Area Forecast Discussion
Issued by NWS Boston, MA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KBOX 230623
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
223 AM EDT WED JUL 23 2014

.SYNOPSIS...
WARM AND HUMID WEATHER IS EXPECTED THROUGH WEDNESDAY NIGHT AHEAD OF
AN APPROACHING COLD FRONT. THE FRONT WILL TRIGGER SCATTERED SHOWERS
AND THUNDERSTORMS WEDNESDAY AFTERNOON AND EVENING. A FEW STRONG
STORMS ARE POSSIBLE ESPECIALLY INLAND. SHOWERS MAY LINGER INTO
THURSDAY ALONG THE SOUTH COAST HOWEVER THE TREND WILL BE FOR DRIER
AND LESS HUMID WEATHER THURSDAY NIGHT INTO SATURDAY. THE WEATHER
PATTERN THEN BECOMES UNSETTLED AND MORE HUMID BEGINNING SUNDAY AND
ESPECIALLY EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1 AM UPDATE...

FORECAST REMAINS ON TRACK OVERNIGHT. OTHER THAN A PATCH OF MID
CLOUDS PASSING OVER THE GREATER BOSTON AREA...SKIES ARE MOSTLY
CLEAR OVER SOUTHERN NEW ENGLAND AND SHOULD REMAIN SO OVERNIGHT.
PATCHY FOG AND STRATUS BOTH ALONG THE SOUTH COAST AND INTERIOR
VALLEYS REMAIN A POSSIBILITY BUT PROBABLY NOT A MAJOR FACTOR. THE
DEWPOINT DEPRESSIONS ARE NARROWING BUT FOR MOST LOCATIONS THERE IS
ENOUGH SURFACE GRADIENT FOR SOME MIXING AND SUNRISE WILL LIKELY
OCCUR BEFORE THE LOWER LAYERS BECOME TOO SATURATED.

DID NOT MAKE ANY CHANGES TO THE TEMPERATURE FORECAST FOR THE REST
OF THE NIGHT.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...

* A FEW STRONG TO SEVERE STORMS POSSIBLE LATE THIS AFTERNOON INTO
  THE EVENING HOURS *
* SHOWERS WILL LIKELY LINGER ACROSS THE CAPE...ISLANDS AND
  ADJACENT SE MASSACHUSETTS DURING MUCH OF THURSDAY

TODAY AND TONIGHT...

WE CONTINUE TO ANTICIPATE STRONG THUNDERSTORMS TO DEVELOP LATE
THIS  AFTERNOON IN THE WEST AND MOVE/REDEVELOP FURTHER EAST THIS
EVENING. LOOKS LIKE MARGINALLY STRONG ENOUGH WIND SHEAR AND
SUFFICIENTLY ROBUST INSTABILITY FOR A FEW THUNDERSTORMS TO REACH
SEVERE LIMITS...MOST LIKELY IN THE FORM OF POCKETS OF DAMAGING
WINDS...AS A COLD FRONT APPROACHES NEW ENGLAND LATE TODAY.

MODEL FORECAST SOUNDINGS...INDICES AND CAPE ALL POINT TO
SUFFICIENT INSTABILITY FOR STRONG THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING. SBCAPES OF 1200 TO 1800 J/KG INDICATED WITH
THE 00Z GFS AND 2500 TO 3000+ J/KG PER THE NAM...WHICH HAS A
TENDENCY TO OVERDO THE CAPE. NEVERTHELESS...SHOWATERS DROP TO
AROUND -3 AND K INDICES REACH INTO THE MID TO UPPER 30S.
ANTICIPATE FAIRLY STRONG LOW LEVEL LAPSE RATES AND MODERATE MID
LEVEL LAPSE RATES AROUND 6.5C/KM LATE THIS AFTERNOON/EARLY
EVENING. THERE IS A MID LEVEL CAP IN PLACE AROUND 11K FT AT THE
START OF THE AFTERNOON BUT LOWERING 500 MB HEIGHTS AND THE
APPROACHING COLD FRONT HAS THE CAP ERODING BY MID AFTERNOON IN THE
WEST AND LATE AFTERNOON/VERY EARLY EVENING IN THE EAST. AT THE
VERY LEAST THE INSTABILITY ALONE IS ENOUGH TO SUPPORT STRONG PULSE
THUNDERSTORMS.

THE 0 TO 6 KM BULK SHEAR MAGNITUDE...HOWEVER...IS MARGINAL AT BEST...25
TO 30 KT AND STRONGEST TO THE NORTH AND NORTHWEST OF WORCESTER.
ANOTHER FACTOR TO CONSIDER IS THE RIGHT ENTRANCE REGION OF THE
UPPER JET APPROACHES THIS EVENING ALTHOUGH NOT IDEALLY SITUATED
OVER THE AREA UNTIL THU MORNING WHEN THE SURFACE COLD FRONT
REACHES THE SE COASTAL WATERS. A MORE GENERAL SYNOPTIC RECOGNITION
OF THIS EVENT SUGGESTS THE TIMING OF THE SURFACE COLD FRONT SHOULD
SUPPORT CONVECTION IN AT LEAST WESTERN AND CENTRAL SECTIONS AND
PROBABLY IN A WEAKENED STATE IN THE EAST LATER INTO THE EVENING.
THE AXIS OF INSTABILITY IS INITIALLY ACROSS WESTERN MA AND WESTERN
CT LATE THIS AFTERNOON AND THEN WORKS ACROSS SW NH AND CENTRAL MA
DURING THE EARLY EVENING AND MORE INTO NE MA LATER INTO THE
EVENING. OVERNIGHT THE AXIS OF INSTABILITY SHIFTS TO THE SOUTHEAST
ZONES BUT WEAKENS.

PUTTING THIS ALL TOGETHER...WE PERCEIVE A RISK OF SEVERE
THUNDERSTORMS WITH DAMAGING WINDS THE GREATEST THREAT ALONG AND TO
THE RIGHT OF A LINE EXTENDING FROM SALISBURY MA TO BVY TO BED TO
IJD TO HFD TO BRISTOL CT. THE TIME FRAME LOOKS TO BE PRIMARILY 4
PM TO 11 PM...EARLIER IN THE WEST AND LATER IN THE EAST.
THUNDERSTORMS MAY REACH BOSTON LATER IN THE EVENING BUT LIKELY IN
A WEAKENED STATE. WITH PWATS NEAR 2 INCHES IN A PLUME AHEAD OF THE
COLD FRONT...THE POTENTIAL ALSO EXISTS FOR INTENSE RAINFALL AND
LOCALIZED FLASH FLOODING. THIS CONCERN IS HEIGHTENED WITH THE
SLOWING OF FRONTAL BOUNDARY AS IT MOVES ACROSS SOUTHERN NEW
ENGLAND TONIGHT. HOWEVER...WE DO NOT SEE A STRONG TROPICAL PLUME
CONNECTION AND SO THINK IT MAY NOT BE APPROPRIATE TO PUT A LARGE
PART OF THE FORECAST AREA UNDER A FLASH FLOOD WATCH AT THIS TIME.
NEVERTHELESS...WE WILL STILL NEED TO BE VIGILANT FOR THE
POSSIBILITY OF LOCALIZED FLASH FLOODING...A THREAT THAT MAY
PERSIST TONIGHT AFTER THE DAMAGING WIND THREAT HAS FADED.

THURSDAY...

THE FRONT DEACCELERATES AS IT APPROACHES SOUTHEAST NEW ENGLAND AND
THEN A WAVE MOVES ALONG THE FRONT DURING THE DAY THURSDAY.
THUS...EXPECT SHOWERS TO LINGER THURSDAY MORNING ACROSS THE
SOUTHEAST HALF OF THE AREA AND FOR MOST OF THE DAY ACROSS CAPE
COD...THE ISLANDS AND ADJACENT SOUTHEAST MA.

WILL BE MUCH COOLER THURSDAY BEHIND THE FRONT...AND SOUTHEAST OF
THE BOSTON TO PROVIDENCE CORRIDOR CLOUDS WILL ALSO ACT TO CAP THE
TEMPERATURE. FOR MOST LOCATION...EXPECT HIGHS IN THE 70S ON
THURSDAY. THE ATMOSPHERE MAY BE MARGINALLY UNSTABLE ENOUGH TO
SUPPORT A FEW EMBEDDED THUNDERSTORMS OVER THE CAPE AND ISLANDS AS
WELL AS SOUTHEAST COASTAL WATERS ON THURSDAY.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
HIGHLIGHTS...

* MUCH COOLER THU ALONG WITH RAIN LINGERING SOUTH COAST
* DRY...LESS HUMID AND SEASONABLE THU NGT THRU SAT
* PATTERN BECOMES UNSETTLED AND MORE HUMID SUN INTO NEXT WEEK

SYNOPTIC OVERVIEW AND MODEL PREFERENCES....

NORTHERN STREAM MID LEVEL TROUGH MOVES ACROSS THE AREA THU WITH ITS
SURFACE COLD FRONT SLOWLY EXITING THE SOUTH COAST. POST FRONTAL
AIRMASS OVERSPREADS THE REGION FRI. THE MID LEVEL MEAN TROUGH AXIS
THEN MOVES OFFSHORE SAT WITH SUBTLE HEIGHT RISES AND ANTICYCLONIC
FLOW OVERSPREADING NEW ENGLAND. THIS WILL MAINTAIN DRY WEATHER OVER
THE AREA THRU SAT. BY SUNDAY AND ESPECIALLY EARLY NEXT WEEK ALL
MODEL GUIDANCE INCLUDING THE GEFS AND ECENS ENSEMBLES ARE IN GOOD
AGREEMENT ON A HIGH AMPLITUDE /+2 SD/ LONG WAVE TROUGH SETTING UP
OVER SOUTHEAST CANADA SOUTHWARD INTO THE OH VLLY. BOTH DETERMINISTIC
AND ENSEMBLE GUIDANCE ARE IN VERY GOOD AGREEMENT ON THE LARGE SCALE
FLOW ACROSS NORTH AMERICA THIS PERIOD. THEREFORE WILL BASE THIS
PORTION OF THE FORECAST ON A MODEL BLEND.

DAILY DETAILS...

THURSDAY...

MID LEVEL TROUGH AXIS STILL WELL WEST OF NEW ENGLAND AT 12Z THU.
THUS COLD FRONT WILL BE SLOW TO EXIT THE SOUTH COAST WHICH WILL
INCREASE THE RISK FOR SHOWERS AND POSSIBLE A TSTM TO LINGER ACROSS
THIS REGION. THE HIGH RES DETERMINISTIC GUID /GFS AND NAM/ ARE
SLOWER WITH THE FROPA AS THESE MODELS FORM A STRONGER FRONTAL WAVE
THAN THE ENSEMBLES. THIS IS POSSIBLE GIVEN THE HIER RES MODELS WOULD
PERFORM BETTER THAN THE COURSE ENSEMBLES SIMULATING A SMALL SCALE
FRONTAL WAVE. THEREFORE WILL GO WITH LIKELY POPS THU MORNING ACROSS
RI AND SOUTHEAST MA AND TRENDING TO CHANCE AS THE RAIN SHIELD MOVES
SLOWLY SOUTHEAST AND EVENTUALLY OFFSHORE LATER THU. DEPARTURE OF
RAIN WILL BE CRITICAL TO TEMP FORECAST AS THE WETTER GFS 2 METER
TEMPS NEVER CLIMB OUT OF THE 60S! EVEN THE WARMER ECMWF AND NAM 2
METER TEMPS ARE ONLY INTO THE L70S. THUS A COOLER DAY ON TAP THU AND
IF THE GFS VERIFIES OUR TEMPS WILL BE TOO WARM.

ELSEWHERE ACROSS INTERIOR CT/MA INTO SOUTHWEST NH MAINLY DRY
CONDITIONS SHOULD PREVAIL WITH LOTS OF MID AND HIGH CLOUDS ALONG
WITH N-NE WINDS YIELDING A COOLER DAY.

THURSDAY NIGHT THRU SATURDAY...

POST FRONTAL AIRMASS OVERSPREADS THE AREA THU NIGHT AND FRI WITH A
850 TEMP ANOMALIES AROUND 1 STANDARD DEVIATION COOLER THAN CLIMO...
ABOUT +10C/+11C. HENCE REFRESHING AIRMASS WITH DEW PTS IN THE 50S.
THE CORE OF THE DRY/COOLER AIRMASS WILL BE OVER SOUTHERN NEW ENGLAND
AROUND 12Z FRI. THIS WILL YIELD A VERY COMFORTABLE AND COOL TEMPS
THU NIGHT/EARLY FRI AM.

SUNDAY THRU TUESDAY...

PATTERN BECOMES UNSETTLED AS LONG WAVE TROUGH SETS UP OVER SOUTHEAST
CANADA SOUTHWARD INTO THE OH VALLEY. THIS PROVIDES DEEP CYCLONIC
FLOW ACROSS THE NORTHEAST ALONG WITH A BROAD SURFACE LOW PRES OVER
NY AND NEW ENGLAND. LOW LEVEL FLOW WILL BE SSW OFF THE ATLANTIC INTO
NEW ENGLAND SO EXPECT INCREASING HUMIDITY ALONG WITH THE RISK OF
SCATTERED SHOWERS AND THUNDERSTORMS.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH TONIGHT/...

GENERALLY MODERATE CONFIDENCE ON FORECAST.

THROUGH THIS MORNING...CONDITIONS SHOULD REMAIN VFR FOR MOST OF
THIS PERIOD EXCEPT FOR PATCHY FOG AND STRATUS ALONG THE SOUTH
COAST AND INTERIOR VALLEYS. THERE IS ENOUGH LOW LEVEL GRADIENT FOR
ENOUGH MIXING TO LIMIT ANY VISIBILITIES BELOW MVFR. ANY STRATUS OF
PATCHY FOG SHOULD BURN OFF FAIRLY QUICKLY AFTER SUNRISE.

LATE THIS AFTERNOON INTO TONIGHT...MVFR CIGS AND VSBYS IN
VICINITY OF SCT TSTMS AHEAD OF A COLD FRONT. A FEW TSTMS MAY
BRIEFLY LOWER CIGS/VSBYS TO IFR LEVELS. ALSO...A FEW TSTMS MAY
PRODUCE STRONG WIND GUSTS. VSBYS MAY BE REDUCED IN PATCHY FOG
AHEAD OF FRONTAL PASSAGE AS WELL. SREF PROBABILITIES ARE HIGH FOR
LOW CLOUDINESS TO FORM OVER SOUTHEAST MA AND RI MID TO LATE WED
AFTERNOON IN THE WARM MUGGY AIRMASS...SO WILL NEED TO WATCH FOR
THIS SEPARATE AREA OF CLOUDINESS WELL AHEAD OF ANY STORMS.

KBOS TAF...HIGH CONFIDENCE. VFR THROUGH MOST IF NOT ALL OF THE
DAY. TSTMS POSSIBLE AFT 00Z OR 8 PM...AFT 22Z TO THE N AND W.

KBDL TAF...HIGH CONFIDENCE IN TAF. LOW PROB ON A BRIF PERIOD OF
MVFR VSBYS IN FOG OVERNIGHT BUT LOOKING LESS LIKELY. TSTMS
POSSIBLE AFT 21Z. ANY TSTMS COULD CONTAIN STRONG WIND GUSTS.

OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE

MVFR POSSIBLE BOSTON TO PROVIDENCE IN RAIN...POSSIBLY IFR SOUTH
COAST WITH VFR NORTHWEST MA INTO SOUTHWEST NH. THEN VFR ALL
TERMINALS THU NIGHT INTO SAT. LOW RISK OF MVFR IN SCATTERED
SHOWERS/TSTMS SUN AFTN WESTERN NEW ENGLAND.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH WEDNESDAY/...MODERATE CONFIDENCE.

WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
LEVELS THROUGH TONIGHT. THE SW FLOW WILL STRENGTHEN AHEAD OF A
COLD FRONT ON WED WITH A RISK OF GUSTS APPROACHING 25 KT. AREAS OF
FOG MAY DEVELOP ALONG THE SOUTH COASTAL WATERS TONIGHT.

OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE.

THU...MODEST N-NE WIND ALONG WITH PERIODS OF RAIN ESPECIALLY SOUTH
COASTAL WATERS.

FRI/SAT...PLEASANT BOATING WEATHER WITH DRY CONDITIONS AND LIGHT
WINDS BECOMING A MODEST SSW SAT AFTN.

SUN...MODEST SSW WIND ALONG WITH LOW RISK OF A FEW SHOWERS NEAR
SHORE. OTHERWISE MAINLY GOOD VSBYS.

&&

.EQUIPMENT...
KBOX RADAR MAY BE IN STANDBY MODE WEDNESDAY MORNING WHILE
CONSTRUCTION TAKES PLACE NEARBY. THE RADAR WILL RETURN TO SERVICE
BY EARLY AFTERNOON PRIOR TO START OF ANY CONVECTION IN OUR
FORECAST AREA.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
NH...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 7 PM EDT THIS
     EVENING FOR ANZ230>237-251.
     SMALL CRAFT ADVISORY UNTIL 3 AM EDT THURSDAY FOR ANZ250-254.

&&

$$
SYNOPSIS...NOCERA/DUNTEN
NEAR TERM...THOMPSON
SHORT TERM...DUNTEN/THOMPSON
LONG TERM...NOCERA
AVIATION...NOCERA/DUNTEN/GAF/THOMPSON
MARINE...NOCERA/DUNTEN/GAF
EQUIPMENT...THOMPSON


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.