EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1153 AM EDT FRI JUN 30 2017 VALID 12Z MON JUL 03 2017 - 12Z FRI JUL 07 2017 OVERVIEW ~~~~~~~~ PATTERN NEXT WEEK WILL EVOLVE INTO A BUILDING UPPER RIDGE OVER THE FOUR CORNERS REGION AND TROUGHING THROUGH THE GREAT LAKES AND NORTHEAST, THOUGH 500MB HEIGHTS ARE FORECAST TO BE ABOVE AVERAGE OVER THE ENTIRE LOWER 48. SURFACE FRONTS WILL PASS FROM WEST TO EAST ACROSS THE NORTHERN TIER WITH THE PARENT LOWS MOVING THROUGH SOUTHERN CANADA IN TYPICAL JULY FASHION. BUILDING HEIGHTS IN THE INTERIOR WEST WILL BE LOATHE TO LET NORTHEASTERN PACIFIC TROUGHING PUSH INTO WASHINGTON/OREGON. SUMMER SHOULD BE ON CRUISE CONTROL BY THE END OF THE WEEK. GUIDANCE EVALUATION AND PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MODELS WERE STILL HAVING A HARD TIME WITH HOW TO TAKE MID-LEVEL ENERGY EASTWARD OUT OF THE MID-MISSISSIPPI VALLEY MIDWEEK -- 00Z UKMET AND 06Z GFS FORMED THE FASTER AND SLOWER ENDS OF THE GUIDANCE, RESPECTIVELY. 00Z ECMWF/CANADIAN/GFS WERE A BIT CLOSER TO A CONSENSUS THAT WAS 2/3RDS TOWARD THE ECMWF ENSEMBLE MEAN AND 1/3RD TOWARD THE 06Z GEFS MEAN, WHICH SEEMS TO BE THE GUIDANCE CONVERGENCE POINT. QUESTION WILL BE HOW THE TROUGH SWINGS THROUGH SOUTHERN CANADA AND THE NORTHEAST LATER NEXT WEEK -- CONTINGENT UPON HOW A SHORTWAVE MOVES THROUGH CENTRAL CANADA (ALONG 60N) AND DIVES INTO THE TROUGH. WESTERN ATLANTIC UPPER HIGH/RIDGE MAY KEEP HEIGHTS FROM LOWERING TOO MUCH IN THE NORTHEAST AS THE OVERALL PATTERN IS WARM. TO THE WEST, ENSEMBLES HAVE TRENDED TOWARD A STRONGER UPPER HIGH (>594DM) BY THURSDAY OVER COLORADO (GFS/GEFS QUICKER TO PICK UP ON THIS THAN THE ECMWF) WHICH SHOULD KEEP THE UPSTREAM UPPER LOW NEAR 140W. BLEND OF THE 00Z GUIDANCE TO START SERVED WELL THROUGH ABOUT TUE BEFORE FAVORING THE 00Z ECMWF ENSEMBLE MEAN WITH THE ECMWF AND 06Z GEFS MEAN NEXT WED/THU AND AN ENSEMBLE MEAN SPLIT BY NEXT FRI. SENSIBLE WEATHER HIGHLIGHTS ~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4TH OF JULY (TUE) LOOKS TO BE MAINLY QUIET OVER MUCH OF THE COUNTRY WITH THE BEST CHANCE OF RAIN OVER THE MISSOURI INTO ILLINOIS AND SCATTERED SHOWERS/STORMS FROM THE UPPER MIDWEST THROUGH THE OHIO VALLEY INTO THE SOUTHEAST. TEMPERATURES WILL BE WITHIN A FEW DEGREES OF AVERAGE IN THE EAST BUT GENERALLY ABOVE AVERAGE IN THE WEST AND WELL ABOVE AVERAGE OVER THE INTERIOR NORTHWEST THROUGH MONTANA INTO THE WESTERN DAKOTAS. OVERALL TEMPERATURES ARE EXPECTED TO BE NEAR TO ABOVE AVERAGE NEARLY COAST TO COAST (IMMEDIATE WEST COAST BEING THE EXCEPTION -- JUNE GLOOM (MARINE LAYER) WILL CONTINUE INTO EARLY JULY BUT WILL WANE WITH TIME). RECORD HIGHS MAY AGAIN BE POSSIBLE OVER THE INTERIOR WEST FROM THE AZ DESERTS NORTHWARD TO EASTERN OR/WA INTO MONTANA. RAINFALL WILL BE LARGELY ABSENT TO START WEST OF THE DIVIDE BUT ENSEMBLES DO INDICATE INCREASING MOISTURE ALONG THE ROCKIES INTO SE ARIZONA AND CENTRAL/EASTERN MONTANA. 90S WILL BE COMMON OVER THE INTERIOR WITH LOW 100S THROUGH THE LOWER VALLEYS OF W CO AND E UT AS WELL AS EASTERN MONTANA. BEST CHANCE OF RAINFALL WILL BE ACROSS THE MID-MS VALLEY INTO THE OHIO VALLEY ALONG THE INITIALLY STATIONARY FRONTAL BOUNDARY. AS THAT LIFTS NORTHWARD AND EASTWARD IT WILL CARRY THE RAIN/STORM CHANCE INTO THE NORTHEAST LATER IN THE WEEK. ACROSS THE SOUTHEAST AND FLORIDA, SCATTERED MAINLY AFTERNOON SHOWERS/STORMS WILL DEVELOP EACH DAY. FRACASSO