EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 112 AM EST WED JAN 11 2017 VALID 12Z SAT JAN 14 2017 - 12Z WED JAN 18 2017 ...WET PATTERN OVER THE SOUTHERN PLAINS, MID-MISSISSIPPI, AND LOWER OHIO VALLEYS INTO MID NEXT WEEK... ...A SWATH OF FROZEN PRECIPITATION EXPECTED FROM CO ACROSS THE SOUTHERN PLAINS, OHIO VALLEY, GREAT LAKES, MID-ATLANTIC STATES, AND NEW ENGLAND... ...FREEZING RAIN A CONCERN FOR THE COLUMBIA BASIN SUNDAY INTO TUESDAY... PATTERN OVERVIEW/MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ THE GUIDANCE REMAINED IN GOOD AGREEMENT CONCERNING THE LARGE SCALE FLOW PATTERN OVER THE LOWER 48 LATE THIS WEEKEND AND INTO EARLY NEXT WEEK...WHICH WILL INCLUDE RIDGING DEVELOPING ACROSS THE EAST AS AN UPPER TROUGH DIGS INTO THE SOUTHWESTERN U.S. THE BIGGEST DETAIL ISSUE WAS HOW FAR NORTH TO NORTHEAST AN UPPER LOW EJECTS THROUGH THE PLAINS AND MIDWEST, WITH THE GFS TRENDING IN THE DIRECTION OF THE ECMWF AS OF LATE. AS A NORTHERN STREAM RIDGE MOVES EASTWARD INTO QUEBEC AND ENERGY WITHIN THE LEADING EDGE OF A QUASI-ZONAL FLOW REGIME MOVING INTO THE NORTHWEST TUESDAY, THERE SEEMS TO BE LITTLE TO STOP ITS EJECTION. TELECONNECTIONS WITH A POSITIVE ANOMALY BUILDING ACROSS NORTHERN QUEBEC FAVOR A CYCLONE TRACK INTO THE GREAT LAKES MID NEXT WEEK, FASTER THAN THE 12Z ECMWF AND PERHAPS FASTER THAN THE 00Z GFS PORTRAYS. TO DEAL WITH THE DISCREPANCIES, FOR THE PRESSURES, WINDS, 500 HPA HEIGHTS, A COMPROMISE OF THE 12Z CANADIAN, 12Z UKMET, 12Z ECMWF, 18Z GFS, 12Z NAEFS MEAN, AND 12Z ECMWF ENSEMBLE MEAN WERE USED. FOR THE TEMPERATURES, DEW POINTS, CLOUDS, WEATHER, AND PRECIPITATION CHANCE GRIDS, A MORE ENSEMBLE MEAN HEAVY BLEND WAS UTILIZED. THE DAYS 4-7 QPF ARE A PRIMARILY A COMPROMISE OF THE 18Z GFS, 00Z GFS, AND 00Z ECMWF SOLUTIONS. WEATHER HIGHLIGHTS/THREATS ~~~~~~~~~~~~~~~~~~~~~~~~~~ AHEAD OF THE UPPER TROUGH DIGGING INTO THE SOUTHWESTERN U.S, PACIFIC MOISTURE ALOFT AND GULF MOISTURE IN THE LOW TO MID LEVELS WILL INCREASE AND EXPAND PRECIPITATION NEAR A WAVY FRONTAL BOUNDARY EXTENDING THROUGH TEXAS AND NORTHEASTWARD/EASTWARD ACROSS THE MIDDLE MISSISSIPPI VALLEY...OHIO VALLEYS...AND MID-ATLANTIC REGION LATER THIS WEEK AND INTO THE WEEKEND. THIS WILL SET THE STAGE FOR A WIDESPREAD AND POTENTIALLY MAJOR ICING EVENT WITHIN THE NORTHERN EDGE OF THE PRECIPITATION SHIELD ACROSS PORTIONS OF OK, KS, MO, IA, AND IL -- ENSEMBLE MEAN BASED PROBABILITIES SHOW A 70-90% CHANCE OF 0.05" ICE ACCRETION BETWEEN SATURDAY AND MONDAY. LIGHT TO MODERATE SNOW IS POSSIBLE ACROSS THE UPPER MIDWEST, GREAT LAKES, AND NEW ENGLAND. FREEZING RAIN WILL BE POSSIBLE WITH A SYSTEM APPROACHING THE NORTHWEST SUNDAY THROUGH TUESDAY ACROSS PORTIONS OF THE COLUMBIA BASIN AND COLUMBIA GORGE WHERE WARM AIR ALOFT WILL MOVE IN OVER SUB-FREEZING SURFACE TEMPERATURES. IN TERMS OF TEMPERATURES ACROSS THE NATION...ARCTIC HIGH PRESSURE WILL BRING BELOW NORMAL TEMPERATURES TO MUCH OF THE NORTH CENTRAL U.S. AND EVEN EXTENDING INTO THE SOUTHERN PLAINS. BELOW NORMAL TEMPERATURES ARE ALSO EXPECTED WITH THE UPPER TROUGH DIGGING INTO THE WEST...WHILE ABOVE NORMAL TEMPERATURES ARE EXPECTED UNDER STRONG UPPER RIDGING SETTING UP OVER THE SOUTHEAST/LOWER MISSISSIPPI VALLEY. ROTH/GERHARDT