Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 220810
AFDBOX

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

.SYNOPSIS...
FAST-MOVING LOW PRESSURE WILL BRING A PERIOD OF LIGHT RAIN TO RHODE
ISLAND AND SOUTHEAST MASSACHUSETTS EARLY THIS MORNING FOLLOWED BY
CLEARING THEREAFTER. THEN A COLD FRONT MAY TRIGGER AN ISOLATED
SHOWER LATE THIS AFTERNOON AND 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/...

PER LATEST WATER VAPOR IMAGERY POTENT SHORT WAVE AND ASSOCIATED JET
STREAK MOVING ACROSS NJ/NYC/LI AREA WITH STRONG FORCING FOR ASCENT
DOWNSTREAM ON THE NOSE OF THE DRY SLOT ENTERING SOUTHERN NEW
ENGLAND. DEEP LAYER MOISTURE IS LACKING SO PRECIP IS SOMEWHAT
FRAGMENTED WITH ONE BAND OF LIGHT RAIN FORMING OVER NORTHWEST MA AND
THE MAIN RAIN SHIELD ALONG THE COAST OF CT/RI AND MA. THIS IS WHERE
BEST DEEP LAYER /ESP LOW LEVEL/ MOISTURE IS LOCATED IN RESPONSE TO
SURFACE CIRCULATION TRACKING NEAR THE 40N/70W BENCHMARK.

FOR THE REMAINDER OF THE EARLY MORNING HOURS THE STEADIEST AND MORE
APPRECIABLE RAINFALL WILL BE FOCUSED ALONG THE SOUTH COAST OF MA AND
RI WITH LIGHTER RAINS NORTHWARD INTO THE GREATER PROVIDENCE AREA
NORTHEASTWARD INTO PLYMOUTH COUNTY OF MA. A SEPARATE BUT LIGHTER
BAND OF RAIN WILL IMPACT MUCH OF NORTHERN MA.

AFTER 12Z THIS 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...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 /08Z 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/...

TODAY...RAIN SHIELD TRACKS OVER SOUTHEAST CT...SRN HALF OF RI AND
INTO SOUTHEAST MA THRU 12Z...THEN OFFSHORE. MVFR WITHIN THIS AREA
ALONG WITH LOW RISK OF BRIEF IFR. RAIN MAINLY LIGHT. VFR ELSEWHERE.
THEN BECOMING VFR AFT 12Z AS RAIN MOVES OFFSHORE. LOW RISK OF A
SPOT SHOWER LATE THIS AFTERNOON INTO EARLY EVENING.

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
SHORT TERM...NOCERA
LONG TERM...SIPPRELL
AVIATION...NOCERA/SIPPRELL
MARINE...BELK/NOCERA/SIPPRELL
CLIMATE...STAFF


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