614  
FXUS02 KWBC 101601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST SUN FEB 10 2019  
 
VALID 12Z WED FEB 13 2019 - 12Z SUN FEB 17 2019  
   
..OVERVIEW
 
 
FROM THE MULTI-DAY MEAN PERSPECTIVE THE MODELS AND MEANS ARE  
FAIRLY STABLE AND AGREEABLE IN SHOWING A REX BLOCK CONFIGURATION  
OVER THE EAST-CENTRAL PACIFIC, WITH THE RIDGE THAT EXTENDS INTO  
ALASKA SUPPORTING A POSITIVELY TILTED DOWNSTREAM TROUGH NEAR THE  
WEST COAST. OVER TIME THE CORE OF NEGATIVE HEIGHT ANOMALIES  
WITHIN THIS TROUGH MAY DRIFT A FRACTION EASTWARD FROM THE PACIFIC  
NORTHWEST COAST. MEAN FLOW TO THE EAST OF THE TROUGH SHOULD  
GENERALLY BE WEST-SOUTHWESTERLY, WITH WEAKER EVIDENCE OF  
SOUTHEASTERN RIDGING THAN EXPECTED IN THE SHORT RANGE TIME FRAME  
EARLY THIS WEEK. WITHIN THIS BROAD SCALE PATTERN THERE CONTINUE  
TO BE SIGNIFICANT UNCERTAINTIES REGARDING PHASING/STREAM  
INTERACTION FOR INDIVIDUAL FEATURES AND THUS CORRESPONDING  
SENSIBLE WEATHER EFFECTS. HOWEVER THE SPECIFICS TURN OUT, THE  
PATTERN SHOULD PROMOTE PERIODS OF SIGNIFICANT PRECIPITATION OVER  
AREAS OF THE WEST AS WELL AS OVER THE NORTH-CENTRAL PLAINS AND  
MUCH OF THE EAST AS DEEPENING LOW PRESSURE TRACKS ALONG THE STRONG  
GRADIENT BETWEEN VERY COLD AIR OVER THE NORTHERN STATES AND WARMTH  
OVER THE SOUTH.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
AT THE START OF THE PERIOD CONFIDENCE IS MUCH LOWER THAN WOULD  
TYPICALLY BE THE CASE FOR A DAY 3 FORECAST REGARDING TROUGH  
EVOLUTION ALONG THE WEST COAST, WITH THE FEATURE COMPOSED OF  
MULTIPLE PIECES OF SHORTWAVE ENERGY. OVER THE PAST 24-36 HOURS  
THE MAJORITY OF GUIDANCE HAS MADE A PRONOUNCED SHIFT TOWARD A  
SLOWER/SHARPER TROUGH THAT RECENT ECMWF RUNS HAVE BEEN ADVERTISING  
VERSUS THE FLATTER AND MORE PROGRESSIVE SCENARIO WHICH NOW IS  
DEPICTED ONLY BY THE GFS. THE 00Z GFS/FV3 GFS IS A LITTLE CLOSER  
TO THE ECMWF CLUSTER THAN THE 06Z GFS. PREFERENCE MORE TOWARD THE  
CURRENT MAJORITY WOULD LEAD TO STRONGER LOW PRESSURE ALONG THE  
WEST COAST AT THE START OF THE PERIOD AND A SIGNIFICANT INFLOW OF  
LOW LATITUDE MOISTURE INTO CALIFORNIA. CONSULT THE MODEL  
DIAGNOSTICS DISCUSSION PMDHMD FOR UPDATED PREFERENCES BASED ON NEW  
12Z GUIDANCE.  
 
THE FORECAST OF LOW PRESSURE PROGRESSING THROUGH THE WEST AND THEN  
LIKELY DEEPENING AS IT TRACKS NORTHEAST FROM THE CENTRAL PLAINS  
WILL DEPEND NOT ONLY ON THE SHORTWAVE SPECIFICS INITIALLY NEAR THE  
WEST COAST AND HOW THE ENERGY EVOLVES OVER THE CENTRAL U.S., BUT  
THEN THE DEGREE OF INTERACTION WITH NORTHERN STREAM FLOW OVER THE  
CENTRAL/EASTERN STATES. ULTIMATELY THERE IS ACTUALLY STILL DECENT  
AGREEMENT IN PRINCIPLE ON THE GENERAL LONGITUDE OF UPPER TROUGHING  
BUT INDIVIDUAL MODELS/ENSEMBLE MEMBERS ARE STILL QUITE DISPERSED  
FOR THE SURFACE LOW DUE TO VARIATIONS IN ENERGY/PHASING ALOFT.  
BEST CONSENSUS HAS THE SURFACE SYSTEM REACHING THE MIDDLE  
MISSISSIPPI VALLEY BY DAY 5 FRI AND NEAR THE EASTERN GREAT LAKES  
BY DAY 6 SAT. THE 06Z GEFS MEAN AND 00Z FV3 GFS APPEAR LESS  
LIKELY WITH LOW TRACKS FARTHER NORTH THAN MOST OTHER MODELS/MEANS.  
AS THE UPPER TROUGH REACHES THE EAST, GFS RUNS AND THE 06Z  
VERSION IN PARTICULAR MAY STILL BE OVERDOING THE AMPLITUDE OF THE  
UPPER TROUGH GIVEN TELECONNECTION-FAVORED FLOW THAT FAVORS SOME  
DEGREE OF ABOVE AVERAGE HEIGHTS ALOFT. NOTE THAT THIS  
RELATIONSHIP DOES NOT PRECLUDE AN AMPLIFIED TROUGH THAT IS  
SUFFICIENTLY PROGRESSIVE BUT OTHER GUIDANCE IS SOMEWHAT CLOSER TO  
THE FAVORED PATTERN.  
 
THE NEXT SYSTEM TRACKING SOUTHEASTWARD TOWARD THE PACIFIC  
NORTHWEST LATE THIS WEEK INTO THE WEEKEND SHOWS BETTER THAN  
AVERAGE CLUSTERING, WITH AN AVERAGE AMONG MODELS/ENSEMBLE MEANS  
GENERALLY PROVIDING A REASONABLE STARTING POINT. TOWARD THE END  
OF THE PERIOD LATE IN THE WEEKEND THE GUIDANCE SPREAD INCREASES  
FOR DETAILS OF THE OVERALL MEAN TROUGH, IN RESPONSE TO DIFFERENCES  
IN HOW UPSTREAM SHORTWAVE ENERGY HEADS INTO THE MEAN RIDGE.  
DIFFERENCES ARE GENERALLY WITHIN TYPICAL ERROR RANGE FOR DAY 7  
FORECASTS SO AN INTERMEDIATE MODEL/ENSEMBLE MEAN SOLUTION WOULD BE  
REASONABLE, TONING DOWN THE MORE WESTERN NORTHERN PART OF THE AXIS  
IN THE 00Z ECMWF/CMC VERSUS SHARPER/MORE ELONGATED SOUTHERN PART  
OF THE TROUGH IN THE GFS RUNS (WHICH CREATES SOMEWHAT MORE  
WEST-CENTRAL U.S. SHORTWAVE RIDGING THAN WHAT MAY BE FAVORED BY  
TELECONNECTIONS). HOWEVER DOWNSTREAM AS MENTIONED ABOVE THE GFS  
IS SOMEWHAT MORE QUESTIONABLE--THUS TILTING THE OVERALL BLEND  
SOMEWHAT MORE IN THE ECMWF/ECMWF MEAN DIRECTION.  
 
FINALLY, AROUND MIDWEEK A CONSENSUS APPROACH LOOKS GOOD FOR THE  
STORM SYSTEM OVER/NEAR NEW ENGLAND WITH A TRIPLE POINT DEVELOPMENT  
TAKING OVER AND TRACKING INTO OR NEAR THE CANADIAN MARITIMES.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
AREAS OF THE WEST WILL SEE SIGNIFICANT PRECIPITATION DURING THE  
PERIOD WITH MEAN TROUGHING SUPPORTING PERIODS OF ACTIVE WEATHER.  
RAIN AND HIGHER ELEVATION SNOW MAY BE PARTICULARLY HEAVY OVER  
CALIFORNIA AROUND WED-THU AS A POTENTIALLY COMPLEX SYSTEM COULD  
PROMOTE A FLOW OF LOW LATITUDE MOISTURE INTO THE AREA. THIS  
SYSTEM WILL THEN SPREAD MOISTURE ACROSS THE REMAINDER OF THE  
INTERIOR WEST AND ROCKIES. ADDITIONAL THOUGH LESS EXTREME  
MOISTURE SHOULD REACH THE NORTHWEST AND CENTRAL WEST COAST LATE  
WEEK INTO THE WEEKEND AS LOW PRESSURE TRACKS TOWARD THE PACIFIC  
NORTHWEST. SNOW LEVELS WILL LIKELY REMAIN QUITE LOW OVER THE  
NORTHWEST THROUGH THE WEEKEND.  
 
EXPECT THE LOW PRESSURE SYSTEM AFFECTING NEW ENGLAND ON WED TO  
PRODUCE WINTRY PRECIPITATION ACROSS MUCH OF NEW ENGLAND WITH BEST  
POTENTIAL FOR HEAVIEST SNOW OVER PORTIONS OF NORTHERN MAINE. THE  
NEXT DEEPENING LOW PRESSURE SYSTEM MOVING FROM THE CENTRAL U.S.  
TOWARD THE GREAT LAKES THU ONWARD COULD PRODUCE AN AREA OF WINTRY  
WEATHER NORTH OF THE LOW TRACK, ACROSS PORTIONS OF THE  
MIDWEST/GREAT LAKES ON THU AND PERHAPS PORTIONS OF NEW ENGLAND ON  
FRI-SAT. LOWER THAN DESIRED CONFIDENCE IN THE TRACK OF THIS  
SECOND SYSTEM CONTINUES TO MAKE IT DIFFICULT TO PINPOINT EXACT  
LOCATIONS AND DEGREE OF WINTER WEATHER IMPACTS. FARTHER SOUTH  
THIS SECOND SYSTEM SHOULD PRODUCE WIDESPREAD SHOWERS AND  
THUNDERSTORMS AS GULF OF MEXICO MOISTURE STREAMS NORTHWARD INTO  
THE DEEPENING SURFACE LOW. LOCALLY HEAVY RAINS WILL BE POSSIBLE  
FROM PORTIONS OF THE SOUTHEAST/TENNESSEE VALLEY REGIONS TO THE  
MID-ATLANTIC.  
 
THE PATTERN WILL CONTINUE TO FAVOR VERY COLD TEMPERATURES FROM THE  
PACIFIC NORTHWEST TO THE NORTHERN ROCKIES AND NORTHERN PLAINS  
THROUGH THE WEEK. HIGH TEMPERATURES OF 15 TO 30 DEG F BELOW  
AVERAGE ARE LIKELY ACROSS MANY OF THESE AREAS THROUGH THE FORECAST  
PERIOD. ANOMALIES COULD BECOME EVEN A LITTLE MORE EXTREME OVER  
THE EXTREME NORTHERN PLAINS BY NEXT SUN. MEANWHILE AREAS FROM THE  
SOUTHERN/CENTRAL PLAINS TO THE EASTERN SEABOARD WILL SEE NEAR TO  
ABOVE AVERAGE TEMPERATURES VARYING BY DAY WITH THE WARMEST  
TEMPERATURES AHEAD OF THE LATE WEEK LOW PRESSURE SYSTEM, WHEN  
HIGHS MAY REACH 10 TO 15 DEG ABOVE AVERAGE FOR SOME AREAS.  
ANOMALIES FOR MORNING LOWS COULD BE SOMEWHAT HIGHER.  
 
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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