EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT WED OCT 28 2015 VALID 12Z SAT OCT 31 2015 - 12Z WED NOV 04 2015 ...HEAVY RAIN POSSIBLE FOR THE PACIFIC NORTHWEST---SOUTHERN PLAINS TO THE LOWER MS VALLEY... ...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT... CHALLENGES TODAY ARE--- HOW MUCH DETERMINISTIC GUIDANCE TO UTILIZE--- AND TO WHAT EXTENT---WITH RESPECT TO DURATION--- THEIR DETAILS ARE USEFUL IN THE SOUTHERN PLAINS...OZARKS AND MID MS VALLEY AFTER DAY 4---WITH RESPECT TO LARGE QPF OUTPUT. THEN FOR DAYS 6-7...HOW TO HANDLE THE GRADUAL EVOLUTION OF THE HIGHLY-UNSTABLE PACIFIC TROUGH THAT DIGS ACROSS THE GREAT BASIN AND THE EXACT TIMING/STRENGTH OF A SERIES OF YET-TO-BE DETERMINED SHORTWAVE EJECTIONS INTO THE PLAINS. TO HANDLE THE SURFACE DETAILS ACROSS THE LOWER 48...THE 28/00Z DETERMINISTIC ECMWF AND 28/00Z DETERMINISTIC GFS SEEMED A REASONABLE COMPROMISE ACROSS THE SOUTHERN STATES AT 500MB AND WITH THE DEPTH OF THE (UPPER-LEVEL JET-SUPPORTED) SURFACE REFLECTION(S) FROM NORTHEAST TEXAS TO THE NORTH CENTRAL TN/SOUTH CENTRAL KY BORDER BETWEEN 31/12Z AND 2/12Z. BEYOND 2/12Z...TAPERED AWAY FROM THE DETERMINISTIC GUIDANCE AND USED AN ECENS/NAEFS MEANS-BASED MASS FIELD FORECAST TO ALLOW THE SOUTHERN PORTION OF THIS SYSTEM---TO SHEAR NORTHEASTWARD---AND BECOME ENTRAINED IN A NORTHERN STREAM FLOW AND ALLOW A DEEP-LAYERED RIDGE ACROSS THE SOUTHEAST TO MODIFY...THEN COMBINE WITH SOMETHING THAT RESEMBLES A BACK-DOOR SURFACE RIDGE THAT ESSENTIALLY ANCHORS A 'BLOCKY' LOW-LEVEL FLOW PATTERN EAST OF 85W-90W FOR DAYS 6-7. THIS COMPROMISE SOLUTION WORKS IN THE PACIFIC NORTHWEST WITH THE NORTHEAST PACIFIC UPPER-LEVEL TROUGH MIGRATION. LIKED THE IDEA THAT SEVERAL PROGRESSIVELY COLDER SHORTWAVES CONTINUE TO CARVE OUT A RATHER COLD/UNSTABLE MARITIME PACIFIC-MODIFIED TROUGH ACROSS THE GREAT BASIN FOR DAYS 6-7. THE CONCERN---AND PRIMARY REASON TO TAPER TOWARDS THE ECENS/NAEFS AFTER DAY 5 IS---THE DETERMINISTIC SOLUTION REGARDING THE NOSE OF THE UPPER-LEVEL JET AXIS EXITING THE CONTINENTAL DIVIDE. WOULD PREFER A MORE-AMPLIFIED JET STRUCTURE AND SLOWER PROGRESSION OF THE ENTIRE TROUGH...SOMETHING SEEN IN MEDIUM RANGE PERIODS. VOJTESAK ...SENSIBLE WEATHER HIGHLIGHTS... MODERATE TO HEAVY RAINFALL CONTINUES TO BE A SIGNAL ACROSS EASTERN TEXAS TO THE LOWER/MIDDLE MISSISSIPPI VALLEY AS THE FIRST UPPER-TROUGH MOVES NORTHEASTWARD THIS WEEKEND. UNCERTAINTY LIES IN HOW MUCH OF THIS SHORTWAVE ENERGY CAN MAINTAIN ITSELF AS IT LIFTS UP AND OVER BUILDING HEIGHTS ACROSS FLORIDA. ECMWF ENSEMBLES ARE NOT QUITE CONVINCED THAT THE QPF PLUME WILL EXTEND INTO THE SOUTHERN MID-ATLANTIC LIKE THE GFS/ECMWF AND GEFS ENSEMBLES. AT THE SAME TIME... WET PATTERN WILL BE IN PLACE FOR MUCH OF WA/OR INTO ID AND W MT SAT THRU MON. THE QPF FOCUS WILL SLOWLY BUT STEADILY SINK SOUTHWARD AND EASTWARD AS THE HEIGHTS CONTINUE TO FALL... WHICH SHOULD ALLOW COLDER AIR TO SINK IN AND LOWER SNOW LEVELS. QPF TOTALS ARE FORECAST TO BE SEVERAL INCHES IN THE HIGHER TERRAIN -- AIDED BY FLOW GENERALLY STRAIGHT INTO THE MOUNTAINS. GEFS REFORECAST QPF DATASET SHOWS THIS EVENT TO BE IN THE TOP 1 PERCENT OF SIMILAR FORECASTS FOR THIS TIME OF YEAR FROM AN M-CLIMATE PERSPECTIVE. REFORECAST QPF VALUES ALIGN WITH THE DETERMINISTIC MODELS GUIDANCE... ADDING CONFIDENCE FOR A HEFTY EVENT FOR THE CASCADES AND COASTAL RANGE BUT ALSO FOR THE BITTERROOTS. TEMPERATURES AHEAD OF THE FRONT WILL BE QUITE MILD... ABOUT 10-20 DEG ABOVE CLIMO FOR MINS AND 5-15 ABOVE CLIMO FOR MAXES. THE ONLY COOLER THAN AVERAGE TEMPERATURES WILL BE CONFINED TO MAXES NEAR THE PATH OF THE FIRST TROUGH AND AGAIN WITH THE SECOND IN THE WEST... WHERE MAXES MAY BE 10-20F BELOW CLIMO IN THE GREAT BASIN AND MUCH OF THE SOUTWEST WEST OF 110W. FRACASSO