EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 100 AM EST FRI JAN 06 2017 VALID 12Z MON JAN 09 2017 - 12Z FRI JAN 13 2017 ...WET PATTERN TO CONTINUE FOR MUCH OF THE WEST... PATTERN OVERVIEW AND MODEL ASSESSMENT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A RETROGRADING AND ANOMALOUS RIDGE CROSSES THE BERING SEA INTO SIBERIA AND GENERALLY SUPPORTS A DEEP CYCLONE OFFSHORE THE PACIFIC NORTHWEST, PART OF A POSITIVELY TILTED TROUGH THAT EXTENDS INTO HUDSON BAY, WHICH TENDS TO FAVOR DOWNSTREAM RIDGING ACROSS THE SOUTHEAST. WHILE THERE ARE DETAIL ISSUES, THE GUIDANCE REMAINS IN BETTER THAN AVERAGE AGREEMENT. THE 500 HPA HEIGHTS, PRESSURES, AND WINDS WERE BASED ON A COMPROMISE OF THE 12Z CANADIAN, 12Z UKMET, 18Z GFS, AND 12Z ECMWF FOR MONDAY INTO WEDNESDAY, BEFORE INCREASING AMOUNTS OF THE 12Z NAEFS AND 12Z ECMWF ENSEMBLE MEANS REPLACE THE UKMET. THE TEMPERATURE, DEW POINT, CLOUD, WEATHER, AND PRECIPITATION CHANCE GRIDS WERE MORE ENSEMBLE MEAN BASED, AS USUAL. THE DAYS 4-7 QPF IS ESSENTIALLY A COMPROMISE OF THE 12Z ECMWF AND 18Z GFS, WITH SOME COMPONENTS OF THE 00Z GFS USED OUT WEST. OVERALL, THIS SOLUTION MAINTAINED REASONABLE CONTINUITY. WEATHER HIGHLIGHTS/THREATS ~~~~~~~~~~~~~~~~~~~~~~~~~~ THE WEST IS THE MAIN STORY AS AN ANOMALOUS SURGE OF MOISTURE WITHIN ONSHORE FLOW AHEAD OF A DEEP-LAYERED VORTEX OFF THE NORTHWEST COAST SPREADS HEAVY PRECIPITATION INTO THE REGION WITH SIGNIFICANT PRECIPITATION TOTALS ALONG THE COASTAL RANGES OF NORTHERN/CENTRAL CALIFORNIA AND THE SIERRA NEVADA RANGE COULD PILE UP 10-15" LIQUID EQUIVALENT AMOUNTS THIS PERIOD, WITH SNOW TOTALS MEASURED IN METERS AT THE HIGHEST ELEVATIONS. SNOW LEVELS WILL START QUITE HIGH (700MB TEMPS NEAR OR ABOVE ZERO) BUT WILL VARY DURING THE PERIOD. INTENSE AND PROLONGED RAINFALL COULD LEAD TO HYDROLOGIC ISSUES WHICH MAY INCLUDE MUDSLIDES AND DEBRIS FLOWS, THOUGH SUCH PRECIPITATION IS MUCH NEEDED ACROSS AREA RESERVOIRS AS THE SIERRA NEVADA REMAINS IN EXTREME TO EXCEPTIONAL DROUGHT. AS MILD AIR MAKES INROADS INTO THE WEST ALOFT, FREEZING RAIN FOR PORTIONS OF THE PACIFIC NORTHWEST IS POSSIBLE ACROSS INTERIOR OR/WA. THE CHANCE FOR PRECIPITATION, INCLUDING SNOW, SLEET, AND FREEZING RAIN, WILL INCREASE WITH A POSSIBLE SURFACE CYCLONE TRACKING FROM THE PLAINS TO THE UPPER MIDWEST MID NEXT WEEK, FOCUSED MOSTLY ACROSS THE HIGH PLAINS AND UPPER MIDWEST BUT PERHAPS SOME ONSET FROZEN PRECIP AHEAD OF THE WARM FRONT IN THE NORTHEAST AS WELL. PRECIPITATION COULD BE HEAVY FOR PORTIONS OF THE MISSISSIPPI AND OHIO VALLEYS MONDAY AND TUESDAY. TEMPERATURES ARE FORECAST TO BE BELOW AVERAGE EAST OF THE DIVIDE FROM MONTANA INTO THE HIGH PLAINS THROUGH THE PERIOD. A WARMING TREND IS FORECAST FOR THE EAST ONCE THE SURFACE HIGH MOVES OFFSHORE ON MONDAY, THOUGH TEMPERATURES MAY BE QUITE COLD/CLOSE TO 30F BELOW AVERAGE IN PORTIONS OF THE CAROLINAS MONDAY ASSUMING CLEAR/CALM CONDITIONS ATOP RECENT SNOWFALL WHICH HAS YET TO OCCUR. MODERATION OCCURS THEREAFTER WITH DAYTIME HIGHS RISING INTO THE 60S ACROSS THE CAROLINAS LATER NEXT WEEK. ROTH/FRACASSO