EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 237 AM EDT SUN AUG 27 2017 VALID 12Z WED AUG 30 2017 - 12Z SUN SEP 03 2017 ...HARVEY IS EXPECTED TO LINGER ACROSS TX THROUGH AT LEAST FRIDAY...WITH TROPICAL FLOODING RAINS... OVERVIEW/GUIDANCE EVALUATION/PREFERENCES... THE MAIN FOCUS OF THE FORECAST CONTINUES TO BE THE REMAINS OF WHAT IS CURRENTLY TROPICAL STORM HARVEY. LEADING UP TO THE MEDIUM RANGE PERIOD...THE NATIONAL HURRICANE CENTER SHOWS VERY LITTLE FORWARD MOTION GIVEN EXTREMELY WEAK STEERING CURRENTS IN PLACE. AS IT SHOULD GENERALLY RESIDE OVER LAND FOR MULTIPLE DAYS...IT IS BEING ADVERTISED AS A TROPICAL DEPRESSION DURING THE FORECAST WITH A SLOW MOTION TOWARD THE NORTHEAST. MANY SOLUTIONS FAVOR SOME FORM OF CYCLONIC CIRCULATION REMAINING INTO LABOR DAY WEEKEND ACROSS THE ARKLATEX. RECENT RUNS OF THE GFS CONTINUE TO FAVOR A MORE WESTWARD JOG WHILE THE 12Z ECMWF AND 00Z CMC/UKMET KEEP THE SYSTEM ACROSS EASTERN TX WHICH IS MORE CONSISTENT WITH THE OFFICIAL TRACK. THE 00Z UKMET ACTUALLY SHOWS QUITE A HEALTHY SURFACE LOW REMAINING INTO FRIDAY WITH A 997-MB LOW LOCATED OVER NORTHEAST TX. THIS PARTICULAR SOLUTION IS A BIT QUICK AND IT DID TREND FASTER RELATIVE TO THE PREVIOUS 12Z RUN. REGARDLESS OF WHICH MODEL IS EVALUATED...HARVEY WILL REMAIN A HEAVY RAINFALL PRODUCER GIVEN ITS SLOW MOVEMENT AND EXTREME TROPICAL MOISTURE PUMPING INTO EASTERN TX. FARTHER EAST...THERE CONTINUES TO BE A THREAT FOR TROPICAL DEVELOPMENT OVER THE GULF STREAM. THIS IS IN RESPONSE TO CONVECTION CURRENTLY IMPACTING AREAS OF FL. BASED ON THE LATEST TROPICAL WEATHER OUTLOOK...THERE IS A 50 PERCENT CHANCE FOR CYCLONE DEVELOPMENT. MANY OF THE OPERATIONAL MODELS SHOW A VERY WOUND UP AXIS OF LOW PRESSURE LIFTING NORTH-NORTHEAST OVER THE WESTERN ATLANTIC. HOWEVER...THIS DOES NOT APPEAR TO BE ANY THREAT TO THE EASTERN SEABOARD AS ONLY A COUPLE OF THE 12Z ECMWF ENSEMBLE MEMBERS SKIRT THE SOUTHERN NOVA SCOTIA COAST. ELSEWHERE ON THE MAP DOMAIN...AMPLIFIED FLOW ACROSS ONTARIO ON WEDNESDAY WILL CONTINUE TO MARCH EAST-SOUTHEASTWARD BRINGING STRONG HEIGHT FALLS INTO NEW ENGLAND BY LATE THURSDAY/EARLY FRIDAY. MOST AVAILABLE SOLUTIONS DEPICT A WELL ESTABLISHED UPPER LOW SPINNING OVER SOUTHEASTERN QUEBEC ON 01/1200Z WITH THE 00Z/12Z UKMET BEING QUICKER OUTLIERS BASED ON RECENT ENSEMBLE SPAGHETTI PLOTS. THE AXIS OF LOWER HEIGHTS SHOULD BE SLOW TO EXIT NEW ENGLAND MOVING UP TOWARD NEWFOUNDLAND BY THE FOLLOWING DAY. AN UPPER RIDGE WILL CONTINUE TO INHABIT THE WESTERN HALF OF THE COUNTRY WHILE LONGWAVE TROUGHING APPROACHES THE PACIFIC NORTHWEST/BRITISH COLUMBIA COAST ON WEDNESDAY. GIVEN THE CORE OF THE STRONGER FORCING STAYS CLOSER TO THE U.S./CANADIAN BORDER...THE PERSISTENT RIDGE SHOULD EASILY RE-ESTABLISH ITSELF THEREAFTER AND POTENTIALLY STRENGTHEN LATER IN THE WEEK PER RUNS OF THE GFS. THE TIGHTEST MID-LEVEL HEIGHT GRADIENT SHOULD STAY ACROSS THE SOUTHERN EXTENT OF CANADA WITH PROGRESSIVE FLOW USHERING EMBEDDED SHORTWAVES EASTWARD TOWARD CENTRAL NORTH AMERICA. A BROAD NEGATIVE HEIGHT ANOMALY WILL LIKELY EXTEND OVER THE NORTHERN PLAINS INTO THE GREAT LAKES DURING THE LABOR DAY WEEKEND AS DEPICTED IN MUCH OF THE OPERATIONAL/ENSEMBLE MODEL SUITE. THE PAST THREE RUNS OF THE GFS REMAIN MORE AGGRESSIVE WITH A HIGHER AMPLITUDE PATTERN UNFOLDING WHICH HELPS ESTABLISH A 594-DM RIDGE OVER THE WEST COAST BY SATURDAY. WHILE POSSIBLE...IT IS ALSO ON ITS OWN WITH SUCH AN INTENSITY. THE FORECAST PACKAGE WAS DRIVEN HEAVILY BY THE 12Z ECMWF/ECMWF ENSEMBLE MEAN GIVEN IT MORE CLOSELY MIMICS THE TRACK OF HARVEY. EARLY ON...THE 18Z GFS OFFERED SOME USEFUL DETAILS ACROSS TX BEFORE SHIFTING WELL WEST OF THE OFFICIAL TRACK. UTILIZED ROUGHLY 70 PERCENT OF THE ECMWF/ECMWF ENSEMBLE MEAN THROUGHOUT THE PERIOD. THIS SOLUTION IS USEFUL ELSEWHERE ON THE MAP DOMAIN AS WELL GIVEN AGREEMENT WITH THE NEGATIVE HEIGHT ANOMALY OVER THE NORTHEASTERN U.S. AND ALSO HELPS TEMPER THE MID-LEVEL RIDGE STRENGTH OVER THE WEST LATE IN THE PERIOD. SENSIBLE WEATHER HIGHLIGHTS... GIVEN HARVEY STILL REMAINS A MAJOR PLAYER IN THE FORECAST...EXPECT ADDITIONAL HEAVY RAINFALL ACROSS EASTERN TX AND EXTENDING TOWARD THE OZARKS AND LOWER MS VALLEY IN TIME. THIS OF COURSE IS ALL DEPENDENT ON THE FORECAST TRACK OF WHAT REMAINS OF HARVEY DEEPER INTO THE PERIOD. GIVEN HOW MUCH RAIN WILL HAVE FALLEN BEFORE WEDNESDAY MORNING...ANY ADDITIONAL PRECIPITATION SHOULD FALL ON ALREADY SATURATED SOILS OR ACTIVE REGIONS OF FLOODING. FORECAST SOLUTIONS KEEP SHOWING 4 TO 8 INCH AMOUNTS IN 24-HOUR PERIODS POSSIBLE THROUGH AT LEAST THE END OF THE UPCOMING WORK WEEK. FARTHER NORTH...RAINFALL WILL BE POSSIBLE FROM THE MID-SOUTH/GULF COAST REGION EASTWARD TO THE SOUTHEASTERN U.S. GIVEN THE POTENTIAL FOR MOISTURE BEING ROBBED BY HARVEY...PROJECTED AMOUNTS ACROSS THE MENTIONED LOCATIONS SHOULD BE ON THE LIGHTER/MODERATE END. ELSEWHERE...SOME DIURNALLY FORCED CONVECTION IS POSSIBLE OVER THE INTERMOUNTAIN WEST/ROCKIES. HOWEVER...PERSISTENT RIDGING SHOULD STUNT A MORE WIDESPREAD EVENT FROM OCCURRING WITH FORECAST AMOUNTS ON THE LOWER END. THE WARM SPOT ON THE MAP WILL BE ACROSS THE WESTERN U.S. GIVEN THE AFOREMENTIONED UPPER RIDGE IN PLACE. FORECAST HIGH TEMPERATURES SHOULD BE ROUGHLY 10 TO 15 DEGREES ABOVE CLIMATOLOGY WHICH EQUATES TO 100 DEGREE PLUS READINGS OVER THE DESERT SOUTHWEST AND INTO THE INTERIOR CENTRAL VALLEYS IN CA. OTHERWISE...90S ARE EXPECTED TO EXTEND INTO THE CENTRAL GREAT BASIN/UPPER INTERMOUNTAIN WEST AND TOWARD LOCATIONS EAST OF INTERSTATE 5 ACROSS WA/OR. MEANWHILE...EXTENSIVE CLOUD COVER AND RAINFALL WILL KEEP TEMPERATURES 5 TO 10 DEGREES BELOW AVERAGE ACROSS MUCH OF THE SOUTHERN PLAINS/LOWER MS VALLEY. AND INTO THE GREAT LAKES/NORTHEASTERN U.S...COOLER WEATHER IS LIKELY GIVEN THE AMPLIFIED TROUGH PUSHING THROUGH THE REGION AS HIGHS STAY IN THE 70S. RUBIN-OSTER