Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 161805 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 205 PM EDT THU APR 16 2015 .SYNOPSIS... CANADIAN HIGH PRESSURE BUILDS INTO NEW ENGLAND THIS MORNING AND THEN OFFSHORE LATER TODAY...PROVIDING DRY AND SEASONABLY COOL WEATHER. A COLD FRONT BRINGS A PERIOD OF RAIN TO THE REGION FRI MORNING FOLLOWED BY A DRYING TREND IN THE AFTERNOON. WARM WEATHER EXPECTED SAT AHEAD OF A DRY COLD FRONT. CANADIAN HIGH PRESSURE BRINGS COOLER WEATHER SUNDAY. A COASTAL LOW DELIVERS A WIND SWEPT SOAKING RAIN TO THE REGION LATE MON INTO MON NIGHT. A DRYING TREND IS LIKELY TUE BUT THE RISK OF SHOWERS RETURNS MID WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 200 PM UPDATE... HIGH PRESSURE CONTINUE TO TAKE HOLD OVER THE REGION AS IT BEGINS TO PASS TO OUR SOUTH EAST THIS AFTERNOON. WINDS ARE BEGINNING TO SWITCH FROM THE EAST TO THE SOUTH THIS AFTERNOON. A FEW GUSTS NEAR 15 KTS WILL OCCUR ACROSS THE CT RIVER VALLEY. HIGH LEVEL CLOUDS ARE SLOWLY COMING INTO THE REGION THIS AFTERNOON...THIS IS AHEAD OF THE FRIDAY SYSTEM. THANKS TO FULL SUNSHINE TEMPS CONTINUE TO RISE WITH HIGH TOPPING OUT IN THE MID TO LOWER 60S AWAY FROM THE SOUTH COAST. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... TONIGHT INTO FRIDAY... S-STREAM DISTURBANCE CAPTURED BY THE N-STREAM QUASI-ZONAL FLOW INVOKES WEAK TROUGHING ACROSS THE NE CONUS CONTRIBUTING TOWARDS AN ISENTROPIC OVER-RUNNING EVENT OF AVAILABLE MOISTURE /AS NOTED BY THE PREVIOUS FORECASTER...A DECENT THETA-E RIDGE CREEPS INTO S NEW ENGLAND/. COMBINED WITH ENHANCED ASCENT BENEATH DIVERGENCE ALOFT COLLOCATED WITH THE RIGHT-REAR QUADRANT OF THE UPPER-LEVEL-JET YIELDS A PERIOD OF DEEP-LAYER FORCING POTENTIALLY ENHANCED ALONG THE W-SLOPES OF HIGHER TERRAIN PER OROGRAPHIC INFLUENCES. EXPECTING A BROAD AREA OF LIGHT SHOWERY WEATHER BEGINNING AROUND MIDNIGHT FRIDAY CONCLUDING TOWARDS EARLY AFTERNOON. RAINFALL AMOUNTS AROUND ONE- TO TWO-TENTHS WITH LOCALLY HIGHER AMOUNTS ACROSS THE HIGHER TERRAIN. WHILE CONVECTIVE INDICES ON THE THRESHOLDS...NOT SEEING MUCH TO WARRANT THE MENTION OF THUNDER. AS FOR TEMPERATURES...INCREASING CLOUD COVER DURING THE OVERNIGHT PERIOD WITH BREEZY ONSHORE S-FLOW USHERING HIGHER DEWPOINT AIR SHOULD KEEP CONDITIONS MILD AROUND THE LOW-40S...WHILE DECREASING CLOUD COVER TOWARDS FRIDAY EVENING SHOULD ALLOW ENOUGH SUNSHINE LATE IN THE DAY TO WARM TEMPERATURES TO AROUND THE LOW-60S RESULTING IN A WELL-MIXED BOUNDARY-LAYER UP TO H8 AND A BRIEF PERIOD OF GUSTY WINDS BEHIND THE ACCOMPANYING WEAK FRONTAL BOUNDARY TO THE WEAK TROUGHING DISTURBANCE ALOFT. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGHLIGHTS... * WARM SAT W/HIGHS IN THE 70S COOLING OFF INTO THE U50S/L60S SUNDAY * SEASONABLY COOL MUCH OF NEXT WEEK * WIND SWEPT SOAKING RAIN LIKELY LATE MON/MON NIGHT INTO EARLY TUE SYNOPTIC OVERVIEW... THIS FORECAST PERIOD BEGINS WITH AN AMPLIFIED NORTHERN STREAM ACROSS THE GREAT LAKES AND NORTHEAST WHICH YIELDS A FAIRLY LARGE TEMP SWING THIS WEEKEND IN SOUTHERN NEW ENGLAND. TEMPERATURES SAT WILL AVERAGE 10-15 DEGS WARMER THAN NORMAL THEN COOLING OFF TO NEAR NORMAL SUNDAY. THIS TRANSITION WILL BE MARKED BY A DRY FRONTAL PASSAGE SAT AFTN. THEN THE UPPER AIR PATTERN TRANSITIONS FROM SPLIT FLOW TO STREAMS PHASING OVER THE NORTHERN PLAINS SUN NGT YIELDING A CLOSED LOW ACROSS THE WESTERN GREAT LAKES MON THEN INTO ONTARIO MID WEEK. WITH THE CLOSED LOW AND COLD POOL ALOFT WELL WEST OF NEW ENGLAND TEMPERATURES HERE SHOULD BE CLOSE TO NORMAL. AS FOR PRECIP... SOUTHERN STREAM MOISTURE AND ASSOCIATED COASTAL LOW LATE MON/MON NIGHT INTO TUE LIKELY YIELDS A SOAKING WIND SWEPT RAIN ACROSS SOUTHERN NEW ENGLAND. A DRYING TREND LATER TUE BEHIND THIS DEPARTING FEATURE BUT ANOTHER THREAT OF SHOWERS AROUND MID WEEK AS ONTARIO CLOSED LOW PIVOTS NORTHERN STREAM ENERGY AND COOLING TEMPS ALOFT ACROSS NEW ENGLAND. OBVIOUSLY TIMING HERE IS SUBJECT TO CHANGE GIVEN DAYS6-7. MODEL PREFERENCES... 00Z DETERMINISTIC AND ENSEMBLE GUIDANCE ARE IN VERY GOOD AGREEMENT THIS PERIOD ESPECIALLY REGARDING TIMING OF SYNOPTIC FEATURES. THUS A USED A MODEL BLEND AS A BASE FOR THIS FORECAST PERIOD. DAILY SENSIBLE WEATHER DETAILS... FRI NIGHT...DRY AND MILD W/LOWS IN THE MU40S. SAT...ALMOST A SUMMER-LIKE DAY WITH A MILD START COMBINED WITH WAA AHEAD OF APPROACHING NORTHERN STREAM TROUGH AND ATTENDING COLD FRONT WILL PROMOTE TEMPS SOARING INTO THE L70S AWAY FROM THE SOUTH COAST. THESE TEMPS ARE ABOUT 15 DEGS ABOVE NORMAL! IMPRESSIVE SHORT WAVE TROUGH WITH DYNAMIC TROPOPAUSE LOWERING TO ABOUT 600 MB...FAIRLY ANOMALOUS FOR MID APR. HOWEVER PREFRONTAL ENVIRONMENT IS FAIRLY DRY. THUS ONLY EXPECTING MODERATE BUILDUPS IN THE LATE MORNING AND EARLY AFTERNOON WITH JUST A LOW RISK OF A SPOT SHOWER NORTHERN AND EASTERN MA. MUCH IF NOT THE ENTIRE REGION COULD REMAIN RAIN-FREE GIVEN THE DRY PREFRONTAL ENVIRONMENT. THIS IS CONSISTENT WITH RECENT MODEL TRENDS WHICH HAVE BEEN LOWERING POPS PAST TWO CYCLES. SUN...MUCH COOLER BEHIND THE FRONT WITH HIGHS SUN SLIPPING BACK TO THE U50S AND L60S...NEAR NORMAL FOR MID APR. NEVERTHELESS LOTS OF SUNSHINE AND LIGHT WINDS WILL YIELD FABULOUS WEATHER CONDITIONS. MARATHON MONDAY...A DRY START BUT A SOAKING WIND SWEPT RAIN LIKELY LATE MON/MON NIGHT. IMPRESSIVE MOISTURE PLUME FROM THE LOWER LATITUDES STREAMING NORTHWARD UP THE EASTERN SEABOARD WITH PWATS +2 STANDARD DEVIATIONS ABOVE CLIMO. WITHIN THIS MOIST/WARM CONVEYOR BELT SOUTHERLY WIND ANOMALIES APPROACHING +3 STANDARD DEVIATIONS ABOVE CLIMO. THESE WIND AND MOISTURE ANOMALIES SUGGEST A PERIOD OF HEAVY WIND SWEPT RAIN. IN FACT 00Z GEFS HAVE ABOUT 30-50% PROBABILITY OF 1" RAINFALL 12Z MON TO 12Z TUE...WITH 2" PROBS CREEPING INTO CT. DETERMINISTIC 00Z GFS AND ECMWF SIMILAR WITH QPF UP TO 1.5". IN ADDITION STRONG WAA IN THE 925-850MB LAYER WILL RESULT IN STEEPENING LAPSE RATES ABOVE THIS LAYER AND YIELD A RISK OF ELEVATED CONVECTION...WHICH WILL ONLY ENHANCE HEAVY RAINFALL POTENTIAL. TUE AND WED...UNSETTLED AT TIMES WITH CHANCE OF RAIN EARLY TUE FROM DEPARTING MON SYSTEM. THEN A DRYING TREND THEREAFTER WITH NEXT CHANCE OF SHOWERS SOMETIME MID WEEK AS GREAT LAKES/ONTARIO CLOSED LOW EJECTS ANOTHER TROUGH TOWARD SOUTHERN NEW ENGLAND. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY NIGHT/...HIGH CONFIDENCE. BEFORE 00Z...VFR. TONIGHT INTO TOMORROW...VFR TO START. CIGS WILL LOWER TO MVFR BY EARLY FRIDAY MORNING WITHIN -SHRA. EXPECT BREEZY S-WINDS GUSTING AROUND 20 KTS TOMORROW AFTERNOON. FRIDAY NIGHT...CONDITIONS IMPROVE TO VFR AS WINDS BACK OUT OF THE WEST...REMAINING GUSTY. KBOS TAF...HIGH CONFIDENCE IN TAF. WINDS SHOULD BE SHIFTING TO THE SOUTH AROUND 20-21Z. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...SATURDAY THROUGH MONDAY... SATURDAY...MAINLY VFR BUT WITH LOW RISK OF MVFR IN ISOLATED SHOWER SAT AFTN. WEST-SOUTHWEST WIND SATURDAY MORNING BECOMES NORTHWEST SATURDAY AFTERNOON WITH GUSTS TO 25 KNOTS. HIGH FORECAST CONFIDENCE. SUNDAY...VFR. DIMINISHING WIND. HIGH FORECAST CONFIDENCE. MONDAY...VFR EARLY THEN INCREASING CHANCE OF MVFR/IFR LATE IN THE DAY AND ESPECIALLY AT NIGHT WITH DEVELOPING WIND SWEPT RAIN. SOME UNCERTAINTY ON EXACT TIMING LENDS TO MODERATE FORECAST CONFIDENCE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY/...HIGH CONFIDENCE. AS S WINDS INCREASE WITH THE POTENTIAL FOR GUSTS OF 25 KTS AHEAD OF A WET WEATHER DISTURBANCE FOR LATE THURSDAY NIGHT INTO FRIDAY... WILL SEE SUBSEQUENT SWELL THAT WILL GENERATE WAVE HEIGHTS OF 4-5 FEET ON THE OUTER WATERS. BUT NOT ENOUGH CONFIDENCE TO ISSUE A SMALL-CRAFT ADVISORY JUST YET. IMPACTS MAY JUST REMAIN BELOW THRESHOLDS. OUTLOOK...FRIDAY NIGHT THROUGH MONDAY... FRIDAY NIGHT...IMPROVING VSBY WITH RAIN DURING THE DAYLIGHT HOURS OFFSHORE. LIGHT WINDS WITH PATCHY FOG NEAR SHORE. HIGH FORECAST CONFIDENCE. HIGH FORECAST CONFIDENCE. SATURDAY...A DRY COLD FRONT MOVES ACROSS THE AREA DURING THE AFTERNOON. HIGH FORECAST CONFIDENCE. SUNDAY...DIMINISHING WIND AND SEAS AS HIGH PRESSURE BUILDS OVER EASTERN CANADA. DRY WEATHER. HIGH FORECAST CONFIDENCE. MONDAY...COASTAL LOW LIKELY TRACKS NEAR OR ALONG THE SOUTHERN NEW ENGLAND COAST. THIS MAY YIELD EAST TO SOUTHEAST GALES FOR MUCH OF THE RI AND MA COASTAL WATERS. HEAVY RAIN LATE MON INTO MON NIGHT REDUCES VSBY. MODERATE FORECAST CONFIDENCE. && .FIRE WEATHER... DRY WEATHER CONCERNS CONTINUE. FOR TODAY...HIGH PRESSURE ACROSS THE REGION WILL RESULT IN ABUNDANT SUNSHINE ALLOWING TEMPERATURES TO WARM WELL INTO THE 60S. THOUGH HUMIDITY VALUES WILL DROP BELOW 30 PERCENT...WINDS VEERING OUT OF THE S WILL ONLY INCREASE TOWARDS 10-15 MPH BY EVENING. SO WHILE THE ABOVE CONDITIONS ARE BELOW POTENTIAL FIRE WEATHER THRESHOLDS...AND RED FLAG CONDITIONS ARE NOT ANTICIPATED...IT WILL CONTINUE TO BE CONSIDERABLY DRY AS IT HAS BEEN SO OVER THE PAST SEVERAL DAYS. SOME LIGHT SHOWERY WEATHER IS EXPECTED OVERNIGHT INTO FRIDAY...BUT EXPECTING LIGHT AMOUNTS AROUND A TENTH OR TWO THAT MAY NOT BE SUBSTANTIAL ENOUGH TO COUNTER THE RECENT DRY CONDITIONS. HIGH PRESSURE AND DRY WEATHER RETURN FOR FRIDAY AND SATURDAY DURING WHICH TIME MINIMUM RELATIVE HUMIDITY VALUES MAY FALL AT OR BELOW 30 PERCENT. A MORE SUBSTANTIAL SLUG OF RAIN IS EXPECTED MONDAY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...DUNTEN SHORT TERM...SIPPRELL LONG TERM...NOCERA AVIATION...NOCERA/DUNTEN MARINE...NOCERA/SIPPRELL FIRE WEATHER...

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