616  
FXUS02 KWBC 111510  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1109 AM EDT MON JUN 11 2018  
 
VALID 12Z THU JUN 14 2018 - 12Z MON JUN 18 2018  
   
..PATTERN OVERVIEW
 
 
COORDINATION WITH THE ALASKA MEDIUM RANGE DESK LED TO DISCUSSION  
OF THE DOWNSTREAM RAMIFICATIONS OF THE ONGOING EXTRATROPICAL  
TRANSITION OF MALIKSI OFFSHORE JAPAN, WHICH IS EXPECTED TO LEAD TO  
A MORE AMPLIFIED FLOW PATTERN THAN USUAL FOR MID TO LATE JUNE  
ACROSS NORTH AMERICA. AS MALIKSI SWINGS INTO ALASKA AS A STILL  
ROBUST SYSTEM, RIDGING BUILDS ACROSS THE EASTERN PACIFIC WHICH  
LEADS TO A PRONOUNCED TROUGH ACROSS THE WEST, WHICH LEADS TO A  
SIMILARLY PRONOUNCED RIDGE/TROUGH COUPLET ACROSS THE MISSISSIPPI  
VALLEY/WESTERN ATLANTIC RESPECTIVELY.  
 
   
..MODEL GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE GUIDANCE SHOWS REASONABLE AGREEMENT FOR MUCH OF THE PERIOD.  
THE BIGGEST ISSUE INVOLVES WHETHER OR NOT A CLOSED LOW IN THE  
WESTERN ATLANTIC RETROGRADES INTO THE EAST COAST, WHICH ONLY THE  
OPERATIONAL 00Z ECMWF SHOWS BEYOND DAY 6/SUNDAY MORNING. WHILE  
THE CANADIAN IS FAVORABLE ACROSS THE WESTERN ATLANTIC LATE IN THE  
PERIOD, ITS PATTERN ACROSS THE WEST AND MIDWEST LEAVES A BIT TO BE  
DESIRED. TAKING THAT INTO ACCOUNT, A COMPROMISE OF THE 00Z ECMWF,  
00Z UKMET, 00Z GFS, AND 00Z CANADIAN WERE USED FOR THE  
FRONTS/PRESSURES/WINDS THROUGH SATURDAY. FROM SUNDAY ONWARD,  
PHASED OUT THE 00Z CANADIAN AND 00Z ECMWF SOLUTIONS SUBSTITUTING  
THE 00Z GFS, 00Z ECMWF ENSEMBLE MEAN, AND 00Z NAEFS MEAN IN THEIR  
PLACE. THIS SOLUTION LED TO REASONABLE CONTINUITY. FOR THE  
REMAINDER OF THE MEDIUM RANGE GRIDS, A MORE EVEN BLEND OF THE  
ENSEMBLE MEANS (LEANING MORE ECMWF ENSEMBLE MEAN) AND 00Z GFS/06Z  
GFS SOLUTIONS WAS UTILIZED. FOR THE DAYS 4-7 QPF, THE INITIAL  
TEMPLATE IS A BLEND OF THE 00Z GFS, 06Z GFS, 00Z ECMWF, AND 12Z  
NATIONAL BLEND OF MODELS. SHOULD THE 12Z GFS LOOK REASONABLE IN A  
COUPLE HOURS, IT COULD BE UTILIZED FOR THE DAYS 4-7 QPF AS WELL.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
A WEAKENING SURFACE FRONT AND MOIST AIR MASS WILL SUPPORT  
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS THROUGH THE  
WEEKEND, ESPECIALLY DURING THE AFTERNOONS AND EVENINGS, ACROSS THE  
SOUTHEASTERN STATES, WITH THE POTENTIAL FOR LOCALLY HEAVY  
RAINFALL. A BROAD TROUGH/AREA OF DISTURBED WEATHER MOVING WESTWARD  
ACROSS THE GULF OF MEXICO IS ALSO EXPECTED TO BRING THE POTENTIAL  
FOR MORE WIDESPREAD RAINS TO PORTIONS OF THE WESTERN GULF COAST  
STATES FROM THE WEEKEND INTO EARLY NEXT WEEK. FARTHER NORTH, A  
SHORTWAVE, SURFACE LOW PRESSURE SYSTEM CROSSING THE NORTHERN  
PLAINS AND UPPER MIDWEST WILL PRODUCE AREAS OF CONVECTION WITH  
POTENTIALLY HEAVY RAINFALL. THE FRONTAL BOUNDARY MAY SLOW OR STALL  
FOR A PERIOD OF TIME SAT-SUN FROM THE CENTRAL PLAINS TO THE UPPER  
MIDWEST, RESULTING IN SEVERAL DAYS WITH SHOWER/THUNDERSTORMS  
POTENTIAL, AND POTENTIAL FLOODING THREAT FOR SOME AREAS. MOISTURE  
ASSOCIATED WITH TROPICAL STORM BUD SHOULD BEGIN TO SPREAD INTO THE  
SOUTHWESTERN U.S. AND THE ROCKIES BY THE WEEKEND, BRINGING THE  
POTENTIAL FOR AREAS OF HEAVY RAINFALL. INTERACTIONS WITH A  
STATIONARY FRONTAL BOUNDARY DRAPED FROM THE GREAT BASIN INTO THE  
CENTRAL ROCKIES COULD LEAD TO AN ENHANCEMENT OF HEAVY RAINFALL  
POTENTIAL. SOME MODEL SOLUTIONS EVEN SUGGEST THE POSSIBILITY THAT  
THE MOISTURE FROM BUD COULD SPREAD EAST INTO THE CENTRAL/NORTHERN  
PLAINS, FURTHER ENHANCING HEAVY RAIN POTENTIAL ALONG THE FRONTAL  
BOUNDARY.  
 
TEMPERATURES WILL ALSO BECOME A BIGGER STORY DURING THE NEXT WEEK  
AS THE UPPER RIDGE EXPANDS ACROSS THE CENTRAL U.S. AND THEN DRIFTS  
EAST INTO THE OHIO VALLEY. HIGH TEMPERATURE ANOMALIES OF +10 TO  
+18 DEG F ARE EXPECTED THU-SAT ACROSS AREAS FROM THE CENTRAL  
PLAINS TO THE MID-MISSISSIPPI VALLEY, WITH HIGHS APPROACHING 100  
DEGREES FOR SOME AREAS. FORECAST HIGHS AND LOWS ARE EXPECTED TO  
APPROACH BUT FALL SHORT OF RECORD WARM/HOT VALUES THROUGH THE  
PERIOD. BY SUNDAY AND NEXT MONDAY, THE GREATEST TEMPERATURE  
ANOMALIES WILL SHIFT A BIT EAST FROM THE MID-MISSISSIPPI VALLEY  
INTO THE OHIO VALLEY. HIGH DEW POINTS IN ADDITION TO THE HOT  
TEMPERATURES WILL MAKE FOR DANGEROUS HEAT INDEX VALUES FOR SOME  
AREAS, WHICH WOULD IMPACT URBAN AREAS THE GREATEST AS THEY WOULD  
RECEIVE THE DOUBLE WHAMMY OF HIGH AFTERNOON TEMPERATURES AND  
URBANLY-INDUCED WARM OVERNIGHT LOWS.  
 
ROTH/RYAN  
 
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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