Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 231458
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
1058 AM EDT WED JUL 23 2014

.SYNOPSIS...
WEATHER WILL BE HOT AND HUMID WEATHER TODAY AHEAD OF AN
APPROACHING COLD FRONT. THE FRONT WILL TRIGGER SCATTERED SHOWERS
AND THUNDERSTORMS LATE THIS AFTERNOON AND EVENING. A FEW STRONG
THUNDERSTORMS ARE POSSIBLE WEST OF I-495 AND NORTH OF THE MASS
PIKE AND I-84. SHOWERS WILL LIKELY LINGER INTO THURSDAY SOUTHEAST
OF THE BOSTON TO PROVIDENCE CORRIDOR. HIGH PRESSURE BUILDS WITH
DRIER WEATHER FOR FRIDAY AND SATURDAY. AN APPROACHING WARM FRONT
SUNDAY WILL BRING MORE HUMID UNSETTLED WEATHER FOR THE EARLY PART
OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

OVERALL TREND FOR THE LATE MORNING HOURS IS ON TRACK FOR TODAY.
COLD FRONT IS SITUATED BACK ACROSS BUFFALO AND WILL CONTINUE TO
MOVE EASTWARD. A FEW SHOWERS ARE ALREADY STARTING TO POP UP ACROSS
THE SYRACUSE REGION. BELIEVE THAT IT WILL TAKE SOME TIME FOR THE
FRONT TO APPROACH SOUTHERN NEW ENGLAND AND THUS DELAYING STORM
INITIATION UNTIL THE LATE AFTERNOON.

MIXING IS ALREADY INCREASING ACROSS THE AREA WITH HYA GUSTING TO
28KTS AND BID AT 23KTS. EXPECT GUSTS TO INCREASE THROUGHOUT THE
DAY REACHING 20-30 MPH. THIS WILL ALSO ALLOW FOR US TO MIX WELL UP
TO 800 MB. THIS HELP TEMPS WARM UP TO OR ABOVE 90F SO TEMPERATURE
FORECAST IS ON TRACK.

&&

.SHORT TERM /6 PM THIS EVENING 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

MID AFTERNOON THROUGH 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. LATEST
THINKING IS THAT THE SEVERE RISK WILL BE MAINLY ALONG AND WEST OF
I495 AND ALONG AND NORTH OF THE MASS PIKE AND I84. THIS IS CLOSE
TO ALTHOUGH JUST A TAD BROADER THAN THE AREA OUTLOOKED BY SPC.

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 AND TOTAL
TOTALS APPROACH 50. 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/EARLY EVENING IN THE
EAST. AT THE VERY LEAST THE INSTABILITY ALONE IS ENOUGH TO SUPPORT
STRONG PULSE THUNDERSTORMS ACROSS THE NW INTERIOR.

THE 0 TO 6 KM BULK SHEAR MAGNITUDE...HOWEVER...IS MARGINAL AT BEST...25
TO 30 KT AND EVEN WEAKER TO THE SOUTHEAST OF THE WORCESTER AREA.
ANOTHER FACTOR TO CONSIDER IS THE RIGHT ENTRANCE REGION OF THE
UPPER JET WHICH APPROACHES THIS EVENING BUT 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. IT CURRENTLY SEEMS DOUBTFUL WHETHER DEEP
CONVECTION WILL SURVIVE PAST THE BOS TO PVD CORRIDOR.

PUTTING THIS ALL TOGETHER...WE PERCEIVE A RISK OF SEVERE
THUNDERSTORMS WITH DAMAGING WINDS THE GREATEST THREAT OVER A
SIZABLE CHUNK OF THE NW INTERIOR BOUNDED TO THE EAST BY I495 AND
TO THE SOUTH BY THE MASS PIKE AND I84. THE TIME FRAME LOOKS TO BE
PRIMARILY 4 PM TO 11 PM...STARTING IN THE WEST. THUNDERSTORMS MAY
REACH METRO BOSTON LATER IN THE EVENING BUT LIKELY IN A WEAKENED
STATE.

WITH PWATS NEAR 2 INCHES AHEAD OF THE COLD FRONT...THE POTENTIAL
ALSO EXISTS FOR INTENSE RAINFALL AND LOCALIZED FLASH FLOODING.
THIS CONCERN IS HEIGHTENED WITH THE SLOWING OF THE FRONTAL
BOUNDARY AS IT MOVES ACROSS SOUTHERN NEW ENGLAND TONIGHT.
HOWEVER...WE DO NOT SEE A STRONG TROPICAL PLUME CONNECTION AND SO
CONTINUE TO BE INCLINED TO HOLD OFF ON PUTTING 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/...
BIG PICTURE...
FOUR FEATURES IN THE LARGE SCALE FLOW. TROUGH ALONG THE PACIFIC
NORTHWEST COAST...RIDGE EXTENDING FROM THE ROCKIES AND PLAINS TO
NORTHERN CANADA...CLOSED LOW OVER NORTHERN QUEBEC WITH TROUGH AXIS
ACROSS THE GREAT LAKES...BUILDING RIDGE OVER THE WESTERN ATLANTIC.

THE QUEBEC TROUGH HANGS OVER NORTHEAST NORTH AMERICA...THE TROUGH
AXIS AND COLDEST TEMPS ALOFT SWING ACROSS NEW ENGLAND THURSDAY
NIGHT/FRIDAY.  THE PACIFIC NORTHWEST TROUGH RUNS OVER THE TOP OF THE
ROCKIES RIDGE...THEN MERGES WITH THE QUEBEC LOW OVER THE WEEKEND.
THIS DRAWS THE CLOSED LOW SOUTH OVER THE GREAT LAKES/NORTHEAST EARLY
NEXT WEEK.  THE ATLANTIC HIGH PRESSURE MEANWHILE BLOCKS OFF THE
EASTWARD EXIT OF THIS MERGER. THE COMBINATION OF UPPER LOW PRESSURE
OVER THE LAKES AND HIGH PRESSURE OVER THE ATLANTIC CREATES A
SOUTHWEST FLOW UP THE EAST COAST FROM THE DEEP SOUTH FOR THE FIRST
HALF OF NEXT WEEK.

MODELS HAVE BEEN SHOWING CONSISTENCY BOTH RUN TO RUN AND WITH EACH
OTHER. THIS INCREASES CONFIDENCE IN THE OVERALL SOLUTION...BUT WITH
THE USUAL UNCERTAINTY IN TIMING SHORTWAVES MOVING THROUGH THE
FLOW. THIS IS ESPECIALLY TRUE FOR MONDAY AND TUESDAY.

THE DAILIES...

THURSDAY NIGHT...COLD FRONT LINGERS OFFSHORE WHILE THE UPPER JET
RIGHT ENTRANCE REGION MOVES OVERHEAD. THIS MAY SUPPORT A WAVE ALONG
THE FRONT DURING THE FIRST PART OF THE NIGHT...BUT THE JET SHIFTS
EAST AFTER MIDNIGHT AS SHOULD THE SUPPORTING DYNAMICS. WE WILL KEEP
CHANCE POPS ON THE CAPE AND ISLANDS EARLY IN THE NIGHT. IF THE JET
POSITION AT 00Z IS AS ADVERTISED...WE MAY BE A LITTLE CONSERVATIVE
ON EVENING POPS. OTHERWISE THE MOVEMENT OF THE UPPER JET SHOULD
TREND SOUTHERN NEW ENGLAND TO END ANY REMAINING PCPN AND BRING
CLEARING SKIES.

FRIDAY-SATURDAY... SURFACE HIGH PRESSURE BUILDS OVER THE REGION WITH
DRY WEATHER AND DEWPOINTS IN THE 50S. TEMPS AT THE TOP OF THE MIXED
LAYER WILL SUPPORT UPPER 70S TO MID 80S BOTH DAYS...A LITTLE WARMER
SATURDAY.

ONE CONCERN WILL BE SEA BREEZE DEVELOPMENT ON FRIDAY WHICH MAY HOLD
DOWN AFTERNOON TEMPS ON THE EASTERN COAST. OTHER CONCERN WOULD BE
THE PASSAGE OF THE UPPER TROUGH AND COLDER TEMPS ALOFT. THIS LATTER
CONCERN COULD DESTABLIZE THE AIRMASS AND PROMOTE CUMULUS
DEVELOPMENT. BUT MODEL RH FIELDS SHOW A DRY AIRMASS WITH RH VALUES
BELOW 700 MB BELOW 50 PERCENT. WILL KEEP SKY COVER LOW FRIDAY...THEN
INCREASING CIRRUS ON SATURDAY AFTERNOON.

SUNDAY... PACIFIC NORTHWEST SHORTWAVE DIGS AS IT APPROACHES THE
GREAT LAKES AND GENERATES A SURFACE LOW. STRONG LOW LEVEL JET IS
EXPECTED TO DEVELOP IN THE OHIO VALLEY SATURDAY WITH 35-40 KNOT
WINDS AT 850 AND 900 MB. AS THIS MOVES EAST IT WILL BRING DEEPER
MOISTURE TO NEW ENGLAND WITH PRECIP WATER VALUES CLIMBING TO 1.5
INCHES BY SUNDAY. THE LIFTING OF THIS AIR OVER THE DEPARTING SURFACE
LAYER WOULD GENERATE SOME SHOWERS/SCT TSTMS. WE WILL MENTION CHANCE
POPS LATER SATURDAY NIGHT INTO SUNDAY.

MONDAY-TUESDAY...THE MERGING LOW OVER THE GREAT LAKES SURFACE AND
ALOFT WILL SWING A FRONT THROUGH NEW ENGLAND. TIMING IS IN QUESTION
AT THIS POINT WITH THE GFS SHOWING FROPA MONDAY NIGHT WHILE THE
ECMWF STALLS THE FRONT OVER US. WITH NO CLEAR TREND ON A DAY 7
FORECAST...WE WILL STAY CLOSE TO BLENDED GUIDENCE SOLUTION OF
DIMINISHING POPS TUESDAY.  BUT WITH LOW CONFIDENCE.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH THURSDAY/...

GENERALLY MODERATE CONFIDENCE ON FORECAST.

THROUGH EARLY AFTERNOON...GENERALLY VFR. LOW CLOUDS AT BLOCK
ISLAND SHOULD BREAK BY MID MORNING. AREA OF CLOUDS OVER THE OCEAN
SOUTH OF LONG ISLAND IS MOVING NORTHEAST. ON IR IMAGERY IT LOOKED
LIKE CIRRUS. ON EARLY VISIBLE IMAGERY IT LOOKS A LITTLE THICKER.
7 AM OBSERVATONS IN SRN CT SUGGEST SOME CLOUDS AROUND 10 THOUSAND
FEET MAY BE MIXED IN. WE HAVE EXTRAPOLATED THESE THICKER CLOUDS
ACROSS RI AND SOUTHEAST MASS THIS MORNING...MOVING OFF CAPE COD
AROUND MIDDAY.

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. SREF PROBABILITIES ARE HIGH FOR LOW
CLOUDINESS TO FORM OVER SOUTHEAST MA AND RI AFTER 03Z TONIGHT.
THIS SUGGESTS A FAIRLY HIGH RISK OF AREAS OF IFR CIGS FORMING
TONIGHT ACROSS THE CAPE AND ISLANDS. MVFR CIGS AND VSBYS
ANTICIPATED IN RAIN OR SHOWERS ALONG AND SE OF A PYM-UUU LINE
DURING MUCH OF THU...IMPROVING LATE.

KBOS TAF...HIGH CONFIDENCE. VFR THROUGH MOST IF NOT ALL OF THE
DAY. TSTMS POSSIBLE AFT 23Z TO THE N AND W OF BOS AND CLOSER TO
THE AIRFIELD ITSELF AFT 01Z.

KBDL TAF...HIGH CONFIDENCE IN TAF. TSTMS POSSIBLE AFT 21Z. ANY
TSTMS COULD CONTAIN STRONG WIND GUSTS.

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

THURSDAY NIGHT THROUGH SATURDAY...VFR. LOCAL IFR POSSIBLE IN EARLY
MORNING FOG/LOW CLOUDS. POTENTIAL SEA BREEZE FRIDAY AFTERNOON.

SUNDAY...
VFR BUT WITH AREAS OF MVFR IN SHOWERS/TSTMS/FOG.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH THURSDAY/...MODERATE CONFIDENCE.

THE SW FLOW WILL STRENGTHEN AHEAD OF A COLD FRONT TO PRODUCE GUSTS
APPROACHING 25 KT ACROSS MANY OF THE WATERS. SEAS MAY APPROACH 5
FEET EAST OF CAPE ANN...ACROSS THE E PORTION OF STELLWAGEN
BANK...AND E OF CAPE COD THIS AFTERNOON. ALTHOUGH THE WIND WAVE
WILL BE FORMED FROM THE SW FLOW...THERE IS ALSO A SWELL THAT IS
ENCROACHING THE COASTAL WATERS FROM THE EAST. ALTHOUGH OF FAIRLY
LOW AMPLITUDE OF LESS THAN 3 FEET...THE SWELL APPEARS TO BE
ENOUGH TO TRIGGER A MODERATE RIP CURRENT RISK ALONG PORTIONS OF
THE EAST FACING COAST. AREAS OF FOG MAY DEVELOP ALONG THE SOUTH
COASTAL WATERS TONIGHT.

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

THURSDAY NIGHT-FRIDAY-SATURDAY... NORTH TO NORTHEAST WIND THURSDAY
NIGHT BECOMES LIGHT FRIDAY WITH AFTERNOON SEA BREEZES DEVELOPING.
WINDS BECOME SOUTHWEST SATURDAY BUT REMAIN BELOW 25 KNOTS.  SEAS 4
FEET OR LESS THROUGH THE PERIOD.

SUNDAY...A WARM FRONT APPROACHES THE WATERS WITH WARMER MORE HUMID
AIR AND WITH CLOUDS/SHOWERS/TSTMS. INCREASING SOUTH-SOUTHWEST WINDS
WITH GUSTS 20-22 KNOTS...APPROACHING SMALL CRAFT THRESHOLD. THESE
WINDS WILL ALSO BUILD SEAS ON THE EXPOSED WATERS TO 5 OR 6 FEET.  A
SMALL CRAFT ADVISORY MAY BE NEEDED.

&&

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

&&

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

&&

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



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