847  
FXUS02 KWBC 071557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1156 AM EDT THU JUN 07 2018  
 
VALID 12Z SUN JUN 10 2018 - 12Z THU JUN 14 2018  
   
..PATTERN OVERVIEW
 
 
GUIDANCE CONTINUES TO SUGGEST AN EVOLUTION FROM AN OMEGA BLOCK  
APPEARANCE OVER CANADA AND ABOUT THE NORTHERN HALF OF THE  
CONTIGUOUS U.S. TO A POSSIBLE REX BLOCK CONFIGURATION OVER CANADA  
AS NORTHERN U.S./SOUTHERN CANADA FLOW CUTS THROUGH THE INITIAL  
RIDGE. AT THIS TIME THE PRECISE DETAILS OF THIS TRANSITION AND  
THE EVENTUAL SHAPE OF THE PATTERN BY THE MIDDLE OF NEXT WEEK ARE  
STILL FAIRLY UNCERTAIN THOUGH. MEANWHILE THERE IS AN IMPROVING  
SIGNAL TOWARD A MEAN TROUGH SETTLING ALONG OR SLIGHTLY INLAND FROM  
THE WEST COAST BY NEXT WED-THU. A WEAKENING MEAN RIDGE OVER THE  
SOUTHERN PLAINS EARLY IN THE PERIOD WILL REBUILD OVER THE SOUTHERN  
ROCKIES/HIGH PLAINS AND THEN POSSIBLY EXPAND OR SHIFT EASTWARD.  
THE WESTERN PERIPHERY OF AN ATLANTIC/CARIBBEAN RIDGE ALOFT WILL  
GRADUALLY BUILD WESTWARD OVER THE COURSE OF NEXT WEEK.  
 
   
..MODEL GUIDANCE/PREDICTABILITY EVALUATION/PREFERENCES
 
 
INTO ABOUT DAY 5 TUE A CONSENSUS BLEND (MOSTLY OPERATIONAL  
GUIDANCE, INCLUDING 06Z GFS/00Z ECMWF/00Z CMC/00Z UKMET, WITH A  
LITTLE ECMWF MEAN) BEST REPRESENTS THE MOST LIKELY FORECAST  
SCENARIO, AS THE CORE OF A STRONG WESTERN NORTH AMERICA TROUGH  
HEADS INTO WEST-CENTRAL CANADA AND ENERGY EAST OF HUDSON BAY  
DESCENDS WITHIN A PERSISTENT MEAN TROUGH. WITHIN THIS EASTERN  
MEAN TROUGH, THE 06Z GFS IS CLOSER TO THE MAJORITY CLUSTER OVER  
THE PAST COUPLE DAYS VERSUS THE FARTHER WESTWARD AND SOUTHWARD 00Z  
GFS/UKMET WHICH BRING THE CENTER OF A COMPACT UPPER LOW CLOSE TO  
THE NORTHERN TIP OF MAINE.  
 
BY LATER IN THE PERIOD GUIDANCE HAS GENERALLY MAINTAINED THE IDEA  
(WHICH WAS FAIRLY NEW 24-36 HOURS AGO) THAT NORTHERN U.S. FLOW  
WILL CONTINUE EASTWARD AND ULTIMATELY LEAD TO A LOW AMPLITUDE  
PATTERN ACROSS THE NORTHERN STATES BY NEXT WED-THU WHILE AN  
ILL-DEFINED AXIS OF LOWER HEIGHTS PREVAIL OVER SOUTHERN CANADA,  
SOUTH OF A CLOSED HIGH. CONFIDENCE IS LOW IN THE SPECIFICS  
THOUGH, FAVORING A BLENDED APPROACH. UPSTREAM THE PREVIOUSLY  
CHAOTIC MODEL/ENSEMBLE PLOTS SHOW IMPROVED CLUSTERING TODAY TOWARD  
A TROUGH SETTLING NEAR THE WEST COAST LATE IN THE PERIOD. OVERALL  
THE MEANS BEST DEPICTED THIS IDEA YESTERDAY AND HAD TELECONNECTION  
SUPPORT FROM SURROUNDING ANOMALY CENTERS IN THE D+8 MEANS.  
HOWEVER THE DEEP/AMPLIFIED ECMWF LIES NEAR THE EXTREME SIDE OF THE  
ENSEMBLE ENVELOPE SO ONLY A SMALL MINORITY OF ITS FORECAST COULD  
BE INCORPORATED BY LATE IN THE PERIOD. FARTHER SOUTHEAST, AN  
AVERAGE OF THE GEFS/ECMWF MEANS IS REASONABLE FOR RESOLVING  
DIFFERENCES IN SPECIFICS OF THE SOUTHERN ROCKIES/PLAINS RIDGE  
WHILE THE GFS/GEFS STILL APPEAR TO SHOW PREMATURE DEVELOPMENT AND  
PROGRESSION OF A TROPICAL SYSTEM OVER THE NORTHWESTERN  
CARIBBEAN/GULF OF MEXICO. THE HISTORICALLY ENTHUSIASTIC CMC AS  
WELL AS THE NAVGEM SEEM TO REMAIN AS A MORE REALISTIC "EXTREME  
BOUND" THAT IS MUCH MORE SUPPRESSED THAN THE GFS/GEFS. THUS GFS  
FORECASTS HAD TO BE EXCLUDED FROM THE FAVORED BLEND LATE IN THE  
PERIOD. THE LATER PART OF THE PERIOD TRENDED TOWARD MORE ENSEMBLE  
MEAN INPUT, FROM THE 00Z ECMWF MEAN AND A SPLIT OF 00Z GEFS/NAEFS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
A WAVY FRONTAL BOUNDARY EXTENDING FROM THE EAST COAST THROUGH THE  
OHIO VALLEY AND INTO THE NORTHERN PLAINS WILL PROVIDE A FOCUS FOR  
SHOWERS/STORMS OVER MULTIPLE DAYS, WITH SOME RAINFALL LOCALLY  
HEAVY. CONVECTION MAY ALSO BE STRONG IN SOME CASES. CURRENT SPC  
OUTLOOK INDICATES THAT PARTS OF THE NORTHERN PLAINS MAY HAVE  
FAVORABLE INGREDIENTS FOR SEVERE POTENTIAL DURING THE LATTER HALF  
OF THE WEEKEND. THE WESTERN PART OF THIS FRONT WILL CONNECT TO  
THE STRONG SYSTEM EMERGING FROM THE WEST AND CONTINUED PROGRESSION  
OF THE WESTERN FRONT WILL LIKELY BRING FURTHER CONVECTION TO THE  
NORTHERN PLAINS INTO THE MS VALLEY BEFORE POSSIBLE WEAKENING. THE  
SOUTHEAST WILL SEE DIURNALLY FAVORED CONVECTION MOST DAYS WITH  
ACTIVITY ENHANCED BY LOCALIZED BOUNDARIES AND POSSIBLY THE FRONT  
TO THE NORTH. DEPARTURE OF THE STRONG WEEKEND SYSTEM WILL LEAD TO  
A DRIER TREND OVER THE NORTHWEST FOR THE FIRST HALF OF NEXT WEEK.  
THEN THE ARRIVAL OF UPPER TROUGHING SHOULD BRING SOME  
PRECIPITATION BUT WITH GENERALLY LIGHT AMOUNTS.  
 
THE NORTHERN HALF OF THE INTERMOUNTAIN WEST AND NORTHERN ROCKIES  
WILL SEE A DAY OR TWO OF HIGHS AT LEAST 10F BELOW NORMAL EARLY IN  
THE PERIOD AS STRONG UPPER TROUGHING PASSES OVER THE AREA. AT THE  
SAME TIME WARM SECTOR HIGHS/LOWS ARE LIKELY TO REACH 10-20F ABOVE  
NORMAL OVER AND NEAR THE NORTHERN-CENTRAL PLAINS SUN-MON.  
REBUILDING OF THE UPPER RIDGE OVER THE SOUTHERN ROCKIES AND  
VICINITY WILL PROMOTE AN EXPANDING AREA OF PLUS 5-15F ANOMALIES  
FOR MIN/MAX READINGS OVER THE WEST BY MIDWEEK, EVENTUALLY  
SPREADING INTO PARTS OF THE HIGH PLAINS. EXPECT MEAN TROUGHING  
ALOFT TO KEEP THE NORTHEAST/MID ATLANTIC ON THE COOL SIDE THROUGH  
AT LEAST EARLY NEXT WEEK. FLATTENING OF THE MEAN PATTERN SHOULD  
LEAD TO NEAR-NORMAL TEMPERATURES NEAR THE EAST COAST BY NEXT  
WED-THU.  
 
RAUSCH  
 
WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS, SURFACE SYSTEMS,  
WEATHER GRIDS, QUANTITATIVE PRECIPITATION, AND WINTER WEATHER  
OUTLOOK PROBABILITIES CAN BE FOUND AT:  
 
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
 

 
 
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