Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 221117
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
717 AM EDT FRI MAY 22 2015

.SYNOPSIS...

CLEARING ACROSS THE REGION AS RAIN EXITS OFFSHORE. A COLD FRONT
WILL SWEEP THE REGION THIS AFTERNOON AHEAD OF WHICH AN ISOLATED
SHOWER IS POSSIBLE INTO EARLY EVENING. BEHIND THIS FRONT...FROST
AND MAYBE EVEN RECORD-BREAKING COLD...IS POSSIBLE FRIDAY NIGHT
INTO SATURDAY MORNING. DRY AND SEASONABLE FOR SUNDAY. A CHANCE OF
SHOWERS MAINLY TO THE NORTH AND WEST FOR MEMORIAL DAY...NOT
ANTICIPATING TO BE A WASHOUT. COULD BE WARM AND MUGGY WHILE
REMAINING MOSTLY DRY FOR MIDWEEK...AN UNCERTAIN FORECAST FOR THE
LATE-WEEK PERIOD.

&&

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

7 AM UPDATE...

MID LEVEL TROUGH AND SURFACE CIRCULATION MOVE OFFSHORE WITH SHORT
WAVE RIDGING BRIEFLY MOVING ACROSS THE AREA. THIS WILL RESULT IN
CLOUD COVER RAPIDLY ERODING AND MOVING OFFSHORE AS SEEN PER LATEST
SATELLITE TRENDS...GIVING WAY TO SUNSHINE BY MID MORNING.

HOWEVER LATER THIS AFTERNOON WILL HAVE TO WATCH VORTEX SWIRLING
SOUTHWARD FROM ONTARIO AND QUEBEC. THIS WILL PROVIDE CYCLONIC FLOW
AND A COLD FRONT ENTERING THE REGION THIS AFTERNOON. ALSO TEMPS
WILL BE RAPIDLY COOLING ALOFT WITH 500 MB TEMPS DROPPING TO -24C
BY DAYS END! THIS WILL PROVIDE STEEPENING MID LEVEL LAPSE RATES.
HOWEVER THE COLUMN BECOMES FAIRLY DRY THIS AFTERNOON. SO WHILE
THERE WILL LIKELY BE MODEST BUILD-UPS THIS AFTERNOON...DEEP DRY
AIR ALOFT WILL PROVIDE A CAP/LID ON CONVECTION.

THUS OTHER THAN A SPOT SHOWER THIS AFTERNOON/EARLY EVENING...
EXPECTING A PLESANT DRY AFTERNOON WITH SEASONABLY MILD TEMPS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...

*** NEAR RECORD COLD TEMPS TONIGHT INTO EARLY SAT MORNING ***

TONIGHT...

OTHER THAN A SPOT EVENING SHOWER ASSOCIATED WITH THE FRONTAL
PASSAGE...DRY WEATHER PREVAILS IN THE POST FRONTAL AIRMASS LATER
THIS EVENING AND OVERNIGHT.  STRONG COLD AIR ADVECTION BEHIND
DEPARTING FRONTAL BOUNDARY WITH 850 TEMPS FALLING TO -4C TO -6C BY
12Z SAT! THESE VALUES ARE -3 SD BELOW CLIMO! MORE TYPICAL OF A FALL-
LIKE AIRMASS. TEMPS ACROSS NORTHWEST MA WILL LIKELY APPROACH
FREEZING. THUS HAVE ISSUED A FREEZE WATCH FOR THIS AREA. TRICKY
FORECAST AS PGRAD MAY PRECLUDE WINDS FROM DECOUPLING...YIELDING
TEMPS NOT AS COLD AND PRECLUDING A FROST FORMING AND/OR A HARD
FREEZE. GIVEN HOW ANOMALOUSLY COLD THIS AIRMASS WILL BE COMBINED
WITH UNCERTAINTY ISSUED A FREEZE WATCH TO INCREASE PUBLIC AWARENESS.

AS FOR TEMPS...MANY LOCATIONS WILL FALL WITHIN 3-5 DEGREES OF RECORD
LOW VALUES. NOT VERY SUMMER-LIKE FOR MEMORIAL DAY WEEKEND.

SATURDAY...

A CHILLY START TO THE DAY BUT CORE OF THE COLD AIRMASS AND
ASSOCIATED VORTEX MOVE OFFSHORE. THIS WILL PROVIDE HEIGHT RISES OVER
THE AREA YIELDING PLENTY OF SUNSHINE AND A NICE REBOUND IN TEMPS.
MORNING LOWS IN THE 30S AND 40S SHOULD CLIMB WELL INTO THE 60S FOR
THE AFTERNOON. A BIT BREEZY WITH WEST WINDS 10 TO 20 MPH...BECOMING
SW LATE IN THE DAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

*/ HIGHLIGHTS...

 - DRY AND SEASONABLE FOR SUNDAY WITH INCREASING CLOUDS LATE
 - SHOWERS MEMORIAL DAY MAINLY N/W...NOT A WASHOUT!
 - MUGGY AND DRY PATTERN POTENTIALLY PREVAILING FOR MIDWEEK
 - A LOW CONFIDENCE FORECAST FOR THE LATE-WEEK PERIOD.

*/ DISCUSSION...

CONTINUANCE OF A CONSENSUS BLEND OF DETERMINISTIC/ENSEMBLE GUIDANCE.
CHALLENGES IN OBTAINING CONFIDENCE WITH THE WEAKER MARITIME FLOW AND
OVERALL FLAT-FLOW REGIME AS WELL AS INTERPRETING AND ANTICIPATING
CONVECTION. BUT THE PATTERN ECHOES SOME SIMILARITY TO EARLY MAY WITH
THE CONVERGENT FLOW AND WET-WEATHER HELD N BY THE BERMUDA RIDGE. FLY
IN THE OINTMENT THOUGH IS POSSIBLE WITH THE CUTOFF RETROGRADING LOW
LATE IN THE FORECAST PERIOD. BREAKING IT ALL OUT BELOW.

WILL KEEP IT DRY AND SEASONABLE FOR THE WEEKEND BENEATH INFLUENTIAL
BERMUDA HIGH WITH BREEZY SW-FLOW ALONG ITS W-PERIPHERY. ISENTROPIC
ASCENT THROUGH THE LOW- TO MID-LEVELS. TOP-DOWN MOISTENING WITH
INCREASING AND THICKENING CLOUDS TOWARDS LATE.

AS WE GO INTO MEMORIAL DAY...THERE IS A CHANCE OF SHOWERS. BUT HOLD
UP. NOT A WASHOUT. ENHANCING RIDGE AHEAD OF AN OPEN-WAVE DISTURBANCE
ACROSS THE W-HALF OF THE CONUS STRENGTHENS THE SURFACE BERMUDA HIGH.
THINK THIS WILL INCREASE THE SUBSIDENCE AND DRY AIR ACROSS OUR AREA
KEEPING THE SW WARM-MOIST CONVEYOR-BELT FLOW TO THE N/W. ITS LEADING
EDGE WARM-FRONT WITH A COLLOCATED CONVERGENT NOSE OF A LOW-LEVEL-JET
IS THE FOCUS OF LOW- TO MID-LEVEL FORCING THE BETTER OF WHICH IS
CLOSER TO FAVORABLE DYNAMICS AND ASSOCIATED DEEP-LAYER LIFT WITH THE
OPEN-WAVE IMPULSE TO THE W. SO PER DISCUSSION ABOVE AND EVALUATING
CIPS ANALOGS...CONFIDENCE IS THAT BETTER WET-WEATHER CHANCES WILL BE
N/W. NOT SURE ON TIMING BUT THINKING LATE MONDAY INTO MONDAY NIGHT.
WONDER WITH THE INCREASING SUBSIDENCE INVERSION WHETHER THERE WILL
BE ISSUES ALONG THE COAST WITH MARITIME STRATUS/FOG.

WITH A PREVALENT RIDGE AGAINST THE VORTEX OVER N CANADA...FEEL THE
CONVERGENT FLOW PATTERN THROUGH WHICH MID-LEVEL DISTURBANCES BECOME
STRETCHED REMAINS N. S NEW ENGLAND REMAINS WITHIN THE WARM-SECTOR
WITH MUGGY YET DRY CONDITIONS. BETTER WET-WEATHER CHANCES REMAIN N
AND W FOR THE MIDWEEK PERIOD. CONFIDENCE IS GAINED PER CIPS ANALOGS
BUT CONVECTION IS A TRICKY BEAST. CAN NOT RULE OUT EVOLUTION OF ANY
CONVECTION ANTICIPATED N AND W TO EVOLVE S AND E WITH THE STEERING
FLOW TOWARDS BETTER MOIST-INSTABILITY AXES...THOUGH PERHAPS ERODING
INTO AN ENVIRONMENT OF SUBSIDENCE AND DRY AIR. FAVOR THE CANADIAN
AND ECMWF BLEND OVER THE GFS.

BY LATE WEEK...RIDGE POTENTIALLY ERODES WITH THE RETROGRADGING CUT-
OFF LOW. FLAT-FLOW REGIME PREVAILING? PERHAPS MARITIME-CONVERGENT
FLOW REMAINS N KEEPING US BENEATH A ZONE OF DRY AIR / SUBSIDENCE?
LOW CONFIDENCE AT THIS TIME BUT PREFER THE ECMWF FOR THE FORECAST
TIME-FRAME.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...

FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH FRIDAY/...

12Z UPDATE...

TODAY...
VFR. IMPROVEMENT OVER CAPE / ISLANDS IMMEDIATE. COLD FRONT SWEEPS
THE TERMINALS THIS AFTERNOON. LOW RISK OF AN ISOLATED -SHRA. WINDS
BACK OUT OF THE NW AND BECOME BLUSTERY.

TONIGHT...WNW WINDS INCREASE UP TO 25 KT IN GUSTS. SPOT SHOWER
POSSIBLE UNTIL 03Z OR SO. OTHERWISE VFR AND DRY WEATHER.

SATURDAY...WEST WINDS UP TO 20 KT IN GUSTS. VFR AND DRY WEATHER
PREVAIL.

KBOS TERMINAL...HIGH CONFIDENCE IN TAF.

KBDL TERMINAL...HIGH CONFIDENCE IN TAF.

OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY...

VFR. BREEZY SW-WINDS. CIGS LOWERING AND THICKENING LATE.

MONDAY INTO MONDAY NIGHT...MODERATE CONFIDENCE.

LOW-END VFR TOWARDS THE LATER-HALF WITH INCREASING -SHRA CHANCES
MAINLY TO THE N AND W. LOW CONFIDENCE BUT PERHAPS IFR-LIFR MARINE
STRATUS / FOG ACROSS THE S/SE-COAST.

TUESDAY INTO TUESDAY NIGHT...MODERATE CONFIDENCE.

VFR. -SHRA CHANCES N AND W. CONTINUED LOW CONFIDENCE WITH IFR-LIFR
MARINE STRATUS / FOG ACROSS THE S/SE-COAST.

&&

.MARINE...

FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH SATURDAY/...

TODAY...LIGHT AND VARIABLE WINDS THIS MORNING BECOME WSW THIS
AFTERNOON AND INCREASE TO 25 KT LATE IN THE DAY IN GUSTS. LIGHT RAIN
EARLY THIS MORNING GIVES WAY TO DRY WEATHER AND GOOD VSBY BY MID
MORNING.

TONIGHT...COLD FRONT SWEEPS ACROSS THE WATERS WITH WNW WINDS GUSTING
UP TO 25 KT. GOOD VSBY.

SAT...WNW WINDS 15 TO 20 KT POSSIBLY GUSTING UP TO 25 EARLY BECOMES
WSW 15 TO 20 KT DURING THE AFTERNOON. NO PRECIP AND GOOD VSBY.

OUTLOOK...SATURDAY THROUGH TUESDAY...

SATURDAY NIGHT INTO SUNDAY NIGHT...HIGH CONFIDENCE.

SW-WINDS WITH GUSTS UP TO 20 KTS ESPECIALLY DURING THE DAY AND ALONG
THE NEAR-SHORE WATERS. LOOKING AT WAVES POTENTIALLY BUILDING IN
EXCESS OF 5 FEET ON THE OUTER WATERS.

MONDAY INTO TUESDAY NIGHT...MODERATE CONFIDENCE.

SW-FLOW WITH GUSTS IN EXCESS OF 20 KTS ESPECIALLY DURING THE DAY AND
ALONG THE NEAR-SHORE WATERS. THE PERSISTENT FETCH COULD POTENTIALLY
YIELD A PROLONGED PERIOD OF WAVES IN EXCESS OF 5-FEET ON THE OUTER
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...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR
     MAZ002-003.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 AM EDT
     SATURDAY FOR ANZ231>235-237-250-251-254>256.
     SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 8 AM EDT
     SATURDAY FOR ANZ230-236.

&&

$$

SYNOPSIS...NOCERA/SIPPRELL
NEAR TERM...NOCERA/SIPPRELL
SHORT TERM...NOCERA
LONG TERM...SIPPRELL
AVIATION...NOCERA/SIPPRELL
MARINE...NOCERA/SIPPRELL
CLIMATE...WFO BOX STAFF



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