Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 241756
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
156 PM EDT TUE MAR 24 2015

.SYNOPSIS...
HIGH PRESSURE BRINGS DRY BUT COLD CONDITIONS TONIGHT...THEN MOVES
OFFSHORE WEDNESDAY ALLOWING MORE SEASONABLE TEMPERATURES TO
RETURN. A WARM FRONT BRINGS A PERIOD OF RAIN LATE WEDNESDAY
AFTERNOON AND EVENING FOLLOWED BY MILD BUT SHOWERY WEATHER THU. A
COLD FRONT THEN SWEEPS ACROSS THE REGION THURSDAY NIGHT BRINGING
HEAVY SHOWERS TO THE AREA. COLDER WEATHER FOLLOWS LATE FRIDAY INTO
THE WEEKEND WITH SNOW SHOWERS POSSIBLE FRI NIGHT INTO SAT NIGHT.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...

2 PM UPDATE...

DESPITE FULL LATE MARCH SUN ANOMALOUS COLD/DRY AIRMASS ONLY
WARMING INTO THE LOW AND MID 30S ACROSS THE AREA AT 130 PM.
ALTHOUGH LIGHT WINDS AND FULL SUNSHINE TAKING A BIT OF THE EDGE
OFF THE COOL TEMPS.

OCEAN EFFECT CLOUDS OVER CAPE COD CONTINUE TO SLIDE SOUTH AND
SHOULD PUSH OFFSHORE IN A FEW HOURS.

WEAK PRES GRADIENT HAS RESULTED IN LIGHT AFTERNOON SEABREEZES.

OTHERWISE PREVIOUS FORECAST LOOKS TO BE IN GOOD SHAPE.


&&

.SHORT TERM /7 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...

2 PM UPDATE...

TONIGHT...

ANOTHER CHILLY NIGHT AHEAD AS DRY AIRMASS IN PLACE /DEW PTS IN THE
SINGLE DIGITS AND TEENS/ COMBINES WITH MAINLY CLEAR SKIES AND LIGHT
WINDS IN RESPONSE TO 1030 MB HIGH DRIFTING OVER THE REGION. COLDEST
TEMPS WILL BE REALIZED WHERE RADIATIONAL COOLING IS MAXIMIZED...
VALLEYS AND LOW LYING AREAS. THUS MIN TEMPS WILL BE DERIVED FROM THE
COLDEST MOS DATASET ALONG WITH UNDERCUTTING GUIDANCE IN THE
TYPICALLY COLDER LOCATIONS.

WEDNESDAY...

CHILLY START TO THE DAY BUT SUNSHINE AND LIGHT SOUTHERLY FLOW WILL
HELP BOOST TEMPS INTO THE 40S DURING THE AFTERNOON. HOWEVER STRONG
WARM AIR ADVECTION /WARM FRONT ALOFT/ ON THE NOSE OF THE 850-700 MB
JET WILL RESULT IN A PERIOD OF OVERRUNNING RAIN FROM LATE
AFTERNOON INTO THE EVENING. COLUMN WARM ENOUGH TO SUPPORT RAIN
ESPECIALLY WITH VERY WARM NOSE OF +4C TO +5C AROUND 850-800 MB
LAYER. HOWEVER PREFRONTAL AIRMASS IS STILL COOL AND VERY DRY IN
THE LOW LEVELS PROVIDING COLD WET BULB TEMPS OF AROUND -6C AT 925
MB. THIS MAY BE SUFFICIENT FOR A LOW RISK OF SOME SLEET TO MIX IN
WITH THE RAIN AT TIMES ACROSS THE INTERIOR LATE AFTERNOON/EARLY
EVENING. IN ADDITION SURFACE WET BULB TEMPS INLAND ARE CLOSE TO
FREEZING...SO NOT COMPLETELY OUT OF THE QUESTION THAT A FEW
LOCATIONS COULD HAVE BRIEF SPOTTY FREEZING RAIN. HOWEVER SHOULD
NOT BE MUCH OF A PROBLEM GIVEN SUNSHINE IN THE MORNING INTO EARLY
AFTERNOON WILL WARM PAVEMENT SUFFICIENTLY FOR ICING NOT TO BE AN
ISSUE.

NEVERTHELESS...ONCE RAIN DEVELOPS LATE IN THE AFTERNOON AND EVENING
EXPECT A NOTICEABLE TEMP DROP GIVEN COLD WET BULB TEMPS.

WED NIGHT...

ANY EVENING RAIN SHOULD TAPER OFF BY MIDNIGHT OR THEREAFTER AS
INITIAL BURST OF WARM AIR ADVECTION LIFTS OFF TO THE NORTHEAST.
STRONG LOW LEVEL WARM ADVECTION THEN DEVELOPS SECOND HALF OF THE
NIGHT PROVIDING TEMPS RISING TOWARD MORNING ESPECIALLY ACROSS RI AND
SOUTHEAST MA. THUS WILL FOLLOW A NON DIURNAL TEMP TREND WED NIGHT
WITH MODEL 2 METER TEMPS PROBABLY MORE REALISTIC THAN MOS. THIS
LOW LEVEL WARM ADVECTION ACROSS EXISTING SNOW COVER MAY RESULT IN
AT LEAST SOME PATCHY FOG OVERNIGHT INTO THU AM.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...

HIGHLIGHTS...

* WARM BUT HEAVY RAIN ON THURSDAY AHEAD OF COLD FRONT
* BLUSTERY AND BELOW AVERAGE TEMPS FOR THE WEEKEND
* WEAK DISTURBANCE POSSIBLE ON MONDAY

MODEL GUIDANCE...

LATEST GUIDANCE IS SUGGESTING THAT THE AMPLIFIED WRN RIDGE/ERN
TROUGH PATTERN FCST TO BE IN PLACE FOR MOST OF THE PERIOD MAY BEGIN
TO EVOLVE TOWARD FLATTER MEAN FLOW BY NEXT WEEK. WHILE SOME EMBEDDED
DETAILS WITHIN THE RIDGE/TROUGH CONFIGURATION HAVE BEEN AND CONTINUE
TO BE PROBLEMATIC... ENSEMBLE GUIDANCE AND THE LIKELY TREND TOWARD
FLATTER FLOW SUGGEST THAT OVERALL PREDICTABILITY OF SIGNIFICANT
FEATURES MAY DECLINE RAPIDLY AFTER EARLY NEXT WEEK.

OVERALL AMPLIFIED PATTERN WILL CONTINUE WITH 00Z GUIDANCE IN GOOD
AGREEMENT. STILL SOME TIMING/INTENSITY ISSUES FOR UPCOMING WED PM
INTO FRIDAY SYSTEM. SEVERAL SHORTWAVES WILL MOVE THROUGH THE FLOW
DEVELOPING WAVES ALONG STALLED FRONTAL SYSTEM. DEPENDING ON INTENSITY
AND STRENGTH...COULD HAVE FLOODING ISSUES FROM LEFTOVER SNOWPACK AND
HIGH DEWPOINTS. OTHERWISE GUIDANCE IS IN GOOD AGREEMENT WITH POLAR
JET DROPPING SOUTH...BRINGING BELOW AVG TEMPS FOR THE WEEK. GUIDANCE
IS THEN SPLIT ON WEAK WAVE PASSING ON MONDAY.

DETAILS...

* THURSDAY INTO FRIDAY...MODERATE CONFIDENCE. HIGH CONFIDENCE
  PRECIP WILL OCCUR LOWER CONFIDENCE ON EXACT TIMING.

JUST ONE OF MANY SHORTWAVES WILL PASS THROUGH THE FLOW ON WEDNESDAY
NIGHT. AS WARM FRONT APPROACHES...TEMPS AND DEWPOINTS WILL REMAINS
STEADY/SLOWLY INCREASE THROUGH THE NIGHT. THIS WILL INCREASE THE FOG
POTENTIAL AND WE COULD SEE WIDESPREAD DENSE FOG. LOW CONFIDENCE ON
WHERE EXACTLY THIS FAR OUT.

PRECIP WILL BEGIN TO INCREASE IN THE MORNING HOURS AS THE FIRST WAVE
WILL MOVE OFFSHORE BY EARLY WED NIGHT. THIS PRECIP WILL BE ALONG THE
EAST TO WEST WARM FRONT AS IT MOVES INTO SOUTHERN NEW ENGLAND.
BIGGEST QUESTION IS HOW FAR NORTH WILL THE FRONT REACH. GUIDANCE
SEEMS TO ALWAYS STRUGGLE WITH THAT ASPECT...THEREFORE TRENDED A
MODEL BLEND TO GET A DOWN THE MIDDLE APPROACH. TEMPS SOUTH OF THE
FRONT WILL REACH INTO THE MID TO PERHAPS THE UPPER 50S WHILE
NORTHWARDS WILL STAY IN THE 40S. REGARDLESS RAIN WILL BE
OVERSPREADING FROM SOUTH TO NORTH ON THURSDAY WITHIN A VERY MOIST
ENVIRONMENT AS DEWPOINTS CONTINUE TO RISE.

THURSDAY AFTERNOON INTO THE OVERNIGHT HOURS SEEMS TO BE WHEN THE
HEAVIEST PRECIP WILL OCCUR. NEXT SHORTWAVE WILL PUSH THROUGH
ALLOWING FOR SURFACE LOW DEVELOPMENT ALONG THE EXTENDED COLD FRONT
APPROACHING SOUTHERN NEW ENGLAND. THIS FRONT WILL BE THE FOCUS ON
THE HEAVY PRECIP DURING THE AFTERNOON/EVENING HOURS. SW LLJ WILL BE
ON THE INCREASE REACHING 50-65 KTS ACROSS THE REGION POOLING IN MORE
MOISTURE INTO THE AREA. PWAT VALUES ARE ABOVE 1 INCH WHICH IS 2 TO 3
STANDARD DEVIATIONS AWAY WHILE THE MOISTURE FLUX IS 4 TO 5 STANDARD
DEVIATIONS AWAY. DUE TO THE AMOUNT OF MOISTURE IN THE ATMOSPHERE AND
THE APPROACHING FRONTAL SYSTEM...EXPECT HEAVY DOWNPOURS AND PERHAPS
ISOLATED THUNDER. IN FACT MODELS HAVE INCREASED THEIR QPF FROM JUST
12 HOURS AGO. WITHIN THESE HEAVY DOWNPOURS...WE COULD MIX DOWN THE
GUSTY WINDS ALOFT DOWN TO THE SURFACE.

THIS HIGHLY ANOMALOUS SYSTEM COMBINED WITH THE SNOW PACK...COULD
SEE SIGNIFICANT INCREASE IN RUNOFF AND RISES IN AREA STREAMS FROM
WHAT WILL LIKELY BE MAJOR SNOWMELT. MORE DETAILS IN HYDRO SECTION.

AS FRONT PASSES THROUGH PRECIP WILL END FROM WEST TO EAST OVERNIGHT
THURSDAY INTO FRIDAY MORNING. FRIDAY WE WILL BEGIN TO DRY OUT AS
TEMPS WARM INTO THE MID TO LOWER 40S. A SECONDARY COLD FRONT WILL
PASS THROUGH LATE FRIDAY BRINGING IN STRONG CAA AND BLUSTERY
CONDITIONS.

* THE WEEKEND...HIGH CONFIDENCE IN TEMPS.

DEEP UPPER LEVEL TROUGH WILL MOVE FROM THE GREAT LAKES TO OVER
SOUTHERN NEW ENGLAND. THIS TROUGH AXIS WILL SETTLE OVER THE REGION
LATE FRIDAY INTO SATURDAY. WELL BELOW AVG TEMPS ARE EXPECTED AT 850MB
TEMPS DROP DOWN TO -12C. HOWEVER...WEAK RIDGE WILL PASS THROUGH ON
SUNDAY INCREASE TEMPS AND ALLOWING FOR A MOSTLY PLEASANT DAY WITH
HIGH TEMPS REACHING THE MID TO UPPER 40S.

MONDAY...LOW CONFIDENCE.

NEXT UPPER LEVEL DISTURBANCE WILL IMPACT SOUTHERN NEW ENGLAND LATE
SUNDAY INTO MONDAY. THIS SYSTEM WILL BRING PRECIP AND COOLER TEMPS
TO THE REGION. THIS MAY CAUSE FOR P-TYPE ISSUES BUT IT WILL NEED TO
BE WATCHED OVER THE NEXT SEVERAL DAYS.

&&

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

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

2 PM UPDATE...

HIGH CONFIDENCE THROUGH WEDNESDAY THEN SOME UNCERTAINTY ON EXACT
TIMING OF LOWER CIGS/VSBYS WITH RAIN LATE WED INTO WED EVENING.

VFR THROUGH EARLY WED AFTERNOON THEN MVFR CIGS IN A PERIOD OF RAIN
LATE WED AFTERNOON AND EVENING. RAIN ENDS OVERNIGHT WED NIGHT BUT
CIGS AND VSBYS LOWER TO IFR IN AREAS OF FOG.

KBOS TAF...HIGH CONFIDENCE THRU 21Z WED THEN SOME UNCERTAINTY ON
EXACT TIMING OF LOWERING CONDITIONS.

KBDL TAF...HIGH CONFIDENCE THRU 18Z WED THEN SOME UNCERTAINTY ON
EXACT TIMING OF LOWERING CONDITIONS.

OUTLOOK...THU THROUGH SATURDAY...MODERATE TO HIGH CONFIDENCE

THURSDAY MORNING...GENERALLY VFR CONDITIONS EXCEPT POSSIBLY MVFR
CIGS ALONG SOUTH COAST WEDNESDAY NIGHT INTO THE THURSDAY MORNING.
IFR IS POSSIBLE IN FOG OVERSPREADING THE REGION.

THURSDAY AFTERNOON AND NIGHT...WIDESPREAD MVFR CIGS AND VSBYS IN
SHOWERS. MAY SEE AREAS OF IFR CIGS/VSBY IN HEAVY DOWNPOURS. LOW
RISK OF THUNDER.

FRIDAY THROUGH SATURDAY...HIGH UNCERTAINTY. COULD SEE A PERIOD OF
MVFR OR EVEN IFR IN SNOW SHOWERS FRI NIGHT INTO SAT NIGHT
ESPECIALLY RI AND SOUTHEAST MA.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

2 PM UPDATE...

HIGH CONFIDENCE THROUGH WEDNESDAY THEN SOME UNCERTAINTY HOW STRONG
WINDS GET WED NIGHT AND BEYOND.

TONIGHT...LIGHT WINDS AND TRANQUIL SEAS WITH HIGH PRES BUILDING
OVERHEAD. GOOD VSBY AND DRY WEATHER TOO.

WED...LIGHT/VARIABLE WINDS BECOME SOUTH DURING THE AFTERNOON AS
HIGH PRES MOVES OFFSHORE. CHANCE OF RAIN LATE IN THE DAY.

WED NIGHT...SSW WINDS INCREASE TO POSSIBLY 20-25 KT LATE. VSBY
LOWERS IN AREAS OF FOG.

OUTLOOK...THU THROUGH SATURDAY...

MODERATE TO HIGH CONFIDENCE THROUGH FRIDAY. MODERATE CONFIDENCE
FRIDAY NIGHT INTO SATURDAY.

CONDITIONS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
CONDITIONS WEDNESDAY NIGHT THROUGH THURSDAY MORNING. STRONG SW WINDS
DEVELOP ALOFT THURSDAY AFTERNOON AND EVENING BUT ANTICIPATE ONLY
SOME OF THE WINDS MIXING TO THE SURFACE. MAY NEED A GALE WATCH BUT
DEF SMALL CRAFT ADVISORY. AREAS OF DENSE FOG MAY BE A SIGNIFICANT
HAZARD WED NIGHT INTO THURSDAY...ESPECIALLY ALONG THE SOUTH COASTAL
WATERS.

THERE IS A LOW RISK THAT JUST ENOUGH COLD AIR ADVECTION WITH
NORTHERLY WINDS FRIDAY NIGHT AND SATURDAY COULD CAUSE A PERIOD
NEARING SMALL CRAFT ADVISORY WIND GUSTS...BUT CURRENTLY LOOKS MORE
LIKELY THAT GUSTS WILL NOT EXCEED 20 KT.

&&

.HYDROLOGY...
SEVERAL FACTORS ARE OCCURRING ON THURSDAY WHICH WILL INCREASE THE
POTENTIAL FOR RUNOFF AND RISES IN AREA STREAMS. FIRST IS THE
ANOMALOUS DEWPOINTS WHICH WILL BE STREAMING INTO THE REGION. 40+F
DEWPOINTS WILL HELP EAT AWAY AT THE SNOW PACK ON TOP OF 50+ DEGREE
TEMPERATURES. THIS MOISTURE LADEN AIR WILL ALLOW FOR CONDENSATION
AND THUS HEAT UPON THE SNOW PACK INCREASING THE RATE OF MELTING.
GUIDANCE SNOWS THAT THERE IS STILL ABOUT 2-5 INCHES OF WATER WITHIN
THE SNOW PACK OR SWE...ACROSS THE REGION SO THESE HIGH DEWPOINTS
WILL HELP RELEASE A GOOD PORTION OF THIS WATER.

SECOND ASPECT IS THE UPCOMING RAIN POTENTIAL. EXPECT AROUND AN INCH
OF QPF TO OCCUR ACROSS SOUTHERN NEW ENGLAND WITH HIGHER AMOUNTS
LIKELY WITHIN HEAVIER DOWNPOURS BY THURSDAY NIGHT INTO FRIDAY
MORNING.

THEREFORE COMBINING THE RAPID SNOW MELT WITH THE UPCOMING QPF...WE
COULD SEE ON THE ORDER OF 1.5-3 INCHES OF WATER HEADING INTO AREA
RIVERS AND STREAMS. CURRENTLY THINK THAT SOME RIVERS WILL GET CLOSE
TO OR ABOVE MINOR FLOODING...BUT MOST WILL FALL SHORT OF FLOOD
LEVELS. HOWEVER IF DEWPOINTS ARE HIGHER OR QPF INCREASES THEN
SEVERAL STREAMS WILL GO INTO FLOOD.

LASTLY...MINOR URBAN FLOODING ALSO LOOKS LIKE A POSSIBILITY ESP IF
DRAINAGE SYSTEMS ARE STILL BLOCKED FROM SNOW.

&&

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

&&

$$
SYNOPSIS...NOCERA
NEAR TERM...NOCERA
SHORT TERM...NOCERA
LONG TERM...DUNTEN
AVIATION...NOCERA/DUNTEN
MARINE...NOCERA/DUNTEN
HYDROLOGY...



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