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 08 2002 6 TO 10 DAY OUTLOOK FOR APRIL 14 - 18 2002 . . . . . . . . MODEL COMPARISONS: THE MRF ... THE MRF ENSEMBLE MEAN...THE DAVA... AND TO A LESSER EXTENT THE ECMWF...ARE IN ROUGHLY GOOD AGREEMENT TODAY CONCERNING THE 500 HPA LONGWAVE PATTERN OVER NORTH AMERICA...ALTHOUGH THERE ARE DIFFERENCES IN THE DETAILS. A CONSENSUS OF THESE MODEL RUNS SHOWS A STRONG POSITIVE HEIGHT ANOMALY CENTER OVER THE NORTHEAST...A MODERATELY STRONG POSITIVE CENTER NEAR OR OVER SOUTHERN CALIFORNIA...A RELATIVE WEAKNESS OVER THE CENTRAL U.S. THOUGH HEIGHTS ARE STILL CONSIDERABLY ABOVE AVERAGE...BELOW NORMAL HEIGHTS OVER ALASKA - WESTERN CANADA - AND THE PACIFIC NORTHWEST...AND A STRONG POSITIVE CENTER OFF THE SOUTHWESTERN TIP OF THE ALEUTIAN ARCHIPELAGO. THE MORE IMPORTANT DIFFER- ENCES INCLUDE THE ECMWF SOLUTION...WHICH HAS A CHANNEL OF BELOW NORMAL HEIGHTS ACROSS THE PLAINS REGION IN THE WEAKNESS AREA NOTED ABOVE...AND THE DAVA EX- TENDS THE NORTH PACIFIC RIDGE EASTWARD AND NORTHEASTWARD ACROSS MOST OF ALASKA. CONFIDENCE IN THE FORECAST TODAY IS SLIGHTLY ABOVE AVERAGE... RATED 4 ON A SCALE FROM 1 TO 5... DUE TO GENERALLY GOOD MODEL AGREEMENT OVER MOST AREAS OF THE NORTH AMERICAN SECTOR. RECENT MEAN ERRORS...AS WELL AS TELECONNECTIONS FROM THE TWO POSITIVE CENTERS OVER THE LOWER 48... LEND SOME SUPPORT TO THE IDEA OF A WEAKNESS OVER THE PLAINS...ESPECIALLY IF THE SOUTHERN CALIFORNIA RIDGE IS ONLY OF MODERATE INTENSITY. THE OFFICIAL 500-MB HEIGHT FORECAST FOR THE 6 TO 10 DAY PERIOD CONSISTS OF 50 PERCENT OF THE ENSEMBLE MEAN CENTERED ON DAY 8 ... 20 PERCENT OF THE MRF CENTERED ON DAY 8 ... 10 PERCENT OF THE DAVA CENTERED ON DAY 8... AND 20 PERCENT OF THE ECMWF CENTERED ON DAY 7. . . . . . . . . MODEL OF THE DAY: ENSEMBLE MEAN... HOWEVER ALL MODELS SKILL SCORES RECENTLY SHOW A SLIGHT DECLINE... TYPICAL FOR THE SPRING SEASON. THE TEMPERATURE PROG IS BASED ON THE KLEIN AND NEURAL NET SPECIFICATIONS FROM THE OFFICIAL 500 MB PROG... MOS OUTPUT FROM THE ENSEMBLE FORECASTS... AND BIAS CORRECTED 850 MB MODEL TEMPERATURES. THE PRECIPITATION PROG IS BASED ON HISTORICAL ANALOGS TO THE VARIOUS MODELS... AND BIAS CORRECTED VERSIONS OF THE ACCUMULATED PRECIPITATION FORECASTS FROM THE MRF AND MRF-BASED ENSEMBLE MEAN. 8 TO 14 DAY OUTLOOK FOR APRIL 16 - 22 2002 MODEL COMPARISONS: THE GENERAL CIRCULATION PATTERN CALLS FOR AN EAST-WEST ORIENTED RIDGE STRETCHING ACROSS THE LOWER 48 DURING WEEK 2...WITH A HINT OF SOME INCURSIONS OF COOL AIR ACROSS THE NORTH-CENTRAL REGION. UPSTREAM OVER THE GULF OF ALASKA...THE MRF HAS A MODERATELY INTENSE TROUGH...WHEREAS THE ENSEMBLE MEAN CONNECTS POSITIVE ANOMALIES OVER THE WESTERN U.S. TO THE ALEU- TIAN RIDGE VIA THE GULF OF ALASKA VICINITY. THE DAVA PREDICTS ABOVE NORMAL HEIGHTS OVER THIS ENTIRE REGION...FROM THE WESTERN U.S. THROUGH THE GULF INCLUDING ALASKA...AND THE NORTHEASTERN PACIFIC. CONFIDENCE IN THE FORECAST IS AVERAGE FOR A WEEK TWO FORECAST - RATED 3 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 11... 15 PERCENT OF THE MRF CENTERED ON DAY 11... 15 PERCENT OF THE 5-DAY MEAN ECMWF MODEL CENTERED ON DAY 7...AND 10 PERCENT OF THE DAVA CENTERED ON DAY 11. THE TEMPERATURE OUTLOOK IS BASED ON THE KLEIN AND NEURAL NET SPECIFICATIONS FROM THE OFFICIAL HEIGHT PROG... BIAS CORRECTED 850 MB TEMPERATURE ANOMALIES FROM THE MRF AND COMPOSITE ANALOGS FOR THE ENSEMBLE MEAN PROG. THE PRECIPITATION FORECAST IS BASED ON ANALOGS FOR THE VARIOUS MODELS... AND MRF MODEL OUTPUT CORRECTED FOR RECENT BIASES. FORECASTER: A. ARTUSA . . . . . . . . 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 APRIL 18. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON B A OREGON N N NRN CALIF A N SRN CALIF N B IDAHO N N NEVADA A B W MONTANA N N E MONTANA N N WYOMING N N UTAH N N ARIZONA A B COLORADO A N NEW MEXICO A N N DAKOTA A N S DAKOTA A A NEBRASKA A N KANSAS A N OKLAHOMA A N N TEXAS A N S TEXAS A A W TEXAS A A MINNESOTA A A IOWA A A MISSOURI A A ARKANSAS A A LOUISIANA A N WISCONSIN A A ILLINOIS A A MISSISSIPPI A N MICHIGAN A A INDIANA A A OHIO A A KENTUCKY A A TENNESSEE A N ALABAMA A N NEW YORK A N VERMONT A N NEW HAMP A N MAINE A N MASS A N CONN A N RHODE ISL A N PENN A N NEW JERSEY A N W VIRGINIA A N MARYLAND A N DELAWARE A N VIRGINIA A N N CAROLINA A N S CAROLINA A N GEORGIA A N FL PNHDL A N FL PENIN A B AK N SLOPE B B AK ALEUTIAN A A AK WESTERN B B AK INT BSN B B AK S INT B B AK S COAST N B AK PNHDL N B 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N A OREGON A N NRN CALIF A B SRN CALIF N B IDAHO A N NEVADA A B W MONTANA N N E MONTANA B N WYOMING A N UTAH A B ARIZONA A B COLORADO A N NEW MEXICO A B N DAKOTA B N S DAKOTA N A NEBRASKA N A KANSAS A A OKLAHOMA A N N TEXAS A N S TEXAS A A W TEXAS A N MINNESOTA N A IOWA A A MISSOURI A A ARKANSAS A A LOUISIANA A N WISCONSIN A A ILLINOIS A A MISSISSIPPI A A MICHIGAN A A INDIANA A N OHIO A N KENTUCKY A N TENNESSEE A N ALABAMA A A NEW YORK A N VERMONT N N NEW HAMP N N MAINE N N MASS N N CONN N N RHODE ISL N N PENN A N NEW JERSEY A N W VIRGINIA A N MARYLAND A N DELAWARE A N VIRGINIA A N N CAROLINA A N S CAROLINA A A GEORGIA A A FL PNHDL A N FL PENIN A B AK N SLOPE B N AK ALEUTIAN N A AK WESTERN B B AK INT BSN B B AK S INT B B AK S COAST B N 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 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