EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1126 AM EDT MON JUL 06 2015 VALID 12Z THU JUL 09 2015 - 12Z MON JUL 13 2015 ...OVERVIEW... THIS APPEARS TO BE ONE OF THOSE PATTERN THAT WHILE LO0KING A BIT MESSY/DISORGANIZED INITIALLY...A FAIRLY DISTINCT PATTERN ARISES LATER IN THE FORECASTS AS SMALLER SCALE FEATURES TRANSITION TO A LARGER SCALE PATTERN. THE MAIN MESSAGE FROM THE MEDIUM RANGE FORECAST IS THAT ENHANCED UPPER LEVEL RIDGING AND EAST COAST TROUGHING IS A FAIRLY RELIABLE SIGNAL DESPITE BEING TOWARD THE END OF THE FORECAST OR 6 TO 7 DAYS OUT IN THE FUTURE. WHILE AN UPPER LOW MOVES OVER THE WEST COAST EARLY IN THE FORECAST...IT LIFTS NORTHEASTWARD AS A SERIES OF SHORTER WAVELENGTH DISTURBANCES REACH THE NORTHERN ROCKIES BY SATURDAY/DAY 3. AT THE SAME TIME... A MEAN CLOSED UPPER HIGH FORMS OVER THE SOUTHEAST US AND THEN RETROGRADES STEADILY WESTWARD. AS THE SHORTWAVES OVER THE NORTHERN ROCKIES CROSS THE NORTHERN PLAINS ON SUNDAY/DAY 6...THEY BEGIN TO DROP SOUTHEASTWARD TOWARD THE GREAT LAKES BY THE END OF THE FORECAST AS THE CLOSED UPPER HIGH DEVELOPS INTO A FULL LATITUDE RIDGE EXTENDING NORTH FROM THE SOUTHWEST ACROSS THE ROCKIES INTO WEST CENTRAL CANADA. ...GUIDANCE EVALUATION/PREFERENCES... THE MOST RECENT VERSIONS OF THE EUROPEAN/GEFS AND NAEFS ENSEMBLE MEANS PAINT A PRETTY CONSISTENT PICTURE AS THE PERIOD STARTS WITH THE UPPER LOW OVER THE WEST COAST AND A BROAD SOUTHWESTERLY UPPER FLOW CUTS ACROSS THE SOUTHERN AND EASTERN PORTION OF THE NATION WITH A MEAN RIDGE OVER THE SOUTHEAST AND A MEAN TROUGH OVER HUDSON BAY. THESE THREE ENSEMBLE SYSTEMS CONTINUE TO RESEMBLE EACH OTHER AS THE UPPER LOW LIFTS NORTHEASTWARD ACROSS NEVADA ON DAY 4/FRIDAY. BY DAY 5/SATURDAY...THE TROUGH LOSES ANY IDENTIFIABLE CHARACTERISTICS SINCE THIS THESE ARE THE MEANS FLOWS BUT CLEARLY BY DAY 6/SUNDAY IT BECOMES CLEAR THAT A SIGNIFICANT SHIFT IS SHOWING UP IN ALL ENSEMBLE SYSTEMS...WITH A BUILDING UPPER HIGH DRIFTING WESTWARD ACROSS THE SOUTHERN US...A DEVELOPING RIDGE FROM THE GREAT BASIN/ROCKIES NORTHWARD INTO WESTERN CANADA AND MEAN TROUGHING OVER THE NORTHERN PLAINS/MISSISSIPPI VALLEY...WITH THE EUROPEAN ENSEMBLE MEAN SHOWING THE MOST EXTENSIVE TROUGHING. BY DAY 7/MONDAY...THE ENSEMBLE MEANS ARE STILL IN LOCK STEP WITH DEEPENING TROUGH OVER EASTERN CANADA INTO THE NORTHEAST THIRD OF THE COUNTRY WHILE A HIGH AMPLITUDE UPPER RIDGE EXTENDS FROM THE SOUTHWEST NORTHWARD INTO WEST CENTRAL CANADA. OF THE OVERNIGHT OPERATIONAL MODELS...THE UKMET SEEMS THE LARGEST OUTLIER...THROUGH DAY 5...WITH A STRONG SHORTWAVE TROUGH HEADED FOR NEW ENGLAND. THE OOZ CANADIAN IS SOMEWHAT SIMILAR TO THE 06Z GFS/00Z ECMWF BUT SLIGHTLY SLOWER. BOTH THE 00Z/06Z AND 00Z ECMWF APPEAR TO BE MORE SIMILAR TO EACH OTHER AND MORE CONSISTENT WITH THE SMOOTHED AVERAGES OF THE ENSEMBLE MEANS SO A COMBINATION OF OPERATIONAL RUNS AND MEANS WERE USED TO GENERATE THE MANUAL GRAPHICS. A COMBINATION OF THE 00Z ECMWF AND THE 00Z GFS WERE HEAVILY WEIGHTED IN THE FIRST TWO DAYS OF THE FORECAST. BUT EVEN ON DAYS 5 AND 6...A 60/40 BLEND STILL FAVORED THE OPERATIONAL GFS/ECMWF SLIGHTLY OVER THE MEANS...SINCE THEY WERE GENERALLY SIMILAR. ONLY ON DAY 7 DID THE BLEND REVERT TO 70/30 MEANS/OPERATIONALS DUE TO GREATER SPREAD IN THE OPERATIONAL RUNS AND THE CONSISTENCY OF THE SIGNAL OBSERVED IN THE ENSEMBLE MEANS. CONTINUITY HAS BEEN GOOD WITH THE IDEA OF PERSISTENT TROUGHING OFF THE WEST COAST IN THE WAKE OF THE CALIFORNIA UPPER LOW. HOWEVER MODELS/ENSEMBLE MEANS HAVE BEEN SHOWING SOME DAY TO DAY OSCILLATION IN DEPTH. TRENDS OVER THE PAST 24 HRS HAVE BEEN SOMEWHAT DEEPER IN CONTRAST TO THE OPPOSITE TREND SEEN OVER THE DAY BEFORE. ...SENSIBLE WEATHER HIGHLIGHTS... THE POTENTIAL EXISTS FOR ONE OR MORE EPISODES OF HEAVY SHOWERS/THUNDERSTORMS AT SOME LOCATIONS WITHIN AN AREA FROM THE NORTHERN PLAINS ACROSS THE MID-UPPER MISSISSIPPI VALLEY... GREAT LAKES/OHIO VALLEY/TENNESSEE VALLEY... AND THE MID ATLANTIC STATES. INITIAL FOCUS SHOULD BE ALONG A WEAK FRONTAL SYSTEM SPANNING KANSAS ACROSS THE MISSISSIPPI AND OHIO VALLEYS...WITH A POSSIBLE SHORTWAVE ENHANCING RAINFALL AMOUNTS. THE LIFTING OF THE CALIFORNIA LOW ACROSS THE NORTHWEST AND THEN ITS PROGRESSION EASTWARD AND SOUTHEASTWARD WOULD ALSO BE ANOTHER SOURCE FOR ENHANCED PRECIPITATION WITH DIURNAL ENHANCEMENT OF THE CONVECTION. THE INTERIOR NORTHWEST SHOULD FINALLY SEE A PERIOD OF COOLING AFTER THURSDAY... STABILIZING WITHIN A FEW DEGREES OF NORMAL. OTHERWISE BELOW NORMAL HIGHS SHOULD PREVAIL OVER THE WEST WITH SOME MODERATION LATE WEEKEND/EARLY NEXT WEEK. FARTHER EASTWARD TEMPERATURES WILL DEPEND TO SOME EXTENT ON TIMING OF CLOUDS/RAINFALL. TENDENCY SHOULD BE TOWARD BELOW NORMAL READINGS NRN-CNTRL AREAS THU AND THEN NEAR TO SLIGHTLY ABOVE NORMAL BEFORE TRENDING DOWN AGAIN NEAR THE LATE PERIOD MIDWEST/GRTLKS SYSTEM. RIDGING ALOFT SHOULD PROMOTE ABOVE NORMAL TEMPS ESPECIALLY OVER THE SOUTHEAST BUT GRADUALLY SPREADING WESTWARD WITH TIME CORRESPONDING TO LIKELY MOVEMENT AND DEVELOPMENT OF THE WESTERN RIDGE LATE IN THE FORECAST. KOCIN