Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 051120
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
720 AM EDT SUN JUL 5 2015

.SYNOPSIS...
HIGH PRESSURE RETURNS TODAY...AND LINGERS THROUGH MONDAY. BECOMING
MORE HUMID TUESDAY AND WEDNESDAY. A SERIES OF FRONTS WILL BRING
A RISK FOR SHOWERS AND THUNDERSTORMS TUESDAY AND WEDNESDAY. A
FRONT WILL STALL SOUTH OF THE AREA ON THURSDAY AND FRIDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
7AM UPDATE...
LOOKING AROUND AT AREA OBS SUGGEST THAT FOG IS ALREADY BEGINNING
TO LIFT SO THE SPS CURRENTLY OUT FOR PATCHY DENSE FOG SHOULD BE
GOOD TO LET GO BY 1230Z. OTHERWISE...BOOSTED HIGHS A LITTLE BIT
TODAY BASED ON EXPECTED TRENDS AND PLENTY OF SUNSHINE WITH A
SLIGHT W COMPONENT TO THE FLOW. OTHER PARAMETERS ON TRACK.

PREVIOUS DISCUSSION...

HIGH PRESSURE FROM THE PLAINS BUILDS EAST OVER NEW ENGLAND. AS
NOTED BY PREVIOUS FORECASTER...MODEL CROSS SECTIONS OF RH SHOW
A VERY SHALLOW LAYER OF MOISTURE NEAR 800 MB. THIS SUGGESTS THE
POSSIBILITY OF SOME DIURNAL CUMULUS DEVELOPING. PLENTY OF SUNSHINE
TODAY WILL MEAN MUCH HIGHER TEMPERATURES THAN WHAT WE SAW ON
INDEPENDENCE DAY. WEAK PRESSURE GRADIENT WILL LEAD TO THE
DEVELOPMENT OF SEABREEZES...MAINLY THIS AFTERNOON.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
FAIR SKIES TONIGHT WITH LIGHT WINDS AND RADIATIONAL COOLING. DEW
POINTS RISE TO AROUND 60...SO TEMPERATURES SHOULD NOT BE AS LOW AS
THEY HAVE BEEN THE PAST FEW DAYS. THIS MAY ALSO SUPPORT PATCHES
OF FOG DEVELOPING LATE AT NIGHT...ESPECIALLY ACROSS WESTERN MA.

HIGH CONFIDENCE FOR DRY CONDITIONS MONDAY...AS DEEP HIGH PRESSURE
SHOULD BE IN PLACE NEAR SOUTHERN NEW ENGLAND. WARMER STILL...WITH
THE HIGHER STARTING POINT. DEW POINTS CONTINUE TO SLOWLY INCREASE
AS WELL. WEAK PRESSURE GRADIENT SHOULD LEAD TO MORE SEABREEZES.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
HIGHLIGHTS...

 * SHOWERS AND THUNDERSTORMS ON TUESDAY AND WEDNESDAY
 * UNSETTLED WEATHER MAY CONTINUE INTO LATE WEEK

OVERVIEW AND MODEL PREFERENCES...GRADUAL TRANSITION PERIOD IS
EXPECTED THROUGH THE LONG TERM...AS RIDGING ACROSS THE NE CONUS
GIVES WAY TO NEAR ZONAL FLOW THANKS TO PINWHEELING SHORTWAVES
AROUND A CENTRALIZED VORTEX IN N CENTRAL CANADA. ALTHOUGH SRN NEW
ENGLAND REMAINS ON THE SRN PERIPHERY OF THE MEAN JET WITHIN THIS
ZONAL FLOW /EVEN H5 HEIGHT ANOMALIES ARE NEAR TO ABOVE NORMAL/
THIS FLOW MAKES NAILING DOWN TIMING OF WEAK RIDGE/TROUGH COUPLETS
DIFFICULT FOR LATE IN THE WEEK. THIS DIFFICULTY IS EXACERBATED BY
A STALLED FRONTAL BOUNDARY NOT TOO FAR TO THE S...WHICH WILL
PROVIDE A NEAR SFC BAROCLINIC ZONE FOR THESE WAVES TO WORK UPON.
THEREFORE...EXACTLY HOW UNSETTLED THE LATE WEEK PERIOD WINDS UP
BEING REMAINS IN FLUX...BUT GIVEN FAIR AGREEMENT ON AT LEAST THE
SYNOPTIC SCALE BETWEEN OPERATIONAL/ENSEMBLE GUIDANCE A BLEND WILL
BE A GOOD STARTING POINT WITH THIS UPDATE.

DETAILS...

MON NIGHT INTO TUE...HIGH PRES WILL SHIFT OFFSHORE OF THE
REGION...ALLOWING FOR RETURN FLOW AND WARM ADVECTION IN INCREASE.
THIS WILL LEAD TO THE SLOW APPROACH OF A WEAKENING WARM FRONT
DURING THE DAY ON WED. BUFKIT DATA DOES SHOW SFC INSTABILITY IS
AVAILABLE...MAINLY IN THE FORM OF THIN-PROFILED 500-1000 J/KG OF
CAPE AND PWATS NEARLY 1.5 STD DEVIATIONS ABOVE NORMAL. SPEED-
SHEAR IS MINIMAL BUT STILL NOTE TYPICAL STRONG VEERING OF THE
PROFILE IN THE LOWEST LEVELS AHEAD OF THE FRONT. THEREFORE...
THUNDER WILL STILL BE INCLUDED IN THE FORECAST FOR TUE
AFTERNOON...BUT SEVERE POTENTIAL WILL BE MAINLY DEPENDENT ON
SHEAR...WHICH IS BETTER FURTHER N...BUT NON-ZERO HERE. TEMPS WILL
BE DICTATED BY CLOUD COVER...BUT WILL LIKELY SEE MID-UPPER 80S
WHERE ANY SUNNY BREAKS ARE OBSERVED.

WED...AFTER A BRIEF PERIOD WITHIN THE WARM SECTOR...A COLD FRONT
WILL BE SLOWLY CROSSING THE REGION BY DAY ON WED. HOW MUCH
INSTABILITY IS AVAILABLE WILL DEPEND UPON HOW DEEP IN THE WARM
SECTOR WE GET AND HOW MANY BREAKS OF SUN ARE ALLOWED BEFORE THE
FRONT ARRIVES /LOOKS LIKE AROUND MID DAY/. SFC DWPT/TEMPS PROMOTE
A BIT MORE POTENTIAL FOR CAPE VALUES TO EXCEED 1000 J/KG BUT ONCE
AGAIN SHEAR IS A LIMITING FACTOR. PWATS ARE HIGH...ABOUT 2.0
INCHES OR 2 STD DEVIATIONS ABOVE NORMAL. THEREFORE...AGREE WITH
PREVIOUS FORECASTERS ASSESSMENT OF HEAVY RAIN BEING THE MOST
LIKELY THREAT. WILL CONTINUE TO INCLUDE THIS IN THE HWO.

THU AND FRI...UNCERTAINTY PEAKS DURING THIS PERIOD PRIMARILY DUE
TO THE STALLING FRONTAL BOUNDARY OFF THE S COAST AS ZONAL STEERING
FLOW BEGINS TO PARALLEL. THIS ZONAL FLOW WILL ALSO FEATURE SEVERAL
WEAK SHORTWAVES LEAVING THE CONFINES OF A STRONG VORTEX TO THE NW.
THEREFORE...DEPENDING ON HOW CLOSE THIS WAVE STAYS...PERIODIC
SHOWERY WEATHER IS LIKELY FOR THE END OF THE WEEK. STUDIES ALSO
SUGGEST THIS IS A GOOD CONDUIT FOR UPSTREAM MCS DEVELOPMENT WHICH
WILL NEED TO BE MONITORED. NOT A TRUE RING-OF- FIRE HERE...BUT ANY
REMNANTS OF UPSTREAM CONVECTION WILL CERTAINLY NEED TO BE WATCHED.
IN ANY CASE...NOT A WASHOUT HERE AS THERE IS LIKELY TO BE SOME DRY
PERIODS AS WELL. TEMPS ARE LIKELY TO BE NEAR OR SLIGHTLY ABOVE
NORMAL...AS H85 TEMPS ARE IN THE +12C TO +14C RANGE AS AN ENSEMBLE
MEAN.

NEXT WEEKEND...THERE ARE A COUPLE OF DIFFERENT CAMPS TO FOLLOW.
WITH THE ROBUST VORTEX ELONGATED AND SHIFTING E...RIDGING IS
EXPECTED TO BUILD AHEAD....WHICH COULD PROVIDE ENOUGH OF A BLOCK
TO YIELD MAINLY DRY CONDITIONS. HOWEVER...THE APPROACH OF THIS
VORTEX COULD ALSO SIGNIFY CONTINUING THE UNSETTLED PATTERN WITH
COOLING UPPER LVL TEMPS AND INCREASED MOISTURE. FEEL THAT LOW END
POPS WILL COVER THE SPREAD FOR NOW...BUT WITH ENSEMBLES IN BOTH
CAMPS HAVE A HARD TIME GOING WITH ANY ONE SOLUTION AT THIS TIME.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT-TERM /THROUGH MONDAY/...

12Z UPDATE...NO SIGNIFICANT CHANGES.

HIGH CONFIDENCE VFR MOST OF THE TIME. WEAK PRESSURE GRADIENT WILL
LEAD TO SEA BREEZE DEVELOPMENT BOTH TODAY AND MONDAY. PATCHY IFR
IN FOG TONIGHT...MAINLY IN THE CT RIVER VALLEY OF MA.

KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SEA BREEZE STARTS A BIT
LATER TODAY ONCE WINDS ALOFT RECEDE.

KBDL TERMINAL...HIGH CONFIDENCE IN TAF THROUGH TODAY. LOWER
CONFIDENCE IN FOG DEVELOPMENT AGAIN LATE TONIGHT.

OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...

MON NIGHT THROUGH WED...MODERATE CONFIDENCE. A SERIES OF FRONTS
WILL MOVE ACROSS THE AREA TUE AND WED. THIS WILL LEAD TO SHOWERS
AND THUNDERSTORMS POSSIBLE BY DAY...AND FOG BY NIGHT. THEREFORE...
VFR BY DAY WITH PERIODIC MVFR/IFR IN SHOWERS/STORMS. WITH THE
POSSIBILITY MVFR/IFR IN FOG AT NIGHT.

THU...MODERATE CONFIDENCE. TRANSITIONING TO MORE WIDESPREAD VFR.
BUT SHOWERS WILL LINGER.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

HIGH CONFIDENCE THROUGH MONDAY. LATEST MODEL WAVE GUIDANCE IS TOO
HIGH COMPARED TO LATEST OBSERVATIONS. WOUND UP SUBTRACTING 1 FOOT
FROM THE FORECAST GUIDANCE. NO LONGER EXPECTING SEAS TO REACH 5 FT
THROUGH MONDAY. WITH WEAK WINDS ALREADY IN PLACE. CANCELED THE
SMALL CRAFT ADVISORY FOR THE SOUTHERN OUTER COASTAL WATERS.

OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...

MON NIGHT INTO WED...MODERATE CONFIDENCE. A SERIES OF FRONTS WILL
CROSS THE WATER...WITH THE THREAT FOR DAYTIME THUNDERSTORMS AND
NIGHTTIME FOG. S WINDS SHOULD REMAIN BELOW SCA THRESHOLDS...AS
SHOULD SEAS.

THU...MODERATE CONFIDENCE. A FRONT WILL STALL NEAR THE SOUTH
COAST. WHILE PERIODIC SHOWERS AND FOG ARE LIKELY...THERE MAY BE A
BUILDING SWELL REACHING NEAR SMALL CRAFT ADVISORY THRESHOLDS.
HOWEVER...THIS IS UNCERTAIN AT THIS TIME.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...BELK/DOODY
NEAR TERM...BELK/DOODY
SHORT TERM...BELK
LONG TERM...DOODY
AVIATION...BELK/DOODY
MARINE...BELK/DOODY



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