962  
FXUS02 KWBC 091600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST SAT FEB 09 2019  
 
VALID 12Z TUE FEB 12 2019 - 12Z SAT FEB 16 2019  
   
..OVERVIEW
 
 
LATEST MODEL/ENSEMBLE GUIDANCE PERSISTS IN SHOWING A NORTH PACIFIC  
THROUGH ALASKA MEAN RIDGE THAT WILL BE A DOMINANT INFLUENCE ON  
DOWNSTREAM FLOW AFFECTING THE LOWER 48 STATES AND VICINITY.  
MULTI-DAY MEANS ARE REMARKABLY AGREEABLE AND CONSISTENT IN SHOWING  
A STRONG CORE OF ASSOCIATED POSITIVE HEIGHT ANOMALIES SOUTH OF THE  
ALASKA PENINSULA NEAR 50N 160W. TELECONNECTIONS RELATIVE TO THIS  
CENTER SUPPORT THE DEEP POSITIVELY TILTED MEAN TROUGH WHICH  
GUIDANCE KEEPS OVER THE PACIFIC NORTHWEST, WHILE ABOVE NORMAL  
HEIGHTS SHOULD PREVAIL OVER THE SOUTHERN/EASTERN STATES--AROUND  
THE NORTHERN PERIPHERY OF A SUBTROPICAL RIDGE. OVER RECENT DAYS  
GUIDANCE HAS BEEN SOMEWHAT INCONSISTENT WITH THE DEGREE OF  
POSITIVE HEIGHT ANOMALIES OVER THE SOUTH/EAST, WITH SOME  
DIFFERENCES NOTED AGAIN TODAY. WITHIN THIS FLOW REGIME EXPECT AN  
ACTIVE PATTERN WITH STORM SYSTEMS AFFECTING THE WEST COAST AND  
THEN INTENSIFYING AS THEY TRACK FROM THE CENTRAL PLAINS  
NORTHEASTWARD--ALONG A STRONG GRADIENT BETWEEN VERY COLD AIR OVER  
THE NORTHERN PLAINS AND WARMTH OVER THE SOUTH/EAST.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
THE MOST PROMINENT FORECAST UNCERTAINTY CONTINUES TO BE WITH UPPER  
TROUGHING FORECAST TO BE NEAR THE WEST COAST AROUND DAYS 3-4  
TUE-WED. IN THE PAST COUPLE 12-HOURLY CYCLES THE ECMWF AND ITS  
MEAN HAVE REVERTED BACK A BIT TOWARD MORE WESTWARD ELONGATION FOR  
A TIME BEFORE EJECTING INLAND. ON THE OTHER HAND THE 00Z UKMET  
STRAYS WELL AHEAD OF OTHER GUIDANCE, LEAVING THE 00-06Z GFS/GEFS  
MEAN AND CMC AS THE INTERMEDIATE SOLUTIONS. AT THE SAME TIME AS  
GUIDANCE SPREAD FOR THIS TROUGH INCREASES, THERE IS BEEN AN  
INCREASING SIGNAL TOWARD A LOW LATITUDE WAVE APPROACHING  
CALIFORNIA, WITH DEVELOPMENT ALONG A FORMING FRONTAL BOUNDARY TO  
THE EAST OF THE STRONG STORM AFFECTING HAWAI'I. THE EXACT TIMING  
OF THE NORTHERN STREAM TROUGH WILL BE CRUCIAL FOR DETERMINING THE  
TRACK/STRENGTH OF THE LOW LATITUDE WAVE. OVERALL PREFERENCE AT  
THIS TIME IS FOR AN INTERMEDIATE SOLUTION NO SLOWER THAN A  
COMPROMISE BETWEEN GFS/GEFS/CMC AND ECMWF/ECMWF MEAN CLUSTERS,  
GIVEN SPACING CONSIDERATIONS RELATIVE TO RAPIDLY APPROACHING  
UPSTREAM NORTH PACIFIC SHORTWAVE ENERGY. THIS SOLUTION REMAINS  
CLOSE TO CONTINUITY, WITH A LOW LATITUDE WAVE THAT IS WEAKER AND  
FARTHER SOUTH THAN DEPICTED IN THE PAST COUPLE ECWMF RUNS.  
 
AS THE WESTERN TROUGH EJECTS EASTWARD, GUIDANCE ACTUALLY TRENDS  
CLOSER TOGETHER FOR THE OVERALL TROUGH AXIS BUT DIFFERS  
CONSIDERABLY OVER EXACT DISTRIBUTION OF ENERGY WITHIN THE TROUGH  
AND DEPTH OF ANY EMBEDDED UPPER LOW. AS A RESULT THERE IS WIDE  
ARRAY OF POSSIBLE SURFACE LOW TRACK/DEPTH--AS SHOWN BY A  
BROAD/POORLY CLUSTERED SPREAD OF SURFACE LOWS AMONG THE ENSEMBLES.  
OVER THE EASTERN HALF OF THE COUNTRY BY FRI-SAT THE GFS/GEFS  
MEAN/CMC RUNS SHOW GREATER UPPER TROUGH AMPLITUDE VERSUS OTHER  
GUIDANCE OR WHAT WOULD BE FAVORED BY THE TELECONNECTION-FAVORED  
PATTERN SO PREFERENCES WOULD BE TO LEAN AWAY FROM THAT SCENARIO  
LATE IN THE PERIOD. NOTE THAT IN RECENT DAYS SOME GUIDANCE HAD  
BEEN MORE AMPLIFIED ALOFT THAN CURRENT FORECAST FOR THE LEADING  
SYSTEM EXPECTED TO AFFECT THE EAST EARLY IN THE PERIOD. AS FOR  
THIS LEADING SYSTEM, A MAJORITY CLUSTER APPROACH PROVIDES A  
REASONABLE STARTING POINT FOR THE FORECAST.  
 
OVERALL THE NEXT STORM SYSTEM APPROACHING THE PACIFIC NORTHWEST BY  
LATE WEEK/WEEKEND SHOWS AVERAGE OR BETTER AGREEMENT RELATIVE TO  
TYPICAL DAYS 6-7 FORECASTS. THE 00-06Z GFS RUNS LEAN SOMEWHAT  
TOWARD THE SOUTHWESTERN PART OF THE FULL GUIDANCE ENVELOPE FOR THE  
UPPER SYSTEM AND SURFACE LOW CENTER SO PREFER TO LEAN AWAY FROM  
THE GFS SOLUTION FOR THIS PART OF THE FORECAST.  
 
AS FORECAST CONSIDERATIONS EVOLVE OVER THE COURSE OF THE PERIOD,  
THE STARTING BLEND USED SOMEWHAT MORE TOTAL 00-06Z GFS/00Z CMC  
CONTRIBUTION RELATIVE TO THE PAST COUPLE ECMWF RUNS DAYS 3-5  
TUE-THU AND THEN TRANSITIONED TO MORE ECMWF/ECMWF MEAN WEIGHT BY  
DAY 7 SAT.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
OVER THE WEST EXPECT ONE PERIOD OF ENHANCED PRECIPITATION TO  
SPREAD ACROSS THE REGION TUE-THU WITH THE COMBINATION OF A PACIFIC  
NORTHWEST SYSTEM AND POSSIBLE LOWER LATITUDE WAVE THAT COULD BRING  
A SURGE OF HEAVY RAIN AND HIGH ELEVATION SNOW TO CALIFORNIA  
INCLUDING SOUTHERN PARTS OF THE STATE. ANOTHER AREA OF MOISTURE  
IS LIKELY TO OVERSPREAD PARTS OF THE WEST FROM THU OR THU NIGHT  
INTO THE WEEKEND WITH THE NEXT SYSTEM DROPPING SOUTHEASTWARD  
TOWARD THE PACIFIC NORTHWEST. AS HAS BEEN THE CASE WITH THE  
PRECEDING SYSTEM THERE IS CONSIDERABLE UNCERTAINTY OVER THE  
SOUTHWARD EXTENT/INTENSITY OF PRECIPITATION OVER CALIFORNIA.  
PERSISTENTLY COLD TEMPERATURES WILL MAINTAIN THE THREAT FOR SNOW  
AT VERY LOW ELEVATIONS OVER THE NORTHWEST, WHILE RAIN AND HIGHER  
ELEVATION SNOW WILL PREVAIL FARTHER SOUTH. OVER THE INTERIOR WEST  
AND ROCKIES THE MAJORITY OF PRECIPITATION SHOULD BE SNOW EXCEPT  
OVER SOUTHERN AREAS. EXPECT HIGHEST 5-DAY TOTALS OVER WESTERN  
OREGON AND NORTHERN-CENTRAL CALIFORNIA.  
 
THE SYSTEM TRACKING FROM THE MIDWEST INTO GREAT LAKES/NORTHEAST  
TUE-WED WILL BRING POTENTIALLY MODERATE TO HEAVY SNOWFALL TO AREAS  
NORTH OF THE LOW TRACK. OVERRUNNING MOISTURE NORTH OF THE LEADING  
WARM FRONT MAY ALSO BRING WINTRY PRECIPITATION TO PORTIONS OF THE  
MID-ATLANTIC AND NORTHEAST, WITH THE POTENTIAL FOR HEAVIER SNOW  
ACROSS PORTIONS OF NEW ENGLAND AS ANOTHER LOW CENTER DEVELOPS  
ALONG THE COAST TUE NIGHT/EARLY WED. THE STORM SYSTEM EMERGING  
FROM THE WEST BY THU AND THEN TRACKING NORTHEASTWARD SHOULD BRING  
ANOTHER WIDESPREAD AREA OF PRECIPITATION TO THE EASTERN HALF OF  
THE COUNTRY LATE WEEK INTO THE WEEKEND. DEPENDING ON SIMILARITY  
OF TRACK, WINTER WEATHER IMPACTS MAY COVER SOME OF THE SAME AREAS  
AFFECTED BY THE PRECEDING STORM. WARM SECTOR RAINFALL MAY BE  
HEAVY OVER AND SOMEWHAT NORTHWESTWARD OF THE SOUTHEAST.  
 
WITHIN THE BROAD AREA OF BELOW NORMAL TEMPERATURES OVER THE WEST  
AND NORTHERN PLAINS, EXPECT THE MOST EXTREME ANOMALIES OVER THE  
NORTHERN PLAINS AND TO SOME DEGREE THE INTERIOR OF THE NORTHWEST  
WITH SOME READINGS 15-25F BELOW NORMAL. WITHIN THE GENERALLY WARM  
PATTERN OVER THE SOUTH/EAST (ALBEIT WITH SOME DAY-TO-DAY  
VARIABILITY DUE TO SYSTEM PROGRESSION) THERE MAY BE MULTIPLE DAYS  
WITH TEMPERATURES OF AT LEAST 10-20F ABOVE NORMAL.  
 
RAUSCH  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES 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  
 

 
 
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