EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1154 AM EDT WED JUL 26 2017 VALID 12Z SAT JUL 29 2017 - 12Z WED AUG 02 2017 ...OVERVIEW... RIDGING IS FORECAST TO BUILD INTO THE INTERIOR WEST NEXT WEEK AS TROUGHING DIPS INTO THE EASTERN STATES. AFTER A ROBUST LOW PRESSURE SYSTEM DEPARTS THE MID-ATLANTIC AND NEW ENGLAND WATERS ON SATURDAY, A SURFACE FRONT WILL SETTLE ALONG THE GULF COAST AS A NORTHERN STREAM SYSTEM THROUGH CANADA DRAGS ANOTHER COLD FRONT THROUGH THE HIGH PLAINS AND UPPER MIDWEST INTO THE GREAT LAKES AND NORTHEAST THROUGH THE PERIOD. ...GUIDANCE EVALUATION/PREFERENCES... MODELS AND ENSEMBLES REMAIN IN GOOD OVERALL AGREEMENT OVER THE CONUS WITH THE SYNOPTIC PATTERN AND A GENERAL MODEL BLEND OFFERED A GOOD STARTING POINT. THIS INCLUDED THE GFS/ECMWF/UKMET/CANADIAN TO START, WHICH SUPPORTS A RATHER DEEP (FOR JULY) NON-TROPICAL LOW PRESSURE CENTER EAST OF ATLANTIC CITY (NEAR THE LOWEST PMSL VALUES PER THE CFSR CLIMATOLOGY (1979-PRESENT) FOR THIS TIME OF YEAR). AFTER SATURDAY, REMOVED THE UKMET FOLLOWED BY THE CANADIAN AS THEY DIFFERED FROM THE ENSEMBLE CONSENSUS AROUND THE EDGES OF THE CONUS AND THEN THE GFS RUNS BY NEXT MONDAY AS THE 00Z/06Z RUNS TOOK THE REMNANTS OF CURRENT HURRICANE HILARY NORTHWARD TOWARD THE OFFSHORE WATERS OF SOUTHERN CALIFORNIA. LATEST NHC TRACK MAINTAINS THE CONSENSUS OF A WESTWARD TURN ALONG 20N. BY NEXT TUE/WED, A BLEND OF THE ECMWF WITH THE GEFS/ECENS MEANS AND OVERNIGHT CONTINUITY ROUNDED OUT THE FORECAST AS TROUGHING LINGERED IN THE EAST AS SUBTROPICAL ATLANTIC UPPER RIDGING ATTEMPTS TO BUILD WESTWARD. ...WEATHER HIGHLIGHTS... THE PRIMARY CONCERNS FOR HEAVY RAINFALL THIS WEEKEND AND INTO EARLY NEXT WEEK WILL BE FROM THE SOUTHEAST AND NORTHERN FLORIDA TO THE CENTRAL GULF COAST, WHERE THE TAIL END OF A FRONTAL BOUNDARY PUSHING OFF THE EAST COAST ON SATURDAY WILL STALL AND SERVE AS A FOCUS FOR CONVECTION. THE FOUR CORNERS STATES WILL ALSO SEE PERSISTENT MONSOONAL MOISTURE WHICH SHOULD LEAD TO MULTIPLE DAYS OF LOCALLY HEAVY SHOWERS AND THUNDERSTORMS (ESPECIALLY IF THERE IS ANY CONNECTION WITH MOISTURE FROM EASTERN PACIFIC TROPICAL SYSTEMS). HEAVY RAINFALL COULD ALSO BECOME A THREAT OVER THE CENTRAL/SOUTHERN HIGH PLAINS BACK TO THE FOOTHILLS DURING THE FIRST HALF OF NEXT WEEK AS ENERGY DROPPING SOUTHWARD AROUND THE WESTERN U.S. RIDGE INTERACTS WITH ANOMALOUS MOISTURE ACROSS THE REGION, BUT THE DETAILS OF THIS FEATURE REMAIN VERY UNCERTAIN. LOWER LEVEL FLOW OUT OF THE GULF THROUGH THE TX/OK PANHANDLE COULD SUSTAIN HIGHER MOISTURE LEVELS FOR SEVERAL DAYS. THE GEFS M-CLIMATE QPF SHOWS THESE PREDICTED RAINFALL VALUES LIE ABOVE THE 99TH PERCENTILE OVER SE CO AND NE NM. TEMPERATURES SHOULD GENERALLY BE BELOW NORMAL FROM THE MISSISSIPPI TO THE EAST COAST BENEATH ANOTHER UPPER TROUGH SETTING UP OVER THE EASTERN HALF OF THE NATION THIS WEEKEND AND EARLY NEXT WEEK. MEANWHILE, RIDGING BUILDING BACK INTO THE WESTERN U.S. WILL BRING ABOVE NORMAL TEMPERATURES TO MUCH OF THE WEST, WITH THE EXCEPTION OF THE FOUR CORNERS REGION, WHERE MONSOONAL CONVECTION SHOULD KEEP DAYTIME TEMPERATURES CLOSER TO SUMMERTIME AVERAGES. FRACASSO/GERHARDT