PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT MON AUG 25 2003 6 TO 10 DAY OUTLOOK FOR AUG 31 - SEP 4 2003 . . . . . . . THE MODELS ARE IN GOOD AGREEMENT THAT THE 500 HPA PATTERN...WHICH BEGINS AS HIGHLY AMPLIFIED OVER CANADA BUT FLAT AND DOMINATED BY A BROAD RIDGE OVER THE U.S. ...ALSO AMPLIFIES OVER THE U.S. BY DAY 5. THIS SUPPRESSES THE RIDGE TO THE SOUTH AND PUSHES THE JET STREAM FROM SOUTHERN CANADA TO WELL INTO THE CENTRAL AND IN PLACES SOUTHERN U.S. BY THE BEGINNING OF THE 6 TO 10 DAY PERIOD. DURING THE 6 TO 10 DAY PERIOD THE MODELS REMAIN IN FAIRLY GOOD AGREEMENT ON THE OVERALL MEAN 500 HPA PATTERN...ALTHOUGH THE 6Z GFS BUILDS MORE RIDGE THROUGH THE U.S. ROCKIES AND INTERMOUNTAIN REGION THAN THE OTHER SOLUTIONS. HOWEVER ALL MODELS...EVEN THE DAVA... FORECAST A HIGHLY AMPLIFIED PATTERN OVER THE EASTERN PACIFIC AND NORTH AMERICA...WITH A SPLIT FLOW OVER WESTERN NORTH AMERICA REJOINING AT THE BASE OF A DEEP TROUGH OVER THE EASTERN U.S. WHICH EXTENDS FROM A CLOSED LOW IN THE VICINITY OF HUDSON BAY. THERE ARE SOME FAIRLY MINOR DIFFERENCES AMONG THE SOLUTIONS ON THE EXACT STRENGTH AND POSITION OF THE CLOSED LOW OVER EASTERN CANADA...WITH THE ECMWF AND 6Z GFS BEING THE DEEPEST WITH THIS FEATURE. THE BOTTOM LINE IS THE SAME IN ALL THE SOLUTIONS...THAT THE SUMMER-LIKE PATTERN IS GIVING WAY TO A MORE FALL-LIKE PATTERN OVER THE U.S. ...ALTHOUGH A TROUGH OVER THE EASTERN U.S. HAS BEEN A COMMON FEATURE FOR MUCH OF THE SUMMER. EXTENSIVE POSITIVE HEIGHT ANOMALIES ARE FORECAST AT HIGH LATITUDES OVER GREENLAND AND NORTHERN CANADA. THESE TELECONNECT WELL WITH PREDOMINATELY NEGATIVE ANOMALIES OVER MIDDLE LATITUDES...BUT DO SUGGEST SOME POSITIVE ANOMALIES HOLDING ON OVER THE SOUTHEASTERN U.S. AS IN THE ECMWF AND 0Z GFS. HOWEVER TELECONNECTIONS FROM THE NEGATIVE HEIGHT ANOMALY CENTER NEAR 45N/160W SUGGEST NEGATIVE HEIGHT ANOMALIES OVER THE SOUTHEASTERN STATES. AGREEMENT WITH YESTERDAYS SOLUTIONS IS REASONABLY GOOD. THE GFS AND ECMWF ENSEMBLE SPAGHETTI DIAGRAMS SHOW REASONABLE AGREEMENT OVER THE EASTERN U.S. BUT SIGNIFICANT SPREAD OVER THE EASTERN PACIFIC AND WESTERN NORTH AMERICA...REFLECTING UNCERTAINTY IN THE DETAILS OF HOW TO HANDLE THE SPLIT FLOW. THIS IS REFLECTED IN THE GFS AND ECMWF ENSEMBLE MEANS WHICH INDICATE THAT THE GFS ENSEMBLE TENDS TOWARD MORE UNDERCUTTING FLOW OVER WESTERN NORTH AMERICA THAN THE ECMWF ENSEMBLE. MODEL OF THE DAY: TIE BETWEEN 0Z GFS AND ECMWF. FORECAST CONFIDENCE FOR THE 6 TO 10 DAY PERIOD IS RATED ABOVE AVERAGE TODAY...4 ON A SCALE FROM 1 TO 5...DUE TO GOOD MODEL AGREEMENT...CONTINUITY...AND TELECONNECTIVITY. THE OFFICIAL HEIGHT PROG FOR TODAY CONSISTS OF 30 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 8...35 PERCENT OF TODAYS 0Z GFS SOLUTION CENTERED ON DAY 8...AND 35 PERCENT OF TODAYS ECMWF CENTERED ON DAY 7. THE TEMPERATURE PROG IS BASED ON THE KLEIN AND NEURAL NET SPECIFICATIONS FROM THE OFFICIAL 500-HPA HEIGHT PROG...THE MOS TEMPERATURES FROM THE GFS ENSEMBLES...AND ANALOGS TO THE 0Z GFS... ECMWF...AND GFS ENSEMBLE MEAN HEIGHT PROGS. TEMPERATURE TOOLS WERE IN REASONABLE AGREEMENT. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET PRECIPITATION FROM THE OFFICIAL 500-HPA HEIGHT PROG...CALIBRATED PRECIPITATION FROM THE 0Z GFS...AND ON ANALOGS TO THE 0Z GFS...ECMWF...AND GFS ENSEMBLE MEAN HEIGHT PROGS. . . . . . . . 8 TO 14 DAY OUTLOOK FOR SEP 2 - SEP 8 2003 DURING THE WEEK 2 PERIOD THE OPERATIONAL GFS RUNS AND THE GFS ENSEMBLE MEAN FORECAST OVERALL PATTERNS SIMILAR TO THOSE EACH OF THESE MODELS FORECAST FOR 6 TO 10 DAY PERIOD. THERE IS A TENDENCY FOR THE HIGH LATITUDE BLOCKING TO RETROGRADE IN THE FORECASTS... ESPECIALLY IN THE 0Z GFS RUN. THE GFS ENSEMBLE SPAGHETTI DIAGRAMS SHOW LOWER THAN NORMAL SPREAD FOR THIS TIME RANGE OVER EASTERN NORTH AMERICA AND AT HIGHER LATITUDES OVER WESTERN NORTH AMERICA. AT MIDDLE LATITUDES OVER THE WESTERN U.S. THERE IS SIGNIFICANT SPREAD AMONG THE GFS ENSEMBLE MEMBERS...AGAIN REFLECTING DIFFERENCES IN THE DETAILS OF THE SPLIT FLOW. CONSISTENCY WITH YESTERDAYS SOLUTIONS IS GENERALLY GOOD. CONFIDENCE IN THE WEEK 2 FORECAST IS RATED ABOVE AVERAGE...4 ON A SCALE OF 1 TO 5. THE OFFICIAL 500-HPA HEIGHT BLEND FOR THE 8 TO 14 DAY PERIOD CONSISTS OF 40 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 11...20 PERCENT OF TODAYS 0Z GFS CENTERED ON DAY 11...20 PERCENT OF THE ECMWF 5-DAY MEAN CENTERED ON DAY 7...AND 20 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 7. THE TEMPERATURE PROG IS BASED ON THE KLEIN AND NEURAL NET SPECIFICATIONS FROM THE OFFICIAL 500-HPA HEIGHT PROG AND ON ANALOGS TO THE ENSEMBLE MEAN HEIGHT FIELD. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET PRECIPITATION FROM THE OFFICIAL 500-HPA HEIGHT PROG...CALIBRATED PRECIPITATION FROM THE 0Z GFS MODEL...AND ON ANALOGS TO THE ENSEMBLE MEAN HEIGHT FIELD. FORECASTER: R. MARTIN . . . . . . . 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 PRECIPITATION. THE NARRATIVE DESCRIPTION OF THE FORECAST PATTERNS FOR TEMPERATURE AND PRECIPITATION 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. . . . . . . . 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. AO - ARCTIC OSCILLATION - A MEASURE OF THE DIFFERENCE BETWEEN THE MEAN MID-TROPOSPHERIC HEIGHT OR SEA LEVEL PRESSURE ANOMALY OVER THE POLAR BASIN AND THE CORRESPONDING AVERAGE ANOMALY IN A RING SURROUNDING THE POLAR BASIN AT MIDDLE LATITUDES. THE AO IS CONSIDERED TO BE THE LEADING MODE OF CLIMATE VARIABILITY OF THE EXTRATROPICAL NORTHERN HEMISPHERE. THE AO CAN ALSO BE CONSIDERED TO INCLUDE THE NAO (NORTH ATLANTIC OSCILLATION) WITH WHICH IT IS POSITIVELY CORRELATED - BUT NOT IDENTICAL. THE PHASE OF THE AO IS CONSIDERED TO BE POSITIVE WHEN HEIGHTS OR PRESSURES ARE BELOW NORMAL OVER THE ARCTIC BASIN AND ABOVE NORMAL OVER SURROUNDING MID- LATITUDES - AND IS NEGATIVE FOR THE REVERSE ANOMALY PATTERN. 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 (00 GMT) IS CURRENTLY THE ONLY ONE USED BY CPC IN ITS OFFICIAL BLEND FORECAST - ALTHOUGH THE OTHERS CAN BE CONSIDERED BY THE FORECASTER IN FORMULATING THE TEMPERATURE AND PRECIPITATION FORECASTS. GFS ENSEMBLE - A SET OF GFS FORECASTS WHICH ARE ALL VALID AT THE SAME TIME BUT WHOSE STARTING CONDITIONS DIFFER BY SMALL AMOUNTS. THERE ARE CURRENTLY 25 MEMBERS IN THE GFS ENSEMBLE. THE AVERAGE OF THESE IS THE GFS ENSEMBLE MEAN. 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. MJO - MADDEN-JULIAN OSCILLATION - ALSO CALLED TROPICAL INTRA-SEASONAL OSCILLATION - 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. IT CAN ALSO BE VIEWED AS THE ATLANTIC HALF OF THE AO (ARCTIC OSCILLATION) TELECONNECTION PATTERN - STRONGLY INFLUENCES TEMPERATURES OVER EUROPE AND MUCH OF NORTH AMERICA - ESPECIALLY DURING THE COLD SEASONS - AND DETERMINES THE MEAN LATITUDE OF THE PREVAILING STORM TRACKS ACROSS THE NORTH ATLANTIC. THE PHASE OF THE NAO IS CONSIDERED POSITIVE WHEN PRESSURES AND HEIGHTS ARE BELOW NORMAL OVER GREENLAND AND ICELAND (STRONG ICELANDIC LOW) AND ABOVE NORMAL AT MIDDLE AND SUBTROPICAL LATITUDES (STRONG BERMUDA-AZORES HIGH) - AND NEGATIVE FOR THE REVERSE ANOMALIES. PNA - PACIFIC NORTH AMERICAN TELECONNECTION PATTERN. PROG - PROGNOSIS - OR FORECAST. PROGRESSION OR PROGRESSIVE MOTION - THE NORMAL MOVEMENT OF ATMOSPHERIC WEATHER SYSTEMS (HIGHS... LOWS... RIDGES... OR TROUGHS) FROM WEST TO EAST IN THE MIDDLE LATITUDES. RETROGRESSION OR RETROGRADE MOTION - A TYPE OF MOTION SOMETIMES OBSERVED IN WEATHER SYSTEMS WHEN THEY END UP IN POSITIONS FURTHER TO THE WEST THAN THEIR ORIGINAL LOCATIONS - CONTRARY TO THEIR USUAL WEST TO EAST MOTION. 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 SOUTHERN 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 TELECONNECTIONS 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 SEP 18 2003. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N B OREGON N N NRN CALIF N N SRN CALIF N N IDAHO B N NEVADA N A W MONTANA B A E MONTANA B A WYOMING B A UTAH N A ARIZONA N N COLORADO B A NEW MEXICO N N N DAKOTA B N S DAKOTA B N NEBRASKA B A KANSAS B A OKLAHOMA B A N TEXAS N A S TEXAS N N W TEXAS N A MINNESOTA B N IOWA B N MISSOURI B N ARKANSAS N N LOUISIANA N A WISCONSIN B N ILLINOIS B N MISSISSIPPI N N MICHIGAN B B INDIANA B N OHIO B N KENTUCKY B N TENNESSEE B N ALABAMA N 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 A NEW JERSEY N A W VIRGINIA B A MARYLAND N A DELAWARE N A VIRGINIA N A N CAROLINA N A S CAROLINA N A GEORGIA N A FL PNHDL N A FL PENIN A A AK N SLOPE A B AK ALEUTIAN N B AK WESTERN A N AK INT BSN A N AK S INT A A AK SO COAST A A AK PNHDL A B 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N B OREGON N N NRN CALIF N N SRN CALIF N N IDAHO B N NEVADA N N W MONTANA B A E MONTANA B A WYOMING B A UTAH N A ARIZONA N N COLORADO B A NEW MEXICO N N N DAKOTA B N S DAKOTA B N NEBRASKA B A KANSAS B A OKLAHOMA B A N TEXAS B A S TEXAS N A W TEXAS N A MINNESOTA B B IOWA B N MISSOURI B N ARKANSAS N N LOUISIANA N A WISCONSIN B N ILLINOIS B N MISSISSIPPI N N MICHIGAN B B INDIANA B N OHIO B N KENTUCKY B N TENNESSEE B N ALABAMA N 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 A NEW JERSEY B A W VIRGINIA B A MARYLAND B A DELAWARE B A VIRGINIA B A N CAROLINA N A S CAROLINA N A GEORGIA N A FL PNHDL N A FL PENIN N A AK N SLOPE A B AK ALEUTIAN N B AK WESTERN A N 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 KWBC - ON AWIPS AS PMDMRD. $$