EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1057 AM EST FRI FEB 02 2018 VALID 12Z MON FEB 05 2018 - 12Z FRI FEB 09 2018 ...PATTERN OVERVIEW... A PERSISTENT MID/UPPER-LEVEL PATTERN REMAINS IN PLACE THROUGHOUT THE FORECAST PERIOD. LONGWAVE TROUGHING SHOULD CONTINUE TO DOMINATE OVER THE CENTRAL/EASTERN U.S. WHILE MULTIPLE SMALLER-SCALE PERTURBATIONS IN THE FLOW WILL BE CONDUITS FOR SURFACE WAVE DEVELOPMENT AND A CORRESPONDING THREAT FOR ACTIVE PRECIPITATION. INITIAL HEIGHT FALLS WILL LIKELY BE IN THE PROCESS OF EXITING THE NORTHEASTERN U.S. ON 05/1200Z AS A SURFACE LOW RAPIDLY DEEPENS ACROSS FAR EASTERN CANADA. FARTHER UPSTREAM...AMPLIFIED FLOW EMERGING OUT OF THE SOUTHERN PLAINS SHOULD RESULT IN ANOTHER DEFINED AXIS OF LOW PRESSURE PROGGED TO RACE THROUGH THE UPPER OH VALLEY AND EVENTUALLY INTO THE INTERIOR NORTHEAST BY MID-WEEK. ACROSS THE WESTERN STATES...RIDGING WILL REMAIN A FIXTURE IN THE FORECAST AS 500-MB HEIGHT ANOMALIES RANGE FROM 1.5 TO 2 SIGMA ABOVE CLIMATOLOGY OVER THE FAR EASTERN PACIFIC. SOME OF THE GUIDANCE HINTS AT EROSION OF THIS POSITIVE HEIGHT ANOMALY BY DAY 7/FEBRUARY 9 BUT BUILDING MODEL SPREAD PRECLUDES ANY LARGE SHIFTS TO THE FORECAST. ...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES... CONSIDERING THE EXITING FRONTAL ZONE OVER THE WESTERN ATLANTIC ON MONDAY...ENSEMBLE LOW PLOTS STILL INDICATE SOME SPREAD WITH PLACEMENT OF THESE FEATURES. WHILE THE NORTHERN STREAM WAVE SHOULD DOMINATE...A VAST MAJORITY OF THE ENSEMBLE MEMBERS DEPICT A WEAKER AREA OF LOW PRESSURE TO FORM OFF THE MID-ATLANTIC COAST EARLY ON. AT THIS TIME...THE 06Z/00Z GFS AND 00Z CMC ARE FARTHER NORTH WITH THE OVERALL WAVE PLACEMENT WHILE THE LATTER IS CONSIDERABLY WEAKER. TO THE SOUTH...THE 00Z ECMWF/UKMET CLUSTER REASONABLE WELL AS THE LOW RAPIDLY INTENSIFIES ACROSS THE HIGHER LATITUDES ON MONDAY NIGHT. IN ITS WAKE...ALL EYES ARE ON THE NEXT SYSTEM IN THE WAVE TRAIN AS HEIGHTS LOWER ACROSS THE SOUTHERN HIGH PLAINS MIDDAY TUESDAY. MULTI-DAY ENSEMBLE SPAGHETTI PLOT COMPARISONS SHOW A SLOWING TREND WITH THE 00Z ECMWF/UKMET FORECAST SYSTEMS BEING SLOWER/MORE AMPLIFIED. EVENTUAL DOWNSTREAM DIFFERENCES EMERGE REGARDING THE TIMING/EVOLUTION OF THE RESULTANT SURFACE LOW EJECTING TOWARD THE EASTERN U.S. EARLY WEDNESDAY. RELATIVE TO THE FORECAST 24 HOURS AGO...THE UNCERTAINTY HAS SLIGHTLY INCREASED AS THERE ARE NOW OPERATIONAL MODELS TAKING A TRACK TO THE EAST OF THE APPALACHIAN CHAIN. MORE SPECIFICALLY...THE 00Z GFS DEPICTS THIS WHILE THE 06Z GFS IS CONSIDERABLY MORE DIFFUSE. THE PREVIOUS THREE RUNS OF THE ECMWF HAVE MAINTAINED A SIMILAR LOW TRACK WITH A BROAD 1016-MB ISOBAR CENTERED OVER THE EASTERN SIDE OF THE OH RIVER VALLEY ON 07/1200Z WITH STRONGLY CLUSTERED ENSEMBLE MEMBERS. THIS ULTIMATELY FAVORS A WAVE TRACKING INTO INTERIOR NEW ENGLAND BY WEDNESDAY EVENING ALTHOUGH THERE DOES REMAIN CMC/GEFS SPREAD THAT CANNOT BE COMPLETELY IGNORED. TOWARD THE END OF THE PERIOD...THE FOCUS SHIFTS TOWARD THE STABILITY OF THE MEAN UPPER RIDGE ACROSS THE EASTERN PACIFIC/FAR WESTERN U.S. CURRENTLY...ONLY THE 06Z/00Z GFS SHOW ENOUGH UPSTREAM TROUGHING TO ERODE THE RIDGE AND ALLOW AN INSIDE SLIDER TO SWEEP THROUGH THE CENTRAL GREAT BASIN ON DAY 7/FEBRUARY 9. THE PAST FEW ECMWF RUNS AS WELL AS THE 00Z CMC AND GLOBAL ENSEMBLES FAVOR MAINTAINING THE RIDGE WHICH MAKES SENSE GIVEN THIS HAS BEEN THE FAVORED PATTERN MUCH OF THE WINTER SEASON. THROUGH DAY 4/TUESDAY...GENERALLY LEANED ON A MULTI-OPERATIONAL MODEL BLEND APPROACH LED BY THE 00Z GFS/ECMWF WITH SOME CONTRIBUTIONS FROM THE 00Z UKMET. AS THE 00Z GFS STARTED TO DIVERGE ON DAY 5/WEDNESDAY...MOVED MUCH MORE TOWARD THE CONSENSUS FORMED BY THE 00Z ECMWF AND 00Z GEFS/ECMWF ENSEMBLE MEANS THROUGHOUT THE REMAINDER OF THE PERIOD. THIS GENERALLY STAYED THE COURSE WITH WHAT THE OVERNIGHT SHIFT PRODUCED. ...WEATHER HIGHLIGHTS/THREATS... GIVEN THE STOUT UPPER RIDGE IN PLACE ACROSS THE WEST COAST...AN IMPRESSIVE PERIOD OF WARMTH IS ANTICIPATED FROM THE ROCKIES WESTWARD AS FORECAST TEMPERATURE ANOMALIES SHOULD GENERALLY RANGE FROM 10 TO 20 DEGREES ABOVE CLIMATOLOGY. WHILE WIDESPREAD DAILY RECORDS WILL NOT BE BROKEN...SCATTERED REPORTS FOR WARM OVERNIGHT LOWS/AFTERNOON HIGHS WILL BE POSSIBLE THROUGHOUT THE PERIOD. HIGH TEMPERATURES IN THE 50S/60S ARE EXPECTED ACROSS THE PACIFIC NORTHWEST AND CENTRAL GREAT BASIN WHILE THE SOUTHWESTERN STATES WILL SEE READINGS IN THE 70S WITH SOME LOW 80S IN THE DESERT REGIONS. MEANWHILE...PERSISTENT TROUGHING WILL ENSURE COLDER TEMPERATURES ARE TO PREVAIL ACROSS THE CENTRAL U.S. WITH HIGHS ONLY IN THE SINGLE DIGITS AND TEENS FROM THE NORTHERN ROCKIES EASTWARD INTO THE DAKOTAS AND UPPER MIDWEST/GREAT LAKES. SOME PERIODS OF WARMTH ARE LIKELY FROM THE SOUTHERN PLAINS OUT TO THE EAST COAST IN ADVANCE OF THE SYSTEM MOVING THROUGH THE TN/OH VALLEYS EARLY WEDNESDAY. A RETURN TO SLIGHTLY BELOW NORMAL TEMPERATURES IS EXPECTED IN THE WAKE OF THE FRONTAL PASSAGE. ON MONDAY...PRECIPITATION EAST OF THE I-95 CORRIDOR SHOULD BE WINDING DOWN WITH THE HEAVIER AMOUNTS CONFINED TO COASTAL AREAS OF NEW ENGLAND AS 850-700 MB MOISTURE FLUX ANOMALIES RANGE FROM 2 TO 3 SIGMA ABOVE AVERAGE. A BRIEF LULL IN THE PATTERN IS ANTICIPATED BEFORE THE UPSTREAM SHORTWAVE BRINGS A THREAT FOR MODERATE/HEAVY RAINFALL FROM THE LOWER MS VALLEY INTO THE TN/OH VALLEYS ON TUESDAY/WEDNESDAY. THE CURRENT FORECAST LOW TRACK WOULD SUGGEST THE BEST CHANCES FOR ACCUMULATING SNOWS EXISTS FROM THE OH VALLEY THROUGH INTERIOR PORTIONS OF THE MID-ATLANTIC AND INTO THE LOWER GREAT LAKES/INTERIOR NEW ENGLAND. CONDITIONS SHOULD QUICKLY IMPROVE OVER THE EASTERN U.S. THEREAFTER ALTHOUGH SOME LINGERING PRECIPITATION IS POSSIBLE ALONG THE TRAILING FRONTAL ZONE OVER THE SOUTHEASTERN U.S. LOOKING OUT WEST...A BROAD SHIELD OF PRECIPITATION IS LIKELY ALONG THE STALLED ARCTIC BOUNDARY STRETCHING FROM THE CENTRAL/NORTHERN ROCKIES BACK INTO THE UPPER INTERMOUNTAIN WEST. ACCUMULATING SNOW WOULD FALL OVER THE HIGHER ELEVATIONS WITH THE COVERAGE AND INTENSITY DECREASING AS MID-LEVEL HEIGHT RISES SPREAD OVER MUCH OF THE WEST. DEPENDING ON THE MODEL...SOME THREAT FOR PRECIPITATION EXISTS LATER NEXT WEEK ALONG A WEST/EAST FRONTAL ZONE STRETCHING FROM THE UPPER INTERMOUNTAIN WEST TOWARD THE NORTHERN/CENTRAL PLAINS AND MIDDLE MS VALLEY. RUBIN-OSTER