EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 107 AM EST SUN JAN 08 2017 VALID 12Z WED JAN 11 2017 - 12Z SUN JAN 15 2017 ...WET PATTERN TO SHIFT INTO THE MID-MISSISSIPPI VALLEY LATE NEXT WEEK... PATTERN OVERVIEW AND MODEL ASSESSMENT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ STRONG RETROGRADING RIDGING IS FORECAST TO CROSS THE BERING SEA INTO SIBERIA NEXT WEEK WHICH GENERALLY SUPPORTS A DEEP CYCLONE OFFSHORE THE PACIFIC NORTHWEST THAT WILL WEAKEN SLOWLY WITH TIME. THIS IS PART OF A POSITIVELY TILTED TROUGH THAT EXTENDS INTO HUDSON BAY, WHICH TENDS TO FAVOR RIDGING ACROSS THE SOUTHEAST WHICH SHOULD BUILD WITH TIME. WHILE THERE ARE EXPECTED DETAIL ISSUES, THE GUIDANCE REMAINS IN VERY GOOD AGREEMENT THROUGH AT LEAST LATE WEDNESDAY. USED A COMPROMISE OF THE 12Z CANADIAN, 12Z UKMET, 12Z ECMWF, AND 18Z GFS EARLY ON BEFORE TRANSITIONING TO THE 12Z NAEFS AND 12Z ECMWF ENSEMBLE MEAN SOLUTIONS WITH TIME FOR PRESSURES, WINDS, AND 500 HPA HEIGHTS. THE REMAINDER OF THE MEDIUM RANGE GRIDS WERE MORE HEAVILY BASED ON THE ENSEMBLE MEAN SOLUTIONS, AS USUAL. THE DAYS 4-7 QPF WERE PRIMARILY BASED ON A BLEND OF THE 18Z GFS/00Z GFS AND 12Z ECMWF SOLUTIONS. WEATHER HIGHLIGHTS/THREATS ~~~~~~~~~~~~~~~~~~~~~~~~~~ THE WEST IS THE INITIAL 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. SIGNIFICANT PRECIPITATION TOTALS ARE POSSIBLE ALONG THE COASTAL RANGES OF NORTHERN/CENTRAL CALIFORNIA AND THE SIERRA NEVADA RANGE THAT COULD EXCEED 4" LIQUID EQUIVALENT THIS PERIOD (IN ADDITION TO WHAT IS EXPECTED OVER THE NEXT FEW DAYS). ACCUMULATED SNOW TOTALS MAY BE MEASURED IN YARDS/METERS AT THE HIGHEST ELEVATIONS BY NEXT WEEKEND. THE CHANCE FOR PRECIPITATION, INCLUDING THE FROZEN VARIETY, WILL INCREASE WITH A DEEPENING SURFACE CYCLONE TRACKING FROM THE PLAINS TO THE UPPER MIDWEST ON TUESDAY INTO WEDNESDAY. THIS SHOULD BE FOCUSED MOSTLY ACROSS THE HIGH PLAINS AND UPPER MIDWEST BUT MAY INCLUDE SOME ONSET FROZEN PRECIP AHEAD OF THE WARM FRONT IN THE INTERIOR MID-ATLANTIC AS WELL AS ACROSS THE HIGHER ELEVATIONS OF THE NORTHEAST BEFORE MILDER AIR INVADES ON THE HEELS OF SOUTHWESTERLY FLOW. PRECIPITATION COULD BE HEAVY ALONG AND AHEAD OF THE FRONTS IN THE MISSISSIPPI/OHIO VALLEYS LATE NEXT WEEK, WITH THE GUIDANCE INDICATING LOCAL AMOUNTS IN THE 4-8" RANGE. WITH COLD HIGH PRESSURE TO THE NORTH, FREEZING RAIN AND MEASURABLE SNOWS ARE A CONCERN FOR THE CENTRAL/SOUTHERN PLAINS ACROSS PORTIONS OF THE MIDWEST INTO THE GREAT LAKES AS OVERRUNNING PRECIPITATION FALLS INTO A COLD ATMOSPHERE NORTH OF THE FRONT. TEMPERATURES ARE FORECAST TO BE BELOW AVERAGE EAST OF THE DIVIDE FROM MONTANA INTO THE HIGH PLAINS THROUGH THE PERIOD (ABOUT 20-30F BELOW AVERAGE IN PARTS OF MT/ND/SD) BUT ALSO INTO WA/OR AS THE ARCTIC BOUNDARY ATTEMPTS TO SINK SOUTHWARD. GENERALLY NEAR TO ABOVE AVERAGE TEMPERATURES ARE FORECAST FOR THE INTERIOR WEST INTO TEXAS WHERE RECORD HIGHS MAY BE POSSIBLE NEXT WEEK. A WARMING TREND IS FORECAST FOR THE EAST. ROTH/FRACASSO