EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1212 PM EDT WED JUL 20 2016 VALID 12Z SAT JUL 23 2016 - 12Z WED JUL 27 2016 ...GENERAL OVERVIEW AND UNCERTAINTY ASSESSMENT... ELONGATED UPPER RIDGING WILL DOMINATE THE FLOW PATTERN OVER THE SOUTHERN HALF OF NATION THIS WEEKEND AND INTO THE MIDDLE OF NEXT WEEK...WHILE MULTIPLE SHORTWAVES WILL PROGRESS WEST TO EAST THROUGH THE NORTHERN TIER STATES. THE LATEST MODEL GUIDANCE REMAINS IN GOOD AGREEMENT WITH ADVERTISING AN INITIAL SHORTWAVE LIFTING THROUGH THE NORTHEAST ON SATURDAY...AN UPSTREAM SHORTWAVE TRACKING FROM THE UPPER MIDWEST TO THE GREAT LAKES SUNDAY INTO MONDAY...AND A THIRD SHORTWAVE POSSIBLY DIGGING INTO THE NORTHERN PLAINS BY NEXT TUESDAY. DESPITE THE CONSENSUS WITH THE LARGE SCALE EVOLUTION OF FLOW OVER THE LOWER 48...THERE IS STILL SOME SPREAD WITH THE EXACT TIMING AND AMPLITUDE OF EACH IMPULSE OF SHORTWAVE ENERGY...ESPECIALLY BY THE DAY 5/MONDAY FORECAST. THE WPC DAY 3-7 FORECAST USED A MULTI-MODEL APPROACH WHICH SPLIT THE DIFFERENCE BETWEEN A GENERALLY SLOWER/MORE AMPLIFIED ECMWF AND FASTER/LESS AMPLIFIED GFS. ...WEATHER HIGHLIGHTS... ABOVE NORMAL TEMPERATURES ARE EXPECTED ACROSS MUCH OF THE NATION...WITH TEMPERATURES POSSIBLY APPROACHING OR EXCEEDING RECORD HIGHS OVER THE OHIO VALLEY AND MID-ATLANTIC STATES THIS WEEKEND. ALSO...THE COMBINATION OF HIGH TEMPERATURES AND DEW POINTS COULD LEAD TO WIDESPREAD TRIPLE DIGIT HEAT INDICES. SHORTWAVES TRACKING THROUGH THE NORTHERN TIER SHOULD OFFER SOME RELIEF FROM THE HEAT AND HUMIDITY...BUT HEAVY RAINS AND STRONG THUNDERSTORMS WILL BE POSSIBLE AHEAD AND ALONG THE ASSOCIATED FRONTAL BOUNDARIES...ESPECIALLY WITH A COLD FRONT PRESSING FROM THE UPPER MIDWEST TO THE GREAT LAKES SATURDAY THROUGH MONDAY. GERHARDT