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FXUS61 KBOX 180543
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
1243 AM EST WED DEC 18 2024
SYNOPSIS
HIGH PRESSURE BRINGS DRIER WEATHER WITH A PERIOD OF MILDER THAN
NORMAL TEMPERATURES THROUGH WEDNESDAY. A FAST-MOVING AREA OF LOW
PRESSURE PROGRESSES THROUGH SOUTHERN NEW ENGLAND WEDNESDAY
EVENING INTO THE PRE-DAWN HOURS ON THURSDAY, BRINGING MAINLY
RAIN WITH MINOR ACCUMULATIONS OF LIGHT SNOW IN THE HIGHEST
ELEVATIONS. BRIEF DRY WEATHER THEN RESUMES FOR THURSDAY.
MONITORING AN OFFSHORE AREA OF LOW PRESSURE THAT COULD BRING
ADDITIONAL LIGHT PRECIPITATION ON FRIDAY. THIS WILL BE FOLLOWED
BY VERY COLD AND BLUSTERY WEATHER THIS WEEKEND INTO EARLY NEXT
WEEK.
NEAR TERM /UNTIL 6 AM THIS MORNING/
945 PM UPDATE...
HIGH PRES BUILDS IN FROM THE SW TONIGHT WITH RELAXING GRADIENT
ALTHOUGH THERE WILL BE SOME HIGH CLOUD COVER TO DEAL WITH.
MODEST RADIATIONAL COOLING WILL LEAD TO LOWS 30-35 FOR MOST
(MID/UPPER 30S CAPE AND ISLANDS), WITH SOME UPPER 20S ACROSS
INTERIOR NORTHERN AND WESTERN MA.
PREVIOUS DISCUSSION...
FOR TONIGHT, CENTER OF HIGH PRESSURE OVER THE EASTERN OH VALLEY
WILL PROGRESS EASTWARD INTO THE NORTHERN MID-ATLC STATES.
LOOKING AT TRANQUIL CONDITIONS TONIGHT WITH MOSTLY CLEAR SKIES
AND WESTERLY WINDS EASING TO AROUND 5-10 MPH. SO WE SHOULD SEE
SOME RADIATIONAL COOLING POST-SUNDOWN, BUT NOT ESPECIALLY
STRONG. LOW TEMPS TONIGHT ARE ABOVE NORMAL, BUT HOW LOW WE DROP
IS IN SOME QUESTION SINCE TEMPERATURE ADVECTION IS NEUTRAL TO
WEAKLY COLD AND WITH ONLY SOME RADIATIONAL COOLING. I KEPT LOWS
AROUND 30-35 FOR MOST (MID/UPPER 30S CAPE AND ISLANDS); IN AN
UNLIKELY CASE THAT WINDS EASE OFF EARLIER, THEN LOWS COULD BE IN
THE MID TO UPPER 20S IN THE INTERIOR AND CLOSER TO THE FREEZING
MARK SOUTH COAST/CAPE AND ISLANDS.
SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/
330 PM UPDATE:
WEDNESDAY:
HIGH PRESSURE WILL QUICKLY EXPAND EASTWARD AND OFFSHORE THROUGH
THE DAYTIME HRS ON WED, WITH INITIALLY WEAK 500 MB HEIGHT RISES
TRANSITIONING TO HEIGHT FALLS DURING THE AFTN. MOSTLY CLEAR
SKIES TO START WITH WARMING TEMPS INTO THE 40S TO LOWER 50S WITH
RATHER SHALLOW MIXING. HOWEVER, WILL SEE INCREASED CLOUD COVER
DURING THE AFTERNOON IN RESPONSE TO AN APPROACHING WEAK
AMPLITUDE 500 MB SHORTWAVE DISTURBANCE AND ASSOCIATED SFC
FRONTAL SYSTEM. THE VAST MAJORITY OF MODEL SOLUTIONS SEEM TO
HAVE SLOWED DOWN THE ARRIVAL OF PRECIPITATION UNTIL AFTER
SUNDOWN; HOWEVER START TO BRING AN INCREASE IN POPS FROM WEST TO
EAST. THE AIRMASS IS PRETTY DRY AT ONSET BOTH AT SFC AND ALOFT,
SO THAT SHOULD ALLOW FOR SOME EVAPORATIVE/WET-BULB COOLING ONCE
PRECIP BEGINS.
WEDNESDAY NIGHT:
KEY MESSAGES:
* PLAIN RAIN WITH HIGHER TERRAIN MINOR ACCUMULATING WET SNOW WED
NIGHT INTO THE PRE-DAWN HRS.
* RAIN MAY END AS WET SNOWFLAKES DURING THE PRE-DAWN HOURS BUT
IS NOT EXPECTED TO IMPACT THE THURS AM COMMUTE.
APPROACHING WAVE OF LOW PRESSURE SPREADS A ROUND OF
PRECIPITATION INTO SOUTHERN NEW ENGLAND DURING THE EVENING AND
OVERNIGHT. WE EXPECT MOST OF THE PRECIP TO FALL AS PLAIN RAIN IN
MOST LOCATIONS WITH TEMPERATURES BEING WARM ENOUGH SUPPORTIVE OF
RAIN, ALTHOUGH TEMPERATURES IN THE HIGHEST ELEVATIONS IN
WORCESTER COUNTY AND THE BERKSHIRES SHOULD BE MARGINALLY COLD
ENOUGH TO ALLOW FOR A MINOR ACCUMULATION OF WET SNOW. MODELS
SEEM TO BE COMING AROUND TO LOW PRESSURE TRACKING THROUGH
COASTAL SOUTHERN NEW ENGLAND AND OFFSHORE BY THE PRE-DAWN HOURS.
THERMAL PROFILES AFTER INITIAL WETBULB COOLING BOTH AT SURFACE
AND ALOFT ARE MORE ISOTHERMAL THRU THE EVENING AND EARLY
OVERNIGHT, WITH SUB-OC AIR OVER AREAS NORTH OF SPRINGFIELD TO
WORCESTER TO LAWRENCE. IN THE COLDER AIR, RELATIVELY WEAK
VERTICAL MOTION IS ALSO LOCATED BELOW THE DENDRITE SNOW GROWTH
LAYER HEIGHT, AND THE RATHER SHORT DURATION ACCUMULATION PERIOD
COMBINED WITH THAT SHOULD KEEP ACCUMULATIONS TO LESS THAN
ADVISORY LEVELS. FORECAST ACCUMULATIONS IN THE HIGHEST
ELEVATIONS AROUND 1 TO 3 INCHES. OVERALL QPF AMTS RANGE FROM A
THIRD TO A LITTLE MORE THAN A HALF INCH.
WILL MENTION AS LOW PRESSURE PULLS AWAY, THAT INCREASING COLD
ADVECTION ALOFT ON NW WINDS COULD ALLOW FOR RAIN IN THE LOWER
ELEVATIONS TO END BRIEFLY AS WET SNOWFLAKES DURING THE THURS AM
COMMUTE IN THE INTERIOR TO THE I-95 CORRIDOR, WITH PERHAPS
SLUSHY COATINGS ON GRASS, BUT THE BULK OF THE PRECIP WILL HAVE
BY-AND-LARGE ENDED BY THAT POINT.
TEMPS MAINLY IN THE 30S, WITH 30-32F READINGS IN THE HIGHER
TERRAIN AND AROUND 33-37F IN THE LOWER ELEVATIONS/VALLEYS.
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
KEY MESSAGES:
* DRIER AND COOLER THURSDAY
* OCEAN STORM PASSING OFFSHORE FRIDAY INTO SATURDAY?
* COLD RETURNS SATURDAY INTO MONDAY
PRECIPITATION...
EXPECTING MUCH OF THIS PORTION OF THE FORECAST TO REMAIN DRY,
COURTESY OF A LARGE HIGH PRESSURE MOVING ACROSS NEW ENGLAND FROM
CANADA. HOWEVER, WE WILL HAVE TO GET PAST A COMPLICATED PATTERN
FRIDAY INTO SATURDAY FIRST. THE SYNOPTIC PATTERN IS EXPECTED TO
FEATURE A HIGH PRESSURE OVER EASTERN CANADA, WITH ONE LOW
PRESSURE OVER THE GREAT LAKES, AND ANOTHER OVER THE GULF STREAM
OFF THE CAROLINA COAST. UNLIKE THE SOLUTIONS YESTERDAY, TODAY'S
GUIDANCE SUITE TRANSFERS ALL THE ENERGY FROM THE GREAT LAKES LOW
PRESSURE INTO THE OFFSHORE LOW. THIS PATTERN IS A COLDER ONE,
SO SOME LIGHT SNOWFALL IS MORE OF AN OUTCOME. STILL SOME
UNCERTAINTY ON HOW CLOSE THIS LOW PRESSURE MAY TRACK TO OUR
REGION. STILL TOO EARLY TO LOCK IN ON A SPECIFIC SOLUTION JUST
YET, FURTHER CHANGES ARE POSSIBLE WITH LATER FORECASTS.
HIGH PRESSURE SHOULD DOMINATE LATE THIS WEEKEND INTO EARLY NEXT
WEEK, LEADING TO DRY WEATHER.
TEMPERATURES...
NEAR NORMAL TEMPERATURES THURSDAY. TRENDING BELOW NORMAL INTO
FRIDAY, BEFORE EVEN COLDER AIR ARRIVES SATURDAY NIGHT INTO
MONDAY. TURNING WARMER EARLY NEXT WEEK ONCE THE HIGH PRESSURE
MOVES OFFSHORE.
AVIATION /05Z WEDNESDAY THROUGH SUNDAY/
FORECAST CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
06Z TAF UPDATE...
TODAY...HIGH CONFIDENCE.
VFR, WITH LOWERING CIGS LATE, ESPECIALLY WESTERN MA/CT WHERE
SOME LIGHT RAIN IS POSSIBLE TOWARD EVENING. WIND BECOMING LIGHT
S DURING THE AFTERNOON.
TONIGHT...MODERATE CONFIDENCE.
WIDESPREAD IFR-LIFR CIGS DEVELOPING AS RAIN OVERSPREADS THE
REGION FROM W TO E DURING THE EVENING. HIGHER ELEVATION SNOW
OVER HIGHER ELEVATIONS, MAINLY ALONG AND NORTH OF ROUTE 2.
PRECIP ENDS 06-09Z WESTERN NEW ENG AND 09-12Z EASTERN NEW ENG,
WITH CONDITIONS IMPROVING TO VFR BY 12Z. A PERIOD OF GUSTY SW
WINDS AND LLWS POSSIBLE OVER CAPE/ISLANDS AND POSSIBLY PORTIONS
OF THE SOUTH COAST DURING THE EVENING ASSOCD WITH A LOW LEVEL
JET. OTHERWISE WINDS BECOMING N-NW 5-15 KT OVERNIGHT.
THURSDAY...HIGH CONFIDENCE.
PATCHY MVFR CIGS MAY LINGER OVER OUTER CAPE AND ACK EARLY,
OTHERWISE VFR. NW WIND 10-20 KT WITH SOME HIGHER GUSTS.
KBOS TAF...HIGH CONFIDENCE IN TRENDS BUT MODERATE ON TIMING.
VFR THROUGH 00Z, THEN LOWERING CIGS TO MVFR-IFR AFTER 02Z AS
RAIN DEVELOPS. IMPROVING TO VFR BY 12Z.
KBDL TAF...HIGH CONFIDENCE IN TRENDS BUT MODERATE ON TIMING.
VFR TODAY, THEN LOWERING CIGS TO MVFR-IFR AFTER 00Z AS RAIN
DEVELOPS. IMPROVING TO VFR BY 09Z.
OUTLOOK /THURSDAY NIGHT THROUGH SUNDAY/...
THURSDAY NIGHT: VFR.
FRIDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. CHANCE RA, CHANCE
SN.
FRIDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. CHANCE SN.
SATURDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY. CHANCE
SN.
SATURDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SN.
SUNDAY: VFR. BREEZY.
MARINE
FORECASTER CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
SCAS CONTINUE OVER THE OUTER WATERS THROUGH EARLY TONIGHT AS
LEFTOVER 5 FT SEAS BEGIN TO GRADUALLY DECREASE. THEREAFTER,
TRANQUIL CONDITIONS FOR MARINERS THROUGH THE DAYTIME HRS ON
WEDNESDAY WITH WEST WINDS AROUND 10-15 KT BECOMING SW LATE.
ANOTHER PERIOD OF LIKELY SCAS WILL BE NEEDED FOR WEDNESDAY NIGHT
ESPECIALLY OVER THE SOUTHERN OUTER WATERS AS LOW PRESSURE MOVES
THROUGH THE SOUTHERN NEW ENGLAND WATERS. SW WINDS 20-30 KT WITH
SEAS BUILDING TO 4-6 FT.
OUTLOOK /THURSDAY NIGHT THROUGH SUNDAY/...
THURSDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. SEAS UP TO 5 FT.
THURSDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS
APPROACHING 5 FT.
FRIDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.
RAIN LIKELY.
FRIDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. AREAS OF ROUGH SEAS. RAIN LIKELY, SNOW
LIKELY. LOCAL VISIBILITY 1 TO 3 NM.
SATURDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. ROUGH SEAS UP TO 9 FT. CHANCE OF SNOW, RAIN
LIKELY. AREAS OF VISIBILITY 1 TO 3 NM.
SATURDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS.
CHANCE OF SNOW. LOCAL VISIBILITY 1 TO 3 NM.
SUNDAY: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE OF
SNOW.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST EARLY THIS MORNING FOR
ANZ254>256.
SYNOPSIS...BELK/LOCONTO
NEAR TERM...KJC/LOCONTO
SHORT TERM...LOCONTO
LONG TERM...BELK
AVIATION...BELK/KJC
MARINE...BELK/LOCONTO
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