Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 011801
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
201 PM EDT MON SEP 1 2014

.SYNOPSIS...
A WARM HUMID FLOW WILL CONTINUE ACROSS NEW ENGLAND THROUGH
TUESDAY WITH SCATTERED SHOWERS AND THUNDERSTORMS EACH DAY. A
COLD FRONT WILL PUSH ACROSS THE REGION TUESDAY NIGHT. WARM BUT
LESS HUMID WEATHER WILL FOLLOW FOR WEDNESDAY THROUGH FRIDAY.
ANOTHER COLD FRONT MAY BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS SATURDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
2 PM UPDATE...DIURNAL CUMULUS CLOUDS HAVE DEVELOPED ACROSS THE
REGION AND SEA BREEZES HAVE DEVELOPED ALONG BOTH COASTS. STARTING
TO SEE A FEW SHOWERS POP UP IN SOUTHERN CONNECTICUT THIS
AFTERNOON. WILL START TO SEE MORE SHOWERS AND THUNDERSTORMS AS THE
AFTERNOON WEARS ON...MAINLY SOUTH OF THE CT/MA BORDER AND EASTWARD
INTO SOUTHEASTERN MASSACHUSETTS. THIS IS WHERE THE BEST
INSTABILITY IS LOCATED.

PREVIOUS DISCUSSION...

WARM HUMID AIR WITH DEWPOINTS IN THE UPPER 60S AND 70S. A FRONT
IS STALLED ALONG THE CANADIAN BORDER. MEANWHILE A LEE TROUGH WILL
BE POSITIONED NEAR THE MID ATLANTIC COAST. BOTH OF THESE WILL
SERVE AS FOCI FOR THUNDERSTORM DEVELOPMENT.

SOMEWHAT DRIER AIR MOVES INTO NORTHERN NEW ENGLAND WITH PRECIP
WATER VALUES NEAR 1 INCH. MEANWHILE...2 INCH VALUES LINGER ALONG
THE SOUTH COAST. THIS MOISTURE WILL BE THE POTENTIAL FUEL FOR ANY
DAYTIME CONVECTION. STABILITY PARAMETERS LOOK FAVORABLE FOR TSTMS
BUT LIKELY NOT AT SEVERE LEVELS. TOTALS START LOW AND CLIMB TO
46-47 IN THE AFTERNOON WITH HIGHEST VALUES ACROSS CT-RI-SE MASS.
THE GFS SHOWS SHOWS SBCAPE REACHING 1000-1500 J/KG ESPECIALLY IN
CT. LOW LEVEL HELICITY IS MUCH LOWER THAN SUNDAY...20-30 M2/S2.
POPS WILL FAVOR AFTERNOON/EVENING TSTMS WITH HIGHEST VALUES AT THE
SOUTH COAST. WITH PRECIP WATER VALUES AT 1.5-2.0 INCHES SOUTH OF
THE MASS PIKE...ANY STORMS IN THIS AREA WILL HAVE POTENTIAL FOR
HEAVY DOWNPOURS AND POSSIBLE URBAN/POOR DRAINAGE FLOODING. MAX SFC
TEMPS WILL AGAIN BE IN THE MID 80S.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
TONIGHT...
LINGERING CONVECTION IN THE EVENING BUT DIMINISHING. HIGH HUMIDITY
AND LIGHT WIND WILL AGAIN FAVOR DEVELOPMENT OF FOG OVERNIGHT.
MIN SFC TEMPS WILL BE NEAR THE DEW POINTS...MAINLY UPPER 60S AND
LOWER 70S.

TUESDAY...
UPPER SHORTWAVE DIGS OVER THE GREAT LAKES WHILE HIGH PRESSURE
REMAINS TO OUR EAST. THIS WILL MAINTAIN THE WARM MOIST SOUTHWEST
FLOW ACROSS NEW ENGLAND. A COLD FRONT ASSOCIATED WITH THE UPPER
SHORTWAVE WILL MOVE EAST THROUGH THE EASTERN GREAT LAKES TO
EASTERN NEW YORK BY EVENING. A PRE-FRONTAL TROUGH WILL REMAIN OVER
THE HUDSON AND DELAWARE VALLEYS. FAVORABLE JET DYNAMICS REMAIN
WELL TO OUR WEST MUCH OF THE DAY...BUT APPROACH WESTERN
MASS/SOUTHERN NH LATE. TOTALS ON THE GFS ARE 50-51 WHILE THE
ECMWF AND GGEM ARE 47-48. MID LEVEL LAPSE RATES ARE AROUND 6C/KM.
SBCAPES ARE 500-1000 J/KG BY THE GFS HINTS AT 1000-1500 J/KG.
OVERALL WE WILL FAVOR CHANCE POPS FOR SHOWERS/TSTMS IN THE
AFTERNOON WITH THE BEST CHANCE IN WESTERN MASS/SOUTHERN NH AND
DIMINISHING VALUES FARTHER EAST. PRECIPITABLE WATER VALUES START
AROUND 1.5 INCHES AND CLIMB TO NEAR 2 INCHES...SO LOCALLY HEAVY
DOWNPOURS WILL AGAIN BE A CONCERN.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
OVERVIEW AND MODEL PREFERENCES...
MEDIUM RANGE MODELS CONTINUE TO SHOW GOOD CONTINUITY EARLY IN THE
FORECAST CYCLE...AS H5 TROUGH LIFTS INTO SOUTHERN QUEBEC AND
ONTARIO AS IT FLATTENS OUT. THE UPPER PATTERN THEN BECOMES MORE
TYPICAL OF MID SUMMER RATHER THAN EARLY FALL...WITH BROAD RIDGING
DOMINATING FOR THE MIDDLE AND LATTER PORTIONS OF THE WEEK. BEYOND
THIS...MODELS START TO DIVERGE IN BREAKING DOWN THIS RIDGE...WITH
THE 12Z/00Z ECMWF OP RUNS AS WELL AS ECENS AND GFS MEANS SHOWING A
SLOWER BREAKDOWN OF THE UPPER PATTERN WHILE THE GFS OP RUNS
TENDING TO SIGNAL A QUICKER BREAKDOWN. ALSO NOTING UPPER LEVEL
ENERGY CROSSING CENTRAL AND NORTHERN CANADA AROUND THE MIDDLE AND
LATTER PORTIONS OF THIS FORECAST...THOUGH LOOKS LIKE THIS WILL
REMAIN WELL N OF THE U.S./CANADIAN BORDER...FOR NOW.

HAVE LEANED THIS FORECAST TOWARD A BLEND OF AVAILABLE GUIDANCE
THROUGH LATE THIS WEEK...AS THIS BLEND HAS SHOWN VERY GOOD
CONSISTENCY OVER THE LAST SEVERAL DAYS...THEN PUSHED CLOSER TO THE
EC/ECENS MEANS FOR NEXT WEEKEND WHICH TEND TO BE SLOWER THAN MOST
OF THE OTHER GUIDANCE. EXPERIENCE SHOWS THAT...WITH A STRONG
DOMINANT PATTERN IN PLACE SUCH AS WHAT WILL BE DEVELOPING...THIS
TENDS TO TAKE MORE TIME TO BREAK DOWN UNLESS SOME MAJOR SYSTEM
SHOWS UP IN THE OVERALL FLOW.

DAILY DETAILS...

TUESDAY NIGHT...COLD FRONT CONTINUES TO MOVE OFFSHORE OVERNIGHT.
LEFTOVER ENERGY WILL LIFT NE INTO NORTHERN NEW ENGLAND AND THE
MARITIMES OVERNIGHT AS H5 SHORT WAVE LIFTS INTO SOUTHERN QUEBEC.
EXPECT DRIER AIR TO START FILTERING IN...MAINLY ACROSS S NH/N
CENTRAL AND W MA. WILL TAKE SOME TIME FOR SW WINDS TO SHIFT ACROSS
SOUTHERN AND EASTERN AREAS OVERNIGHT...SO MORE HUMID CONDITIONS
WILL HOLD IN. OVERNIGHT LOWS WILL RANGE FROM THE LOWER-MID 60S OF
THE HIGHER INLAND TERRAIN OF SW NH/W MA TO AROUND 70 ALONG THE
IMMEDIATE COAST.

WEDNESDAY...SURFACE HIGH PRES WILL BUILD E OUT OF THE GREAT
LAKES...ALLOWING DRIER AIR TO SPILL IN ACROSS THE REGION DURING
THE DAY AS WINDS SHIFT TO NW. HOWEVER...WITH THE GENERAL OFFSHORE
FLOW IN PLACE AND H5 HEIGHTS RISING WITH BROAD RIDGE BUILDING
ALOFT... LOOKS LIKE TEMPS WILL REMAIN ON THE WARM SIDE. TEMPS WILL
TOP OFF IN THE LOWER-MID 80S...EXCEPT FROM 75 TO 80 ALONG THE
IMMEDIATE COAST.

MAY SEE SOME PATCHY FOG DEVELOP IN NORMALLY PRONE VALLEY AREAS
WED NIGHT AS TEMPS FINALLY FALL BACK TO THE 50S...THOUGH HOLDING
IN THE LOWER-MID 60S ALONG THE IMMEDIATE COAST. WINDS BECOME
LIGHT/VRBL OR CALM...WHICH MAY HELP TO PROMOTE THE FOG
DEVELOPMENT.

THURSDAY AND FRIDAY...HIGH PRESSURE WILL DOMINATE...SO EXPECT DRY
AND WARM CONDITIONS TO CONTINUE ACROSS THE REGION. DEWPTS WILL BE
COMFORTABLE...MAINLY IN THE MID 50S TO AROUND 60 ON THURSDAY...BUT
LOOK TO START CREEPING BACK UP AGAIN ON FRIDAY AS THE HIGH WILL
SLIP OFF THE COAST AND SW WINDS TAKE OVER. HIGHS THURSDAY WILL BE
IN THE LOWER-MID 80S AGAIN...THOUGH SOME READINGS MAY REACH THE
UPPER 80S WELL INLAND ON FRIDAY.

SATURDAY AND SUNDAY...MODEL RUNS TENDING TO DIVERGE ON THE
BREAKDOWN OF THE UPPER LEVEL PATTERN ACROSS THE EASTERN U.S.
DURING THIS TIMEFRAME AND THE APPROACH OF A COLD FRONT...SO LOWER
FORECAST CONFIDENCE. AT THIS POINT...A COLD FRONT WILL APPROACH
THE REGION DURING SAT...PUSHING OFFSHORE SAT NIGHT OR EARLY SUNDAY
WITH HIGH PRES RETURNING.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH MONDAY NIGHT/...HIGH CONFIDENCE IN
TRENDS...LOWER CONFIDENCE IN TIMING.

THROUGH 00Z...IFR CIGS LINGER ALONG THE SOUTH COAST WITH VFR
CONDITIONS ELSEWHERE. ISOLD TO SCT SHRA/TSRA ACROSS CT/RI/SE MASS
THIS AFTERNOON/EVENING WITH LOCALLY HEAVY DOWNPOURS POSSIBLE.
BRIEF MVFR/IFR IN ANY TSTMS. SEA BREEZE ALONG BOTH COASTS
RESULTING IN SOUTHEASTERLY WINDS AT LOGAN.

TONIGHT...EVENING SHRA/TSRA ESPECIALLY OVER THE CAPE AND ISLANDS.
BRIEF MVFR/IFR IN ANY STORMS. QUIET WEATHER THE REMAINDER OF THE
NIGHT WITH AREAS OF IFR IN STRATUS AND FOG. BEST CHANCE WILL
AGAIN BE ALONG THE SOUTH COAST AND ISLANDS AS WELL AS THE CT RIVER
VALLEY.

TUESDAY...MORNING FOG AND IFR CONDITIONS BURN OFF. VFR THROUGH
MUCH OF THE DAY. INCREASING CLOUDS FROM THE WEST DURING THE
AFTERNOON/EVENING WITH POTENTIAL FOR BRIEF MVFR IN SCATTERED
THUNDERSTORMS.

TUESDAY NIGHT...MVFR/IFR CONDITIONS IN STRATUS AND FOG LIKELY
AGAIN...PARTICULARLY ALONG THE SOUTH COAST...CAPE...AND ISLANDS.
COLD FRONT MOVES THROUGH AFTER MIDNIGHT ALLOWING SHRA/TSRA TO END
AND CONDITIONS TO IMPROVE.

KBOS TERMINAL...HIGH CONFIDENCE IN TRENDS. LOWER CONFIDENCE ON
TIMING.  SEABREEZE CONTINUES THROUGH SUNSET.

KBDL TERMINAL...HIGH CONFIDENCE IN TRENDS. LOWER CONFIDENCE ON
TIMING.

OUTLOOK...WEDNESDAY THROUGH FRIDAY...

WEDNESDAY THROUGH FRIDAY...MODERATE CONFIDENCE. EXPECTING MAINLY
VFR CONDITIONS. LOCAL MVFR-IFR VSBYS AND CIGS IN LATE NIGHT PATCHY
FOG AND LOW CLOUDS. MAIN AREAS OF CONCERN WILL BE THE TYPICALLY
PRONE LOCATIONS ACROSS THE FAR INTERIOR /SW NH AND NORTH CENTRAL
AND WESTERN MA/. ON THU NIGHT...WITH SW WINDS IN PLACE...MAY SEE
PATCHY FOG ALONG THE S COAST WITH LOCAL MVFR-IFR CONDITIONS AS
WELL.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

MODERATE CONFIDENCE THROUGH TUESDAY.

TODAY...
HIGH PRESSURE OFFSHORE AND LOW PRESSURE OVER THE GREAT LAKES WILL
MAINTAIN A SOUTHWEST WIND FLOW ACROSS THE WATERS THROUGH TUESDAY.
WINDS WILL REMAIN AT OR BELOW 20 KNOTS. SEAS WILL START AROUND 5
FEET ON THE OUTER WATERS BUT WILL DIMINISH THROUGH THE DAY. WE
HAVE MAINTAINED SMALL CRAFT ADVISORY ON THE SOUTHERN OUTER WATERS
THROUGH THE DAY DUE TO THE LINGERING ROUGH SEAS. A FEW
THUNDERSTORMS WILL MOVE ACROSS SOUTHERN NEW ENGLAND WITH THE BEST
CHANCE ON THE WATERS OCCURRING SOUTH OF BOSTON.

TONIGHT...
EVENING THUNDERSTORMS DIMINISH EARLY AT NIGHT. LIGHT SOUTHWEST
FLOW WILL ALLOW AREAS OF FOG OVERNIGHT WITH POOR VISIBILITY.

TUESDAY...
AREAS OF FOG WILL START THE MORNING...WITH VISIBILITY IMPROVING
DURING THE MORNING. SHOWERS AND THUNDERSTORMS WILL MOVE INTO
WESTERN NEW ENGLAND DURING THE AFTERNOON AND MAY THREATEN THE
COASTAL WATERS TOWARD EVENING. TSTMS COULD CAUSE STRONG WIND
GUSTS...OTHERWISE EXPECT WINDS AND SEAS TO REMAIN BELOW SMALL
CRAFT LEVELS.

OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY...

MODERATE CONFIDENCE THROUGH THE PERIOD.

EXPECT WINDS AND SEAS TO REMAIN BELOW SMALL CRAFT CRITERIA. MAY
SEE SW WIND GUSTS UP TO 20 KT TUE NIGHT ON THE SOUTHERN WATERS
BEFORE SHIFTING TO W AND DIMINISHING BY WED MORNING. WINDS BACK
AROUND TO SW AGAIN LATE THU NIGHT/FRI.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
NH...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR
     ANZ254>256.

&&

$$
SYNOPSIS...WTB/EVT
NEAR TERM...WTB/RLG
SHORT TERM...WTB
LONG TERM...EVT
AVIATION...RLG/EVT
MARINE...WTB/EVT



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