131  
FXUS02 KWBC 091559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT SAT JUN 09 2018  
 
VALID 12Z TUE JUN 12 2018 - 12Z SAT JUN 16 2018  
   
..PATTERN OVERVIEW
 
 
LATEST GUIDANCE CONTINUES TO SHOW HIGHER LATITUDE BLOCKING, THE  
DETAILS OF WHICH WILL AFFECT FORECAST DETAILS ACROSS THE NORTHERN  
HALF OF THE CONTIGUOUS U.S. THE MOST COMMON THEME SEEN IN THE  
MODELS/ENSEMBLES IS THAT SOME ENERGY FROM A SOUTHERN CANADA CLOSED  
LOW AND FLOW TO ITS SOUTH AND EAST WILL PROGRESS RAPIDLY EASTWARD  
UNDER AN UPPER HIGH THAT CLOSES OFF JUST NORTHWEST OF HUDSON BAY  
WHILE REMAINING ENERGY MAY RETROGRADE BACK INTO WESTERN CANADA.  
THIS EVOLUTION SHOULD LEAD TO EASTERN CANADA/U.S. TROUGHING BY THE  
LATTER HALF OF THE PERIOD. MEANWHILE A STRONG CONSENSUS HAS AN  
UPPER TROUGH MOVING INTO THE WEST BY THU, ANCHORED BY AN UPPER LOW  
MOST LIKELY TO TRACK OVER VANCOUVER ISLAND. BY THE LATTER HALF OF  
THE FORECAST THERE IS STILL SIGNIFICANT SPREAD REGARDING DETAILS  
OF FLOW WITHIN THE OVERALL TROUGH. INTERESTINGLY THE END RESULT  
BY NEXT FRI-SAT COULD BE ANOTHER HIGH AMPLITUDE  
TROUGH-RIDGE-TROUGH CONFIGURATION ALBEIT WITH MEANINGFUL DETAIL  
DIFFERENCES FROM THE SAME OVERALL PATTERN TAKING SHAPE THIS  
WEEKEND. FARTHER SOUTH, AN UPPER RIDGE SHOULD PERSIST OVER THE  
SOUTHERN ROCKIES/PLAINS BUT WITH SOME SPREAD AND DAY TO DAY  
VARIABILITY FOR POSITION.  
 
   
..MODEL GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE OVERALL FORECAST PHILOSOPHY REMAINS INTACT, FOLLOWING A BLEND  
OF PRIMARILY OPERATIONAL GUIDANCE (06Z GFS/00Z ECMWF AND LESS 00Z  
UKMET/CMC) EARLY WITH A DAY 5 THU TRANSITION TOWARD A LATE PERIOD  
BLEND CONSISTING OF 40 PERCENT 00Z ECMWF MEAN AND THE REST EQUAL  
PARTS 00Z ECMWF, 06Z GEFS MEAN, AND WPC CONTINUITY.  
 
TODAY THERE IS SOMEWHAT GREATER CLUSTERING TOWARD THE IDEA OF A  
MORE EVEN SPLITTING OF INITIAL SOUTHERN CANADA CLOSED LOW ENERGY  
AND SURROUNDING FLOW, WITH LATEST ENSEMBLE MEANS REFLECTING SOME  
OPERATIONAL GUIDANCE THAT HAS SOME OF THE ENERGY RETROGRADING BACK  
INTO WESTERN CANADA. WHAT ENERGY PROGRESSES EASTWARD SHOULD  
SUPPORT A SURFACE SYSTEM THAT BRUSHES NEW ENGLAND AROUND MIDWEEK  
AND TRAILING FRONT THAT REACHES AS FAR SOUTH AS THE CENTRAL  
LATITUDES OF THE EASTERN U.S. BEFORE STALLING. THERE IS DECENT  
CONTINUITY IN PRINCIPLE TOWARD THE COMBINATION OF EJECTING ENERGY  
AND EASTERN CANADA FLOW YIELDING AN EASTERN NORTH AMERICA TROUGH  
BY THE LATTER HALF OF THE PERIOD, THOUGH WITH A SLIGHTLY FASTER  
TREND IN THE MEANS AT MOST VALID TIMES.  
 
INTO DAY 5 THU GUIDANCE HAS GRAVITATED TOWARD A COMMON SOLUTION  
FAIRLY WELL REGARDING THE UPPER TROUGH HEADING INTO THE WEST.  
AFTER THAT TIME MODELS/ENSEMBLES DIVERGE FAIRLY RAPIDLY. ONCE  
AGAIN THE ENSEMBLE MEANS PROVIDE A GOOD INTERMEDIATE SOLUTION  
BETWEEN OPERATIONAL MODEL EXTREMES--THE PROGRESSIVE ECMWF/CMC AND  
SLOWER/DEEPER GFS THAT CLOSES OFF A LOW OVER OR NORTHEAST OF  
CALIFORNIA. AS WAS THE CASE YESTERDAY, TELECONNECTIONS RELATIVE  
TO THE UPSTREAM RIDGE'S POSITIVE HEIGHT ANOMALY CENTER RECOMMEND  
MORE MODEST WEST COAST TROUGHING THAN FORECAST BY THE GFS (BUT  
PERHAPS WITH AN AXIS NOT FAR FROM THE GFS), WHILE OFFERING  
POTENTIAL THAT THE NORTHERN TIER STATES COULD SEE SOMEWHAT BROADER  
TROUGHING ALOFT THAN SEEN IN THE MEANS. THIS SEEMS TO ARGUE FOR  
HOLDING ONTO A SMALL ECMWF COMPONENT IN THE FORECAST. IT REMAINS  
TO BE SEEN WHETHER THERE WILL BE FASTER TRENDS OVER A MULTI-DAY  
TIME FRAME AS WAS SEEN WITH THE PRECEDING SYSTEM.  
 
THE AREA EXTENDING FROM THE WESTERN CARIBBEAN INTO THE GULF OF  
MEXICO CONTINUES TO EXHIBIT FAIRLY HIGH FORECAST UNCERTAINTY.  
ONCE AGAIN THE 06Z GFS HAS HEDGED SLOWER/WESTWARD WITH ITS  
TROPICAL DEVELOPMENT VERSUS THE 00Z RUN WHILE THE GEFS AND NAVGEM  
ARE ABOUT THE ONLY OTHER SOLUTIONS TO SHOW GFS-LIKE POTENTIAL. IF  
ANY TYPE OF WEAK FEATURE WERE TO EXIST, THE COMBINATION OF LOW  
LEVEL STEERING AND MOST COMMON GUIDANCE LOCATION OF ANY UPPER  
LEVEL WEAKNESS WOULD MORE LIKELY TEND TO DIRECT IT INTO THE  
WESTERN GULF.  
 
LATE IN THE PERIOD A SYSTEM LIKELY TO DEVELOP IN TROPICAL EASTERN  
PACIFIC (TO THE EAST OF ALETTA) MAY REACH CLOSE TO SOUTHERN BAJA  
CALIFORNIA. THIS SYSTEM WILL BEAR WATCHING ESPECIALLY WITH  
RESPECT TO THE POTENTIAL FLOW OF MOISTURE AHEAD OF THE WESTERN  
U.S. TROUGH.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
A FAVORED AXIS FOR HIGHEST RAINFALL TOTALS FOR THE 5-DAY PERIOD  
SHOULD EXTEND FROM THE NORTHERN PLAINS THROUGH THE MIDWEST AND  
INTO THE CENTRAL APPALACHIANS, AS A FRONTAL BOUNDARY HEADING INTO  
THE EAST STALLS FROM THE MID ATLANTIC INTO THE PLAINS WHILE THE  
WESTERN PART OF THE FRONT EVENTUALLY LIFTS UP AS A WARM FRONT  
AHEAD OF ROCKIES/PLAINS LOW PRESSURE. THE SOUTHEAST WILL SEE  
PERIODS OF SHOWERS/THUNDERSTORMS AS WELL WITH SOME LOCALLY HEAVY  
AMOUNTS POSSIBLE. THE STRONG UPPER TROUGH MOVING INTO THE WEST  
WILL BRING SCATTERED LIGHT TO LOCALLY MODERATE PRECIPITATION TO  
SOME AREAS. BY LATE NEXT WEEK/WEEKEND THE POTENTIAL FLOW OF  
MOISTURE FROM THE TROPICAL EAST PACIFIC WILL HAVE TO BE MONITORED,  
AS IT MAY BEGIN TO ENHANCE RAINFALL OVER PORTIONS OF THE FOUR  
CORNERS STATES.  
 
THE MOST PROMINENT TEMPERATURE ANOMALIES WILL BE ASSOCIATED WITH  
WARM TO HOT READINGS EXPECTED TO SPREAD/PROGRESS FROM CALIFORNIA  
AND THE GREAT BASIN/SOUTHWEST INTO THE PLAINS OVER THE COURSE OF  
THE PERIOD. EXPECT DECENT COVERAGE OF MIN AND/OR MAX READINGS OF  
10-15F ABOVE NORMAL WITHIN THIS AREA. THE UPPER TROUGHING MOVING  
INTO THE WEST WILL BRING A COOLING TREND FIRST TO THE NORTHWEST  
AND THEN TO A HIGHER PERCENTAGE OF THE WEST BY FRI-SAT.  
 
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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