078  
FXUS02 KWBC 081558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1158 AM EDT FRI JUN 08 2018  
 
VALID 12Z MON JUN 11 2018 - 12Z FRI JUN 15 2018  
   
..PATTERN OVERVIEW
 
 
THE HIGHER LATITUDES OF NORTH AMERICA IN PARTICULAR ARE LIKELY TO  
SEE A SIGNIFICANT DEGREE OF BLOCKING DURING THE PERIOD, WITH THE  
EVOLUTION OF EMBEDDED/SURROUNDING FLOW PROVIDING SOME SIGNIFICANT  
FORECAST CHALLENGES FOR SPECIFICS BY THE MID-LATE PART OF NEXT  
WEEK. THERE IS CURRENTLY A MAJORITY SCENARIO THAT HAS STRONG  
WESTERN NORTH AMERICA TROUGH/UPPER LOW ENERGY PROGRESSING  
UNDERNEATH AN ANOMALOUSLY STRONG NORTHERN CANADA UPPER HIGH THAT  
CLOSES OFF (HIGHEST STANDARD DEVIATIONS FROM NORMAL LIKELY TO BE  
AROUND TUE-WED). THE SOUTHERN CANADA/NORTHERN U.S. ENERGY MAY  
COMBINE WITH EASTERN CANADA FLOW TO YIELD AN OVERALL TROUGH  
COVERING PARTS OF EASTERN CANADA AND U.S. BY LATE NEXT WEEK.  
ELSEWHERE, EXPECT AN UPPER TROUGH TO REACH THE WEST COAST AROUND  
MIDWEEK WITH SOME DEGREE OF INLAND PROGRESSION POSSIBLE THEREAFTER  
WHILE RIDGING THAT BUILDS OVER THE SOUTHERN ROCKIES/PLAINS DURING  
THE FIRST HALF OF THE WEEK SHOULD PERSIST INTO FRI WITH A HINT OF  
SOUTHEASTWARD DRIFT.  
 
   
..MODEL GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
EVEN THOUGH THERE HAS BEEN SOME PRONOUNCED TRENDING WITH SOME  
ASPECTS OF THE FORECAST FROM THE PERSPECTIVE OF MULTI-DAY  
CONTINUITY, THE ENSEMBLE MEANS HAVE PROVIDED LESS RUN TO RUN  
VARIABILITY THAN OTHER INDIVIDUAL SOLUTIONS. IN ADDITION THE  
LIKELY CLOSURE OF AN UPPER HIGH FOR A TIME OVER NORTHERN-CENTRAL  
CANADA LENDS ITSELF TO LOW PREDICTABILITY FOR FORECAST DETAILS  
ACROSS MUCH OF SOUTHERN CANADA AND NORTHERN CONTIGUOUS U.S. AS A  
RESULT THE OVERALL FORECAST PREFERENCE PLACES THE GREATEST FOCUS  
ON THE ENSEMBLE MEANS. AN OPERATIONAL MODEL BLEND (06Z GFS/00Z  
ECMWF AND TO A LESSER DEGREE 00Z CMC/UKMET) COMPARED WELL TO THE  
MEANS WHILE PROVIDING ADDED DETAIL DAYS 3-4 MON-TUE SO THE EARLY  
PART OF THE FORECAST DID NOT USE THE MEANS PER SE, BUT SUBSEQUENT  
DIVERGENCE OF OPERATIONAL RUNS LED TO EXCLUSIVE USE OF THE MEANS  
(MORE 00Z ECMWF MEAN THAN 06Z GEFS) AND SOME CONTINUITY BY DAYS  
6-7 THU-FRI WITH A MODEL-MEAN BLEND FOR WED.  
 
MOST GUIDANCE AS A WHOLE HAS SHOWN FASTER MULTI-DAY TRENDS FOR THE  
GREATEST PROPORTION OF ENERGY THAT SHOULD PROGRESS EASTWARD ALONG  
THE U.S.-CANADIAN BORDER INTO MIDWEEK. HOWEVER THE 06Z GFS  
DIFFERS FROM THE MAJORITY IN HOLDING A GREATER PART OF CLOSED LOW  
ENERGY OVER WESTERN CANADA, WHILE SOME SOLUTIONS LIKE THE ECMWF  
OFFER POTENTIAL FOR ENERGY TO LINGER OVER CENTRAL LONGITUDES FOR A  
TIME BEFORE CONTINUING EASTWARD. THE FASTER TREND HAS LED TO  
EARLIER FLATTENING OF NEW ENGLAND TROUGHING ALOFT AFTER MON, WHILE  
KEEPING THE COMPACT UPPER LOW OVER EASTERN CANADA--WHICH ITSELF  
HAS TRENDED NOTICEABLY SLOWER VERSUS PREVIOUS CONSENSUS--WELL  
NORTH OF MAINE. BEYOND THAT THERE IS THE QUESTION OF HOW MUCH  
EASTERN CANADA FLOW COULD RETROGRADE AND INTERACT WITH FLOW COMING  
FROM THE WEST. TYPICAL BIASES SUGGEST LEANING AWAY FROM THE SIDE  
OF THE ENVELOPE THAT SHOWS THE MOST RETROGRESSION. NOTE THAT  
CMC/CMC ENSEMBLE RUNS HAVE OFFERED VERY DIFFERENT SCENARIOS THAT  
SEEM MORE REFLECTIVE OF IDEAS FROM MULTIPLE DAYS AGO, BUT AT LEAST  
THEY PROVIDE SOME ADDED RESERVATIONS ABOUT ANY SPECIFIC  
DETERMINISTIC FORECAST. SO AFTER TUE OVERALL CONFIDENCE RAPIDLY  
DECREASES REGARDING DETAILS OF SURFACE LOWS/FRONTS AFFECTING  
SOUTHERN CANADA AND THE EASTERN HALF OF THE U.S.  
 
REGARDING THE WESTERN U.S. TROUGH, THE MOST NOTABLE ASPECT OF THE  
FORECAST IS THAT COMPARED TO 24 HOURS AGO THE GFS AND ECMWF HAVE  
ESSENTIALLY FLIPPED, WITH THE 00Z/06Z GFS NOW SHOWING A DEEP/SLOW  
SOLUTION THAT THE 00Z ECMWF HAD YESTERDAY. ENSEMBLE MEANS HAVE  
BEEN MORE CONSISTENT OVER RECENT DAYS AND ARGUING FOR AN  
INTERMEDIATE SOLUTION, THOUGH THE 06Z GEFS MEAN HAS TRENDED  
SOMEWHAT DEEPER IN DEFERENCE TO ITS OPERATIONAL COUNTERPART.  
STRENGTH/SHARPNESS OF THE UPSTREAM RIDGE SUPPORTS A FAIR DEGREE OF  
AMPLITUDE BUT TELECONNECTIONS RELATIVE TO THE RIDGE'S POSITIVE  
HEIGHT ANOMALY CENTER SUGGEST THE WESTERN TROUGH SHOULD BECOME A  
LITTLE WEAKER AND MORE PROGRESSIVE THAN THE GFS SCENARIO AT OR  
SHORTLY AFTER THE END OF THE FORECAST.  
 
GFS/GEFS GUIDANCE STILL APPEARS OVERDONE WITH THE SURFACE  
DEVELOPMENT/MOISTURE HEADING INTO THE GULF OF MEXICO FROM THE  
WESTERN CARIBBEAN BUT HAS BEEN GRADUALLY TRENDING TOWARD OTHER  
GUIDANCE THAT HAS MORE CONSISTENTLY SIGNALED A MORE SUPPRESSED  
PATTERN.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
A COLD FRONT PROGRESSING EASTWARD FROM THE PLAINS, WITH THE  
TRAILING END STALLING OVER THE SOUTH-CENTRAL PLAINS AND EVENTUALLY  
LIFTING BACK NORTH AS A WARM FRONT, WILL LIKELY PROVIDE A  
MULTI-DAY FOCUS FOR SHOWERS AND STORMS OVER THE CENTRAL-EASTERN  
U.S. WITH SOME RAINFALL LOCALLY HEAVY. SPC OUTLOOK CURRENTLY  
SHOWS POTENTIAL FOR SEVERE WEATHER OVER PARTS OF THE MIDWEST EARLY  
IN THE WEEK. OTHER CONVECTION MAY BE ON THE STRONG SIDE AS WELL.  
DIURNALLY FAVORED CONVECTION OVER THE SOUTHEAST MAY BE ENHANCED  
EARLY IN THE WEEK BY A LEADING FRONT OVER THE EAST AND AN UPPER  
LEVEL WEAKNESS. THE SYSTEM MOVING INTO THE WEST MID-LATE WEEK  
SHOULD BRING CLOUDS AND SCATTERED PRECIPITATION. MOST ACTIVITY  
SHOULD BE ON THE LIGHTER HALF OF THE SPECTRUM BUT A FEW POCKETS OF  
AT LEAST MODERATE TOTALS CANNOT BE RULED OUT.  
 
THE STRONG UPPER SYSTEM DEPARTING FROM WESTERN NORTH AMERICA EARLY  
IN THE WEEK WILL BRING CHILLY TEMPERATURES TO THE NORTHERN ROCKIES  
AND VICINITY ON MON FOLLOWED BY A WARMING TREND. RIDGING ALOFT  
OVER THE SOUTHERN ROCKIES/PLAINS WILL PROMOTE A BROAD AREA OF WARM  
TO HOT WEATHER OVER THE WESTERN-CENTRAL U.S. DURING THE WEEK.  
HIGHEST ANOMALIES FOR MIN AND/OR MAX TEMPERATURES IN THE PLUS  
10-15F RANGE SHOULD EXPAND FROM CALIFORNIA THROUGH MUCH OF THE  
INTERMOUNTAIN WEST AND THEN PORTIONS OF THE ROCKIES/PLAINS. ON  
MON THERE WILL ALSO BE AN AXIS OF WELL ABOVE NORMAL READINGS JUST  
AHEAD OF THE PLAINS COLD FRONT.  
 
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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