814  
FXUS02 KWBC 160701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EST SAT DEC 16 2023  
 
VALID 12Z TUE DEC 19 2023 - 12Z SAT DEC 23 2023  
 
...COASTAL STORM TO BRING HEAVY RAIN/WIND AND MARITIME THREATS  
FROM THE MID-ATLANTIC TO NEW ENGLAND EARLY NEXT WEEK...  
...EMERGING HEAVY PRECIPITATION THREAT TO FOCUS INTO CALIFORNIA  
AND THE SOUTHWEST NEXT WEEK...  
 
   
..OVERVIEW
 
 
A DEEP COASTAL STORM IS FORECAST TO TRACK UP ALONG THE EAST COAST  
EARLY NEXT WEEK WITH WIDESPREAD HEAVY RAINFALL, HIGH WINDS, AND  
MARITIME THREATS. THERE MAY ALSO BE SOME SNOW ON THE FAR  
NORTHWESTERN/BACK SIDE OF THE STORM. SOME UNCERTAINTY REMAINS IN  
THE AMOUNTS AND PLACEMENT OF THE HEAVY RAIN DUE TO MODEL  
DIFFERENCES IN THE UPPER LEVELS AND A COMPLEX SURFACE LOW TRACK.  
AFTER THIS SYSTEM PUSHES OFFSHORE, A DRIER PATTERN WILL DEVELOP  
OVER THE EASTERN TWO-THIRDS OF THE NATION AS AN UPPER LOW MOVES  
SOUTH ALONG THE WEST COAST. THIS FEATURE WILL BRING PERIODS OF  
INCREASINGLY ORGANIZED PRECIPITATION AS IT SLOWLY MOVES INLAND  
INTO THE SOUTHWEST.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL AGREEMENT CONCERNING THE EAST COAST SYSTEM HAS IMPROVED OVER  
THE PAST COUPLE DAYS. THE SOUTHERN STREAM LOW WILL QUICKLY SWING  
UP THE EAST COAST WHILE A NORTHERN STREAM LOW MOVES FROM THE UPPER  
MIDWEST TOWARDS THE MID-ATLANTIC. MOST RECENT MODEL RUNS HAVE BEEN  
TRENDING FASTER WITH THE SOUTHERN STREAM LOW, WHICH WOULD ALLOW AT  
LEAST A PORTION OF THE UPPER LEVEL ENERGY OF THE NORTHERN STREAM  
LOW TO CONTINUE TO PUSH INTO THE ATLANTIC. THE MOST UNCERTAINTY IN  
THE FORECAST IS SURROUNDING THIS SPLIT IN UPPER LEVEL ENERGY  
MID-NEXT WEEK. EVEN SO, THE OVERALL PATTERN AND THREAT POTENTIAL  
SEEMS MORE UNIVERSALLY NOTED, SO A COMPOSITE GUIDANCE SOLUTION WAS  
USED TO MITIGATE SMALLER VARIANCES.  
 
AGREEMENT AMONG MODELS REMAINS MUCH BETTER IN THE WEST WITH  
RIDGING OVER THE INTERIOR WEST EARLY NEXT WEEK AND AN UPPER LEVEL  
TROUGH/LOW MOVING SOUTH ALONG THE WEST COAST MID-NEXT WEEK. THIS  
FEATURE WILL GRADUALLY PUSH INTO THE SOUTHWEST WITH ORGANIZED  
PRECIPITATION LATER NEXT WEEK. THERE ARE EXPECTED DIFFERENCES IN  
THE POSITION AND TIMING OF THE SYSTEM, AND A GENERAL MIDDLE OF THE  
ROAD SOLUTION WAS USED FOR THIS FORECAST.  
 
THE WPC FORECAST WAS BASED ON THE 00/06Z GUIDANCE THAT WAS  
AVAILABLE AT FORECAST PRODUCTION TIME. A BLEND OF THE 00Z  
ECMWF/UKMET/CMC AND 06Z GFS DETERMINISTIC GUIDANCE ALONG WITH THE  
GEFS AND ECMWF ENSEMBLE MEANS WAS USED OVER THE PERIOD WITH  
GRADUALLY INCREASING WEIGHT ON ENSEMBLE GUIDANCE OVER TIME.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A DEEP COASTAL LOW AND DEEP TROUGHING ALOFT WILL SUPPORT  
WIDESPREAD HEAVY RAINFALL AND STRONG COASTAL WINDS EARLY NEXT  
WEEK. THERE ARE SOME LINGERING DIFFERENCES IN THE PLACEMENT AND  
AMOUNTS OF RAINFALL, BUT FORECAST SPREAD IS DECREASING. BY MONDAY,  
THE LOW IS FORECAST TO LIFT QUICKLY NORTHWARD AND RAIN (AND SOME  
PLOWABLE SNOW ON THE BACKSIDE OF THE SYSTEM) WILL SPREAD/FOCUS  
INTO THE NORTHEAST. A DAY 4/MONDAY MARGINAL RISK OF EXCESSIVE  
RAINFALL IS IN PLACE FOR THE POTENTIALLY HEAVY RAINFALL WITH AN  
EMBEDDED SLIGHT RISK AREA FOR NORTHERN NEW ENGLAND GIVEN THE WET  
ANTECEDENT CONDITIONS AND MODEL/ENSEMBLE PROBABILITIES FOR  
ENHANCED WRAP-BACK AXIS AMOUNTS. PRECIPITATION SHOULD PULL AWAY ON  
TUESDAY, BUT LINGERING COASTAL SHOWERS COULD CONTINUE.  
 
PRECIPITATION CHANCES WILL BE INCREASING NEXT WEEK FOR CALIFORNIA  
AS SHORTWAVE ENERGY SUPPORTING A POSSIBLE ATMOSPHERIC RIVER  
APPROACHES. RAIN AMOUNTS AND RATES ON MONDAY COULD BE SUFFICIENT  
TO CAUSE SOME FLOODING CONCERNS, ESPECIALLY GIVEN SOME INSTABILITY  
COULD REACH COASTAL AREAS. MARGINAL RISKS OF EXCESSIVE RAINFALL  
ARE IN PLACE FOR MONDAY AND TUESDAY WHERE FLOODING MAY BE A  
CONCERN. MODERATE PRECIPITATION IS FORECAST TO ALSO PICK UP IN THE  
PACIFIC NORTHWEST MONDAY INTO TUESDAY AS A AN UPPER LOW MOVES DOWN  
THE COAST. SOME HIGHER ELEVATION SNOW WILL ALSO BE POSSIBLE. THE  
SLOW APPROACH OF THE CLOSED SYSTEM TOWARD SOUTHERN CALIFORNIA  
MID-LATER NEXT WEEK WOULD ACT TO SPREAD PRECIPITATION GRADUALLY  
INLAND, WITH ORGANIZED LEAD ACTIVITY WORKING INTO THE SOUTHWEST  
LATER NEXT WEEK. THERE MAY BE AN EMERGING WET PATTERN LATER NEXT  
WEEK IN THE SOUTH-CENTRAL U.S. WITH SOME DOWNSTREAM ENERGY FLOW  
AND RETURN GULF INFLOW.  
 
TEMPERATURES WILL BE WELL ABOVE AVERAGE IN THE NORTHEAST MONDAY  
INTO TUESDAY IN THE WARM SECTOR OF THE EAST COAST STORM SYSTEM,  
BUT TEMPERATURES WILL TREND DOWNWARDS THROUGH THE REST OF THE  
WEEK. ABOVE AVERAGE TEMPERATURES ARE ALSO EXPECTED TO PERSIST  
ACROSS THE WEST AND SPREAD INTO THE CENTRAL U.S. FOR THE SECOND  
HALF OF NEXT WEEK. TEMPERATURES IN THE SOUTHEAST WILL LIKELY  
REMAIN BELOW AVERAGE MONDAY THROUGH WEDNESDAY AS A COLD FRONT  
PASSES THROUGH AND HIGH PRESSURE BUILDS INTO THE REGION, AND FROST  
AND FREEZE CONDITIONS MAY EXTEND INTO PARTS OF NORTH FLORIDA.  
 
DOLAN/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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,  
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY  
MESSAGES 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/#PAGE=ERO  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 

 
 
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