EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1036 AM EST SAT JAN 07 2017 VALID 12Z TUE JAN 10 2017 - 12Z SAT JAN 14 2017 ...WET PATTERN FOR MUCH OF THE WEST 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. A CONSENSUS BLEND OF THE 06Z/00Z GFS, 00Z GEFS MEAN, AND 00Z ECMWF/ECENS MEAN ALONG WITH OVERNIGHT CONTINUITY OFFERED A GREAT STARTING POINT FOR TUE/WED. THIS WILL TAKE A LEAD SYSTEM OUT OF THE PLAINS ON TUESDAY AND THROUGH THE GREAT LAKES INTO CANADA ON WEDNESDAY AS OTHER SYSTEMS ENTER THE WEST COAST ON LATE TUESDAY AND THURSDAY NIGHT. THE FRONTAL BOUNDARY DRAPED ACROSS THE MID-MISSISSIPPI VALLEY WILL SPAWN ANOTHER AREA OF LOW PRESSURE BY THURSDAY THAT SHOULD PUSH INTO THE GREAT LAKES. CANADIAN HIGH PRESSURE IN ITS WAKE IS FORECAST HELP PUSH THE NORTHERN PART OF THE FRONT EASTWARD BUT THE RIDGE IN THE SOUTHEAST WOULD PREVENT ITS MOVEMENT SOUTHWARD. THIS MAY SLOW AND STRETCH THE BOUNDARY NE-SW BY FRIDAY AND PERHAPS E-W NEXT SATURDAY OVER THE OHIO OR TENNESSEE VALLEY. FOR THE SECOND HALF OF THE PERIOD, THE DETERMINISTIC MODELS SHOWED TOO MUCH INCONSISTENCY IN DETAILS/TIMING/TRACK OF THE UPPER/SFC SYSTEMS TO RENDER A USABLE BLEND, SO DEFERRED TO CONTINUITY WITH THE 00Z ECMWF AND GEFS MEANS. ECMWF ENSEMBLE MEAN HAS BEEN QUICKER TO PICK UP THE EVOLVING PATTERN LATELY SO PUT MORE WEIGHTING IN ITS SOLUTION. 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 6" LIQUID EQUIVALENT THIS PERIOD (IN ADDITION TO SEVERAL INCHES ALREADY). 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 FROM THE SOUTHWEST. PRECIPITATION COULD BE HEAVY ALONG AND AHEAD OF THE FRONTS IN THE MISSISSIPPI/OHIO VALLEYS LATE NEXT WEEK. WITH COLD HIGH PRESSURE TO THE NORTH, FREEZING RAIN IS A CONCERN FOR THE CENTRAL/SOUTHERN PLAINS INTO MISSOURI/ARKANSAS AS OVERRUNNING PRECIPITATION MAY FALL INTO A COLD LOWER 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 THOUGH PERHAPS SLOWED BY THE RECENT SNOWFALL ACROSS THE SOUTHEAST/VIRGINIA. FRACASSO/ROTH