EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1143 AM EDT SUN JUN 18 2017 VALID 12Z WED JUN 21 2017 - 12Z SUN JUN 25 2017 ...THE SWELTERING HEAT WAVE ACROSS CA AND DESERT SOUTHWEST WILL PERSIST THROUGH THURS BEFORE SHIFTING INTO PARTS OF CO/NM AND WEST TX... ...THE NHC IS MONITORING AN AREA OF DISTURBED WEATHER IN THE NORTHWESTERN CARIBBEAN, WHICH COULD MOVE INTO THE GULF OF MEXICO AND COULD IMPACT AREAS ALONG THE GULF COAST WITH HEAVY RAINFALL BUT MUCH REMAINS UNCERTAIN... ...PATTERN OVERVIEW/MODEL EVALUATION... THE MEANS SUGGEST A RATHER STABLE UPPER-LEVEL PATTERN FOR MUCH OF THE MEDIUM RANGE PERIOD, WITH A POSITIVE ANOMALY BASED ALONG THE CENTRAL WEST COAST GRADUALLY SHIFTING TO SOUTH OF AK BY D+8, A NEG ANOMALY REMAINING RELATIVELY STATIONARY NEAR THE UPPER GREAT LAKES WITH LOWER HEIGHTS SPREADING SOUTH INTO THE MIDWEST AND A POSITIVE ANOMALY MAINLY REMAINING EAST OF THE CANADIAN MARITIMES. HOWEVER, SOME PARTICULAR SMALL SCALE DETAILS EARLY IN THE FORECAST PERIOD HINDER THE OVERALL LARGE SCALE PATTERN OF THE OPERATIONAL MODELS BY LATE WEEK INTO THE WEEKEND. ONE CONSTANT FEATURE EARLY ON WILL BE THE EXPANSIVE HEAT RIDGE ANCHORED OVER THE SOUTHWEST WITH A CLOSED 594DM HEIGHT CONTOUR. RECORD HIGH TEMPS AND DANGEROUS HEAT LIKE CONDITIONS WILL LINGER THROUGH MID WEEK OR THURS BEFORE CRASHING UPPER HEIGHTS NEAR THE PAC NW/NRN ROCKIES SKIRT THE GREAT BASIN BEFORE REACHING THE MIDWEST. THE LARGEST UNCERTAINTY IN THE FORECAST PERIOD IS THE FUTURE OF AN AREA OF DISTURBED WEATHER IN THE NWRN CARIBBEAN. STARTING ON WED, A VARY OF SOLUTIONS RANGE FROM A FORMIDABLE VORT MAX AT 500MB AND DECENT SURFACE LOW POSSIBLE NEAR THE TX GULF COAST TO THE FL PANHANDLE, BASED ON ALL OPERATIONAL MODELS AND ENSEMBLE DATA. THE LAST FEW RUNS OF THE GFS SHOW VERY GOOD CONTINUITY BUT IS TO THE FAR RIGHT OF THE GUIDANCE (FL PANHANDLE), THE CANADIAN HAS SHIFTED LEFT AND NOW IS LOCATED NEAR THE CENTRAL GULF COAST AND THE ECMWF/UKMET AND EVEN NAM ARE MORE DIRECTED TOWARD THE CENTRAL TX COASTLINE. THE MEANS GENERALLY SUPPORT EACH OPERATIONAL SOLUTION FOR THE MOST PART. ITS THE INTERACTION TO A CLEAR SHEAR LINE OF VORTICITY STRETCHING NE TO SW THROUGH THE GULF OF MEXICO AND ITS POSSIBLE INTERACTION WITH THE TROPICAL DISTURBANCE IS UNKNOWN AND MIGHT CONTINUE TO BE UNTIL ALL FACETS ARE BETTER DIAGNOSED BY THE GUIDANCE. WPC FOR THE TIME BEING WENT JUST NORTH AND EAST OF THE ECMWF/UKMET/EC MEAN AND CARRIED A TROUGH AXIS EXTENDING BACK TO THE NORTH AND EAST IN CONSIDERATION TO THE OTHER SOLUTIONS, GFS/GEFS/CANADIAN. EITHER WAY, THE THREAT FOR LOCALLY HEAVY RAIN WILL BE POSSIBLE ANYWHERE FROM TX TO THE SOUTHEAST. THE FORECAST BEYOND WED BECOMES EVEN MORE UNCERTAIN, AS SOME SOLUTIONS ALLOW THE WESTERLIES TO PICK UP THE DISTURBANCE, WHILE OTHERS ALLOW THE SEMI-AMPLIFIED UPPER TROUGH OVER THE EAST TO LIFT OUT AND LEAVE THE SYSTEM BEHIND. BOTH SOLUTIONS REMAIN VERY MUCH POSSIBLE AND NOT OUT OF THE REALM OF POSSIBILITIES. ALSO THIS UNCERTAINTY THEN EVENTUALLY BEGINS TO IMPACT THE LARGE SCALE PATTERN FRI-SUN ACROSS THE COUNTRY, NOT PROVIDING MUCH CONFIDENCE IN THE UPCOMING FORECAST. WPC STARTED WITH AN EXTENSIVE BLEND OF ALL GLOBAL MODEL OPERATIONAL SOLUTIONS WITH ECMWF/GEFS MEANS THROUGH THURS/FRI, GOOD AGREEMENT WITH THE TROUGH OVER THE EAST AND FAST UPSTREAM FLOW ALONG, WHILE INCLUDING ALL SOLUTIONS CONCERNING THE THREAT IN THE GULF/GULF COAST. HOWEVER BY NEXT WEEKEND, 80 PERCENT OF THE BLEND WAS BASED ON THE ECMWF/GEFS AND NAEFS MEANS TO HOPEFULLY REDUCE THE SPREAD AND CAPTURE THE OVERALL LARGE SCALE UPPER-LEVEL PATTERN ACROSS THE COUNTRY. ...WEATHER HIGHLIGHTS... CONSECUTIVE DAYS OF POTENTIALLY RECORD BREAKING HEAT IS EXPECTED FROM CA/NV EAST INTO THE FOUR CORNERS REGION THROUGH THURS, WITH DAYTIME TEMPERATURES POSSIBLY EXCEEDING THE 120 DEGREE MARK IN SOME DESERT LOCATIONS ON WED. THE OVERALL WPC 5 DAY MEAN MAX TEMP ANOMALY SHOWS WELL ABOVE AVG HIGHS ACROSS THE CORRIDOR AND STRETCHING UP SOME INTO THE PAC NW AND BELOW AVG HIGHS FOR THE NRN PLAINS/UPPER MIDWEST AND SOUTH/GULF COAST STATES. TROPICAL HEAVY RAINFALL COULD BE A THREAT WED THROUGH FRI ANYWHERE FROM TX TO SOUTHEAST, DEPENDING ON HOW EVERYTHING EVOLVES ACROSS THE SRN TIER OF THE COUNTRY, JUST ABSOLUTELY TOO UNCERTAIN TO PINPOINT THIS FAR OUT IN ADVANCE. ALSO ON WED THROUGH FRI, CONVECTIVE HEAVY RAINFALL WILL BE POSSIBLE FROM THE CENTRAL PLAINS AND MID/UPPER MS VALLEY INTO THE GREAT LAKES/OH VALLEY AND NORTHEAST. THEN ON SAT, A DEEP MOISTURE PLUME WILL STRETCH FROM THE GREAT LAKES INTO THE OH/TN VALLEYS AND MID TO LOWER MS VALLEY INTO THE SOUTH FOR SCATTERED SHOWERS/STORMS WITH LOCALLY HEAVY RAINS. THEN FINALLY BY NEXT SUN, MOST OF THE PRECIP SHOULD BE OVER THE EAST INTO PERHAPS THE SOUTH AND UP INTO THE GREAT LAKES/UPPER MS VALLEY. MUSHER