928
FXUS02 KWBC 242105
PMDEPD
EXTENDED FORECAST DISCUSSION...AMENDED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 PM EST WED JAN 24 2024
VALID 12Z SAT JAN 27 2024 - 12Z WED JAN 31 2024
..GENERAL OVERVIEW
THE STORM SYSTEM THAT IS FORECAST TO BE OVER THE SOUTH-CENTRAL
U.S. ON SATURDAY IS EXPECTED TO REACH THE MID-ATLANTIC COAST BY
SUNDAY NIGHT. THIS WILL RESULT IN LOCALLY HEAVY RAINFALL ACROSS
THE SOUTHERN APPALACHIANS, AND INLAND SNOW FROM PORTIONS OF
PENNSYLVANIA TO CENTRAL NEW ENGLAND. THE WEST COAST WILL ALSO BE
RATHER UNSETTLED AT TIMES WITH MULTIPLE ROUNDS OF PRECIPITATION
EXPECTED AND A LARGER ATMOSPHERIC RIVER EVENT TOWARDS THE MIDDLE
OF NEXT WEEK. MEANWHILE, A RELATIVELY QUIET WEATHER PATTERN
SHOULD BE IN PLACE ACROSS THE ROCKIES AND INTO THE CENTRAL U.S.
AND MIDWEST STATES WITH HIGH PRESSURE IN PLACE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 12Z MODEL GUIDANCE SUITE IS IN GOOD OVERALL AGREEMENT ON THE
SYNOPTIC SCALE, INCLUDING THE POTENT SOUTHERN STREAM SHORTWAVE
TROUGH FOR THIS WEEKEND. THERE HAS BEEN AN OVERALL SLOWER TREND
IN THE GUIDANCE COMPARED TO THE 00Z CYCLE, WITH THE SURFACE LOW
DEPARTING THE EAST COAST LATER SUNDAY EVENING COMPARED TO EARLIER
FORECASTS. LOOKING AHEAD TO EARLY NEXT WEEK, THE GFS/GEFS MEAN
ARE FARTHER WEST WITH THE AXIS OF THE UPPER RIDGE ACROSS THE
NORTHERN ROCKIES, WHEREAS THE CMC/ECMWF ARE MORE DISPLACED TO THE
EAST. THERE IS GENERALLY GOOD AGREEMENT THAT A LARGE UPPER TROUGH
WITH A POTENTIAL ATMOSPHERIC RIVER WILL APPROACH THE WEST COAST
TOWARDS THE MIDDLE OF NEXT WEEK, BUT MORE UNCERTAINTY RESIDES
ACROSS THE UPPER MIDWEST WITH A TROUGH DROPPING SOUTHWARD FROM
CENTRAL CANADA. THE FRONTS/PRESSURES FORECAST WAS PRIMARILY
DERIVED FROM A MULTI-DETERMINISTIC MODEL BLEND THROUGH SUNDAY,
FOLLOWED BY GRADUALLY INCREASING PERCENTAGES OF THE ENSEMBLE MEANS
GOING INTO THE FIRST HALF OF NEXT WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
DEEP LAYERED SOUTHERLY FLOW IN ADVANCE OF A SLOW MOVING AND
AMPLIFIED EASTERN PACIFIC UPPER TROUGH WILL LIFT DEEP AND LONG
FETCH MOISTURE UP ACROSS THE EASTERN PACIFIC AND INTO NORTHERN
CALIFORNIA AND ALSO WESTERN OREGON AND THE OLYMPIC PENINSULA.
THIS WILL FUEL A PROTRACTED WET PERIOD OVER THE NEXT WEEK, WITH
CONDITIONS ERODING OVER TIME WITH THE CUMULATIVE BUILDING OF
RAINFALL TOTALS. LIFTING SYSTEMS EMBEDDED WITHIN THE LARGER SCALE
FLOW WILL PERIODICALLY ENHANCE ACTIVITY RIDING THE WESTERN
PERIPHERY OF AN AMPLIFIED DOWNSTREAM UPPER RIDGE OVER THE WEST,
AND MAY OVER TIME LEAD TO RUNOFF ISSUES MAINLY FOR FAVORED FACING
TERRAIN. THE WPC EXCESSIVE RAINFALL OUTLOOKS (EROS) FOR DAY
4/SATURDAY AND DAY 5/SUNDAY SHOW SMALL MARGINAL RISK THREAT AREAS
CENTERED OVER NW CALIFORNIA/SW OREGON AND FOR BOTH DAYS OVER THE
OLYMPICS TO HIGHLIGHT BEST MODEL GUIDANCE SIGNALS AND
TOPOGRAPHICAL FORCING.
AN ONGOING AND SIGNIFICANT RAINFALL EPISODE OVER THE GULF COAST
REGION WILL FINALLY TAPER OFF SATURDAY. DEEP 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. A REMAINING
THREAT FOR HEAVY RAIN UP FROM THE SOUTHEAST THROUGH THE SOUTHERN
APPALACHIANS AND VICINITY WITH SYSTEM APPROACH/PASSAGE AND
DEEPENING LOW FOCUS HAS PROMPTED A DAY 4/SATURDAY ERO MARGINAL
RISK AREA. FOR THE 12Z UPDATE, THE EXISTING DAY 4 MARGINAL RISK
WAS EXPANDED SOME TO ACCOUNT FOR MODEL VARIATIONS IN HIGHER QPF
PLACEMENT. THERE WAS ALSO A MODEST UPWARD TREND IN QPF ACROSS
PORTIONS OF THE SOUTHERN APPALACHIANS, AND IT'S POSSIBLE A SLIGHT
RISK AREA COULD EVENTUALLY BE NEEDED IN LATER FORECASTS.
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 OVER THE
INTERIOR NORTHEAST BY 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/HAMRICK
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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