EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1159 AM EDT WED OCT 14 2015 VALID 12Z SAT OCT 17 2015 - 12Z WED OCT 21 2015 ...GUIDANCE/UNCERTAINTY/CONTINUITY ASSESSMENT AND SENSIBLE WEATHER HIGHLIGHTS... MODELS AND ENSEMBLES SHOW BELOW NORMAL FORECAST SPREAD/UNCERTAINTY ACROSS MEDIUM RANGE TIME SCALES OVER THE NORTH AMERICAN AND VICINITY DOMAIN. A BLEND OF QUITE COMPATABLE GUIDANCE FROM THE 00 UTC GFS/ECMWF AND NAEFS/ECMWF ENSEMBLE MEANS WAS USED TO WEED OUT LINGERING AND GENERALLY LESS PREDICTABLE SMALLER SCALE DIFFERENCES AND LOCAL EMPHASIS. THIS FORECAST OFFERS GOOD WPC CONTINUITY. AMPLIFIED TROUGH FLOW ALOFT AND COOLING CANADIAN HIGH PRESSURE AT THE SURFACE SPREADS ACROSS THE EASTERN HALF OF THE NATION THIS WEEKEND INTO EARLY NEXT WEEK. THIS SETS THE STAGE FOR EARLY SEASON FROSTY CONDITIONS WITH COLD ADVECTION...BUT ESPECIALLY WITH OVERNIGHT RADIATIONAL COOLING. THIS TROUGH ALOFT SHOULD BE KICKED GRADUALLY EASTWARD EARLY NEXT WEEK...WITH GUIDANCE REMAINING ON TRACK TO SHIFT THE TROUGH NORTHEASTWARD INTO ATLANTIC CANADA AND DAVIS STRAIT. THIS WILL BRING AN ERODING END TO THIS PATTERN IN ITS WAKE THAT SHOULD INCLUDE SOME EARLY SEASON SNOW THREAT OFF THE GREAT LAKES AND INTO HIGHER TERRAIN OF THE NERN US...WITH HIGHEST PROBABILITY FOR MDT-HEAVIER WEEKEND SNOW FOR NRN MAINE. AN ACTIVE PACIFIC FLOW MEANWHILE UPSTREAM BEGINS TO MIGRATE EASTWARD FROM THE GULF OF ALASKA AND EAST CENTRAL PACIFIC INTO THE WEST COAST THIS WEEKEND AND THEN RELOADS AGAIN OFFSHORE IN ABOUT A WEEK. THE LEAD TROUGH ENERGIES SPREAD MORE ERNESTLY DOWNSTREAM OF THE CONTINENTAL DIVIDE INTO THE CENTRAL US INTO TUESDAY/NEXT WEDNESDAY. SCATTERED SHOWERS THEN COOLER WEATHER ARE EXPECTED OVER A LARGE PORTION OF THE WEST AND EASTWARD TO THE CONTINENTAL DIVIDE AND CENTRAL US. IN THIS PATTERN THERE REMAINS POTENTIAL FOR WIDESPPREAD LEAD PCPN ESPECIALLY OVER THE SWRN US AND S-CENTRAL GREAT BASIN/ROCKIES GIVEN A BUILDING MOISTURE FEED INTO AND IN ADVANCE OF MORE SRN LATITUDE BASED TROUGH ENERGY SLOWLY WORKING OVER THE REGION. LATER WITH SYSTEM PROGRESSION INTO THE CENTRAL US EARLY-MID NEXT WEEK...A DEVELOPING MOISTURE RETURN PATTERN INTO A DIGGING FRONTAL SYSTEM COULD LEAD TO ENHANCED LEAD CONVECTION..WITH SOME POTENTIAL FOR DEEPER MOISTURE/CONVECTION EMERGING VICINITY OF THE SRN PLAINS. SCHICHTEL