EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 238 AM EDT MON JUL 11 2016 VALID 12Z THU JUL 14 2016 - 12Z MON JUL 18 2016 ...PATTERN OVERVIEW/GUIDANCE EVALUATION/PREFERENCES... TO COMMENCE THE MEDIUM RANGE PERIOD...14/1200Z...THE LONGWAVE PATTERN FEATURES A HIGHLY AMPLIFIED TROUGH OVER HUDSON BAY EXTENDING DOWN INTO SOUTHERN ONTARIO. MEANWHILE...MEAN RIDGING ANCHORS MUCH OF WESTERN CANADA ALTHOUGH A COMPACT UPPER LOW IS ABLE TO SLIP UNDERNEATH THIS DOME OF HIGH PRESSURE. TO THE SOUTH OF THE WAVY SYNOPTIC PATTERN WILL BE A WEST-EAST ORIENTED RIDGE EXTENDING ACROSS NORTHERN MX INTO THE SOUTHERN PLAINS. THE GENERAL EVOLUTION OF THIS PATTERN IS FOR LOWER HEIGHTS TO START SETTING UP OFF THE WEST COAST WHICH ULTIMATELY WILL HELP LIFT THE DOWNSTREAM TROUGH FARTHER UP INTO EASTERN CANADA. THIS SHOULD LEAD TO WEST-SOUTHWESTERLY FLOW ALOFT FROM THE INTERMOUNTAIN WEST ACROSS THE NORTHERN TIER STATES AND INTO NEW ENGLAND. A PRETTY IMPRESSIVE UPPER RIDGE TAKES SHAPE UNDERNEATH WITH ABOVE 594-DM HEIGHTS GENERALLY ENCOMPASSING THE SOUTHERN HALF OF THE U.S. REGARDING THE MODELS...THERE IS DECENT AGREEMENT WITH THE PLACEMENT OF THE UPPER TROUGH CROSSING THE GREAT LAKES ON THURSDAY. MORE OF THE DIFFERENCES SEEM TO BE DRIVEN BY THE AMPLITUDE OF THIS PATTERN WITH THE 12Z UKMET BEING THE MOST SUPPRESSED. SUCH A SOLUTION PERSISTED AFTER EVALUATING THE 00Z UKMET. ON THE OPPOSITE END...THE 12Z CMC FAVORED MORE AMPLITUDE ALONG THE SOUTHERN EXTENT OF THE TROUGH AS IT WAS MORE AGGRESSIVE WITH A PERTURBATION TRACKING THROUGH THE OZARKS EARLY SATURDAY. LOOKING ACROSS THE NORTHWESTERN U.S...SOME UNCERTAINTY IS EVIDENT WITH THE APPROACHING CLOSED LOW...PARTICULARLY WITH TIMING. ONE SOLUTION WHICH APPEARS OUTLYING IN NATURE IS THE 12Z UKMET WHICH DIVERGES SIGNIFICANTLY FROM THE ENSEMBLES IN THE 12Z SPAGHETTI PLOTS. IT SUGGESTS BUILDING HEIGHTS RELATIVE TO THE CONSENSUS OF A SLOW-MOVING CLOSED LOW MIGRATING TOWARD THE BC/WA BORDER. THE GENERAL IDEA IS FOR THIS SYSTEM TO ADVANCE EASTWARD INTO THE UPPER INTERMOUNTAIN WEST EARLY IN THE WEEKEND BEFORE SHEARING ALONG THE INTERNATIONAL BORDER WITH CANADA. THIS EVOLUTION IS SUPPORTED BY ALL ENSEMBLE MEANS WHILE LOWER HEIGHTS BEGIN TO SETTLE INTO THE FAR EASTERN PACIFIC BY DAY 6/7...JULY 17-18. OVERALL...RECENT RUNS OF THE GFS/ECMWF PAINT A REASONABLE PICTURE OF THE MEDIUM RANGE PERIOD. WAS ABLE TO AFFORD AN EQUAL BLEND OF THE 18Z GFS/12Z ECMWF THROUGH DAY 4 WHILE ADDING A SMALL AMOUNT OF THEIR RESPECTIVE MEANS FOR DAY 5. THEREAFTER...STILL KEPT A SMALL FRACTION OF THE 18Z GFS/12Z ECMWF IN THE BLEND WITH HEAVIER WEIGHTING ON THE ENSEMBLES. ...WEATHER HIGHLIGHTS/THREATS... THE FORECAST SHOULD GENERALLY BE DOMINATED BY AT OR ABOVE NORMAL TEMPERATURES DURING THE MEDIUM RANGE. HIGH TEMPERATURES APPROXIMATELY 5 TO 10 DEGREES ABOVE CLIMATOLOGY WILL BE LIKELY ANYWHERE FROM THE DESERT SOUTHWEST EASTWARD INTO THE SOUTHERN PLAINS. THE CURRENT FORECAST SUGGESTS READINGS IN THE 110 TO 115 RANGE ACROSS THE DESERTS OF NV/CA/AZ. GRADUALLY WARMER TEMPERATURES WILL LIFT NORTHWARD ACROSS THE CENTRAL PLAINS TO THE NORTHEASTERN STATES AS BROAD SOUTHWESTERLY FLOW ALOFT BECOMES MORE PREVALENT. THE ONLY SPOT WHICH MAY SEE A PROLONGED PERIOD OF BELOW NORMAL READINGS WILL BE ALONG THE NORTHERN TIER STATES WHICH SHOULD BE POST-FRONTAL DURING MUCH OF THE PERIOD. LOOKING AT PRECIPITATION...HEAVY BOUTS OF SHOWERS AND THUNDERSTORMS ARE LIKELY ALONG THE MEANDERING WEST-EAST BOUNDARY. EXACTLY WHERE THIS RESIDES SHOULD PROVE DIFFICULT TO DETERMINE AS IT WILL LIKELY RELOCATE BASED ON CONVECTION. AND OF COURSE THE WARM SECTOR CAN EXPECT DAILY ROUNDS OF THUNDERSTORMS AMIDST AMPLE DIURNAL HEATING. GIVEN SUFFICIENT REMOVAL FROM THE WESTERLIES...THESE STORMS SHOULD BE SOMEWHAT DISORGANIZED AND MORE INSTABILITY DRIVEN. RUBIN-OSTER