EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT TUE APR 18 2017 VALID 12Z FRI APR 21 2017 - 12Z TUE APR 25 2017 ...PATTERN OVERVIEW/MODEL EVALUATION... MODEL GUIDANCE IS GENERALLY IN GOOD AGREEMENT WITH THE LARGE SCALE FLOW PATTERN OVER THE LOWER 48 THIS WEEKEND AND INTO EARLY NEXT WEEK. EARLY IN THE PERIOD...THE FOCUS WILL BE WITH A CLOSED MID-LEVEL VORTEX EXITING EAST/NORTHEASTWARD OUT OF THE GREAT LAKES REGION ON FRIDAY...BUT THEN ATTENTION SHOULD QUICKLY SHIFT UPSTREAM TO AGGRESSIVE SHORTWAVE ENERGY DIGGING FROM THE NORTHERN/CENTRAL ROCKIES TO THE CENTRAL PLAINS/MIDDLE MISSISSIPPI VALLEY THIS WEEKEND...WHICH COULD POSSIBLY CLOSE OFF OVER THE SOUTHEAST WHILE PROGRESSING THROUGH THE EASTERN U.S. EARLY NEXT WEEK. ALSO...UPPER RIDGING INITIALLY ALIGNED ALONG THE WEST COAST ON FRIDAY SHOULD SHIFT EASTWARD THIS WEEKEND BEFORE GRADUALLY BREAKING DOWN EARLY NEXT WEEK. DESPITE THE DECENT AGREEMENT WITH THE MEAN FLOW PATTERN...FORECAST CONFIDENCE BEGINS TO BREAK DOWN WITH SOME OF THE SMALLER SCALE DETAIL DIFFERENCES...ESPECIALLY WITH THE AGGRESSIVE SHORTWAVE ENERGY DIGGING INTO THE CENTRAL PLAINS/MIDDLE MISSISSIPPI VALLEY THIS WEEKEND. ON SATURDAY...THE GFS HAS BEEN MORE CONSOLIDATED WITH THE MID-LEVEL ENERGY AND ON THE SLOWER/STRONGER SIDE OF MODEL SPREAD WITH THE ASSOCIATED SURFACE LOW LIFTING THROUGH THE SOUTH CENTRAL U.S....COMPARED TO THE ECMWF...WHICH HAS BEEN SUGGESTING MORE SHEARED MID-LEVEL ENERGY AND A FASTER/WEAKER SURFACE LOW. THE SPREAD AND UNCERTAINTY WITH THIS SYSTEM CONTINUES INTO EARLY NEXT WEEK...WHERE THE ECMWF HAS BEEN AN OUTLIER BUT FAIRLY CONSISTENT IN CLOSING THE MID-LEVEL ENERGY OFF OVER THE SOUTHEASTERN U.S. AND THEN PIVOTING IT NORTHEASTWARD UP THE EASTERN SEABOARD...WHILE THE GFS HAS BEEN WAVERING BETWEEN ENERGY CLOSING OFF OVER THE SOUTHEAST (ALTHOUGH NOT AS EXTREME AS THE ECMWF) AND THE POTENTIAL FOR THE ENERGY TO STAY A POSITIVELY TILTED TROUGH WHILE PROGRESSING THROUGH THE EASTERN U.S.. SINCE THERE WAS NOT A STRONG TREND IN THE PAST FEW RUNS OF ENSEMBLE GUIDANCE TOWARDS EITHER SOLUTION...THE WPC FORECAST STAYED CLOSE TO A BLEND BETWEEN THE 06Z GEFS MEAN AND THE 00Z ECMWF ENSEMBLE MEAN BEYOND DAY 3...WHICH SEEMED TO BEST REPRESENTED THE MIDDLE OF MODEL SPREAD WHILE ALSO MATCHING CONTINUITY. GERHARDT ...WEATHER HIGHLIGHTS... AS MENTIONED EARLIER, MULTIPLE SPOTS IN THE COUNTRY WILL BE VULNERABLE FOR HEAVY PRECIPITATION DURING THE PERIOD. ON FRI, SEVERE CONVECTION AND VERY HEAVY/EXCESSIVE RAINS WILL BE LIKELY FROM OK/KS AND NORTH TX INTO MO/AR WITH LOCALLY HEAVY PRECIP EXTENDING BACK UPSTREAM TO THE FRONT RANGE OF CO/WY. THEN ON SAT, WIDESPREAD HEAVY CONVECTIVE RAINS WILL EXTEND FROM THE MID TO LOWER MS VALLEY INTO THE OH/TN VALLEYS AND SOUTH. BY SUN, PRECIPITATION CHANCES WILL BE NUMEROUS ACROSS THE EAST WITH THE GREATEST POTENTIAL ACROSS THE SOUTHEAST/MID-ATL INTO THE NORTHEAST. THEN EARLY NEXT WEEK, PRECIP IN THE EAST COULD RIDE UP THE EAST COAST OR BE MOSTLY OFFSHORE, JUST TOO MUCH SPREAD TO ELIMINATE EITHER SOLUTION. ALSO ON MON/TUES, EXPECT WARM ADVECTION PRECIP ACROSS THE UPPER MS VALLEY AND MOISTURE REACHING THE WEST COAST AND SPREADING INTO THE INTER-MOUNTAIN WEST. FOR TEMPS, MEAN MAX TEMP ANOMALY INDICATES ABOVE AVG TEMPS ACROSS THE SOUTHEAST AND SOUTHWEST/FOUR CORNERS/GREAT BASIN AND NRN PLAINS. PARTS OF THE SOUTHWEST INTO THE FOUR CORNERS COULD SEE TEMPS AVG 10 TO 15 DEG ABOVE AVG DURING THE PERIOD. BELOW AVG TEMPS WILL BE EXTENSIVE FROM CENTRAL PLAINS AND MID/UPPER MS VALLEY INTO THE GREAT LAKES/OH VALLEY AND NERN SECTION OF THE COUNTRY, WHILE THE PAC NW WILL BE NEAR AVG OR SLIGHTLY BELOW. MUSHER