417  
FXUS02 KWBC 300701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT SAT MAR 30 2019  
 
VALID 12Z TUE APR 02 2019 - 12Z SAT APR 06 2019  
   
..MIDWEEK NOR'EASTER CONTINUING ITS GRADUAL OFFSHORE TREND
 
 
   
..OVERVIEW
 
 
A SHORT RANGE ALASKA RIDGE ALOFT (REBUILDING INTO NORTHEASTERN  
RUSSIA NEXT WEEK) AND THEN ANOTHER RIDGE BUILDING INTO WESTERN  
CANADA BY LATE WEEK WILL TEND TO FAVOR CYCLONIC MEAN FLOW ACROSS  
SOUTHERN CANADA AND INTO THE NORTHERN CONUS EAST OF THE ROCKIES.  
BENEATH THE RIDGES EXPECT A CONTINUED PROGRESSION OF PACIFIC  
SHORTWAVES INTO THE LOWER 48. THE SERIES OF FEATURES WILL LIKELY  
SUPPORT LOW PRESSURE TRACKING OFF THE EAST COAST TUE-WED, A  
TRAILING SYSTEM MOVING FROM THE WEST COAST INTO THE EASTERN U.S.  
TUE-SAT, AND THEN A FRONT REACHING THE WEST COAST TO START THE  
WEEKEND.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
MODELS AND ENSEMBLES CONTINUE TO AGREE ON THE LARGE SCALE  
EVOLUTION BUT NOT FOR EMBEDDED IMPORTANT DETAILS, INCLUDING  
WHETHER ANY STREAM INTERACTION MAY OCCUR OVER THE EASTERN HALF OF  
THE COUNTRY. A BLEND FOCUSING MORE ON LATEST OPERATIONAL MODELS  
EARLY IN THE PERIOD AND ABOUT 2/3 TOWARD THE ENSEMBLE MEANS BY DAY  
7 SAT CAPTURED THE MOST AGREEABLE ASPECTS OF THE FORECAST WHILE  
ACCOUNTING FOR SIGNIFICANT MODEL/ENSEMBLE MEMBER SPREAD FOR SOME  
FEATURES.  
 
THE SYSTEM EXPECTED TO TRACK OVER THE WESTERN ATLANTIC FROM OFF  
THE SOUTHEASTERN COAST TUE ONWARD IS STILL PROBLEMATIC WITH  
TRACK/TIMING SPREAD LEADING TO A VARIETY OF POTENTIAL OUTCOMES FOR  
THE EAST COAST STATES. OVER THE PAST DAY OR SO THERE HAS BEEN A  
NOTABLE TREND IN ECMWF-BASED GUIDANCE TOWARD SOME OTHER GUIDANCE  
THAT HAS BEEN SOMEWHAT FASTER/EASTWARD. THIS MIGHT WELL FAVOR  
UNDER-WEIGHTING THE ECMWF SCENARIO AS IT CONTINUES TO BE IN THE  
WESTERN PART OF THE FULL ENVELOPE (ESPECIALLY THROUGH TUE).  
HOWEVER SOME GEFS/CMC ENSEMBLES ARE NOT YET CONVINCED OF A TRACK  
AS FAR OFFSHORE AS SOME OPERATIONAL MODELS, WHILE LATEST GFS RUNS  
ARE QUITE ERRATIC FOR STRENGTH/TIMING--THE 18Z RUN WEAK/FAST AND  
THE NEW 00Z RUN SLOW AND DEEP. POOR CLUSTERING AND RUN TO RUN  
VARIABILITY THUS FAR SEEM TO SUGGEST A MODEST POTENTIAL FOR A  
TREND REVERSAL AT SOME POINT, BUT SOME REFLECTION OF THE OFFSHORE  
TREND IS REASONABLE. BY WED THE CHARACTER OF A TROUGH CROSSING  
THE NORTHEASTERN U.S. MAY PLAY A PART IN SYSTEM  
EVOLUTION/TRACK--WITH CURRENT GUIDANCE SPLIT ON HOW MUCH  
INTERACTION WILL OCCUR.  
 
AN UPSTREAM TROUGH NEAR THE WEST COAST STILL HAS SOME QUESTION  
MARKS ABOUT SPECIFICS OF A COUPLE SEPARATE PIECES OF ENERGY MAKING  
UP THE FEATURE. AS THE UPPER TROUGH CONTINUES ITS WAY ACROSS THE  
COUNTRY THE MODELS/MEANS AGREE FAIRLY WELL FOR ITS EXISTENCE AND  
TIMING BUT THERE ARE A LOT OF DIFFERENCES IN EXACT DISTRIBUTION OF  
EMBEDDED ENERGY AT ANY PARTICULAR POINT IN TIME. THIS LEADS TO  
ONGOING DIFFICULTIES IN DETERMINING THE PATH AND STRENGTH OF  
BEST-DEFINED LOW PRESSURE OVER THE CENTRAL/EASTERN STATES DURING  
THE LATTER HALF OF THE WEEK. AS OF DAY 6 FRI A SLIGHT MAJORITY OF  
GUIDANCE THROUGH THE 12-18Z CYCLES WAS INDICATING A FARTHER SOUTH  
TRACK THAN PRIOR CONSENSUS BUT THE 00Z CYCLE (ASIDE FROM THE NEW  
ECMWF) SEEMS TO BE RETURNING NORTHWARD.  
 
DURING THE LATTER HALF OF THE PERIOD THE MODELS AND ENSEMBLE  
MEMBERS DIVERGE FOR THE PARTICULARS OF EASTERN PACIFIC SHORTWAVES,  
WITH FAIRLY LOW CONFIDENCE FOR SPECIFICS. THERE IS A GENERAL  
THEME OF SOME LEADING SHORTWAVE ENERGY HEADING INTO A DEVELOPING  
WESTERN NORTH AMERICA MEAN RIDGE, FOLLOWED BY A POTENTIALLY MORE  
ENERGETIC TROUGH NEARING THE COAST BY EARLY SAT. AT THE SAME TIME  
A SOUTHERN STREAM SHORTWAVE MAY REACH THE SOUTHERN  
ROCKIES/NORTHERN MEXICO TO START THE WEEKEND.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE FORECAST REMAINS FAIRLY WELL ON TRACK FOR AREAS OF RAIN AND  
HIGHER ELEVATION SNOW ACROSS THE NORTHERN HALF TO TWO-THIRDS OF  
THE WEST DUE TO THE SYSTEM CROSSING THE REGION TUE-WED, WITH  
FAVORED TERRAIN SEEING THE HIGHEST AMOUNTS. ANOTHER ROUND OF  
MOISTURE SHOULD SPREAD INTO THE WEST DURING THE THU-SAT PERIOD  
WITH PRECIPITATION EXTENDING FROM THE NORTHERN/CENTRAL WEST COAST  
INTO THE NORTHERN ROCKIES. WITHIN THIS AREA OF LATE WEEK  
RAIN/SNOW THE NORTHERN CALIFORNIA-SIERRA NEVADA REGION CURRENTLY  
SHOWS THE BEST POTENTIAL FOR HIGHEST TOTALS. THE SYSTEM TRACKING  
OUT OF THE WEST AROUND MIDWEEK WILL LIKELY SPREAD A BROAD SHIELD  
OF PRECIPITATION ACROSS THE EASTERN HALF OF THE LOWER 48 BUT WITH  
BELOW AVERAGE CONFIDENCE FOR INTENSITY AT ANY PARTICULAR LOCATION.  
POCKETS OF LOCALLY HEAVY ACTIVITY ARE POSSIBLE BUT SO FAR THERE  
IS COHERENT SIGNAL FOR THEIR LOCATION AND TIMING. SOME OF THE  
PRECIPITATION MAY BE IN THE FORM OF SNOW OVER FAR NORTHERN AREAS.  
BEHIND THIS SYSTEM ANOTHER AREA OF RAIN MAY DEVELOP BY SAT IN  
RESPONSE TO AN APPROACHING SOUTHERN STREAM SHORTWAVE. FINALLY,  
TUE-WED TRENDS FOR THE WESTERN ATLANTIC SYSTEM CONTINUE TO LOWER  
POTENTIAL PRECIPITATION AMOUNTS/WESTWARD EXTENT ALONG THE EAST  
COAST. DAY 4-7 WINTER WEATHER OUTLOOK PROBABILITIES REFLECT SOME  
LINGERING MODEST ENSEMBLE SUPPORT FOR SNOWFALL POTENTIAL OVER  
HIGHER ELEVATIONS FROM WESTERN NC INTO WV AND PARTS OF THE  
NORTHEAST--BUT MARGINAL TEMPERATURES AND 00Z GUIDANCE TRENDS  
SUGGEST FURTHER LOWERING OF SNOW CHANCES.  
 
THE PROGRESSIVE PATTERN OVER MOST OF THE LOWER 48 WILL KEEP  
TEMPERATURES VARIABLE, BUT WITH A GENERAL INCREASE OF ABOVE-NORMAL  
TEMPERATURE COVERAGE WITH TIME. THIS IS ESPECIALLY THE CASE FOR  
MIN TEMPS. SOME LOCALIZED ANOMALIES OF MINUS 10-15F ARE POSSIBLE  
OVER THE SOUTHERN TIER ON TUE FOLLOWED BY A WARMING TREND. THE  
UNSETTLED PATTERN OVER THE WEST SHOULD KEEP MORNING LOWS WELL  
ABOVE AVERAGE MOST DAYS.  
 
RAUSCH  
 
ADDITIONAL 3-7 DAY HAZARDS INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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