Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 211458
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
1058 AM EDT THU MAY 21 2015

.SYNOPSIS...
CHILLY THIS MORNING. SEASONABLY MILD BY AFTERNOON. FAST MOVING
LOW PRESSURE WILL BRING A PERIOD OF RAIN TO RHODE ISLAND AND
SOUTHEAST MASSACHUSETTS TONIGHT INTO FRIDAY MORNING. THEN A COLD
FRONT MAY TRIGGER SCATTERED SHOWERS LATE FRIDAY AFTERNOON INTO
EARLY EVENING. BEHIND THE FRONT FROST AND MAYBE EVEN RECORD
BREAKING COLD IS POSSIBLE FRIDAY NIGHT INTO SATURDAY MORNING. DRY
AND SEASONABLE BENEATH HIGH PRESSURE FOR THE WEEKEND. AN ACTIVE
WET-WEATHER PATTERN BEGINS TO EMERGE MEMORIAL DAY AND MAY
CONTINUE THRU THE REMAINDER OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
11 AM UPDATE...NO MAJOR CHANGES TO THE FORECAST. MAINLY BROUGHT
FORECAST FOR THE NEXT FEW HOURS BACK IN LINE WITH OBSERVED TRENDS.
THE MOST SIGNIFICANT CHANGE WAS TO SLOW THE RATE OF TEMPERATURE
RISE ACROSS WESTERN MA AND NORTHERN CT...DUE TO MORE OPAQUE CLOUD
COVER. TWEAKED TIMING AND AMOUNT OF SKY COVER THROUGH THIS
AFTERNOON AS WELL...TO BETTER REFLECT LATEST SATELLITE DATA.

PREVIOUS DISCUSSION...

AS HIGH PRES BUILDS SOUTH OF NEW ENGLAND TODAY RETURN SSW WIND FLOW
WILL MODIFY CHILLY AIRMASS OVER THE REGION ALONG WITH SUNSHINE THRU
HIGH CLOUDS. THIS WILL BOOST TEMPS TO 65 TO 70. IT WILL FEEL MILDER
THAN YESTERDAY GIVEN LESS WIND. ALTHOUGH A MODEST SSW WIND WILL
DEVELOP THIS AFTERNOON WITH SPEEDS 15 TO 20 MPH.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
TONIGHT...

NORTHERN STREAM SHORT WAVE ENERGY OVER THE HIGH PLAINS EARLY THIS
MORNING WILL TRACK EASTWARD TODAY AND CAPTURE SOME SOUTHERN STREAM
MOISTURE AS IT APPROACHES THE EAST COAST. THIS FEATURE WILL SPAWN A
LATE SEASON COASTAL LOW/BAROCLINIC WAVE OVER THE SOUTHEAST STATES
THAT WILL TRACK NEAR OR JUST SOUTHEAST OF THE 40N/70W BENCHMARK BY
FRI MORNING. MORE IMPORTANTLY ALL GUIDANCE HAS MODEST MID LEVEL FGEN
OVER EASTERN CT/RI AND SOUTHEAST MA. MODELS VARY ON THE EXACT
LOCATION OF MID LEVEL FGEN BUT ALL MODELS HAVE BEEN TRENDING FARTHER
NORTH. HI RES ARW AND NMM ARE FARTHEST NORTH WITH MODEST MID LEVEL
RAIN BANDS OVER EASTERN CT/RI TO NEAR OR JUST SOUTH OF BOSTON.
DIDN/T WANT TO GO FULL THROTTLE ON THIS MOST NORTHERN SOLUTION BUT
DID INCORPORATE SOME OF THIS HI RES GUIDANCE INTO THE FORECAST TO
TREND THE FORECAST FARTHER NORTH WITH RAIN SHIELD. GIVEN MODEST
FORCING AND SIGNS OF SOME INSTABILITY /NEG EPV/ COULD SEE A FEW
MODERATE TO PERHAPS BRIEFLY HEAVY RAIN BANDS 06Z-12Z FRI OVER
EASTERN CT/RI AND SOUTHEAST MA...POSSIBLE NORTHWARD TO THE MASS
PIKE.

FRIDAY...

A 3 PART DAY WITH MORNING RAINS LIKELY OVER RI AND SOUTHEAST MA
POSSIBLY NORTHWARD TO BOSTON. THEN AS MID LEVEL TROUGH AND
ATTENDING COASTAL LOW EXIT DRY WEATHER ALONG WITH SUNSHINE DEVELOP
MID TO LATE MORNING IN RESPONSE TO SHORT WAVE RIDGING. HOWEVER
THIS WILL BE SHORT LIVED AS VORTEX OVER QUEBEC DROPS SOUTHWARD
ALONG WITH ATTENDING COLD FRONT. THIS SHOULD BE SUFFICIENT TO KICK
OFF WIDELY SCATTERED SHOWERS MID TO LATE AFTERNOON AND EARLY
EVENING. VERY COLD TEMPS ALOFT ADVECT OVER THE NORTHEAST WITH 500
MB TEMPS FALLING TO -24C BY DAYS END AT 00Z. THIS PROVIDES MID
LEVEL LAPSE RATES OF 6.5-7.0C/KM ALONG WITH TT/S CLIMBING TO 50.
THESE COLD TEMPS ALOFT MAY BE SUFFICIENT FOR CHANCE OF THUNDER AND
LOW RISK OF SMALL HAIL.

OTHERWISE TEMPS WILL CLIMB INTO THE L70S FRI AFTERNOON.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
*/ HIGHLIGHTS...

 - UNSEASONABLY COOL SATURDAY
 - FROST / FREEZE HEADLINES LIKELY FOR SATURDAY MORNING
 - SEASONABLE AND DRY FOR SUNDAY
 - BEGINNING MEMORIAL DAY...A WET-WEATHER PATTERN BEGINS TO EMERGE
 - COULD REMAIN SEASONABLE AND WET THROUGH THE REMAINDER OF THE WEEK

*/ DISCUSSION...

CONFIDENT WITH THE COLD FRONT PUSHING OFFSHORE FRIDAY NIGHT THAT
COLD AIR ADVECTION WILL BE IN FULL SWING INTO SATURDAY MORNING.
BREEZY NW FLOW REARWARD OF THE PIVOTING VORTEX THRU N NEW ENGLAND
WILL USHER AN ANOMALOUSLY COLD AIRMASS S ALOFT. EXPECT WIDESPREAD
FROST/FREEZE HEADLINES ACROSS THE INTERIOR WITH THE BIGGEST IMPACT
OVER N/W PORTIONS OF MA. BUT AGREE WITH PREVIOUS FORECASTER THINKING
THAT THE BREEZY NW-FLOW COULD MITIGATE FROST DEVELOPMENT DESPITE
COLD TEMPERATURES. WILL BE CLOSE TO RECORD LOWS /SEE THE CLIMATE
SECTION BELOW/. COLD AIRMASS LINGERS AS HIGH PRESSURE BUILDS S OF
NEW ENGLAND. COOL AND DRY FOR SATURDAY. MORE SEASONABLE SUNDAY WITH
RETURN S-FLOW.

BEGINNING MEMORIAL DAY AM LESS CONFIDENT WITH THE FORECAST. PACIFIC-
ORIGIN IMPULSES ROTATING THROUGH THE W-HALF OF THE CONUS INVOKE DOWN-
STREAM RIDGING INTO NEW ENGLAND. BERMUDA HIGH REAFFIRMS ROUND THE W-
PERIPHERY WHICH SW-FLOW PREVAILS. THE WARM-FRONTAL LEADING EDGE OF
WARM-MOIST AIR WILL BE A FOCUS FOR WET-WEATHER AS PACIFIC IMPULSES
EJECT E THROUGH RIDGE PATTERN. COMBINATION OF ISENTROPIC ASCENT
BENEATH DIFFLUENCE ALOFT ALLOWING FOR BROADSCALE LIFT...CAN NOT RULE
OUT SHOWERS AROUND MONDAY - TUESDAY. FEEL BETTER CHANCES ARE N/W
AWAY FROM THE ANTICYCLONIC FLOW / DRY AIR AND TOWARDS MORE FAVORABLE
DYNAMICS.

FOR THE REST OF THE WEEK ENSEMBLE AND DETERMINISTIC GUIDANCE SUGGEST
A FLAT-FLOW REGIME ACROSS THE CONUS THROUGH WHICH PACIFIC-ORIGIN
IMPULSES PREVAIL. CONSIDERING THE OFFSHORE BERMUDA HIGH AND A VORTEX
PREVAILING ACROSS CANADA...MAY BE DEALING WITH A MORE ACTIVE PATTERN
AS THE WARM-MOIST FLOW IS STRETCHED ACROSS THE NE CONUS
UNDERGOING LIFT AND ENHANCEMENT AS MID-LEVEL IMPULSES TRANSLATE
THROUGH THE REGION. UNCERTAINTY AS ANY WOBBLE IN THE FLOW PATTERN
BETWEEN THE VORTEX N AND THE BERMUDA HIGH S WOULD MODIFY THE
CONVERGENT FLOW. GFS SUGGESTS A +1 SD OF H925 TEMPERATURES FOR
NEXT WEEK. IF +2 IT WOULD BE MORE LIKELY THAT THE CONVERGENT FLOW
WOULD BE N AND W WITH S NEW ENGLAND WARMER AND DRY BENEATH THE
RIDGE. WITH A CONSENSUS BLEND...WILL KEEP IT SEASONABLE WITH
SLIGHT CHANCE TO CHANCE POPS. ECHOING THE POINT MADE BY THE
PREVIOUS FORECASTER...COULD FIND OURSELVES WITHIN THE STEERING
FLOW OF UPSTREAM MCS/S. CONTINUED SIGNALS OF A CUTOFF LOW WOBBLING
ACROSS THE NW-ATLANTIC. WILL HAVE TO KEEP AN EYE ON THAT.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH THURSDAY NIGHT/...

12Z UPDATE...

TODAY...VFR. WNW WINDS BECOMING SSW THIS AFTERNOON. WINDS PICKING
UP DURING THE AFTERNOON. WEAK SEABREEZE ALONG E-COASTAL MA HAS SET
IN...AS PREVIOUSLY ANTICIPATED. EXPECTING A PERSISTENT SOUTHWEST
SYNOPTIC FLOW TO BECOME MORE DOMINANT LATE THIS AFTERNOON INTO
THIS EVENING.

TONIGHT...RAIN OVERSPREADS MUCH OF RI AND SE MA. UNCERTAINTY
REGARDING N EXTENT OF -RA. COULD GET AS FAR N AS IJD-SFZ-BOS.
MODERATE CONFIDENCE. WHILE MAINLY LOW-END VFR TO MVFR OVER RI AND
SE MA WITH VFR ELSEWHERE...RA/+RA WITH VSBY IMPACTS POSSIBLE OVER
CAPE COD AND ISLANDS LEADING TO IFR.

FRIDAY...MORNING -RA EXITS SE MA. DRY LATE MORNING INTO EARLY
AFTERNOON. THEN A COLD FRONT WILL LIKELY TRIGGER SCT -SHRA FROM
LATE AFTERNOON INTO EARLY EVENING. LOW RISK OF SMALL HAIL IN MORE
ROBUST SHRA WITH ISOLATED TSRA. OVERALL VFR. MODERATE CONFIDENCE.

KBOS TERMINAL...HIGH CONFIDENCE IN TAF. A BRIEF SEA BREEZE FROM
THE SE IS POSSIBLE ABOUT 14Z TO 18Z.

KBDL TERMINAL...HIGH CONFIDENCE IN TAF.

OUTLOOK...FRIDAY NIGHT THROUGH MONDAY...

FRIDAY NIGHT INTO SUNDAY NIGHT...HIGH CONFIDENCE.

VFR. BREEZY NW-WINDS THROUGH SATURDAY VEERING SW INTO SUNDAY.

MONDAY INTO MONDAY NIGHT...MODERATE CONFIDENCE.

LOW-END VFR TOWARDS THE LATER-HALF WITH INCREASING -SHRA CHANCES.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH FRIDAY/...

TODAY...

WNW WINDS BECOME SSW BY MIDDAY. DRY WEATHER AND GOOD VSBY.

TONIGHT...

RAIN OVERSPREADS THE SOUTHERN WATERS AS LOW PRES TRACKS NEAR OR JUST
SOUTH OF 40N/70W BENCHMARK. SOME UNCERTAINTY ON NORTHERN EXTENT OF
RAIN SHIELD.

FRIDAY...

RAIN SHIELD OVER SOUTHEAST MA EXITS BY MID TO LATE MORNING. THEN A
PERIOD OF DRY WEATHER FOLLOWED BY ISOLATED TO WIDELY SCATTERED
SHOWERS DURING MID TO LATE AFTERNOON INTO THE EVENING AS A COLD
FRONT APPROACHES FROM THE WEST.

OUTLOOK...FRIDAY NIGHT THROUGH MONDAY...

BREEZY NW-WINDS WITH GUSTS OVER 25 KTS THROUGH SATURDAY VEERING SW
INTO SUNDAY AND REMAINING BRISK WITH GUSTS UP TO 20 KTS. LOOKING AT
WAVES BUILDING IN EXCESS OF 5 FEET ON THE OUTER WATERS

MONDAY INTO MONDAY NIGHT...MODERATE CONFIDENCE.

CONTINUED BREEZY SW-WINDS WITH GUSTS UP TO 20 KTS. WAVES IN EXCESS
OF 5-FEET MAY REMAIN ON THE S/SE-WATERS.

&&

.CLIMATE...
RECORD LOWS FOR MAY 23RD...

BOSTON - 40 /1967/
HARTFORD - 37 /1976/
PROVIDENCE - 40 /1950/
WORCESTER - 32 /1929/

&&

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

&&

$$
SYNOPSIS...NOCERA/SIPPRELL
NEAR TERM...BELK/NOCERA/SIPPRELL
SHORT TERM...NOCERA
LONG TERM...SIPPRELL
AVIATION...BELK/NOCERA/SIPPRELL
MARINE...NOCERA/SIPPRELL
CLIMATE...SIPPRELL


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