459
FXUS02 KWBC 041848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 PM EDT WED OCT 04 2023
VALID 12Z SAT OCT 07 2023 - 12Z WED OCT 11 2023
...HEAVY RAIN AND FLASH FLOODING THREATS LIKELY IN THE NORTHEAST
SATURDAY DUE IN PART TO PHILIPPE...
..OVERVIEW
AN UPPER TROUGH AND LIKELY AN EMBEDDED UPPER LOW ARE FORECAST TO
SWING SLOWLY THROUGH THE GREAT LAKES REGION AND SOUTH THIS
WEEKEND. AT THE SURFACE A COLD FRONT WILL SWEEP THROUGH THE
EASTERN U.S., WHILE AMPLE MOISTURE STREAMS IN AHEAD OF IT, AND THE
LOW CIRCULATION ASSOCIATED WITH PHILIPPE (WHICH SHOULD BE
POST-TROPICAL BY THEN) COULD TRACK NEAR OR INTO MAINE. THIS
COMBINATION WILL LEAD TO HEAVY RAIN AND FLOODING CONCERNS IN THE
NORTHEAST ON SATURDAY. THEN SOME RAIN COULD LINGER INTO EARLY NEXT
WEEK UNDERNEATH THE UPPER LOW, WITH LAKE EFFECT ENHANCEMENT
LIKELY. MEANWHILE AN UPPER RIDGE SHOULD OVERTAKE THE WESTERN U.S.
FOR WARMER THAN AVERAGE TEMPERATURES AND GENERALLY DRY CONDITIONS
THROUGH SATURDAY, THOUGH EARLY NEXT WEEK A TROUGH AND FRONTAL
SYSTEM LOOKS TO PUSH INTO THE PACIFIC NORTHWEST AND FARTHER INTO
THE INTERIOR WEST AS NEXT WEEK PROGRESSES WITH SOME LOCALLY HEAVY
RAINFALL POSSIBLE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE HAS REMAINED IN GOOD AGREEMENT ON THE OVERALL
PATTERN THROUGH MUCH OF THE MEDIUM-RANGE PERIOD (SATURDAY OCT 7 -
WEDNESDAY OCT 11), BEGINNING WITH A NORTHERN STREAM TROUGH OVER
SOUTH-CENTRAL CANADA/THE NORTH-CENTRAL U.S. DEEPENING AS IT SHIFTS
EASTWARD OVER SOUTHEASTERN CANADA AND THE GREAT LAKES/INTERIOR
NORTHEAST. A CLOSED LOW IS EXPECTED TO DEVELOP AND BECOME ANCHORED
OVER THE REGION FOR SEVERAL DAYS, LIKELY THROUGH AT LEAST THE END
OF THE CURRENT PERIOD (WEDNESDAY). EMBEDDED SHORTWAVE ENERGY MAY
PLAY A ROLE IN THE OVERALL GYRE WHICH DIFFERS MODEL TO MODEL, AND
MAY HAVE RELATED SURFACE WEATHER IMPACTS, BUT AN OVERALL WET AND
COOLER TREND CAN BE EXPECTED ACROSS THE REGION REGARDLESS.
HOWEVER, THERE IS ONE NOTABLE SHIFT IN SOME OF THE MORE RECENT
MODEL RUNS NOTED IN THE PRIOR FORECAST RELATED TO THE TRACK OF
WHAT IS NOW TROPICAL STORM PHILIPPE. THE GUIDANCE HAS TRENDED
TOWARDS A TRACK THAT WOULD BRING PHILIPPE INTO MAINE/ATLANTIC
CANADA, WITH THE POST-TROPICAL ENERGY BEING ABSORBED INTO THE
ANCHORED CLOSED LOW. THE SMALLER-SCALE NATURE OF THIS FEATURE
LOWERS PREDICTABILITY AT THIS TIME FRAME, AND THE EVOLUTION OF THE
SYSTEM APPEARS COMPLEX GIVEN THE LIKELY INTERACTION WITH THE
SYNOPTIC SYSTEM OVER THE GREAT LAKES/SOUTHEAST CANADA, THOUGH THE
EXPECTATION FOR A VERY WET SATURDAY IN THE INTERIOR NORTHEAST/NEW
ENGLAND WILL REMAIN REGARDLESS. REFER TO THE NATIONAL HURRICANE
CENTER FOR THE LATEST OFFICIAL UPDATED STORM TRACK FOR PHILIPPE.
TO THE WEST, AN UPPER-LEVEL RIDGE OVER THE WESTERN U.S. SHOULD
SHIFT A BIT EASTWARD, WITH RIDGING AMPLIFYING INTO THE NORTHERN
PLAINS/SOUTH-CENTRAL CANADA IN RESPONSE TO THE DEEPENING TROUGH TO
THE EAST. THE 00Z ECMWF AND CMC ARE A BIT MORE AMPLIFIED COMPARED
TO SOME RECENT RUNS OF THE GFS, THOUGH THE 06/12Z GFS HAVE TRENDED
MORE IN THIS DIRECTION, WITH THE GEFS MEAN ALSO IN AGREEMENT. THE
LARGEST SPREAD IN THE GUIDANCE IS RELATED TO UPSTREAM ENERGY OVER
THE NORTHEASTERN PACIFIC APPROACHING AND ENTERING THE NORTHWEST
EARLY NEXT WEEK, WITH DIFFERENCES IN THE TIMING, TRACK, AND
STRENGTH OF THE ENERGY ENTERING THE NORTHWEST BOTH ACROSS THE
GUIDANCE AND INDIVIDUALLY RUN-TO-RUN. FOR EXAMPLE, THE ECMWF HAS
WAVERED BACK AND FORTH IN THE LATEST FEW RUNS WITH A STRONGER,
DEEPER TROUGH DIGGING ALONG THE WEST COAST. THE MOST RECENT 00Z
RUN TRENDED WEAKER, WHICH IS MORE IN LINE WITH THE OTHER
DETERMINISTIC AND ENSEMBLE GUIDANCE. THE SPREAD INCREASES INTO
WEDNESDAY WITH GENERALLY POOR AGREEMENT ON THE ENERGY TRANSLATING
THROUGH THE WEST, EITHER HANGING BACK OVER THE GREAT BASIN (GFS)
OR DIGGING OVER THE HIGH PLAINS (ECMWF), WITH THE GEFS AND ECENS
MEANS EXPECTEDLY IN THE MIDDLE OF THE GUIDANCE ENVELOPE. ONE FINAL
POTENTIAL WRINKLE LATE IN THE FORECAST PERIOD IS FOR THE REMNANTS
OF A TROPICAL SYSTEM OVER THE EASTERN PACIFIC DRIFTING NORTHWARD
OVER MEXICO INTO THE SOUTHWEST/SOUTH TEXAS, HINTED AT IN SOME RUNS
OF THE GFS AND THE LATEST 00Z RUN OF THE CMC, WHICH WILL NEED TO
BE MONITORED OVER THE COMING DAYS IF THIS TREND CONTINUES AND
PREDICTABILITY INCREASES.
THE UPDATED WPC FORECAST BEGINS WITH A COMPOSITE BLEND OF THE
DETERMINISTIC GUIDANCE (00Z CMC/ECMWF/UKMET AND 06Z GFS) GIVEN
GOOD OVERALL AGREEMENT EARLY IN THE PERIOD. THE CONTRIBUTION FROM
THE 00Z CMC IS REDUCED MID-PERIOD GIVEN A MORE AGGRESSIVE
ASSESSMENT OF THE ENERGY UPSTREAM OVER THE NORTHEASTERN PACIFIC. A
CONTRIBUTION FROM THE 00Z ECENS AND GEFS MEANS IS STEADILY
INCREASED TO MORE THAN HALF THE BLEND BY THE END OF THE PERIOD
GIVEN THE NOTABLE INCREASE IN SPREAD WITH RESPECT TO THE HANDLING
OF THIS ENERGY OVER THE NORTHEASTERN PACIFIC AFTER IT ENTERS THE
WEST, OFFERING A COMPROMISE IN THE MIDDLE OF THE RESPECTIVE
SOLUTIONS.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER TROUGH AND FORMING EMBEDDED LOW TRACK ACROSS THE
GREAT LAKES LATE WEEK, ATLANTIC MOISTURE IS LIKELY TO FLOW INTO
THE NORTHEASTERN U.S., LEADING TO INCREASING RAIN TOTALS
ESPECIALLY BY SATURDAY ALONG AND AHEAD OF THE COLD FRONT.
INSTABILITY MAY BE SOMEWHAT LIMITED, BUT THE FORCING FOR ASCENT
WILL BE STRONG WITH THE RIGHT ENTRANCE REGION OF THE JET OVERHEAD,
AND PRECIPITABLE WATER ANOMALIES ARE FORECAST TO BE AT LEAST ABOVE
THE 75TH IF NOT THE 90TH PERCENTILE. ADDITIONALLY, THE LOW
PRESSURE SYSTEM THAT IS CURRENTLY TROPICAL STORM PHILIPPE, BUT IS
FORECAST TO BE POST-TROPICAL BY THAT TIME PER THE NATIONAL
HURRICANE CENTER, HAS SHOWN A WESTWARD TREND OVER THE PAST DAY AND
IS CURRENTLY EXPECTED TO TRACK INTO MAINE OR SURROUNDING AREAS.
NOT ONLY WOULD THIS BRING THE POTENTIAL FOR RAINFALL ASSOCIATED
WITH THE SYSTEM DIRECTLY, BUT THE INCREASED MOISTURE ALONG WITH
THE NOTED OVERLAP OF THE COLD FRONT AND UPPER JET MAY LEAD TO
LOCALLY ENHANCED RAINFALL IN THE INTERIOR AS PART OF A PREDECESSOR
RAIN EVENT AHEAD OF THE SYSTEM. UPSLOPE FLOW/TERRAIN ENHANCEMENT
COULD PLAY A CONTRIBUTING ROLE IN PRODUCING LOCALLY HEAVIER TOTALS
IN SOME TERRAIN AREAS AS WELL. GIVEN ALL THIS, A SLIGHT RISK
REMAINS IN PLACE FOR NORTHEASTERN NEW YORK INTO PARTS OF NEW
ENGLAND FOR DAY 4/SATURDAY, AND IT IS POSSIBLE THIS MAY NEED TO BE
UPGRADED IN FUTURE OUTLOOKS WITH MORE CONFIDENCE IN THE TRACK OF
PHILIPPE AND THIS CULMINATION OF SCENARIOS. THE HEAVY RAIN THREAT
WILL LIKELY BE OVER BY SUNDAY, THOUGH THERE IS A SMALL CHANCE IT
COULD PERSIST IN MAINE, BUT SHOWERS WILL LINGER FOR PORTIONS OF
NORTHERN NEW ENGLAND ALONG WITH LAKE EFFECT/ENHANCED SHOWERS FOR
THE LOWER GREAT LAKES UNDERNEATH THE DEEP UPPER LOW.
ELSEWHERE, MUCH OF THE COUNTRY SHOULD BE DRY THROUGH THE WEEKEND,
ASIDE FROM SOME LINGERING LIGHT RAIN POSSIBLE IN SOUTH TEXAS AND
SOME LIMITED SHOWERS IN THE SOUTHWEST. BUT THE PACIFIC NORTHWEST
SHOULD START TO SEE INCREASING PRECIPITATION CHANCES EARLY NEXT
WEEK AS A FRONT AND UPPER TROUGH APPROACH, AND PRECIPITATION IS
FORECAST TO SPREAD EAST WITH TIME INTO THE INTERIOR WEST. LOCALLY
HEAVY RAINFALL WILL BE POSSIBLE ALONG UPSLOPE AREAS OF THE COASTAL
MOUNTAIN RANGES, OLYMPICS, AND CASCADES AS THE SYSTEM DRAWS A
PLUME OF PACIFIC MOISTURE NORTHEASTWARD INTO THE REGION. SOME SNOW
IS ALSO POSSIBLE IN THE HIGHER ELEVATIONS OF THE CASCADES AND
NORTHERN ROCKIES.
COOLER THAN NORMAL TEMPERATURES WILL BE IN PLACE ACROSS THE
CENTRAL U.S. ON SATURDAY, WITH THE NORTHERN HALF OF THE PLAINS AT
RISK OF ITS FIRST FROST OR FREEZE OF THE SEASON. THESE BELOW
AVERAGE TEMPERATURES ARE FORECAST TO SHIFT EAST EARLY NEXT WEEK
UNDER THE UPPER TROUGH/LOW BEHIND THE COLD FRONT. LOWS AROUND
10-15F BELOW NORMAL AND HIGHS OF 10-20F BELOW NORMAL ARE LIKELY
ACROSS THE EAST-CENTRAL U.S. AND REACHING THE EASTERN SEABOARD.
THESE LOOK TO GRADUALLY MODERATE TOWARDS MIDWEEK, LINGERING
LONGEST IN VICINITY OF THE LOWER GREAT LAKES/INTERIOR NORTHEAST AS
THE STUBBORN UPPER-LOW IS EXPECTED TO REMAIN. MEANWHILE, THE
INITIAL UPPER RIDGE ACROSS THE WEST WILL RAISE TEMPERATURES ALONG
THE WEST COAST TO 10-15F ABOVE NORMAL ON SATURDAY, WITH SOME
RECORD WARM LOWS POSSIBLE. THE SHIFT/EXPANSION OF THE RIDGE
FARTHER EAST SHOULD LEAD TO WARMER THAN AVERAGE TEMPERATURES
ACROSS THE NORTHERN ROCKIES AND INTO THE HIGH PLAINS EARLY NEXT
WEEK. BUT THE WEST COAST IS EXPECTED TO FLIP TO BELOW AVERAGE
ESPECIALLY IN TERMS OF HIGHS BY TUESDAY-WEDNESDAY AS THE NEXT
TROUGH AND LOW APPROACH.
PUTNAM/TATE
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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