215  
FXUS02 KWBC 161600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SAT JUN 16 2018  
 
VALID 12Z TUE JUN 19 2018 - 12Z SAT JUN 23 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE MEDIUM RANGE PERIOD (TUE-SAT) STARTS OUT WITH A CLOSED LOW  
OVER THE WESTERN U.S., WITH THE GUIDANCE NOW SHOWING A FASTER  
WEAKENING OF THE UPPER LOW AND EJECTION OF SHORT WAVE ENERGY INTO  
THE PLAINS AND THE MISSISSIPPI VALLEY BY THE END OF THE WEEK.  
STRONG RIDGING OVER THE PACIFIC NORTHWEST WILL RETREAT EASTWARD AS  
A SHORTWAVE ENTERS THE WEST COAST BY FRIDAY. MEANWHILE, THE  
NORTHERN PERIPHERY OF THE PERSISTENT DOWNSTREAM RIDGING ACROSS THE  
EAST/SOUTHEAST IS FINALLY ERODED BY NORTHERN STREAM CYCLONIC FLOW  
ACROSS THE GREAT LAKES AND THE NORTHEAST, WHICH SHOULD SUPPRESS  
THE OPPRESSIVE HEAT AND HUMIDITY EXPECTED THIS WEEKEND AND EARLY  
NEXT WEEK.  
 
OVERALL, THE MODELS AND ENSEMBLES SHOW A REASONABLY SIMILAR LARGER  
SCALE PATTERN OVER THE NEXT WEEK, BUT SMALLER MID-SCALE EMBEDDED  
FEATURES STILL OFFER A BIT OF FORECAST SPREAD. THIS CYCLE OF THE  
WPC MEDIUM RANGE SUITE USED A BLEND OF THE LATEST RUNS OF THE  
GFS/ECMWF WITH THEIR ENSEMBLE MEANS. SIGNIFICANT CONTRIBUTION FROM  
DETERMINISTIC RUNS WERE INCLUDED DAYS 3-4, WITH INCREASING  
ENSEMBLE CONTRIBUTION BY THE END OF THE FORECAST PERIOD TO TRY AND  
DE-EMPHASIZE THE LESS PREDICTABLE SMALLER SCALE FEATURES WHICH  
STILL REMAIN HIGHLY UNCERTAIN. THE SOLUTION MAINTAINS REASONABLY  
GOOD WPC CONTINUITY. THE BIGGEST SHIFT IS AT THE END OF THE PERIOD  
WITH A SLIGHTLY FASTER PROGRESSION OF TROUGHING INTO THE PLAINS/MS  
VALLEY WHICH MAY HELP SPIN UP A WAVE ALONG THE BOUNDARY, WITH THE  
NEARLY STATIONARY BOUNDARY ACROSS THE PLAINS NOW BEGINNING TO DROP  
SLOWLY SOUTH/EASTWARD.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A LONG STANDING AND WAVY FRONTAL BOUNDARY REMAINS QUASI-STATIONARY  
FROM THE CENTRAL PLAINS TO THE OHIO VALLEY AND MID-ATLANTIC.  
PERIODS OF LOCALLY EXCESSIVE CONVECTION WILL FOCUS ALONG THIS  
BOUNDARY AND IN THE WARM SECTOR AIDED BY EARLY PERIOD TROPICAL  
MOISTURE INFLUX FROM THE GULF OF MEXICO. WPC MEDIUM RANGE 48-HOUR  
QPF SHOWS THE HEAVIEST POTENTIAL ALONG THE IMMEDIATE TX COAST DUE  
TO A POTENTIAL TROPICAL WAVE/DISTURBANCE. MOISTURE STREAMING  
NORTHWARD INTERSECTS THE WAVY BOUNDARY TO THE NORTH TO PRODUCE  
POSSIBLY SEVERAL INCHES OF RAINFALL ACROSS THE CENTRAL PLAINS AND  
BACK INTO THE NORTHERN/CENTRAL ROCKIES. AS THE TROUGH AND FRONT  
SHIFTS SLOWLY EASTWARD DAYS 5-7, THE BEST RAINFALL WILL FOCUS  
ALONG THE SURFACE BOUNDARY AND TO THE NORTH OF ANY POTENTIAL WAVE  
DEVELOPMENT ACROSS THE UPPER MIDWEST.  
 
TEMPERATURE WISE, RIDGING ACROSS THE SOUTHEAST SHOULD WEAKEN IN  
RESPONSE TO CYCLONIC FLOW IN THE NORTHERN STREAM AND THE WESTERN  
U.S. TROUGH SLIDING EASTWARD. AFTERNOON HIGHS ABOVE NORMAL ARE  
STILL LIKELY HEADING THROUGH NEXT WEEK ACROSS MUCH OF THE EAST,  
BUT NOT NEARLY AS EXTREME AS THE LATE WEEKEND/EARLY WEEK HEAT  
EXPECTED. JUST A HANDFUL OF NEAR RECORD MAX TEMPS ARE EXPECTED  
TUESDAY, BUT THERES A HIGHER PROBABILITY OF NEAR OR RECORD  
BREAKING HIGH MINIMUMS, AS OVERNIGHT TEMPS HOVER IN THE 70S. WELL  
ABOVE NORMAL TEMPS EXPECTED ACROSS THE PACIFIC NORTHWEST AS WELL  
WITH DAYTIME HIGHS WELL INTO THE 90S ACROSS INTERIOR REGIONS,  
WHICH WOULD COME CLOSE TO RECORDS. ACROSS THE INTERMOUNTAIN WEST  
AND CENTRAL STATES, TEMPS SHOULD BE BELOW NORMAL UNDERNEATH UPPER  
LEVEL TROUGHING AND CLOUDY/RAINY CONDITIONS.  
 
SANTORELLI  
 
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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