EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT THU JUL 28 2016 VALID 12Z SUN JUL 31 2016 - 12Z THU AUG 04 2016 ...OVERVIEW... ANOTHER SPLIT-FLOW PATTERN ACROSS ALASKA...THE GULF OF ALASKA AND WESTERN NORTH AMERICA SHOULD PRODUCE A 'SOUTHERN BRANCH' SHORTWAVE PATTERN FOR THE LOWER 48 AND MIGRATORY CYCLONE TRACK ACROSS CENTRAL CANADA. DURING THIS MEDIUM RANGE PERIOD...BUT NOT IN A CLASSIC HEMISPHERIC 'LONG WAVE SENSE' --- THE INTERIOR PORTION OF NORTH AMERICA WILL TRANSITION FROM A 3-WAVE PATTERN TO A 2-WAVE PATTERN (DAYS 4 THROUGH 6). ...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT... THROUGH DAY 4 (2/00Z)...THE 28/00Z DETERMINISTIC CANADIAN APPEARED TO BE THE LEAST LIKELY SOLUTION --- (1) IN THE SOUTHEAST BERING SEA (TOO SLOW)... (2) WEST OF THE OLYMPIC PENINSULA (TOO SLOW) AND (3) WITH THE SHORTWAVE SEQUENCING EXPECTED TO BECOME ESTABLISHED ALONG NORTH AMERICA'S WEST CENTRAL COAST. ACROSS EASTERN CANADA...THE CANADIAN ALSO WAS THE LEAST LIKELY SOLUTION (TOO DEEP ACROSS SOUTHEAST ONTARIO) WITH THE MIGRATORY MID-LEVEL TROUGH AXIS. PRETTY MUCH ANYTHING ELSE LOOKS GOOD---AND THAT INCLUDES THE 28/00Z NAVGEM WITH THE TRACK OF A MID-LEVEL SHORTWAVE MIGRATING ACROSS WASHINGTON STATE AND INTO THE LOWER 48. AFTER 2/00Z...THE 28/00Z DETERMINISTIC GUIDANCE --- AND THIS LATEST 'SPLIT-FLOW PATTERN' AT HIGH LATITUDE --- GENERATES ANOTHER TRICKY 'PHASING ERROR' TRANSITION PERIOD BETWEEN 110W AND 85W ALONG ~ 55N LATITUDE. THE 3-WAVE TO 2-WAVE TRANSITION PUTS INTO QUESTION THE DETAILS ASSOCIATED WITH THE 28/00Z ECMWF SOLUTION. IN SHORT...THE ECMWF'S 'WASHINGTON STATE' MID-LEVEL WAVE SPEED AND PATH AT DAY 4 IS ACCELERATED THROUGH THE NORTHERN PLAINS BY DAY 6. SUCH THAT BY DAY 6...THE SHORTWAVE PATTERN GOES FROM A 3-TROUGH PATTERN TO 2-TROUGH PATTERN WEST OF 100W LONGITUDE. SILLY AT IT MIGHT SEEM...THE 28/00Z DGEX...NAVGEM AND GFS ARE THE TRIO OF SOLUTIONS THAT 'FIT' WHAT SHOULD OCCUR OUT WEST---ALLOWING FOR A SLOWER TRANSITION ACROSS THE NORTHERN DIVIDE AND ADDITIONAL SHORTWAVE ENERGY FROM THE GREAT BASIN TO MIGRATE NORTHEASTWARD INTO SOUTHERN CENTRAL CANADA. WHAT THAT COMBINATION OF SOLUTIONS SAYS (TO ME ANYWAY) GOING FORWARD --- IS TO USE THE 28/00Z ECENS...NAEFS AND GEFS MEAN BY 2/12Z AT A 50/30/20 RATIO AND TAPER AWAY FROM ANY DETERMINISTIC SOLUTION BY/AFTER 2/00Z. VOJTESAK PREVIOUS DISCUSSION INCLUDED--- ...SENSIBLE WEATHER HIGHLIGHTS... THE WAVY FRONT EXTENDING FROM THE MID ATLC BACK INTO THE PLAINS WILL CONTINUE TO SERVE AS A FOCUS FOR LOCALLY ENHANCED RNFL. THE STEADIEST SIGNAL FOR HIGHEST TOTALS DURING THE 5-DAY PERIOD IS NEAR THE SRN MID ATLC COAST BUT POCKETS OF HVY RNFL ARE PSBL OVER OTHER AREAS FROM THE MS VLY TO EAST COAST. EXPECT THE NRN TIER TO SEE ONE OR MORE EPISODES OF CONVECTION WITH THE LEADING FRONT PUSHING ACROSS THE PLAINS AND ANY TRAILING WAVES SFC/ALOFT. SOME OF THIS CONVECTION MAY BE STRONG TO SEVERE. MONITOR SPC OUTLOOKS AS IMPORTANT DETAILS COME INTO CLEARER FOCUS. MONSOONAL CONVECTION IS LIKELY TO BE ACTIVE OVER PARTS OF THE SOUTHWEST/GREAT BASIN/SRN-CNTRL ROCKIES WITH SOME SHWRS/TSTMS PRODUCING LOCALLY HVY RNFL. WARM FLOW AHEAD OF THE ADVANCING NRN PLAINS FRONT WILL SPREAD A FAIRLY BROAD AREA OF PLUS 5-10F OR SO ANOMALIES FOR TEMPS FROM THE PLAINS INTO THE MID-UPR MS VLY AND EVENTUALLY INTO PARTS OF THE EAST... WHILE NWRN U.S./NRN PLAINS LOCATIONS BEHIND THE FRONT SHOULD TREND TO OR MODESTLY BELOW NORMAL. THE SRN 2/3 OF THE INTERIOR WEST AND PORTIONS OF THE SOUTHEAST SHOULD REMAIN SOMEWHAT ABOVE NORMAL FOR MOST OF THE PERIOD. IF THERE ARE ANY DAILY RECORDS TO BE SET THEY WOULD MOST LIKELY BE FOR WARM LOWS OVER THE SOUTHEAST/FLORIDA. RAUSCH