EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1149 AM EDT WED JUN 29 2016 VALID 12Z SAT JUL 02 2016 - 12Z WED JUL 06 2016 ...HEAVY RAIN POSSIBLE IN THE CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY THIS WEEKEND... THE FAIRLY PREDICTABLE MEDIUM RANGE FORECAST OF THE PAST FEW DAYS HAS BEGUN TO DEGRADE AS A VARIETY OF SHORTRANGE FEATURES ARE EXHIBITING INCREASING MODEL SPREAD WITH THE OVERNIGHT MODELS. WHILE THE OVERALL SYNOPTIC PATTERN CONTINUES TO BE RELATIVELY GOOD...THERE ARE INCREASING DIFFERENCES AMONG THE OPERATIONAL MODELS ESPECIALLY WITH SHORTWAVE FEATURES ACROSS THE CENTRAL US INTO SOUTH CENTRAL CANADA...WHICH COULD YIELD SIGNIFICANT DIFFERENCES IN QPF FORECASTS. IN GENERAL...USED A BLEND OF THE 00Z GFS/ECMWF/00Z NAEFS MEAN AND ECMWF ENSEMBLE MEAN EARLIER IN THE FORECAST WHILE TRENDED TOWARD THE ECWMF ENSEMBLE FORECAST FOR DAYS 5 AND BEYOND/MONDAY ETC. ON DAYS 3 AND 4/SATURDAY AND SUNDAY...DESPITE INCREASING DIFFERENCES...HEAVY RAIN STILL APPEARS TO BE A THREAT ACROSS THE CENTRAL PLAINS INTO THE MID MISSISSIPPI VALLEY...ESPECIALLY MISSOURI. THERE ALSO HAS BEEN A TREND FOR THE STATIONARY FRONT OVER THE CENTRAL US TO MOVE FARTHER NORTH THAN EARLIER INDICATED. THIS COULD BRING PRECIPITATION ACROSS THE MIDDLE ATLANTIC STATES AS EARLY AS JULY 4 AND ON THE FOLLOWING DAY. TROUGHING OVER THE NORTHWEST CONTINUES TO BE AN IMPORTANT SIGNAL LATER IN THE FORECAST. KOCIN