939
FXUS61 KBOX 051854
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
ISSUED BY NATIONAL WEATHER SERVICE GRAY ME
254 PM EDT MON MAY 5 2025
SYNOPSIS
UNSETTLED WEATHER WILL CONTINUE MUCH OF THIS WEEK WITH
SHOWERS/ISOLATED THUNDERSTORMS THAT WILL PRODUCE HEAVY RAINFALL AT
TIMES. APPEARS WE MAY BRIEFLY DRY OUT BY THURSDAY, BEFORE MORE RAIN
ARRIVES FRIDAY INTO SATURDAY. DEPENDING ON HOW MUCH RAIN FALLS, WE
COULD SEE RISES OVER BANKFULL ON LARGER RIVERS AND SMALLER STREAMS
ACROSS INTERIOR SOUTHERN NEW ENGLAND.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES...
* PERIODS OF SHOWERS TODAY WITH THE FOCUS FOR THEM NORTHWEST OF I-95
AND ESPECIALLY IN WESTERN MA AND CT
* MUCH COOLER TODAY WITH AM HIGHS IN THE 50S ACROSS CENTRAL/EASTERN
MA TO THE 60S IN CT/RI/SE ME WITH FALLING TEMPS PERHAPS INTO THE
UPPER 40S ACROSS CENTRAL AND EASTERN MA BY AFTERNOON
DETAILS...
HIGH PRESSURE OVER QUEBEC WILL SHIFT INTO THE MARITIMES TODAY. THIS
WILL COMBINED WITH AN ANOMALOUS CLOSED UPPER LEVEL LOW IN THE OHIO
VALLEY. THE PRESSURE GRADIENT WILL RESULT IN AN INCREASING SE LLJ
WITH THE FOCUS OF IT ACROSS WESTERN MA/CT AND INTO PORTIONS OF
EASTERN NY. THIS MODEST SOUTHEAST LLJ WILL HAVE A PWAT PLUME OF OVER
1.25 INCHES TO TAP THAT WILL ALSO BE OVER RUNNING A SHALLOW BACKDOOR
COLD FRONT TO THE SOUTHWEST OF THE REGION. GIVEN ALL THESE
INGREDIENTS...PERIODS OF SHOWERS ARE EXPECTED TODAY WITH THE FOCUS
TO THE NORTHWEST OF I-95 AND ESPECIALLY INTO WESTERN MA/CT WHERE THE
STRONGER FORCING IS LOCATED. AND WITH THE RELATIVELY HIGH PWAT PLUME
IN PLACE...SOME OF THESE SHOWERS WILL CONTAIN HEAVY RAINFALL.
IT WILL BE QUITE A BIT COOLER TODAY BEHIND THE BACKDOOR COLD FRONT.
MORNING HIGHS WILL ONLY BE IN THE 50S FOR CENTRAL AND NORTHEAST MA
AND IN THE 60S ACROSS PARTS CT/RI/SE MA. HOWEVER...TEMPS WILL FALL
THROUGH THE DAY AS COOLER NE LOW LEVEL FLOW CONTINUES TO PUSH INTO
THE REGION. AFTERNOON TEMPS MAY FALL INTO THE UPPER 40S ACROSS
CENTRAL AND NORTHEAST MA BY AFTERNOON!
SO IN A NUTSHELL...MUCH COOLER TEMPS WITH PERIODS OF SHOWERS ARE ON
TAP TODAY WITH THE FOCUS FOR THEM NORTHWEST OF I-95 AND ESPECIALLY
IN WESTERN MA/CT. MEANWHILE...SOUTHEAST OF THE I-95 CORRIDOR AND
PARTICULARLY TOWARDS THE CAPE/ISLANDS WE STILL MAY SEE A FEW SHOWERS
BUT MUCH OF THE DAY MAY END UP DRY.
SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
KEY MESSAGES:
* PERIODS OF SHOWERS WITH BANDS OF HEAVY RAINFALL AND PERHAPS A FEW
EMBEDDED T-STORMS TONIGHT INTO TUE ESPECIALLY ACROSS INTERIOR MA/CT
* LOW PROBABILITY FOR ISOLATED FLASH FLOODING ACROSS INTERIOR MA & CT
DETAILS...
TONIGHT AND TUESDAY...
ANOMALOUS DEEP CLOSED LOW OVER THE OHIO VALLEY WILL SLOWLY LIFT INTO
WESTERN PA THROUGH TUE. THIS WILL CONTINUE TO RESULT IN A MODEST SSE
LLJ WITH A PWAT PLUME BETWEEN 1.25 AND 1.50 INCHES. AT THE SAME
TIME...THE BACKDOOR COLD FRONT WILL BEGIN TO MOVE BACK NORTHWARD AS
A WARM FRONT. THESE INGREDIENTS WILL CONTINUE TO GENERATE PERIODS OF
SHOWERS AND WITH THE PWAT PLUME IN PLACE EXPECT BANDS OF EMBEDDED
HEAVY RAINFALL. THERE IS ALSO A FEW HUNDRED J/KG OF MUCAPE
PRESENT...SO A FEW EMBEDDED T-STORMS ARE CERTAINLY POSSIBLE.
WHILE THE ENTIRE REGION WILL BE SUBJECT TO SHOWERS WITH BANDS OF
HEAVY RAINFALL...THE MOST SIGNIFICANT RAINFALL TOTALS ARE EXPECTED
ACROSS INTERIOR MA AND CT. MUCH OF THE GUIDANCE INDICATES THE
POTENTIAL FOR WIDESPREAD TOTAL RAINFALL AMOUNTS OF 2-3" WITH
LOCALIZED 4-5" AMOUNTS ACROSS INTERIOR MA AND CT THROUGH TUE
AFTERNOON. GIVEN LOW LEVEL E/SE FLOW...WE MAY SEE SOME ENHANCED
RAINFALL AMOUNTS ON THE UPSLOPE FLOW ACROSS THE EAST SLOPES OF THE
BERKS AND PERHAPS THE EASTERN PORTIONS OF THE WORCESTER HILLS.
GIVEN THOSE EXPECTATIONS ABOVE...THERE IS A LOW PROBABILITY FOR
ISOLATED FLASH FLOODING ACROSS PARTS OF INTERIOR MA AND CT. IN
FACT...THE ECMWF EXTREME FORECAST INDEX AND SHIFT OF TAILS IS
HIGHLIGHTED ACROSS INTERIOR SOUTHERN NEW ENGLAND. THIS IS CERTAINLY
SOMETHING WILL HAVE TO KEEP A CLOSE EYE ESPECIALLY THOSE AREAS IN
THE TERRAIN THAT ARE PRONE TO UPSLOPE ENHANCEMENT.
HIGH TEMPS SHOULD RECOVER INTO THE UPPER 50S AND WELL INTO THE 60S
ACROSS MUCH OF THE REGION AS TODAY/S BACKDOOR COLD FRONT BEGINS TO
LIFT NORTHWARD AS A WARM FRONT ON TUE.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
KEY POINTS
* SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE WEDNESDAY AND
THURSDAY
* CONTINUED WET AND UNSETTLED WEATHER FRIDAY AND SATURDAY
* TRENDING DRIER SUNDAY AND MONDAY
UPPER-LEVEL CUTOFF LOW AND COLD POOL MOVES DIRECTLY OVER SNE,
CONTINUING THE COOL AND WET WEATHER. SCATTERED SHOWERS AND
THUNDERSTORMS ARE POSSIBLE TO OCCUR ON WEDNESDAY AS 500MB TEMPS DROP
TO -20C AND MODEST INSTABILITY AROUND 500 J/KG BUILDS DUE TO DIURNAL
HEATING. VERY LITTLE TO NO SHEAR WILL BE PRESENT, WHICH SHOULD
LIMIT THE SEVERE THREAT. HOWEVER, THE COLD TEMPS ALOFT AND NEAR THE
SURFACE COULD ALLOW GRAUPEL/SMALL HAIL TO REACH THE GROUND. ISOLATED
SHOWERS ARE POSSIBLE ON THURSDAY, DEPENDING ON THE TIMING OF THE
TRAILING SHORTWAVE AS THE FIRST CUTOFF SHORTWAVE EXITS THE REGION. A
SLOWER ARRIVAL OF THE NEXT SHORTWAVE WOULD LEAVE THE REGION UNDER A
BRIEF PERIOD OF RIDGING AND DRY WEATHER ON THURSDAY. HIGH
TEMPERATURES ON WEDNESDAY AND THURSDAY WILL BENEFIT FROM AT LEAST
PARTIAL SUNSHINE, REACHING THE UPPER 60S TO LOW 70S.
FORECAST CONFIDENCE DECREASES ON FRIDAY AND SATURDAY AS GUIDANCE IS
MIXED ON WHERE THE TRAILING SHORTWAVE STALLS. THE GFS STALLS THE
TROUGH OVER SNE, BRINGING ANOTHER COUPLE OF DAYS OF SCATTERED
SHOWERS. THE ECMWF AND CANADIAN MODELS KEEP A MORE VIGOROUS
SHORTWAVE FURTHER WEST OVER THE OHIO RIVER VALLEY. THIS CAUSES A
COASTAL LOW TO FORM NEAR THE VIRGINA COAST AND MOVE NORTH TOWARDS
SNE, BRINGING ANOTHER ROUND OF HEAVY PRECIPITATION WITH IT. SOME OF
THE 7-DAY QPF TOTALS ARE QUITE IMPRESSIVE OVER SNE, WITH THE
DETERMINISTIC EURO SHOWING 6-9 INCHES. HOWEVER, GIVEN THE
UNCERTAINTY WITH THE COASTAL LOW, CONFIDENCE IN THAT MUCH RAIN IS
LITTLE TO NONE AT THIS TIME. THE LREF GRAND ENSEMBLE, WHICH INCLUDES
THE GEFS, GEPS, AND ENS ENSEMBLE SYSTEMS, HAS A MEAN 7-DAY QPF
BETWEEN 2-4 INCHES, WITH LOW PROBABILITIES (10-20%) FOR GREATER THAN
6IN. HIGH TEMPERATURES ON BOTH DAYS COOL INTO THE 50S WITH NE FLOW
ANTICIPATED.
THE TROUGHING PATTERN LOOKS TO FINALLY COME TO AN END SUNDAY INTO
MONDAY AS THE STALLED CUTOFF TROUGH FINALLY MOVES OFFSHORE WITH A
WEAK RIDGE POSSIBLY BUILDING IN BEHIND. THIS SHOULD USHER DRIER AND
WARMER CONDITIONS TO ROUND OUT THE WEEKEND AND START THE NEXT WORK
WEEK. OF COURSE, THIS COULD ALL CHANGE THROUGH THE WEEK AS GUIDANCE
GENERALLY STRUGGLES WITH BLOCKING PATTERNS.
AVIATION /19Z MONDAY THROUGH FRIDAY/
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
18Z TAF UPDATE:
REST OF THIS AFTERNOON THROUGH TUESDAY: MODERATE CONFIDENCE.
IFR TO LIFR CONDITIONS FOR MOST AIRPORTS, ALTHOUGH CATEGORIES
TO DETERIORATE TO THESE LEVELS SHORTLY FROM VFR CONDITIONS. A
COUPLE PERIODS OF STEADY MODERATE TO HEAVY RAIN ARE EXPECTED,
STARTING BETWEEN 22-00Z IN WESTERN TAFS, THEN GRADUALLY SHIFTING
EASTWARD INTO CENTRAL AND EASTERN TERMINALS AFTER 04Z TUE. WE
THEN GET INTO A BRIEF BREAK IN THE RAIN THRU MIDMORNING TUE
BEFORE ANOTHER ROUND OF STEADY LIGHT TO MODERATE RAINS ENSUES
FROM TUE LATE MORNING TO EARLY TUE EVENING. IT IS UNLIKELY THAT
IFR-LIFR CATEGORIES IMPROVE MUCH AT ALL, WITH VISBYS IN RAIN/FOG
IN THE 2-6 SM RANGE. NE WINDS AROUND 10-15 KT THROUGH MOST OF
TONIGHT, WITH COASTAL GUSTS TO 25 KT; WINDS THEN BECOMING MORE
OF AN E/ESE AROUND 10 KT INTO TUE. LOW LEVEL WIND SHEAR IS
POSSIBLE TONIGHT INTO TUE.
TUESDAY NIGHT: MODERATE CONFIDENCE.
SOME GUARDED OPTIMISM FOR ONE-CATEGORY IMPROVEMENT IN
CATEGORIES AS RAIN MOVES OFFSHORE TUE NIGHT TO MVFR-IFR LEVELS.
WINDS SHIFT FROM ESE/SE TO S/SW OVERNIGHT.
KBOS TAF...MODERATE CONFIDENCE.
KBDL TAF...MODERATE CONFIDENCE.
OUTLOOK /WEDNESDAY THROUGH FRIDAY/...
TUESDAY NIGHT: MAINLY IFR, WITH AREAS MVFR POSSIBLE. CHANCE
SHRA, ISOLATED TSRA, PATCHY BR.
WEDNESDAY: MVFR/IFR CONDITIONS POSSIBLE. CHANCE SHRA, ISOLATED
TSRA.
WEDNESDAY NIGHT THROUGH THURSDAY: MAINLY VFR, WITH LOCAL MVFR
POSSIBLE. CHANCE SHRA.
THURSDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. CHANCE
SHRA.
FRIDAY: MVFR/IFR CONDITIONS POSSIBLE. CHANCE SHRA.
MARINE
FORECASTER CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
TODAY THROUGH TUESDAY...HIGH CONFIDENCE.
ENE WINDS TODAY WILL GRADUALLY SHIFT TO MORE OF AN ESE DIRECTION ON
TUE. THIS A RESULT OF AN ANOMALOUS CLOSED UPPER OVER THE OHIO VALLEY
GRADUALLY MOVING INTO WESTERN PA OVER THE NEXT 36 HOURS. WHILE SOME
20+ KNOT WIND GUSTS WILL BE POSSIBLE AT TIMES...WINDS/SEAS WILL
GENERALLY REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS.
HOWEVER...PERIODS OF SHOWERS AND AREAS OF FOG WILL REDUCE VSBYS FOR
MARINERS.
OUTLOOK /WEDNESDAY THROUGH FRIDAY/...
TUESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. RAIN
SHOWERS, ISOLATED THUNDERSTORMS, PATCHY FOG.
WEDNESDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. CHANCE OF
RAIN SHOWERS, ISOLATED THUNDERSTORMS.
WEDNESDAY NIGHT THROUGH THURSDAY: WINDS LESS THAN 25 KT. SEAS
UP TO 5 FT. SLIGHT CHANCE OF RAIN SHOWERS.
THURSDAY NIGHT THROUGH FRIDAY: WINDS LESS THAN 25 KT. SEAS UP
TO 5 FT. CHANCE OF RAIN SHOWERS.
HYDROLOGY
235 PM UPDATE:
FLOOD WATCH NOW IN EFFECT FOR INTERIOR SOUTHERN NEW ENGLAND
TONIGHT THROUGH TUESDAY. IT MAY NEED TO BE EXPANDED EASTWARD
INTO EASTERN MA/RI IF HIGHER RAINFALL TOTALS MATERIALIZE.
ENTERING INTO A PROLONGED SOGGY WEATHER PATTERN, AS AN UPPER
LEVEL LOW PRESSURE OVER THE OHIO VALLEY DRAWS IN A STREAM OF
RICH SUBTROPICAL MOISTURE NORTHWARD INTO THE MID-ATLANTIC AND
INTO SOUTHERN NEW ENGLAND TONIGHT INTO AT LEAST TUESDAY. THIS
WILL LEAD TO AN ENHANCED PERIOD OF INTEGRATED WATER VAPOR
TRANSPORT AND THE POTENTIAL FOR SLOW-MOVING "TRAINING" RAINFALL
AREAS, WITH UPSLOPE ENHANCEMENT FAVORING HIGHER RAIN TOTALS IN
WESTERN NEW ENGLAND. TWO PERIODS OF STEADY RAIN WITH EMBEDDED
DOWNPOURS ARE EXPECTED: (1) TONIGHT INTO EARLY ON TUESDAY, BEING
MORE FOCUSED INTO WESTERN AND CENTRAL MA AND INTO ALL OF
NORTHERN CT THROUGH THE FIRST HALF OF THE OVERNIGHT, THEN
GRADUALLY SHIFTING EASTWARD INTO EASTERN MA AND RI AS WE MOVE
INTO THE TUESDAY MORNING HOURS. HEAVIEST RAIN TOTALS IN THIS
INITIAL ROUND. (2) TUESDAY LATE- MORNING TO THE AFTERNOON ACROSS
MOST OF SOUTHERN NEW ENGLAND, ALTHOUGH WITH LESSER RAIN TOTALS
THAN THE FIRST ROUND.
THE EXACT AMOUNT OF RAINFALL WE MAY SEE IS STILL A BIT
UNCERTAIN, ALTHOUGH RECENT TRENDS IN HREF LOCALIZED PMM GUIDANCE
AND CMC/ECMWF ENSEMBLE QPF PROBS SUGGEST RAIN TOTALS COULD BE AS
HIGH AS 4 INCHES THRU TUESDAY WHERE SLOW-MOVING HEAVY RAIN
BANDS MATERIALIZE. THE PLACEMENT IS SOMEWHAT MORE CONFIDENT, TO
BE FOCUSED OVER WESTERN MA AND CT, WITH LESSER RAINFALL TOTALS
IN EASTERN MA AND RI. OFFICIAL FORECAST CALLS FOR RAIN TOTALS OF
UP TO 1.5 INCHES THROUGH TUESDAY EARLY EVENING IN EASTERN
MA/RI, WITH 1.75 TO 2.5 INCHES IN LOCATIONS COVERED BY THE FLOOD
WATCH.
INSTANCES OF URBAN AND POOR DRAINAGE STREET FLOODING COULD
DEVELOP IN RESPONSE TO THIS RAIN, ALTHOUGH WE DO NOT EXPECT
FLOODING TO RISE TO SIGNIFICANT LEVELS. RISES ON MOST SMALLER
CREEKS AND LARGER MAINSTEM RIVERS ALSO ARE LIKELY. ALTHOUGH
LATEST RIVER STAGE FORECASTS FROM THE NERFC INDICATE RISES TO
ACTION STAGE, IF HIGHER RAINFALL TOTALS DO DEVELOP, PORTIONS OF
THE CT RIVER COULD SEE RISES TO MINOR FLOOD STAGE PER MMEFS
WATER GUIDANCE OUTPUT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...FLOOD WATCH FROM 8 PM EDT THIS EVENING THROUGH TUESDAY EVENING
FOR CTZ002>004.
MA...FLOOD WATCH FROM 8 PM EDT THIS EVENING THROUGH TUESDAY EVENING
FOR MAZ002>004-008>012.
RI...NONE.
MARINE...NONE.
SYNOPSIS...LOCONTO
NEAR TERM...LOCONTO
SHORT TERM...LOCONTO
LONG TERM...LOCONTO
AVIATION...LOCONTO
MARINE...LOCONTO
HYDROLOGY...LOCONTO
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