063  
FXUS02 KWBC 160726  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
225 AM EST THU DEC 16 2021  
 
VALID 12Z SUN DEC 19 2021 - 12Z THU DEC 23 2021  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE IS IN GOOD AGREEMENT INTO EARLY NEXT WEEK IN A PATTERN  
WITH ABOVE AVERAGE FORECAST CONFIDENCE. FORECAST SPREAD AND  
EMBEDDED SYSTEM CONTINUITY ISSUES BECOME MORE OF AN ISSUE INTO  
NEXT MIDWEEK BOTH WITH EASTERN PACIFIC SYSTEM INTERACTIONS AND  
POTENTIAL SOUTHEAST U.S. COASTAL LOW DEVELOPMENT AND PROXIMITY.  
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS DERIVED FROM A COMPOSITE OF  
WELL CLUSTERED SOLUTIONS FROM THE 18 UTC GFS, THE 12 UTC  
ECWMF/UKMET/CANADIAN AND THE 01 UTC NATIONAL BLEND OF MODELS DAYS  
3-5 (SUN-TUE). THIS SOLUTION OFFERS GOOD WPC CONTINUITY AND HAS  
FAVORABLE ENSEMBLE SUPPORT. SWITCHED FOCUS TO THE STILL COMPATIBLE  
ENSEMBLE MEANS INTO DAYS 6/7 AMID GROWING SYSTEM UNCERTAINTY AND  
RUN TO RUN VARIANCES. LATEST 00 UTC GUIDANCE OVERALL REMAINS IN  
LINE WITH THIS FORECAST PLAN.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
NORTHERN STREAM UPPER TROUGH PASSAGE AND AN EXITING FRONTAL LOW  
MAY SUPPORT SOME LINGERING SNOWS SUN OVER NORTHERN NEW ENGLAND AND  
OFF THE LOWER GREAT LAKES. LOCALLY ENHANCED RAIN SHOULD FOCUS WITH  
WAVES ALONG A TRAILING/STALLING FRONT SUNK THROUGH THE GULF COAST  
AND SOUTHEAST INTO EARLY NEXT WEEK. GUIDANCE HAS BECOME BETTER  
CLUSTERED WITH APPROACH OF A SEPARTED/AMPLIFIED SOUTHERN STREAM  
SHORTWAVE, BUT STILL OFFERS LESS THAN STELLAR RUN TO RUN  
CONTINUITY INTO NEXT MIDWEEK WITH THE DEPTH AND COASTAL PROXIMITY  
OF A POTENTIALLY WELL ORGANIZED SOUTHEAST U.S. COASTAL LOW AND  
INLAND EXTENT FOR ENHANCED WRAPPED RAINS. MANUALLY ADJUSTED WPC  
PROGS SHOW A DECENT COASTAL LOW OFFSHORE GIVEN FAVORABLE BUT  
STEADILY PROGRESSIVE UPPER TROUGH SUPPORT AND IMPROVING GUIDANCE  
SIGNAL.  
 
UPPER TROUGH AND SURFACE SYSTEM PASSAGE WILL SUPPORT LINGERING  
TERRAIN ENHANCED PRECIPITATION OVER THE NORTHWEST SUN. DETAILS  
REMAIN LESS CERTAIN UPSTREAM OVER THE EASTERN PACIFIC, BUT THERE  
REMAINS A GOOD GUICANCE SIGNAL THAT AMPLIFIED UPPER TROUGH DIGGING  
EARLY NEXT WEEK WOULD OFFERS POTENTIAL TO FOCUS INGREDIENTS FOR  
MODERATE TO HEAVY PRECIPITATION FOR NORTH-CENTRAL CA CONSIDERING  
SLOW SYSTEM APPROACH, DEVELOPING MOISTURE PLUME APPROACH AND  
FAVORED SOUTHERN FACING TERRAIN ENHANCEMENT. SOME HEAVIER MODEL  
QPF SOLUTIONS WITHIN THE FULL ENVELOPE OF SOLUTIONS WOULD BETTER  
PORTEND LOCAL RUNOFF ISSUES. MAIN PRECIPITATION FOCUS, INCLUDING  
HEAVY SHASTA AND SIERRA SNOWS, IS SET TO SPREAD DOWN ACROSS  
CENTRAL-SOUTHERN CA THROUGH THROUGH NEXT MIDWEEK, WITH ADDITIONAL  
ACTIVITY SPREADING ACROSS GREAT BASIN TERRAIN TO THE ROCKIES WITH  
INLAND SHORTWAVE SYSTEM PROGRESSION. THERE IS ALSO THEN AN  
EMERGING GUIDANCE SIGNAL TO DIG UPPER TROUGH ENERGY FROM ALASKA TO  
RENEW PRECIPITATION INTO THE PACIFIC NORTHWEST BY NEXT WED/THU.  
 
SCHICHTEL  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE 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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