215  
FXUS02 KWBC 041553  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1053 AM EST SUN MAR 04 2018  
 
VALID 12Z WED MAR 07 2018 - 12Z SUN MAR 11 2018  
   
..MORE SNOW FOR THE NORTHEAST
 
 
   
..OVERVIEW
 
 
ANOTHER NOR'EASTER WILL PARALLEL THE NEW ENGLAND COAST WED/THU AND  
DELIVER A SWATH OF LIGHT TO MODERATE SNOW ACROSS AT LEAST THE  
INTERIOR OF THE NORTHEAST AND NORTHERN MID-ATLANTIC. IN THE WEST,  
AN UPPER LOW AND ASSOCIATED SURFACE FRONT WILL PUSH INTO THE  
PACIFIC NORTHWEST THURSDAY AND THROUGH THE INTERIOR WEST AND  
ROCKIES ON FRIDAY. THIS WILL REDEVELOP IN THE SOUTHERN PLAINS ON  
SATURDAY AND MOVE THROUGH THE LOWER MISSISSIPPI VALLEY AND  
SOUTHEAST NEXT SUNDAY.  
 
   
..GUIDANCE AND PREDICTABILITY ASSESSMENT
 
 
LATEST DETERMINISTIC GUIDANCE OFFERS GOOD CLUSTERING WITH THE  
SURFACE LOW EVOLUTION OFF THE MID-ATLANTIC ON WEDNESDAY AND TRACK  
OVER OR NEAR CAPE COD AND INTO THE GULF OF MAINE BY THURSDAY  
MORNING. THERE REMAINS LINGERING UNCERTAINTY WITH THE COMPLEX  
UPPER PATTERN OVER ONTARIO AND HOW MUCH OF THE MID-LEVEL VORTICITY  
GETS DRAWN BACK INTO THE EASTERN UPPER LOW CIRCULATION VS LEFT  
BEHIND (GFS IN THE FORMER CAMP, ECMWF/UKMET/CANADIAN IN THE  
LATTER). THE MODELS HAVE BEEN RATHER ABYSMAL WITH THEIR HANDLING  
OF THIS FEATURE AND THE DOWNSTREAM RIDGING THAT HAS TRENDED MUCH  
STRONGER INTO LABRADOR AND EASTERN QUEBEC (WHICH ALSO ESSENTIALLY  
BLOCKS THE NOR'EASTER FROM GAINING MUCH LATITUDE PAST MAINE).  
BLEND OF THE GUIDANCE WILL AGAIN HAVE TO SUFFICE SINCE THERE HAS  
BEEN TOO MUCH VARIABILITY IN THE MODELS.  
 
IN THE WEST, 00Z MODELS/ENSEMBLES HAVE COMPLETELY ABANDONED THE  
IDEA OF DROPPING A SHORTWAVE SOUTHWARD ON THE BACK SIDE OF THE  
IN-SITU UPPER LOW AND RATHER ALLOW IT TO CONTINUE EASTWARD IN MUCH  
WEAKER FASHION. THIS HAS THE EFFECT OF A MUCH QUICKER PUSH INLAND  
OF THE TROUGH AND SFC FRONT THAN EVEN 12 HRS AGO FOR FRIDAY. FROM  
THAT POINT ONWARD, ENSEMBLES SHOW THAT TROUGH DIVING INTO THE  
PLAINS AND THEN THE LOWER MS VALLEY NEXT WEEKEND BUT DIFFER  
GREATLY ON TIMING. OPTED TO RELY HEAVILY ON THE ENSEMBLE MEANS  
(06Z GEFS AND 00Z ECMWF EPS) WHICH WERE CLOSE TO A 06Z GFS/00Z  
ECMWF BLEND.  
 
   
..WEATHER HIGHLIGHTS
 
 
WITH MARGINAL THERMAL PROFILES OVER THE NORTHEAST WED-THU, THE  
SYSTEM WILL LIKELY BRING A MIXED BAG OF PRECIPITATION TYPES WITH  
THE TRANSITION ZONE ALONG OR WEST OF THE I-95 CORRIDOR. INTERIOR  
SECTIONS STAND THE BEST CHANCE OF ALL FROZEN PRECIPITATION BUT  
THESE DETAILS WILL HAVE TO BE REFINED IN THE SHORT RANGE. TOTAL  
MELTED PRECIPITATION MAY EXCEED AN INCH BETWEEN ABOUT I-84 AND THE  
COAST WITH HEAVIER AMOUNTS POSSIBLE IN MAINE AS THE SYSTEM PAUSES  
BRIEFLY BEFORE TURNING EASTWARD. WRAP-AROUND SNOW FOR NORTHERN NEW  
ENGLAND IS LIKELY AS THE SYSTEM DEPARTS AS WELL AS LAKE ENHANCED  
SNOWS OFF LAKE ONTARIO AND ERIE. TEMPERATURES WILL DROP TO BELOW  
AVERAGE BEHIND THE SYSTEM THU/FRI BEFORE REBOUNDING NEXT WEEKEND.  
 
IN THE WEST, PRECIPITATION WILL SPREAD INLAND AS THE UPPER TROUGH  
MOVES THROUGH, WITH GENERALLY LIGHT TO MODERATE RAIN/SNOW. UPSLOPE  
FLOW WILL AIDE IN PRODUCING LOCALLY HEAVIER SNOWFALL FOR THE  
CASCADES AND NORTHERN SIERRAS INTO THE MOUNTAINS ACROSS THE GREAT  
BASIN INCLUDING IDAHO INTO WYOMING AND SOUTHWARD THROUGH UTAH INTO  
COLORADO. OVERALL MOISTURE APPEARS LIMITED SO AMOUNTS MAY BE  
MODEST AT BEST WITH EVEN LESS RAINFALL FOR THE DRIER VALLEY  
LOCATIONS. BY THE WEEKEND, GULF MOISTURE SHOULD INCREASE AHEAD OF  
THE DEVELOPING SURFACE FRONT OVER TEXAS AS IT MOVE EASTWARD.  
RAINFALL IS FORECAST TO EXPAND IN COVERAGE AND INTENSITY WITH  
LOCALLY HEAVY RAINFALL POSSIBLE EAST OF THE MISSISSIPPI. ABOVE  
AVERAGE TEMPERATURES OVER MUCH OF THE WEST EARLY IN THE PERIOD  
WILL COOL WITH TIME AS THE TROUGH MOVES THROUGH, SETTLING BACK TO  
NEAR OR JUST BELOW AVERAGE FOR EARLY MARCH.  
 
FRACASSO  
 

 
 
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