Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250740 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 340 AM EDT SAT JUL 25 2015 .SYNOPSIS... */ NEAR- AND SHORT-TERM UPDATES WITH THIS AFD ISSUANCE UNSETTLED WEATHER EXPECTED THROUGH EARLY NEXT WEEK...WITH MAINLY DIURNAL SHOWERS AND THUNDERSTORMS. STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE AGAIN SOMETIME SUNDAY INTO MONDAY. THE NEXT MAIN WEATHER HEADLINE WILL BE A POSSIBLE HEAT WAVE TUESDAY THROUGH THURSDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... INTO MORNING... WITH SUNRISE WE SHOULD SEE FOG ACROSS LOW-LYING VALLEY LOCALES BURN OFF. WILL SEE LIGHT WINDS BEGIN TO TURN E UNDER MOSTLY CLEAR CONDITIONS. TODAY... CONTINUED FORECAST CONSENSUS OF SOME LIGHT LOW-TOPPED SHOWERY WEATHER ALONG THE LEADING EDGE OF A BACKDOOR COLD FRONT PUSHING W ACROSS THE INTERIOR. AS ALLUDED TO PRIOR...TYPICALLY SUBSIDENCE REARWARD OF THE DEPARTING TROUGH THAT AFFECTED OUR AREA YESTERDAY WOULD LEND TO A DRY FORECAST. IN FACT MID-LEVEL SUBSIDENCE IS ECHOED THROUGHOUT VARIOUS BUFKIT PROFILES. BUT WITH A DESTABILIZING LAYER AHEAD OF THE FRONT BENEATH THE INVERSION ALONG WITH PLENTY OF REMNANT MOISTURE TO WORK WITH FROM ANTECEDANT RAINS AND SOME MINOR ELEVATED INSTABILITY...LIGHT SHOWERY WEATHER CAN NOT BE RULED OUT. NOT EXPECTING A WASHOUT. JUST SCATTERED LIGHT SHOWERS. FOCUS ACROSS CENTRAL AND WESTERN PORTIONS OF S NEW ENGLAND WHERE THERE IS GREATER RESIDENCY-TIME FOR THE BOUNDARY-LAYER TO DESTABILIZE AHEAD OF THE ONCOMING W-PROGRESSING COLD FRONT. SLIGHT CHANCE POPS WITH CHANCE POPS UP AGAINST THE E-SLOPES OF HIGHER TERRAIN. EXPECTING ONSET OF SHOWERY WEATHER TOWARDS THE AFTERNOON HOURS. SCATTERED TO BROKEN CLOUD DECKS WITH TEMPERATURES AT OR BELOW SEASONABLE LEVELS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... SATURDAY NIGHT... LOW- TO MID-LEVEL WARM-FRONTAL BOUNDARY PUSHES E ALONG THE NOSE OF ISENTROPICALLY ASCENDING HIGHER THETA-E AIR TO THE W. UNDERGOING MID- LEVEL FORCING PER H5 VORTMAX ALOFT SWEEPING ACROSS THE NE-CONUS THRU THE BROADER CYCLONIC FLOW AN OVER-RUNNING PRECIP SETUP SEEMS LIKELY. LIKELY POPS ACCORDINGLY. OVERWHELMING QUESTION IS IF INSTABILITY IS PRESENT AND IF ANY TO WHAT EFFECT TO SUGGESTED CONSENSUS FORECAST MODEST 0-1/0-3 HELICITY VALUES HAVE ON THE LOCAL ENVIRONMENT? EVALUATING...NAM/GFS BUFKIT PROFILES SUGGEST A WARM-DRY INSTRUSION AROUND H9 THAT EFFECTUALLY CAPS THE BOUNDARY LAYER AT THE SURFACE OF WHICH THERE ARE LOW TEMPERATURE-DEWPOINT SPREADS. THIS KEEPS ANY INSTABILITY ELEVATED WITHIN A CONDITIONALLY UNSTABLE BOUNDARY-LAYER PROFILE DESPITE SOME MODEL DISCREPANCIES AS TO THE MAGNITUDE OF H5-7 LAPSE RATES. MEANWHILE THE 24.21Z SREF DOES NOT PROVIDE MUCH CONFIDENCE CONCERNING CONVECTIVE THREATS. BUT TO REITERATE AGAIN THERE IS A FAIR AMOUNT OF HELICITY WITHIN THE 0-1/0-3 KM LAYER. SO WILL NEED TO MONITOR THIS SITUATION CLOSELY AS IT PROGRESSES THRU THE OVERNIGHT PERIOD ACROSS UPSTATE NY INTO NEW ENGLAND BY MORNING. FEEL LIKELY POPS ARE WARRANTED WITH A MENTION OF THUNDER AS IT IS ANTICIPATED THAT PARCELS WILL UNDERGO FORCING WITHIN THE LOW- TO MID- LEVELS IN THE CONSENSUS FORECASTED CONDITIONALLY UNSTABLE MID-LEVEL PROFILE. NOT ENOUGH CONFIDENCE TO GO WITH ENHANCED WORDING IN THE FORECAST OF CONVECTIVE OUTCOMES. LOOKING AT WARM-HUMID CONDITIONS WITH S/SE-ONSHORE FLOW DURING THE PERIOD AS THE PREVIOUS FORECASTER MENTIONED. CERTAINLY THE POSSIBILITY FOR PATCHY DENSE FOG. SUNDAY... MID-LEVEL VORTEX AND ACCOMPANYING TROUGH AXIS LIFT NORTHEAST INTO MAINE THROUGH THE DAY. WILL SEE OVER-RUNNING SYNOPTICS LIFT OUT OF THE REGION STILL ACCOMPANIED WITH DECENT 0-1/0-3 KM HELICITY AND ELEVATED INSTABILITY BENEATH A WARM-NOSE LOCATED AROUND H9. ECHOING THE FORECAST DISCUSSION ABOVE...WILL NEED TO MONITOR THIS SITUATION VERY CLOSELY. SOME UNCERTAINTY THOUGH CONCERN AS TO WHETHER THE BOUNDARY-LAYER CAN DESTABILIZE AND ERODE THE CAP ALOFT. SUCH BE THE CASE THEN SUBSEQUENTLY WE COULD HAVE DEEP-LAYER CAPE IN AN OVERALL PRONOUNCED ENVIRONMENT OF SIGNIFICANT HELICITY. MEANWHILE WHAT APPEARS TO BE A SURFACE REFLECTION WITHIN THE LOW- TO MID-LEVELS LAGS TO THE W. ACTING AS AN AREA OF CONVERGENCE OF HIGHER THETA-E AND WARMER AIR FROM THE W/SW...GREATER INSTABILITY DEVELOPS THOUGH IN WHAT APPEARS TO BE A MARGINAL-SHEAR ENVIRONMENT. WITH THE RETURN OF A WARM-MUGGY AIRMASS AND PWATS OF AROUND 1.25-1.50 INCHES THERE IS THE POSSIBILITY OF DISCREET FORCING WHETHER IT BE THROUGH LOW-LEVEL CONVERGENCE...AIRMASS INSTABILITY/RAPID DESTABILIZATION... AND/OR OROGRAPHIC LIFT. ANY ONE OR A COMBINATION OF WHICH SEEMS TO LEND TO SCATTERED SHOWER AND THUNDERSTORM ACTIVITY. MEAN-WIND FLOW IS RATHER MEAGER AROUND 15 KTS...SO SOME CONCERN WITH RESPECT TO HEAVY RAIN AND LOCALIZED FLOODING ISSUES. OVERALL WE COULD BE LOOKING AT A PERIOD OF STRONG TO SEVERE THUNDER- STORMS THAT MAY CONTAIN ANY ONE OF SEVERAL THREATS INCLUDING LARGE HAIL... DAMAGING WINDS...EVEN THE POSSIBILITY OF A TORNADO. BUT AS BOTH THE CIPS ANALOGS AND SREF PROBABILISTIC GUIDANCE ILLUSTRATE IS THAT SUCH THREATS LOOK TO BE DISCREET. NOT ENOUGH CONFIDENCE IN GOING WITH ENHANCED WORDING IN THE FORECAST. NOT REALLY SURE HOW THIS IS ALL GOING TO PLAY OUT. A CHAOTIC FORECAST WITH MULTIPLE PARTS AND NO REAL CERTAINTY OTHER THAN AN ANTICIPATED OUTCOME OF WARM AND MUGGY CONDITIONS DURING THE DAY. LOW CONFIDENCE. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... HIGHLIGHTS... * SCATTERED STRONG THUNDERSTORMS POSSIBLE SUNDAY * HEAT WAVE POSSIBLE TUESDAY THROUGH THURSDAY * SCATTERED STORMS POSSIBLE LATE THURSDAY SUNDAY...STILL LOOKS LIKE IT COULD BE AN ACTIVE WEATHER DAY. 0-1 KM HELICITY VALUES REMAIN RATHER ROBUST...ALTHOUGH INSTABILITY APPEARS TO BE LAGGING A FEW HOURS BEHIND. WITH MORNING SUNSHINE BREAKING OUT BEHIND THE DEPARTING UPPER DISTURBANCE...RAPID DESTABILIZATION IS EXPECTED DURING THE LATE MORNING HOURS WITH THE GFS CONTINUING TO INDICATE SURFACE-BASED CAPES APPROACHING 3000 J/KG ACROSS MOST OF THE REGION DURING THE AFTERNOON. A WARM FRONT WILL HAVE MOVED NORTHWARD INTO NORTH CENTRAL AND NORTHEASTERN MA BY THE AFTERNOON. WE ARE STILL VERY FAR AWAY AT THIS POINT...AND DO NOT WANT TO GET TOO CARRIED AWAY. THAT SAID...WE WILL NEED TO MONITOR THE POTENTIAL FOR MORNING CONVECTION INITIATION. EVEN IF THE WIND SHEAR AND INSTABILITY DO NOT PHASE IN TIME AND SPACE...THERE COULD BE ENOUGH INSTABILITY TO PRODUCE STRONG TO SEVERE THUNDERSTORMS SUNDAY AFTERNOON. THE MAIN RISK WOULD BE ACROSS INTERIOR SOUTHERN NEW ENGLAND. SUNDAY NIGHT AND MONDAY... A COLD FRONT STALLS ACROSS THE AREA. THIS IS SOMEWHAT TRICKY. THE MAJORITY OF THE LATEST GUIDANCE DEPICTS THIS FRONT BEING SQUEEZED BETWEEN TWO HIGH PRESSURES. AGAIN A LOT OF UNCERTAINTY AS THERE IS A GOOD AMOUNT OF CAPE AROUND...YET THERE IS HARDLY ANY SHEAR AS GUIDANCE SHOWS 10-20 KTS. HAVE COMPROMISED WITH SLIGHT CHANCE POPS FOR SHOWERS OR TSTMS. HIGH TEMPERATURES FORECAST TO BE A FEW DEGREES WARMER THAN SUNDAY...MAINLY 80 TO 85. TUESDAY THROUGH THURSDAY... THE COLD FRONT FINALLY GETS WASHED OUT SOMEWHERE OVER SOUTHERNMOST NEW ENGLAND BY TUESDAY. CANNOT RULE OUT AN ISOLATED SHOWER TUESDAY. OTHERWISE...AN UPPER LEVEL HIGH PRESSURE WILL SPREAD FROM THE MIDWEST TOWARD NEW ENGLAND. THIS WILL TRANSLATE TO MAINLY SUNNY CONDITIONS AND MUCH HOTTER WEATHER. IN FACT...925 MB TEMPERATURES REACH +28C WED AND THU AFTERNOONS. WE ARE FORECASTING NEAR 90 FOR HIGHS ON TUE AND LOWER TO MID 90S WEDNESDAY AND THURSDAY FOR MUCH OF THE INTERIOR...COOLER AT THE COAST. IT WOULD BE A HEAT WAVE IF WE COULD HIT 90 DEGREES FOR THREE CONSECUTIVE DAYS. THURSDAY EVENING INTO FRIDAY...MODELS ARE TRENDING TOWARD HAVING A COLD FRONT MOVE THROUGH THURSDAY NIGHT INTO FRIDAY. THERE SHOULD BE SOLID CAPPING DURING THE DAY ON THURSDAY WITH 700 MB TEMPERATURES FORECAST TO APPROACH +10C. THIS CAP COULD ERODE THURSDAY NIGHT INTO FRIDAY. THERE IS A CHANCE OF THUNDERSTORMS AS THIS COLD FRONT APPROACHES. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH SUNDAY/...HIGH CONFIDENCE. TODAY...MODERATE CONFIDENCE. COLD FRONT SWEEPS W OFF THE WATERS ALONG THE LEADING EDGE OF WHICH SOME -SHRA ARE POSSIBLE ALONG WITH LOW-END VFR / MVFR CIGS...ESP ALONG THE E-COAST. LIGHT WINDS TURNING E. TONIGH...MODERATE CONFIDENCE. SCT -SHRA WITH POSSIBLE TSRA FOCUSED MOSTLY OVER N NEW ENGLAND. WILL NEED TO MONITOR TERMINALS ACROSS MA ESP FOR POTENTIAL CONVECTIVE THREATS ALONG WITH MVFR-IFR IMPACTS. PATCHY DENSE FOG ANTICIPATED WITH INCREASING SE-ONSHORE WINDS. SUNDAY...LOW CONFIDENCE. OVERNIGHT WET-WEATHER PUSHES N AND E AS SCT -SHRA/TSRA EMERGE FROM THE W. MVFR-IFR IMPACTS POSSIBLE WITH TSRA WHICH MAY ALSO CONTAIN MULTIPLE CONVECTIVE THREATS SUCH AS HAIL AND GUSTY WINDS. LOW-END VFR CIGS WITH ONSHORE S-FLOW. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. WINDS TURNING E. COULD SEE SOME LOW-END / MVFR CIGS DEVELOP. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. -SHRA POTENTIALLY DEVELOPING TOWARDS THE LATER HALF OF SATURDAY. OUTLOOK /SUNDAY NIGHT THROUGH WEDNESDAY/... SUNDAY NIGHT INTO MONDAY...MODERATE CONFIDENCE. MVFR IN SCATTERED SHOWERS AND THUNDERSTORMS. A FEW STRONG STORMS POSSIBLE EARLY WITH LOCAL IFR VSBYS. TUESDAY...MODERATE CONFIDENCE. VFR. POSSIBLE MVFR IN ISOLATED SHOWERS OVER THE INTERIOR. WEDNESDAY...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 SUNDAY/...HIGH CONFIDENCE. TODAY... E-ONSHORE WINDS WITH SEAS REMAINING AROUND 3-FEET OR LESS. TONIGHT... INCREASING CHANCES FOR SHOWERS TOWARDS MORNING OUT OF THE W POSSIBLY ACCOMPANIED WITH THUNDER. WINDS VEERING SE AND INCREASING. POTENTIAL FOR PATCHY DENSE FOG AROUND THE CAPE AND ISLANDS. SUNDAY... CONTINUED CHANCES OF WET-WEATHER...ESPECIALLY OVER THE E-WATERS. SE-WINDS CONTINUE TO VEER S WITH THE POTENTIAL FOR GUSTS OF 15-20 KTS. SEAS BUILD UP TO AROUND 4-FEET. OUTLOOK /SUNDAY NIGHT THROUGH WEDNESDAY/... HIGH CONFIDENCE. WINDS AND SEAS BELOW SMALL CRAFT ADVISORY LEVELS THROUGH THIS PERIOD AS WEAK PRESSURE GRADIENT PERSISTS ACROSS WATERS. WARM FRONT LIFTS N ACROSS THE WATERS EARLY SUNDAY. A SLOW-MOVING COLD FRONT APPROACHES THE WATERS MONDAY INTO TUESDAY...BUT MAY DISSIPATE BY TUESDAY. A FEW STRONG THUNDERSTORMS ARE POSSIBLE OVER THE WATERS SUNDAY INTO SUNDAY EVENING. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...SIPPRELL/BELK NEAR TERM...SIPPRELL SHORT TERM...SIPPRELL LONG TERM...BELK AVIATION...SIPPRELL/BELK MARINE...SIPPRELL/BELK

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