Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 281536
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
1036 AM EST SUN DEC 28 2014

.SYNOPSIS...
A COLD FRONT WILL MOVE ACROSS SOUTHERN NEW ENGLAND BY MID
AFTERNOON. LIGHT RAIN SHOWERS WILL ACCOMPANY THE FRONT. FAR
REACHING HIGH PRESSURE INITIALLY CENTERED OVER THE HIGH PLAINS AND
THEN SHIFTING TO THE EAST COAST BY THE END OF THE WEEK WILL KEEP
THE REGION DRY AND COLD THROUGH FRIDAY. AN APPROACHING WARM FRONT
WILL BRING A CHANCE OF PRECIPITATION TO THE REGION ON SATURDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

AT 15Z THE COLD FRONT EXTENDED FROM NORTHWEST MAINE TO THE
BERKSHIRES. RADAR SHOWED MOST OF THE SHOWERS IN OUR AREA WERE IN
EASTERN MASSACHUSETTS. THERE WERE SCATTERED LIGHT SHOWERS IN RI
AND CT AS WELL. WE SHOULD SEE THE SHOWERS WINDING DOWN THROUGH
18Z. GRID POPS HAVE BEEN TWEAKED TO REFLECT THIS TIMING.

PLENTY OF CLOUDS UPSTREAM...SO CLEARING THIS AFTERNOON WILL TAKE
ITS TIME.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
TONIGHT...SKIES WILL BECOME CLEAR AND THIS WILL ALLOW TEMPERATURES
TO DROP TO COLDER THAN GUIDANCE VALUES IN NORTHWEST MA AND IN THE
NORMALLY COLDER LOCATIONS. FORECASTING LOWS IN THE MID 20S AWAY
FROM THE COAST...TO 30 TO 35 FOR THE CAPE AND ISLANDS.

MONDAY...HIGH PRESSURE BUILDING IN FROM THE NORTHWEST MEANS MOSTLY
SUNNY SKIES AND COLDER WEATHER. FAR NW MA...IN THE SLOPES OF THE
BERKSHIRES...COULD HAVE A PERIOD OF PARTLY TO MOSTLY CLOUDY SKIES.
HIGHS FROM THE MID 30S TO LOWER 40S...MORE TOWARD SEASONAL NORMALS.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
HIGHLIGHTS...
* DRY AND COLD THROUGH FRIDAY
* CHANCE OF RAIN OR MIXED PRECIPITATON TO RAIN ON SATURDAY AS WARM FRONT
  APPROACHES

OVERVIEW...

MEDIUM RANGE MODELS NOW APPEAR IN GOOD AGREEMENT ON AT LEAST THE
LARGE SCALE PATTERN THROUGH NEXT WEEKEND. OVER THE COURSE OF THE
COMING WEEK...A HIGH AMPLITUDE RIDGE BUILDS OVER ALASKA WHILE THE
NORTH AMERICAN POLAR VORTEX SETS UP OVER HUDSON BAY. THIS OPENS THE
DOOR TO ARCTIC INTRUSION INTO NEW ENGLAND BUT WITH WHAT WILL
PROBABLY BE A TEMPORARY RELAPSE TO MILD TEMPERATURES NEXT WEEKEND IN
ASSOCIATION WITH WHAT LOOKS TO BE STILL ANOTHER INSIDE RUNNER.
ENSEMBLE MEMBERS SUGGEST A RETURN TO A POSITIVE NAO INDEX AFTER JAN
1 AND A STRONG RIDGE REMAINS ROOTED ACROSS THE BAHAMAS.
THUS...ALTHOUGH THE PATTERN IN GENERAL FAVORS COLD TEMPERATURES
ACROSS SOUTHERN NEW ENGLAND FOR THE FORESEEABLE FUTURE...SHORT WAVE
ENERGY CAN DISLODGE THE COLD AIR AT LEAST TEMPORARILY WITH NO
DOWNSTREAM BLOCKING AVAILABLE TO EITHER HOLD IN THE COLD AIR OR
PROMOTE SIGNIFICANT COASTAL CYCLOGENESIS.

DAY TO DAY...

MON NIGHT THROUGH WED...GENERALLY DRY AND COLDER THAN NORMAL
TEMPERATURES SUPPORTED BY BROAD TROF ALOFT CENTERED OVER HUDSON BAY
AND MASSIVE 1059 MB HIGH SPREADING S AND SE FROM WESTERN
SASKATCHEWAN. TUE NIGHT/WED AM LOOKS TO BE THE COLDEST NIGHT WITH
850 MB TEMPERATURES OF -15C TO -16C...PROBABLY MOSTLY CLEAR SKIES
AND LIGHT WINDS. WILL LIKELY EXPERIENCE SURFACE TEMPERATURES IN
TEENS ACROSS MOST OF INTERIOR SOUTHERN NEW ENGLAND WITH POSSIBLY
POCKETS OF 5 TO 10 ABOVE TEMPERATURES NW MA. LACK OF SNOWCOVER
PREVENTS WHAT MIGHT OTHERWISE BE COLDER TEMPERATURES.

WED NIGHT THROUGH FRI...SHORT WAVE TROF EMBEDDED IN BROAD CYCLONIC
FLOW ALOFT PASSES ACROSS NEW ENGLAND ON THU BUT LACKS MOISTURE.
HOWEVER...IT IS NOT OUT OF THE QUESTION THAT LOW LEVEL LAPSE RATES
COULD SUPPORT OCEAN EFFECT FLURRIES OR SNOW SHOWERS ACROSS NANTUCKET
WITH WESTERLY GRADIENT. THE 00Z GFS THERMAL PROFILE IS MORE
FAVORABLE THAN THE 00Z ECMWF THERMAL PROFILE FOR THIS. THE OTHER
POTENTIAL ISSUE FOR THU IS WIND. MEDIUM RANGE MODELS HAVE DEPICTED
FOR QUITE A FEW RUNS A TIGHTENING OF THE SURFACE PRESSURE GRADIENT
ON THU WITH BRISK WESTERLY WINDS THE RESULT...POSSIBLY GALE FORCE
GUSTS JUST OFF THE COAST. THIS COULD MAKE THU FEEL COLDER DUE TO
LOWER WIND CHILLS. WINDS WILL LIKELY SLACKEN BY FRI MORNING AS
MEDIUM RANGE MODELS CONSISTENT WITH SURFACE RIDGE MOVING ACROSS THE
REGION.

FRI NIGHT THROUGH SAT...THIS IS THE ONLY VIABLE OPPORTUNITY FOR
SIGNIFICANT PRECIPITATION DURING THIS FORECAST PERIOD. MEDIUM
RANGE OPERATIONAL MODELS AND NEARLY ALL ENSEMBLE MEMBERS POINT TO
AN INSIDE RUNNER WITH SOME VARIATIONS IN TIMING AND STRENGTH OF
THE SYSTEM. AT THIS TIME IT LOOKS LIKE THIS SHOULD BE MAINLY A
RAIN EVENT...BUT ENOUGH LOW LEVEL COLD AIR AT THE OUTSET COULD SET
THE STAGE FOR A PERIOD OF MIXED PRECIPITATION AT THE START OF THE
EVENT ACROSS SOME OF THE INTERIOR. BOTH THE ECMWF AND GFS
OPERATIONAL RUNS DEPICT A STRONG LOW LEVEL JET AT 925 MB OF 70+
KT. DEPENDING UPON MIXING POTENTIAL...THIS COULD RESULT IN STRONG
WINDS ACROSS THE SE COASTAL PLAIN SOMETIME ON SAT...PROBABLY
AFTERNOON. A STRONG LOW LEVEL JET COULD ALSO SIGNAL SIGNIFICANT
QPF...BUT THE EVENT IS TOO FAR OUT TO HAVE MUCH CONFIDENCE IN
RAINFALL AMOUNTS.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
FORECASTER CONFIDENCE LEVELS...

LOW...LESS THAN 30 PERCENT.
MODERATE...30 TO 60 PERCENT.
HIGH...GREATER THAN 60 PERCENT.

THIS AFTERNOON...HIGH CONFIDENCE. GENERALLY VFR CEILINGS WITH 2
TO 4 HOURS OF CEILINGS 3500-6000 FT. RAIN SHOWERS EXITING EASTERN
MASSACHUSETTS THIS AFTERNOON WILL LIKELY REDUCE VISIBILITIES TO 5
TO 6 MILES AT MOST LOCATIONS FOR AN HOUR OR TWO. ISOLATED 3 TO 4
MILES VISIBILITY POSSIBLE IN HEAVIER RAIN SHOWERS. THUS VFR
VISIBILITIES EXPECTED MOST OF THE PERIOD BUT MANY LOCATIONS MAY
DROP INTO THE MVFR CATEGORY FOR 2 OR 3 HOURS. SW WINDS GUSTING TO
15 TO 20 KT...SHIFTING TO THE W AT THE SAME SPEEDS.

TONIGHT...HIGH CONFIDENCE. VFR WITH A LIGHT WEST TO NORTHWEST WIND.

MONDAY...HIGH CONFIDENCE. VFR. MVFR CEILINGS POSSIBLE IN EXTREME
NW MA IN THE SLOPES OF THE BERKSHIRES.

KBOS TERMINAL...HIGH CONFIDENCE IN TAF.

KBDL TERMINAL...HIGH CONFIDENCE IN TAF.

OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...

MODERATE TO HIGH CONFIDENCE OF MAINLY VFR THROUGH THE PERIOD.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

LOW...LESS THAN 30 PERCENT.
MODERATE...30 TO 60 PERCENT.
HIGH...GREATER THAN 60 PERCENT.

SHORT TERM /THROUGH MONDAY/...MODERATE TO HIGH CONFIDENCE.

THIS AFTERNOON...A MARGINAL SMALL CRAFT ADVISORY IS IN EFFECT FOR
ALL WATERS EXCEPT FOR BOSTON HARBOR AND NARRAGANSETT BAY. WE COULD
SEE SW WIND GUSTS TO AROUND 25 KT EARLY AFTERNOON... FOLLOWED BY
A SHIFT TO THE W AND WNW LATER THIS AFTERNOON AT THE SAME SPEEDS.
SEAS SHOULD BE BUILDING FROM 3 FT UP TO 5 OR 6 FT ON THE
OUTERMOST WATERS LATER THIS AFTERNOON.

TONIGHT...WINDS DIMINISH AND SEAS SUBSIDE. HOWEVER A SMALL CRAFT
ADVISORY WILL REMAIN POSTED FOR THE SOUTHEASTERN WATERS UNTIL
ABOUT 1 AM BECAUSE THE 5 FT SEAS WILL BE SLOWEST TO SUBSIDE IN
THOSE AREAS.

MONDAY...NORTHWEST WINDS 10 TO 15 KT WITH GUSTS TO 20 KT OFF THE
NORTHEAST MA COAST. SEAS GENERALLY 3 TO 4 FT OVER THE OUTER
WATERS.

OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...

MODERATE TO HIGH CONFIDENCE.

MON NIGHT THROUGH WED NIGHT...EXPECT WINDS AND SEAS BELOW SMALL
CRAFT ADVISORY THRESHOLDS.

THU...W WIND WILL LIKELY INCREASE ABOVE SMALL CRAFT ADVISORY THRESHOLDS
ALL WATERS WITH A CHANCE OF GALE FORCE GUSTS OVER AT LEAST THE OUTER
WATERS.

ALTHOUGH THIS OUTLOOK GOES ONLY TO THU...THE HWO IS FOR 7 DAYS.
WILL MENTION A RISK OF SOUTHERLY GALES ACROSS THE WATERS ON SAT
IN THE HWO. TYPICALLY, AN INVERSION AT THIS TIME OF YEAR LIMITS
HOW MUCH MOMENTUM IS MIXED TO THE SEA SURFACE IN A SOUTHERLY
GRADIENT. HOWEVER...GIVEN A SIGNAL OF 70+ KT AT 925 MB...THINK
THERE IS A CHANCE OF MIXING WINDS STRONG ENOUGH TO RESULT IN
POSSIBLE GALE FORCE GUSTS ACROSS THE OUTER WATERS.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR
     ANZ231>235-237-250-251.
     SMALL CRAFT ADVISORY UNTIL 1 AM EST MONDAY FOR ANZ254>256.

&&

$$
SYNOPSIS...GAF/THOMPSON
NEAR TERM...WTB
SHORT TERM...GAF
LONG TERM...THOMPSON
AVIATION...WTB/GAF/THOMPSON
MARINE...WTB/GAF/THOMPSON


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