EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 159 AM EDT SUN AUG 24 2014 VALID 12Z WED AUG 27 2014 - 12Z SUN AUG 31 2014 ...PATTERN/MODEL EVALUATION... THE MEDIUM RANGE PERIOD WILL FEATURE A PROGRESSIVE NORTHERN STREAM WITH ENERGY RACING EASTWARD IN A LOW-AMPLITUDE FLOW ACROSS CANADA. TO THE SOUTH...A SLOW MOVING UPPER TROF WILL BEGIN OVER THE CENTRAL ROCKIES EARLY WEDNESDAY WITH HEIGHT FALLS GRADUALLY WORKING THEIR WAY EASTWARD IN TIME. THE MODELS WHICH WERE FASTER IN PREVIOUS DAYS WITH THIS SYSTEM HAVE TRENDED SLOWER WHICH IS A GOOD SIGN GIVEN THE TROF IS CUT-OFF FROM THE POLAR JET. BY THE END OF THE WEEK THE TROF SHOULD REACH THE OH VALLEY/MID-ATLANTIC WHILE POSSIBLY SHEARING APART DEPENDING UPON THE PIECE OF GUIDANCE. THE GREATER UNCERTAINTY IN THE MID-LATITUDES IS WITH THE UPSTREAM PATTERN EVOLVING ACROSS THE WESTERN/CENTRAL U.S...PARTICULARLY DURING DAYS 5 THROUGH 7...AUGUST 29-31. THE TIMING OF A FEATURE DEVELOPING OVER THE NORTHEASTERN PACIFIC PLAYS A KEY ROLE IN HOW THE 500-MB PATTERN SETS UP ACROSS WESTERN STATES. THE 18Z GFS/GEFS MEAN WERE QUICKER AND A BIT MORE AMPLIFIED WHICH LEADS TO STRONGER HEIGHT RISES ACROSS THE WEST COAST. THIS BECOMES EVEN MORE PRONOUNCED BY DAY 5/FRIDAY. MEANWHILE...THE 12Z ECMWF/ECMWF ENSEMBLE MEAN SUITE FAVOR A SLOWER NORTHEASTERN PACIFIC TROF WITH MORE OR LESS ZONAL FLOW ACROSS THE PACIFIC NORTHWEST AND INTO THE NORTHERN ROCKIES. AT LEAST THROUGH EARLY FRIDAY THE 12Z UKMET FAVORS THE HIGHER AMPLITUDE PATTERN OF THE GFS WHILE THE 12Z CMC SUPPORTS MORE ZONAL FLOW WHICH IS ALONG THE LINES OF THE ECMWF. BY NEXT WEEKEND THE MODEL DIFFERENCES ARE RATHER HIGH AS EVIDENT BY THE CHAOTIC 576-DM SPAGHETTI PLOT. FORTUNATELY THE 18Z GEFS/12Z ECMWF ENSEMBLE MEAN ARE IN HALF DECENT AGREEMENT WHICH SEEMS TO SPLIT THE DIFFERENCE BETWEEN THE AMPLIFIED 18Z GFS AND FLATTER 12Z ECMWF. LOOKING INTO THE TROPICS...TROPICAL DEPRESSION FOUR MAY BE AN IMPORTANT PLAYER DURING THE PERIOD DEPENDING UPON THE TRACK. THE GUIDANCE SHOW A VARIETY OF POSSIBLE SOLUTIONS WITH THE 12Z UKMET SHOWING A PAIR OF LANDFALLS IN SOUTHEASTERN FL AND EVENTUALLY SOUTHERN AL. ON THE OTHER SIDE IS THE 12Z CMC WHICH QUICKLY LIFTS THE TROPICAL SYSTEM UP TOWARD BERMUDA. THESE ARE PROBABLY TWO OF THE MORE EXTREME SOLUTIONS WHICH WERE NOT UTILIZED IN THE 03Z NHC TROPICAL POINTS. IT APPEARED SOME FORM OF 18Z GFS/12Z ECMWF BLEND AT LEAST CAPTURED THEIR TRACK TO SOME EXTENT BUT NOT ALL THE WAY. AT THIS POINT IN TIME...THE TRACK STAYS OFFSHORE OF THE EASTERN SEABOARD BUT THERE IS STILL PLENTY OF UNCERTAINTY AS TROPICAL DEPRESSION FOUR IS STILL DEVELOPING NEAR HISPANIOLA. ...WPC PREFERENCE... FOR DAYS 3 THROUGH 5...AUGUST 27-29...WPC FAVORED AN EQUAL BLEND OF THE 18Z GFS/12Z ECMWF. THIS WAS PRIMARILY UTILIZED TO ACCOUNT FOR THE TRACK OF TROPICAL DEPRESSION FOUR AS THE 12Z CMC/UKMET WERE OUTLIERS WITH THIS SYSTEM. ADDITIONALLY...DID NOT HAVE A GOOD GRASP ON HOW TO HANDLE THE UNCERTAINTY IN THE NORTHEASTERN PACIFIC TOWARD DAY 5 SO SPLIT THE DIFFERENCE. THEREAFTER...LEANED MORE HEAVILY ON A 50/50 BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS GIVEN THE RATHER HIGH SPREAD BETWEEN THE DETERMINISTIC MODELS. THESE MEANS WERE FAIRLY STABLE IN THE SINUSOIDAL PATTERN EVOLVING ACROSS THE WESTERN/CENTRAL U.S. LATE NEXT WEEK. ...SENSIBLE WEATHER HIGHLIGHTS... THE HIGHEST ANOMALIES DURING THE PERIOD WILL BE ON DAYS 3/4...AUGUST 27-28...WHERE TEMPERATURES WILL BE APPROXIMATELY 10 TO 15 DEGREES BELOW NORMAL OVER THE NORTHERN TIER STATES. THIS EQUATES TO HIGH TEMPERATURES GENERALLY IN THE UPPER 60S/LOWER 70S. SOUTH OF THE BAROCLINIC ZONE IT WILL BE QUITE WARM OVER THE SOUTHERN PLAINS AS HIGHS REACH THE MID/UPPER 90S. AS HEIGHTS BUILD ACROSS THE WESTERN U.S. MID/LATE NEXT WEEK...IT SHOULD BE RATHER WARM ACROSS THE WESTERN STATES WITH WIDESPREAD 90S FORECAST OVER THE INTERIOR VALLEYS. IN TERMS OF PRECIPITATION...THE BAROCLINIC ZONE SLIDING FROM THE CENTRAL U.S. EASTWARD WILL BE FOCUS FOR HEAVY RAINFALL THROUGHOUT THE PERIOD. GIVEN THE CLOSE PROXIMITY OF TROPICAL DEPRESSION FOUR TO THE SOUTHEASTERN U.S. COAST...SOME IMPACTS MAY OCCUR...PARTICULARLY OVER THE OFFSHORE WATERS. RUBIN-OSTER