Special Weather Statement, NWS Boston/Norton, MA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
342 PM EDT WED JUL 13 2011

.SYNOPSIS...
A MID LEVEL DISTURBANCE AND SURFACE TROUGH WILL MOVE ACROSS THE
REGION THIS AFTERNOON AND EVENING...AND WILL LIKELY TRIGGER
SCATTERED THUNDERSTORMS. HIGH PRESSURE WILL BRING DRIER AND LESS
HUMID CONDITIONS FRIDAY AND SATURDAY. HUMIDITY AND TEMPERATURES
WILL GRADUALLY INCREASE SUNDAY. A COLD FRONT WILL AFFECT SOUTHERN
NEW ENGLAND MONDAY AND TUE.

&&

.NEAR TERM /UNTIL 10 PM THIS EVENING/...
345 PM UPDATE...STRONG SHORTWAVE MOVING ACROSS THE U.S./CANADA BORDER
PER WATER VAPOR IMAGERY. THIS WITH ACCOMPANYING COLD POOL ALOFT IS
PRODUCING SHOWERS AND THUNDERSTORMS ON THE BORDER AND SPREADING
ACROSS NEW ENGLAND. THESE STORMS ARE PROPAGATING SOUTHEASTWARD
MOVING INTO AN AREA OF DECENT SHEAR /40-50 KTS/ AND MODEST CAPE
/500-1000 J/KG/. WITH AVAILABLE INSTABILITY AND THE COLD POOL
ALOFT...THE STRONGEST OF THESE STORMS WILL BE CAPABLE OF PRODUCING
SMALL HAIL AND GUSTY WINDS. THE BEST INSTABILITY OVER SOUTHERN NEW
ENGLAND IS STILL FORECAST TO BE LATE THIS AFTERNOON AND EVENING.

AT LEAST SCATTERED CUMULUS CLOUD COVER ACROSS THE REGION...SOME
AREAS ALSO HAVE A CEILING OF MID AND HIGH LEVEL CLOUDS. THE
THICKER CLOUD COVER HAS LIMITED TEMPERATURES SOMEWHAT ACROSS
NORTHWEST MASS AND SOUTHWEST NH AS WELL AS THE CAPE AND ISLANDS.
TEMPS IN THESE AREAS ARE IN THE UPPER 70S TO LOW 80S WHILE
ELSEWHERE ACROSS THE REGION...TEMPERATURES ARE REACHING INTO THE
MID TO UPPER 80S. THE SEABREEZE ALONG THE EAST COAST HAS FINALLY
DEVELOPED...KEEPING NEAR SHORE AREAS A FEW DEGREES COOLER THAN
NEARBY INLAND LOCATIONS.

&&

.SHORT TERM /10 PM THIS EVENING THROUGH THURSDAY NIGHT/...
OVERNIGHT...SCATTERED SHOWERS AND THUNDERSTORMS SHOULD HAVE DISSIPATED
OR MOVED OFFSHORE BY MIDNIGHT. A FEW WEAKENING SHOWERS/STORMS MAY
LINGER ALONG THE EAST COAST AND CAPE WITH THE SURFACE TROUGH.
THESE SHOULD MOVE OFFSHORE OR DIMINISH COMPLETELY BY SUNRISE.
BEHIND THIS TROUGH...COOLER AND NOTICEABLY LESS HUMID AIR WILL
OVERSPREAD THE REGION. EXPECT CLEARING SKIES OVERNIGHT...WITH TEMPS
FALLING TO THE MID AND UPPER 50S ACROSS THE FAR INTERIOR...UPPER
50S TO MID 60S ELSEWHERE.

THURSDAY...HIGH PRESSURE BUILDS INTO THE REGION FROM THE GREAT
LAKES. DEWPOINTS FALL INTO THE UPPER 40S TO LOW 50S...RESULTING
IN FAR MORE COMFORTABLE CONDITIONS. BOUNTIFUL SUNSHINE AND TEMPERATURES
AROUND 80 DEGREES MAKE FOR A WONDERFUL DAY TO BE OUTDOORS. NOT
SURE IF THE GRADIENT WILL WEAKEN ENOUGH FOR SEA BREEZES TO
FORM...BUT THEY DO REMAIN A POSSIBILITY. LOW DEWPOINTS REMAIN IN
THE AREA THROUGH THE NIGHT...AND COUPLED WITH GOOD RADIATIONAL
COOLING CONDITIONS WILL RESULT IN LOW TEMPERATURES DROPPING DOWN
TO AROUND 50 IN THE FAR INTERIOR AND IN THE MID TO UPPER 50S
ACROSS THE REST OF THE REGION.

THERE IS A MODERATE RISK OF RIP CURRENTS ON THE EAST FACING
SHORELINES THURSDAY. SEE THE SURF ZONE FORECAST /SRFBOX/ FOR MORE
DETAILS.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
HIGHLIGHTS...
 * HIGH PRESSURE DOMINATES THROUGH SUN
 * A COLD FRONT WILL AFFECT THE REGION MON AND TUE

OVERALL...
MODELS CONTINUE TO SHOW GOOD AGREEMENT ON THE SYNOPTIC PATTERN
THROUGH NEXT WEEK. STRONG UPPER LVL SUBTROPICAL RIDGE CONTINUES TO
BUILD TOWARD THE N AND E FROM THE CENTRAL PLAINS. THIS ALLOWS FLOW
TO WEAKEN ALOFT...PUSHING PRIMARY TIME MEAN JET TO THE N.
SUBSIDENCE AND DRY AIR AT ALL LVLS LOOK TO DOMINATE THE COLUMN
RIGHT THROUGH EARLY NEXT WEEK. THE NEXT MAJOR PATTERN SHIFT LOOKS
TO BEGIN SUN NIGHT INTO MON...AS MODELS CONTINUE TO FAVOR ROBUST
NRN QC CUTOFF BEGINS TO DIVE TOWARD THE SE PUSHING THE PRIMARY JET
TO THE S AND IN CLOSER PROXIMITY TO SNE. WHILE THERE IS AN
AGREEMENT THAT THE SFC REFLECTION OF THIS FEATURE IS A SLOW MOVING
SFC LOW WELL TO THE N...ITS ATTENDANT COLD FRONT WILL LIKELY
EFFECT THE REGION SOMETIME DURING THE SUN NIGHT TO MON TIME FRAME.
THIS IS WHERE MODELS DIVERGE IN SOLNS A BIT...ECMWF IS CURRENTLY A
BIT FASTER WHILE OPNL GFS AND GEFS MEAN ARE A BIT SLOWER. THIS
DIFFERENCE IS MOST LIKELY DUE TO THE FACT THAT ECMWF IS PUSHES THE
NWLY FLOW ALOFT FURTHER S...KEEPING KEEPING THE FLOW PERPENDICULAR
TO THE FRONT. WITH STRONG SUBTROPICAL RIDGING STILL ENTRENCHED TO
THE SW...THINK THE SLOWER SOLN IS FAVORED...WITH BEST JET DYNAMICS
REMAINING N. FROM THERE THROUGH MID NEXT WEEK...MODELS GENERALLY
AGREE ON THE OVERALL PATTERN...SUGGESTING A STALLING FRONT
SOMEWHERE IN THE VICINITY OF SNE WITH A SECOND COOL AND DRY HIGH
PRES BUILDING OVER THE REGION FROM ON AND QC. THERE IS A FAIR
AMOUNT OF UNSTABLE AIR ROTATING AROUND THE SUBTROPICAL RIDGE...AND
AS SUCH...MODELS ARE TRYING TO BRING A WEAKENING MCS THROUGH THE
AREA SOMETIME DURING MID WEEK AFTER THE FRONT PUSHES JUST TO THE
S. NO STRONG CONFIDENCE IN ANY OF THESE FEATURES ATTM...BUT IT
WILL HAVE TO BE MONITORED AS THE TIME APPROACHES.

FRI THRU SUN...
HIGH PRES BUILDS OVER SNE THROUGH THE PERIOD. COLUMN LOOKS DRY
FRI AND SAT WITH DWPTS IN THE 50S EXPECTED FOR BOTH DAYS. MIXING
TO H85 OR EVEN H8 IS LIKELY DURING BOTH OF THESE DAYS...SO
EXPECTING THE H85 TEMPS OF 13 TO 15C TO BE FULLY REALIZED.
SUGGESTING HIGHS REACHING WELL INTO THE 80S. THE LOW DWPTS AND
MOSTLY CLEAR SKIES WITH A DRY COLUMN SUGGEST OVERNIGHT MINS DIP
INTO THE MID 50S IN COOLER SPOTS.

SUN RETURN FLOW BEGINS WITH INCREASING LLVL MOISTURE AND WAA AS
THE HIGH PUSHES TO THE E. WHILE DWPTS AND MID LVL TEMPS
INCREASE...SUGGESTING WARMER TEMPS...THE OTHER ISSUE THAT MAY COME
INTO PLAY FOR SUN HIGHS WILL BE THE POTENTIAL FOR INCREASING CLOUD
COVER IN ADVANCE OF STRONG SHORTWAVE TO THE N. GIVEN THIS...NOT
EXPECTING MIXING TO REACH AS HIGH OF A LVL AS PREVIOUS DAYS. H85
TEMPS OF 16 TO 18C...COULD STILL PROMOTE UPPER 80S TO LOWER 90S IN
THE CT VALLEY WHERE DOWNSLOPE MAY CONTRIBUTE.

SUN NIGHT THRU TUE...
AS MENTIONED EARLIER STRONG LOW PRES WELL TO THE N WILL DRAG ITS
ATTENDANT COLD FRONT THROUGH THE AREA DURING SUN NIGHT THRU MON
PERIOD. WHILE THE ECMWF REMAINS THE FASTER SOLN...THE GFS/GEFS
SOLN IS MORE FAVORABLE GIVEN THE SUGGESTED UPPER LVL PATTERN. THIS
KEEPS SUN NIGHT HUMID WITH INCREASING CLOUD COVER BUT DRY IN TERMS
OF PRECIP. DURING THE DAY MON...THE FRONT WILL APPROACH THE NW
CORNER OF MA. WITH MID LVL LAPSE RATES INCREASING TO AROUND
6.5C/KM AND THE COLUMN SUPPORTING CAPES OF 1000 TO 1500 J/KG...THE
FRONT/PRE FRONTAL TROF WILL LIKELY BE A FOCAL POINT FOR
CONVECTION. THE BEST SHEAR/JET DYNAMICS REMAIN TO THE N...BUT WITH
DECREASING STABILITY AND FAIRLY ROBUST LIFT TSTMS WILL BE A THREAT
DURING THE DAY MON. MODELS THEN DISAGREE WITH THE PASSAGE OF THE
FRONT...PUSHING IT S OF SNE. CURRENTLY...THE MOST LIKELY SCENARIO
KEEPS THE FRONT JUST S OF SNE THROUGH CENTRAL NJ. THIS MAY KEEP
THE THREAT FOR CONTINUED ACTIVITY INTO TUE. THE PRIMARY CHANGE TO
THIS WILL BE THE NATURE OF THE DRY AIR BUILDING IN WITH HIGH PRES
BEHIND THE FRONT. FOR NOW...WILL CONTINUE THE THREAT OF AT LEAST
SOME DIURNALLY DRIVEN -SHRA/TSTM ACTIVITY TUE AND INTO MID WEEK.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
FORECASTER CONFIDENCE LEVELS...
  LOW...LESS THAN 30 PERCENT
  MODERATE...30 PERCENT TO 60 PERCENT
  HIGH...GREATER THAN 60 PERCENT

THIS AFTERNOON...HIGH CONFIDENCE FOR VFR ALL TERMINALS. HOWEVER
SCATTERED SHOWERS AND THUNDERSTORMS AND CIGS BKN050 MOVE INTO THE
REGION BECOMING MORE WIDESPREAD AFTER 20Z. LOW PROB OF A FEW
STRONG STORMS CONTAINING GUSTY WINDS AND SMALL HAIL. BRIEF MVFR IN
STORMS.

TONIGHT...LOW TO MEDIUM CONFIDENCE IN TIMING OF STORMS...OTHERWISE
HIGH CONFIDENCE IN CONDITIONS.  MOST STORMS IN THE REGION WILL
DISSIPATE OR MOVE OFFSHORE BY 03Z. ANY LINGERING MVFR CONDITIONS
WILL QUICKLY IMPROVE TO VFR.

THURSDAY...HIGH CONFIDENCE VFR. SEA BREEZES ARE POSSIBLE ALONG THE
EAST AND SOUTH COASTS.

KBOS TERMINAL...
HIGH CONFIDENCE FOR VFR. ISOLATED SHOWERS AND THUNDERSTORMS ARE
POSSIBLE MAINLY 13/20Z-14/03Z. ANY SHOWERS/STORMS IMPACTING BOS
WILL LOWER CONDITIONS TO MVFR BRIEFLY.  LOW PROB OF A STRONG TSTM
DURING LATE AFTERNOON WITH GUSTY WINDS AND SMALL HAIL. AFTER
03Z...HIGH CONFIDENCE IN VFR/TAF.

OUTLOOK...FRIDAY THROUGH MONDAY...

HIGH CONFIDENCE VFR THROUGH AT LEAST SUN AS HIGH PRESSURE BUILDS
OVER THE REGION. SEA BREEZES POSSIBLE BEGINNING LATE MORNING AT
COASTAL TERMINALS. LOW TO MEDIUM CONFIDENCE LOCALIZED MVFR IN
-SHRA/TSTMS AS A COLD FRONT APPROACHES LATE SUN NIGHT INTO MON.
LOW TO MEDIUM CONFIDENCE OF FOG AND STRATUS REDUCING CIGS AND
VSBYS OVER CAPE AND ISLAND TERMINALS BEGINNING SUN WITH S TO SW
FLOW.

&&

.MARINE...

TONIGHT...ANY EVENING TSTMS WILL BE SHORT LIVED. PATCHY FOG POSSIBLE
LATE. N WINDS INCREASE AFTER MIDNIGHT WITH OCCASIONAL GUSTS TO 20
KTS POSSIBLE.

THURSDAY...A TIGHTENING PRESSURE GRADIENT BETWEEN OFFSHORE LOW AND
HIGH PRESSURE MOVING EAST FROM THE GREAT LAKES MAY RESULT IN WIND
GUSTS TO 20-25 KT FOR A PERIOD OF TIME...WITH SEAS BUILDING UP TO
5 TO 6 FT ALONG SOME OF THE OUTER COASTAL WATERS. LOW CONFIDENCE
AT THIS TIME...BUT SMALL CRAFT ADVISORY MAY BE NECESSARY.

OUTLOOK...FRIDAY THROUGH MONDAY...

WINDS AND SEAS GENERALLY BELOW SCA THRESHOLDS AS HIGH PRES BUILDS
OVER THE REGION. THERE IS A LOW PROBABILITY OF A FEW GUSTS OVER 25
KT AND SEAS OVER 5 FT ACROSS OUTER PORTIONS OF THE SRN WATERS MON.

&&

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

&&

SYNOPSIS...DOODY/RLG
NEAR TERM...RLG
SHORT TERM...RLG
LONG TERM...DOODY
AVIATION...DOODY/RLG
MARINE...DOODY/RLG

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