EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1051 AM EST FRI DEC 18 2015 VALID 12Z MON DEC 21 2015 - 12Z FRI DEC 25 2015 ...AMPLIFIED PATTERN TO REASSERT ITSELF NEXT WEEK... ...COLD/WET IN THE WEST BUT RECORD WARMTH IN THE EAST... ...OVERVIEW... STRONG UPPER RIDGING BETWEEN ALASKA AND HAWAI'I AND ALSO NEAR THE EAST COAST OF THE US WILL LARGELY MAINTAIN/RELOAD TROUGHING IN THE WESTERN STATES. THIS KEEPS THE STORM TRACK THROUGH THE WESTERN STATES INTO THE SOUTHERN PLAINS AND THEN INTO THE GREAT LAKES AND NEW ENGLAND IN AN OCTOBER/NOVEMBER-LIKE PATTERN. ENSEMBLES CONTINUE TO FORECAST STRONG/EXTREME RIDGING -- NEAR THE MAXIMUM OBSERVED VALUES FOR THIS TIME OF THE YEAR -- OFF THE SOUTHEAST COAST WHICH SUPPORT RECORD WARM TEMPERATURES OVER MUCH OF THE EASTERN THIRD OF THE COUNTRY. MOISTURE TAP FROM THE PACIFIC OCEAN INTO THE COASTAL AND INTERIOR NORTHWEST AS WELL AS FROM THE GULF INTO THE SOUTHEAST/SOUTHERN APPALACHIANS WILL PROVIDE SEVERAL AREAS OF MODEST RAIN OR SNOW NEXT WEEK INTO THE HOLIDAY. ...GUIDANCE PREFERENCES... 06Z GEFS MEAN AND 00Z ECENS MEAN OFFER GOOD CORRELATION DESPITE SOME DETAIL DIFFERENCES THROUGH NEXT FRIDAY. INCORPORATING THE 06Z GFS AND 00Z ECMWF NEXT MON-WED (AND THE ECMWF INTO THU) ALLOWS FOR SOME BETTER DETAILS WITH THE SYSTEMS IN THE GREAT LAKES AND WEST/PLAINS. DIFFERENCES ARISE IN THE WEST REGARDING HOW THE FRONT PROGRESSES SOUTHWARD AND WHETHER OR NOT A DISCREET SURFACE WAVE WILL DEVELOP AND MOVE INTO OR/CA AROUND THURSDAY. RECENT VERIFICATION HAS SHOWN THE GFS TO BE TOO BULLISH WITH SUCH DEVELOPMENT BUT IT IS NOT OUT OF THE QUESTION. BY THE 25TH, ENSEMBLES SUGGEST THAT THE FRONT IN THE EAST WILL MAKE A RATHER CLEAN PUSH THROUGH AT LEAST THE NORTHERN MID-ATLANTIC BUT SPREAD VARIES FROM NEW ENGLAND TO SC/GA. A SLOWER DIGGING TROUGH OUT WEST COULD ALLOW FOR A FARTHER SOUTH FRONT IN THE EAST BUT THE RIDGE OFF THE SOUTHEAST COAST MAY NOT ALLOW THAT TO HAPPEN. SPLIT THE DIFFERENCE BETWEEN THE 06Z GEFS AND 00Z ECENS MEAN TO ROUND OUT THE FORECAST. ...SENSIBLE WEATHER HIGHLIGHTS... WEST WILL REMAIN QUITE ACTIVE IN A COLD AND UNSTABLE MARITIME AIRMASS. TEMPERATURES WILL TREND MUCH COOLER THAN AVERAGE BY THE 24TH-25TH AS HEIGHTS CONTINUE TO LOWER. THE CENTRAL AND EASTERN STATES WILL SEE WELL ABOVE AVERAGE TEMPERATURES -- ABOUT +10 TO +25F WHICH IS NEAR AND BEYOND DAILY RECORDS FOR DOZENS OF CITIES AND CLOSE TO MONTHLY EXTREMES AS WELL. PLACEMENT OF FRONTAL BOUNDARY COMBINED WITH UNCERTAINTIES IN CLOUD COVER/PRECIP WILL TEMPER SOME MAX TEMP FORECASTS BUT MIN TEMPS SHOULD STAY QUITE MILD FOR THE END OF DECEMBER. THE 25TH SHOULD BE QUITE GREEN FOR THE EASTERN HALF OF THE COUNTRY. PRECIPITATION WILL BE HEAVIEST IN THE WEST -- SW OREGON INTO NORTHERN CALIFORNIA -- AS WELL AS IN THE NE GULF AND SOUTHEAST STATES WITH AMPLE RETURN FLOW. LOWER AMOUNTS ARE EXPECTED IN THE INTERIOR WEST, BUT COMPARED TO CLIMATOLOGY THIS WILL BE A HIGH PRECIP EVENT FOR SOUTHEASTERN OREGON AND NORTHERN NEVADA/SOUTHERN IDAHO, ESPECIALLY FOR THE HIGH ELEVATIONS WHERE SEVERAL FEET OF SNOW ARE POSSIBLE OVER THE MULTI-DAY PERIOD. FRACASSO