200  
FXUS02 KWBC 081608  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1107 AM EST THU MAR 08 2018  
 
VALID 12Z SUN MAR 11 2018 - 12Z THU MAR 15 2018  
   
..THREAT FOR ANOTHER EASTERN U.S. COASTAL STORM ON MONDAY
 
   
..A WET PATTERN FOR THE WEST COAST BY THE MIDDLE OF NEXT WEEK
 
 
   
..PATTERN OVERVIEW/MODEL ASSESSMENT/PREFERENCES
 
 
ALL MEANINGFUL CLIMATE INDICES SHOW THE PREFERENCE FOR  
HIGH-LATITUDE BLOCKING AS SEEN WITH THE RATHER LOW NORTH ATLANTIC  
OSCILLATION AND ARCTIC OSCILLATION VALUES. WHILE NUMBERS HAVE BEEN  
ON THE RISE...THEY REMAIN NEGATIVE AND CONTINUE TO FAVOR THE  
THREAT FOR EASTERN U.S. COASTAL STORM TRACKS. AS SUCH...HEIGHT  
FALLS BARRELING THROUGH THE MID-SOUTH SUNDAY EVENING WILL LIKELY  
AID IN CYCLOGENESIS OFF THE CAROLINAS WITH AN EVENTUAL NORTHWARD  
TRACK LIKELY CROSSING NEAR THE 40N/70W BENCHMARK LATE MONDAY.  
WHILE THE NEGATIVE HEIGHT ANOMALY REMAINS FIXED OVER MUCH OF  
NORTHEASTERN NORTH AMERICA...THE PATTERN SHOULD BE EQUALLY  
AMPLIFIED ACROSS THE WESTERN/CENTRAL STATES. AN OMEGA BLOCK SETUP  
WILL UNFOLD WITH FAIRLY IMPRESSIVE 500-MB ANOMALIES NOTED IN EACH  
PART OF THE PATTERN...GENERALLY 2 TO 2.5 SIGMA DEPARTURES FROM  
CLIMATOLOGY TO BE EXACT. THE CLOSED LOW OVER THE WEST COAST WILL  
LIKELY BE SLOW MOVING AND REMAIN A FOCUS FOR UNSETTLED CONDITIONS  
THROUGH MUCH OF THE WEEK.  
 
CONSIDERING THE 552-DM/558-DM ENSEMBLE SPAGHETTI PLOTS DURING THE  
PAST FOUR MODEL CYCLES...A GREAT DEAL OF UNCERTAINTY CONTINUES TO  
EXIST WITH THE TROUGH SLIDING FROM THE MID-SOUTH TOWARD THE  
EASTERN SEABOARD. WITH THE POTENTIAL FOR A THIRD COASTAL LOW  
DEVELOPMENT IN A SPAN OF ONLY 10 DAYS...IT DEFINITELY BEARS  
WATCHING. DETAILS VARY WITH THE POSITION/STRENGTH OF THE SHORTWAVE  
WITH NUMEROUS PLACEMENT DIFFERENCES AS A WAVE OF LOW PRESSURE  
SWINGS TOWARD THE CAROLINAS SUNDAY EVENING. MULTI-DAY ENSEMBLE LOW  
PLOT COMPARISONS SUGGEST ONLY A SUBTLE INCREASE IN CONFIDENCE  
GIVEN VAST SPREAD CONTINUING EVEN AT THE DAY 3.5 TIMEFRAME. A  
NOTABLE OUTLIER ARE THE 00Z CMC/CMC ENSEMBLE MEAN AS THEY ARE  
DECIDEDLY SLOW PUSHING THE PARENT TROUGH DOWNSTREAM.  
LIKEWISE...THE 00Z UKMET FAVORED A LOW TRACK WHICH REMAINED ALONG  
THE PERIMETER OF THE BROAD SPREAD. REGARDING CONSISTENCY...THE GFS  
LEADS THE WAY HERE WITH TRENDS SHOWING A GRADUAL SHIFT SOUTHWARD  
WITH THE LOW TRACK. MEANWHILE...THE 00Z/12Z ECMWF HAVE MOVED  
TOWARD THE GFS PROPOSAL BUT DETAILS DIFFER CONSIDERABLY ONCE THE  
WAVE MIGRATES OFFSHORE. BY TUESDAY MORNING...THE 00Z ECMWF PUSHES  
WELL NORTHEAST OF THE CONSENSUS ALBEIT A BROAD ONE AT THAT. THE  
SYSTEM SHOULD REACH NOVA SCOTIA BY TUESDAY EVENING WHILE  
CONTINUING TO LINGER GIVEN THE BLOCKING REGIME TO THE NORTH.  
 
ACROSS THE WESTERN/CENTRAL STATES...THE CONFIDENCE IS MUCH GREATER  
WITH THE EVOLVING OMEGA BLOCK PATTERN. WHILE MULTI-DAY GUIDANCE  
COMPARISONS HAVE SHOWN SOME SHIFTS IN THE DETAILS OF THE  
FORECAST...THE LARGE-SCALE SYNOPTIC REGIME REMAINS RATHER FIXED.  
MID-LEVEL HEIGHTS SHOULD CONTINUE TO RISE OVER THE CENTER OF THE  
COUNTRY AS A POWERFUL UPPER LOW DRIFTS TOWARD THE WEST COAST ON  
DAYS 5-7...MARCH 13-15. WHILE THE ENSEMBLE SPAGHETTI PLOTS SHOW A  
BRIEF JUMP IN THE 00Z GUIDANCE...IT DOES NOT APPEAR MEANINGFUL  
ENOUGH TO COMMENT ON FURTHER. A MULTITUDE OF EMBEDDED SURFACE LOWS  
WILL SPIN COUNTERCLOCKWISE WITHIN THE MEAN CIRCULATION. A GRADUAL  
EASTWARD MIGRATION OF ATTENDANT FRONTAL ZONES AND MOISTURE FLUXES  
WILL INCREASE CHANCES FOR PRECIPITATION TO LOCATIONS FURTHER  
INLAND.  
 
DURING THE DAY 3-5...MARCH 11-13 TIME PERIOD...TOOK A DIRECT  
COMBINATION OF THE 06Z/00Z GFS WITH THE 00Z/12Z ECMWF WHILE  
GRADUALLY INCORPORATING EACH CORRESPONDING ENSEMBLE MEAN INTO THE  
PICTURE. THIS GENERALLY FAVORED A COMPROMISE BETWEEN THE SOLUTIONS  
ACROSS THE EASTERN SEABOARD GIVEN MANY UNKNOWNS AT HAND. TOWARD  
THE END OF THE PERIOD...UNCERTAINTIES IN THE DETAILS OF THE  
WESTERN U.S. UPPER LOW LED TO MORE OF AN ENSEMBLE BASED APPROACH  
WITH EQUAL WEIGHTING GIVEN TO THE 06Z GEFS/00Z ECMWF ENSEMBLE  
MEANS...RESPECTIVELY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE BEST FOCUS FOR ORGANIZED PRECIPITATION WILL BE OVER THE  
EASTERN SEABOARD...AS WELL AS ACROSS THE ENTIRE WEST COAST.  
INITIALLY CONSIDERING THE FORMER AREA...DETAILS OF COURSE WILL BE  
DRIVEN BY THE INHERENT MODEL DIFFERENCES. AT THIS TIME...THE MOST  
ORGANIZED THREAT FOR WINTRY PRECIPITATION WILL EXIST FROM THE  
LOWER MID-ATLANTIC NORTHWARD ALONG THE CENTRAL APPALACHIANS AND  
INTO NEW ENGLAND. AS THE SYSTEM MOVES INTO THE SHORT  
RANGE...HOPEFULLY THE DIFFERENCES IN THE GUIDANCE WILL DECREASE  
ALLOWING FOR IMPROVED CONFIDENCE IN THIS COMPLEX FORECAST. ACROSS  
THE WEST COAST...IT WILL REMAIN WET FOR SEVERAL DAYS GIVEN THE  
STAGNANT NATURE OF THE OFFSHORE UPPER LOW. SOME OF THE HEAVIEST  
AMOUNTS ARE CURRENTLY EXPECTED OVER MUCH OF NORTHERN  
CA...PARTICULARLY OVER THE FAVORED TERRAIN LIKE THE  
SHASTA...SISKIYOU...AND SIERRA NEVADA RANGES. THE HIGHER  
ELEVATIONS OF THESE MOUNTAINS CAN EXPECT SNOW DURING THE PERIOD  
WITH RAIN DOMINATING CLOSER TO THE COASTLINE.  
 
REGARDING TEMPERATURES...IT SHOULD REMAIN ON THE COOLER SIDE FROM  
THE GREAT PLAINS EASTWARD WITH LOWER HEIGHTS PREVAILING AT LEAST  
INTO EARLY NEXT WEEK. MARKED IMPROVEMENT IN TEMPERATURES IS  
EXPECTED STARTING WEDNESDAY AS HEIGHTS RAPIDLY BUILD UNDERNEATH  
THE BUILDING RIDGE ACROSS THE CENTRAL U.S. FORECAST ANOMALIES WILL  
BE IN THE 10 TO 15 DEGREE ABOVE AVERAGE RANGE...MOST NOTABLY  
ACROSS THE CENTRAL ROCKIES INTO THE ADJACENT PLAINS.  
MEANWHILE...OVER THE WEST COAST...EXPECT COOLER WEATHER TO BE THE  
NORM GIVEN ENHANCED CLOUD COVER AND WIDESPREAD PRECIPITATION.  
WHILE NOT LARGE IN NUMBER...IT SHOULD BE CHILLY OVER CA WITH  
FORECAST HIGHS AROUND 10 DEGREES BELOW CLIMATOLOGY.  
 
RUBIN-OSTER  
 

 
 
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