EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1156 AM EDT THU JUN 29 2017 VALID 12Z SUN JUL 02 2017 - 12Z THU JUL 06 2017 PATTERN OVERVIEW ~~~~~~~~~~~~~~~~ A LOW AMPLITUDE WAVELENGTH UPPER PATTERN WILL TRANSITION TO AN EXPANDING UPPER RIDGE OVER MOST OF THE CONUS CENTERED OVER THE SOUTHERN ROCKIES/FOUR CORNERS REGION. THIS WILL FAVOR TROUGHING OFF THE PAC NW AND BRITISH COLUMBIA AND WEAKER TROUGHING IN THE NORTHEAST. GENERALLY WEAK SURFACE FRONTS WILL PUSH FROM WEST TO EAST ACROSS THE NORTHERN TIER WITH THEIR PARENT LOW PRESSURE CENTERS IN SOUTHERN CANADA. MODEL EVALUATION AND PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ THE MODELS AND ENSEMBLES START IN GOOD AGREEMENT WITH THE TROUGH PUSHING THROUGH THE NORTHEAST SUN-TUE AND ANOTHER INTO BRITISH COLUMBIA. BY NEXT WED/THU, DIFFERENCES BETWEEN THE ECMWF AND ITS ENSEMBLES VS THE GFS AND ITS ENSEMBLES WITH HOW QUICKLY THE FLOW PROGRESSES (THE FORMER GENERALLY A BIT QUICKER THAN THE LATTER). THIS WAS ESPECIALLY TRUE IN THE OH VALLEY EASTWARD AS THE ECMWF AND ITS ENSEMBLES SHEAR OUT A SHORTWAVE INTO THE NORTHEAST WHILE THE GFS/GEFS LINGER ITS SOUTHERN EXTENT BACK THROUGH THE CENTRAL MS VALLEY. FARTHER WEST, THE GFS/GEFS WERE SLOWER WITH AN UPPER LOW SOUTH OF THE GULF OF ALASKA AND W OF BRITISH COLUMBIA WHILE THE ECMWF WAS ESPECIALLY FAST (FASTEST OF THE ENSEMBLES) BY NEXT THU. THOUGH THE UPPER FLOW SHOULD BECOME/STAY AT LEAST SOMEWHAT AMPLIFIED IT SEEMS THE BEST AGREEMENT BETWEEN THE GEFS/ECENS CENTERS ON BUILDING THE UPPER HIGH OVER THE FOUR CORNERS (FAIRLY TYPICAL FOR EARLY JULY) AND AN UPPER LOW NEAR THE DAVIS STRAIT. TELECONNECTIONS FROM THAT UPPER LOW SUPPORT WEAK TROUGHING (THOUGH ABOVE AVERAGE HEIGHTS) THROUGH THE EASTERN GREAT LAKES INTO NY AND SW QUEBEC WHICH IS IN BETWEEN THE QUICKER ECENS MEAN AND SLOWER GEFS MEAN. THUS, A BLEND BETWEEN THESE TWO ENSEMBLE SYSTEMS ROUNDED OUT THE FORECAST WITH DIMINISHED DETERMINISTIC WEIGHTING OF THE GFS/ECWMF. SENSIBLE WEATHER ~~~~~~~~~~~~~~~~ RISING HEIGHTS OVER BASICALLY ALL OF THE CONUS SIGNALS NEAR TO ABOVE AVERAGE TEMPERATURES FOR NEARLY ALL OF THE LOWER 48 NEXT WEEK. THE LARGEST ANOMALIES (10-15 DEG F ABOVE AVERAGE) WILL CENTER OVER THE HIGH PLAINS INTO EASTERN MONTANA WHERE TEMPERATURES MAY PEAK NEAR OR JUST OVER 100F. HUMIDITY WILL GRADUALLY INCREASE IN THE EAST AS DEW POINTS RISE TO THE UPPER 60S AND LOWER 70S AS THE SFC FRONT LIFTS NORTH LATER NEXT WEEK. NEW ENGLAND WILL BE LAST TO SEE THE SURGE IN HUMIDITY, LIKELY LATE IN THE PERIOD INTO NEXT FRI/SAT. PRECIPITATION WILL FOCUS ALONG/AHEAD OF THE FRONTAL BOUNDARY INITIALLY THROUGH THE GREAT LAKES SUNDAY/MONDAY AND THEN INTO THE NORTHEAST. SCATTERED SHOWERS/STORMS WILL FLARE UP IN THE AFTERNOON ACROSS THE SOUTHEAST EACH DAY. ACROSS THE CENTRAL PLAINS INTO THE MID-MS VALLEY, WESTERLY FLOW ALOFT AND THE LINGERING/APPROACHING FRONTAL BOUNDARIES MAY ACT AS A FAVORED PATH FOR OVERNIGHT MCS ACTIVITY AS THE WEAK UPPER TROUGH MOVES THROUGH THE REGION LATE MON THROUGH WEDNESDAY. THE MODELS SHOW THIS IN VARIOUS FLAVORS VIA SMALL CONVECTIVE BULLSEYES BUT WITH LITTLE CONSISTENCY FROM RUN TO RUN. HEAVY RAIN WILL BE POSSIBLE AS THESE PUSH THROUGH. LATEST SPC CONVECTIVE OUTLOOKS NOTES THE POTENTIAL BUT LOW PREDICTABILITY OF SEVERE WEATHER (DAYTIME OR OTHERWISE). FRACASSO