085  
FXUS02 KWBC 021558  
PMDEPD  
 
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  
 

 
 
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