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 APR 29 2002 6 TO 10 DAY OUTLOOK FOR MAY 5 - 9 2002 . . . . . . . . MODEL COMPARISONS: MODELS IN FAIR AGREEMENT TODAY... FORECASTING A STRONG MEAN RIDGE IN OR NEAR THE GULF OF ALASKA... A WEAKER MEAN RIDGE CENTERED SOUTHWEST OF GREENLAND... AND A BROAD BUT SUBSTANTIAL MEAN RIDGE EXTENDING FROM THE PLAINS EASTWARD THROUGH THE SOUTHEAST AND MID-ATLANTIC REGIONS. THE MAIN DISAGREEMENT CONCERNS A TROUGH DEVELOPING SOMEWHERE IN OR NEAR WESTERN NORTH AMERICA. THE ENSEMBLE MEAN... ECMWF... AND DAVA ALL FAVOR A RELATIVELY WEAK FEATURE IN THE MEAN... WITH THE BROAD RIDGE CENTERED TO THE EAST EXTENDING WESTWARD ACROSS THE FOUR CORNERS AND FAR WEST. THE MRF MAKES THIS FEATURE MUCH STRONGER AND MORE PERSISTENT. TELECONNECTIONS WITH THE POSITIVE 500 MB ANOMALY CENTERS SOUTH OF ALASKA AND NEAR THE DAVIS STRAIT ALL FAVOR A WEAKER FEATURE. HOWEVER... 500 MB BIAS-CORRECTED PATTERNS... BOTH FOR 7-DAY AND 30-DAY BIASES... TEND TO FAVOR A SOLUTION SOMEWHERE BETWEEN THE MRF AND THE GENERAL CONSENSUS OF THE OTHER FORE- CAST MODELS IN AMPLITUDE. ALSO... BIAS CORRECTIONS INDICATE THAT THE ANOMALY CENTER OF THE MEAN CENTRAL AND EASTERN U.S. RIDGE WILL BE NEAR THE OHIO AND MISSISSIPPI RIVERS CONFLUENCE... MORE IN LINE WITH THE OPERATIONAL MRF THAN THE ENSEMBLE MEAN... ECMWF... OR DAVA. THUS THE MRF SOLUTION WAS GIVEN THE MOST WEIGHT FOR THIS PERIOD... BUT OTHER MODELS ALSO FIGURED SUBSTANTIALLY INTO THE OFFICIAL BLEND IN AN EFFORT TO DAMP THE ANTICIPATED OVER-FORECAST AMPLITUDE OF THE WESTERN U.S. TROUGH BY THE MRF. THE OFFICIAL 500 MB BLEND IMPLIES A FAIRLY SIGNIFICANT SEVERE WEATHER AND HEAVY RAIN THREAT FOR PARTS OF THE PLAINS... MISSISSIPPI VALLEY... AND OHIO VALLEY. CONFIDENCE IN THE FORECAST TODAY IS ABOUT AVERAGE ...RATED 3 ON A SCALE FROM 1 TO 5. IN SPITE OF GOOD CONFIDENCE IN THE OFFICIAL BLEND... ISSUES REGARDING THE TIMING AND AMPLITUDE OF THE WESTERN U.S. TROUGH... AND THE LATITUDE OF A BACKDOOR-TYPE FRONTAL BOUNDARY ALONG THE EAST COAST EARLY IN THE PERIOD... LEAD TO UNCERTAINTY IN THE EXACT POSITION OF PRECIPITATION ANOMALIES... AND IN THE PLACEMENT OF TEMPERATURE ANOMALIES IN THE PLAINS AND ALONG THE EAST COAST. THE OFFICIAL 500-MB HEIGHT FORECAST FOR THE 6 TO 10 DAY PERIOD CONSISTS OF 40 PERCENT OF THE OPERATIONAL MRF CENTERED ON DAY 8... 20 PERCENT OF THE ENSEMBLE MEAN CENTERED ON DAY 8... 20 PERCENT OF THE ECMWF CENTERED ON DAY 8... AND 20 PERCENT OF THE DAVA MODEL CENTERED ON DAY 8. . . . . . . . . MODEL OF THE DAY: OPERATIONAL MRF THE TEMPERATURE PROG IS BASED ON MOS OUTPUT FROM THE ENSEMBLE FORECASTS... THE KLEIN SPECIFICATIONS FROM THE OFFICIAL 500 MB HEIGHT PROG... THE COMPOSITE ANALOG FROM THE OFFICIAL BLEND... AND THE DISTRIBUTION OF INDIVIDUAL ENSEMBLE MEMBERS. THE PRECIPITATION PROG IS BASED ON THE HISTORIC ANALOG FROM THE OFFICIAL 500 MB HEIGHT BLEND... NEURAL NET SPECIFICATIONS FROM THE OFFICIAL BLEND... AND BIAS- ADJUSTED OPERATIONAL MRF OUTPUT. 8 TO 14 DAY OUTLOOK FOR MAY 7 - 13 2002 MODEL COMPARISONS: THE ENSEMBLE MEAN AND OPERATIONAL MRF ARE IN EXCELLENT AGREEMENT THIS PERIOD... WITH BOTH RESEMBLING THE OPERATIONAL MRF PATTERN FORECAST FOR THE 6 TO 10 DAY PERIOD. MEANWHILE THE DAVA BRINGS THE MEAN WEST COAST TROUGH JUST ABOUT BODILY NORTHEASTWARD... CARVING OUT A BROAD FLAT ANOM- ALOUS TROUGH ACROSS MUCH OF CENTRAL CANADA WHILE WEAK RIDGES FORM IN THE SOUTH- WEST AND OFF THE NORTHEAST COAST. HOWEVER... THE ENSEMBLE MEAN CENTERED ON DAY 7 FOLLOWS MORE LOGICALLY FROM THE OFFICIAL 6 TO 10 DAY BLEND... WITH WEAKER TROUGHING FORECAST ALONG THE WEST COAST... AND A FLATTENED RIDGE OVER THE CENTRAL AND SOUTHEASTERN U.S. SOUTH OF NEAR- OR BELOW-NORMAL 500MB HEIGHTS ALONG THE NORTHERN TIER OF THE COUNTRY. AS A RESULT... TODAY WE FAVOR THE EN- SEMBLE MEAN CENTERED ON DAY 7... BUT BOTH THE ENSEMBLE MEAN AND OPERATIONAL MRF CENTERED ON DAY 11 WERE GIVEN SOME WEIGHT BECAUSE OF THEIR UNUSUALLY STRONG AGREEMENT. CONFIDENCE IN THE FORECAST IS ABOVE AVERAGE FOR A WEEK TWO FORECAST AT THIS TIME OF YEAR - RATED 4 ON A SCALE FROM 1 TO 5. THE OFFICIAL 500-MB HEIGHT FORECAST FOR THE 8 TO 14 DAY PERIOD CONSISTS OF 60 PERCENT OF THE ENSEMBLE MEAN CENTERED ON DAY 7... 20 PERCENT OF THE OPERATIONAL MRF CENTERED ON DAY 11... AND 20 PERCENT OF THE ENSEMBLE MEAN CENTERED DAY 11. THE TEMPERATURE OUTLOOK IS BASED ON THE KLEIN AND NEURAL NET SPECIFICATIONS FROM THE OFFICIAL BLEND AND THE DISTRIBUTION OF ENSEMBLE MEMBERS MEAN HEIGHT FIELDS CENTERED ON DAY 7. THE PRECIPITATION FORECAST IS BASED ON SPECIFICATIONS FROM THE NEURAL NET... THE DISTRIBUTION OF ENSEMBLE MEMBERS MEAN HEIGHT FIELDS CENTERED ON DAY 7... AND BIAS-ADJUSTED OUTPUT FROM THE OPERATIONAL MRF. 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 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. 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:----------------------------------------------------- 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. 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. AVN - THE RUN OF THE MRF MODEL INITIATED AT 12 UTC. 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 - CONTINENTAL 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. LA NINA - THE COLD 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. 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 SURFACCE 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. MRF ENSEMBLE - A SET OF MRF FORECASTS WHICH ARE ALL VALID AT THE SAME TIME BUT WHOSE STARTING CONDITIONS DIFFER BY SMALL AMOUNTS. THERE ARE CURRENTLY 25 MEMBERS IN THE MRF ENSEMBLE. THE AVERAGE OF THESE IS THE MRF 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 EAST- WARD 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 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 ON THURSDAY MAY 16. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON B A OREGON B A NRN CALIF B A SRN CALIF B N IDAHO B A NEVADA B N W MONTANA B A E MONTANA B A WYOMING N N UTAH N N ARIZONA N N COLORADO A N NEW MEXICO A N N DAKOTA B A S DAKOTA N A NEBRASKA A N KANSAS A A OKLAHOMA A N N TEXAS A N S TEXAS A B W TEXAS A N MINNESOTA B A IOWA N A MISSOURI A A ARKANSAS A N LOUISIANA A B WISCONSIN N A ILLINOIS A A MISSISSIPPI A N MICHIGAN A A INDIANA A A OHIO A A KENTUCKY A A TENNESSEE A A ALABAMA A N NEW YORK N A VERMONT N A NEW HAMP N N MAINE N N MASS N N CONN N N RHODE ISL N N PENN A A NEW JERSEY N A W VIRGINIA A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA A N FL PNHDL A N FL PENIN A N AK N SLOPE A A AK ALEUTIAN N N AK WESTERN N A AK INT BSN N A AK S INT B A AK S COAST B A 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 B A SRN CALIF B N IDAHO B A NEVADA B N W MONTANA B A E MONTANA B A WYOMING N N UTAH N N ARIZONA N N COLORADO A N NEW MEXICO A N N DAKOTA N A S DAKOTA N A NEBRASKA N N KANSAS A N OKLAHOMA A N N TEXAS A N S TEXAS A B W TEXAS A N MINNESOTA N A IOWA N A MISSOURI A A ARKANSAS A N LOUISIANA A B WISCONSIN N A ILLINOIS N A MISSISSIPPI A N MICHIGAN N A INDIANA N A OHIO N A KENTUCKY A A TENNESSEE A A ALABAMA A N NEW YORK N N VERMONT B A NEW HAMP B A MAINE B A MASS B N CONN B N RHODE ISL B N PENN N N NEW JERSEY N N W VIRGINIA A A MARYLAND N N DELAWARE N N VIRGINIA A N N CAROLINA A N S CAROLINA A N GEORGIA A N FL PNHDL A B FL PENIN A B AK N SLOPE A A AK ALEUTIAN N N AK WESTERN N A AK INT BSN N B AK S INT B A AK S COAST B N AK PNHDL B B LEGEND TEMPS WITH RESPECT TO NORMAL PCPN WITH RESPECT TO MEDIAN A - ABOVE N - NEAR NORMAL A - ABOVE N - NEAR MEDIAN N - NEAR NORMAL 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