EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT SUN MAY 25 2014 VALID 12Z WED MAY 28 2014 - 12Z SUN JUN 01 2014 ...OVERVIEW... AN AMPLIFIED PATTERN ALOFT RESULTS IN APPRECIABLE WARMTH/HUMIDITY BENEATH THE UPPER-LEVEL RIDGE...AND OCEAN INFLUENCES/COOLER SENSIBLE WEATHER CONDITIONS EMBEDDED WITHIN TROUGHS--POSITIONED ALONG BOTH COASTLINES OF THE NORTH AMERICAN CONTINENT---US WEST COAST AND CANADIAN MARITIMES. DURING THE FIRST PART OF THE MEDIUM RANGE FORECAST...THE EXCEPTION(S) WILL BE ACROSS THE SOUTH CENTRAL STATES...WHERE THE PREVAILING CONDITIONS WILL BE DOMINATED BY A VERY SLOW-MOVING...BUT WEAKENING MID-LEVEL CLOSED LOW AND ITS CHAOTIC CONVECTIVE PATTERN. AND THE LATTER HALF OF THE PERIOD...FOCUS SHIFTING FROM THE SOUTHERN PLAINS TO THE INTERMOUNTAIN WEST AND DESERT SOUTHWEST. ...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT... THROUGH DAY 4 (30/00Z)...CONTINUED TO BLEND THE 25/00Z ECENS...GEFS AND NAEFS TO HANDLE THE 500MB TROUGH AXIS MIGRATION THROUGH THE CASCADES AND THE POSITIVE-TILT PORTION OF THE TROUGH INLAND THROUGH BC AND ALBERTA INTO MID-DAY 5 (30/12Z). TO THAT POINT (MID-DAY 5)...THE DETERMINISTIC 25/00Z GFS AND ECMWF WERE VERY USEFUL...CARRYING THE PRIMARY SURFACE REFLECTION ACROSS WEST CENTRAL CANADA AND WEAKER... CONVECTIVELY-DRIVEN/-INDUCED WAVES NORTHEASTWARD---OFF OF THE HIGHER TERRAIN AND INTO THE LOWER ELEVATIONS. THOSE 2 DETERMINISTIC RUNS EQUALLY SUPPORTIVE OF THE HURRICANE CENTER TRACK FOR 'AMANDA'...THE WEAKENED STATE AND/OR DISSIPATION OF THE 'WET' SYSTEM 'DRAGGING ITS HEELS' THROUGH EASTERN TEXAS...ARKANSAS AND LOUISIANA. AND LIKEWISE...WITH THE DEPICTION OF AN EAST-SOUTHEASTWARD-MOVING SHORTWAVE THROUGH HUDSON BAY/NORTHWEST QUEBEC AND CHANNELED MID-LEVEL SUBTROPICAL MOISTURE PLUME THROUGH THE LOWER COLORADO BASIN. BEYOND DAY 5...THE THREE MEANS WILL CONTINUE TO SERVE AS THE BASELINE FOR THE WPC SURFACE AND 500MB GRAPHICS---SOLIDLY SUPPORTING BROAD RIDGING FOR MUCH OF THE SOUTHEAST QUARTER/GREAT LAKES REGIONS---AND TROUGHS OF VARIED WAVELENGTH ALONG BOTH COASTS OF THE CONTINENT. IN THIS COMPLICATED PATTERN...NEVER EXPECT PERFECTION. BUT MORE RUNS OF THE GFS HAVE 'OUT-SHINED' THE ECMWF WEST OF THE MISSISSIPPI. THIS WAS NOT NECESSARILY THE CASE ACROSS THE CANADIAN MARITIMES. BUT BEYOND DAY 5...RELIED ON THE GFS TO HOLD THIS AMPLIFIED PATTERN ALOFT TOGETHER...ALONG THE SOUTHERN END OF THE PACIFIC TROUGH...THROUGH CENTRAL CANADA AND AN EASTWARD PROGRESSION OF THE NORTHWEST ATLANTIC UPPER-LEVEL TROUGH. ...SENSIBLE WEATHER... THE TRAPPED MID-LEVEL CIRCULATION IN THE ARKANSAS/LOWER MISSISSIPPI RIVER BASINS BEGINS TO WEAKEN/DISSIPATE TOWARDS THE END OF THE MEDIUM RANGE...BUT NOT BEFORE DUMPING MORE RAIN ACROSS EASTERN OK/TX (I-35 EASTWARD)...THE SOUTHERN OZARKS AND THE LOWER 1/3RD OF THE MS VALLEY. WIDE BERTH OF ISOLATED CLUSTERS OF SHOWERS AND THUNDERSTORMS TO THE NORTHEAST AND EAST OF THE DYING SYSTEM...AND FOCUSED ALONG THE CONFLUENCE ZONE ALOFT (EASTERN FLANKS OF THE UPPER-LEVEL RIDGE AND SOUTHWEST FLANKS OF THE UPPER TROUGH OVER NOVA SCOTIA. THE SOUTHERN HALF OF THE CONTINENTAL DIVIDE...SOUTHERN GREAT BASIN AND DESERT SOUTHWEST BEGINS TO NOTICE A SUBTLE INCREASE IN DEW POINTS...MID-LEVEL CLOUDINESS AND HIGH-ELEVATION CONVECTION AS THE PACIFIC TROUGH TRACKS INLAND NEXT WEEKEND. VOJTESAK