PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS CLIMATE PREDICTION CENTER NCEP NATIONAL WEATHER SERVICE WASHINGTON DC 3 PM EST TUE DEC 10 2002 6 TO 10 DAY OUTLOOK FOR DEC 16 - 20 2002 . . . . . . . . MODEL COMPARISONS: THE VARIOUS MODEL SOLUTIONS FOR THE MAIN FEATURES OF THE 6 TO 10 DAY MEAN 500-HPA FLOW OVER NORTH AMERICA ARE IN REASONABLY CLOSE AGREEMENT ... AND CONSISTENT WITH YESTERDAYS RUNS. THE MODELS ARE IN VERY CLOSE AGREEMENT IN THE PREDICTION OF STRONG WESTERLY FLOW INTO THE WESTERN U.S. BUT VARY CONSIDERABLY ON THE DAILY FORECASTS OF SHORT WAVES IN THE CENTRAL AND EASTERN U.S. TIMING OF PRECIPITATION EVENTS WILL BE VERY DIFFICULT... WITH MOST STORM ACTIVITY OCCURRING ON DAY 5. A STORM IS EXPECTED TO BE OFF THE EAST COAST... AND MOST PRECIPITION OUT TO SEA BY THE START OF THE 6 TO 10 DAY PERIOD. AN EXTENDED PERIOD OF HEAVY PRECIPITION IS ANTICIPATED FOR THE WEST COAST... WITH THE HEAVIEST AMOUNTS EXPECTED JUST PRIOR TO THE START OF THE 6 TO 10 DAY PERIOD. THE 500-HPA HEIGHTS ARE EXPECTED TO BE WELL ABOVE NORMAL IN THE NORTHEASTERN U.S. BRINGING MILD TEMPERATURES FOR MUCH OF THE EAST FOR THE PERIOD. TEMPERATURES IN THE WESTERN U.S WILL BE VERY DIFFICULT TO PREDICT WITH MILD SOUTHERLY FLOW AHEAD OF RAPIDLY MOVING SYSTEMS BALANCED BY COLDER AIR BEHIND THEM. AS NOTED IN YESTERDAYS DISCUSSION... THE FORECAST FLOW IS A MIXTURE OF A NORTH ATLANTIC BLOCKING PATTERN AND AN ENHANCED PACIFIC JET STREAM TYPICAL IN AN EL NINO WINTER. THE SURFACE PATTERN FORECAST IS BASED ON THE EL NINO FLOW PATTERN GENERALLY DOMINATING FOR THIS PERIOD. THE FLOW PATTERN EXPECTED OVER THE CONUS IN 6 TO 10 DAY PERIOD IS SOMEWHAT AT ODDS WITH THE MAJOR NORTHERN HEMISPHERE EXTRA-TROPICAL TELECONNECTION PATTERNS PRECICTED BY THE MODELS... POSITIVE PNA AND NEGATIVE NAO... AND THE MODEL SOLUTION OVER THE U.S. TREND TOWARDS A SOLUTION MORE CONSISTENT WITH THE FORECAST STATES OF THE NAO AND PNA LATE IN THE PERIOD. FORECAST CONFIDENCE IS ABOVE AVERAGE TODAY...4 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 GFS ENSEMBLE MEAN CENTERED ON DAY 8...35 PERCENT OF THE ECMWF MODEL CENTERED ON DAY 7...15 PERCENT OF THE 00Z OPERATIONAL GFS CENTERED ON DAY 8... AND 10 PERCENT OF THE DAVA MODEL CENTERED ON DAY 8. MODEL OF THE DAY: GFS ENSEMBLE MEAN THE TEMPERATURE PROG IS BASED ON KLEIN AND NEURAL NETWORK SPECIFICATIONS FROM THE OFFICIAL HEIGHT PROG...WHICH WERE IN REASONABLY GOOD AGREEMENT AND AGREE WITH MOS PREDICTIONS FOR THE PERIOD. MOS INDICATED WARMER THAN NORMAL TEMPERATURES FOR ALASKA... WHICH WAS AT ODDS WITH ALL OTHER TOOLS AND WAS THEREFORE DISCOUNTED. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500-HPA BLEND...CALIBRATED PRECIPITATION FROM THE GFS...ACCUMULATED PRECIPITATION FROM THE RECENT GFS OPERATIONAL RUNS...AND ANALOGS FROM THE VARIOUS MODELS. . . . . . . . . 8 TO 14 DAY OUTLOOK FOR DEC 18 - 24 2002 MODEL COMPARISONS: THE VARIOUS ENSEMBLE MEMBERS FROM THE GFS TREND TOWARD A SOLUTION SIMILAR TO THE PERSISTENT 500-HPA PATTERN OBSERVED IN THE PAST SEVERAL WEEKS - WITH A RIDGE STARTING TO REESTABLISH IN THE WESTERN U.S.. THIS INDICATES A TRANSITION TO A FLOW PATTERN OVER THE CONUS THAT IS MORE CONSISTENT WITH A NEGATIVE AO/NAO PATTERN PREDICTED BY THE MODELS THAN ON THE 6 TO 10 DAY MEAN. HOWEVER THERE IS VERY LOW CONFIDENCE IN THE FORECAST - SINCE THE DAVA HOLDS ON TO THE 6 TO 10 DAY SOLUTION - AND EVEN ENHANCES THE EASTERN RIDGE. THIS SUGGESTS THAT BAROCLINIC DEVELOPMENT LATE IN THE 6 TO 10 DAY PERIOD IS ALTERING THE FLOW PATTERN. IN VIEW OF THE DIFFICULTY IN FORECASTING STORM DEVELOPMENT AT THOSE TIME RANGES... THE CONFIDENCE IN THE FORECAST IS VERY LOW. TEMPERATURES WILL BE PARTICULARLY DIFFICULT TO FORECAST... AS WILL PRECIPITATION IN THE SOUTHERN AND EASTERN PART OF THE COUNTRY. THE PACIFIC COAST SHOULD STILL SEE ENHANCED PRECIPITATION IN ACTIVE... BUT WEAKENING ONSHORE FLOW. CONFIDENCE IN THE WEEK 2 FORECAST IS MUCH BELOW AVERAGE...1 ON A SCALE FROM 1 TO 5. THE OFFICIAL 500-HPA HEIGHT FORECAST FOR THE 8 TO 14 DAY PERIOD USES 50 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 11...40 PERCENT OF TODAYS OPERATIONAL GFS CENTERED ON DAY 11...AND 10 PERCENT OF THE DAVA CENTERED ON DAY 11. THE TEMPERATURE PROG IS BASED ON THE KLEIN AND NEURAL NETWORK SPECIFICATIONS FROM THE OFFICIAL FORECAST 500-HPA BLEND WHICH WERE IN GOOD AGREEMENT WITH EACH OTHER AND WITH THE ANALOGS FROM THE MODELS... BUT WERE QUITE DIFFERENT FROM THE EXPECTED CONDITIONS IN THE 6 TO 10 DAY PERIOD. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET SPECIFICATIONS FROM THE 500-HPA BLEND...ANALOGS FROM THE VARIOUS MODELS... AND THE CALIBRATED PRECIPITATION FROM THE OPERATIONAL GFS. FORECASTER: D. UNGER . . . . . . . . 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. 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 (OO GMT) IS THE ONE USED BY CPC IN ITS FORECASTS. 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 THURSDAY DECEMBER 19 2002. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N A OREGON N A NRN CALIF N A SRN CALIF A A IDAHO N A NEVADA A A W MONTANA A B E MONTANA A B WYOMING A B UTAH A A ARIZONA A A COLORADO A N NEW MEXICO N A N DAKOTA A B S DAKOTA A B NEBRASKA A B KANSAS A B OKLAHOMA A B N TEXAS A N S TEXAS N N W TEXAS N N MINNESOTA A B IOWA A B MISSOURI A B ARKANSAS A N LOUISIANA N A WISCONSIN A B ILLINOIS A B MISSISSIPPI A A MICHIGAN A B INDIANA A N OHIO A N KENTUCKY A A TENNESSEE A A ALABAMA N A NEW YORK A N VERMONT A B NEW HAMP A N MAINE A B MASS A N CONN A N RHODE IS A N PENN A A NEW JERSEY A A W VIRGINIA A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA N A FL PNHDL N A FL PENIN N A AK N SLOPE B B AK ALEUTIAN B N AK WESTERN N B AK INT BSN B B AK S INT B B AK SO COAST B B AK PNHDL A N 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N A OREGON N A NRN CALIF N A SRN CALIF N A IDAHO N A NEVADA N A W MONTANA N B E MONTANA N B WYOMING N B UTAH N A ARIZONA N N COLORADO B N NEW MEXICO B B N DAKOTA N B S DAKOTA N B NEBRASKA B N KANSAS B N OKLAHOMA B N N TEXAS B N S TEXAS B N W TEXAS B B MINNESOTA A N IOWA A A MISSOURI N A ARKANSAS B A LOUISIANA B A WISCONSIN A A ILLINOIS A A MISSISSIPPI N A MICHIGAN A A INDIANA A A OHIO A A KENTUCKY A A TENNESSEE A A ALABAMA N A NEW YORK A A VERMONT A A NEW HAMP A A MAINE A A MASS A A CONN A A RHODE IS A A PENN A A NEW JERSEY A A W VIRGINIA A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA N A FL PNHDL N A FL PENIN N A AK N SLOPE N B AK ALEUTIAN N A AK WESTERN N N AK INT BSN A B AK S INT N A AK SO COAST N 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