592
FXUS02 KWBC 031858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT TUE OCT 03 2023
VALID 12Z FRI OCT 06 2023 - 12Z TUE OCT 10 2023
...HEAVY RAIN AND FLASH FLOODING THREATS RAMP UP IN THE NORTHEAST
LATE WEEK...
..OVERVIEW
AN UPPER TROUGH AND LIKELY AN EMBEDDED UPPER LOW ARE FORECAST TO
SWING SLOWLY THROUGH THE GREAT LAKES REGION SOUTHWARD LATE THIS
WEEK INTO EARLY NEXT WEEK, WHILE A COLD FRONT SWEEPS THROUGH THE
EASTERN U.S. AT THE SURFACE. RAIN CHANCES WILL INCREASE ALONG AND
AHEAD OF THE FRONT, AND HEAVY RAINFALL MAY CAUSE FLOODING CONCERNS
IN THE NORTHEAST ON FRIDAY AND SATURDAY. SOME RAIN (WITH LAKE
EFFECT ENHANCEMENT) COULD LINGER INTO EARLY NEXT WEEK UNDERNEATH
THE UPPER LOW. MEANWHILE AN UPPER RIDGE SHOULD OVERTAKE THE
WESTERN U.S. FOR WARMER THAN AVERAGE TEMPERATURES AND GENERALLY
DRY CONDITIONS, UNTIL EARLY NEXT WEEK WHEN A TROUGH AND FRONTAL
SYSTEM COULD PUSH INTO THE PACIFIC NORTHWEST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN GOOD AGREEMENT IN THE OVERALL PATTERN
THROUGH MOST OF THE FORECAST PERIOD AS A TROUGH OVER THE CENTER OF
THE COUNTRY EARLIER IN THE PERIOD WILL BE REINFORCED BY ADDITIONAL
SHORTWAVE ENERGY, DEEPENING OVER THE GREAT LAKES AS RIDGING OVER
THE WEST SHIFTS EASTWARD AND AMPLIFIES IN ITS WAKE OVER PORTIONS
OF THE NORTH-CENTRAL U.S. A DEEP UPPER-LEVEL LOW IS EXPECTED TO
DEVELOP IN THE VICINITY OF THE GREAT LAKES/INTERIOR NORTHEAST AS
INDICATED IN THE LAST FEW RUNS OF THE GFS AND NOW A SUPPORTED
TREND IN THE MORE RECENT RUNS OF THE ECMWF. THE CMC EVENTUALLY
ALSO DEVELOPS A CLOSED LOW BY MID-PERIOD. THE SPREAD AROUND THE
EXACT EVOLUTION OF THE CORE OF UPPER-LEVEL ENERGY ASSOCIATED WITH
THIS TROUGH EXPECTEDLY INCREASES MID- TO LATE PERIOD, THOUGH DEEP
MEAN TROUGHING SHOULD REMAIN IN PLACE OVER GREAT LAKES/NORTHEAST
THROUGH THE END OF THE PERIOD. TO THE WEST, THERE IS A BIT MORE
DISAGREEMENT WITH BOTH THE AMPLIFICATION OF THE RIDGING FROM THE
WESTERN INTO THE NORTH-CENTRAL U.S. AND THE APPROACH OF UPSTREAM
ENERGY OVER THE NORTHEASTERN PACIFIC. BOTH THE MORE RECENT RUNS OF
THE ECMWF AND GFS HAVE VARIED A BIT IN HOW AMPLIFIED THE PATTERN
WILL BE, WITH THE 00Z ECMWF MORE AMPLIFIED AND THE GFS TRENDING
LESS AMPLIFIED. THE ECENS MEAN IS A BIT MORE AMPLIFIED THAN THE
GEFS MEAN, THOUGH THESE SOLUTIONS AT LEAST PROVIDE A CLOSER
COMPROMISE BETWEEN THE MORE VARIED DETERMINISTIC SOLUTIONS. THIS
WILL HAVE AN IMPACT ON THE TIMING AND AMOUNT OF POTENTIAL
PRECIPITATION COMING INTO THE NORTHWESTERN U.S. BY EARLY NEXT
WEEK, WITH MORE SHORTWAVE ENERGY OVERSPREADING THE REGION EARLIER
WITH THE LESS AMPLIFIED SOLUTIONS DUE TO THE LACK OF RIDGING
UPSTREAM. FINALLY, THERE IS A BIT OF DISAGREEMENT WITH RESPECT TO
A WEAKNESS IN THE SOUTHERN STREAM OVER THE SOUTHWEST MID- TO LATE
PERIOD, BUT THIS CURRENTLY LOOKS TO HAVE LITTLE SENSIBLE WEATHER
IMPACT DUE TO THE LACK OF AVAILABLE MOISTURE FOLLOWING A STRONG
FRONTAL PASSAGE.
THE UPDATED WPC FORECAST BEGAN WITH A COMPOSITE BLEND OF THE 00Z
ECMWF/CMC/UKMET AND 06Z GFS GIVEN GOOD OVERALL AGREEMENT. THE
CONTRIBUTION FROM THE CMC WAS REDUCED A BIT MID- TO LATE PERIOD AS
THE TIMING AND EVOLUTION OF THE UPPER LEVEL LOW OVER THE GREAT
LAKES/NORTHEAST DIVERGED SOME FROM THE ECMWF/UKMET/GFS SOLUTIONS.
A RAMP UP TO A 50% CONTRIBUTION FROM THE ECENS/GEFS MEANS WAS
ADDED BY THE END OF THE PERIOD AS FURTHER SPREAD ARISES WITH
RESPECT TO THE AMPLIFYING PATTERN OVER THE WESTERN/CENTRAL U.S.
..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 ON FRIDAY
AND 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. FORECAST RAIN AMOUNTS ACROSS
THE GUIDANCE HAVE BEEN TRENDING UPWARD, PARTICULARLY ON SATURDAY,
WITH UPSLOPE FLOW/TERRAIN ENHANCEMENT LIKELY PLAYING A
CONTRIBUTING ROLE FOR LOCALLY HEAVIER TOTALS IN THE INTERIOR
NORTHEAST. THUS, A MARGINAL RISK REMAINS IN PLACE ACROSS THE LOWER
GREAT LAKES REGION AND PARTS OF THE NORTHERN MID-ATLANTIC AND
NORTHEAST FOR DAY 4/FRIDAY WITH A SLIGHT RISK ACROSS THE INTERIOR
NORTHEAST AND INTO NORTHERN NEW ENGLAND ON DAY 5/SATURDAY. THE
HEAVY RAIN THREAT WILL LIKELY BE OVER BY SUNDAY BUT SHOWERS WILL
LINGER FOR PORTIONS OF NORTHERN NEW ENGLAND ALONG WITH LAKE-EFFECT
ENHANCED SHOWERS FOR THE LOWER GREAT LAKES AS A DEEP UPPER-LOW
REMAINS OVERHEAD.
FARTHER SOUTH, THE TAIL END OF THE COLD FRONT COULD LINGER INTO
SOUTH TEXAS INTO AT LEAST FRIDAY, SPARKING ADDITIONAL SHOWERS AND
THUNDERSTORMS THERE AFTER A FEW WET DAYS. A MARGINAL RISK REMAINS
IN PLACE FOR THE DAY 4 ERO/FRIDAY. RAIN AMOUNTS LOOK TO GRADUALLY
LESSEN THIS WEEKEND INTO EARLY NEXT WEEK. MEANWHILE, CONDITIONS IN
THE WEST LOOK TO BE DRY UNDER THE UPPER RIDGE, ASIDE FROM LIMITED
SHOWERS POSSIBLE IN THE SOUTHWEST. THIS IS LIKELY TO CHANGE EARLY
NEXT WEEK AS A FRONT AND UPPER TROUGH BRING SOME MODERATE TO
LOCALLY HEAVY RAIN TO THE PACIFIC NORTHWEST, EVENTUALLY SPREADING
INTO THE NORTHERN GREAT BASIN/ROCKIES.
HIGH TEMPERATURES ACROSS THE PLAINS INTO MIDWEST WILL BE BELOW
AVERAGE BY 10-20F FRIDAY FOLLOWING A COLD FRONTAL PASSAGE WHILE
ONE MORE WARMER THAN AVERAGE DAY IS POSSIBLE IN THE NORTHEAST.
LOWS LOOK TO BE A LITTLE LESS ANOMALOUS FRIDAY MORNING BUT COULD
DROP FURTHER ON SATURDAY, WITH LOW 30S AND PERHAPS A FEW
TEMPERATURES IN THE UPPER 20S IN THE NORTHERN HALF OF THE PLAINS,
CREATING THE POSSIBILITY OF THE FIRST FROST OR FREEZE OF THE
SEASON. AS THE UPPER TROUGH AND COLD FRONT(S) MARCH EAST INTO THE
WEEKEND, TEMPERATURES SHOULD COOL TO BELOW AVERAGE ACROSS THE
EAST-CENTRAL U.S. MEANWHILE, THE ARRIVAL OF AN UPPER RIDGE ACROSS
THE WEST WILL FIRST RAISE TEMPERATURES ALONG THE WEST COAST TO
10-15F ABOVE NORMAL, 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.
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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