PROGNOSTIC DISCUSSIONS FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD 300 PM EDT MON SEP 22 2003 6 TO 10 DAY OUTLOOK FOR SEP 28 - OCT 2 2003 . . . . . . . THE MODELS ARE IN GOOD AGREEMENT ON THE LARGE SCALE 500-MB CIRCULATION OVER NORTH AMERICA. AN AMPLIFIED FLOW PATTERN IS PREDICTED... WITH STRONG RIDGES OVER WESTERN NORTH AMERICA AND IN THE NORTH ATLANTIC SOUTH OF GREENLAND. A DEEP TROUGH IS PREDICTED OVER THE NORTH PACIFIC AT ABOUT 150W WITH ANOTHER ALONG THE EASTERN U.S. COAST. THE ECMWF PREDICTS SOMWHAT LESS AMPLITUDE THAN THE 00Z GFS AND ITS ENSEMBLES. A LOOK AT TODAYS 06Z AND 12Z GFS RUNS SUPPORTS THE 00Z GFS PREDICTION. A STRONG RIDGE OVER THE WESTERN U.S. IS CONFIDENTLY PREDICTED... WHICH FORCES THE WESTERLIES AND ASSOCIATED LOW PRESSURE SYSTEMS INTO THE ALASKAN PANHANDLE. GENERALLY WARM AND DRY CONDITIONS CAN BE EXPECTED THROUGHT THE WESTERN U.S. WITH BELOW NORMAL TEMPERATURES IN THE EAST. SHORT WAVES DIVING SOUTHWARD FROM CENTRAL CANADA INTO THE EASTERN TROUGH WILL MAKE FOR UNCERTAIN CONDITIONS IN THE MISSISSIPPI VALLEY... ALTHOUGH TRENDS BETWEEN THE 0Z AND 6Z GFS SUGGEST THAT THE EASTERN TROUGH POSITION MAY BE SOMEWHAT WEST OF ITS POSITION ON THE OFFICAL BLEND... BRINGING BELOW NORMAL MEAN TEMPERATURES TO THE MISSISSIPPI VALLEY IN THE 6 TO 10 DAY PERIOD. WITH MOST OF THE COUNTRY UNDER A RIDGE -- OR IN NORTHWEST UPPER LEVEL FLOW... DRY CONDITIONS OR LIGHT PRECIPITATION SHOULD PREVAIL EXCEPT ALONG THE EAST COAST. ABOVE MEDIAN PRECIPITATION IS EXPECTED IN THE EAST -- FOLLOWING THE TREND IN THE MODEL SOLUTIONS FOR THE TROUGH TO BE SLIGHTLY SHARPER AND FURTHER WEST THAN THE ECMWF OR GFS ENSEMBLE MEAN PREDICT... ALTHOUGH PRECIPITATION AMOUNTS WILL DEPEND GREATLY ON WHERE THE AXIS OF THE EASTERN TROUGH EVENTUALLY DEVELOPS. MODEL OF THE DAY: GFS ENSEMBLE MEAN FORECAST CONFIDENCE FOR THE 6 TO 10 DAY PERIOD IS ABOVE AVERAGE TODAY... 4 ON A SCALE FROM 1 TO 5...DUE TO EXCELLENT MODEL AGREEMENT AND THE PREDICTION OF A WELL TELECONNECTED PATTERN. THE OFFICIAL HEIGHT PROG FOR TODAY CONSISTS OF 50 PERCENT OF TODAYS 0Z GFS ENSEMBLE MEAN CENTERED ON DAY 8... 40 PERCENT OF THE MOST RECENT ECMWF SOLUTION CENTERED ON DAY 7... AND 10 PERCENT OF THE TODAYS OPERATIONAL GFS CENTERED ON DAY 8. THE TEMPERATURE PROG IS BASED ON THE KLEIN SPECIFICATIONS FROM THE BLENDED HEIGHT FIELD AND ANALOGS BASED ON THE VARIOUS MODEL SOLUTIONS. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET PRECIPITATION FROM THE OFFICIAL BLEND...ANALOGS BASED ON VARIOUS MODEL SOLUTIONS AND ON THE CALIBRATED PRECIPITATION FROM THE OPERATIONAL 0Z GFS. . . . . . . . 8 TO 14 DAY OUTLOOK FOR SEP 30 - OCT 6 2003 THE 0Z OPERATIONAL GFS FORECAST AND ITS ENSEMBLES INDICATE THAT THE HIGHLY AMPLIFIED FLOW PATTERN EXPECTED IN THE EARLY PART OF THE PERIOD WILL RELAX INTO A MORE ZONAL FLOW PATTERN AS TIME PROGRESSES. THE 8-14 DAY MEAN TROUGH AND RIDGE POSITIONS REMAIN NEARLY UNCHANGED FROM THE 6 TO 10 DAY MEAN POSITIONS.. SO THE OVERALL PATTERNS IN EXPECTED SURFACE TEMPERATURES AND PRECIPITATION FOR THIS 8-14 DAY FORECAST WILL BE SIMILAR TO THE 6 TO 10 DAY PROG. CONFIDENCE IN THE WEEK 2 FORECAST IS ABOVE AVERAGE... 4 ON A SCALE OF 1 TO 5. THE OFFICIAL 500-HPA HEIGHT PROG FOR TODAY CONSISTS OF 60 PERCENT OF TODAYS GFS ENSEMBLE MEAN CENTERED ON DAY 11 AND 40 PERCENT OF TODAYS 0Z GFS CENTERED ON DAY 11. THE TEMPERATURE PROG IS BASED ON THE KLEIN SPECIFICATIONS FROM THE OFFICIAL 500-HPA HEIGHT PROG AND ANALOGS BASED ON THE VARIOUS MODEL SOLUTIONS. THE PRECIPITATION PROG IS BASED ON THE NEURAL NET PRECIPITATION FROM THE OFFICIAL BLEND... THE CALIBRATERD PRECIPITATION FROM THE 0Z GFS MODEL RUN AND ON ANALOGS BASED ON THE MODEL SOLUTIONS. 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 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 OCT 16 2003. 6 to 10 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A B OREGON A B NRN CALIF A B SRN CALIF A B IDAHO A B NEVADA A B W MONTANA A B E MONTANA A B WYOMING A B UTAH A B ARIZONA A B COLORADO A B NEW MEXICO A B N DAKOTA N B S DAKOTA A B NEBRASKA A B KANSAS A B OKLAHOMA A B N TEXAS N B S TEXAS N B W TEXAS A B MINNESOTA N B IOWA N B MISSOURI B B ARKANSAS B B LOUISIANA B B WISCONSIN B B ILLINOIS B B MISSISSIPPI B B MICHIGAN B N INDIANA B N OHIO B N KENTUCKY B N TENNESSEE B N ALABAMA B N NEW YORK B A VERMONT B A NEW HAMP B A MAINE N A MASS B A CONN B A RHODE IS B A PENN B A NEW JERSEY B A W VIRGINIA B A MARYLAND B A DELAWARE B A VIRGINIA B A N CAROLINA B A S CAROLINA B A GEORGIA B A FL PNHDL B A FL PENIN B A AK N SLOPE B B AK ALEUTIAN N B AK WESTERN N B AK INT BSN N N AK S INT A A AK SO COAST A A AK PNHDL A A 8 to 14 day Outlook Table STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A N OREGON A B NRN CALIF A B SRN CALIF A B IDAHO A B NEVADA A B W MONTANA A B E MONTANA A B WYOMING A B UTAH A B ARIZONA A B COLORADO A B NEW MEXICO A B N DAKOTA A B S DAKOTA A B NEBRASKA A B KANSAS A B OKLAHOMA A B N TEXAS N B S TEXAS N B W TEXAS A B MINNESOTA A B IOWA A B MISSOURI N B ARKANSAS N B LOUISIANA N B WISCONSIN N B ILLINOIS N B MISSISSIPPI N B MICHIGAN B B INDIANA N B OHIO B B KENTUCKY B B TENNESSEE B B ALABAMA B B NEW YORK B N VERMONT B A NEW HAMP B A MAINE B A MASS B A CONN B N RHODE IS B A PENN B N NEW JERSEY B N W VIRGINIA B B MARYLAND B N DELAWARE B N VIRGINIA B B N CAROLINA B B S CAROLINA B B GEORGIA B B FL PNHDL B B FL PENIN B N AK N SLOPE B B AK ALEUTIAN B B AK WESTERN B B AK INT BSN B B AK S INT N A AK SO COAST N A AK PNHDL A A 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. $$