867
FXUS61 KBOX 190559
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
1259 AM EST SUN JAN 19 2025
SYNOPSIS
A WAVE OF LOW PRESSURE MOVING IN LATER SUNDAY AND SUNDAY NIGHT
WILL BRING ACCUMULATING, PLOWABLE SNOWFALL TO SOUTHERN NEW
ENGLAND. AN ARCTIC AIRMASS WILL BRING FRIGID TEMPERATURES AND
WIND CHILLS ON THE ORDER OF 5 TO 15 BELOW ZERO MONDAY EVENING
THROUGH THURSDAY MORNING. TEMPERATURES BEGIN TO WARM AGAIN
THURSDAY AND FRIDAY.
NEAR TERM /UNTIL 6 AM THIS MORNING/
KEY MESSAGES...
* AREAS OF FOG & PATCHY BLACK ICE POSSIBLE OVERNIGHT
* TEMPS DROPPING TO NEAR OR JUST BELOW FREEZING OVERNIGHT
THE LAST OF THE SHOWERS WERE EXITING NORTHEAST MA, CAPE AND
ISLANDS THIS EVENING. OTHERWISE...THERE IS NOT REALLY A PUSH OF
DRY AIR BEHIND THIS SHORTWAVE. THEREFORE...PARTIAL CLEARING
COUPLED WITH RESIDUAL MOISTURE/LIGHT WINDS WILL RESULT IN AREAS
OF FOG. IN ADDITION...TEMPS DROPPING TO NEAR OR JUST BELOW
FREEZING IN SOME LOCATIONS COMBINED WITH OUR RECENT COLD WEATHER
MAY RESULT IN PATCHY BLACK ICE DEVELOPING OVERNIGHT. MOTORISTS
DRIVING OVERNIGHT SHOULD BE PREPARED FOR AREAS OF FOG AND PATCHY
BLACK ICE. ROADS THAT APPEAR WET MAY ACTUALLY BE BLACK
ICE...ESPECIALLY ACROSS BRIDGES AND OVERPASSES.
SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/
KEY MESSAGES...
* PLOWABLE SNOW LATE SUNDAY AND THROUGH SUNDAY NIGHT.
* A WINTER STORM WARNING IS IN EFFECT FOR MUCH OF THE INTERIOR,
WHILE THE WINTER STORM WATCH HAS BEEN EXPANDED INTO SOUTHEAST
MA AND NORTHERN RI WHERE POTENTIAL FOR HIGHER SNOWFALL TOTALS
HAS INCREASED.
DETAILS...
FOCUS THEN RETURNS TO A WINTER STORM WHICH WILL PRODUCE A SWATH OF
HEAVY SNOW FROM THE NORTHERN MID-ATLANTIC TO THE NORTHEAST INCLUDING
SOUTHERN NEW ENGLAND. BEFORE WE GET TO THAT, THOUGH, THE FIRST HALF
OF THE DAY ON SUNDAY WILL BE LESS EVENTFUL, WITH QUIET WEATHER AND
LINGERING MILD AIR, EVEN AS WARM AS THE UPPER 30S AND LOW 40S IN
SOUTHEAST MA. BREAKS OF SUN ARE LIKELY IN THE MORNING BEFORE MID
CLOUDS OVERSPREAD MID MORNING THROUGH NOON.
SUNDAY AFTERNOON AN AREA OF LOW PRESSURE EMERGES OFF THE CAROLINA
COAST OUT JUST AHEAD OF A BROAD MID LEVEL TROUGH DIGGING INTO THE
EASTERN SEABOARD. THIS LOW THEN QUICKLY DEEPENS AS IT RACES UP THE
EAST COAST FROM THE CAROLINA COAST SUNDAY AFTERNOON TO THE GULF OF
MAINE BY EARLY MONDAY MORNING. THE EXACT TRACK THAT THE SYSTEM TAKES
BETWEEN THESE TWO POINTS IS SLOWLY COMING INTO FOCUS, AND WILL BE
THE GREATEST DETERMINER OF WHO SEES SNOW AND HOW MUCH.
GUIDANCE SHOWS INDICATORS OF POTENTIAL FOR A SIGNIFICANT SNOW MAKER
WITH THIS SYSTEM. FOR ONE, SNE WILL BE PLACED BENEATH THE LEFT EXIT
REGION OF A 160 KT UPPER JET AS THE LOW PASSES BY; AND WHILE THERE
REMAINS DISCREPANCIES AMONGST THE GUIDANCE AS TO HOW STRONG THE 850
MB LOW IS AS WELL AS THE TRACK, MUCH OF THE GUIDANCE INDICATES A
CLOSED OFF 850 MB LOW WITH A SWATH OF 850-700M FRONTOGENESIS TO THE
NORTHWEST OF THE LOW CENTER THAT WILL HELP TO INCREASE SNOWFALL
RATES (LIKELY JUST TO THE NORTHWEST OF WHEREVER THOSE BANDS OF FGEN
SET UP). THE HREF INDICATES A RATHER HIGH PROBABILITY OF GREATER
THAN 1"/HR SNOWFALL RATES IN THE INTERIOR (AS HIGH AS 50-60%). THIS,
TOGETHER WITH THE SURGING IN OF COLDER AIR THROUGHOUT THE EVENT,
STEADILY RAISING SNOW-TO-LIQUID RATIOS EVENTUALLY ABOVE 10:1
(ESPECIALLY IN THE INTERIOR) AND A GOOD LOW END WINTER WEATHER
WARNING EVENT (6-7 INCHES OR MORE) REMAINS A DECENT POSSIBILITY. THE
FLY IN THE OINTMENT AND WHY THE WINTER STORM WATCHES REMAIN IN
EFFECT IS THE LINGERING UNCERTAINTY AS TO THE EXACT TRACK AND
STRENGTH OF THE SYSTEM.
12Z GUIDANCE PROVIDED SOME CLARITY AS MODELS BEGAN TO SHIFT A
CLOSER, WITH THE RGEM MOVING A BIT SOUTHEAST, CLOSER TO THE GFS
SOLUTION WHILE THE ECMWF AND NAM SHIFTED FURTHER NORTHWEST, CLOSER
TO THE CONSENSUS AND INSIDE THE BENCHMARK. THIS INCREASES THE
LIKELIHOOD OF A LOW END END WINTER STORM WARNING EVENT VS THE
PREVIOUSLY POSSIBLE WIDESPREAD 3-4 INCH STORM.
OVERALL THE DIFFERING CAMPS HAVE COME A BIT CLOSER TO CONVERGING.
STILL, MORE UNCERTAINTY THAN YOU'D LIKE (OR EXPECT) TO HAVE GIVEN
BEING 24 HOURS OUT FROM THE ONSET. TAKING A LOOK AT THE ENSEMBLE
GUIDANCE, THE GEFS MEMBER LOW LOCATIONS INDICATE MUCH MORE
CLUSTERING AROUND ITS STRONGER SOLUTION VS THE MORE SPREAD OUT EPS
POTENTIAL LOW LOCATIONS WHICH WOULD SEEM TO INDICATE THAT THE ECMWF
HAS YET TO CONVERGE ON ONE SOLUTION. FOR NOW, WE CONTINUE WITH A
COMPROMISE APPROACH (BETWEEN THESE TWO SCENARIOS) IN WHICH WE DO SEE
MIXING/PTYPE ISSUES (I.E. RAIN MIXING IN) OVER SOUTHEAST MA
INITIALLY, FLIPPING TO SNOW AT SOME POINT IN THE OVERNIGHT HOURS
(SAVE FOR PERHAPS CAPE COD AND THE ISLANDS). THE STRONGER/CLOSER
TRACK COULD ACTUALLY HURT SNOWFALL TOTALS IN SOUTHEAST MA BY KEEPING
STRONG ONSHORE/WARMER FLOW GOING PREVENTING A QUICKER FLIP TO SNOW.
THAT THEN PLACES THE SWATH OF HEAVIEST SNOW, GENERALLY 4-8 INCHES
NORTH AND WEST OF I-95, WITH THE CAVEAT THAT EXPECTED BANDING COULD
LEAD TO LOCALIZED AMOUNTS CLOSER TO 10 INCHES. OVERALL CONFIDENCE IN
SPECIFIC SNOWFALL TOTALS AND LOCATION OF BANDING IS ON THE LOWER
END, BUT THE POSSIBILITY OF WARNING LEVEL SNOWS HAS SHIFTED
SOUTHEAST, SO THE WINTER STORM WATCH HAS BEEN EXPANDED INTO
SUFFOLK, NORFOLK, AND PROVIDENCE COUNTIES. WHAT IS MORE SOLIDLY
KNOWN IS THAT SNOW WILL BE ENDED BY SUNRISE ON MONDAY FOR MOST,
THOUGH FRIGID TEMPERATURES TO FOLLOW SHOULD SOLIDIFY THINGS AND
CAUSE SLICK CONDITIONS ON UNTREATED ROADS.
LONG TERM /MONDAY NIGHT THROUGH SATURDAY/
KEY POINTS
*ARCTIC AIRMASS MOVES IN FOR MONDAY PM THROUGH THURSDAY AM
*LOWS NEAR ZERO WITH WIND CHILLS BETWEEN NEGATIVE 5 TO 15
*HIGHS IN THE LOW TEENS WITH WIND CHILLS NEAR ZERO
*WATCHING SNOW POTENTIAL WEDNESDAY, THEN AGAIN FRIDAY, BUT
CONFIDENCE IS LOW AT THIS TIME
AS SNOW COMES TO AN END EARLY MONDAY MORNING, THE COLD ARCTIC
AIRMASS FOLLOWS QUICKLY BEHIND. 850MB TEMPS FALL FROM -12C EARLY IN
THE DAY TO -22C BY MIDNIGHT ON TUESDAY. HIGH TEMPERATURES ON MONDAY
ARE LIKELY TO OCCUR EARLY IN THE UPPER TEENS TO LOW 20S BUT WILL
DROP INTO THE SINGLE DIGITS SHORTLY AFTER SUNSET MONDAY EVENING. THE
ARCTIC AIRMASS STAYS OVER SOUTHERN NEW ENGLAND THROUGH THURSDAY
MORNING. OVERNIGHT LOWS TUESDAY THROUGH THURSDAY MORNING WILL BE
NEAR OR BELOW ZERO FOR MUCH OF THE REGION, WITH WIND CHILL VALUES IN
THE 5-15 BELOW RANGE. HIGH TEMPERATURES ON TUESDAY AND WEDNESDAY
WILL STRUGGLE TO REACH THE LOW TEENS, WITH LOW PROBS FOR HIGHS IN
THE SINGLE DIGITS. BLUSTERY WINDS AROUND 10-20MPH DURING THE DAY
WILL KEEP THE WIND CHILL INDEX NEAR ZERO DURING THE DAY.
AS FOR SNOW POTENTIAL NEXT WEEK, SOME GUIDANCE HINTS AT A COASTAL
LOW PASSING OFFSHORE SOMETIME ON WEDNESDAY, THEN ANOTHER ONE
POSSIBLY ON FRIDAY. STARTING WITH WEDNESDAYS SYSTEM, THE ENSEMBLES
25TH TO 75 PERCENTILE SNOW SHOWS A COATING TO 2 INCHES OF SNOW
ACROSS THE CAPE AND ISLANDS, WITH A COATING POSSIBLE INLAND TO THE I-
95 CORRIDOR BETWEEN BOSTON AND PROVIDENCE. WITH THIS SYSTEM STILL
SEVERAL DAYS OUT, ANY SHIFT IN THE TRACK OF THE LOW WILL RESULT IN
CHANGES IN EXPECTED SNOW ACCUMULATIONS; HENCE, CONFIDENCE IS LOW.
CONFIDENCE IN FRIDAYS COASTAL LOW AND PRECIPITATION IS EVEN LOWER,
WITH A VERY LARGE SPREAD BETWEEN THE DIFFERENT DETERMINISTIC AND
ENSEMBLE GUIDANCE SOURCES, BUT SOMETHING TO MONITOR AS THE WEEK
PROGRESSES. TEMPERATURES LATE IN THE WEEK MODERATE BACK INTO THE
UPPER 20S TO LOW 30S.
AVIATION /06Z SUNDAY THROUGH THURSDAY/
FORECAST CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
06Z TAF UPDATE...
TODAY AND TONIGHT...MODERATE CONFIDENCE.
IFR/LIFR CONDITIONS IN LOW CLOUDS AND AREAS OF FOG ARE THEY MAIN
STORY VERY EARLY THIS MORNING. WE SHOULD SEE THE LOW CLOUDS AND
FOG DISSIPATE AFTER SUNRISE...ALTHOUGH THIS PROCESS WILL
PROBABLY BE SOMEWHAT SLOWER IN SPOTS ESPECIALLY IN THE CT RIVER
VALLEY AS WELL AS THE CAPE/ISLANDS.
AFTER THE LOW CLOUDS AND FOG BURN OFF WE SHOULD SEE A PERIOD OF
MAINLY VFR CONDITIONS LATER THIS MORNING INTO A GOOD PORTION OF
THE AFTERNOON. PRECIPITATION SHOULD THEN OVERSPREAD THE REGION
FROM WEST TO EAST BETWEEN 20Z AND 23Z. CONDITIONS SHOULD LOWER
TO MVFR/IFR LEVELS. PTYPE WILL MAINLY BE SNOW NW OF I-95...BUT
A PERIOD OF RAIN MAY OCCUR NEAR AND ESPECIALLY SOUTHEAST OF
I-95. PTYPE SHOULD TRANSITION TO MAINLY SNOW NORTHWEST OF THE
CAPE COD CANAL BY 00Z/01Z OR SO. THE HEAVIEST OF THE SNOW WILL
LIKELY OCCUR THROUGH 04Z/05Z WHEN IFR/LIFR CONDITIONS ARE
EXPECTED. SNOWFALL RATES OF 1-2" PER HOUR WILL BE POSSIBLE AT
TIMES. TOTAL SNOW ACCUMULATIONS OF 3-6"/4-8" WILL BE COMMON FOR
MUCH OF THE REGION NORTHWEST OF THE CAPE COD CANAL. PTYPE
PROBABLY CHANGES TO ALL SNOW BEFORE ENDING EVEN ACROSS THE CAPE.
THE LAST OF THE STEADY SNOW SHOULD EXIT THE COAST BY 09Z/10Z
MON. CONDITIONS WILL IMPROVE TO VFR BY DAYBREAK MONDAY.
WINDS SHOULD BECOME N AT 5 TO 10 KNOTS TODAY BY AFTERNOON. THE
WINDS WILL THEN BECOME MORE NW LATER TONIGHT WITH GUSTS OF 20-25
KNOTS DEVELOPING AND PERHAPS UP TO 30 KNOTS IN A FEW OF THE
TYPICAL SPOTS.
MONDAY...HIGH CONFIDENCE.
MAINLY VFR OUTSIDE A FEW BRIEF SPOT SNOW SHOWERS THAT WILL BE
POSSIBLE. NW WIND GUSTS OF 20 TO 30 KNOTS.
KBOS TAF...MODERATE CONFIDENCE IN TAF. HEAVIEST OF THE SNOW
ROUGHLY BETWEEN 00Z AND 05Z. 1" PER HOUR SNOWFALL RATES POSSIBLE
AT TIMES.
KBDL TAF...MODERATE CONFIDENCE IN TAF. HEAVIEST OF THE SNOW
ROUGHLY BETWEEN 22Z AND 03Z. 1" PER HOUR SNOWFALL RATES POSSIBLE
AT TIMES.
IFR/MVFR THIS EVENING, BECOMING VFR OVERNIGHT. VFR MOST OF
SUNDAY. LIGHT SNOW AND MVFR CIGS MOVE IN BETWEEN 21-23Z.
OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...
MARTIN LUTHER KING JR DAY THROUGH TUESDAY: VFR. BREEZY.
TUESDAY NIGHT: VFR. SLIGHT CHANCE SN.
WEDNESDAY: VFR. BREEZY. SLIGHT CHANCE SN.
WEDNESDAY NIGHT THROUGH THURSDAY: VFR. BREEZY.
MARINE
FORECASTER CONFIDENCE LEVELS:
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH- GREATER THAN 60 PERCENT.
HIGH CONFIDENCE...
S TO SW WINDS GUST 25-30 KTS TODAY. SEAS 4-6 FT FOR THE OUTER
COASTAL WATERS. SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE OUTER
COASTAL WATERS INTO EARLY SUNDAY MORNING. WINDS/SEAS GRADUALLY
DECREASE TOWARD MIDNIGHT. SUNDAY WINDS ARE LIGHT MOST OF THE DAY,
INCREASING TO 15-20 KTS SUNDAY NIGHT WITH GUSTS TO 30 KTS AS A LOW
PRESSURE PASSES FROM SOUTHWEST TO NORTHEAST.
OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...
MARTIN LUTHER KING JR DAY: MODERATE RISK FOR SMALL CRAFT
ADVISORY WINDS WITH GUSTS UP TO 30 KT. ROUGH SEAS UP TO 10 FT.
CHANCE OF FREEZING SPRAY.
MONDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT. LOCAL ROUGH SEAS. CHANCE OF FREEZING SPRAY.
TUESDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.
TUESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT. CHANCE OF SNOW.
WEDNESDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT. CHANCE OF SNOW, CHANCE OF FREEZING SPRAY.
WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS
APPROACHING 5 FT.
THURSDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST
MONDAY FOR CTZ002-003.
WINTER STORM WATCH FROM THIS AFTERNOON THROUGH MONDAY MORNING
FOR CTZ004.
MA...WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST
MONDAY FOR MAZ002>012-014-026.
WINTER STORM WATCH FROM THIS AFTERNOON THROUGH MONDAY MORNING
FOR MAZ013-015-016.
RI...WINTER STORM WATCH FROM THIS AFTERNOON THROUGH MONDAY MORNING
FOR RIZ001-002.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EST EARLY THIS MORNING FOR
ANZ250-254>256.
SYNOPSIS...BW/KP
NEAR TERM...FRANK
SHORT TERM...BW
LONG TERM...KP
AVIATION...FRANK/KP
MARINE...BW/KP
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