Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 232115 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 415 PM EST TUE DEC 23 2014 .SYNOPSIS... WEAK LOW PRESSURE PASSES OFFSHORE TONIGHT. A MUCH STRONGER STORM TRACKING ACROSS THE GREAT LAKES WILL BRING HEAVY RAIN...GUSTY WINDS AND MINOR COASTAL FLOODING WEDNESDAY INTO CHRISTMAS MORNING. DRY WEATHER WITH ABOVE NORMAL TEMPERATURES WILL FOLLOW FROM CHRISTMAS AFTERNOON INTO SAT. A COLD FRONT MAY BRING A FEW RAIN OR SNOW SHOWERS SUNDAY THEN A STORM MAY AFFECT THE REGION SUN NIGHT INTO MON...BUT IT COULD ALSO PASS WELL TO THE SOUTH. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... TWO AREAS OF SHOWERS ON RADAR ARE MOVING EAST-NORTHEAST...WITH THE TRAILING EDGES MOVING EAST OF OUR AREA EARLY TONIGHT. ADDITIONAL LIGHT SHOWERS AND CLOUDS/FOG/DRIZZLE SHOULD LINGER THROUGH THE NIGHT AS THE LOW LEVEL EAST-NORTHEAST FLOW OFF THE GULF OF MAINE CONTINUES. DEWPOINTS RANGE FROM THE MID 30S NORTHWEST THROUGH THE 40S MOST AREAS...WHICH SHOULD SERVE AT A LOWER BOUNDARY FOR MIN TEMPS. ACTUALLY TEMPERATURES SHOULD REMAIN NEAR STEADY OVERNIGHT. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... UPPER RIDGE BUILDS TO HIGHER AMPLITUDE BUT SHIFTS EAST OF NEW ENGLAND. DEEP TROUGH OVER THE PLAINS MOVES EAST. THIS BRINGS A DEEP SOUTH-SOUTHWEST FLOW OVER THE EASTERN USA WITH A STRONG 150 KNOT UPPER JET DRIVING NORTH THROUGH IT. THIS WILL BRING AN AIRMASS WITH PRECIPITABLE WATER VALUES OF 1.5" OR HIGHER...OVER 3 STD DEVIATIONS ABOVE NORMAL AND NEAR THE MAXIMUM HISTORICAL VALUE. LOW LEVEL SOUTHWEST JET OF 50-65 KNOTS ARRIVES WEDNESDAY AFTERNOON AND CONTINUES THROUGH WEDNESDAY NIGHT...THEN SHIFTS EAST CHRISTMAS MORNING. LOW PRESSURE LIFTS NORTH FROM THE GULF OF MEXICO TO THE GREAT LAKES...THEN SWINGS A COLD FRONT TOWARD NEW ENGLAND. GOOD MODEL AGREEMENT ON MOVEMENT OF THE FRONT...REACHING THE CONNECTICUT VALLEY BY 12Z THURSDAY. THIS SYSTEM WILL GENERATE GOOD LOW LEVEL LIFT...AND BY WEDNESDAY NIGHT THE APPROACHING UPPER JET SHOULD SUPPORT LIFT FROM THE UPPER PART OF THE STORM. COMBINE THIS WITH THE VERY HUMID AIRMASS...AND WE SHOULD EXPECT PERIODS OF RAIN WEDNESDAY AND ESPECIALLY WEDNESDAY NIGHT WITH SOME HEAVY DOWNPOURS. THIS SHOULD BRING AN ADDITIONAL 1-2 INCHES OF RAIN. THE DYNAMICS MAY ALSO DRIVE SOME ISOLATED THUNDER...WITH THE BEST CHANCE LATE WEDNESDAY NIGHT AHEAD OF THE COLD FRONT. CONCERNS...RAIN. THE AIRMASS HAS A HIGH RAINFALL POTENTIAL BUT MAY NOT TAP ALL OF THAT POTENTIAL. HOWEVER THERE MAY BE SOME LOCALLY HEAVIER DOWNPOURS THAT PUSH TOTALS IN A FEW SPOTS ABOVE 2 INCHES. WITH OR WITHOUT THIS...THE AMOUNT OF RAIN MAY BE ENOUGH TO CAUSE SOME URBAN/POOR DRAINAGE FLOODING. WE HAVE ISSUED A FLOOD WATCH FOR MOST OF OUR AREA FOR LATE WEDNESDAY THROUGH THURSDAY MORNING. CONCERNS...WIND...PER BUFKIT THE LOW LEVEL JET OF 55 TO 65 KNOTS WILL REACH DOWN TO ABOUT 1000 FEET AGL. THIS WILL BE LOW ENOUGH TO REACH THE HIGHER HILLTOPS AND MAY INCH CLOSER TO THE SURFACE. IT IS FACING A STRONG TEMPERATURE INVERSION NEAR THE GROUND WHICH MAY KEEP SOME OF THIS WIND ABOVE THE GROUND. HEAVY DOWNPOURS MAY PROVIDE A CHANNEL TO BRING SOME OF THAT WIND DOWN THE FINAL THOUSAND FEET TO THE SURFACE. IN ANY CASE...WE EXPECT SOME GUSTY SOUTH WINDS WEDNESDAY AFTERNOON THROUGH 12Z THURSDAY WITH VALUES TO AT LEAST 30 KNOTS AND POSSIBLY APPROACHING 40 KNOTS. CONCERNS...COASTAL FLOODING...ASTRONOMICAL TIDES WILL REMAIN HIGH WITH A CONTINUED SOUTHEAST WIND ALONG THE MASS EAST COAST DURING THE MORNING. MORE ON THIS IN THE COASTAL FLOOD SECTION. WARM ADVECTION WEDNESDAY AFTERNOON WILL BRING WARMER TEMPERATURES WITH VALUES REACHING THE 50S AND POSSIBLY REACHING 60 IN SOME SPOTS. TEMPERATURES AND DEW POINTS WEDNESDAY NIGHT WILL NOT FALL MUCH WITH VALUES LINGERING IN THE 50S. && .LONG TERM /THURSDAY THROUGH TUESDAY/... HIGHLIGHTS... * RAIN...HEAVY AT TIMES AND UNSEASONABLY MILD WEDNESDAY INTO CHRISTMAS MORNING WITH GUSTY SOUTH WINDS IN THE COASTAL PLAIN WED NIGHT * DRY AND WINDY CHRISTMAS AFTERNOON WITH GUSTS TO 45 MPH POSSIBLE * CONTINUED DRY WITH ABOVE NORMAL TEMPS FRI AND SAT * A STORM MAY AFFECT THE REGION SUN NIGHT INTO MON...BUT CONFIDENCE IS LOW OVERVIEW... HIGH AMPLITUDE TROF OVER THE MS VALLEY ON WED LIFTS NE THROUGH THE GT LAKES AND INTO CANADA BY CHRISTMAS DAY. DEEP SOUTHERLY FLOW AND ANOMALOUS PWAT AIRMASS AHEAD OF THE TROF WILL BRING A PERIOD OF HEAVY RAINFALL TO THE REGION WED AND WED NIGHT BEFORE DRYING OUT CHRISTMAS AFTERNOON. BEYOND CHRISTMAS...MODELS IN AGREEMENT ON ANOMALOUSLY STRONG MID LEVEL RIDGE OVER THE SE US FRI THROUGH THE WEEKEND WHICH WILL RESULT IN CONTINUED MILD CONDITIONS. BY SUNDAY...NORTHERN STREAM SHORTWAVE DELIVERS A COLD FRONT...THEN THERE IS QUITE A BIT OF UNCERTAINTY REGARDING A SOUTHERN STREAM SHORTWAVE EJECTING NE FROM SOUTHERN PLAINS TROF WITH POSSIBLE FRONTAL WAVE SUN NIGHT INTO MON. PREVIOUS RUNS OF THE ECMWF SHOWED A MORE AMPLIFIED SHORTWAVE AND FRONTAL WAVE...BUT LATEST RUN OF THE ECMWF HAS TRENDED FLATTER AND MORE SUPPRESSED ALTHOUGH IT STILL BRINGS SOME SNOW SUN NIGHT INTO MON. GFS CONTINUES TO BE WELL SUPPRESSED WITH THE WAVE WITH HIGH PRES DOMINATING. DUE TO UNCERTAINTY...WE USED A BLEND OF ECMWF/GFS CHRISTMAS... HEAVY RAIN WILL LIKELY BE ONGOING CHRISTMAS MORNING IN THE COASTAL PLAIN...THEN RAIN MOVES OUT BY MIDDAY WITH SKIES BECOMING PTSUNNY IN THE AFTERNOON. GUSTY SW WINDS IN THE MORNING NEAR THE COAST ASSOCD WITH THE LLJ...THEN ALL AREAS WILL SEE STRONG WEST WIND GUSTS IN THE AFTERNOON AS COLD ADVECTION DEVELOPS WITH STEEPENING LOW LEVEL LAPSE RATES. WIND GUSTS TO 45 MPH WILL BE POSSIBLE AND WIND ADVISORIES MAY BE NEEDED. MAX TEMPS IN THE 50S TO NEAR 60 DEGREES WILL OCCUR IN THE MORNING...WITH TEMPS FALLING IN THE AFTERNOON. FRIDAY INTO SAT... HIGH PRES BRINGS DRY WEATHER WITH ABOVE NORMAL TEMPS. THE MILDER DAY WILL BE SATURDAY WITH TEMPS REACHING INTO THE 50S AS THE HIGH SLIDES TO SE WITH SW FLOW DEVELOPING. SUNDAY INTO MONDAY... LOW CONFIDENCE FORECAST. A COLD FRONT MAY BRING A FEW RAIN/SNOW SHOWERS SUNDAY...THEN WILL HAVE TO WATCH FOR POSSIBLE FRONTAL WAVE SUN NIGHT INTO MON. THIS WAVE MAY END UP TOO FAR SOUTH BUT WILL KEEP LOW POPS IN THE FORECAST. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY NIGHT/...MODERATE CONFIDENCE. TONIGHT...WITH MOIST EASTERLY FLOW...WE EXPECT CIGS TO REMAIN MOSTLY BELOW 1000 FEET AND VSBYS MOSTLY 1 TO 3 MILES THROUGH THE NIGHT. CLOUDS/FOG/DRIZZLE THROUGH THE NIGHT. WEDNESDAY AND WEDNESDAY NIGHT...IFR CONDITIONS CONTINUE IN WIDESPREADY RAIN. LOCALLY HEAVY DOWNPOURS EXPECTED ESPECIALLY IN THE AFTERNOON. INCREASING SOUTH WIND AT 1500-2000 FEET WITH SPEEDS REACHING 50 KNOTS. THIS SHOULD CREATE LOW LEVEL WIND SHEAR BY THE AFTERNOON AND THROUGH THE NIGHT. KBOS TERMINAL...HIGH CONFIDENCE IN IFR CONDITIONS. KBDL TERMINAL...MODERATE CONFIDENCE. MVFR CIGS SHOULD LOWER TO IFR BUT TIMING UNCERTAIN. OUTLOOK...THURSDAY THROUGH SATURDAY... CHRISTMAS...MODERATE CONFIDENCE. IFR IN RAIN TO START...THEN CONDITIONS IMPROVE TO VFR IN THE AFTERNOON. WEST WIND GUSTS TO 35-40 KT POSSIBLE IN THE AFTERNOON. FRIDAY AND SATURDAY...HIGH CONFIDENCE. VFR. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY NIGHT/...HIGH CONFIDENCE. TONIGHT... EAST WINDS NEAR 20 KNOTS WILL DIMINISH. BUT ROUGH SEAS WILL KEEP SMALL CRAFT ADVISORY GOING ON MOST WATERS. WEAK LOW PRESSURE MOVING UP THE COAST WILL PASS JUST OFFSHORE...BRINGING DIMINISHING LIGHT RAIN ALONG WITH CLOUDS/FOG/DRIZZLE. WEDNESDAY AND WEDNESDAY NIGHT...STRONG SOUTH WINDS WILL MOVE UP THE COAST FROM THE CAROLINAS WEDNESDAY...REACHING THE NEW ENGLAND WATERS IN THE AFTERNOON AND LINGERING THROUGH THE NIGHT. WINDS WILL REACH 50-65 KNOTS ABOUT 2000 FEET ABOVE THE OCEAN SURFACE. BUT A STRONG TEMPERATURE INVERSION MAY KEEP ALL OF THIS WIND FROM REACHING THE SURFACE. EVEN SO...HEAVY DOWNPOURS MAY PROVIDE A CHANNEL FOR SOME OF THIS WIND TO REACH THE SURFACE IN GUSTS. WE ARE CURRENTLY FORECASTING GUSTS TO 30 KNOTS OR THE LOWER 30S. LOW CONFIDENCE FOR GUSTS REACHING GALE FORCE. EXPECT FOG AND RAIN WITH LOCAL HEAVY DOWNPOURS. OUTLOOK...THURSDAY THROUGH SATURDAY...MODERATE CONFIDENCE CHRISTMAS...WINDS SHIFT TO SW/W WITH GALE FORCE GUSTS POSSIBLE. IMPROVING VSBYS IN THE AFTERNOON AS RAIN MOVES OUT. FRI AND SAT...EXPECT WEST WINDS BELOW SCA FRI...THEN INCREASING SW WINDS SAT WITH GUSTS TO 25 KT. && .TIDES/COASTAL FLOODING... EASTERN MASSACHUSETTS COAST: HIGH TIDE AT BOSTON WILL BE 11.7 FT AT MIDDAY WEDNESDAY WITH A SURGE OF AROUND 1.0 FT. THE SURGE TODAY /TUESDAY/ SHOWED MINOR SPLASHOVER ALONG THE EAST MASSACHUSETTS COAST. EXPECT SIMILAR EFFECTS WEDNESDAY. A COASTAL FLOOD ADVISORY HAS BEEN ISSUED FOR THE EAST MASSACHUSETTS COAST FOR THE MIDDAY WEDNESDAY HIGH TIDE. SOUTH COAST: WE DO NOT EXPECT MUCH IF ANY COASTAL FLOODING ALONG THE SOUTH COAST. NOT ENOUGH WIND OR SURGE FOR THE WEDNESDAY EVENING HIGH TIDE. HIGHEST SURGE OF 1-2 FEET LIKELY TO OCCUR DURING LOW TIDE LATE WED NIGHT WITH THE SURGE AND SEAS DECREASING DURING THE CHRISTMAS MORNING HIGH TIDE. WORST CASE IS MINOR SPLASHOVER FOR THE CHRISTMAS MORNING HIGH TIDE BUT EVEN THIS IS NOT LOOKING FAVORABLE. && .CLIMATE... RECORD HIGHS FOR DEC 24 / DEC 25... BOS... 61 IN 1996 / 65 IN 1889 PVD... 60 IN 1990 / 63 IN 1964 BDL... 59 IN 1996 / 64 IN 1964 ORH... 57 IN 1996 / 60 IN 1964 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ231- 232. SMALL CRAFT ADVISORY UNTIL 6 AM EST WEDNESDAY FOR ANZ235-237- 250-251-254>256. && $$ SYNOPSIS...WTB/KJC NEAR TERM...WTB/KJC SHORT TERM...WTB LONG TERM...KJC AVIATION...WTB/KJC MARINE...WTB/KJC TIDES/COASTAL FLOODING... CLIMATE...

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