EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1201 PM EST WED JAN 11 2017 VALID 12Z SAT JAN 14 2017 - 12Z WED JAN 18 2017 ...A WIDESPREAD FREEZING RAIN EVENT COULD IMPACT LOCATIONS FROM THE SOUTHERN PLAINS TO THE MID-ATLANTIC REGION THIS WEEKEND, WITH THE GREATEST THREAT FOR SIGNIFICANT ICE ACCUMULATIONS EXPECTED TO CENTER OVER OKLAHOMA, KANSAS, AND MISSOURI... ...THE PATTERN SHOULD BECOME INCREASINGLY WET OVER THE SOUTHERN/CENTRAL PLAINS THIS WEEKEND, SHIFTING EASTWARD TO THE LOWER/MIDDLE MISSISSIPPI AND LOWER OHIO VALLEYS EARLY TO MID NEXT WEEK... ...HEAVY RAIN, MOUNTAIN SNOW, AND FREEZING RAIN WILL BE A CONCERN WITH THE NEXT SYSTEM MOVING INTO THE PACIFIC NORTHWEST EARLY TO MID NEXT WEEK... PATTERN OVERVIEW/MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MODELS ARE IN REASONABLE AGREEMENT WITH EDGING AN ANOMALOUS UPPER LOW THROUGH NORTHERN MEXICO WHILE DOWNSTREAM RIDGING BUILDS IN OVER THE SOUTHEASTERN U.S. THIS WEEKEND, BUT THEN MODELS QUICKLY BEGIN TO DIVERGE WITH THE DETAILS BY EARLY NEXT WEEK AS THE UPPER LOW LIFTS NORTHEASTWARD TOWARDS THE CENTRAL U.S. AND A POSSIBLE SURFACE LOW DEEPENS WHILE LIFTING FROM THE SOUTHERN PLAINS TO THE MIDDLE/UPPER MISSISSIPPI VALLEY NEXT MONDAY-TUESDAY. ALSO, DESPITE SOME DIFFERENCES IN THE EXACT TIMING AND AMPLITUDE OF MULTIPLE SHORTWAVES MOVING INTO BRITISH COLUMBIA/NORTHWEST THIS WEEKEND, THERE IS SOME FORECAST CONFIDENCE WITH THE POTENTIAL FOR A HEAVY PRECIPITATION EVENT IMPACTING THE NORTHWEST NEXT TUESDAY-WEDNESDAY. THE WPC DAY 3-7 FORECAST WAS LARGELY BASED ON A BLEND OF THE 00Z GFS/GEFS MEAN AND 00Z ECMWF/ECWMF ENSEMBLE MEAN...WITH SLIGHTLY MORE WEIGHT TOWARDS THE 00Z ECMWF/ECWMF ENSEMBLE MEAN SINCE THEY SEEMED TO BETTER REPRESENT THE MIDDLE OF MODEL SPREAD WITH THE SURFACE LOW POSSIBLY TRACKING FROM THE SOUTHERN PLAINS TO MIDDLE MISSISSIPPI VALLEY EARLY NEXT WEEK. WEATHER HIGHLIGHTS/THREATS ~~~~~~~~~~~~~~~~~~~~~~~~~~ INITIALLY THE FOCUS OF THE FORECAST WILL BE WITH PRECIPITATION DEVELOPING ALONG A WAVY FRONTAL BOUNDARY STRETCHED FROM THE SOUTHERN PLAINS TO THE MID-ATLANTIC STATES THIS WEEKEND, WHERE WARM MOIST AIR MOVING IN OVER AN ARCTIC AIRMASS COULD LEAD TO PERIODS OF SNOW AND ESPECIALLY FREEZING RAIN WITHIN THE NORTHERN EDGE OF THE PRECIPITATION SHIELD. PRECIPITATION SHOULD BECOME ESPECIALLY HEAVY AND WIDESPREAD ACROSS THE SOUTHERN PLAINS/ROCKIES AND CENTRAL PLAINS ON SUNDAY AS MOISTURE AND INSTABILITY INCREASE AHEAD OF AN ANOMALOUS UPPER LOW LIFTING NORTHEASTWARD OUT OF NORTHERN MEXICO. MODELS ARE SHOWING A STRONG SIGNAL FOR A SECOND ROUND OF ICE (POTENTIALLY MAJOR AND HIGH-IMPACT ICE ACCUMULATIONS) CENTERING OVER OKLAHOMA, KANSAS, AND MISSOURI, WHILE ACCUMULATING SNOW COULD BE A CONCERN OVER THE SOUTHERN/CENTRAL ROCKIES AND HIGH PLAINS AS THE SYSTEM LIFTS NORTHEASTWARD. WITHIN THE WARM SECTOR, HEAVY RAINS WILL BE POSSIBLE WITH AN ASSOCIATED COLD FRONT PRESSING THROUGH THE SOUTHERN PLAINS SUNDAY INTO MONDAY. THE FORECAST BECOMES A LITTLE LESS CERTAIN BY NEXT MONDAY THROUGH WEDNESDAY, BUT THE LATEST GUIDANCE SUGGESTS THE UPPER LOW WILL WEAKEN AND LIFT TOWARDS THE UPPER MIDWEST WHILE THE COLD FRONT CONTINUES TO PUSH EASTWARD OUT OF THE CENTRAL/SOUTHERN PLAINS...SHIFTING THE CHANCE FOR SNOW AND ICE INTO THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES AND THE CHANCE FOR HEAVY RAINFALL INTO THE LOWER/MIDDLE MISSISSIPPI AND LOWER OHIO VALLEYS. A RELATIVELY QUIET WEEKEND IS EXPECTED OVER THE WESTERN U.S., BUT THEN THE CHANCE FOR HEAVY RAIN, MOUNTAIN SNOW, AND EVEN FREEZING RAIN WILL INCREASE WITH THE NEXT SURGE OF MOISTURE AND HEIGHT FALLS REACHING THE NORTHWEST NEXT TUESDAY-WEDNESDAY. GERHARDT