EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 223 AM EDT MON OCT 30 2017 VALID 12Z THU NOV 02 2017 - 12Z MON NOV 06 2017 ...COLDER AND STORMY PATTERN FOR THE WEST LATER THIS WEEK INTO NEXT WEEK... ...OVERVIEW, GUIDANCE/UNCERTAINTY ASSESSMENT AND PREFERENCES... AMPLIFIED FLOW OVER THE PACIFIC OCEAN AND ALASKA INTO WESTERN NORTH AMERICA SUPPORTS DIGGING TROUGHING INTO THE WEST LATER THIS WEEK THROUGH THE WEEKEND WITH ZONAL TO SW FLOW IN THE CENTRAL/EASTERN STATES. THE RECENT GFS/ECMWF/CANADIAN OFFERED A GOOD STARTING POINT FOR THE FORECAST THU-SAT AS AN UPPER LOW DROPS SOUTHWARD OUT OF BRITISH COLUMBIA IN THE PAC NW. FOR SUN/MON, TRENDED TOWARD THE GEFS/ECMWF ENSEMBLE MEANS WITH LESS DETAIL FROM THE GFS/ECMWF AS THEIR REMAINS DIFFERENCES IN HOW THE TROUGHING EJECTS INTO THE PLAINS. TREND HAS BEEN A BIT QUICKER OVERALL WHICH FAVORED THE GFS OVER THE ECMWF IN PREVIOUS RUNS BUT THE ENSEMBLE CONSENSUS REMAINED THE BEST GUIDE. FORECAST REVOLVES AROUND TWO MAIN SYSTEMS: 1) NORTHERN STREAM LOW MOVING OUT OF THE GREAT LAKES THURSDAY AND DRAGGING ITS COLD FRONT OFF THE NORTHEAST/MID-ATLANTIC COAST FRIDAY AND 2) DIGGING UPPER TROUGHING ALONG THE WEST COAST WHICH WILL PUSH A STRONG COLD FRONT SOUTHWARD/EASTWARD THROUGH THE WEST, OUT INTO THE PLAINS SUNDAY AND THEN THROUGH THE GREAT LAKES NEXT MONDAY. ...WEATHER THREATS/HIGHLIGHTS... MUCH COLDER AIR WILL SETTLE INTO MUCH OF MONTANA AND EVENTUALLY WA/OR AS THE COLD FRONT SLOWLY SPILLS OVER THE DIVIDE. RAIN AND SNOW WILL BE ON THE INCREASE ESPECIALLY BY NEXT WEEKEND WHEN SNOW LEVELS DROP TO ABOUT 2000-3000 FT IN THE PAC NW. TEMPERATURES ABOUT 10-20F BELOW AVERAGE ARE LIKELY FOR NORTHERN AND NW MONTANA WHICH WILL BLEED WESTWARD AND SOUTHWARD THROUGH OR/WA/ID AND CALIFORNIA THIS WEEKEND. SNOW IS LIKELY TO BE HEAVY OVER NW MONTANA AT TIMES AS UPSLOPE FLOW STRENGTHENS BY FRIDAY WITH A 1036-1040MB HIGH OVER ALBERTA. PRECIPITATION WILL EXPAND THROUGH THE WEST/INTERMOUNTAIN WEST AS THE UPPER TROUGH AND PACIFIC FRONT WORK INLAND. BY NEXT WEEKEND, SEVERAL INCHES OF PRECIPITATION ARE LIKELY FOR MUCH OF NORTHERN CALIFORNIA INTO SW OREGON, ESPECIALLY OVER THE COASTAL RANGES, KLAMATH MOUNTAINS, NORTHERN SIERRAS, ETC. WITH SEVERAL FEET OF SNOW POSSIBLE FOR THE FAVORED HIGHER TERRAIN. EVEN SOUTHERN CALIFORNIA COULD SEE SOME PRECIPITATION NEXT WEEKEND DEPENDING ON THE DEPTH OF THE TROUGH AND INFLUX OF MOISTURE. BACK TO THE EAST, A WARM FRONT WILL MOVE THROUGH THE NORTHEAST ON THURSDAY WITH AN AXIS OF LIGHT TO MODERATE RAIN ALONG/AHEAD OF THE COLD FRONT FROM E TEXAS NORTHEASTWARD INTO THE EASTERN GREAT LAKES. SOUTHERN PART OF THE FRONT WILL LINGER THROUGH THE MID-MISSISSIPPI VALLEY/TENNESSEE VALLEY/CAROLINAS WITH SCATTERED SHOWERS ALONG ITS BOUNDARY FRI-SAT BEFORE LIFTING BACK TO THE NORTH AS THE WESTERN SYSTEM MOVES THROUGH THE HIGH PLAINS SUNDAY. FRACASSO