EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1051 AM EST SAT JAN 24 2015 VALID 12Z TUE JAN 27 2015 - 12Z SAT JAN 31 2015 ...OVERVIEW... THE PERSISTENCE OF AN EASTERN NORTH AMERICAN TROUGH---SETS UP A MUCH COLDER AND LIGHT WINTRY PRECIPITATION SCENARIO BY PERIOD'S END FOR THE MIDWEST AND NORTHEAST. IN THE WEST...A MILD UPPER-LEVEL RIDGE WILL BE ACCENTED BY A PERSISTENT AREA OF LOW PRESSURE OFF THE COAST OF SOUTHERN CALIFORNIA AND BAJA CALIFORNIA---WHICH CREATES A SPLIT-FLOW PATTERN ALOFT---ALONG AND EAST OF THE CONTINENTAL DIVIDE. SUBTLE SENSIBLE WEATHER CHANGES WILL FOLLOW THE MIGRATORY SHORTWAVE ENERGY EXITING THE AREA OF LOW PRESSURE EMBEDDED IN THIS SOUTHERN STREAM. ...UNCERTAINTY ASSESSMENT... THERE IS NOT MUCH MODEL DISAGREEMENT WITH THE KEY SYNOPTIC-SCALE FEATURES. AT DAY 7...THE 24/00Z ECENS...GEFS AND NAEFS SUPPORT A DEEP AND STATIONARY UPPER-LEVEL LOW INVOF 60N 80W (CENTRAL HUDSON BAY) AND BROAD UPPER-LEVEL RIDGE AXIS ALONG THE WEST COAST OF THE CONTINENT ALONG 130W FROM THE YUKON SOUTHWARD TO NORTHERN CALIFORNIA. A 24/00Z FORECAST CYCLE 'PERFECT PROG' AT THE SURFACE WOULD CARRY A SUB 984MB SURFACE LOW (DAY 3_27/12Z) THAT MAKES LANDFALL OVER EASTERN NOVA SCOTIA ON/AFTER 28/12Z (DAY 4). THE TREND FOR THE LOW TRACK IS TO SWING/ARC IT JUST SOUTHEAST AND NORTHEAST OF THE 40N 70W BENCHMARK BETWEEN DAY 3-4. THE DEFORMATION PRECIPITATION SHIELD---ACCOMPANYING THIS SURFACE CYCLONE---PRODUCES THE FORECAST UNCERTAINTY WITH RESPECT TO THE AREAL COVERAGE AND INTENSITY OF COLD-SECTOR PRECIPITATION. THE NEXT SENSIBLE 'WEATHER-MAKER'---FOR THE LOWER 48---ORIGINATES IN THE LOWER COLORADO RIVER BASIN AND TAKES A MIGRATORY PATH ACROSS UTAH AND WYOMING---IN THE FORM OF A MID-LEVEL WAVE---DAYS 3-4. THE SYSTEM EMERGES OVER THE MIDWEST ON DAY 5 (29/12Z) LOW INVOF NORTHEAST ILLINOIS. AT THIS TIME SCALE...THE 24/00Z CANADIAN/ECMWF DETERMINISTIC GUIDANCE AND 24/06Z GFS ARE A WELL-CLUSTERED CONSENSUS SOLUTION (FOR LOCATION AND DEPTH)---WITH THE 24/00Z GFS...A WEAKER/SLOWER SOLUTION INVOF THE QUAD CITIES. ALONG THE WEST COAST...THE SYNOPTIC PATTERN IS A RESIDUAL 'GRAVEYARD' OF DYING MID-LATITUDE NORTH PACIFIC FRONTS ALONG 130W---THE RESULT OF A VERY STABLE...DRY AND MILD...MID-TO UPPER-LEVEL RIDGE. THE DAY 6-7 'REPLACEMENT' SYSTEM IN THE UPPER LEVELS---OFF THE COAST OF NORTHERN BAJA---IS A SPLITTING SHORTWAVE THAT ORIGINATES IN THE NORTH CENTRAL PACIFIC AND SUPER-IMPOSES ATOP THE 'GRAVEYARD' OF LOWER-LEVEL BAROCLINICITY AND CONVERGENT AIRFLOW. ...MODEL PREFERENCES... THOUGHT A BLEND OF THE 24/00Z ENSEMBLE GUIDANCE AND THE 24/00Z DETERMINISTIC ECMWF...CANADIAN AND 24/06Z GFS WILL WORK FOR THIS MEDIUM RANGE FORECAST PERIOD. ...SENSIBLE WEATHER HIGHLIGHTS... THE DAY 3-5 MID-LEVEL WAVE AND SURFACE CYCLONE MOVING ACROSS THE INTERMOUNTAIN WEST...MISSOURI VALLEY AND REACHING THE CENTRAL MIDWEST WILL LIKELY BE THE PRIMARY WEATHER FEATURE IN THE LOWER 48 THIS MEDIUM RANGE PERIOD. ITS EFFECTS...TEMPERING THE WARMTH BENEATH THE SOUTHERN FLANKS OF THE WESTERN NOAM RIDGE---WITH CLOUDS AND PERIODS OF SCATTERED PRECIPITATION. THE DEPTH OF THE SURFACE LOW IN THE MIDWEST MAY PRODUCE A NOTABLE SWATH OF LIGHT/MODERATE SNOWFALL INTENSITY ALONG THE NORTHERN PERIPHERY OF ITS LOW TRACK. THE DAY 3-4 EAST COAST SYSTEM STILL HAS A DEPTH AND TRACK THAT WILL PRODUCE SOME WRAP-AROUND PRECIPITATION POTENTIAL FOR NEW ENGLAND---INCLUDING MAINE AND THE MOUNTAINS OF FAR NORTHERN NEW ENGLAND. THE PRIMARY SENSIBLE WEATHER CHANGE IN THE NORTHEAST...APPEARS TO BE THE INFLUX OF A COLDER NORTHERLY FLOW. VOJTESAK