EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1217 AM EDT TUE JUL 14 2015 VALID 12Z FRI JUL 17 2015 - 12Z TUE JUL 21 2015 ...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... UPPER RIDGING IS FORECAST TO RETROGRADE SLOWLY TO THE WEST THIS PERIOD FROM THE LOWER MS VALLEY ACROSS THE SOUTHERN PLAINS INTO NEW MEXICO. STRONG RIDGING IN THE NORTHEASTERN PACIFIC WILL FAVOR TROUGHING IN SW CANADA EXTENDING THROUGH THE PAC NW AND INTO NORTHERN CALIFORNIA. THE MODELS AND ENSEMBLES REMAIN IN GOOD AGREEMENT ON THE SYNOPTIC SCALE BUT CONTINUE TO WAVER ON THE DETAILS. OVERALL THE TREND HAD BEEN FIRST TOWARD A GEFS/ECENS MEAN COMPROMISE IN THE PAC NW FRI-SUN BUT THEN TRENDED TOWARD THE NEWER GFS/ECMWF RUNS... WHICH LIED TO THE EAST OF THE ENSEMBLES FOR A FEW RUNS. SPLITTING/SEPARATING ENERGY FRI-SAT SHOULD LEAVE THE EASTERN SHORTWAVE FREE TO HEAD EAST THROUGH CENTRAL CANADA... WITH ITS TRAILING SURFACE COLD FRONT PUSHING THROUGH THE NORTHERN TIER FRI-TUE. BOUNDARY IN THE EAST SHOULD MOSTLY DISSIPATE BUT WILL INDICATE A SURGE OF WARM/HUMID AIR NORTHWARD AHEAD OF THE APPROACHING AND BETTER-DEFINED SYSTEM. CONSENSUS BLEND OF THE 18Z GFS/GEFS AND 12Z ECMWF/ECENS MEAN OFFERED A REASONABLE STARTING POINT... WITH THE OPERATIONAL RUNS EITHER CLOSE TO OR ON EITHER SIDE OF THE ENSEMBLE CONSENSUS. ...SENSIBLE WEATHER HIGHLIGHTS... PRECIPITATION SHOULD BE SUPPRESSED UNDER THE UPPER RIDGE IN THE SOUTHERN PLAINS... WITH SHOWERS/STORMS FOCUSED IN ADVANCE OF THE FRONTAL BOUNDARIES IN THE NORTHERN PLAINS TO UPPER MS VALLEY THIS WEEKEND... THE GREAT LAKES SUN-MON... AND INTO THE NORTHEAST MON-TUE. A POOL OF RELATIVELY HIGH PW AIR WILL LINGER OVER FLORIDA... HELPING TO ENHANCE PRECIP THROUGH ESPECIALLY THE NORTHERN/CENTRAL PORTIONS. SSE FLOW OUT OF OLD MEXICO INTO THE SW STATES WILL KEEP THE CHANCES OF SHOWERS/STORMS INTO PORTIONS OF THE FOUR CORNERS REGION AND SOUTHEASTERN CALIFORNIA INTO NEVADA. THIS MAY BE AFFECTED BY THE PATH OF HURRICANE DOLORES WEST OF BAJA CALIFORNIA... AT LEAST INDIRECTLY. ENSEMBLE POPS WERE NOTICEABLY HIGHER SN-MON ACROSS THE DESERTS FROM SE CA INTO AZ AND S NV. PLEASE CONSULT THE NATIONAL HURRICANE CENTER FOR THE LATEST INFORMATION. TEMPERATURES ARE FORECAST TO BE HOT IN THE SOUTHERN PLAINS AND LOWER MS VALLEY... WITH AFTERNOON HIGHS NEAR 100F IN MANY LOCATIONS WHICH MAY GET CLOSE TO RECORD HIGHS OR RECORD HIGH MINS. BEHIND THE FRONT TO THE NORTH... TEMPERATURES SHOULD BE SEVERAL DEGREES BELOW AVERAGE. FRACASSO