475  
FXUS02 KWBC 011600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST TUE JAN 01 2019  
 
VALID 12Z FRI JAN 04 2019 - 12Z TUE JAN 08 2019  
   
..OVERVIEW
 
 
THE MAJORITY OF GUIDANCE GENERALLY SHOWS A TROUGH-RIDGE-TROUGH  
PATTERN ALOFT FROM THE MULTI-DAY MEAN PERSPECTIVE, WITH EMBEDDED  
FEATURES SHOWING AT LEAST A MODERATE DEGREE OF PROGRESSION. THE  
FLOW WILL BE SUFFICIENTLY PROGRESSIVE TO LOWER PREDICTABILITY OF  
INDIVIDUAL FEATURES AND UNCERTAINTY OVER INTERACTION AMONG  
SEPARATE STREAMS WILL ADD COMPLEXITY TO THE FORECAST. THIS  
PATTERN SHOULD PROMOTE MULTIPLE EPISODES OF SIGNIFICANT  
PRECIPITATION OVER PARTS OF THE WEST COAST WHILE A LEADING SYSTEM  
TRACKING NORTHEAST FROM THE LOWER MISSISSIPPI VALLEY LATE THIS  
WEEK INTO THE WEEKEND SHOULD PRODUCE ANOTHER AREA OF MEANINGFUL  
PRECIPITATION TO PORTIONS OF THE EAST.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
FOR THE SYSTEM TRACKING NORTHEAST FROM THE LOWER MISSISSIPPI  
VALLEY DAY 3 FRI ONWARD, GUIDANCE HAS DISPLAYED A PRONOUNCED  
SLOWER TREND OVER THE PAST COUPLE DAYS WITH ECMWF/ECMWF MEAN RUNS  
CATCHING ONTO THIS TREND A BIT SOONER THAN THE GFS AND ESPECIALLY  
GEFS MEAN. THE SLOWER TRENDS FAVOR LEANING AT LEAST 2/3 TOWARD  
THE GFS/ECMWF WHOSE LATEST RUNS AS OF 00Z/06Z ARE A BIT SLOWER  
THAN THE 00Z UKMET/CMC.  
 
FARTHER WESTWARD, ALREADY BY DAY 4 SAT THERE IS SIGNIFICANT  
GUIDANCE SPREAD WITH A SYSTEM THAT MOST GUIDANCE BRINGS CLOSE TO  
THE WEST COAST. RAPID DEVELOPMENT FROM INITIALLY LOW  
AMPLITUDE/PROGRESSIVE ENERGY SUGGESTS IT MAY TAKE WELL INTO THE  
SHORT RANGE TIME FRAME TO RESOLVE. NORTH-SOUTH SPREAD AMONG  
ENSEMBLE MEMBERS IS VERY WIDE AND RUN-RUN MODEL/ENSEMBLE SPREAD  
FOR DEPTH IS CONSIDERABLE AS WELL. AT THE MOMENT THE OPERATIONAL  
GFS RUNS ARE DEEPEST WHILE THE 00Z CMC DETACHES A LOW FROM THE  
WESTERLIES LEADING TO A COMPLETELY DIFFERENT EVOLUTION OFFSHORE  
CALIFORNIA AND EXTREME NORTHWEST MEXICO. AN INTERMEDIATE SOLUTION  
CLOSEST TO THE 00Z ECMWF APPEARS TO BE THE BEST STARTING POINT  
GIVEN THE FULL RANGE OF GUIDANCE, BUT AGAIN WITH FAIRLY LOW  
CONFIDENCE.  
 
AS THE OVERALL TROUGH PROGRESSES EASTWARD, THERE HAS BEEN A LOT OF  
SPREAD AND RUN-RUN VARIABILITY WITH TIMING AND DEGREE OF PHASING.  
THE PAST COUPLE ECMWF RUNS RACE AHEAD OF LATEST GEFS/ECMWF MEAN  
RUNS. THE 00Z GFS MATCHES UP WITH THE MEANS BETTER UNTIL BECOMING  
A LITTLE FASTER WITH THE NEXT UPPER TROUGH NEARING THE WEST COAST  
TOWARD THE END OF THE PERIOD NEXT TUE. ON THE OTHER HAND THE 06Z  
GFS BRINGS A FAIRLY STRONG TROUGH INTO THE NORTHWEST ON DAY 6 MON,  
A SCENARIO DIFFERENT FROM MOST OTHER SOLUTIONS. THE CMC/CMC MEAN  
SHOW GREATER SEPARATION AND THUS MUCH SLOWER SOUTHERN STREAM  
TIMING, BUT GEFS MEAN TRENDS TOWARD THE ECMWF MEAN (PLUS SUPERIOR  
VERIFICATION FOR SOME FEATURES WITHIN PACIFIC/WESTERN NORTH  
AMERICAN FLOW OVER RECENT WEEKS) SUGGEST GREATER PROBABILITY OF  
THE CURRENT GEFS/ECMWF MEANS.  
 
BASED ON THESE CONSIDERATIONS A GENERAL MODEL BLEND ON DAY 3 FRI  
REMOVES THE CMC THEREAFTER, THEN THE UKMET AFTER DAY 4 SAT DUE TO  
BECOMING SLOWER THAN CONSENSUS WITH THE WEST COAST TROUGH, THE  
ECMWF AFTER DAY 5 SAT GIVEN ITS FASTER WESTERN TROUGH PROGRESSION.  
THEN 00Z GFS WEIGHT DECREASED DAY 7 TUE. 06Z GEFS/00Z ECMWF MEAN  
WEIGHT INCREASED WITH THE GRADUAL REDUCTION OF OPERATIONAL MODEL  
INPUT.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
WHILE SPECIFICS REMAIN UNCERTAIN, THE OVERALL PATTERN SHOULD BE  
FAVORABLE FOR SIGNIFICANT RAINFALL AND HIGH ELEVATION SNOW NEAR  
THE WEST COAST DURING THE PERIOD. THE BEST POTENTIAL FOR HIGHEST  
5-DAY TOTALS WILL BE CENTERED OVER OR NEAR NORTHERN CALIFORNIA  
WITH SOME LOCATIONS POSSIBLY RECEIVING AT LEAST 5-10 INCHES LIQUID  
DURING FRI-TUE. FAVORED LOCATIONS OVER WESTERN WASHINGTON/OREGON  
AND NORTHERN ROCKIES WILL LIKELY SEE SIGNIFICANT TOTALS AS WELL.  
IN LESS EXTREME FASHION SOME MOISTURE SHOULD EXTEND FARTHER  
SOUTHWARD OVER CALIFORNIA AND THE INTERIOR WEST/ROCKIES.  
DEPENDING ON HOW THE STORM FORECAST TO BE NEAR THE WEST COAST ON  
SAT EVOLVES THERE COULD BE AREAS WITH STRONG WINDS.  
 
OVER THE EAST, THE SYSTEM TRACKING NORTHEASTWARD FROM THE LOWER  
MISSISSIPPI VALLEY LATE THIS WEEK INTO THE WEEKEND SHOULD PRODUCE  
SOME AREAS OF LOCALLY MODERATE TO HEAVY RAINFALL. THE  
MID-MISSISSIPPI VALLEY THROUGH OHIO VALLEY INTO  
MID-ATLANTIC/SOUTHERN NEW ENGLAND MAY BE ONE FAVORED AREA FOR  
ENHANCED RAINFALL, JUST NORTH OF THE UPPER LOW TRACK. BRIEFLY  
INTENSE RAINFALL COULD CROSS THE SOUTHEAST AHEAD OF THE COLD FRONT  
TRAILING FROM THE SURFACE LOW. THE MAJORITY OF PRECIPITATION WITH  
THIS SYSTEM SHOULD BE IN THE FORM OF RAIN. ANY WINTRY PRECIP  
TYPES SHOULD BE CONFINED TO THE VERY NORTHERN/NORTHWESTERN FRINGE  
OF THE MOISTURE SHIELD. A WAVY FRONTAL SYSTEM EMERGING FROM THE  
PLAINS MAY BRING AN EPISODE OF LIGHT TO MODERATE PRECIPITATION TO  
PARTS OF THE EASTERN HALF OF THE LOWER 48 DURING THE LATTER HALF  
OF THE PERIOD. WINTRY PRECIP TYPES SHOULD AGAIN BE CONFINED TO  
FAR NORTHERN LATITUDES.  
 
THE EXPECTED PATTERN ALOFT WILL TEND TO FAVOR BELOW NORMAL HIGH  
TEMPERATURES OVER THE SOUTHWEST/FOUR CORNERS REGION, WITH THE  
SOUTHERN ROCKIES AND VICINITY ALSO ON THE COOL SIDE FOR MINS LATE  
THIS WEEK. OTHERWISE EXPECT FAIRLY MILD TEMPERATURES FOR THE TIME  
OF YEAR, ESPECIALLY FOR MORNING LOWS. SOME LOCATIONS OVER THE  
EXTREME NORTHERN TIER MAY SEE LOWS AT LEAST 20-30F ABOVE NORMAL  
FRI-SAT.  
 
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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