Special Weather Statement, NWS Boston/Norton, MA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
436 PM EDT FRI JUL 24 2015

.SYNOPSIS...
UNSETTLED WEATHER EXPECTED THROUGH EARLY NEXT WEEK...WITH MAINLY
DIURNAL SHOWERS AND THUNDERSTORMS. STRONG TO SEVERE THUNDERSTORMS
REMAIN POSSIBLE THIS EVENING...AND WILL BE POSSIBLE AGAIN SOMETIME
SUNDAY INTO MONDAY. THE NEXT MAIN WEATHER HEADLINE WILL BE A
POSSIBLE HEAT WAVE TUESDAY THROUGH THURSDAY.

&&

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

HIGHLIGHTS...

 * STRONG TO PERHAPS A FEW SEVERE STORMS INTO EARLY EVENING
 * POTENTIAL IMPACTS: HAIL/STRONG WINDS AND FREQUENT LIGHTNING

DISCUSSION...

4 PM UPDATE...

PER LATEST WATER VAPOR IMAGERY A CLOSED MID LEVEL LOW IS LOCATED
OVER THE MARITIMES AND IS ACCOMPANIED BY A POTENT SHORT WAVE TROUGH
ENTERING NORTHERN MA AT 330 PM. ATTENDING AIRMASS WITH THUS FEATURE
IS ANOMALOUSLY COLD WITH CORE OF COLD AIR AT H5 AT -17C! THIS IS
ABOUT 2.5 STD DEVIATIONS BELOW CLIMO. THIS IS YIELDING MID LEVEL
LAPSE RATES OF UP TO 6.5 C/KM /MOIST ADIABATIC/. THIS ANOMALOUS COLD
TEMPS ALOFT ARE COMBINING WITH SURFACE TEMPS 75 TO 80 YIELDING
SBCAPES UP TO 1000 J/KG. THIS INSTABILITY IS PROVIDING SUFFICIENT
BUOYANCY FOR ROBUST UPDRAFTS COUPLED WITH STRONG FORCING FOR
ASCENT FROM HIGH AMPLITUDE SHORT WAVE TROUGH.

STRONGEST STORMS AT 330 PM ARE ALIGNED ALONG THE SOUTHERN PERIPHERY
OF THE -17C CONTOUR FROM JUST NORTH OF ALBANY NY EASTWARD TO ALONG
THE MA/VT/NH BORDER. GOOD MODEL AGREEMENT THAT THE CORE OF COLD AIR
ALOFT WILL TRACK ACROSS NORTHERN MA AND THEN INTO RI AND EASTERN MA
LATE THIS AFTERNOON AND EARLY EVENING. THUS THIS IS THE AREA OF
GREATEST RISK FOR STRONG STORMS. HI RES MODELS /NMM-ARW-NAM/ CONCUR
AND ARE LINING UP WELL WITH LATEST RADAR TRENDS.

THUNDERSTORM IMPACTS REMAIN UNCHANGED...GUSTY WINDS AND SMALL HAIL
WITH A LOW PROBABILITY OF A FEW STORMS REACHING SEVERE CRITERIA. IN
ADDITION...GIVEN MAGNITUDE OF COLD AIR ALOFT THE HEAVIER SHOWERS/T-
STORMS WILL BE ACCOMPANIED BY A RAPID BUT BRIEF TEMP DROP.
CONVECTION WILL PEAK NOW THRU ABOUT 5PM/6PM AND THEN BEGIN TO WEAKEN
AND MOVE OFFSHORE 21Z TO 02Z FROM NW TO SE.

OVERNIGHT...

COOL AIRMASS OVERSPREADS THE REGION IN THE WAKE OF THE MID LEVEL
SHORT WAVE TROUGH. AT THE SURFACE THIS WILL BE REFLECTED BY A
BACKDOOR COLD FRONT YIELDING LIGHT N-NE WINDS. COOL NIGHT WITH
WIDESPREAD 50S EXCEPT LOW TO MID 60S IN THE URBAN AREAS.

&&

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

SATURDAY...

MID LEVEL MEAN TROUGH OVER GEORGES BANK MOVES SEAWARD ALLOWING
HEIGHT RISES TO DEVELOP OVER NEW ENGLAND ALONG WITH FLOW BECOMING
LESS CYCLONIC AND MORE ZONAL. TYPICALLY THIS SUBSIDENCE WOULD YIELD
A DRY FORECAST. HOWEVER LEFTOVER BACKDOOR FRONT ACROSS THE REGION
MAY ACT AS A FOCUS FOR SCATTERED LOW TOP AFTERNOON SHOWERS. MOST OF
THE HI RES GUIDANCE HAS SHOWERS DEVELOPING IN THE AFTERNOON IN THE
CT RIVER VALLEY AND THEN MOVING EASTWARD INTO RI AND CENTRAL MA
LATER IN THE DAY. THIS SEEMS REASONABLE BUT WILL BE A BATTLE
BETWEEN MID LEVEL SUBSIDENCE AND LOW LEVEL CONVERGENCE. NOT
EXPECTING A WASHOUT OUT JUST A LOW RISK FOR A FEW SHOWERS.

MARITIME AIRMASS FROM BACKDOOR FRONT WILL RESULT IN A LARGE TEMP
GRADIENT ACROSS THE AREA WITH HIGHS ONLY IN THE U60S TO L70S ACROSS
EASTERN MA TO L80S IN THE CT RIVER VALLEY. MORNING SUNSHINE WILL
MIX WITH AFTERNOON CLOUDS.

SATURDAY NIGHT...

BACKDOOR FRONT LIFTS NORTH AS A WARM FRONT AND WARM ADVECTION
PATTERN BEGINS TO UNFOLD YIELDING AN INCREASED RISK FOR SHOWERS AND
T-STORMS ESPECIALLY SECOND HALF OF THE NIGHT. WARMER AND MORE HUMID
THAN PREVIOUS NIGHTS.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
HIGHLIGHTS...

* SCATTERED STRONG THUNDERSTORMS POSSIBLE SUNDAY
* HEAT WAVE POSSIBLE TUESDAY THROUGH THURSDAY
* SCATTERED STORMS POSSIBLE LATE THURSDAY

SUNDAY...STILL LOOKS LIKE IT COULD BE AN ACTIVE WEATHER DAY. 0-1
KM HELICITY VALUES REMAIN RATHER ROBUST...ALTHOUGH INSTABILITY
APPEARS TO BE LAGGING A FEW HOURS BEHIND. WITH MORNING SUNSHINE
BREAKING OUT BEHIND THE DEPARTING UPPER DISTURBANCE...RAPID
DESTABILIZATION IS EXPECTED DURING THE LATE MORNING HOURS WITH
THE GFS CONTINUING TO INDICATE SURFACE-BASED CAPES APPROACHING 3000
J/KG ACROSS MOST OF THE REGION DURING THE AFTERNOON. A WARM FRONT
WILL HAVE MOVED NORTHWARD INTO NORTH CENTRAL AND NORTHEASTERN MA
BY THE AFTERNOON.

WE ARE STILL VERY FAR AWAY AT THIS POINT...AND DO NOT WANT TO GET
TOO CARRIED AWAY. THAT SAID...WE WILL NEED TO MONITOR THE
POTENTIAL FOR MORNING CONVECTION INITIATION. EVEN IF THE WIND
SHEAR AND INSTABILITY DO NOT PHASE IN TIME AND SPACE...THERE COULD
BE ENOUGH INSTABILITY TO PRODUCE STRONG TO SEVERE THUNDERSTORMS
SUNDAY AFTERNOON. THE MAIN RISK WOULD BE ACROSS INTERIOR SOUTHERN
NEW ENGLAND.

SUNDAY NIGHT AND MONDAY...
A COLD FRONT STALLS ACROSS THE AREA. THIS IS SOMEWHAT TRICKY. THE
MAJORITY OF THE LATEST GUIDANCE DEPICTS THIS FRONT BEING SQUEEZED
BETWEEN TWO HIGH PRESSURES. AGAIN A LOT OF UNCERTAINTY AS THERE
IS A GOOD AMOUNT OF CAPE AROUND...YET THERE IS HARDLY ANY SHEAR
AS GUIDANCE SHOWS 10-20 KTS. HAVE COMPROMISED WITH SLIGHT CHANCE
POPS FOR SHOWERS OR TSTMS. HIGH TEMPERATURES FORECAST TO BE A FEW
DEGREES WARMER THAN SUNDAY...MAINLY 80 TO 85.

TUESDAY THROUGH THURSDAY...
THE COLD FRONT FINALLY GETS WASHED OUT SOMEWHERE OVER SOUTHERNMOST
NEW ENGLAND BY TUESDAY. CANNOT RULE OUT AN ISOLATED SHOWER
TUESDAY. OTHERWISE...AN UPPER LEVEL HIGH PRESSURE WILL SPREAD
FROM THE MIDWEST TOWARD NEW ENGLAND. THIS WILL TRANSLATE TO MAINLY
SUNNY CONDITIONS AND MUCH HOTTER WEATHER. IN FACT...925 MB
TEMPERATURES REACH +28C WED AND THU AFTERNOONS. WE ARE FORECASTING
NEAR 90 FOR HIGHS ON TUE AND LOWER TO MID 90S WEDNESDAY AND
THURSDAY FOR MUCH OF THE INTERIOR...COOLER AT THE COAST. IT WOULD
BE A HEAT WAVE IF WE COULD HIT 90 DEGREES FOR THREE CONSECUTIVE
DAYS.

THURSDAY EVENING INTO FRIDAY...MODELS ARE TRENDING TOWARD HAVING
A COLD FRONT MOVE THROUGH THURSDAY NIGHT INTO FRIDAY. THERE
SHOULD BE SOLID CAPPING DURING THE DAY ON THURSDAY WITH 700 MB
TEMPERATURES FORECAST TO APPROACH +10C. THIS CAP COULD ERODE
THURSDAY NIGHT INTO FRIDAY. THERE IS A CHANCE OF THUNDERSTORMS AS
THIS COLD FRONT APPROACHES.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT-TERM /THROUGH SATURDAY NIGHT/...HIGH CONFIDENCE.

THRU 00Z...

SHOWERS WITH EMBEDDED THUNDER WILL BE MOST NUMEROUS OVER NORTHERN
AND EASTERN MA INTO RI. SMALL HAIL AND GUSTY WINDS ARE THE MAIN
CONCERNS. MOST STORMS WILL BE ACCOMPANIED BY VFR WITH LOW PROB OF
MVFR. ACTIVITY WILL BE LESS NUMEROUS ACROSS CT.

AFTER 00Z..

ANY LINGERING SHOWERS/T-STORMS DISSIPATE BY 01Z/02Z. DRY WEATHER
AND VFR PREVAIL.

SATURDAY...

VFR WITH SCATTERED SHOWERS POSSIBLE ALONG A BACKDOOR FRONT ACROSS
THE INTERIOR.

SAT NIGHT...

VFR TO START BUT LOWERING TO MVFR AND LOW RISK OF IFR BY SUNDAY
MORNING IN SCATTERED SHOWERS AND FOG.

KBOS TERMINAL...ONSHORE WINDS PERSIST THRU SAT NIGHT. HIGH
CONFIDENCE ON SCT SHRA/-TSRA BUT LOWER CONFIDENCE ON SMALL AND
GUSTY WINDS. STORMS PEAK AROUND 21Z THEN DISSIPATE BY 00Z-02Z.
SCATTERED SHOWERS POSSIBLE SAT AFTN BUT THUNDER UNLIKELY.

KBDL TERMINAL...HIGH CONFIDENCE IN TAF. SHRA/TSRA SHOULD MAINLY
STAY N/E OF THE TERMINAL...BUT VCSH/VCTS IS POSSIBLE.

OUTLOOK...SUNDAY THROUGH WEDNESDAY...

SUNDAY INTO MONDAY...MODERATE CONFIDENCE. MVFR IN SCATTERED
SHOWERS AND THUNDERSTORMS. A FEW STRONG STORMS POSSIBLE LATE
SUNDAY MORNING THROUGH SUNDAY EVENING WITH LOCAL IFR VSBYS.

TUESDAY...MODERATE CONFIDENCE. VFR. POSSIBLE MVFR IN ISOLATED
SHOWERS OVER THE INTERIOR.

WEDNESDAY...HIGH CONFIDENCE VFR.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH SATURDAY NIGHT/...HIGH CONFIDENCE.

TONIGHT...EVENING SHOWERS AND T-STORMS...MOST NUMEROUS NEAR SHORE
WITH SMALL HAIL AND GUSTY WINDS POSSIBLE. IMPROVING CONDITIONS LATER
THIS EVENING. BACKDOOR COLD FRONT MOVES ONSHORE WITH LIGHT NORTH TO
NORTHEAST WINDS.

SATURDAY...LIGHT EAST TO SOUTHEAST WINDS. GOOD VSBY AND MAINLY DRY
WEATHER.

SAT NIGHT...SOUTHEAST WINDS WITH LOWERING VSBY IN FOG AND
SHOWERS...POSSIBLE T-STORM.

OUTLOOK...SUNDAY THROUGH WEDNESDAY...

HIGH CONFIDENCE. WINDS AND SEAS BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH THIS PERIOD AS WEAK PRESSURE GRADIENT PERSISTS ACROSS
WATERS.

WARM FRONT LIFTS N ACROSS THE WATERS EARLY SUNDAY. A SLOW-MOVING
COLD FRONT APPROACHES THE WATERS MONDAY INTO TUESDAY...BUT MAY
DISSIPATE BY TUESDAY.

A FEW STRONG THUNDERSTORMS ARE POSSIBLE OVER THE WATERS SUNDAY
INTO SUNDAY EVENING.

&&

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

&&

SYNOPSIS...BELK/NOCERA
NEAR TERM...NOCERA
SHORT TERM...NOCERA
LONG TERM...BELK
AVIATION...BELK/NOCERA
MARINE...BELK/NOCERA

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TAUNTON MA
449 AM EDT FRI JUL 24 2015

CTZ002>004-MAZ002>024-026-RIZ001>008-250900-
HARTFORD CT-TOLLAND CT-WINDHAM CT-WESTERN FRANKLIN MA-
EASTERN FRANKLIN MA-NORTHERN WORCESTER MA-CENTRAL MIDDLESEX MA-
WESTERN ESSEX MA-EASTERN ESSEX MA-WESTERN HAMPSHIRE MA-
WESTERN HAMPDEN MA-EASTERN HAMPSHIRE MA-EASTERN HAMPDEN MA-
SOUTHERN WORCESTER MA-WESTERN NORFOLK MA-SOUTHEAST MIDDLESEX MA-
SUFFOLK MA-EASTERN NORFOLK MA-NORTHERN BRISTOL MA-
WESTERN PLYMOUTH MA-EASTERN PLYMOUTH MA-SOUTHERN BRISTOL MA-
SOUTHERN PLYMOUTH MA-BARNSTABLE MA-DUKES MA-NANTUCKET MA-
NORTHERN MIDDLESEX MA-NORTHWEST PROVIDENCE RI-
SOUTHEAST PROVIDENCE RI-WESTERN KENT RI-EASTERN KENT RI-BRISTOL RI-
WASHINGTON RI-NEWPORT RI-BLOCK ISLAND RI-
449 AM EDT FRI JUL 24 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHERN CONNECTICUT...ALL OF
MASSACHUSETTS EXCEPT BERKSHIRE COUNTY...AND RHODE ISLAND.

.DAY ONE...TODAY AND TONIGHT.

A FEW STRONG THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND EVENING
IN NORTHERN AND EASTERN MASSACHUSETTS. THEY MAY PRODUCE SMALL HAIL
AND GUSTY WINDS. AN ISOLATED SEVERE STORM PRODUCING LARGE HAIL
CANNOT BE RULED OUT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

SCATTERED STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE FROM LATE
SUNDAY MORNING INTO SUNDAY EVENING.

HEAT INDICES COULD APPROACH HEAT ADVISORY CRITERIA AT SOME
INTERIOR LOCATIONS WEDNESDAY AND THURSDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD BE ON THE LOOKOUT FOR HAIL THIS AFTERNOON AND
EVENING IN NORTHERN AND EASTERN MASSACHUSETTS AND BE PREPARED TO
RELAY REPORTS TO THE NATIONAL WEATHER SERVICE.

ANZ230>237-250-251-254>256-250900-
BOSTON HARBOR-CAPE COD BAY-NANTUCKET SOUND-VINEYARD SOUND-
BUZZARDS BAY-RHODE ISLAND SOUND-NARRAGANSETT BAY-BLOCK ISLAND SOUND-
COASTAL WATERS EAST OF IPSWICH BAY AND THE STELLWAGEN BANK NATIONAL
MARINE SANCTUARY-MASSACHUSETTS BAY AND IPSWICH BAY-
COASTAL WATERS FROM PROVINCETOWN MA TO CHATHAM MA TO NANTUCKET MA
OUT 20 NM-
COASTAL WATERS EXTENDING OUT TO 25 NM SOUTH OF MARTHAS VINEYARD AND
NANTUCKET-
COASTAL WATERS FROM MONTAUK NY TO MARTHAS VINEYARD EXTENDING OUT TO
20 NM SOUTH OF BLOCK ISLAND-
449 AM EDT FRI JUL 24 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MASSACHUSETTS AND RHODE
ISLAND COASTAL WATERS.

.DAY ONE...TODAY AND TONIGHT.

A FEW STRONG THUNDERSTORMS ARE POSSIBLE CLOSE TO THE COAST THIS
AFTERNOON AND EVENING.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

FOR THE LATEST UPDATES...PLEASE VISIT OUR WEBPAGE AT
WWW.WEATHER.GOV/BOSTON

YOU CAN FOLLOW US ON FACEBOOK AT
WWW.FACEBOOK.COM/NWSBOSTON

YOU CAN FOLLOW US ON TWITTER AT
@NWSBOSTON

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