230  
FXUS02 KWBC 070651  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
250 AM EDT THU JUN 07 2018  
 
VALID 12Z SUN JUN 10 2018 - 12Z THU JUN 14 2018  
   
..PATTERN OVERVIEW
 
 
AT THE END OF THE UPCOMING WEEKEND, A ROBUST UPPER TROUGH WILL BE  
IN THE PROCESS OF MOVING ACROSS THE NORTHWESTERN U.S. WITH 500-MB  
HEIGHT ANOMALIES IN THE 2 TO 2.5 SIGMA RANGE. THIS WILL ULTIMATELY  
FORM THE WESTERN EXTENT OF A HIGH-LATITUDE OMEGA BLOCK. GRADUALLY  
THIS NEGATIVE HEIGHT ANOMALY SHOULD LIFT ACROSS THE ALBERTA BORDER  
WHERE A SIGNIFICANT UPPER LOW WILL LIKELY DRIFT EASTWARD DURING  
THE FOLLOWING DAYS. ITS PROGRESS COULD NEARLY COME TO A HALT BY  
THE MIDDLE OF NEXT WEEK AS A POSSIBLE REX BLOCK SETS UP WITH A  
CLOSED HIGH PINCHING OFF NORTH OF HUDSON BAY. ELSEWHERE, THE OTHER  
SIDE OF THE OMEGA BLOCK SIGNATURE WILL ALLOW THE PERSISTENCE OF  
UPPER TROUGHING ACROSS FAR EASTERN CANADA DOWN INTO NEW ENGLAND.  
EVENTUALLY THE FORWARD PROGRESSION OF THE SYNOPTIC-SCALE FLOW WILL  
ALLOW THIS MENTIONED UPPER TROUGH TO SLOWLY EXIT INTO THE WESTERN  
ATLANTIC BY THE END OF THE PERIOD, DAY 6/7, JUNE 13/14.  
CONSIDERING LATITUDES SOUTH OF 40 DEGREES NORTH, AN UPPER RIDGE  
SHOULD SITUATE OVER THE DESERT SOUTHWEST/FOUR CORNERS REGION EARLY  
ON. GRADUAL EASTWARD EXPANSION OF THIS ANTICYCLONE IS LIKELY TO  
OCCUR DURING THE DAYS AHEAD AS THE PREVAILING WESTERLIES REMAIN  
ALONG THE INTERNATIONAL BORDER WITH CANADA. BY DAY 7/JUNE 14, THE  
EASTERN EXTENT OF THIS UPPER RIDGE MAY ENCOMPASS AREAS OF THE  
LOWER MISSISSIPPI VALLEY.  
 
   
..MODEL GUIDANCE/PREDICTABILITY EVALUATION/PREFERENCES
 
 
BEGINNING WITH THE NORTHWESTERN U.S. TROUGH, MULTI-DAY ENSEMBLE  
SPAGHETTI PLOT COMPARISONS DEPICT AN EASTWARD TREND, PARTICULARLY  
DURING THE LAST 24 HOURS OF MODEL RUNS. OVERALL, GLOBAL MODELS AND  
THEIR ENSEMBLES ARE FAIRLY CLUSTERED WITH PREVIOUSLY DIVERGENT  
OPERATIONAL RUNS NO LONGER EVIDENT. WHERE THE MODELS CONTINUE TO  
STRUGGLE IS JUST BEYOND DAY 5/JUNE 12 AS THE UPPER LOW BEGINS ITS  
SLOW EASTWARD MARCH ACROSS SOUTH-CENTRAL CANADA. IT IS AT THIS  
POINT WHERE THE GUIDANCE EXHIBITS POOR RUN-TO-RUN CONTINUITY AS  
EVIDENCED BY THE LATEST 00Z GFS SUGGESTING A COMPLETELY DIFFERENT  
PATTERN FROM ITS PREVIOUS RUN. AS A WHOLE, THE ENSEMBLE SPAGHETTI  
PLOTS WOULD AT LEAST SUGGEST THE IDEA OF A CLOSED LOW UNDERCUTTING  
THE DOWNSTREAM RIDGE AS IT IS FORCED NORTH OF HUDSON BAY. THIS  
ULTIMATELY EITHER ALLOWS FOR THE PERSISTENCE OF THE HIGH-LATITUDE  
OMEGA BLOCK OR EVEN FORMS A REX BLOCK ACROSS THE REGION. SUFFICE  
TO SAY, AN ENSEMBLE-BASED APPROACH IS NECESSARY BY THE MIDDLE PART  
OF NEXT WEEK. GIVEN THE DOWNSTREAM IMPACTS ON THE FLOW ACROSS  
EASTERN CANADA, MANY OF THE MENTIONED CHALLENGES WILL ALSO APPLY  
ACROSS EASTERN NORTH AMERICA AS WELL. WHILE LONGWAVE TROUGHING IS  
PRIMED TO IMPACT THE REGION THROUGH MID-WEEK, THE DETAILS AMONGST  
THE GUIDANCE ARE SOMEWHAT UNCERTAIN, PARTICULARLY GIVEN THE TIMING  
DIFFERENCES BETWEEN ENSEMBLE MEMBERS.  
 
THINGS ARE A BIT MORE CLEAR-CUT ACROSS THE MORE SOUTHERN LATITUDES  
OF THE NATION AS A BROAD UPPER RIDGE RETURNS TO THE DESERT  
SOUTHWEST BY AS EARLY AS MONDAY. AS THE ACTIVE MID-LATITUDE FLOW  
BECOMES MORE RESTRICTED TO THE NORTHERN TIER, EXPECT FURTHER  
EXPANSION OF THE ANTICYCLONE TOWARD THE SOUTHERN/CENTRAL PLAINS,  
PARTICULARLY SHOWN BY THE 12Z ECMWF. THE 00Z/12Z CMC/UKMET ALSO  
SUPPORT MODEST HEIGHT RISES ACROSS THIS REGION WHILE THE PREVIOUS  
FEW GFS RUNS HAVE BEEN MORE SUBDUED. ONE FURTHER ISSUE THE  
GFS/GEFS RUNS HAVE BEEN PLAGUED BY IS THE RENEWED TROPICAL  
ACTIVITY ACROSS THE EASTERN GULF OF MEXICO BY DAY 7/JUNE 14. THE  
00Z/12Z CMC SHOW A TROPICAL DISTURBANCE APPROXIMATELY A DAY LATER  
BUT THIS MODEL CAN BE A BIT TOO PRO-ACTIVE IN DEVELOPMENT. BASED  
ON THE WPC-NHC MEDIUM RANGE COORDINATION CALL, THESE SCENARIOS  
WILL REMAIN DOWNPLAYED.  
 
REGARDING PREFERENCES, FAVORED A GENERAL COMBINATION OF THE  
18Z/12Z GFS, 12Z ECMWF/CMC THROUGH TUESDAY WITH SUBTLE ADDITIONS  
OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS TO THE PICTURE. BEYOND  
THIS PERIOD, SIGNIFICANT UNCERTAINTIES LED TO MORE RAPID INCLUSION  
OF THE MENTIONED ENSEMBLE SOLUTIONS BEFORE GOING 50/50 BETWEEN THE  
TWO MEANS BY THE END OF THE PERIOD. WOULD SAY CONFIDENCE IS BELOW  
AVERAGE DURING THE JUNE 13-14 TIMEFRAME.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
RATHER COOL TEMPERATURES CAN BE EXPECTED ACROSS MUCH OF THE  
WESTERN THIRD OF THE COUNTRY TO CONCLUDE THE WEEKEND. IN RESPONSE  
TO THE DEEP UPPER TROUGH, READINGS SHOULD BE AROUND 10 TO 15  
DEGREES BELOW CLIMATOLOGY ACROSS AREAS OF THE PACIFIC NORTHWEST  
INTO THE CENTRAL GREAT BASIN AND UPPER INTERMOUNTAIN WEST. SUCH  
ANOMALIES WILL REDUCE IN MAGNITUDE AND GRADUALLY ADVANCE INTO THE  
NORTHERN ROCKIES BY MONDAY BEFORE RETURNING TO NEAR AVERAGE  
THEREAFTER. WHILE NOT AS ANOMALOUS IN NATURE, THE OTHER COOL SPOT  
WILL BE THE EAST COAST AS NUMBERS STAY VERY NEAR CLIMATOLOGY  
THROUGH TUESDAY. OTHERWISE, EXPECT THE REST OF THE COUNTRY TO BE  
ON THE WARM SIDE, GENERALLY IN ADVANCE OF THE SLOW-MOVING CENTRAL  
U.S. COLD FRONT AS WELL AS UNDER THE EXPANDING INFLUENCE OF THE  
UPPER RIDGE. WITHIN THE FORMER REGIME, TEMPERATURES WELL INTO THE  
LOW/MID 90S ARE LIKELY ACROSS THE NORTHERN/CENTRAL PLAINS ON  
SUNDAY AS NUMBERS MOVE INTO THE 15 TO 20 DEGREE ABOVE AVERAGE  
RANGE. THE TRUE HOT SPOT IN THE COUNTRY WILL BE IN ITS USUAL  
LOCATION, THE DESERT SOUTHWEST AS HIGHS RANGE FROM 105 TO 110  
DEGREE EACH DAY.  
 
ACTIVE CONVECTION SHOULD GENERALLY ACCOMPANY THE SOUTHWARD MOVING  
FRONT ACROSS THE LOWER MID-ATLANTIC/CAROLINAS BACK TOWARD THE OHIO  
VALLEY WITH THE THREAT LINGERING INTO EARLY NEXT WEEK ACROSS THE  
SOUTHEASTERN U.S. CONDITIONS SHOULD REMAIN UNSETTLED ACROSS MUCH  
OF THE GULF COAST UP TOWARD THE MID-SOUTH AND CAROLINAS WITH THE  
SYNOPTIC BOUNDARY LINGERING BEFORE SHEARING OUT BY LATE IN THE  
PERIOD. LOOKING TOWARD THE MIDDLE OF THE COUNTRY, SHOWERS AND  
THUNDERSTORMS WILL BE LIKELY ALONG THE SLOW EASTWARD MOVING COLD  
FRONT. MODELS VARY IN FORECAST AMOUNTS BUT PERHAPS SLIGHTLY  
HEAVIER AMOUNTS MAY BE POSSIBLE OVER THE CENTRAL PLAINS BY  
MID-WEEK AS THE SOUTHERN EXTENT OF THE BOUNDARY STALLS. THERE WILL  
ALSO BE A LINGERING THREAT FOR PRECIPITATION ACROSS THE PACIFIC  
NORTHWEST/UPPER INTERMOUNTAIN WEST EARLY ON BEFORE CLEARING OUT  
ONCE HEIGHTS BEGIN TO RISE. MORE PRECIPITATION MAY BE ON ITS WAY  
BY WEDNESDAY IF THE 12Z ECMWF PANS OUT.  
 
RUBIN-OSTER  
 
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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