284  
FXUS02 KWBC 040656  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
156 AM EST SUN MAR 4 2018  
 
VALID 12Z WED MAR 07 2018 - 12Z SUN MAR 11 2018  
 
 
***WEATHER PATTERN OVERVIEW***  
 
THE FORECAST PERIOD BEGINS ON WEDNESDAY WITH A PAIR OF SURFACE  
LOWS OVER THE EASTERN U.S., WITH ONE WEAKENING OVER THE GREAT  
LAKES REGION AND THE OTHER INTENSIFYING NEAR THE EAST COAST AS A  
RESULT OF MILLER-B CYCLOGENESIS. AS A RESULT, THE ENERGY FROM THE  
GREAT LAKES LOW IS TRANSFERRED TO THE NEW TRIPLE POINT LOW, AND  
THIS IS EXPECTED TO BECOME A NOR'EASTER FOR NEW ENGLAND BY  
WEDNESDAY NIGHT AND INTO THURSDAY MORNING. SURFACE HIGH PRESSURE  
BUILDS IN ACROSS THE CENTRAL U.S. AND GULF COAST REGION BY THE END  
OF THE WEEK BEHIND THE DEPARTING STORM OVER THE NORTHEASTERN  
STATES. MEANWHILE, A PACIFIC STORM SYSTEM STARTS IMPINGING ON THE  
WEST COAST BY THURSDAY, AND THIS IS EXPECTED TO EVENTUALLY LEAD TO  
A NEW STORM SYSTEM OVER THE CENTRAL PLAINS BY NEXT WEEKEND AS THIS  
PACIFIC SHORTWAVE ENERGY CROSSES THE ROCKIES AND LEADS TO SURFACE  
CYCLOGENESUS.  
 
***GUIDANCE AND PREDICTABILITY ASSESSMENT***  
 
THERE IS GOOD OVERALL MODEL AGREEMENT ACROSS THE CONTINENTAL U.S.  
ON WEDNESDAY WITH THE 00Z GFS AND ECMWF WELL CLUSTERED WITH THE  
ENSEMBLE MEANS WITH THE EAST COAST STORM SYSTEM. THE ECMWF HAS  
TRENDED CLOSER TO THE MODEL CONSENSUS AND NOW FARTHER TO THE  
NORTHWEST WITH THE TRACK OF THE NOR'EASTER. THE DETERMINISTIC  
MODELS OVERALL HAVE TRENDED SLIGHTLY STRONGER WITH THE LOW WITH A  
TRACK LIKELY WITHIN 50NM OF THE 40/70 BENCHMARK. THE GFS THEN  
TRENDS EASTWARD WITH THE LOW AFTER THE SYSTEM EXITS EASTERN MAINE.  
 
OFF THE WEST COAST, MODELS/ENSEMBLES WERE STILL STRUGGLING WITH  
THE EVOLUTION OF THE FLOW IN THE EASTERN/NORTHEASTERN PACIFIC  
(SOURCE REGION OVER ALASKA) WITH THE LEAD POSITIVELY TILTED TROUGH  
AND SUBSEQUENT SHORTWAVE DIVING INTO ITS WESTERN SIDE ON THURSDAY.  
GIVEN A MORE AMPLIFIED DOWNSTREAM PATTERN OVER THE NORTHEASTERN  
CONUS AND SE CANADA, FELT THE LATEST 00Z ENSEMBLES (06Z GEFS) HAD  
A BETTER HANDLE ON THE FLOW (ALL THINGS CONSIDERED) INTO NEXT  
WEEKEND THAN EARLIER RUNS. SYSTEM SHOULD MOVE INTO THE PAC NW  
AROUND FRIDAY AND WEAKEN AS IT MOVES EASTWARD NEXT SATURDAY.  
TRENDED TOWARD THE ECMWF ENSEMBLE MEAN AND GFS/GEFS MEAN FOR THE  
END OF THE PERIOD WHICH FIT WELL WITH THE EASTERN CONUS EVOLUTION  
AS WELL.  
 
***SENSIBLE WEATHER AND HAZARDS***  
 
THE NORTHEAST QUADRANT OF THE NATION IS EXPECTED TO HAVE THE  
GREATEST WEATHER IMPACTS FOR THE MIDDLE TO END OF NEXT WEEK AS THE  
DEVELOPING NOR'EASTER BRINGS A MULTITUDE OF HAZARDS TO THE REGION.  
MODEL GUIDANCE HAS TRENDED STRONGER WITH THIS STORM WITH A TRACK  
CLOSE ENOUGH TO MERIT CONCERN. STRONG ONSHORE FLOW NORTH OF THE  
LOW WILL INCREASE THE THREAT OF COASTAL FLOODING FOR THE NORTHEAST  
COAST, AND MODERATE TO HEAVY SNOW IS BECOMING MORE LIKELY FOR  
INTERIOR PORTIONS OF NEW YORK AND NEW ENGLAND, WITH BLIZZARD  
CONDITIONS POSSIBLE AT TIMES. THE PRESSURE GRADIENT DOES NOT  
APPEAR TO BE AS TIGHT AS THE LAST NOR'EASTER ACCORDING TO THE  
LATEST GUIDANCE, BUT STILL ENOUGH TO CAUSE BREEZY TO WINDY  
CONDITIONS FROM THE APPALACHIANS TO MAINE.  
 
PRECIPITATION MAKES A RETURN TO THE WEST COAST BY THE END OF THE  
WEEK. DESPITE LINGERING MODEL DIFFERENCES FOR THE WEST COAST  
REGION IN TERMS OF MASS FIELDS, SHOWERS AND MOUNTAIN SNOW ARE  
EXPECTED FROM CENTRAL CALIFORNIA TO WASHINGTON STATE, AND LIGHTER  
QPF EXPECTED TO REACH THE NORTHERN ROCKIES. THE HEAVIEST SNOW IS  
LIKELY FOR THE SIERRA, WITH AMOUNTS IN EXCESS OF A FOOT LIKELY FOR  
THE HIGHEST ELEVATIONS. BY THE END OF THE FORECAST PERIOD NEXT  
WEEKEND, A DEVELOPING LOW PRESSURE SYSTEM OVER THE CENTRAL PLAINS  
IS EXPECTED TO INCREASE MOISTURE RETURN FROM THE GULF OF MEXICO  
AND ENHANCE RAINFALL CHANCES FROM THE CENTRAL GULF COAST TO THE  
MIDWEST. THERE IS SOME MODEL SIGNAL FOR AREAS OF HEAVY RAIN, AND  
THUS THE POTENTIAL FOR EXCESSIVE RAINFALL THAT COULD RESULT IN  
SOME FLOODING ISSUES.  
 
THE GREATEST COLD TEMPERATURE ANOMALIES ARE EXPECTED FOR THE  
NORTHERN PLAINS AND UPPER MIDWEST THROUGH THE MIDDLE OF THE WEEK,  
WITH READINGS ON THE ORDER OF 5 TO 15 DEGREES BELOW NORMAL,  
PERHAPS MORE. TEMPERATURES SHOULD BE SLIGHTLY ABOVE NORMAL FOR  
THE SOUTHWESTERN STATES.  
 
D. HAMRICK  
 

 
 
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