Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 191752
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
150 PM EDT SUN APR 19 2015

.SYNOPSIS...
CANADIAN HIGH PRESSURE BRINGS MUCH COOLER WEATHER TODAY. A WIND
SWEPT SOAKING RAIN IS EXPECTED MONDAY INTO MONDAY NIGHT. SCATTERED
SHOWERS AND MILD TEMPS TUESDAY MORNING GIVE WAY TO A DRYING TREND
DURING THE AFTERNOON. THEN MUCH COOLER WEATHER OVERSPREADS THE
AREA MID TO LATE NEXT WEEK ALONG WITH THE RISK OF SCATTERED
SHOWERS...ESPECIALLY DURING THE AFTERNOON AND EVENING.

&&

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

150 PM UPDATE...

MOSTLY SUNNY SKIES CONTINUE AT MID AFTERNOON.  LITTLE CHANGE
EXPECTED THROUGH THE DAYLIGHT HOURS...OTHER THAN A GRADUAL
THICKENING OF SOME HIGH LEVEL CLOUDINESS.  ONSHORE FLOW WILL
CONTINUE TO KEEP TEMPS IN UPPER 40S AND LOWER 50S ALONG THE
IMMEDIATE COAST INCLUDING BOSTON.  HIGHS STILL SHOULD REACH INTO THE
LOWER TO MIDDLE 60S ACROSS THE LOWER CONNECTICUT RIVER VALLEY.  IN
BETWEEN THE COAST AND LOWER CT RIVER VALLEY...EXPECT HIGHS WELL UP
INTO THE 50S TO NEAR 60.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
TONIGHT...

HIGH PRESSURE SHIFTS E AS LOW PRESSURE APPROACHES FROM THE W. WINDS
ENHANCE OUT OF THE E/SE AS CLOUDS LOWER AND THICKEN WITH A CHANCE OF
SHOWERS ACROSS W NEW ENGLAND TOWARDS MONDAY MORNING. YET BELIEVE LOW
MARINE STRATUS MAY BECOME AN ISSUE BEFOREHAND AS LONG E-FETCH OFF
THE WATERS COULD YIELD MOISTURE POOLING BENEATH THE DRY-INVERSION
PER LINGERING HIGH PRESSURE THAT CONDENSES WITH NOCTURNAL COOLING AS
WELL AS PROXIMITY OF COOLER WATERS. NOT THINKING SO MUCH FOG WITH
BRISK E/SE SURFACE WINDS BUT NOT OUT OF THE QUESTION. CHILLY OVER-
NIGHT WITH E/SE ONSHORE FLOW...LOWS AROUND THE UPPER-30S.

MONDAY INTO MONDAY NIGHT...

BREAKING THIS DOWN INTO TWO PARTS. THE FIRST PART BEING THE LOW- TO
MID-LEVEL WARM FRONT LIFTING NE ACROSS THE REGION MONDAY. SYNOPTIC
FRONTOGENETICAL FORCING OF DEEP-LAYER MOISTURE. DECENT H85-7 THETA-E
MOIST PLUME OF SUB-TROPICAL ORIGINS FUNNELED N BY ANOMALOUSLY STRONG
LOW-LEVEL S-FLOW OF 50-60 KNOTS THE H925-85 CONVERGENT NOSE OF WHICH
IS COLLOCATED ALONG AND REARWARD OF THE WARM FRONT. PWATS UP TO 1.5-
INCHES...ROUGHLY AROUND +2 STANDARD DEVIATIONS ABOVE NORMAL FOR THE
MONTH OF APRIL ACROSS THE NORTHEAST. COLLOCATION OF BEST INGREDIENTS
AROUND MID-MORNING INTO EARLY EVENING MONDAY DURING WHICH TIME THERE
IS THE EXPECTATION OF A BROAD SWATH OF RAIN WITH EMBEDDED HEAVIER
SHOWERS. LACK OF INSTABILITY SO NOT THINKING ANY THUNDER. WARM FRONT
SHOULD BE PROGRESSIVE WITH H85-3 30-40 KNOT S/SW-FLOW SO FOR THIS
TIMEFRAME THINKING AVERAGE PRECIPITATION AMOUNTS AROUND 0.75-INCHES
WITH LOCALLY HEAVIER AMOUNTS. NOT OUT OF THE QUESTION TO SEE LOCALES
EXCEED AN INCH. BUT THIS IS OVER A NEARLY 12-HOUR PERIOD. EVALUATING
SREF PROBABILITIES ALONG WITH FORECAST THINKING...PERHAPS NUISANCE
URBAN FLOODING BUT A LOW RISK OF FLASH FLOODING. NO LONGER ANY SNOW
COVER EITHER...AND THERE IS A BREAK IN THE ACTION OUTLINED BELOW.

EXPECTING A LULL BETWEEN PARTS AS DRIER AIR ENTRAINS REARWARD OF THE
WARM FRONT WITHIN THE WARM SECTOR. DEEP-LAYER MOISTURE FILLS BACK IN
AHEAD OF THE MID-LEVEL POSITIVELY-TILTED TROUGH. ACCOMPANYING LEFT-
FRONT-QUADRANT OF A JET STREAK ROUNDING THE BASE OF THE TROUGH HAS
THE POTENTIAL OF INVOKING A SURFACE REFLECTION OF LOW PRESSURE OVER
THE NE-CONUS...THAT OR STOUT BROADSCALE DIFFLUENCE ALOFT. COLLOCATED
WEAK INSTABILITY / CONDITIONALLY UNSTABLE MOIST ADIABATIC PROFILE...
AND THERE IS THE LIKELIHOOD OF CONTINUED WET WEATHER WITH POTENTIAL
ELEVATED THUNDER. NOT ABSOLUTELY CERTAIN ON OUTCOMES BUT THE FORCING
SEEMS APPARENT WITHIN A FAVORABLE ENVIRONMENT TO RESULT IN SOMETHING
AT LEAST SHOWERY...BUT CAN NOT RULE OUT POSSIBLE HEAVY RAIN AND AS
PREVIOUSLY MENTIONED THUNDER. SHOWALTERS < 0 WITH TOTAL-TOTALS > 50
IN ADDITION TO ELEVATED INSTABILITY. WILL GO CHANCE THUNDER. ONCE
AGAIN...NUISANCE FLOODING CONSIDERATIONS ESPECIALLY IN URBAN CENTERS
BUT LOW RISK FLASH FLOODING.

IN ALL LOOKING AT STORM-TOTAL RAINFALL FOR ROUGHLY A 24-HOUR PERIOD
OF 1.0-1.5 INCHES. WIDESPREAD RAIN. EMBEDDED HEAVY SHOWERS. CHANCE
THUNDER. SUBSEQUENT NUISANCE POOR-DRAINAGE FLOODING. BREEZY ONSHORE
SE-WINDS WITH GUSTS UP TO AROUND 35 MPH ALONG THE COAST. VISIBILITY
ISSUES WITH A COMBINATION OF FOG AND/OR HEAVY RAIN. FIRST SET OF
IMPACTS MID-MORNING INTO EVENING MONDAY...A LULL...THEN MORE WET WX
IS ANTICIPATED LATE MONDAY NIGHT. HAVE THE UMBRELLA HANDY.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
HIGHLIGHTS...

* TUE...SCATTERED MORNING SHOWERS THEN AN AFTERNOON DRYING TREND
* WED-SAT...COOLER WITH PERIODS OF SHOWERS...MAINLY DIURNAL

SYNOPTIC OVERVIEW AND MODEL PREFERENCES...

AMPLIFYING NORTHERN STREAM PHASES WITH SOUTHERN PLAINS CUTOFF LOW
TODAY TO FORM AN ANOMALOUS LOW/VORTEX OVER THE GREAT LAKES TUE.
THEREAFTER THIS UPPER LOW WILL BE VERY SLOW TO MOVE AS HIGH LATITUDE
BLOCKING DEVELOPS WITH POSITIVE HEIGHT ANOMALY EVOLVING OVER THE
SOUTHERN DAVIS STRAIT. THIS RESULTS IN A VERY SLOW MOVING VORTEX
FROM THE NORTHERN GREAT LAKES WED TO ONLY ADVANCING EASTWARD INTO
MAINE BY NEXT WEEKEND! WHILE THIS SEEMS EXTREME IT/S DOES HAVE
SUPPORT FROM TELECONNECTIONS AS AO/NAO AND EPO AS ALL THREE INDICES
GO NEGATIVE. GIVEN GOOD MODEL AGREEMENT A BLEND OF OPERATIONAL
GUIDANCE WILL WORK BEST AS A BASELINE FOR THIS PORTION OF THE
FORECAST.

DAILY DETAILS...

TUESDAY...TRAILING SHORT WAVE TROUGH AND ATTENDING COLD FRONT ALONG
WITH TRIPLE POINT LOW WILL BE MOVING ACROSS THE AREA DURING THE
MORNING. THIS WILL LIKELY YIELD A ROUND OF SHOWERS TO THE REGION.
INSTABILITY ALOFT MAY BE SUFFICIENT FOR ELEVATED THUNDER. IF NOT AT
THE VERY LEAST THIS INSTABILITY WILL ENHANCE SHOWER INTENSITY AND
ASSOCIATED DOWNPOURS. BY AFTERNOON DRY SLOT WILL BE WORKING ITS WAY
AROUND THE SYSTEM AND INTO THE REGION. SO SUSPECT WITH DEEPENING DRY
LAYER AND COLD ADVECTION TUE AFTERNOON WILL FEATURE A DRYING TREND
FROM SOUTH TO NORTH. IN ADDITION...MILD START TO THE DAY COMBINED
WITH BREAKS OF AFTERNOON SUNSHINE POSSIBLE AND WEAK COLD AIR
ADVECTION HIGHS WILL WARM INTO THE 60S.

WED AND THU...WHILE BOTH ENSEMBLES AND DETERMINISTIC GUIDANCE ARE IN
VERY GOOD AGREEMENT ON THE TIMING AND TRACK OF MID LEVEL CLOSED
LOW...AS EXPECTED MODELS ARE STRUGGLING WITH THE AMPLITUDE AND
TIMING OF INDIVIDUAL SHORT WAVES CIRCULATE AROUND THE VORTEX. THUS
LOW CONFIDENCE ON TIMING SHOWER THREAT THIS PERIOD. TRENDING COOLER
AS MID LEVEL LOW AND ASSOCIATED COLD POOL ALOFT ADVECT EASTWARD INTO
THE REGION. COOLER THU THAN WED.

FRIDAY AND SATURDAY...ECENS/EPS SUGGEST CORE OF COLD AIR ALOFT
SETTLES OVER THE AREA AS MID LEVEL LOW TRACKS ACROSS NORTHERN NY
STATE AND NORTHERN NEW ENGLAND WITH 850 TEMPS COOLING TO -2C TO
-5C! RISK OF SHOWERS TOO GIVEN COLD AIR AND CYCLONIC FLOW ALOFT. NOT
OUT OF THE QUESTION THAT SCATTERED RAIN SHOWERS MIX WITH SOME SNOW
AT TIMES ACROSS THE HIGHER TERRAIN!

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
FORECASTER CONFIDENCE LEVELS...

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

.SHORT-TERM /THIS AFTERNOON THROUGH MONDAY NIGHT/...

THIS AFTERNOON AND TONIGHT...HIGH CONFIDENCE IN VFR CONDITIONS
DESPITE INCREASING MID LEVEL CLOUDINESS.

MONDAY...MODERATE TO HIGH CONFIDENCE.  CONDITIONS DETERIORATE TO
MVFR FROM WEST TO EAST MONDAY MORNING INTO MID AFTERNOON IN
WIDESPREAD RAIN.  IFR CONDITIONS MAY DEVELOP BY MID TO LATE
AFTERNOON FROM WEST TO EAST...AS HEAVIER RAIN WORKS INTO THE REGION.
THIS IN RESPONSE TO WIDESPREAD RAIN WORKING IN FROM THE WEST.
EASTERLY WINDS WILL ALSO GUST TO 30 KNOTS ALONG THE COAST BY
AFTERNOON.

MONDAY NIGHT...MODERATE TO HIGH CONFIDENCE.  MAINLY LOW END MVFR TO
IFR CONDITIONS. PERIODS OF SHOWERS CONTINUE MONDAY NIGHT AS AT LEAST
THE SOUTHERN HALF OF THE REGION PROBABLY ENTERS THE WARM SECTOR.  A
FEW EMBEDDED THUNDERSTORMS ARE ALSO POSSIBLE...WITH THE HIGHEST RISK
ON THE SOUTH COAST NEAR THE NOSE OF THE LOW LEVEL JET BUT THEY ARE
POSSIBLE ACROSS THE ENTIRE REGION.  WHILE SOUTHEAST WINDS MAY GUST
TO 30 KNOTS ALONG THE COAST...LLWS OF 50 TO 60 KNOTS EXPECTED AT
2000 THOUSAND FEET WITH DEVELOPING LOW LEVEL JET.

KBOS TAF...HIGH CONFIDENCE THROUGH 14Z MONDAY IN VFR CONDITIONS.
MVFR CONDITIONS IN SOME RAIN ARE EXPECTED TO REACH THE TERMINAL
BETWEEN 15Z AND 18Z.

KBDL TAF...HIGH CONFIDENCE THROUGH 11 OR 12Z MONDAY IN VFR
CONDITIONS. MVFR CONDITIONS IN SOME RAIN ARE EXPECTED TO REACH THE
TERMINAL BETWEEN 12Z AND 14Z.

OUTLOOK...TUESDAY THROUGH THURSDAY...

TUE...MODERATE CONFIDENCE...SO UNCERTAINTY HOW QUICKLY CONDITIONS
WILL IMPROVE. IFR/MVFR TUE AM IN SCATTERED SHOWERS SHOULD IMPROVE TO
MVFR/VFR DURING THE AFTERNOON WITH DRYING TREND.

WED AND THU...LOW CONFIDENCE GIVEN UNCERTAINTY ON EXACT AMPLITUDE
AND TIMING OF INDIVIDUAL COLD FRONTS AND ATTENDING SHORT WAVE
TROUGHS THIS FAR OUT.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH MONDAY NIGHT/...

TODAY...HIGH CONFIDENCE. NORTH TO NORTHEAST WINDS GUSTING AROUND 25
KNOTS ACROSS NANTUCKET SOUND AND POINTS SOUTHEAST.  THOUGHT ABOUT A
SHORT FUSED SMALL CRAFT HEADLINE...BUT SINCE WE HAVE LONG DURATION
HEADLINES MONDAY INTO MONDAY NIGHT OPTED TO LET IT GO SINCE WINDS
SHOULD DIMINISH SOME OVER THE NEXT FEW HOURS.

TONIGHT...HIGH CONFIDENCE. ENHANCING SE-WINDS WITH GUSTS UP TO 20
KTS ACROSS THE WATERS BY MORNING. MARINE STRATUS DEVELOPING. MAYBE
SOME FOG ISSUES OVER THE WATERS. SEAS BUILDING TO 5 FEET ON THE
S-WATERS.

MONDAY...HIGH CONFIDENCE. WIDESPREAD RAIN WITH EMBEDDED HEAVIER
SHOWERS. VSBY RESTRICTIONS SUBSEQUENTLY ALONG WITH PATCHY FOG.
E/SE WINDS WITH GUSTS UP TO 30 KTS ALONG THE COAST. LOW RISK OF
GALES ON THE E OUTER WATERS. SEAS 8 TO 10 FEET. UP TO 12 FEET ON
THE S OUTER WATERS.

MONDAY NIGHT...MODERATE CONFIDENCE. SHOWERS WITH THE CHANCE OF
THUNDERSTORMS. PATCHY FOG AND VISIBILITY RESTRICTIONS REMAIN AN
ISSUE. CONTINUED E/SE WINDS WITH GUSTS UP TO 30 KTS ALONG THE
COAST. LOW RISK OF GALES ON THE E OUTER WATERS. SEAS 10 TO 12 FEET
ON THE OUTER WATERS.

OUTLOOK...TUESDAY THROUGH THURSDAY...

TUE...STRONG LOW LEVEL JET MON NIGHT MOVING OFFSHORE...THUS WINDS
DIMINISHING THRU THE DAY. LEFTOVER SE SWELLS WILL REMAIN LARGE. HIGH
FORECAST CONFIDENCE.

WED INTO THU...MODERATE CONFIDENCE. SOMEWHAT DRIER WITH IMPROVED
VSBYS FROM TUE AM. ANY PRECIP WILL BE MAINLY DIURNAL AND IN THE FORM
OF SCT SHOWERS.

&&

.TIDES/COASTAL FLOODING...
HIGH ASTRONOMICAL TIDES AND A PERIOD OF STRONG ONSHORE WINDS MAY
YIELD MINOR COASTAL FLOODING ALONG THE RI AND MA COASTLINE. HIGHEST
TIDE MON EVENING AND OVERNIGHT...AROUND 11 PM SOUTH COAST AND 2 AM
EASTERN MA. AT THE MOMENT MUCH OF THE MODEL GUIDANCE HAVE GREATEST
WIND AND SURGE OCCURRING AROUND LOW TIDE MON EVENING. ALTHOUGH HAVE TO
WATCH THIS CLOSELY GIVEN ONLY 6 HR TIME DIFFERENCE BETWEEN LOW AND
HIGH TIDE.

ESTOFS APPEARED MORE REASONABLE AND BULLISH THAN ETSS WITH SURGE
VALUES MON AFTN AND EVENING 1.0 TO 1.5 FT. WAVE MODELS SUGGEST SEAS
NEAR SHORE WAVES 10-15 FT AT THIS TIME. LIKELY NOT SUFFICIENT TO
SUPPORT A WATCH.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 5 AM MONDAY TO 6 AM EDT TUESDAY FOR
     ANZ230>237-250-251-254>256.

&&

$$
SYNOPSIS...NOCERA/SIPPRELL
NEAR TERM...FRANK
SHORT TERM...SIPPRELL
LONG TERM...NOCERA
AVIATION...FRANK/NOCERA
MARINE...FRANK/NOCERA/SIPPRELL
TIDES/COASTAL FLOODING...STAFF


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