735
FXUS02 KWBC 231849
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EST TUE JAN 23 2024
VALID 12Z FRI JAN 26 2024 - 12Z TUE JAN 30 2024
...EXCESSIVE RAINFALL/FLOODING THREAT OVER THE SOUTH TO CONTINUE
LATE WEEK FROM THE GULF COAST STATES TO THE SOUTHERN
APPALACHIANS...
..OVERVIEW
A SIGNIFICANT AND PROTRACTED RAINFALL EVENT IS EXPECTED TODAY
THROUGH SATURDAY WITH HEAVY RAIN/CONVECTION AND RUNOFF THREATS
AMID A SLOW TO TRANSLATE AND AMPLIFIED PATTERN, WITH PRIMARY FOCUS
TO REFORM AND SPREAD FROM SOUTHEAST TEXAS THROUGH THE LOWER
MISSISSIPPI/TENNESSEE VALLEYS AND GULF COAST STATES THROUGH THE
SOUTHERN APPALACHIANS AND VICINITY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, GUIDANCE IS IN GOOD AGREEMENT THAT SHORTWAVE ENERGY
TRANSLATING DOWN FROM CANADA TO REINFORCE MEAN TROUGHING ANCHORED
OVER THE WESTERN/CENTRAL U.S. THE PAST SEVERAL DAYS SHOULD ALSO BE
ENOUGH TO FINALLY PUSH THE TROUGH TOWARDS THE EASTERN U.S. THIS
WEEKEND WITH A RIDGE BUILDING OVER THE WEST. THE PATTERN CHANGE
SHOULD BE WELCOME RELIEF TO PORTIONS OF THE SOUTH THAT WILL HAVE
SEEN A CONTINUOUS MOIST GULF FLOW AND HEAVY RAIN EVENT AHEAD OF
THIS STUBBORN TROUGHING THROUGH THE SHORT RANGE PERIOD AND INTO
THE EARLY MEDIUM RANGE PERIOD. PREDICTABILITY FOR THE LARGE-SCALE
PATTERN LOOKS ABOVE AVERAGE THROUGH AT LEAST THE START OF THE
WEEKEND WITH LITTLE NOTABLE DIFFERENCES IN THE LATEST FEW RUNS OF
THE GFS/ECMWF. HOWEVER, MORE SUBTLE TRENDS FOR STRONGER LEAD
ENERGY/DEEPER CLOSED LOW LIFTING NORTHEASTWARD AS THIS TROUGH
INITIALLY SHIFTS TOWARDS THE EAST COAST, AS WELL AS A MORE
NORTHERLY/COASTAL TRACK OF ACCOMPANYING SURFACE LOW PRESSURE, HAS
LED TO AN UPWARD TREND IN INLAND QPF FROM THE OHIO VALLEY/LOWER
GREAT LAKES INTO THE NORTHEAST.
LATER IN THE PERIOD EARLY NEXT WEEK, MAIN TREND IS STILL A
CONSOLIDATION AROUND MEAN EASTERN TROUGHING/WESTERN RIDGE. THE
OVERALL DEGREE OF AMPLIFICATION SHOWS THE MOST UNCERTAINTY BETWEEN
THE GUIDANCE, WITH SOME EMBEDDED SHORTWAVE ENERGY WITHIN THE RIDGE
IN THE GFS/GEFS MEAN, AND ALSO SOME DISAGREEMENT IN THE DEGREE OF
TROUGHING AND PACIFIC SYSTEM TRACK IMPINGING ON THE PACIFIC
NORTHWEST. UPDATED WPC FORECAST FOLLOWS SUIT WITH THE PRIOR
FORECAST USING A COMPOSITE BLEND OF THE DETERMINISTIC GUIDANCE
EARLY IN THE PERIOD GIVEN GOOD OVERALL AGREEMENT AND NO PARTICULAR
OUTLIER FORECASTS, AND A CONTRIBUTION FROM THE ECENS AND GEFS MEAN
IN THE LATE PERIOD TO HELP SMOOTH OUT EXPECTED INCREASING
DIFFERENCES IN SMALLER-SCALE SHORTWAVE ENERGY.
..WEATHER/HAZARDS HIGHLIGHTS
AN AMPLIFIED UPPER RIDGE WILL BUILD OVER THE WEST COAST BY FRIDAY
THAT SHOULD PROVE SLOW TO SHIFT EASTWARD ACROSS A WARMER AND
STABILIZED WEST THROUGH NEXT TUESDAY. A SERIES OF AMPLIFIED
EASTERN PACIFIC SYSTEMS WILL LIFT OFFSHORE AND BRING AN AXIS OF
LONG FETCH MOISTURE UP ON THE WESTERN PERIPHERY OF THE SHIELDING
RIDGE, WITH MAIN FOCUS INTO FAVORED TERRAIN WITHIN COASTAL AREAS
FROM THE PACIFIC NORTHWEST TO NORTHERN CALIFORNIA. WPC EXCESSIVE
RAINFALL OUTLOOKS (ERO) FOR DAY 4/FRIDAY AND DAY 5/SATURDAY OFFER
MARGINAL RISK THREAT AREAS OVER NW CALIFORNIA/SW OREGON AND THE
OLYMPICS TO HIGHLIGHT BEST GUIDANCE SIGNALS AND LEADS INTO
ADDITIONAL WET COASTAL WEATHER POTENTIAL LATER WEEKEND INTO EARLY
NEXT WEEK. THERE IS A STRONG SIGNAL IN THE GUIDANCE FOR
POTENTIALLY VERY HEAVY TOTALS AND HIGHER-LEVEL IMPACTS FOR NW
CALIFORNIA/SW OREGON DAY 4, ESPECIALLY GIVEN WET PATTERN AND
SUSCEPTIBILITY TO LANDSLIDES, BUT VERY LOCALIZED NATURE LEADS TO
PREDICTABILITY CONCERNS AT THIS TIME FRAME FOR A TARGETED SLIGHT
RISK.
A SIGNIFICANT RAINFALL EPISODE OVER THE SOUTH WILL LINGER INTO
FRIDAY/SATURDAY AS DEEP MOISTURE FEED IN ADVANCE OF THE LAST MAJOR
SOUTHERN STREAM SHORTWAVE IN THE SERIES WORKS ACROSS THE REGION
AND LIFTS ENERGETICALLY NORTHEASTWARD ON THE WESTERN PERIPHERY OF
A SLOW TO RECEDE SOUTHEAST/EAST DOWNSTREAM UPPER RIDGE. A
REMAINING THREAT FOR LEADING HEAVY RAIN AND THUNDERSTORMS THROUGH
THE GULF COAST STATES INTO THE SOUTHEAST/SOUTHERN APPALACHIANS AND
VICINITY WITH SYSTEM APPROACH/PASSAGE AND ENHANCED FRONTAL
WAVE/DEEPENING LOW FOCUS HAS PROMPTED ISSUANCE OF A DAY 4/FRIDAY
SLIGHT RISK AREA ERO OVER THE CENTRAL GULF COAST STATES WITH A
SURROUNDING MARGINAL RISK AREA DAY 4/FRIDAY EXTENDING UP
THROUGH/LEE OF THE SOUTHERN APPALACHIANS DAY 5/SATURDAY. AREAS IN
VICINITY OF THE TRACK OF THE INITIALLY CLOSED UPPER CENTER MAY
ALSO SEE LOCALLY HEAVIER DOWNPOURS AS HIGHLIGHTED BY THE DAY
4/FRIDAY MARGINAL RISK AREA ERO OVER OKLAHOMA/NORTH TEXAS. THIS
LIFTING/SHEARING OF THIS FEATURE FAVORS A MODERATE PRECIPITATION
SWATH NORTHEASTWARD ACROSS THE MID-SOUTH AND OHIO VALLEY/LOWER
GREAT LAKES THROUGH THE CENTRAL APPALACHIANS, MID-ATLANTIC AND NEW
ENGLAND THROUGH THE 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 INTO THE INTERIOR
NORTHEAST AND NEW ENGLAND BY SUNDAY AS AIDED WITH A DEEPENING LOW
TRACK UP/OFF THE EAST COAST. THE TREND IN THE GUIDANCE HAS BEEN
FOR HIGHER QPF FURTHER NORTH AND INLAND, WITH A CORRESPONDING
INCREASE IN THE POTENTIAL FOR THIS WINTRY WEATHER. THIS STORM
SHOULD BECOME STRONG ENOUGH TO BE A MARITIME HAZARD OFF THE
MID-ATLANTIC THEN NEW ENGLAND SUNDAY INTO MONDAY.
PUTNAM/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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