119  
FXUS02 KWBC 041600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST FRI JAN 04 2019  
 
VALID 12Z MON JAN 07 2019 - 12Z FRI JAN 11 2019  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
THE LATEST COLLECTION OF GUIDANCE CONTINUES TO AGREE UPON A FAIRLY  
AMPLIFIED BUT PROGRESSIVE SERIES OF UPPER WAVES PROGRESSING FROM  
THE EASTERN PACIFIC ACROSS THE CONUS NEXT WEEK. D+8 MULTI-DAY  
MEANS ARE PERSISTENT IN SHOWING A STRONG CORE OF POSITIVE HEIGHT  
ANOMALIES OVER THE NORTHEASTERN ATLANTIC WHILE TODAY'S D+8 CHARTS  
ARE MORE AGREEABLE AND BETTER DEFINED WITH A CORE OF NEGATIVE  
HEIGHT ANOMALIES CENTERED A LITTLE SOUTH OF THE WESTERN ALEUTIANS.  
TELECONNECTIONS RELATIVE TO BOTH SUGGEST AN INCREASED TENDENCY  
TOWARD UPPER RIDGING FROM AT LEAST THE NORTHERN HALF OF THE WEST  
COAST UP THROUGH ALASKA BY LATE IN THE PERIOD AND BEYOND, THOUGH  
INDIVIDUAL PROGRESSIVE NORTH PACIFIC SYSTEMS COULD WEAKEN IT AT  
TIMES. TELECONNECTION-FAVORED CYCLONIC FLOW OVER EASTERN NORTH  
AMERICA MAY TAKE UNTIL A LITTLE AFTER DAY 7 FRI TO BECOME  
ESTABLISHED.  
 
00Z/06Z CYCLES OF GUIDANCE HAVE COME IN WITH SIGNIFICANTLY  
IMPROVED AGREEMENT FOR SOME ASPECTS OF THE FORECAST COMPARED TO  
PREVIOUS DAYS. NOW ONLY 00Z CMC ENSEMBLES ARE HOLDING BACK THE  
SOUTHERN PART OF THE UPPER SHORTWAVE EXPECTED TO BE CROSSING THE  
PLAINS AS OF DAY 3 MON, WHILE RECENT TRENDS HAVE ESSENTIALLY GONE  
TOWARD A COMPROMISE BETWEEN GFS/ECMWF-BASED SOLUTIONS FOR UPSTREAM  
ENERGY OVER THE NORTHWEST U.S./WESTERN CANADA. THE END RESULT IS  
SOME NOTICEABLE TRENDING FOR THE SYSTEM AFFECTING THE NORTHEAST  
QUADRANT OF THE LOWER 48 IN THE MON-TUE TIME FRAME (FARTHER NORTH  
TRACK OF THE MS VALLEY-GREAT LAKES WAVE, POSSIBLY MERGING WITH  
CANADIAN LOW PRESSURE) BUT ULTIMATELY ENDING UP WITH A LOW CENTER  
CLOSER TO CONTINUITY ONCE THE SYSTEM REACHES NEAR/OFFSHORE NEW  
ENGLAND BY WED. OVERALL THE ECMWF/ECMWF MEAN HAVE BEEN MORE  
CONSISTENT WHILE THE GEFS MEAN GRAVITATED TOWARD THE CURRENT  
CONSENSUS EARLIER THAN GFS RUNS.  
 
ANOTHER AMPLIFYING UPPER TROUGH WILL BRING A STRONG STORM INTO THE  
PICTURE OFF THE WEST COAST DURING THE FIRST HALF OF THE WEEK.  
THERE IS DECENT MODEL/ENSEMBLE AGREEMENT FOR THE LONGITUDE OF THE  
SYSTEM BUT MUCH MORE LATITUDE SPREAD FOR ONE OR MORE INDIVIDUAL  
LOW CENTERS. SUCH DETAIL WILL BE VERY SENSITIVE TO SHORTWAVE  
SPECIFICS ALOFT, WHICH MAY NOT BE EASILY RESOLVED UNTIL THE SHORT  
RANGE TIME FRAME. AT THE VERY LEAST THE 00Z GFS BECOMES  
NOTICEABLY FARTHER SOUTH WITH ITS MAIN SURFACE LOW VERSUS MOST  
OTHER GUIDANCE FROM ABOUT EARLY TUE ONWARD. ON THE OTHER HAND THE  
00Z CMC/UKMET AND LATEST GEFS/ECMWF MEANS CONCENTRATE LOW PRESSURE  
FARTHER NORTHWARD THAN THE 06Z GFS/00Z ECMWF. SIGNIFICANT  
SOUTHWARD TREND IN THE ENSEMBLE MEANS OVER THE LAST DAY (FOR  
FORECASTS VALID 12Z WED) AND ECMWF CONTINUITY SUGGEST LEANING MORE  
TOWARD THE 06Z GFS/00Z ECMWF AS A STARTING POINT.  
 
AS THE UPPER TROUGH PROGRESSES ACROSS THE WESTERN HALF OF THE  
LOWER 48 DURING THU-FRI, GFS/ECMWF RUNS AND THEIR MEANS HAVE COME  
MUCH CLOSER TOGETHER MOSTLY BY WAY OF FASTER GFS/GEFS TRENDS. THE  
PROGRESSIVE NATURE OF THE PATTERN AND SPECIFICALLY THE RAPID  
APPROACH OF THE NEXT UPPER TROUGH OFF THE WEST COAST--WHICH SHOWS  
BETTER THAN AVERAGE GUIDANCE AGREEMENT--BY LATE IN THE WEEK  
CONTINUE TO SUPPORT LEANING AWAY FROM THE SLOWEST SIDE OF THE  
SPREAD SUCH AS FORECAST BY THE 00Z CMC.  
 
THE CONVERGENCE AMONG LATEST GUIDANCE ALLOWED FOR PRIMARY EMPHASIS  
ON THE 00Z ECMWF/06Z GFS AND 00Z CMC FOR THE FIRST HALF OF THE  
PERIOD OR SO, IN ORDER FROM HIGHEST TO LOWEST WEIGHT. BY DAYS 6-7  
THU-FRI CMC TIMING ISSUES REQUIRED PHASING OUT ITS INPUT WHILE  
TYPICAL DETAIL UNCERTAINTY LED TO RAISING TOTAL GEFS/ECMWF MEAN  
WEIGHT TO 40-60 PERCENT.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
ACROSS THE WEST EXPECT AN EPISODE OF ACTIVE WEATHER TO EXTEND INTO  
MON WITH HEAVIEST RAIN/MOUNTAIN SNOW LIKELY TO FOCUS OVER NORTHERN  
CALIFORNIA. SOME MOISTURE WILL EXTEND EASTWARD AND BRING AREAS OF  
SNOW AND LOW ELEVATION RAIN ACROSS THE INTERMOUNTAIN WEST INTO THE  
NORTHERN-CENTRAL ROCKIES. MOISTURE FROM THE NEXT PACIFIC STORM  
SHOULD REACH THE WEST COAST BY AROUND TUE NIGHT-WED, FOLLOWED BY  
RAIN/HIGHER ELEVATION SNOW PROGRESSING ACROSS THE WEST AND  
TAPERING OFF LATER IN THE WEEK. HIGHEST PROBABILITY FOR HEAVIEST  
PRECIPITATION AGAIN EXISTS OVER NORTHERN CALIFORNIA BUT  
SIGNIFICANT TOTALS ARE ALSO POSSIBLE ALONG THE REMAINDER OF THE  
WEST COAST AND OVER FAVORED TERRAIN INLAND THROUGH THE ROCKIES.  
THE DEEP LOW PRESSURE OFFSHORE MAY BRING A PERIOD OF STRONG WINDS  
TO COASTAL AREAS AS WELL.  
 
ALTHOUGH SOME DETAILS HAVE CHANGED FOR THE MIDWEST/GREAT LAKES  
SYSTEM EARLY IN THE WEEK, AN EVENTUAL TRACK OFF THE NEW ENGLAND  
COAST HAS KEPT THE AXIS OF HIGHEST SNOWFALL POTENTIAL FAIRLY  
STEADY--FROM THE FAR NORTHERN GREAT LAKES ACROSS NORTHEASTERN NEW  
YORK STATE THROUGH NEW ENGLAND. THE PACIFIC ORIGIN OF TRAILING  
AIR SHOULD KEEP TEMPERATURES FROM DROPPING TOO MUCH BELOW NORMAL  
BUT WILL LIKELY BE COLD ENOUGH TO SUPPORT A PERIOD OF LAKE EFFECT  
SNOW AFTER THE STORM'S DEPARTURE. THIS SYSTEM MAY BRING SOME  
LIGHT-MODERATE RAINFALL FARTHER SOUTHWARD.  
 
SOUTHERN TEXAS AND VICINITY MAY SEE SOME RAINFALL AROUND MIDWEEK  
IN ASSOCIATION WITH SOUTHERN STREAM MOISTURE/SHORTWAVE ENERGY  
ALOFT. THEN EXPECT PRECIPITATION TO EXPAND ACROSS THE  
PLAINS/MISSISSIPPI VALLEY TOWARD THU-FRI AS THE SYSTEM AFFECTING  
THE WEST THROUGH MIDWEEK EMERGES INTO THE CENTRAL U.S. NORTHERN  
AREAS MAY SEE SNOW FROM THIS SYSTEM WHILE WARM SECTOR RAINFALL TO  
THE SOUTH COULD BE LOCALLY HEAVY.  
 
THE PROGRESSION OF PACIFIC-ORIGIN SYSTEMS WILL KEEP TEMPERATURES  
MOSTLY ABOVE NORMAL OVER THE LOWER 48. THE EXCEPTIONS CONTINUE TO  
BE WITH HIGHS OVER SOME AREAS FROM THE WEST COAST INTO THE FOUR  
CORNERS STATES THROUGH THE PERIOD AS WELL AS OVER LOCATIONS ALONG  
THE EAST COAST DURING THE LATTER HALF OF THE WEEK, IN BOTH CASES  
GENERALLY BELOW NORMAL BY ONLY SINGLE DIGIT ANOMALIES. EXPECT  
WARMEST ANOMALIES OF PLUS 20F OR GREATER FOR MORNING LOWS AND  
GENERALLY PLUS 10-20F FOR HIGHS OVER PARTS OF THE CENTRAL/EASTERN  
U.S. DURING THE FIRST HALF OF THE WEEK FOLLOWED BY ANOTHER AREA OF  
WARMTH REACHING INTO THE PLAINS LATE WEEK.  
 
RAUSCH  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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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