Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201053 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 653 AM EDT WED MAY 20 2015 .SYNOPSIS... A COLD FRONT OVER CAPE COD AND THE ISLANDS DURING THE PREDAWN HOURS WILL MOVE OFFSHORE LATER THIS MORNING AND WILL USHER IN A MUCH DRIER AND SEASONABLY COOL CANADIAN AIRMASS ACROSS THE AREA TODAY AND THU. SCATTERED SHOWERS ANTICIPATED THURSDAY NIGHT INTO FRIDAY. FROST AND MAYBE EVEN RECORD-BREAKING COLD IS POSSIBLE FOR SATURDAY MORNING. DRY AND SEASONABLE BENEATH HIGH PRESSURE FOR THE WEEKEND. POSSIBLE WET-WEATHER EARLY NEXT WEEK IS NOT OUT OF THE QUESTION. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 AM UPDATE...NO MAJOR CHANGES. PREVIOUS DISCUSSION... BEHIND THE COLD FRONT NOW OFFSHORE A MUCH DRIER AND SEASONABLY COOL CANADIAN AIRMASS OVERSPREADS THE AREA. UPSTREAM MUCH DRIER AIR WITH DEW PTS IN THE 40S OVERSPREADING THE AREA FROM NW TO SE THIS MORNING. GIVEN A DOWNSLOPE WNW WIND TODAY DEW PTS WILL FALL INTO 30S THIS AFTERNOON. THUS A DRY AIRMASS. WNW WINDS WILL BE GUSTY AT TIMES WITH SPEEDS UP TO 25 MPH. STRONG MAY SUNSHINE TODAY /SCT DIURNAL CU-SCU/ WILL BE OFFSET A BIT BY MODEST COLD AIR ADVECTION WITH 850 TEMPS GOING FROM ABOUT +8C THIS MORNING TO +2C BY 00Z/8PM. THUS TEMPS THIS AFTERNOON WILL TEMPERED WITH HIGHS 65-70...WHICH IS JUST ABOUT NORMAL FOR THIS TIME OF YEAR. NEVERTHELESS A FINE SPRING DAY AHEAD WITH MOSTLY SUNNY CONDITIONS...SEASONABLE TEMPS...LOW HUMIDITY AND A REFRESHING WNW BREEZE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... TONIGHT... DRY BUT CHILLY NIGHT AHEAD AS SURFACE RIDGE BUILDS INTO NEW ENGLAND FROM THE GREAT LAKES. WINDS WILL DECOUPLE OUTSIDE OF THE URBAN AREAS AND HIGH TERRAIN. THUS LIGHT WINDS WILL COMBINE WITH CLEAR SKIES AND A DRY AIRMASS TO YIELD TEMPS IN THE LOW TO MID 40S WITH MU 30S ACROSS NORTHWEST MA WHERE A LOW RISK OF FROST EXIST. WILL HOLD OFF ON ANY HEADLINES AS RISK OF FROST IS MARGINAL AT THIS TIME. THURSDAY... ANOTHER DRY DAY WITH TEMPS A FEW DEGS WARMER INLAND COURTSEY OF WEAK WARM ADVECTION AHEAD OF A LOW AMPLITUDE TROUGH APPROACHING FROM THE OH VLY. HOWEVER WITH WINDS BECOMING SW IT WILL BE COOLER ALONG THE SOUTH COAST WITH WIND TRAJECTORY OFF THE CHILLY OCEAN WATERS. MORNING SUNSHINE WILL BE FILTERED BY MID AND HIGH AFTERNOON CLOUDS AHEAD OF APPROACHING MID LEVEL TROUGH. HOWEVER ANY POTENTIAL RAINFALL SHOULD HOLD OFF UNTIL THU NIGHT. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... */ HIGHLIGHTS... - CHANCES FOR WET WEATHER THURSDAY NIGHT INTO FRIDAY - TURNING COLD INTO SATURDAY MORNING - HIGH PRESSURE AND MODERATE TEMPERATURES OVER THE WEEKEND - POTENTIAL FOR WET WEATHER INTO EARLY NEXT WEEK */ DISCUSSION... CERTAINLY A TRICKY FORECAST PATTERN. N-STREAM VORTEX UP AGAINST THE PREFERRED PATTERN AS OF LATE WITH TROUGHING ACROSS THE W CONUS WITH RIDGING TO THE E. THOUGH IT APPEARS TO BE A BLOCKY PATTERN TO THE W THROUGH WHICH PACIFIC-ORIGIN IMPULSES WILL INFLUENCE OUR REGION AS THEY ARE PULLED E AND AROUND THE BROADER VORTEX FLOW. A CHALLENGE TO INTERPRET...THE WAVERING ATMOSPHERE WITH EXCHANGE OF AIRMASSES IS NO STRANGER TO SPRING. SO WITH THE VORTEX FLOW IN CONTROL INITIALLY...EXPECTING SCATTERED WET-WEATHER ACTIVITY FOR THURSDAY NIGHT INTO FRIDAY. AN OPEN-WAVE IMPULSE LOOKS TO CAPTURE THE ANTICYCLONIC BRANCH OF LOW- TO MID- LEVEL ISENTROPIC ASCENT ASSOCIATED WITH AN OFFSHORE STORM. ALONG AN INVERTED TROUGH BRANCHING N- AND S-STREAMS...BEST RAIN CHANCES ARE ACROSS SE NEW ENGLAND INTO FRIDAY MORNING...WHILE MORE WIDESPREAD ON FRIDAY ITSELF AHEAD OF A SWEEPING COLD FRONT ASSOCIATED WITH THE N- STREAM VORTEX. LOW- TO MID-LEVEL FORCING THROUGH THE CYCLONIC FLOW REGIME SHOULD YIELD SOME SCATTERED SHOWER ACTIVITY ALONG AND AHEAD OF THE SHARP COLD FRONT. WILL SEE BRISK NW-FLOW BEHIND THE FRONT USHERING COLDER AIR S WHICH BRINGS US TO THE POTENTIAL FOR FROST HEADLINES AND PERHAPS EVEN RECORD LOW TEMPERATURES SATURDAY MORNING. H85 TEMPERATURES DROPPING AROUND -2 TO -4C. THROUGH MOSTLY CLEAR...NW-WINDS FORECAST TO REMAIN BRISK. SEE THE CLIMATE SECTION BELOW FOR RECORD LOWS ON MARCH 23RD. THE WEEKEND LOOKS DRY WITH HIGH PRESSURE IN CONTROL AND THE VORTEX LIFTING N ALLOWING RETURN S-FLOW. TEMPERATURES MODERATE BACK TO SEASONABLE LEVELS. EARLY NEXT WEEK THINGS GET COMPLICATED. CONSENSUS HAS A CONFLUENT FLOW PATTERN ACROSS OUR REGION THROUGH WHICH PACIFIC- ORIGIN IMPULSES INVOKE A SERIES OF SURFACE LOW PRESSURE CENTERS OVER THE GREAT LAKES INTO THE SAINT LAWRENCE RIVER VALLEY. AS WE HAVE SEEN EARLIER THIS SEASON...ACCOMPANYING SW WARM-MOIST FLUX REARWARD OF THE INDIVIDUAL DISTURBANCES MAY GIVE US A SHOT AT WET WEATHER ALONG THE ATTENDANT WARM-FRONTAL BOUNDARY TO THE NOSE OF THE LOW- LEVEL-JET. FAVOR THE EC-MODEL. SLIGHT CHANCE TO CHANCE POPS. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY/...HIGH CONFIDENCE. 12Z UPDATE... VFR AND DRY WEATHER PREVAILS TODAY/TONIGHT AND THU. WNW WINDS WILL INCREASE TO G25 KT BY MIDDAY AND THEN DIMINISH WITH SUNSET. LESS WIND TONIGHT AND THU. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. GUSTY WNW WINDS G25 KT 14Z-00Z TODAY. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. GUSTY WNW WINDS G25 KT FROM 14Z-00Z TODAY. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY... THURSDAY NIGHT...HIGH CONFIDENCE. SCT-BKN LOW-END VFR CIGS. WORST CONDITIONS WITH PATCHY MVFR OVER SE TERMINALS WITH -SHRA. SW-WINDS. FRIDAY...HIGH CONFIDENCE. SCT-BKN VFR CIGS. SW-FLOW BACKING NW WITH FRONTAL PASSAGE. SCT -SHRA. FRIDAY NIGHT THROUGH SUNDAY NIGHT...MODERATE CONFIDENCE. VFR. LIGHT WINDS. SEA-BREEZES ALONG THE SHORES DURING THE DAY. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY/...HIGH CONFIDENCE. TODAY... WINDS BECOMING WNW WITH GUSTS UP TO 20 KT...STRONGEST WINDS NEAR SHORE. VSBYS LESS THAN A MILE IN AREAS OF DENSE FOG EARLY THIS MORNING IMPROVE RAPIDLY AFTER SUNRISE. DRY WEATHER PREVAILS. TONIGHT... WNW WINDS DIMINISH. VSBY REMAINS GOOD ALONG WITH DRY WEATHER. THU... WINDS BECOME SW. DRY WEATHER AND GOOD VSBY PERSIST. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY...HIGH CONFIDENCE. MODERATE CONFIDENCE FORECAST. SW-WINDS WITH SHOWERS ALONG THE S/SE- COAST FOR THURSDAY NIGHT. COLD FRONT SWEEPS THE WATERS FRIDAY BEHIND WHICH WINDS WILL BACK NW AND BECOME BREEZY. COULD SEE WAVES BUILD TO 5-FEET ON THE OUTER WATERS. HIGH PRESSURE BUILDS OVER THE WATERS FOR THE WEEKEND BENEATH WHICH WINDS AND WAVES ARE EXPECTED TO BE BELOW SMALL-CRAFT-ADVISORY CRITERIA...THOUGH THERE IS THE POSSIBILITY OF 5-FOOT SEAS LATE IN THE PERIOD AS WINDS INCREASE OUT OF THE SW AHEAD OF EARLY-WEEK WET- WEATHER. && .FIRE WEATHER... TODAY... WNW WINDS 10 TO 20 MPH WITH GUSTS UP TO 25 MPH WILL LOWER MIN RH VALUES TO 30-35 PERCENT THIS AFTERNOON. DESPITE YESTERDAY/S RAINS A DRY AIRMASS TODAY COMBINED WITH GUSTY WNW WNDS WILL RAPIDLY DRY OUT FUELS THIS AFTERNOON. THIS COMBINED WITH COLLABORATION WITH OUR FIRE WEATHER PARTNERS...WILL GO AHEAD AND CONTINUE OUR SPECIAL WEATHER STATEMENT HIGHLIGHTING FIRE WEATHER CONCERNS FOR JUST MASSACHUSETTS. THIS IS WHERE THE LEAST AMOUNT OF RAIN FELL YESTERDAY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...NOCERA/SIPPRELL SHORT TERM...NOCERA LONG TERM...SIPPRELL AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL FIRE WEATHER...WFO BOX STAFF

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