Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 262323 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 723 PM EDT SAT JUL 26 2014 .SYNOPSIS... AS LOW PRESSURE DEEPENS FROM THE GREAT LAKES TO SOUTHEAST CANADA AND EVENTUALLY OCCLUDES ACROSS NEW ENGLAND...ANTICIPATE WAVES OF SHOWERS AND THUNDERSTORMS...BEGINNING SUNDAY MORNING AND CONTINUING THROUGH LATE MONDAY. A FEW OF THESE STORMS COULD BE STRONG TO SEVERE. HIGH PRESSURE FOLLOWS WITH COOLER AND DRIER WEATHER INTO THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 730 PM UPDATE... INITIAL MID-LEVEL DISTURBANCE THROUGH THE ZONAL FLOW IS EXITING TO THE E WITH ACCOMPANYING DRIZZLE. ABUNDANCE OF LOW-LEVEL DRY AIR HAS LIMITED ACTIVITY FROM REACHING THE GROUND. EXPECTING A MOSTLY QUIET NIGHT WITH S/SW FLOW. SOME GUSTS POSSIBLE DURING THE EVENING HOURS...BUT OVERALL EXPECT GUSTS TO REMAIN SUBDUED. S-FLOW WILL RESULT IN INCREASING DEWPOINTS. T-D SPREADS ON THE ORDER OF SEVERAL DEGREES ALONG THE S-COAST. COULD SEE THE DEVELOPMENT OF LOW-CLOUDS AND/OR FOG FOR SUCH REGIONS BY MORNING. NOT A LOT OF CONFIDENCE. WILL SEE HIGH CLOUDS BUILDING INTO THE REGION AHEAD OF THE MORNING LINE OF SHOWERS AND THUNDERSTORMS. SPEAKING OF WHICH...EVALUATING FORECAST GUIDANCE FOR WHAT SOLUTIONS ARE HANDLING THE CONVECTION OUT W WELL...IT APPEARS THE WRF-ARW IS DOING THE BEST. SUBSEQUENT TRENDS PUT A LINE OF CONVECTION ACROSS THE FORECAST REGION INTO THE CT-RIVER VALLEY BY 12Z...ACROSS WORCESTER INTO E NEW ENGLAND BY 18Z. SEE DISCUSSION BELOW FOR FURTHER DETAILS. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... SUNDAY... ALL MODELS INDICATE A JET MAX OF 80 KT AT 300 MB PASSING OVER NJ WHICH PLACES SOUTHERN NEW ENGLAND IN THE LEFT FRONT QUADRANT... A POSITION FAVORABLE FOR RISING MOTION. IN ADDITION...AN ELEVATED MIXED LAYER WILL BE PRESENT WITH 500-700 MB LAPSE RATES AROUND 7C/KM. THUS...WITH THE WARM FRONT APPROACHING...THE BAND OF THUNDERSTORMS THAT WILL BE APPROACHING THE BERKSHIRES AROUND DAYBREAK SHOULD CONTINUE TO PROGRESS EASTWARD...ESPECIALLY OVER SOUTHERN NH AND NORTHERN MA...PERHAPS EXITING THE REGION AROUND NOON OR 1 PM. LOW LEVEL WIND FIELDS WILL BE STRENGTHENING DURING THE MORNING...TO 30-40 KT AT 5000 FT...AND THIS MEANS THAT ANY REMAINING STORMS COULD PRODUCE STRONG TO POTENTIALLY DAMAGING WINDS BEFORE EXITING NORTHEAST MA. AFTER THAT...THE FORECAST BECOMES MORE UNCERTAIN. MODELS CONTINUE TO STRUGGLE WITH THE LOCATION AND TIMING OF MESOSCALE FEATURES. FOR EXAMPLE...IT DOES DRY OUT IN THE MID LEVELS AND K INDICES CORRESPONDINGLY DROP TO NEAR 20 OR LESS. THIS WOULD IMPLY THAT THERE COULD BE BREAKS OF SUNSHINE FORMING HOWEVER AND IT COULD MAKE THINGS MORE UNSTABLE. THE GFS SHOWED TOTAL TOTALS INDICES OF 50 TO 55 LURKING CLOSE BY IN SOUTHEAST NY AND THIS UNSTABLE AXIS COULD MOVE INTO CT AND WESTERN MA IN THE LATE AFTERNOON. HODOGRAPH PROFILES DO SHOW SIGNIFICANT TURNING IN THE LOWEST 1 KM...SO ALTHOUGH STORMS MAY BE ONLY SCATTERED ABOUT IN THE AFTERNOON...THERE IS THE POTENTIAL FOR ROTATION AND EVEN AN ISOLATED TORNADO. BY FAR...THE MOST SEVERE WEATHER ACTION WILL BE TAKING PLACE WELL TO OUR SOUTHWEST. IT REMAINS TO BE SEEN IF THAT ACTIVITY WILL TAKE AWAY FROM ENERGY IN OUR REGION OR WHETHER IT WILL ATTEMPT TO MOVE IN OUR DIRECTION BY SUNDAY NIGHT. HIGHS SHOULD REACH INTO THE LOWER 80S BUT COULD BE A FEW DEGREES HIGHER IF THERE ARE MORE BREAKS OF SUN. SOUTH TO SOUTHWEST WINDS SHOULD GUST TO 20 TO 25 MPH ESPECIALLY ACROSS RI AND SOUTHEAST MA. A FEW GUSTS TO 30 MPH ARE POSSIBLE SUNDAY AFTERNOON. SUNDAY NIGHT... SECOND WAVE OF ACTIVITY ANTICIPATED. FOCUS IS ALONG THE CONVERGENCE OF LOW- TO MID-LEVEL THERMAL/MOIST AXES COLLOCATED WITH AN ATTENDANT MID-LEVEL IMPULSE WITHIN THE LFQ OF THE UPPER-LEVEL JET. FALLING HEIGHTS ACROSS THE REGION AS NEARLY-STACKED LOW PRESSURE SHIFTS INTO W NEW ENGLAND BY MORNING. WILL HAVE TO MONITOR ACTIVITY OUT OF THE OH-RIVER VALLEY LIKELY AS A MCS AS IT ROUNDS THE UPPER-LOW...HOW IT WILL TREND WITH 0-6 KM MEAN WIND AND CORFIDI VECTOR FLOW. TRENDS BEGIN TO IMPROVE BY MORNING WITH THE INTRUSION OF MID- TO UPPER- LEVEL DRY AIR. MAIN CONCERN IS WITH A HEAVY RAIN THREAT ACROSS S/E PORTIONS OF NEW ENGLAND CENTERED AROUND MIDNIGHT. SURFACE DEWPOINTS SURGING INTO THE 70S. PWATS INCREASE TO +2-INCHES ACROSS S/SE COASTLINES. ATMOSPHERIC PROFILES BECOME SATURATED MOIST-ADIABATICALLY FROM THE SURFACE ON UP TO H3 FOR A SHORT-PERIOD OF TIME. AND FINALLY...THE MAJORITY OF THE ACTIVITY IS FOCUSED ON THE NOSE OF A H925/85 LOW-LEVEL-JET SWEEPING ROUGHLY S OF LONG-ISLAND INTO THE GULF OF MAINE. IT IS POSSIBLE THAT MOST OF THE ACTIVITY REMAINS OFFSHORE. NEVERTHELESS...THE PROXIMITY TO AREAS WHICH ARE SUSCEPTIBLE TO FLASH FLOODING /I.E. NEW BEDFORD AND FALL RIVER/ AS THEY ARE LOW-LYING WARRANTS THE CONCERN MENTIONED ABOVE. AS FOR SEVERE POTENTIAL WITH THE SECOND WAVE...AGAIN...WILL NEED TO WATCH ACTIVITY OUT OF THE OH-RIVER VALLEY. OTHERWISE...CONCLUSION OF DAYTIME HEATING LENDS TO A CAP JUST ABOVE THE SURFACE. BUT AT ONSET INSTABILITY IS IMPRESSIVE UP TO 2K J/KG PRIOR TO MIDNIGHT WEAKENING AS THE ATMOSPHERIC PROFILE SATURATES. DECENT AVERAGE SW-NE SHEAR WITH SOME SLIGHT TURNING WITHIN 0-1 KM...MAY HAVE TO WATCH FOR AN ELEVATED SEVERE WEATHER POTENTIAL INITIALLY IN THE FORECAST PERIOD WITH THE THREAT OF DAMAGING WIND GUSTS. WITH THE CAP...FEEL ANY THREAT OF TORNADOES WILL BE DIMINISHED. MONDAY... NEARLY STACKED LOW AND MAIN TROUGH AXIS LIFTS INTO NEW ENGLAND AS THE MID-LEVEL DRY PUNCH AHEAD SWEEPS NE ACROSS THE FORECAST REGION. MOST NOTABLY...TROWALING PROCEEDS REARWARD OF THE LOW /NW-QUAD/ CONVERGING WITH THE COLD-CONVEYER-BELT LENDING TO A REGION OF LOW- TO MID-LEVEL FRONTOGENESIS ACROSS UPSTATE NY INTO THE W-SLOPES OF HIGH TERRAIN OF NEW ENGLAND. WITH OVERNIGHT ACTIVITY AND DYNAMICS SHIFTING N/E FOLLOWED BY A MID- LEVEL DRY-PUNCH...S/E PORTIONS OF NEW ENGLAND SHOULD BECOME DRY AND QUIET. SHOULD SEE CLOUDS SCOUR OUT. SOME LOW-CLOUDS AND FOG ISSUES MAY LINGER FROM OVERNIGHT. AS TO THE N/W NEW ENGLAND...CONSIDERING THE FORCING ASSOCIATED WITH LOW- TO MID-LEVEL CONVERGENCE WITHIN THE TROWAL...INSTABILITY ON THE ORDER OF 2K J/KG...DECENT AVERAGE SW-NE SHEAR...AND PWATS UP TO 1.5- INCHES...ANTICIPATE SCATTERED STORM ACTIVITY WITH THE THREAT OF HEAVY RAIN...LARGE HAIL /LOWER FREEZING LEVEL HEIGHTS/...AND DAMAGING WINDS. MUCH OF THIS ACTIVITY LOOKS TO REMAIN OVER UPSTATE- NY INTO N NEW ENGLAND...BUT THERE IS A THREAT FOR THE W-SLOPES OF HIGHER TERRAIN IN W MA AND SW NH. 26.12Z NAM HINTS AT SOME ACTIVITY ACROSS THE CT-VALLEY ON UP INTO SW NH. QUITE POSSIBLE WITH THE FALLING HEIGHTS AND PROXIMITY OF THE LOW. CAN NOT RULE IT OUT...WILL HOLD WITH LIKELY POPS AS SUCH. MONDAY NIGHT... DIURNAL HEATING CONCLUDES AS THE LOW LIFTS OUT OF THE REGION. EXPECT ACTIVITY WITHIN THE TROWAL STRUCTURE REARWARD OF THE LOW TO DIMINISH RESULTING IN A MOSTLY QUIET NIGHT. SCATTERED SHOWER ACTIVITY MAY LINGER ALONG THE W-SLOPES OF HIGHER TERRAIN INITIALLY IN THE PERIOD. BUT WITH HEIGHTS RISING AS HIGH PRESSURE BUILDS INTO THE REGION... EXPECT CONDITIONS TO IMPROVE INTO TUESDAY. && .LONG TERM /TUESDAY THROUGH SATURDAY/... OVERVIEW... SHORTWAVE FROM MONDAY SLOW LIFTS NORTHEAST AS IT MERGES WITH AN UPPER LEVEL LOW IN NORTHEAST CANADA. MEANWHILE AIR CONTINUES TO FLOW INTO THE REGION FROM THE SOUTHWEST AFTER THE COLD FRONT PASSES AND STALLS JUST OFF THE EAST COAST. THE STALLING IS CAUSED BY BLOCKING IN THE WESTERN UNITED STATES AND NORTHWESTERN ATLANTIC. SO FLOW CONTINUES TO BE MERIDIONAL RATHER THAN ZONAL OVER THE UNITED STATES. THIS IS ALSO HINTED AT BY THE PNA WHICH HAS HAD A BETTER HANDLE ON THE BLOCKING THAN THE NAO OF LATE. AM ALSO NOTICING SOME DISCREPANCIES IN THE HANDLING OF THE UPPER LEVEL LOW IN NORTHEAST CANADA. THE ECMWF WANTS TO CLOSE OFF A LOW IN THE EASTERN CENTRAL US WHILE THE GFS HAS SMALLER PACKETS OF ENERGY. THESE LEAD TO THE DIFFERENCES IN PRECIPITATION. FEEL A MODEL BLEND IS THE BEST TO HANDLE THE LATER PERIOD. DAILIES... TUESDAY...A SHORTWAVE PINWHEELS AROUND THE UPPER LEVEL LOW HELPING TO DIG THE TROUGH FURTHER SOUTH. AS MENTIONED BEFORE...A COLD FRONT STALLS JUST EAST OF CAPE COD KEEPING SURFACE FLOW MOSTLY FROM THE WEST. THIS ALLOWS FOR DRYING OVER THE INTERIOR. HOWEVER...CLOSER TO THE FRONT...NEAR THE CAPE AND ISLANDS...CAN/T RULE OUT SEEING MORE HIGH LEVEL CLOUDS. WEDNESDAY AND THURSDAY...WITH THE FLOW BEING STALLED...CAN/T RULE OUT PERIODS OF MORNING AND EVENING FOG ALONG SOUTHERN AND EASTERN SECTIONS ESPECIALLY AS THE LOW LEVEL WINDS GO BELOW 10KTS AND DEW PT DEPRESSIONS GO LESS THAN 5F. ENERGETIC WAVES WILL ALSO CONTINUE TO MOVE NORTHEAST ALONG THE FRONT CHANGING WIND DIRECTION AS THE THEY GO THROUGH. SOME PERIODS OF NORTHEAST WINDS CAN BE SEEN WHERE THE MOISTURE CAN BE BROUGHT INTO THE CAPE AND ISLANDS ALLOWING FOR SOME CLOUDS THERE. PROFILES STILL LOOK PRETTY DRY THOUGH. FRIDAY AND SATURDAY... AS THE UPPER LEVEL LOW IN SOUTHEAST CANADA LIFTS NORTH DURING FRIDAY...CAN EXPECT THE FRONT TO BACK CLOSER TO THE EAST COAST ALLOWING MORE RAIN ON THE CAPE AND ISLANDS. HAVE ALLOWED FOR POPS FOR THIS TIME PERIOD. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... * MODERATE CONFIDENCE WITH RESPECT TO TRENDS * LOW CONFIDENCE IN REGARDS TO SPECIFICS /IMPACTS AND TIMING/ VSBY IMPACTS WITH FOG POSSIBLE TOWARDS MORNING PRIOR TO LOWERING CIGS ASSSOCIATED WITH THE APPROACH OF SHRA/TSRA THAT SHALL LINGER INTO THE AFTERNOON. WILL GO CONSERVATIVE AND HOLD MVFR FOR NOW. MAY SEE A LULL IN ACTIVITY DURING THE EVENING YET OVERNIGHT ANTICIPATE THE INCREASE IN AREAL COVERAGE OF SHRA/TSRA ALONG WITH THE POTENTIAL OF COASTAL FOG FOR THE S/SE SHORELINE TERMINALS. A MIX OF MVFR-IFR CONDITIONS SUBSEQUENT TO SHRA/TSRA ACTIVITY IS POSSIBLE...BUT WILL HOLD OFF IN MENTIONING DUE TO LOW CONFIDENCE. AS CONDITIONS QUIET DOWN INTO MONDAY MORNING...SHRA/TSRA ARE ANTICIPATED TO BE ON THE INCREASE OVER INTERIOR NEW ENGLAND THROUGHOUT THE DAY...WEATHER CONCLUDING INTO THE EVENING AND IMPROVING. WITH ANY SHRA/TSRA ACTIVITY...MIX OF MVFR-IFR POSSIBLE BUT WILL HOLD OFF ON ANY MENTION DUE TO LOW CONFIDENCE. BREEZY S/SW FLOW THROUGHOUT THE PERIOD. KBOS TAF...MODERATE CONFIDENCE. SHRA/TSRA ANTICIPATED AROUND 16-18Z AND LIKELY TO BE ACCOMPANIED WITH A MIX OF MVFR-IFR IMPACTS...THOUGH UNCERTAIN TIMING RESULTS IN LACK OF MENTION. KBDL TAF...MODERATE CONFIDENCE. LINE OF SHRA/TSRA SHOULD SWEEP THE TERMINALS DURING THE MORNING HOURS. A MIX OF MVFR-IFR IMPACTS POSSIBLE...BUT LOW CONFIDENCE LIMITS A PREVAILING MENTION. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...MODERATE CONFIDENCE. MONDAY NIGHT... IMPROVING VFR AS WINDS BACK W/SW AND ACTIVITY MOVES OUT OF THE REGION. SHOULD SEE CIGS/VSBYS LIFT. TUESDAY THROUGH THURSDAY...VFR WITH DRYING WEST WINDS. LOW CONFIDENCE ON A POSSIBILITY OF MVFR WITH ANY FOG IN THE MORNING AND EVENING HOURS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH MONDAY...HIGH CONFIDENCE INTO THIS EVENING AND THEN LOWERING CONFIDENCE LATER TONIGHT THROUGH MONDAY REGARDING TIMING AND AREAL COVERAGE OF SHOWERS/T-STORMS. TONIGHT...QUIET TO START BUT AN APPROACHING WARM FRONT WILL LEAD TO PATCHY FOG/LOW CLOUDS POTENTIALLY REDUCING VSBY TOWARD DAYBREAK SUNDAY. SUNDAY...A SMALL CRAFT ADVISORY HAS BEEN ISSUED. S TO SW WINDS INCREASE TO 15-20 KT WITH GUSTS TO 25 KT ACROSS ALL WATERS. SEAS WILL BE BUILDING TO 5 TO 6 FT OVER THE SOUTHERN OUTER WATERS BY SUNDAY EVENING. SCATTERED T-STORMS POSSIBLE AT ANY TIME DURING THE DAY. ANY STORMS COULD PRODUCE STRONG WIND GUSTS AND LOCALLY HIGHER SEAS. SUNDAY NIGHT INTO MONDAY... BREEZY SW WINDS WITH GUSTS UP TO 25 KTS WITH WAVE HEIGHTS BUILDING UP TO 7 FEET ON THE S/SE OUTER WATERS. SMALL-CRAFT ADVISORIES LIKELY NEEDED TO BE EXTENDED. WIDESPREAD RAIN...HEAVY AT TIMES...WITH EMBEDDED THUNDERSTORMS. ANTICIPATE VISIBILITY RESTRICTIONS DOWN TO A MILE AS FOG IS ALSO POSSIBLE. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...MODERATE CONFIDENCE. MONDAY NIGHT... WINDS SHIFTING W/SW AND DECREASING. SHOULD SEE CONDITIONS IMPROVE AS WAVES DEAMPLIFY. LIKELY WAVE HEIGHTS OVER 5 FEET ON THE OUTER WATERS WILL RESULT IN A PROLONGED PERIOD OF SMALL-CRAFT ADVISORIES. TUESDAY...THE COLD FRONT PUSHES AWAY FROM SOUTHERN NEW ENGLAND... BUT STALLS OFFSHORE SO WATERS WILL BEGIN TO LESSEN FROM 5 TO 6 FT WAVES TO JUST AROUND 5 IN THE OUTER WATERS NEAR WHERE THE FRONT STALLS. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR SOME OF THE WATERS ESPECIALLY THE OUTER WATERS. WEDNESDAY AND THURSDAY...LIGHTER WINDS AND SEAS AS HIGH PRESSURE BUILDS OVER THE WATERS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 1 PM TO 8 PM EDT SUNDAY FOR ANZ230>234-236-237-251. SMALL CRAFT ADVISORY FROM 1 PM SUNDAY TO 6 AM EDT MONDAY FOR ANZ235-250-254>256. && $$ SYNOPSIS...SIPPRELL/GAF NEAR TERM...SIPPRELL/GAF SHORT TERM...SIPPRELL/GAF LONG TERM...99 AVIATION...SIPPRELL/GAF/99 MARINE...SIPPRELL/GAF/99

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