EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1058 AM EST TUE JAN 10 2017 VALID 12Z FRI JAN 13 2017 - 12Z TUE JAN 17 2017 ...WET PATTERN OVER THE MID-MISSISSIPPI/OHIO VALLEYS AND SOUTHERN PLAINS LATE THIS WEEKEND INTO EARLY NEXT WEEK... ...A SWATH OF FROZEN PRECIPITATION IS POSSIBLE FROM THE SOUTHERN PLAINS TO THE MIDWEST AND GREAT LAKES... ...FREEZING RAIN A CONCERN FOR THE COLUMBIA BASIN SUNDAY AND MONDAY... 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 TROUGHING CROSSES THE WEST. EARLY IN THE PERIOD...THE WPC FORECAST STARTED WITH A BLEND HEAVILY WEIGHTED TOWARDS THE 00Z ECMWF/06Z GFS...BUT THEN THE FORECAST TRANSITIONED TO ENSEMBLE MEAN GUIDANCE BY SUNDAY (DAY 5) DUE TO AN INCREASING AMOUNT OF UNCERTAINTY WITH AN UPPER LOW LIFTING FROM NORTHERN MEXICO TO THE CENTRAL PLAINS EARLY NEXT WEEK. WEATHER HIGHLIGHTS/THREATS ~~~~~~~~~~~~~~~~~~~~~~~~~~ WITH THE SUSTAINED SOUTH TO SOUTHWEST FLOW OUT OF THE GULF AT THE SURFACE FROM WEDNESDAY ONWARD AND THE UPPER LOW EXITING OUT OF THE SOUTHWEST, PRECIPITATION WILL EXPAND IN COVERAGE AND INTENSITY LATER THIS WEEK NEAR A WAVY FRONT FROM TEXAS NORTHEASTWARD ACROSS THE MS VALLEY INTO THE MIDWEST AND GREAT LAKES. THE MOISTURE WILL OVERSPREAD AND REINFORCE A COLD AIR WEDGE/DAM, LEADING TO A COOL DOWN ACROSS THE EAST DESPITE THE RISING HEIGHTS ALOFT. A MAJOR ICING EVENT IS POSSIBLE FRIDAY INTO SUNDAY OVER PORTIONS OF THE TX PANHANDLE, OK, KS, MO, IA, AND IL IN THE COLD SECTOR OF THE LOW LEVEL FRONTAL ZONE AS AN ARCTIC HIGH PRESSURE OVER THE UPPER MS VALLEY FUNNELS COLD AIR SOUTH AT THE SURFACE WHILE SOUTHWEST FLOW ALOFT ADVECTS WARMER AIR ALOFT OVER THE REGION. SIGNIFICANT ICING ACCUMULATION, MORE THAN AN INCH OF GLAZE, IS POSSIBLE. LIGHTER ICING IS POSSIBLE ON THE COLD SIDE OF THE OH VALLEY FRONTAL ZONE AS WELL THIS COMING WEEKEND...EXTENDING ACROSS THE SOUTHERN GREAT LAKES INTO CENTRAL/NORTHERN PA/SOUTHERN NY...WHERE THE EVENT MAY BEGIN WITH A PERIOD OF SNOW. A SYSTEM APPROACHING THE NORTHWEST LATE IN THE PERIOD IS SLATED TO BRING WARM AIR ALOFT OVER AN AREA WITH COLD SURFACE TEMPERATURES. FREEZING RAIN APPEARS PLAUSIBLE IN THIS REGION SUNDAY INTO MONDAY PER THE GEFS, ECMWF, AND CANADIAN ENSEMBLE GUIDANCE. BELOW NORMAL TEMPERATURES IN ADVANCE OF THE ARCTIC HIGH ARE FOCUSED IN THE NORTHERN PLAINS DAY 3/THU/...UPPER MS VALLEY TO CENTRAL PLAINS DAY 4/FRI...UPPER GREAT LAKES TO CENTRAL PLAINS DAY 5. AS THE HIGH BEGINS TO WEAKEN AND THE AIRMASS MODIFIES...THE ANOMALIES FADE OVER NEXT WEEKEND. A PERSISTENT NEGATIVE ANOMALY APPEARS OVER EASTERN NEVADA AND UT/SOUTHERN WY/SOUTHEAST ID...WHERE A MULTI-DAY STRETCH OF TEMPERATURES 10 TO AS MUCH 15 DEGREES BELOW NORMAL IS FORECAST. THE MOST PERSISTENT WARM AREA WITH READING 10 TO 15 DEGREES ABOVE NORMAL IS FORECAST UNDER THE STRONG UPPER RIDGE IN THE SOUTHEAST US TO THE LOWER MS VALLEY. GERHARDT/ROTH