973
FXUS61 KBOX 201455
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
955 AM EST WED FEB 20 2019
SYNOPSIS
STRONG HIGH PRESSURE MOVES OFF TO THE EAST THIS AFTERNOON. LOW
PRESSURE FROM THE WESTERN GULF OF MEXICO WILL REDEVELOP ALONG
THE EAST COAST AND MOVE ACROSS NEW ENGLAND EARLY THURSDAY. THIS
WILL BRING A PERIOD OF SNOW AND ICE, CHANGING TO RAIN ALONG THE
COAST. HIGH PRESSURE FOLLOWS FRIDAY AND SATURDAY WITH A RETURN
TO DRY CONDITIONS. ANOTHER ROUND OF A WINTRY MIX OF
PRECIPITATION IS POSSIBLE SATURDAY NIGHT INTO SUNDAY, FOLLOWED
BY DRY AND SEASONABLE CONDITIONS NEXT MONDAY AND TUESDAY.
NEAR TERM /UNTIL 6 PM THIS EVENING/
CIRROSTRATUS LAYER OF CLOUDS OVER SOUTHERN NEW ENGLAND WILL
THICKEN THIS AFTERNOON. MID LEVEL CLOUDS ARE REACHING NEW YORK
CITY AND THE CATSKILLS, AND SHOULD SPREAD NORTHEAST THIS
AFTERNOON. NEAREST PRECIPITATION IS SOUTH OF A PHILADELPHIA-
CENTRAL PA LINE.
SNOW APPROACHING FROM PA WILL RUN INTO DRY SURFACE LAYER AIR,
WHICH SHOULD CAUSE EVAPORATION OF THE LEADING EDGE OF PRECIP,
SLOWING THE ARRIVAL AT THE GROUND. BOTH CURRENT OBSERVATIONS AND
PROJECTED VERTICAL TEMPERATURE PROFILES SUGGEST A FEW HOURS OF
LIGHT SNOW AT THE START IN CT THIS EVENING.
A FEW ADJUSTMENTS TO SKY COVER BASED ON CURRENT OBSERVATIONS,
OTHERWISE NO CHANGES.
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/
A SECONDARY LOW PRESSURE IS STILL EXPECTED TO DEVELOP ALONG THE
EAST COAST TONIGHT, REACHING SOUTHERN NEW ENGLAND TOWARD 7 AM
THURSDAY. BRUNT OF THE PRECIPITATION WITH THIS SYSTEM WILL FALL
TONIGHT, BUT MAY LINGER INTO THURSDAY MORNING, ESPECIALLY ACROSS
THE EASTERN HALF OF SOUTHERN NEW ENGLAND.
ANY PRECIPITATION SHOULD BE SNOW THIS EVENING/EARLY NIGHT. NOT
A LOT GOING FOR DENDRITIC GROWTH, WHICH WILL KEEP SNOW
ACCUMULATIONS ON THE LIGHT SIDE. 20/00Z OPERATIONAL GUIDANCE, AS
WELL AS ENSEMBLE OUTPUT, CONTINUED TO INDICATE A SIGNIFICANT
WARM NOSE BETWEEN 850 AND 925 MB. SHOULD SEE A TRANSITION FROM
SNOW TO A MIX OF SLEET AND FREEZING RAIN, ESPECIALLY AFTER
MIDNIGHT THURSDAY. GIVEN THE THREAT OF FREEZING RAIN FOR A TIME,
EXPANDED THE WINTER WEATHER ADVISORIES ACROSS MOST OF SOUTHERN
NEW ENGLAND. DID NOT HAVE ENOUGH CONFIDENCE IN FREEZING RAIN
ACROSS THE CAPE AND ISLANDS. AN ADVISORY MAY BE EXTENDED INTO
THOSE AREAS SHOULD CONFIDENCE IN FREEZING RAIN INCREASE.
EXPECTING A TRANSITION TO ALL RAIN ALONG THE IMMEDIATE COAST,
AND PERHAPS A GOOD PORTION OF SOUTHERN RI AND SOUTHEAST MA. THIS
IS ONE OF THE AREAS WHICH MAY BE REFINED WITH LATER FORECASTS.
WEAK COASTAL LOW PRESSURE SHOULD MOVE INTO THE GULF OF MAINE BY
LATE THURSDAY MORNING. DRIER AIR FOLLOW IN ITS WAKE, LEADING TO
IMPROVING CONDITIONS BY AFTERNOON. COLDER AIR IS STILL LAGGING
WELL TO THE NORTH, SO IT WILL BE A RELATIVELY MILD AFTERNOON
WITH HIGHS REACHING THE MID 40S TO LOWER 50S. BREEZY WESTERLY
WINDS DEVELOPING IN THE AFTERNOON WITH GUSTS 25-35 MPH,
ESPECIALLY OVER HIGHER TERRAIN.
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
HIGHLIGHTS...
* DRY AND SEASONABLE FRI/SAT
* ANOTHER ROUND OF WINTRY MIXED PRECIP CHANGING TO RAIN SAT NIGHT/SUN
* DRY AND NEAR SEASONABLE WEATHER RETURNS MON/TUE
OVERVIEW...
THE BIG PICTURE WEATHER PATTERN IN THE EXTENDED FEATURES MORE OF
THE SAME...A RELOADING WEST COAST TROUGH AND PERSISTENT
SUBTROPICAL RIDGE. SEVERAL DAYS OF HIGH PRESSURE/DRY WEATHER
INTERRUPTED BY PERIODIC STORM SYSTEMS EJECTED FROM THE MID LEVEL
TROUGH AND DIRECTED OVER THE RIDGE TOWARD SOUTHERN NEW ENGLAND,
FIRST LATE WEEKEND THEN AGAIN AROUND MID WEEK. GIVEN THE
CONSISTENT PATTERN GOING INTO THIS WEEKEND WE CONTINUE TO EXPECT
A MESSY WINTER SYSTEM WITH A PARENT LOW TO THE NORTHWEST AND TOO
MUCH WARM AIR ALOFT AND IN THE LOW LEVELS TO BE A GOOD SNOW
MAKER. AS MENTIONED BY THE PREVIOUS FORECASTER, ONE SYNOPTIC
MODEL CONTINUES TO SHOW QUITE THE INTERESTING TRACK/EVOLUTION OF
THE MID WEEK SYSTEM, BUT IT IS MUCH TOO FAR OUT IN TIME TO GIVE
MUCH CONSIDERATION TO AT THIS TIME.
THURSDAY NIGHT THROUGH SATURDAY...
HIGH PRESSURE MOVING IN OVERNIGHT BRINGS WEAKENING WINDS,
CLEARING SKIES, AND COLDER TEMPS MOVING IN ON NORTHWEST FLOW
WITH CAA AT THE SFC AND LOW LEVELS. TEMPS DROP INTO THE
20S...LOW 30S ALONG THE COAST. FRIDAY AND SATURDAY FEATURE
PLENTY OF SUNSHINE AND SEASONABLE TEMPERATURES UNDER A 1030 MB
HIGH PRESSURE AND PLENTY OF DRY AIR. 850 TEMPS 0 TO -5C AND GOOD
MIXING WILL LEAD TO HIGH TEMPERATURES EACH DAY IN THE LOW
40S...RIGHT AROUND NORMAL FOR LATE FEBRUARY. MID-HIGH CLOUDS
WILL BE ON THE INCREASE FROM WEST TO EAST LATE SATURDAY AS FLOW
BECOMES SOUTHWEST AHEAD OF THE NEXT STORM SYSTEM.
SATURDAY NIGHT THROUGH SUNDAY...
SATURDAY NIGHT A SHORTWAVE APPROACHES AS THE SURFACE LOW MOVES
INTO THE GREAT LAKES REGION, STRENGTHENING AS IT ENTERS CANADA.
A WEAK SECONDARY WAVE FORMS ALONG THE FRONTAL BOUNDARY OVER THE
DELMARVA AND PASSES OVER SOUTHERN NEW ENGLAND LATE SUNDAY. AHEAD
OF THIS WE HAVE ALL THE INGREDIENTS FOR A WET WEATHER EVENT.
PLENTY OF MOISTURE AVAILABLE AS A DEEP FETCH OF SUBTROPICAL
MOISTURE STRETCHES UP FROM THE GULF BRINING PWATS APPROACHING
1.25". THE WARM FRONT MOVES NORTH ACROSS THE REGION SOMETIME
LATE SATURDAY/SUNDAY WITH A GOOD SIGNAL FOR ISENTROPIC LIFT OVER
THE COLDER AIR AT THE SURFACE AND STRONG SPEED CONVERGENCE AT
LOW LEVELS GIVEN AN APPROACHING 45-55 KT 925 JET. CURRENTLY
EXPECTING A MOSTLY RAIN EVENT, MORESO THAN THE PREVIOUS WED/THU
EVENT GIVEN WARMER SURFACE TEMPERATURES AHEAD OF THE SYSTEM.
LIKELY TO START OUT BRIEFLY AS A WINTRY MIX OF SNOW, SLEET, AND
FREEZING RAIN BEFORE BECOMING ALL RAIN. AHEAD OF THE COLD FRONT
TEMPERATURES LOOK QUITE WARM, IN THE UPPER 40S SUNDAY AFTERNOON.
MONDAY AND TUESDAY...
BEHIND THE COLD FRONT DRY AND COLDER WEATHER PREVAILS UNDER
HIGH PRESSURE FOR THE FIRST HALF OF THE WORK WEEK. GUSTY WINDS
ON MONDAY DIMINISH INTO TUESDAY.
AVIATION /15Z WEDNESDAY THROUGH SUNDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
SHORT TERM /THROUGH THURSDAY/...HIGH CONFIDENCE.
THIS AFTERNOON...VFR. LIGHT WINDS BECOMING SW
TONIGHT...CIGS AND VSBYS LOWER AFTER 7 PM WEST AND AFTER 11 PM
EAST. BECOMING MVFR IN SNOW, THEN IFR AFTER MIDNIGHT IN A WINTRY
MIX, INCLUDING SLEET AND FREEZING RAIN. CHANGE TO RAIN EXPECTED ALONG
THE COAST 3 AM TO 6 AM.
THURSDAY...IMPROVING CONDITIONS FROM W TO E. IFR TO START,
BECOMING VFR BY AFTERNOON.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF TRENDS. MODERATE
CONFIDENCE IN TIMING PRECIPITATION TYPE CHANGES AFTER MIDNIGHT.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF TRENDS. MODERATE
CONFIDENCE IN TIMING PRECIPITATION TYPE CHANGES AFTER 10 PM.
OUTLOOK /THURSDAY NIGHT THROUGH SUNDAY/...
THURSDAY NIGHT THROUGH FRIDAY: VFR. BREEZY.
FRIDAY NIGHT: VFR.
SATURDAY: VFR. CHANCE RA.
SATURDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. BREEZY.
RA, SN LIKELY, FZRA.
SUNDAY: MAINLY VFR, WITH AREAS IFR POSSIBLE. BREEZY. RA LIKELY,
FZRA.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
SHORT TERM /THROUGH THURSDAY/...HIGH CONFIDENCE.
THIS AFTERNOON...
LIGHT WINDS AND SEAS.
TONIGHT...
INCREASING SOUTHEAST WINDS, WITH GUSTS TO 25 KT ON THE OUTER
WATERS BY MORNING. SEAS BUILDING TO 5-8 FEET BY MORNING. SNOW
DEVELOPING 9PM TO MIDNIGHT, CHANGING TO SLEET/FREEZING RAIN AND
THEN RAIN BY MORNING. VSBYS OCCASIONALLY 1-3 MILES IN
PRECIPITATION. A SMALL CRAFT ADVISORY MAY BE NEEDED.
THURSDAY...
WINDS SHIFT FROM THE WEST WITH GUSTS 20-25 KT. SEAS REMAIN AT
5-8 FEET. RAIN TAPERS OFF.
OUTLOOK /THURSDAY NIGHT THROUGH SUNDAY/...
THURSDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS
WITH LOCAL GUSTS UP TO 30 KT. AREAS OF ROUGH SEAS.
FRIDAY: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS.
FRIDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT.
SATURDAY: WINDS LESS THAN 25 KT. CHANCE OF RAIN.
SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING
5 FT. RAIN.
SUNDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 25 KT. SEAS UP TO 5 FT. RAIN LIKELY.
TIDES/COASTAL FLOODING
HIGH ASTRONOMICAL TIDES ARE FORECAST FOR BOTH TODAY AND THU,
WITH HEIGHTS AROUND 12 FT AT BOS AND CLOSE TO 6 FT AT PVD.
MAIN CONCERN FOR THU IS THE MID MORNING HIGH TIDE IN NARRAGANSETT
BAY, AND THE LATE MORNING HIGH TIDE ALONG THE EAST COAST.
GUIDANCE IS SUGGESTING A SURGE UP TO 1 FT IS POSSIBLE NEAR HIGH
TIDE WHICH MAY BRING STORM TIDES TO NEAR FLOOD STAGE AT PVD AND
BOS.
BOX WATCHES/WARNINGS/ADVISORIES
CT...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
THURSDAY FOR CTZ002>004.
MA...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
THURSDAY FOR MAZ002>021-026.
RI...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
THURSDAY FOR RIZ001>007.
MARINE...SMALL CRAFT ADVISORY FROM 2 AM TO NOON EST THURSDAY FOR
ANZ232>234.
SMALL CRAFT ADVISORY FROM 2 AM TO 8 AM EST THURSDAY FOR ANZ231.
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 7 PM EST
THURSDAY FOR ANZ235-237-250-254>256.
SYNOPSIS...WTB/BELK/BW
NEAR TERM...WTB/BELK/BW
SHORT TERM...BELK
LONG TERM...BW
AVIATION...BELK/BW
MARINE...BELK/BW
TIDES/COASTAL FLOODING...
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