792  
FXUS02 KWBC 061600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST SUN JAN 06 2019  
 
VALID 12Z WED JAN 09 2019 - 12Z SUN JAN 13 2019  
   
..OVERVIEW
 
 
GUIDANCE IS PERSISTENT IN DEPICTING A GENERAL TROUGH-RIDGE-TROUGH  
MEAN PATTERN ALOFT FROM THE MULTI-DAY MEAN PERSPECTIVE, AND  
CONTAINING MULTIPLE EMBEDDED PROGRESSIVE FEATURES. THERE WILL  
ALSO BE A TENDENCY FOR SOME SPLITTING OF SHORTWAVE ENERGY THAT  
DIGS INTO THE EASTERN PACIFIC/WEST COAST MEAN TROUGH, WITH SOME  
DIFFERENCES IN EXACTLY HOW THE FLOW SPLITS DEPENDING ON THE  
SYSTEM. LATEST D+8 MEANS SHOW AN EVOLUTION TOWARD STRONGER  
POSITIVE HEIGHT ANOMALIES CENTERED NEAR WESTERN ONTARIO.  
CORRESPONDING TELECONNECTIONS HIGHLIGHT THE EXPECTED PERIODS OF  
ACTIVE WEATHER ALONG THE WEST COAST AND RAINFALL POTENTIAL OVER  
THE SOUTHERN PLAINS AS WELL AS POTENTIAL FOR WELL ABOVE NORMAL  
TEMPERATURES OVER THE NORTHERN PLAINS. SIGNALS FOR COOLER  
TEMPERATURES OVER THE EAST ARE NOT VERY PROMINENT RELATIVE TO THE  
AFOREMENTIONED FEATURE BUT SHOW UP A LITTLE MORE WHEN  
TELECONNECTING ON NORTHEASTERN ATLANTIC POSITIVE HEIGHT ANOMALIES  
AND NORTHERN EUROPEAN NEGATIVE HEIGHT ANOMALIES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
FROM THE LATEST CYCLE OF GUIDANCE, GOOD MODEL CONSENSUS EXISTS  
INTO DAY 4 THU. OVER THE PAST DAY OR SO SOLUTIONS HAVE BEEN  
TRENDING TOWARD A MORE CONSOLIDATED AND DEEPER SYSTEM TRACKING  
RATHER SLOWLY FROM NEAR THE NEW ENGLAND COAST INTO THE CANADIAN  
MARITIMES. IN SOME RESPECTS GFS RUNS HAVE PROVIDED AN EXTRA DAY  
OF LEAD TIME IN DEPICTING THE CURRENT CONSENSUS EVOLUTION RELATIVE  
TO THE ECMWF. MEANWHILE DEEP NORTHWARD-TRACKING PACIFIC LOW  
PRESSURE SHOULD REMAIN 400-500 MILES OFFSHORE THE PACIFIC  
NORTHWEST. NO MAJOR TRENDS ARE NOTED FOR THIS SYSTEM.  
 
FROM LATE THU OR EARLY DAY 5 FRI ONWARD THERE IS SOMEWHAT MORE  
SPREAD ALONG WITH TREND IN SOME CASES. THE 00Z UKMET BECOMES A  
PRONOUNCED WEAK/ELONGATED EXTREME WITH THE STRONG SYSTEM FORECAST  
TO COME INTO THE PICTURE OFF THE WEST COAST BY FRI SO IT WAS  
REMOVED FROM THE BLEND AT THIS TIME. THE 00Z GFS ALSO BECOMES  
SOMEWHAT WEAKER/ELONGATED ALOFT VERSUS THE 06Z GFS AND 00Z  
ECMWF/CMC WITH A SURFACE LOW TRACK TO THE SOUTH OF THOSE SOLUTIONS  
AND THE ENSEMBLE MEANS (BUT STILL WITHIN THE FULL ENSEMBLE  
ENVELOPE). AS THE UPPER TROUGH REACHES THE WEST COAST REGION BY  
EARLY SAT THERE IS BETTER THAN AVERAGE CONSENSUS AIDED BY  
FASTER/MORE OPEN TRENDS EXHIBITED BY THE GFS STARTING WITH  
YESTERDAY'S 12Z RUN. THE 06Z GEFS MEAN HAS ALSO NUDGED CLOSER TO  
THE MODEL CONSENSUS VERSUS THE 00Z VERSION. BY DAY 7 SUN THE 00Z  
CMC/FV3 GFS BECOME QUESTIONABLY STRONG WITH REMAINING ENERGY THAT  
PASSES THROUGH THE LONG-TERM MEAN RIDGE POSITION. IN CONTRAST TO  
SOME RECENT CASES FROM THIS PATTERN, GFS RUNS ARE A BIT FASTER  
THAN OTHER SOLUTIONS TO BRING THE NEXT PACIFIC TROUGH TOWARD THE  
WEST COAST BY DAY 7 SUN. GEFS MEANS THUS FAR PROVIDE MORE SUPPORT  
FOR THE ECMWF/ECMWF MEAN/CMC CLUSTER.  
 
FARTHER EASTWARD CONTINUITY IS GOOD WITH SOUTHERN STREAM SHORTWAVE  
ENERGY CROSSING NORTHERN MEXICO LATE IN THE WEEK AND SUPPORTING A  
WESTERN GULF OF MEXICO SURFACE WAVE BY NEXT SAT. ON THE OTHER  
HAND THERE IS A PRONOUNCED TREND IN THE LATEST GUIDANCE TOWARD  
STRONGER HIGH PRESSURE OVER EASTERN NORTH AMERICA BY NEXT WEEKEND,  
ULTIMATELY SUPPRESSING AND POSSIBLY DISSIPATING WHAT WEAK WAVINESS  
EMERGES OVER THE CENTRAL U.S.. IT MAY BE REASONABLE TO INCLUDE A  
MINORITY OF CONTINUITY GIVEN THE SIGNIFICANT CHANGE FROM THE PRIOR  
CYCLE ESPECIALLY IN THE ECMWF. TYPICAL DIFFICULTY OF RESOLVING  
SHORTWAVE DETAILS 6-7 DAYS OUT IN TIME LOWER CONFIDENCE IN  
SPECIFICS OF EXACTLY HOW ONE OR MORE WAVES MAY EVOLVE ALONG A  
FRONTAL BOUNDARY EXTENDING FROM THE GULF OF MEXICO INTO THE  
WESTERN ATLANTIC JUST OFF THE EAST COAST.  
 
BASED ON THE ABOVE CONSIDERATIONS, THE FORECAST TRENDS THE  
EARLY-PERIOD CONSENSUS INCREASINGLY TOWARD THE 06Z GEFS/00Z ECMWF  
MEANS WHILE HOLDING ONTO A MODEST 00Z ECMWF/06Z GFS COMPONENT  
(MORE OF THE FORMER THAN THE LATTER), INCORPORATING 20 PERCENT  
CONTINUITY, AND REMOVING THE CMC AFTER DAY 6 SAT.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
MANY LOCATIONS ALONG THE WEST COAST SHOULD SEE MULTIPLE EPISODES  
OF SIGNIFICANT PRECIPITATION DURING THE PERIOD. THE FIRST EVENT  
EXTENDING INTO MIDWEEK SHOULD ESPECIALLY AFFECT CENTRAL/NORTHERN  
AREAS AND TAPER OFF AFTER WED. EXPECT MORE MOISTURE TO ARRIVE BY  
FRI-SAT WITH MEANINGFUL RAINFALL/HIGH ELEVATION SNOW EXTENDING  
FARTHER SOUTH ACROSS CALIFORNIA THAN WITH THE PRECEDING EVENT.  
SOME OF THIS LATTER SYSTEM'S MOISTURE SHOULD THEN EXTEND INTO THE  
GREAT BASIN/SOUTHWEST/FOUR CORNERS REGION. AFTER ONLY A VERY  
BRIEF BREAK, MORE POTENTIALLY HEAVY RAINFALL/MOUNTAIN SNOW WILL  
LIKE REACH CALIFORNIA IN PARTICULAR AROUND SAT NIGHT WITH SOME OF  
THIS MOISTURE EVENTUALLY SPREADING FARTHER INLAND. CURRENTLY  
EXPECT NORTHERN TO SOUTH-CENTRAL CALIFORNIA TO SEE HIGHEST TOTALS  
FROM THIS EVENT.  
 
THE SYSTEM SLOWLY TRACKING AWAY FROM NEW ENGLAND EARLY IN THE  
PERIOD MAY PRODUCE HEAVY SNOW OVER NORTHERN NEW ENGLAND THROUGH  
WED AND A PERIOD OF LAKE EFFECT/ENHANCED SNOW OVER PARTS OF THE  
GREAT LAKES/APPALACHIANS. THERE SHOULD ALSO BE A COUPLE DAYS WITH  
FAIRLY STRONG WINDS OVER PORTIONS OF THE EASTERN STATES. SOUTHERN  
STREAM ENERGY WILL GENERATE AN AREA OF LOCALLY HEAVY RAINFALL  
OVER/NEAR THE SOUTHERN PLAINS LATE THIS WEEK. EXPECT SOME OF THIS  
MOISTURE TO PROGRESS EASTWARD INTO NEXT WEEKEND. NORTHWARD EXTENT  
OF PRECIPITATION AND WHAT POTENTIAL THERE MAY BE FOR WINTRY  
PRECIPITATION TYPES IN THE NORTHERN FRINGE OF THE MOISTURE SHIELD  
WILL DEPEND ON LOW CONFIDENCE SPECIFICS OF SHORTWAVE ENERGY WITHIN  
THE OVERALL EASTERN U.S. TROUGH ALOFT. CURRENT GUIDANCE SIGNALS  
ARE FOR LOW COVERAGE OF ANY SNOW, PERHAPS WITH BEST POTENTIAL OVER  
THE APPALACHIANS. AT THE SAME TIME AN AREA OF MOSTLY LIGHT SNOW  
MAY CROSS PARTS OF THE UPPER MIDWEST/GREAT LAKES.  
 
THE NORTHERN-CENTRAL HIGH PLAINS AND SOME AREAS EXTENDING TO THE  
EAST WILL BE THE FOCUS FOR HIGHEST TEMPERATURE ANOMALIES DURING  
THE PERIOD WITH HIGHS AND/OR LOWS AT LEAST 10-20F ABOVE NORMAL ON  
MULTIPLE DAYS. THE ACTIVE PATTERN OVER THE WEST SHOULD CONTINUE  
TO PROMOTE ABOVE NORMAL MORNING LOWS BUT NEAR TO SOMEWHAT BELOW  
NORMAL HIGHS OVER CENTRAL/SOUTHERN AREAS. PARTS OF THE PACIFIC  
NORTHWEST/NORTHERN ROCKIES MAY SEE SOMEWHAT ABOVE NORMAL HIGHS.  
THE COMBINATION OF INITIAL UPPER TROUGHING OVER THE EAST AND THEN  
TROUGH RE-AMPLIFICATION BY NEXT WEEKEND WILL LIKELY KEEP DAYTIME  
TEMPERATURES NEAR TO SOMEWHAT BELOW NORMAL. THE NORTHEAST MAY SEE  
READINGS OF AT LEAST 10-20F BELOW NORMAL WITH NEW SNOW COVER  
FOLLOWED BY THE APPROACH OF POTENTIALLY STRONG HIGH PRESSURE.  
 
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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