EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 241 AM EDT FRI JUN 16 2017 VALID 12Z MON JUN 19 2017 - 12Z FRI JUN 23 2017 ...EXTREME RECORD HEAT WAVE FOR PORTIONS OF THE SOUTHWESTERN U.S. NEXT WEEK... ...OVERVIEW/GUIDANCE EVALUATION/PREFERENCES... THE SYNOPTIC-SCALE PATTERN DURING THE MEDIUM RANGE PERIOD WILL BE DOMINATED BY A 594-DM MID-LEVEL RIDGE ENCOMPASSING THE SOUTHWESTERN U.S. INTO THE FOUR CORNERS REGION. THIS FEATURE HAS BEEN WELL ESTABLISHED BY THE GLOBAL GUIDANCE WHILE THE FLOW TO THE NORTH WILL BE MUCH MORE ACTIVE. THE MAIN FEATURE ON MONDAY MORNING WILL BE AMPLIFIED FLOW ACROSS THE GREAT LAKES EXTENDING INTO THE MIDDLE MS/OH VALLEYS. THIS SHOULD EVENTUALLY BE REINFORCED BY ADDITIONAL TRAILING HEIGHT FALLS. ULTIMATELY THIS WILL MAINTAIN A NEGATIVE HEIGHT ANOMALY ACROSS MUCH OF EASTERN THIRD OF THE COUNTRY THROUGH AT LEAST WEDNESDAY INTO PERHAPS THURSDAY. FARTHER UPSTREAM...SOLUTIONS HAVE MADE LARGE CHANGES IN RECENT DAYS WHICH HAVE MOVED FROM FAVORING A RIDGE TO NOW INDICATING A LONGWAVE LOW-AMPLITUDE FLOW REGIME. LOOKING DOWN INTO THE TROPICS...SOME SORT OF DISTURBANCE SHOULD EMERGE INTO THE GULF OF MX DURING THE PERIOD WITH A MEDLEY OF SOLUTIONS STILL AT HAND. MODELS CONTINUE TO EXHIBIT FAIRLY GOOD AGREEMENT ON THE POSITION/STRENGTH OF THE RIDGE EXTENDING OVER THE SOUTHWESTERN U.S. MID-LEVEL HEIGHTS SHOULD LOWER A TAD TOWARD THE END OF NEXT WEEK IN RESPONSE TO AMPLIFICATION ACROSS THE NORTHWESTERN STATES. FOR THE MOST PART...THE FORECAST IS FAIRLY WELL ESTABLISHED THROUGH MID-WEEK WITH SPREAD PICKING UP BY THURSDAY. THE 12Z ECMWF WAS NOTABLY MORE AMPLIFIED WITH THE EASTERN U.S. TROUGH RELATIVE TO MOST OF THE ENSEMBLE MEMBERS. ACROSS THE WESTERN U.S. THERE IS PLENTY OF SPREAD WITH AMPLITUDE OVER THE REGION BUT THE ENSEMBLE MEANS CLUSTER WELL FAVORING A LOW-AMPLITUDE TROUGH SET UP. AS THESE HEIGHT FALLS EJECT TOWARD THE CENTER OF NORTH AMERICA...RECENT RUNS OF THE GFS/ECMWF FAVOR A PERIOD OF SUFFICIENT CYCLOGENESIS ACROSS CENTRAL CANADA. THE MOST CONTENTIOUS REGION OF THE FORECAST APPEARS TO BE OVER THE GULF OF MX. AS IS COMMONLY THE CASE...PREVIOUS RUNS OF THE CMC ARE OVERLY AGGRESSIVE DEEPENING A WAVE OVER THE GULF OF MX AND LIFTING TOWARD THE EASTERN GULF COAST BY TUESDAY. THIS IS GENERALLY ON ITS OWN ALTHOUGH THE 12Z NAVGEM FORMS AN IMPRESSIVE SURFACE WAVE. HOWEVER...THE 00Z/18Z GFS AND 12Z ECMWF CLUSTER REASONABLY WELL WITH THE ENSEMBLE FORECASTS TAKING SOME FEATURE TOWARD NORTHEASTERN MX LATER IN THE PERIOD. THROUGH DAY 4/TUESDAY...FELT AN 18Z GFS/12Z ECMWF BLEND WOULD SUFFICE BEFORE GRADUAL INCLUSIONS OF THE ENSEMBLE MEANS. KEPT A SMALL AMOUNT OF DETERMINISTIC INFLUENCE THROUGH DAY 6/THURSDAY WITH A SLIGHT WEIGHTING TOWARD THE 12Z ECMWF/ECMWF ENSEMBLE MEAN BEFORE GENERALLY DEFERRING TO ALL ENSEMBLE MEANS EXCEPT FOR A SMALL CONTRIBUTION FROM THE 12Z ECMWF. GIVEN MODELS FLIP-FLOPPED BETWEEN A POSITIVE AND NEGATIVE HEIGHT ANOMALY ACROSS THE NORTHWESTERN U.S. IN RECENT DAYS...CONFIDENCE IS AVERAGE AT BEST. ...SENSIBLE WEATHER/HIGHLIGHTS... THE DOMINANCE OF A BROAD UPPER RIDGE OVER THE SOUTHWESTERN U.S. WILL SUPPORT RECORD HEAT ACROSS THE REGION. A NUMBER OF DAYS WILL FEATURE HIGH TEMPERATURES WELL INTO THE 110S WITH EVEN A FEW POCKETS OF 120 DEGREE PLUS READINGS. A NUMBER OF DAILY RECORD MAXIMA MAY BE TIED OR BROKEN DURING THE PERIOD...PARTICULARLY FOR BALMY OVERNIGHT LOWS. SUCH ABUNDANT HEAT AND POTENTIAL RECORDS EXTEND FROM THE CENTRAL VALLEYS OF CA DOWN INTO THE DESERT SOUTHWEST. THIS IS ROUGHLY 10 TO 15 DEGREES ABOVE NORMAL FOR MID-JUNE. THE ONLY AREA OF THE COUNTRY EXPECTING MULTIPLE DAYS OF BELOW AVERAGE TEMPERATURES IS OVER THE GREAT LAKES GIVEN THE PERSISTENCE OF AN UPPER TROUGH FROM MONDAY UNTIL MID-WEEK. WET WEATHER WILL BE LIKELY ALONG AND AHEAD OF A SLOW-MOVING BAROCLINIC ZONE ACROSS THE EASTERN THIRD OF THE COUNTRY. THIS SHOULD GRADUALLY DRIFT EASTWARD AS THE SYSTEM EVENTUALLY EXITS THE COAST BY WEDNESDAY. ANOTHER ROUND OF RAINFALL IS LIKELY ACROSS THE NORTH-CENTRAL U.S. AND TOWARD DOWNSTREAM LOCATIONS AS THE NEXT TROUGH BEGINS TO AMPLIFY. DOWN ALONG THE GULF COAST...DEPENDING ON THE TRACK OF THE TROPICAL DISTURBANCE...SOME AREA COULD EXPERIENCE HEAVY RAINFALL BUT WHERE EXACTLY IS QUITE UNCERTAIN. RUBIN-OSTER