Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 281438
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
1037 AM EDT TUE JUL 28 2015

.SYNOPSIS...
A TROUGH OF LOW PRESSURE ALOFT WILL BRING A RISK OF SCATTERED
SHOWERS AND THUNDERSTORMS TO EASTERN MASSACHUSETTS AND POSSIBLY
RHODE ISLAND TODAY. HOT AND HUMID CONDITIONS EXPECTED THROUGH
THURSDAY. A COLD FRONT MAY BRING SCATTERED THUNDERSTORMS LATE
THURSDAY AND THURSDAY NIGHT. WARM BUT DRIER AND LESS HUMID WEATHER
IS EXPECTED FRIDAY INTO NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...

1030 AM UPDATE...

***A FEW STRONG TO SEVERE THUNDERSTORMS POSSIBLE AFTER 1 OR 2 PM
  MAINLY ACROSS EASTERN MA AND RHODE ISLAND***

OVERALL...A RATHER COMPLEX AND UNCERTAIN SETUP ON CONVECTIVE
POTENTIAL THIS AFTERNOON INTO EARLY THIS EVENING.  LOW CLOUDS HAVE
BURNED OFF ACROSS MOST OF THE REGION BY LATE MORNING...EXCEPT FOR
AREAS NEAR THE SOUTH COAST.  EVEN IN THESE LOCATIONS...SHOULD SEE
SKIES BECOME PARTLY TO MOSTLY SUNNY IN THE NEXT HOUR OR SO.

STRONG EARLY MORNING SHORTWAVE THAT CROSSED NORTHERN NEW ENGLAND WAS
MOVING AWAY FROM THE REGION.  IN ITS WAKE...THERE WAS SOME
SUBSIDENCE WHICH WILL AT LEAST ALLOW FOR A FAIR AMOUNT OF SUNSHINE
FOR THE NEXT FEW HOURS.  HIGH TEMPS WILL TOP OUT IN THE UPPER 80S TO
NEAR 90 AND IT WILL BE HUMID WITH DEWPOINTS GENERALLY IN THE 60S.

THE MAIN UNCERTAINTY CONTINUES TO REVOLVE AROUND CONVECTIVE
POTENTIAL FROM MID AFTERNOON INTO EARLY THIS EVENING.  WILL GO OVER
BOTH THE FAVORABLE AND UNFAVORABLE INGREDIENTS FOR CONVECTION.

1) FAVORABLE:

THE DEPARTING FIRST SHORTWAVE ACTUALLY HAS DELIVERED 500 MB TEMPS OF
-12C TO EASTERN MA LATE THIS MORNING...WHICH IS QUITE COLD ALOFT
CONSIDERING OUR AIRMASS AT THE SURFACE.  THEREFORE...WE SHOULD HAVE
NO PROBLEM ATTAINING 2000 TO 3000 J/KG OF CAPE ACROSS EASTERN NEW
ENGLAND THIS AFTERNOON.  QUITE HIGH FOR OUR NECK OF THE WOODS.  AT
THE SAME TIME...ANOTHER SHORTWAVE WILL BE DROPPING DOWN ALONG THE
EASTERN MA COAST.  IN ADDITION...0 TO 6 KM SHEAR VALUES WILL BE
INCREASING ON THE ORDER OF 35 TO 45 KNOTS DURING THE AFTERNOON.

2)UNFAVORABLE:

THE FIRST SHORTWAVE CREATED SUBSIDENCE AND WHILE IT WILL HELP TO
ALLOW HIGH CAPE TO DEVELOP...DRY MID LEVEL AIR MAY ATTEMPT TO
CUTOFF ANY UPDRAFTS.  THIS IS PROBABLY ONE OF THE MAIN REASONS THAT
SEVERAL MODELS ARE NOT SHOWING MUCH QPF.  ALTHOUGH 0 TO 6 KM SHEAR
IS QUITE IMPRESSIVE...LOW LEVEL WIND FIELDS ARE QUITE WEAK WHICH
WILL BE ANOTHER LIMITING FACTOR.  FINALLY...500 MB TEMPS ALONG THE
EASTERN MA COAST WARM FROM -12C AROUND 18Z TO -9C BY 00Z.

SO OVERALL...THERE ARE QUITE A BIT OF MIXED SIGNALS FROM MID
AFTERNOON AND EVENING.  WE DO THINK THAT THERE SHOULD AT LEAST BE
ISOLATED TO SCATTERED THUNDERSTORMS DEVELOPING ACROSS EASTERN MA/RI
WITH HELP FROM SOME CONVERGENCE ON THE SEA BREEZE FRONT.  MANY HIGH
RESOLUTION MODELS IN FACT SHOW THAT.  HIT AND MISS ACTIVITY MAY
EXTEND INTO CENTRAL MA WITH THE HELP OF THE TERRAIN.  IN FACT...MAY
EVEN SEE AN ISOLATED STORM OR TWO IN OUR FAR WESTERN ZONES ALTHOUGH
PROBABLY FEW AND FAR BETWEEN.

IF THOSE LIMITING FACTORS ARE OVERCOME...THERE IS THE POTENTIAL FOR
A FEW STRONG TO SEVERE STORMS...GIVEN VERY HIGH CAPES AND RATHER
COLD 500 MB TEMPS THROUGH 19 OR 20Z.  BEST SHOT WILL BE ON THE SEA
BREEZE FRONT BUT CAN/T RULE OUT SOMETHING ON THE HIGHER TERRAIN.

AREAL COVERAGE OF ANY STORMS WILL PROBABLY BE LIMITED WITH DRY
WEATHER DOMINATING...ESPECIALLY IN OUR WESTERN ZONES.  IT COULD BE
ONE OF THOSE SCENARIOS WHERE WE COULD END UP WITH JUST A FEW LOW
TOPPED THUNDERSTORMS IF TOO MUCH DRY AIR ENTRAINS.  HOWEVER...THERE
ALSO IS A LOW RISK OF A VERY ISOLATED/LOCALIZED HIGH END SEVERE
WEATHER EVENT IN THE FORM OF LARGE HAIL/MICROBURST GIVEN THE ABOVE
REASONING.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
TONIGHT INTO TOMORROW...

A FEW LINGERING SHOWERS ARE POSSIBLE AFTER 00Z. OTHERWISE EXPECT A
QUIET NIGHT AS MID-LEVEL RIDGE BEGINS TO BUILD INTO THE REGION. WEAK
FLOW AND INCREASING LOW LEVEL MOISTURE WILL ALLOW FOR ANOTHER ROUND
OF FOG TO DEVELOP. ALTHOUGH BELIEVE THAT IT WONT BE AS WIDESPREAD AS
TONIGHT. BEST CHANCE IS ACROSS THE CAPE AND ISLANDS AND WHERE PRECIP
OCCURS TODAY. OVERNIGHT TEMPS WILL DROP INTO THE UPPER 60S TO LOW
70.

HIGH PRESSURE BUILDS ACROSS SOUTHERN NEW ENGLAND TOMORROW BRINGING
18-19C 850MB TEMPS. THIS WILL ALLOW FOR TEMPS TO REACH IN THE LOW TO
MID 90S. DEWPOINTS WILL STILL BE IN THE UPPER 60S TO LOW 70S LEADING
TO HEAT INDEX VALUES IN THE MID 90S. CANNOT RULE OUT A SPOT SHOWER
ON WEDNESDAY IF LOCATIONS REACH THEIR CONVECTIVE TEMPERATURES...ESP
ACROSS THE HIGHER TERRAIN. BECAUSE OF THE UNCERTAINTY KEPT FORECAST
DRY.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
350 AM UPDATE...

HIGHLIGHTS...

* VERY WARM AND HUMID THU
* SCATTERED STORMS POSSIBLE LATE THU/THU NIGHT
* DRIER/LESS HUMID FRI THRU MON BUT STILL WARM

WED NIGHT/THU/THU NIGHT...

GOOD MODEL AGREEMENT ON SHORT WAVE RIDGING OVER THE AREA WED NIGHT
INTO THU. THUS DRY WEATHER TO START THIS PERIOD HOWEVER THE RISK OF
SHOWERS/T-STORMS INCREASES LATE THU INTO THU NIGHT AS POTENT
NORTHERN STREAM TROUGH CURRENTLY EXITING THE NORTHERN ROCKIES INTO
THE HIGH PLAINS BEGINS TO APPROACH NEW ENGLAND FROM THE WEST.
APPEARS TIMING OF THE FRONT COMES THROUGH OVERNIGHT...WELL AFTER
PEAKING HEATING. THIS COMBINED WITH MARGINAL SHEAR KEEPS THE RISK
LOW FOR STRONG CONVECTION LATE THU INTO THU NIGHT. HOWEVER GOOD
SYNOPTIC SCALE LIFT WITH THIS TROUGH SUGGEST AT LEAST SHOWERS SHOULD
BE ABLE TO HOLD TOGETHER AND MOVE ACROSS THE AREA LATE THU AND THU
NIGHT. PWATS ABOVE NORMAL AND DEW PTS 65 TO 70 WILL INCREASE THE
RISK FOR HEAVY DOWNPOURS. ALTHOUGH STILL 2 DAYS AWAY WILL NEED TO
MONITOR LATER MODEL TRENDS.

OTHERWISE VERY WARM AND HUMID CONDITIONS THU AHEAD OF APPROACHING
COLD FRONT. A MODEL BLEND OFFERS HIGHS U80S TO L90S.

FRIDAY THROUGH MONDAY...

ANOMALOUS CLOSED LOW/VORTEX SETS UP OVER HUDSON/JAMES BAY THIS TIME
PERIOD. THIS RESULTS IN BELOW NORMAL HEIGHTS AND MEAN TROUGH OVER
THE GREAT LAKES INTO THE NORTHEAST. THIS WILL KEEP TEMPERATURES NEAR
NORMAL /HIGHS MU80S/ AND LOWS IN THE 60S ALONG WITH TOLERABLE
HUMIDITY AS DEW PTS AVERAGE IN THE 50S DURING THE DAYLIGHT HOURS.
HOWEVER WITH THE NORTHERN STREAM JET SUPPRESSED SOUTHWARD INTO THE
GREAT LAKES AND NORTHEAST THERE WILL BE THE RISK OF SCATTERED
DIURNAL SHOWERS/T-STORMS JUST ABOUT EVERY DAY. TOO DIFFICULT AT THIS
TIME RANGE TO TIME INDIVIDUAL SHORT WAVES. NOT A WASHOUT BUT THE
RISK OF CONVECTION FROM TIME TO TIME.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH TUESDAY AFTERNOON/...

TODAY...MODERATE TO HIGH CONFIDENCE. VFR ALL LOCATIONS RIGHT NOW
EXCEPT FOR A NARROW BAND OF LOW CLOUDS NEAR THE SOUTH COAST...WHICH
SHOULD DISSIPATE SHORTLY. SCATTERED SHOWERS/THUNDERSTORMS WILL
DEVELOP GENERALLY ACROSS EASTERN NEW ENGLAND AFTER 18Z WHILE
ACTIVITY WILL BE HIT AND MISS...THE POTENTIAL IS THERE FOR ISOLATED
STRONG STORMS WITH LOCALLY HEAVY RAINFALL.

TONIGHT...MODERATE CONFIDENCE. VFR FOR MOST SITES. CANNOT RULE OUT
IFR IN STRATUS AND FOG ACROSS SE MASS INCLUDING THE CAPE AND
ISLANDS.

WEDNESDAY...HIGH CONFIDENCE. VFR WITH DIURNAL CU DEVELOPING AROUND
5K. A SPOT SHOWER IS POSSIBLE.

KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SEA BREEZE DEVELOPS BY 15 OR
16Z AS WINDS ARE ALREADY LIGHT AND VARIABLE. LOW CONFIDENCE ON
STRONG/SEVERE THUNDERSTORM HITTING THE TERMINAL.

KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. LOW CLOUDS AND SOME
FOG MAY DEVELOP EARLY THIS MORNING.

OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...

350 AM UPDATE...

WED NGT/THU...PATCHY MVFR/IFR IN FOG WED NGT BUT QUICKLY IMPROVING
TO VFR THU MORNING. LOW PROB THAT MVFR/IFR IN STRATUS LINGERS ALONG
THE SOUTH COAST THU. THEN UNCERTAINTY ON HOW QUICK THIS FOG/STRATUS
BURNS OFF SOUTH COAST.

THU NIGHT...VFR-MVFR IN SCATTERED SHOWERS/T-STORMS. SOME UNCERTAINTY
ON HOW WIDESPREAD PRECIP WILL BE.

FRI AND SAT...VFR LIKELY. HIGH FORECAST CONFIDENCE.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH WEDNESDAY/...HIGH CONFIDENCE.

WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS
THROUGH WEDNESDAY. A FEW SPOT SHOWERS AND PERHAPS A THUNDERSTORM
WILL BE POSSIBLE TODAY. THESE THUNDERSTORMS COULD CONTAIN GUSTY
WINDS. SPECIAL MARINE WARNINGS MAY BE NEEDED WITH THE HIGHEST
RISK ACROSS OUR WATERS ADJACENT TO EASTERN MA. OTHERWISE FOG AND
STRATUS WILL BE THE ISSUE TONIGHT...WITH DRY WEATHER EXPECTED ON
WEDNESDAY.

OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/...

350 AM UPDATE...

WED NIGHT AND THU...FAIRLY TRANQUIL WIND AND SEAS. POSSIBLE PATCHY
FOG IN HUMID AIRMASS.

THU NIGHT...MODEST SSW WIND AHEAD OF APPROACHING COLD FRONT.
SCATTERED SHOWERS WITH EMBEDDED THUNDER POSSIBLE.

FRI AND SAT...COLD FRONT SLOWLY MOVES OFFSHORE. ANOTHER WEAK FRONT
MAY ENTER THE WATERS SAT. WSW WINDS EXPECTED.

&&

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

&&

$$
SYNOPSIS...NOCERA/DUNTEN
NEAR TERM...FRANK
SHORT TERM...DUNTEN
LONG TERM...NOCERA
AVIATION...FRANK/NOCERA/DUNTEN
MARINE...NOCERA/DUNTEN



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