237  
FXUS02 KWBC 030659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
158 AM EST SAT MAR 3 2018  
 
VALID 12Z TUE MAR 6 2018 - 12Z SAT MAR 10 2018  
 
***WEATHER PATTERN OVERVIEW***  
 
THIS FORECAST PERIOD BEGINS ON TUESDAY WITH AN OCCLUDED LOW OVER  
THE MIDWEST AND COLD FRONT CROSSING THE APPALACHIANS, AND AN UPPER  
LEVEL RIDGE SITUATED OVER THE WEST COAST AND A SURFACE HIGH  
COVERING MUCH OF THE INTERMOUNTAIN WEST. BY MIDWEEK, MILLER-B  
CYCLOGENESIS IS FORECAST TO BE UNDERWAY FOR THE EAST COAST AS A  
COASTAL LOW IS LIKELY TO DEVELOP AND BECOME THE DOMINANT FEATURE  
BY THURSDAY WITH THE SURFACE LOW OVER THE OHIO VALLEY GRADUALLY  
BECOMING ABSORBED. THIS WILL LIKELY HAVE NOR'EASTER  
CHARACTERISTICS ASSOCIATED WITH IT, BUT PROBABLY TO A LESSER  
DEGREE THAN THE ONGOING EVENT CURRENTLY DEPARTING NEW ENGLAND.  
SURFACE HIGH PRESSURE BUILDS IN ACROSS THE CENTRAL U.S. BY THE END  
OF THE WEEK WITH A PACIFIC STORM SYSTEM IMPINGING ON THE WEST  
COAST BY FRIDAY EVENING.  
 
***GUIDANCE AND PREDICTABILITY ASSESSMENT***  
 
THERE ARE MODEST DIFFERENCES IN THE PLACEMENT OF THE LOW PRESSURE  
SYSTEM OVER THE MIDWEST ON TUESDAY, WITH THE GFS/GEFS MEAN  
REMAINING ON THE SOUTHERN TIER OF THE MODEL, AND THE ECMWF/EC  
MEAN/CMC SLOWER AND TO THE NORTH ACROSS MICHIGAN WEDNESDAY  
MORNING. THE GFS HAS TRENDED LESS SUPPRESSED OVER THE PAST FEW  
MODEL RUNS AND IS NOW CLOSER TO THE ECMWF. THE 12Z UKMET IS CLOSE  
TO THE CONSENSUS POSITION WITH THIS FIRST SURFACE LOW. WITH  
RESPECT TO THE DEVELOPING NOR'EASTER ON WEDNESDAY ALONG THE  
COASTAL FRONT, THE GFS BECOMES THE QUICKEST IN LIFTING THE STORM  
TO THE NORTHEAST, AND THE ECMWF AND EC MEAN TAKING THE STORM  
FARTHER AWAY FROM THE COAST. SIMILAR TO YESTERDAY, THE STEADIER  
COMBINATION OF THE RECENT ECMWF AND EC MEAN OVER LOWER MICHIGAN  
THROUGH WEDNESDAY IS FAVORED FOR THIS PORTION OF THE FORECAST, AND  
A CONSENSUS APPROACH FOR THE SECOND LOW.  
 
THE GREATEST UNCERTAINTY DURING THE SECOND HALF OF THE FORECAST  
PERIOD IS FOR THE WESTERN THIRD OF THE U.S. IN TERMS OF MASS  
FIELDS AND THE HANDLING OF AN UPPER LEVEL TROUGH AND COLD FRONT  
APPROACHING THE COAST. THERE IS A STRONG QPF SIGNAL ACROSS THE  
BOARD, HOWEVER THE 12Z ECMWF MAINTAINS AN ELONGATED POSITIVELY  
TILTED TROUGH WHEREAS THE GFS HAS A MORE ROBUST CLOSED LOW WITH  
THE TROUGH. THE CMC IS MUCH FARTHER NORTH WITH THIS SAME FEATURE  
AND INDICATES A LESSER DEGREE OF TROUGHING NEAR THE WEST COAST.  
TO ADDRESS THE LINGERING UNCERTAINTY FOR THURSDAY AND FRIDAY HERE,  
AN ENSEMBLE MEAN APPROACH WAS USED, ALTHOUGH DETERMINISTIC  
GUIDANCE WAS HELPFUL WITH THE QPF FORECAST.  
 
***SENSIBLE WEATHER AND HAZARDS***  
 
SNOW IS LIKELY NORTH OF THE OCCLUDED SURFACE LOW THAT IS EXPECTED  
TO TRACK FROM SOUTHERN MICHIGAN TO THE NORTHEAST U.S., AND HEAVIER  
SNOW WITH POSSIBLE BLIZZARD CONDITIONS ACROSS PORTIONS OF INTERIOR  
NEW ENGLAND FOR THE MIDDLE OF THE WEEK DEPENDING ON THE STRENGTH  
AND LOCATION OF THE COASTAL LOW THAT DEVELOPS. PERIODS OF RAIN  
AND EMBEDDED THUNDERSTORMS ARE LIKELY AHEAD OF THE COLD FRONT OVER  
THE DEEP SOUTH AND EXTENDING TO THE SOUTHEAST COAST AND THE  
FLORIDA PENINSULA. SOME STRONG THUNDERSTORMS WILL BE POSSIBLE AND  
LOCALIZED INSTANCES OF HEAVY RAINFALL COULD RESULT IN SOME  
FLOODING ISSUES WITH THE MOST PERSISTENT CONVECTION. DESPITE THE  
MODEL DIFFERENCES FOR THE WEST COAST REGION, SHOWERS AND MOUNTAIN  
SNOW ARE EXPECTED TO MAKE A RETURN TO CALIFORNIA, OREGON, AND  
WASHINGTON FOR THE END OF NEXT WEEK. 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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