National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 092108
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
407 PM EST MON DEC 9 2013

.SYNOPSIS...
-- Changed Discussion --
LOW PRESSURE WILL MOVE AWAY FROM THE REGION THIS EVENING. ANOTHER
DISTURBANCE WILL PROBABLY BRING ACCUMULATING SNOW TUESDAY...MAINLY
SOUTH OF THE MASSACHUSETTS TURNPIKE. MAINLY DRY...BUT UNSEASONABLY
COLD AND BLUSTERY WEATHER IS EXPECTED FOR THE REST OF THE WORK WEEK.
A LOW PRESSURE SYSTEM MAY BRING A WINTRY MIX OF PRECIPITATION
SOMETIME THIS WEEKEND.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

-- Changed Discussion --
LINGERING DRIZZLE SHOULD COME TO AN END THIS EVENING AS DRIER AIR
WORKS IN JUST OFF THE DECK.  MAY TAKE SOMETIME TO MIX OUT THE
SHALLOW INVERSION THOUGH...BUT TEMPS ACROSS THE INTERIOR HAVE
CLIMBED TO FREEZING OR JUST ABOVE.  THEREFORE...WILL CANCEL THE
WINTER WEATHER ADVISORY.  WILL ISSUE A SPECIAL WEATHER STATEMENT AS
LIGHT WINDS MAY LEAD TO THE FORMATION OF PATCHY BLACK ICE IF TEMPS
DROP A DEGREE OR TWO.  AREAS OF FOG WILL ALSO REDUCE VISIBILITIES
THIS EVENING.

LOW CONFIDENCE ON SKY COVER TONIGHT.  WE PROBABLY WILL EVENTUALLY
SEE ENOUGH DRY AIR WORK IN TO SCOUR OUT SOME OF THE LOW CLOUDS...BUT
IT MAY TAKE SOMETIME.

LOW TEMPS BY DAYBREAK SHOULD FALL BACK INTO THE 20S ACROSS THE
INTERIOR...WITH SOME LOWER TO MIDDLE 30S ACROSS THE FAR SOUTHEAST
NEW ENGLAND COAST.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...

-- Changed Discussion --
*/TUESDAY...

SNOW ANTICIPATED MAINLY ALONG AND SOUTH OF THE MASS-TURNPIKE AS AN
UPPER-LEVEL DISTURBANCE DRAGS MOISTURE NORTHWARD ACROSS COLDER AIR
SETTLING INTO SOUTHERN NEW ENGLAND.

EVALUATING THE ENVIRONMENT WITHIN THE LOW-LEVELS...THE ENTIRE COLUMN
IS BELOW-FREEZING WITH THICKNESSES BELOW THEIR CRITICAL THRESHOLDS.
WEST-NORTHWEST SURFACE-H85 WINDS ALLOW FOR UNDERCUTTING LOW-LEVEL
COLD AIR ADVECTION. YET AGEOSTROPHIC FLOW BELOW H925 IS SOUTHERLY
ONSHORE SO THERE IS SOME PLAUSIBILITY ALONG THE IMMEDIATE SOUTH-
SHORE OF WARMING ABOVE-FREEZING. NEVERTHELESS...THERE ARE SUBTLE
HINTS OF LOW-LEVELS BECOMING DRY-ADIABATIC ALLOWING FOR SOME WEAK
INSTABILITY /YET NORMALIZED CAPE VALUES ARE NOT EXCEEDING 0.1 FOR
ANY AREA/.

ALOFT...EXPECTING STRONG- AND DEEP-LIFTING THROUGH THE DENDRITIC
GROWTH ZONE REGION PER THE RIGHT-REAR QUADRANT OF THE UPPER-LEVEL
JET /+ 2 SD/ AND MAIN VORTMAX ASSOCIATED WITH THE BROADER TROUGHING
REGIME SWEEPING EAST OUT OF THE GREAT LAKES REGION. THE STRONGEST
LIFT THROUGH THE DENDRITIC GROWTH ZONE IS MODELED TO STRETCH ACROSS
AN AREA IN PROXIMITY TO NEW YORK CITY TO BOSTON. THIS ALSO INVOKES
NORTHEASTERLY ISENTROPIC ASCENT FROM THE BETTER SUB-TROPICAL BRANCH
EXTENDING FROM THE GULF NORTHEASTWARD THROUGH THE MID-ATLANTIC.

THE OVERALL OUTCOME IS A STRONG POSSIBILITY FOR MESOSCALE BANDING OF
SNOW SOMEWHERE IN PROXIMITY TO THE SOUTH-COAST OF NEW ENGLAND
COLLOCATED WITH THE STRONG FORCING THROUGH THE DENDRITIC GROWTH ZONE
REGION. EVALUATING THE DYNAMICS ABOVE...THERE IS A GOOD INDICATION
OF BANDED FRONTOGENESIS AROUND H600-650 COLLOCATED WITH NEGATIVE
EQUIVALENT POTENTIAL VORTICITY /EPV/ BUT MODELS DIFFER ON THE EXACT
LOCATION OF THIS BAND. OBVIOUSLY ANY WOBBLE IN THE BAND WOULD RESULT
IN SIGNIFICANT IMPACTS AT THE SURFACE. NEVERTHELESS CONFIDENCE IS
GAINED PER THE 15Z SREF WITH AROUND 90 PERCENT PROBABILITY OF 1-INCH
ALONG THE SOUTH-COAST. 4-INCH AMOUNT PROBABILITIES ARE NON-EXISTENT
BUT IT IS NOT OUT OF THE QUESTION TO SEE LOCALIZED HIGHER AMOUNTS.

SO FOR THE FORECAST...WILL FOLLOW CLOSELY WITH SREF/WRF-ARW/ECMWF
SOLUTIONS FOR PRECIPITATION WHICH ARE SUCCINCT WITH HEAVIEST AMOUNTS
ALONG THE SOUTH-COAST. EXPECTING ALL SNOW WITH ICE PRESENT WITHIN
THE ATMOSPHERIC COLUMN. COULD SEE SOME MIXING WITH RAIN ALONG THE
COASTLINES AT TIMES THOUGH SHOULD NOT BE THE CASE IF IT IS SNOWING
MODERATELY. WILL CONCENTRATE THE GREATEST SNOW ACCUMULATIONS ALONG
THE SOUTH-SHORE /LIKELY POPS/ KEEPING ANY ACCUMULATION ALONG AND
NORTH OF THE MASSACHUSETTS TURNPIKE VERY LIGHT /CHANCE TO SLIGHT
CHANCE POPS/. EXPECTING A SCRUNCHED PRECIPITATION EVENT.

AS FOR THE SNOW-BANDING...THERE APPEARS TO BE GREATER MODEL WEIGHT
OF THE BAND TO REMAIN JUST OFFSHORE OF THE SOUTH-COAST...THOUGH THE
15Z SREF HAS DRAGGED THE PRECIPITATION MEAN NORTH COMPARED TO THE
PRIOR 9Z RUN. THERE REMAINS A FAIR AMOUNT OF UNCERTAINTY...AND AS
MENTIONED EARLIER...A SLIGHT WOBBLE IN THE BAND WOULD RESULT IN
SIGNIFICANTLY DIFFERENT OUTCOMES AT THE SURFACE.

THUS WITH REGARDS TO STATEMENTS...WILL HOLD OFF ON THE ADVISORY DUE
TO THE UNCERTAINTY CONCERNING THE SPATIAL CHARACTERISTICS OF THE
POTENTIALLY SNOW-BANDING. A BROAD-SCALE 1 TO 3 INCHES IS EXPECTED FOR
THE SOUTH-COAST NORTH TO THE MASSACHUSETTS TURNPIKE...BUT IF MESO-
SCALE BANDING WERE TO TAKE PLACE...WE COULD BE TALKING UP TO 6
INCHES /AGAIN MAINLY FOCUSING ALONG THE SOUTH-COAST INCLUDING THE
CAPE AND ISLANDS/. ELSEWHERE EXPECTING A TRACE UP TO AN INCH...WITH
VERY LITTLE IN SOUTHERN NEW HAMPSHIRE.

SNOW RATIOS EXPECTED TO BE BETWEEN 1:10 TO 1:12 WITH SUB-FREEZING
TEMPERATURES HOLDING AROUND THE UPPER-20S FOR THE INTERIOR. HIGHS
AROUND THE LOW- TO MID-30S ELSEWHERE.

*/TUESDAY NIGHT...

ACTIVITY USHERS OUT OVERNIGHT TURNING DRY. WELL-MIXED LOW-LEVEL
PROFILES AND INCREASING WINDS ALOFT ALLOW FOR THE MIX-DOWN OF FASTER
MOMENTUM TO THE SURFACE. ANTICIPATE GUSTY WINDS UP TO 20 MPH ACROSS
THE INTERIOR...FASTER ALONG THE IMMEDIATE SHORES WITH GALES OVER THE
WATERS. EXPECT CLEAR CONDITIONS YET LIMITATIONS ON EFFECTIVE
NOCTURNAL COOLING WITH ANTICIPATED WINDS.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

-- Changed Discussion --
... HIGHLIGHTS...

* MAINLY DRY AND UNSEASONABLY COLD WED THROUGH FRI
* SAT AND SUN BRING POTENTIAL FOR WINTRY PRECIPITATION
* LOW CONFIDENCE MON

OVERVIEW AND MODEL PREFERENCES...

00/12Z MODEL LONG RANGE GUIDANCE GENERALLY IN GOOD AGREEMENT WITH
SYNOPTIC PATTERN UNTIL THIS WEEKEND.  FOR THIS WEEKEND 00Z GUIDANCE
INDICATED DIFFERENCES REGARDING EXTENT OF COASTAL LOW DEVELOPMENT
AND AS A RESULT PRECIP POTENTIAL/TIMING AND PRECIP TYPES FOR
SOUTHERN NEW ENGLAND.

12Z GFS IS LESS PROGRESSIVE WITH THE UPPER TROUGH THAN ITS 00Z 12/8
RUN...MORE IN LINE WITH THE 00Z ECMWF...BRINGING THE UPPER TROUGH
INTO THE GREAT LAKES REGION FOR THE WEEKEND. BOTH 00Z/12Z ECMWF AND
12Z GFS RUNS INDICATE POTENTIAL FOR A COASTAL STORM AFFECTING
SOUTHERN NEW ENGLAND DURING LATE SATURDAY INTO SUNDAY.  IN
ADDITION...MODELS SHOW POTENTIAL FOR A SUBSTANTIAL AMOUNT OF WINTRY
PRECIPITATION. PREVIOUS AND CURRENT RUNS HAVE VARIED ON EXTENT OF
LOW DEVELOPMENT AND TRACK...SO AT THIS TIME CONFIDENCE IS LOW AND
FUTURE MODEL RUNS WOULD AFFECT CONFIDENCE LEVEL.

DETAILS...

WED INTO FRI... PERIOD OF ANOMALOUS COLD AND MAINLY DRY WX PREVAILS
WITH COLD HIGH PRESSURE BEING THE PREDOMINANT WEATHER FEATURE. A
COUPLE OF ADDITIONAL FEATURES DURING THIS PERIOD...THE FIRST IS A
PASSAGE OF AN ARCTIC COLD FRONT ON WED NIGHT INTO THU. NOT A LARGE
AMOUNT OF MOISTURE ASSOCIATED WITH THIS FRONT...BUT COULD HAVE SOME
FLURRIES. IN ADDITION...A PERIOD OF LOW LEVEL NW WINDS BEHIND THE
FRONT WED NIGHT AND THU MAY LEAD TO A PERIOD OF OCEAN EFFECT SNOWS
FOR THE CAPE/NANTUCKET.

H850 WINDS ARE BRISK AHEAD OF AND BEHIND THE FRONT /30 TO 35
KTS/...POTENTIAL FOR SURFACE WIND GUSTS OF 20 TO 25 KTS WED AND THU.
OF CONCERN IS THE GFS SHOWING STRONGER WINDS ALOFT WHICH COULD
TRANSLATE GALES OVER THE WATERS.

H85 TEMPS DIPPING AS LOW AS -18C TO -20C BEHIND THE FRONT...SO HIGH
TEMPS ON THU AND FRI MAY STAY IN THE 20S AT MANY LOCATIONS...WHILE
LOWS DIP BACK INTO THE SINGLE DIGITS ACROSS THE FAR INTERIOR. AVG
TEMPS ABOUT 10-15 DEGREES BELOW NORMAL.

THIS COMING WEEKEND...12Z GFS AND 00Z/12Z ECMWF RUNS BRING THE
CONCERN FOR A POTENTIAL COASTAL LOW AFFECTING SOUTHERN NEW ENGLAND
DURING THIS WEEKEND.  HAVE NOT ACHIEVED RUN TO RUN MODEL CONSISTENCY
REGARDING THE STRENGTH OR EXACT TRACK OF THIS LOW. HOWEVER THESE
MODELS DO SHOW A LOW THAT MOVES QUICKLY ACROSS THE AREA...AND
PRODUCES POTENTIALLY GENEROUS QPF. ALL WINTRY P-TYPES
/RAIN/SNOW/FRZRA/SLEET/ LOOK POSSIBLE RIGHT NOW. WILL HIGHLIGHT
CHANCE POPS FOR UNSETTLED WINTRY WX FOR LATE SAT AND SUN.

MON...SURFACE HIGH PRESSURE BUILDS IN WHILE UPPER TROUGH PASSES
ALOFT. HAVE SLIGHT CHANCE POPS FOR POSSIBLE SNOW SHOWERS...DRY AND
COLD MON NIGHT.
-- End Changed Discussion --

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
FORECASTER CONFIDENCE LEVELS...

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

NEAR-TERM /THROUGH TONIGHT/...

IFR CONDITIONS CONTINUE LATE THIS AFTERNOON IN LOW CLOUDS/FOG AND
DRIZZLE. EXPECT THE LEFT OVER DRIZZLE TO COME TO AN END BY EARLY
EVENING...BUT AREAS OF FOG WILL LIKELY LINGER LONGER.
OTHERWISE...CONDITIONS WILL SLOWLY IMPROVE TO VFR FROM WEST TO EAST
LATER THIS EVENING AS DRIER AIR WORKS INTO THE REGION.  TIMING IS A
BIT UNCERTAIN...BUT IT MAY TAKE SOMETIME TO MIX OUT THE SHALLOW
INVERSION.

KBOS TAF...MODERATE TO HIGH CONFIDENCE IN IMPROVING TRENDS LATER
THIS EVENING...BUT LOW CONFIDENCE ON TIMING.

KBDL TAF...MODERATE TO HIGH CONFIDENCE IN IMPROVING TRENDS LATER
THIS EVENING...BUT LOW CONFIDENCE ON TIMING.

OUTLOOK...TUESDAY THROUGH FRIDAY...

TUE...MODERATE CONFIDENCE.
A PERIOD OF SNOWFALL MAY LEAD TO IFR/MVFR CIGS/VSBYS AT TERMINALS
ESPECIALLY S OF THE MASS PIKE. SOME TERMINALS N MAY REMAIN VFR
MOST OF THE DAY /ESPECIALLY IN SRN NH/ CONDITIONS IMPROVE
EVERYWHERE DURING THE EVENING HOURS.

TUE NIGHT INTO FRI...HIGH CONFIDENCE.
MAINLY VFR THRU THE PERIOD. ONLY CAVEAT WILL BE THE POSSIBILITY OF
LOCALIZED MVFR CONDITIONS IN SOME OCEAN EFFECTS -SHSN/SHRA FOR
CAPE/ISLAND TERMINALS WITH THE BEST CHANCES WED NIGHT AND THU.
STRONG NW WIND GUSTS ALSO POSSIBLE LATE TUE NIGHT INTO WED NIGHT.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
FORECASTER CONFIDENCE LEVELS...

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

NEAR-TERM /THROUGH TONIGHT/...MODERATE TO HIGH CONFIDENCE.

WINDS HAVE DIMINISHED BELOW SCA THRESHOLDS ACROSS MOST AREAS AS THE
PRESSURE GRADIENT HAS WEAKENED WITH LOW PRESSURE LOCATED NEAR
NANTUCKET LATE THIS AFTERNOON.  WESTERLY WINDS MAY INCREASE AGAIN
WITH SOME GUSTS TO 25 KNOTS LATER THIS EVENING BEHIND THE COLD
FRONT.  SEAS WILL ALSO REMAIN ABOVE SCA THRESHOLDS ACROSS THE OUTER-
WATERS.

OUTLOOK...TUESDAY THROUGH FRIDAY...HIGH CONFIDENCE.

TUE...MODERATE CONFIDENCE.
SEAS GRADUALLY SLACKEN THROUGH THE DAY BUT MAY REMAIN ABOVE 5 FT
ON THE ERN OCEAN WATERS. WINDS GENERALLY BELOW 20 KT SAVE FOR A
FEW STRONGER GUSTS ON NRN WATERS. SOME SMALL CRAFT ADVISORIES MAY
REMAIN FOR SEAS ALONE.

TUE NIGHT INTO FRI...HIGH CONFIDENCE IN TRENDS BUT LOWER
CONFIDENCE IN EXACT TIMING OF ANY HEADLINES.
A PROLONGED PERIOD OF AT LEAST SMALL CRAFT ADVISORY CONDITIONS
LOOKS LIKELY THROUGH THIS PERIOD AS W-NW WINDS WILL OFTEN REMAIN
25 KT OR HIGHER THROUGH THE PERIOD WITH SEAS 5-8FT ON THE OUTER
WATERS. THERE IS ALSO THE LOW PROBABILITY THAT OCCASIONAL GALE
FORCE WIND GUSTS OCCUR LATE TUE NIGHT AND AGAIN THU NIGHT.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...NONE.
MA...NONE.
NH...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 AM EST TUESDAY FOR ANZ235-237-250-
     251-254>256.
-- End Changed Discussion --

&&

$$
SYNOPSIS...FRANK/SIPPRELL/THOMPSON
NEAR TERM...FRANK
SHORT TERM...SIPPRELL
LONG TERM...NMB/THOMPSON
AVIATION...FRANK/SIPPRELL/NMB
MARINE...FRANK/SIPPRELL/NMB