONTANA N A E MONTANA A A WYOMING A A UTAH A N ARIZONA A B COLORADO A N NEW MEXICO A B N DAKOTA A A S DAKOTA A N NEBRASKA A N KANSAS A A OKLAHOMA A A N TEXAS A N S TEXAS N N W TEXAS A N MINNESOTA A A IOWA A N MISSOURI A B ARKANSAS A N LOUISIANA N B WISCONSIN A A ILLINOIS A B MISSISSIPPI N N MICHIGAN A A INDIANA A B OHIO A N KENTUCKY A B TENNESSEE A B ALABAMA N 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 A B NEW JERSEY N N W VIRGINIA A A MARYLAND A N DELAWARE A B VIRGINIA N N N CAROLINA N N S CAROLINA N N GEORGIA N N FL PNHDL N A FL PENIN N A AK N SLOPE B N AK ALEUTIAN N B AK WESTERN B N AK INT BSN B B AK S INT B N AK SO COAST B B AK PNHDL B 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