632
FXUS02 KWBC 151848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EST FRI DEC 15 2023
VALID 12Z MON DEC 18 2023 - 12Z FRI DEC 22 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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