Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 041858 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 258 PM EDT TUE AUG 4 2015 .SYNOPSIS...
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THUNDERSTORMS CONTINUING INTO THE EVENING HOURS MAINLY PUSHING E. CONTINUED STRONG TO SEVERE THREATS. DRY...WARM AND LESS HUMID WEATHER ARRIVES THURSDAY. A PERIOD OF UNSETTLED WEATHER IS POSSIBLE FRIDAY INTO THIS WEEKEND...BUT CONFIDENCE REMAINS LOW REGARDING THE TIMING AND COVERAGE OF ANY POTENTIAL WET WEATHER.
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&& .NEAR TERM /THROUGH TONIGHT/...
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INTO THIS EVENING... STRONG TO SEVERE THUNDERSTORMS PERSISTING IN AN AREA OF BETTER MOISTURE / HIGHER THETA-E FORCED AHEAD OF A MID-LEVEL IMPULSE. A VERY UNSTABLE ENVIRONMENT WITH DECENT LAPSE RATES THROUGHOUT THE COLUMN WITH SW-NE UNI-DIRECTIONAL 0-6 KM BULK SHEAR EXCEEDING 50 KTS...WITH SOME TURNING EVIDENT WITHIN THE HIGH-RES GUIDANCE IN THE 0-1/0-3 KM LAYER. CHECK OUT THE 18Z ALBANY SOUNDINGS WHERE MUCAPE VALUES ARE NEARLY 3K J/KG AND HIGHLIGHT EXACTLY THE ABOVE POINTS. FOCUS MAINLY ACROSS THE N/W REGIONS AWAY FROM WHERE THE DRY-SLOT IS APPARENT WITHIN THE WATER VAPOR LOOP OVER SE NEW ENGLAND... THOUGH ACTIVITY IS EXPECTED TO SHIFT S/E INTO THE EVENING HOURS AHEAD OF A FRONTAL BOUNDARY PUSHED OFFSHORE BY THE MID-LEVEL IMPULSE. LIKELY POPS WITH PRIORITIZED THREATS OF THE FOLLOWING: HEAVY RAIN / FREQUENT LIGHTNING / URBAN AND POOR DRAINAGE FLOODING ISSUES / STRONG TO DAMAGING WINDS / LARGE HAIL. THERE IS THE POSSIBILITY OF A TORNADO AS WELL AS WE HAVE ALREADY SEEN A FEW DOPPLER-RADAR INDICATED. WATCH NUMBER 469 CONTINUES TILL 8 PM. MAY NEED TO EXPAND INTO N CT AND RI. CONTINUE TO EVALUATE THE ENVIRONMENT. AT THIS TIME DOWN- STREAM TRENDS DO NOT FAVOR AN EXPANSION OF THE WATCH. LOOKS LIKE MOST OF THE ENERGY IS LOCKED ALONG THE LEADING EDGE / PVA OF THE MID-LEVEL VORTEX DISCERNED FROM HIGH-RES GUIDANCE AND WATER VAPOR IMAGERY. TONIGHT... MID-LEVEL IMPULSE AND ACCOMPANYING TROUGH PUSH E SUBSEQUENTLY EASING THE SURFACE FRONTAL BOUNDARY OFFSHORE ALONG WITH DEEPER MOISTURE AND HIGHER THETA-E AIR. WILL SEE SHOWERS / THUNDERSTORMS PUSH OUT TO SEA WITH SOME OF THE STORMS STRONG TO SEVERE LINGERING LONGEST OVER THE CAPE AND ISLANDS WITHIN A LOW-LEVEL CONVERGENT ENVIRONMENT OF HIGHER THETA-E AIR. ANTICIPATED CONCLUSION SHORTLY AFTER MIDNIGHT OF WET- WEATHER. LIGHT W-WINDS PREVAILING AND DRIER AIR WORKING IN. EXPECT IT TO CLEAR OUT W TO E ACCORDINGLY. LOWS DROPPING IN AND AROUND THE LOW-60S WITH SPOTS N/W INTO THE UPPER-50S AS THERE IS AN OPPORTUNITY FOR RADIATIONAL COOLING TO PROCEED. WITH THAT THERE IS THE POTENTIAL FOR PATCHY DENSE FOG...ESPECIALLY THOSE AREAS WHICH OBSERVED RAIN DURING THE DAY.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
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WEDNESDAY... ANOTHER MID-LEVEL IMPULSE SWEEPS THROUGH THE BROAD CYCLONIC FLOW FOLLOWED BY THE MID-LEVEL TROUGH. ENOUGH FORCING WITHIN THE LOW- TO MID-LEVEL ATMOSPHERIC PROFILE TO INVOKE SOME SHOWERY WEATHER...YET TWO THINGS: ONE IS THAT MOISTURE IS LIMITED WITH DRIER AIR AS THE SURFACE...INSTABILITY SHOULD BE RATHER WEAK...AND TWO IS THAT A DRY- SUBSIDENCE INVERSION WILL BE WORKING DOWN THROUGH THE ATMOSPHERIC PROFILE ACROSS THE AREA PUTTING A SQUASH ON ACTIVITY. WHILE CAN NOT DISAGREE WITH PRIOR FORECASTER OF THE COOLER TEMPERATURES ALOFT YIELDING SMALL HAIL...FEEL THAT DRY AIR AND SUBSIDENCE ACROSS THE REGION MAY LIMIT THE LIFT. REMOVED FROM PREVAILING IN THE FORECAST. SO WITH THE FORCING APPARENT WILL GO WITH CHANCE POPS FOR SCATTERED SHOWERS AND MAYBE A THUNDERSTORM FOCUSING ON THE EARLY-HALF OF THE DAY. FROM THEN ON DRIER WEATHER WITH BREEZY W-WINDS. A TAD COOLER AS THE AIR-MASS ALOFT COOLS. HIGHS AROUND THE LOW 80S. SEASONABLE. WEDNESDAY NIGHT... BEHIND THE TROUGH IT LOOKS TO REMAIN A BIT BREEZY W. CAN NOT RULE OUT A FEW LOCALES EXPERIENCING LIGHT WINDS OVERNIGHT. SHOULD SEE QUIET WEATHER AND CLEAR CONDITIONS. ALL FACTORS COMBINED...THERE IS SOME POTENTIAL FOR RADIATIONAL COOLING AND HIGHEST CONFIDENCE IS TO THE N/W WITHIN SHELTERED VALLEY REGIMES. LOWS DOWN INTO THE MID- TO UPPER-50S WHILE LOW-60S ALONG THE COAST. DEWPOINTS IN THE LOW-50S. AN END TO THE HEAT AND HUMIDITY AND QUITE REFRESHING.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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HIGHLIGHTS... * UNSETTLED WEATHER REMAINS POSSIBLE FRIDAY INTO THE WEEKEND * TEMPERATURES TRENDING BELOW NORMAL THROUGH MOST IF NOT THE ENTIRE PERIOD OVERVIEW AND MODEL PREFERENCES... NOTING FAIRLY GOOD AGREEMENT WITH 12Z OPERATIONAL MODELS RUNS INTO FRIDAY...THEN EACH GOES ON THEIR MERRY OWN WAY WHICH LENDS TO LOW CONFIDENCE BEYOND FRIDAY. ONE BIG QUESTION WILL BE HOW THE H5 CUTOFF LOW ACROSS QUEBEC AND MARITIMES FLATTENS OUT...WHICH ALSO FLATTENS OUT THE FLOW ACROSS MOST OF THE NORTHERN STREAM. DEPENDING UPON WHETHER THIS UPPER LEVEL SYSTEM FLATTENS OUT WILL DETERMINE HOW FAR S THE LARGE HIGH PRES RIDGE BUILDS OUT OF CENTRAL CANADA. ALSO NOTING A STALLED FRONT S OF THE REGION WHICH HAS A SHORT WAVE MOVING ALONG IT...WHICH COULD PUSH SOME MOISTURE INTO PORTIONS OF SOUTHERN NEW ENGLAND. ANOTHER FLY IN THE OINTMENT IS THE POSSIBLE AMPLIFICATION OF LONG WAVE TROUGH ACROSS THE MID ATLC REGION THIS WEEKEND. NEEDLESS TO SAY...LOW CONFIDENCE FORECAST BEYOND FRIDAY DUE TO THE WIDE VARIANCE OF OP MODEL RUN SOLUTIONS. WENT ALONG WITH MOST AVAILABLE GUIDANCE /EXCEPT GFS/ THROUGH FRIDAY...THEN TRANSITIONED OVER TO AN ENSEMBLE MODEL BLEND SIMILAR TO WPC GUIDANCE FROM SATURDAY ONWARD. DETAILS... THURSDAY...HIGH PRESSURE BUILDS OUT OF CENTRAL CANADA INTO UPSTATE NY. WEAK SHORT WAVE MOVES ACROSS NORTHERN NEW ENGLAND AND...WITH LACK OF AVAILABLE MOISTURE IN THE GENERAL W-NW FLOW...EXPECT DRY CONDITIONS. HIGHS LOOK TO RUN AROUND 80 DEGREES...SLIGHTLY BELOW SEASONAL NORMS. THURSDAY NIGHT THROUGH SATURDAY...SHORT WAVE MOVING ALONG STALLED FRONT FROM THE OHIO VALLEY. COULD START TO SEE SOME MOISTURE MOVING NE INTO N CT/RI/SE MA OVERNIGHT THU NIGHT THEN PUSH FURTHER N DURING FRI. STILL A LOT OF QUESTION ON HOW FAR THIS RAIN WILL PUSH INTO THE REGION...IF AT ALL. FOR NOW...KEPT CONTINUITY GOING FROM THE PREVIOUS FORECAST WITH MAINLY CHANCE POPS...THOUGH LOW LIKELY IN PLACE ACROSS S COASTAL AREAS FRI INTO FRI NIGHT. HAVE LOWERED POPS TO CHANCE FOR EARLY SATURDAY THEN SHOULD PUSH E DURING THE AFTERNOON INTO SAT EVENING. SUNDAY THROUGH WEDNESDAY...MUCH OF THIS FORECAST CONTINUES TO DEPEND UPON THE FRI-SAT PATTERN SETS UP. AT THIS POINT...LOOKS LIKE IT SHOULD BE MAINLY DRY BUT COOL ON SUNDAY. MODELS SIGNALING ANOTHER H5 LONG WAVE TROUGH DIGGING ACROSS EASTERN GREAT LAKES AS H5 LOW TRYING TO CUT OFF AGAIN ACROSS HUDSON BAY. MAY SEE PERIODS OF WIDELY SCT SHOWERS FROM TIME TO TIME DURING THIS TIMEFRAME...BUT LOW CONFIDENCE ON TIMING AND PLACEMENT.
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&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH WEDNESDAY NIGHT/... INTO THIS EVENING...MODERATE CONFIDENCE. STRONG TO SEVERE TSRA WITH POTENTIAL THREATS: LARGE HAIL / STRONG TO DAMAGING WINDS MAINLY OUT OF THE W / HEAVY RAIN WITH MVFR-IFR VSBYS. MVFR TO LOW-END VFR CIGS. LOW RISK TORNADO. ACTIVITY SWEEPING ENE AT 25-30 KTS. TODAY...MODERATE CONFIDENCE. SHRA/TSRA DEVELOPING TOWARDS MIDDAY GOING W TO E INTO THE EVENING HRS. STRONG TO SEVERE POTENTIAL. +RA WITH GUSTY WINDS AND POSSIBLE HAIL. BRIEF MVFR / IFR CONDITIONS WITH TSRA. TONIGHT...MODERATE CONFIDENCE. SHRA/TSRA LINGER OVER THE SE TERMINALS TILL AROUND 6-9Z. TEMPO MVFR- IFR CONDITIONS. OTHERWISE LIGHT W-WINDS AND VFR...THOUGH TERMINALS WHICH EXPERIENCED RAIN DURING THE DAY LIKELY TO SEE MVFR-LIFR PATCHY DENSE FOG. WEDNESDAY...HIGH CONFIDENCE. SCT SHRA WITH LOWER POSSIBILITY OF TSRA. LOW RISK OF SMALL HAIL. BREEZY W-WINDS WITH GUSTS UPWARDS OF 20 KTS. SCT-BKN LOW-END VFR CIGS. WEDNESDAY NIGHT...HIGH CONFIDENCE. W-WINDS DIMINISHING. VFR. SKC. LOW CONFIDENCE PATCHY DENSE FOG. KBOS TERMINAL...MODERATE CONFIDENCE. ENOUGH CONFIDENCE THAT STORMS WILL IMPACT THE TERMINAL WITH SIGNIFICANT IMPACT...BUT UNCERTAIN ON THE EXACT TIMING. KBDL TERMINAL...MODERATE CONFIDENCE. WATCHING CLOSELY FOR STORM IMPACT. STORMS COULD POTENTIALLY HOLD OFF TO THE N. OUTLOOK /THURSDAY THROUGH SUNDAY/... THURSDAY...HIGH CONFIDENCE. VFR. THURSDAY NIGHT THROUGH SATURDAY...LOW CONFIDENCE ON TIMING...HIGHER CONFIDENCE ON TRENDS. MVFR-IFR CONDITIONS IN AREAS OF RAIN SOMETIME DURING THIS PERIOD. VFR BEFORE AND AFTER PERIODS OF RAIN. SUNDAY...LOW CONFIDENCE MAINLY FOR TIMING. MAY SEE LEFTOVER SHOWERS WITH BRIEF MVFR CONDITIONS EARLY...THEN VFR.
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&& .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH TUESDAY NIGHT/... TONIGHT...MODERATE CONFIDENCE. SHOWERS AND THUNDERSTORMS LINGER OVER THE SE WATERS ALONG WITH BREEZY SW-WINDS. SUBSEQUENT 5-6 FOOT SEAS BEGINNING TO DIMINISH INTO MORNING AS THE WET-WEATHER AHEAD OF A FRONTAL BOUNDARY PUSHES OUT TO SEA BEHIND WHICH WINDS BACK W. WEDNESDAY...HIGH CONFIDENCE. W-WINDS CONTINUING PERHAPS BREEZY WITH GUSTS UPWARDS OF 20 KTS. SEAS WILL GRADUALLY DIMINISH THROUGH THE PERIOD. THERE IS THE POSSIBILITY OF SOME RENEWED SHOWER ACTIVITY THOUGH LIKELY CLOSER TO THE SHORE. WEDNESDAY NIGHT...HIGH CONFIDENCE. W-WINDS DIMINISHING ALLOWING SEAS TO RELAX. SHOULD SEE QUIET BOATING WEATHER. OUTLOOK /THURSDAY THROUGH SUNDAY/... THURSDAY-THURSDAY NIGHT...HIGH CONFIDENCE. WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. LOCALLY REDUCED VSBYS IN LIGHT RAIN THU NIGHT. FRIDAY THROUGH SUNDAY...MODERATE CONFIDENCE. EASTERLY WINDS GUSTING UP TO 20 KT. WITH ONSHORE WINDS...SEAS LOOK TO BUILD UP TO 5-6 FT HIGHEST ACROSS THE EASTERN OUTER WATERS. RAIN LIKELY FRIDAY NIGHT THROUGH SATURDAY NIGHT...LIMITING VISIBILITIES AT TIMES...THEN SHOULD IMPROVE DURING SUNDAY.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ230>234-236-250-251. SMALL CRAFT ADVISORY UNTIL 8 AM EDT WEDNESDAY FOR ANZ235-237- 254>256. && $$ SYNOPSIS...SIPPRELL/EVT NEAR TERM...SIPPRELL SHORT TERM...SIPPRELL LONG TERM...EVT AVIATION...SIPPRELL/EVT MARINE...SIPPRELL/EVT

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