EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 140 AM EDT FRI JUL 28 2017 VALID 12Z MON JUL 31 2017 - 12Z FRI AUG 04 2017 ...PATTERN OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... THE LONG WAVE PATTERN ACROSS THE CONUS WILL BE RELATIVELY STABLE THROUGH THE MEDIUM RANGE, WITH PERSISTENT TROUGHING ACROSS THE EASTERN HALF OF THE COUNTRY, AND AN ANOMALOUS UPPER-LVL RIDGE AMPLIFYING ACROSS THE GREAT BASIN (500 HPA HEIGHT ANOMALIES POTENTIALLY REACH +2 STANDARD DEVIATIONS BY THE MIDDLE OF NEXT WEEK). DETERMINISTIC SOLUTIONS AS WELL AS ENSEMBLE MEANS SHOW GOOD CONSENSUS WITH RESPECT TO THIS LONG WAVE FLOW PATTERN. TELECONNECTIONS ASSOCIATED WITH A PERSISTENT NEGATIVE HEIGHT ANOMALY ACROSS THE GULF OF ALASKA FURTHER SUPPORTS WESTERN U.S. RIDGING AND TROUGHING IN THE EAST. GUIDANCE HAS VARIED FROM RUN TO RUN WITH RESPECT TO THE CHARACTER OF THE EASTERN TROUGH, THE RESULT OF SMALL SCALE FEATURES IN THE FLOW WITH LOW PREDICTABILITY. MANY OF THESE FEATURES ORIGINATE IN THE NERN PAC/GULF OF ALASKA DURING EITHER THE SHORT RANGE OR EARLY MEDIUM RANGE. INITIALLY ON DAYS 3-4 (MON-TUE) THERE IS SOME SPREAD AMONG THE GUIDANCE WITH RESPECT TO A WAVE OF LOW PRESSURE ALONG A PERSISTENT STATIONARY FRONTAL BNDRY EXTENDING FROM THE NRN GULF OF MEXICO INTO THE ATLANTIC OCEAN OFF THE EAST COAST. THE ECMWF HAS BEEN PERSISTENT IN SHOWING A STRONGER SURFACE LOW CLOSER TO THE MID-ATLANTIC COAST, WHILE THE GFS/CMC/UKMET ARE A BIT MORE SUPPRESSED. ECMWF ENSEMBLE MEMBERS PROVIDE RELATIVELY STRONG SUPPORT FOR THE DETERMINISTIC ECMWF, WITH A FAIR DEGREE OF CLUSTERING OF SOLUTIONS, WHILE THE GEFS AND CMC ENSEMBLE MEMBERS ARE MUCH MORE DISBURSED. GIVEN THE HIGH RUN-TO-RUN CONSISTENCY OF THE ECMWF, ALONG WITH SUPPORT FROM ITS ENSEMBLE, WHILE ALSO TAKING INTO ACCOUNT THAT TRACKING FRONTAL WAVES TOO CLOSE TO THE MID-ATLANTIC COASTLINE IS OCCASIONALLY A BIAS OF THE ECMWF, THE WPC FORECAST WAS INITIALLY BASED PRIMARILY ON A BLEND OF THE ECMWF/GFS ALONG WITH THE ECENS MEAN/GEFS MEAN, WITH SLIGHTLY MORE WEIGHTING TOWARD THE EC/EC MEAN SOLUTIONS. DESPITE THE SPREAD WITH RESPECT TO THE SURFACE LOW, MODEL SOLUTIONS GENERALLY SHOW GOOD CONSENSUS WITH RESPECT TO THE SURFACE FRONT LINGERING AND DRIFTING SLOWLY NORTHWARD ACROSS THE GULF COAST THROUGH MUCH OF THE MEDIUM RANGE. VARIOUS SOLUTIONS SHOW THE POTENTIAL FOR ADDITIONAL WAVES OF LOW PRESSURE ALONG THE FRONT, BUT AT THIS TIME THEY GENERALLY APPEAR WEAK AND HIGH DISBURSED AMONG ENSEMBLE GUIDANCE, AND THUS SHOW VERY LOW PREDICTABILITY. ADDITIONAL SHORTWAVE ENERGY WILL TRAVERSE THE NORTHERN TIER DURING THE MEDIUM RANGE, WITH A SURFACE COLD FRONT FORECAST TO MOVE FROM THE NORTHERN ROCKIES ON MON TO THE GREAT LAKES AND NORTHEAST BY WED AND THU, RESPECTIVELY. AS DISCUSSED ABOVE, MUCH OF THIS ENERGY ORIGINATES IN THE NORTH PAC OR GULF OF AK, SPILLING OVER THE TOP OF THE BROAD RIDGE EXTENDING FROM THE WESTERN U.S. INTO WESTERN CANADA, AND MODELS SHOW A FAIR AMOUNT OF RUN-TO-RUN VARIABILITY WITH RESPECT TO BOTH TIMING AND AMPLITUDE. THUS, THE FORECAST WAS GRADUALLY TRANSITIONED TO HEAVIER ENSEMBLE WEIGHTING OVER TIME, INCLUDING THE ECENS, GEFS, AND NAEFS. ...WEATHER HIGHLIGHTS... ABUNDANT FLOW OF MONSOONAL MOISTURE ALONG WITH MULTIPLE RELATIVELY SMALL-SCALE UPPER-LEVEL IMPULSES TRACKING AROUND THE ANOMALOUS RIDGE CENTERED OVER THE GREAT BASIN WILL SUPPORT CONTINUED POTENTIAL FOR AREAS OF HEAVY CONVECTION, ESPECIALLY FROM THE SRN ROCKIES EASTWARD TO THE SRN PLAINS. GEFS STANDARDIZED ANOMALIES INDICATE POTENTIAL FOR PWAT ANOMALIES OF 2+ STANDARD DEVIATIONS ACROSS THESE AREAS EARLY NEXT WEEK, SUPPORTING THE POTENTIAL FOR HEAVY RAINFALL IN ANY CONVECTION THAT OCCURS. CONVECTIVE ACTIVITY WILL EXTEND INTO PORTIONS OF THE SOUTHWEST AS WELL, ALBEIT MORE SCATTERED IN NATURE. THE CORE OF THE UPPER RIDGE WILL SUPPRESS CONVECTIVE CHANCES ACROSS MUCH OF THE GREAT BASIN, HOWEVER. THE PERSISTENT AND WAVY FRONTAL BNDRY SHOULD CONTINUE TO PROVIDE FOCUS FOR AREAS OF POTENTIALLY HEAVY CONVECTION ACROSS PORTIONS OF THE GULF COAST AND THE SOUTHEAST. ENERGY AND ASSOCIATED SURFACE FRONTAL FEATURES ACROSS THE NRN TIER MAY BRING AREAS OF POTENTIAL CONVECTION AS WELL, BUT MODELS CURRENTLY SHOW LITTLE IN THE WAY OF A COHERENT SIGNAL WITH RESPECT TO ANY HEAVY CONVECTION. THE WRN RIDGE ALOFT WILL SUPPORT WELL ABOVE NORMAL TEMPS FROM INLAND PARTS OF NRN-CNTRL CA AND PAC NW INTO THE NRN ROCKIES, WITH MULTIPLE DAYS OF PLUS 5-15F ANOMALIES. OVER THE EAST EXPECT MEAN TROUGHING ALOFT TO MAINTAIN NEAR TO BELOW NORMAL TEMPS FOR A MAJORITY OF THE PERIOD. RYAN