107  
FXUS02 KWBC 021549  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1049 AM EST FRI MAR 02 2018  
 
VALID 12Z MON MAR 05 2018 - 12Z FRI MAR 09 2018  
   
..SIGNIFICANT WINTER STORM FOR THE HIGH PLAINS EARLY NEXT WEEK
 
 
   
..ANOTHER ROUND OF SNOW FOR THE NORTHEAST LIKELY WED/THU
 
 
   
..OVERVIEW AND WEATHER HIGHLIGHTS/THREATS
 
 
A DEEPENING AREA OF LOW PRESSURE WILL MOVE EASTWARD OUT OF THE  
HIGH PLAINS ON MONDAY AND INTO THE LOWER GREAT LAKES/OHIO VALLEY  
TUESDAY BEFORE REDEVELOPING OFF THE MID-ATLANTIC COAST ON  
WEDNESDAY. THAT NEW LOW PRESSURE IS FORECAST TO DEEPEN AS IT LIFTS  
NORTHEASTWARD NEAR OR OVER CAPE COD WEDNESDAY EVENING AND INTO THE  
GULF OF MAINE ON THURSDAY. THIS WILL SPREAD AN AREA OF SNOW FROM  
THE DAKOTAS EASTWARD ACROSS MN/WI AND THE GREAT LAKES INTO THE  
CENTRAL APPALACHIANS AND NORTHEAST AS THE SYSTEM PROGRESSES  
EASTWARD. BLIZZARD CONDITIONS ARE POSSIBLE OVER THE PLAINS AS THE  
SYSTEM DEEPENS LATE SUNDAY INTO MONDAY WITH A STRONG 1040MB HIGH  
TO THE NORTH OVER HUDSON BAY AND HIGH PRESSURE OVER THE GREAT  
BASIN/CENTRAL ROCKIES. TO THE SOUTH, PRECIPITATION AND EMBEDDED  
CONVECTION WILL EXPAND EASTWARD THROUGH THE SOUTHEAST AHEAD OF THE  
COLD FRONT ON MONDAY MOVING OUT OF THE SOUTHERN PLAINS AND THROUGH  
THE LOWER MISSISSIPPI VALLEY. FRONT WILL SINK INTO THE GULF ON  
TUESDAY WHICH WILL LIMIT THE PRECIPITATION TO FLORIDA AND SOUTH  
TEXAS FOR THE END OF THE WEEK. TEMPERATURES WILL BE BELOW AVERAGE  
BY ABOUT 10-20 DEGREES BEHIND THE FRONT WITH A SLOW MODERATION  
AFTER ITS PASSAGE.  
 
OFF THE COAST OF CALIFORNIA, AN UPPER LOW AND ASSOCIATED SURFACE  
FRONT ARE FORECAST TO SLOWLY MOVE TOWARD THE PACIFIC NORTHWEST  
COAST LATER IN THE WEEK, THOUGH THE TREND HAS BEEN A BIT SLOWER  
OVER THE PAST SEVERAL DAYS. PRECIPITATION IS FAVORED FOR NORTHERN  
CALIFORNIA INTO OREGON AND WASHINGTON BY THURSDAY INTO FRIDAY,  
INCLUDING SNOW FOR THE CASCADES, KLAMATH MOUNTAINS, AND NORTHERN  
SIERRAS.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS HAVE COME INTO BETTER AGREEMENT WITH THE INITIAL PLACEMENT  
OF THE LOW PRESSURE NEAR SOUTHEASTERN SOUTH DAKOTA ON MONDAY, BUT  
STILL DIVERGE AFTER THAT WITH THE ECMWF ENSEMBLE MEAN MOST TO THE  
NORTH AND THE 06Z GEFS MEAN TO THE SOUTH. OPTED TO RELY ON THE  
STEADIER COMBINATION OF THE RECENT GFS/ECMWF RUNS (00Z/06Z) WHICH  
MOVE IT EASTWARD ACROSS IOWA THEN TO LOWER MICHIGAN BY WEDNESDAY.  
LINGERING UPPER LOW TO THE NORTHEAST NEAR JAMES BAY HAS NOT BEEN  
HANDLED WELL (OR CONSISTENTLY) BY THE MODELS/ENSEMBLES, WHICH  
AFFECTED THE LOW TRACK ACROSS THE MIDWEST. PRUDENT CHOICE WAS TO  
RELY ON CONTINUITY AND THE FAVORED MODELS WITH THE EVOLUTION OF  
THE ELONGATED UPPER TROUGH OVER JAMES BAY (I.E., ECMWF AND GFS)  
THOUGH THE UKMET/CANADIAN AT LEAST MAINTAIN THE SAME IDEA IN  
PRINCIPLE. BY WEDNESDAY, TRIPLE POINT LOW IS FORECAST TO TAKE OVER  
FROM THE PARENT LOW AND MOVE UP NEAR CAPE COD EARLY THURSDAY. GEFS  
MEMBERS WERE A BIT SLOWER/DEEPER WITH THE LOW THAN THE ECMWF  
ENSEMBLE MEMBERS, AND A CONSENSUS POSITION WAS PREFERRED FOR NOW  
GIVEN THE UNCERTAINTY IN THE MON-TUE FLOW TO THE NORTHWEST.  
 
OFF THE WEST COAST, AGAIN FAVORED THE MIDDLE GROUND SOLUTIONS OF  
THE 06Z GFS AND 00Z ECMWF (00Z GFS/CANADIAN WERE A BIT QUICKER)  
GIVEN HOW BAD THE MODELS HAVE BEEN WITH THIS FEATURE OVER RECENT  
DAYS. ENSEMBLE SPREAD HAS AT LEAST BEEN DECREASING OVER THE LAST  
FEW RUNS SO PERHAPS THE SLOWING TREND HAS STOPPED.  
 
FRACASSO  
 

 
 
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