EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1130 AM EDT FRI JUN 10 2016 VALID 12Z MON JUN 13 2016 - 12Z FRI JUN 17 2016 ...OVERVIEW AND WEATHER... THE MEDIUM RANGE FORECAST CONTINUES TO BE ABOVE AVERAGE IN PREDICTABILITY OUT TO DAY 7/FRIDAY. A PERSISTENT UPPER ANOMALOUS LOW OVER THE NORTHEAST US/SOUTHEAST CANADA WILL PROVIDE A SOURCE OF COOL DRY AIR FROM THE UPPER MIDWEST TO THE NORTHEAST. MEANWHILE...A LIFTING TROUGH FROM THE SOUTHWEST EARLY IN THE PERIOD WILL BECOME EMBEDDED IN THE MEAN RIDGE AS IT MOVES ACROSS THE COUNTRY. ITS SLOW MOVEMENT...COMBINED WITH THE PRESENCE OF THE COOLER DRY AIR TO THE NORTH MAINTAINED BY A PERSISTENT UPPER CONFLUENT PATTERN...AND HOT AND HUMID CONDITIONS ACROSS THE SOUTHEAST INTO THE LOWER MISSISSIPPI VALLEY TO THE MIDWEST/OHIO VALLEY...WILL PRODUCE AN ACTIVE BOUNDARY WITH CONSIDERABLE SHOWERS AND THUNDERSTORMS. THE SLOW MOVEMENT OF BOTH FEATURES WILL RESULT IN AN ACTIVE FRONTAL BOUNDARY THAT COULD YIELD SOME HEADACHES FOR FORECASTERS TRYING TO DETERMINE WHICH SIDE OF THE FRONT THEY WILL BE...CREATING OPPORTUNITIES FOR CHALLENGING TEMPERATURE FORECASTS...AS WELL AS THE THREAT FROM CONVECTION NEAR AND SOUTH OF THE BOUNDARY AND COOLER, WET CONDITIONS NORTH OF THE BOUNDARY. THIS SETUP COULD RESULT IN BOUTS OF HEAVY RAINFALL... POSSIBLE FLOODING AND SEVERE WEATHER. AWAY FROM THE FRONT...NO SUCH PROBLEM WILL LIKELY EXIST WITH THE FORECAST. THERE WILL ALSO BE A TREND TOWARD WEATHER SYSTEMS MOVING MORE SOUTHEASTWARD ACROSS THE EASTERN HALF OF THE COUNTRY ESPECIALLY DURING THE LAST HALF OF THE FORECAST UNDER THE INFLUENCE OF THE POWERFUL UPPER LOW OVER SOUTHEASTERN CANADA. AS A RESULT...COOLER WEATHER APPEARS MORE LIKELY FOR PARTS OF THE EASTERN US DURING THIS PERIOD AS WEATHER SYSTEMS ARE SUPPRESSED SOUTH AND EASTWARD. OUT WEST...ANOTHER ANOMALOUS DEEP UPPER LOW WILL MOVE SOUTHWARD ALONG THE WESTERN NORTH AMERICAN COAST AND WILL LIKELY BECOME A FULL LATITUDE TROUGH JUST OFF THE WEST COAST...RESULTING IN COOLER CONDITIONS AND CHANCES FOR SHOWERS AND THUNDERSTORMS PARTICULARLY OVER ELEVATED TERRAIN. AS THE UPPER TROUGH DEEPENS...COOLER AIR WILL MAKE ITS WAY SLOWLY EASTWARD. CURRENTLY...IT IS STILL TOO UNCERTAIN TO DETERMINE THE EVOLUTION OF EMBEDDED SHORTWAVE SYSTEMS...ESPECIALLY TOWARD THE END OF THE FORECAST...BUT ANY IMPULSES WILL BRING AN ENHANCED CHANCE OF SHOWERS AND STORMS AS THIS DEEP SYSTEM WILL INFLUENCE MUCH OF THE NORTHWEST INTO PARTS OF THE INTERMOUNTAIN WEST AND CALIFORNIA. ...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT... THE MODEL COMBINATION USED FOR THE BLENDS INCLUDE THE 00Z ECMWF/06Z GFS...WHICH IS PREFERRED OVER THE 00Z RUN AND THE 06Z GEFS MEAN AND 00Z ECMWF MEAN. A SLIGHT ADVANTAGE...60/40... IS GIVEN TO THE OPERATIONAL RUNS THROUGH DAY 5/WEDNESDAY WITH AN EQUAL WEIGHT APPLIED TO BOTH THE 06Z GFS AND 00Z ECMWF. ON DAYS 6 AND 7/THURSDAY AND FRIDAY...A 50/50 BLEND OF THE OPERATIONAL/ENSEMBLE MEANS WAS USED WITH AN EDGE TOWARD THE ECMWF/ECMWF MEAN. IN GENERAL...THE ECMWF HAS PERFORMED MORE CONSISTENTLY IN GENERAL OVER THE PAST COUPLE DAYS. THE 00Z UKMET ALSO COULD HAVE PROVIDED AS CONSISTENT A FORECAST AS THESE 2 MODELS. KOCIN