141  
FXUS02 KWBC 180545  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 AM EDT THU OCT 18 2018  
 
VALID 12Z SUN OCT 21 2018 - 12Z THU OCT 25 2018  
   
..PATTERN OVERVIEW
 
 
ENSEMBLES CONTINUE TO ADVERTISE A SLOW RELEASE FROM THE MERIDIONAL  
FLOW AS THE POSITIVE/NEGATIVE HEIGHT ANOMALY CENTERS SURROUNDING  
NORTH AMERICA SEEM TO SHIFT/WEAKEN IN UNISON. THIS WILL LIKELY  
LEAD TO A PERIOD OF DECREASED RELATIVE FORECAST CONFIDENCE LATE  
NEXT WEEK AS A NEW PATTERN TRIES TO TAKE HOLD. UNTIL THEN,  
TROUGHING IN THE EAST WILL BE REINFORCED EARLY NEXT WEEK BUT THEN  
LIFT OUT AS THE WESTERN RIDGE GETS SHUNTED EASTWARD TO THE MIDDLE  
OF THE CONTINENT.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
ONGOING EXCELLENT MODEL/ENSEMBLE AGREEMENT IN THE FIRST HALF OF  
THE MEDIUM RANGE ALLOWED A DETERMINISTIC BLEND TO SERVE AS THE  
STARTING POINT. FORECAST FRONTAL TIMING/TRACK/POSITION HAS NOT  
CHANGED SUBSTANTIALLY FOR A FEW DAYS AS ONE FRONT ESCAPES THROUGH  
THE WESTERN ATLANTIC SUNDAY AND A CANADIAN SYSTEM DIPS THROUGH THE  
LAKES MON/TUE. ALSO BY THEN, A PACIFIC FRONT WILL PUSH INTO  
WASHINGTON AND BRITISH COLUMBIA. THEREAFTER, MODELS AND EVEN THE  
ENSEMBLES DIVERGE IN HOW THE PATTERN BREAKS DOWN. THE ECMWF  
ENSEMBLES HAVE BEEN UNCHARACTERISTICALLY QUICK TO BREAK DOWN THE  
WESTERN RIDGE (PREFER THE SLIGHTLY SLOWER TIMING OF THE 18Z GFS  
AND 12Z ECMWF/CANADIAN) BUT THEY HAVE BEEN SLOWER SLOWER/DEEPER  
WITH THE EASTERN TROUGH NEXT WED/THU THAN THE GEFS. OPTED TO SPLIT  
THE DIFFERENCE GIVEN THE UNCERTAINTY IN TIMING AND CONFLICTING  
SIGNALS. DID NOT PREFER ANY ONE DETERMINISTIC MODEL BY NEXT  
THURSDAY AND RELIED MOSTLY ON THE ENSEMBLE CONSENSUS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
TEMPERATURES WILL GENERALLY BE ABOVE AVERAGE IN THE NORTHWEST BUT  
WILL TREND COOLER (AND EAST) AS RIDGING WEAKENS AND MOVES EAST AS  
WELL. THE REST OF THE LOWER 48 WILL SEE COOLER THAN AVERAGE  
TEMPERATURES, ESPECIALLY THE NORTHEASTERN 1/4 OF THE CONUS (MORE  
TYPICAL OF EARLY NOVEMBER ON SOME DAYS). PRECIPITATION WILL FOCUS  
ALONG THE TEXAS COAST AS A FRONTAL BOUNDARY LINGERS IN THE GULF  
AND PRECIPITABLE WATER VALUES REMAIN HIGH -- AROUND +2 SIGMA  
(BETWEEN 1.75-2") ALONG AN INVERTED SURFACE TROUGH. 5-DAY TOTALS  
WILL LIKELY EXCEED SEVERAL INCHES IN SOME SOUTHERN TEXAS AREAS. A  
WEAK UPPER LOW DRIFTING OUT OF CALIFORNIA EARLY IN THE WEEK WILL  
SPREAD SOME GENERALLY LIGHT RAIN THROUGH THE SOUTHWEST/FOUR  
CORNERS REGION THROUGH THE PERIOD.  
 
FRACASSO  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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