936
FXUS02 KWBC 251859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST THU JAN 25 2024
VALID 12Z SUN JAN 28 2024 - 12Z THU FEB 1 2024
19Z UPDATE: THE 12Z MODEL GUIDANCE SUITE MAINTAINS GOOD OVERALL
AGREEMENT ACROSS THE CONTINENTAL U.S. ON SUNDAY WITH GOOD OVERALL
CONTINUITY FROM THE 00Z GUIDANCE. BY MONDAY, THE GUIDANCE IS
STILL IN GOOD AGREEMENT, BUT THE CMC IS LESS AMPLIFIED AND FASTER
WITH THE TROUGH SETTLING SOUTH ACROSS THE UPPER MIDWEST COMPARED
TO THE ECMWF/GFS, AND THIS HOLDS TRUE AS THIS SECONDARY TROUGH
EXITS THE EAST COAST BY MID-WEEK. THE 12Z GFS IS NOT NEARLY AS
STRONG AS THE 6Z RUN, AND IT IS SLOWER TO EXIT THE COAST COMPARED
TO THE ECMWF. AT THE TIME OF FRONTS/PRESSURES COMPOSITION, THE
00Z GFS SERVED AS A GOOD SUBSTITUTE FOR THE 6Z RUN SINCE THE
FORMER AGREED BETTER WITH THE OVERALL MODEL CONSENSUS FOR THE
SECOND HALF OF THE FORECAST PERIOD. MUCH MORE SUBSTANTIAL
DIFFERENCES COME INTO PLAY BY NEXT THURSDAY WITH THE GFS MUCH
STRONGER WITH A CLOSED LOW OVER SOUTH-CENTRAL CANADA AND DOES NOT
HAVE MUCH SUPPORT FROM IT ENSEMBLE MEAN, WHEREAS OVERALL MODEL
AGREEMENT IS DECENT ACROSS THE WEST COAST REGION THROUGH THIS
TIME. ENSEMBLE MEANS ACCOUNTED FOR ABOUT 50% OF THE FORECAST BY
NEXT THURSDAY. THE PREVIOUS FORECAST DISCUSSION IS APPENDED BELOW
FOR REFERENCE. /HAMRICK
---------------------
..GENERAL OVERVIEW
A STORM SYSTEM FORECAST TO EXIT AN INUNDATED SOUTH SATURDAY WILL
LIFT TO THE MID-ATLANTIC COAST AROUND SUNDAY NIGHT BEFORE EXITING
AS A COASTAL STORM. FOR SUNDAY INTO EARLY MONDAY, THE DEEPENING
SYSTEM SEEMS LIKELY TO PRODUCE A WRAPPED SWATH OF WELL ORGANIZED
PRECIPITATION FROM THE UPPER OHIO VALLEY/CENTRAL APPALACHIANS
THROUGH THE MID-ATLANTIC INTO NEW ENGLAND, WITH INTERIOR SNOWS
POSSIBLE FROM THE CENTRAL APPALACHIANS THROUGH INTERIOR
PENNSYLVANIA/NEW YORK/NEW ENGLAND. FAR UPSTREAM, PORTIONS OF THE
WEST COAST WILL ALSO BE RATHER UNSETTLED AT TIMES WITH MULTIPLE
ROUNDS OF RAIN EXPECTED FOR THE PACIFIC NORTHWEST WELL INTO NEXT
WEEK, LEADING INTO A LARGER ATMOSPHERIC RIVER EVENT SIGNAL NEXT
MIDWEEK FARTHER SOUTHWARD DOWN THE COAST INTO CALIFORNIA TO
MONITOR FOR SEVERITY AND IMPACT. MEANWHILE, A RELATIVELY QUIET
WEATHER PATTERN SHOULD BE IN PLACE FOR MUCH OF THE REST OF THE
LOWER 48.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LAST FEW MODEL CYCLES HAVE BEEN IN GOOD AGREEMENT ON THE
SYNOPTIC SCALE INTO NEXT WEEK, ALBEIT WITH AN OVERALL SLOWER
GUIDANCE TREND. THERE IS GENERALLY GOOD AGREEMENT THAT A LARGE
EASTERN PACIFIC UPPER TROUGH WITH A LEAD ATMOSPHERIC RIVER FOCUS
INTO COASTAL WASHINGTON/OLYMPICS INTO EARLY NEXT WEEK WILL WORK
MORE IN EARNEST TOWARD CALIFORNIA THROUGH NEXT MIDWEEK. THERE ARE
LINGERING DIFFERENCES WITH WEATHER FOCUS OF A MAIN SURFACE LOW TO
TRACK UP/OFF THE EASTERN SEABOARD SUNDAY INTO MONDAY, BUT THE
SYSTEM SEEMS DEEP ENOUGH TO WARRANT A MODERATE INCREASE IN QPF
VERSUS WPC CONTINUITY. LATER, QUITE A BIT OF UNCERTAINTY DEVELOPS
OVER THE CENTRAL TO EASTERN U.S. WITH A SERIES OF UPPER IMPULSES
DROPPING FROM CANADA, ALBEIT IN A RELATIVELY TRANQUIL WEATHER
REGIME. ACCORDINGLY, THE WPC FORECAST WAS PRIMARILY DERIVED FROM A
MULTI-DETERMINISTIC MODEL BLEND VALID FOR SUNDAY AND MONDAY,
TRANSITIONING TUESDAY AND FOR NEXT WEDNESDAY AND THURSDAY TO THE
MORE COMPATIBLE ENSEMBLE MEANS AMID GROWING FORECAST SPREAD AND
MODEL RUN TO RUN CONSISTENCY ISSUES AS NOTED.
..WEATHER/HAZARDS HIGHLIGHTS
DEEP LAYERED SOUTHERLY FLOW IN ADVANCE OF A SLOW MOVING AND
AMPLIFIED EASTERN PACIFIC UPPER TROUGH WILL LIFT AND CHANNEL DEEP
AND LONG FETCH MOISTURE UP ACROSS THE EASTERN PACIFIC, WITH EARLY
NEXT WEEK FOCUS LIKELY SHIFTED NORTHWARD OVER THE PACIFIC
NORTHWEST ON THE WESTERN PERIPHERY OF AN AMPLIFIED UPPER RIDGE
DOWNSTREAM OVER THE WEST. THIS WILL FUEL A PROTRACTED WET PERIOD
NEXT WEEK, WITH CONDITIONS ERODING WITH THE CUMULATIVE BUILDING OF
RAINFALL TOTALS. SYSTEMS EMBEDDED WITHIN THE LARGER SCALE FLOW
WILL PERIODICALLY ENHANCE ACTIVITY, AND MAY OVER TIME LEAD TO
RUNOFF ISSUES MAINLY FOR FAVORED FACING TERRAIN. THE WPC EXCESSIVE
RAINFALL OUTLOOKS (EROS) FOR DAY 4/SUNDAY AND DAY 5/MONDAY NOW
SHOW SMALL MARGINAL RISK THREAT AREAS CENTERED OVER THE OLYMPIC
PENINSULA TO HIGHLIGHT BEST MODEL GUIDANCE SIGNALS AND
TOPOGRAPHICAL FORCING, AND THIS HAS BEEN MAINTAINED FOR THE 12Z
UPDATE. IT IS IMPORTANT TO AGAIN NOTE THAT THE SLOW APPROACH OF A
LARGE EASTERN PACIFIC MEAN UPPER TROUGH IS EXPECTED TO ACT TO
REFOCUS A LEAD ATMOSPHERIC RIVER MORE IN EARNEST TOWARD CALIFORNIA
AROUND NEXT MIDWEEK WITH THE POTENTIAL FOR HEAVY RAINFALL AND
GROWING RUNOFF ISSUES.
AN ONGOING AND SIGNIFICANT RAINFALL EPISODE OVER THE GULF COAST
REGION WILL FINALLY TAPER OFF SATURDAY. GULF OF MEXICO TO ATLANTIC
MOISTURE FEED AHEAD OF THE LAST MAJOR SOUTHERN STREAM SHORTWAVE IN
THE SERIES WILL LIFT NORTHEASTWARD ON THE WESTERN PERIPHERY OF AN
AMPLIFIED DOWNSTREAM UPPER RIDGE. THE LIFTING OF THIS FEATURE AND
LOW ALSO FAVORS A MODERATE WRAPPED PRECIPITATION SWATH ACROSS THE
OHIO VALLEY, APPALACHIANS AND MID-ATLANTIC THROUGH THE NORTHEAST
THIS WEEKEND. WHILE WITHIN A WIDESPREAD AND SIGNIFICANTLY WARMER
PATTERN, ENOUGH COOLED AIR MAY REMAIN IN PLACE TO ALLOW FOR SNOW
ALONG WITH SOME WINDY CONDITIONS ON THE NORTHERN EDGE OF THE BROAD
PRECIPITATION SHIELD FROM THE CENTRAL APPALACHIANS THROUGH THE
INTERIOR NORTHEAST SUNDAY AS AIDED WITH A DEEPENING LOW TRACK
UP/OFF THE EAST COAST. THIS EMERGING COASTAL STORM WILL ALSO OFFER
A MARITIME RISK OFFSHORE THE MID-ATLANTIC THEN NEW ENGLAND SUNDAY
INTO MONDAY.
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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