945  
FXUS02 KWBC 021600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST WED JAN 02 2019  
 
VALID 12Z SAT JAN 05 2019 - 12Z WED JAN 09 2019  
   
..OVERVIEW
 
 
GUIDANCE THUS FAR HAS BEEN CONSISTENT WITH THE ESTABLISHMENT OF  
MEAN TROUGHING JUST OFF THE WEST COAST, A RIDGE OVER THE CENTRAL  
U.S., AND EVENTUALLY AN AMPLIFYING MEAN TROUGH NEAR THE EAST  
COAST. DETAILS FOR SOME INDIVIDUAL FEATURES CONTINUE TO HAVE A  
FAIR DEGREE OF UNCERTAINTY BUT THERE IS BETTER CONFIDENCE IN THE  
THEME OF ACTIVE WEATHER ALONG PARTS OF THE WEST COAST AND SOME  
INLAND LOCATIONS OVER THE WEST. AS THE UPPER SUPPORT FOR A  
LEADING EASTERN PACIFIC SYSTEM PROGRESSES ACROSS THE LOWER 48 IT  
MAY PRODUCE A STORM SYSTEM AFFECTING THE EASTERN U.S. BY THE  
EARLY-MIDDLE PART OF NEXT WEEK. ALSO IN THAT TIME FRAME ANOTHER  
EASTERN PACIFIC SYSTEM SHOULD APPROACH WESTERN NORTH AMERICA BUT  
WITH A FARTHER NORTH TRACK THAN ITS SAT-SUN PREDECESSOR.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
DURING THE FIRST HALF OF THE PERIOD A COMPROMISE AMONG 00Z  
DETERMINISTIC MODEL IDEAS PROVIDED A GOOD STARTING POINT FOR THE  
OVERALL FORECAST. THE STRONG STORM FORECAST TO BE OFF THE WEST  
COAST AS OF EARLY DAY 3 SAT SHOWS BETTER CLUSTERING THAN 24 HOURS  
AGO BUT THERE IS STILL A MODERATE DEGREE OF SPREAD FOR INTENSITY  
AND TIMING. SMALL SCALE ASPECTS OF SYSTEM EVOLUTION WILL CONTINUE  
TO BE IMPORTANT AND REQUIRE MONITORING INTO THE SHORT RANGE TIME  
FRAME. AT THE VERY LEAST TRENDS FROM YESTERDAY SUGGEST THE MODELS  
ARE TRYING TO CONVERGE WITHIN THE DEEPER HALF OF THE PRIOR  
ENVELOPE, BUT OPPOSING DEEPER ECMWF/WEAKER GFS TRENDS ARE  
DISCONCERTING. PREFER TO LEAN AWAY FROM THE 06Z GFS AS IT IS  
WEAKER/SOUTHEAST VERSUS OTHER GUIDANCE WITH THIS LEADING STORM AND  
THEN INTRODUCES A TRAILING EXTRANEOUS SHORTWAVE/SURFACE SYSTEM  
REACHING THE WEST LATE SUN-MON. MEANWHILE GUIDANCE APPEARS TO  
HAVE STABILIZED FOR THE DEPICTION OF THE SYSTEM DEPARTING FROM THE  
EAST COAST THIS WEEKEND.  
 
AS THE LEADING EASTERN PACIFIC TROUGH PROGRESSES THROUGH THE WEST  
INTO THE PLAINS, THE PAST COUPLE ECMWF RUNS ARE CLOSER TO THE  
ENSEMBLE MEANS AND RECENT GFS RUNS FROM 00Z/12Z CYCLES.  
INDIVIDUAL ENSEMBLE MEMBERS STILL DISPLAY MEANINGFUL SPREAD FOR  
THE DEGREE OF PHASING BETWEEN NORTHERN AND SOUTHERN STREAMS, BUT  
FASTER/MORE PHASED TRENDS SEEN IN THE UKMET/CMC TOWARD THE MEANS  
PROVIDE SOME CONFIDENCE IMPROVEMENT VERSUS 24 HOURS AGO. OVER THE  
EASTERN HALF OF THE LOWER 48 BY TUE-WED THE CONTRASTING PAST TWO  
ECMWF RUNS PROVIDE A SIMPLE ILLUSTRATION OF DETAIL UNCERTAINTIES  
THAT REMAIN FOR THE OVERALL TROUGH, BEYOND WHAT THE UPSTREAM  
SHORTWAVE DIFFERENCES IN THE 06Z GFS PRODUCE. HOWEVER FOR THE  
PURPOSES OF A DETERMINISTIC FORECAST THE ENSEMBLE MEANS PROVIDE  
THE MOST CONSISTENT STARTING POINT, WITH THE 00Z GFS/ECMWF  
SUFFICIENTLY CLOSE IN PRINCIPLE TO PROVIDE ABOUT HALF WEIGHT FOR  
ENHANCING THE MEANS. THIS SOLUTION CONTINUES RECENT SLOWER TRENDS  
FOR THE SYSTEM EMERGING FROM THE PLAINS BUT OTHERWISE BY TUE-WED  
MAINTAINS THE IDEA OF A DEFINED STORM SYSTEM TRACKING FROM THE  
GREAT LAKES TO JUST OFF THE NEW ENGLAND COAST TUE-WED. THE 00Z  
CMC WAS REMOVED FROM THE BLEND AFTER DAY 5 MON DUE TO BEING  
NOTABLY SLOWER THAN CONSENSUS.  
 
THERE IS BETTER THAN AVERAGE AGREEMENT RELATIVE TO THE FORECAST  
PROJECTION FOR THE NEXT EASTERN PACIFIC UPPER TROUGH AS OF DAY 6  
TUE. LOW CONFIDENCE EMBEDDED DETAILS WILL DETERMINE SPECIFICS OF  
THE ASSOCIATED SURFACE LOW BUT A SIZABLE MAJORITY OF GUIDANCE  
SHOWS A SURFACE LOW TRACK FARTHER NORTHWEST THAN FOR THE SYSTEM  
ARRIVING DURING THE WEEKEND. BY DAY 7 WED THE SPECIFICS OF  
PROGRESSIVE NORTH PACIFIC FLOW WILL LIKELY BEGIN TO HAVE SOME  
INFLUENCE ON THE CHARACTER OF THE TROUGH NEARING THE WEST COAST.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
CONTINUE TO EXPECT PERIODS OF ACTIVE WEATHER OVER THE WEST, WITH A  
STRONG SYSTEM OFF THE CENTRAL WEST COAST AS OF EARLY SAT LIKELY  
BRINGING ONE EPISODE OF HEAVY RAIN/MOUNTAIN SNOW AND POSSIBLY  
STRONG WINDS FOLLOWED BY AT LEAST ONE OR TWO OTHER EVENTS. THE  
CENTRAL WEST COAST REGION, INCLUDING NORTHERN CALIFORNIA AND  
SOUTHWESTERN OREGON, HAS THE GREATEST PROBABILITY OF SEEING THE  
HIGHEST 5-DAY TOTALS WITH SOME LOCATIONS RECEIVING 5-10 INCHES  
LIQUID. SIGNIFICANT PRECIPITATION IS ALSO LIKELY OVER THE PACIFIC  
NORTHWEST AND NORTHERN ROCKIES. ESPECIALLY WITH THE FIRST SYSTEM  
EXPECT MOISTURE TO EXTEND FARTHER SOUTH THROUGH CALIFORNIA AND THE  
SOUTHWEST INTO PARTS OF THE ROCKIES. THE FRONT TRAILING FROM THE  
WEEKEND STORM MAY INTERACT WITH LOWER LATITUDE EASTERN PACIFIC  
MOISTURE/WAVINESS AND ENHANCE RAIN/HIGHER ELEVATION SNOW OVER  
PARTS OF SOUTHERN ARIZONA AND THE SOUTHERN ROCKIES. THE PRECISE  
AXIS OF THIS MOISTURE WILL TAKE SOME ADDITIONAL TIME TO RESOLVE  
THOUGH.  
 
AS ENERGY ALOFT PROGRESSES ACROSS THE LOWER 48, EXPECT SOME DEGREE  
OF LOW PRESSURE DEVELOPMENT FROM THE PLAINS INTO NORTHEAST/WESTERN  
ATLANTIC MON-WED. THIS SYSTEM MAY INCORPORATE SOME OF THE  
AFOREMENTIONED PACIFIC MOISTURE TO INCREASE PRECIPITATION AMOUNTS  
OVER THE EAST, WITH HIGHEST TOTALS CURRENTLY INDICATED OVER THE  
GREAT LAKES/NEW ENGLAND WITH MEANINGFUL ACTIVITY POSSIBLY  
EXTENDING FARTHER SOUTH. THE UPPER GREAT LAKES AND NEW ENGLAND  
SHOULD SEE THE HIGHEST SNOWFALL POTENTIAL WITH THIS SYSTEM. THE  
SYSTEM DEPARTING FROM THE EAST COAST THIS WEEKEND SHOULD BRING  
MOSTLY RAIN TO PARTS OF THE MID-ATLANTIC/NEW ENGLAND WITH ANY  
WINTRY PRECIPITATION TYPES LIKELY CONFINED TO THE FAR NORTHERN  
PART OF THE MOISTURE SHIELD.  
 
THE LARGE SCALE PATTERN WILL SUPPORT NEAR TO SOMEWHAT BELOW NORMAL  
HIGH TEMPERATURES OVER THE SOUTHWEST FOR MOST OF THE PERIOD.  
COOLEST ANOMALIES SHOULD BE ON SUN WITH SOME LOCATIONS 5-10F BELOW  
NORMAL. OTHERWISE EXPECT TEMPERATURES TO BE ABOVE NORMAL OVER A  
MAJORITY OF THE LOWER 48, THOUGH THE EAST COAST MAY TREND DOWN AT  
LEAST TO NORMAL BY NEXT WED AS UPPER TROUGHING AMPLIFIES OVER THE  
REGION. WARM ANOMALIES TO THE EAST OF THE ROCKIES WILL BE MOST  
PRONOUNCED FOR MORNING LOWS, WITH PLUS 20F OR GREATER DEPARTURES  
FROM NORMAL LIKELY ON MULTIPLE DAYS FROM THE NORTHERN PLAINS  
THROUGH THE UPPER MISSISSIPPI VALLEY AND FROM THE SOUTHERN PLAINS  
INTO OHIO VALLEY AROUND MON-TUE.  
 
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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