Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231840 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 240 PM EDT WED JUL 23 2014 .SYNOPSIS... WEATHER WILL BE HOT AND HUMID WEATHER TODAY AHEAD OF AN APPROACHING COLD FRONT. THE FRONT WILL TRIGGER SCATTERED SHOWERS AND THUNDERSTORMS LATE THIS AFTERNOON AND EVENING. A FEW STRONG THUNDERSTORMS ARE POSSIBLE WEST OF I-495 AND NORTH OF THE MASS PIKE AND I-84. SHOWERS WILL LIKELY LINGER INTO THURSDAY SOUTHEAST OF THE BOSTON TO PROVIDENCE CORRIDOR. HIGH PRESSURE BUILDS WITH DRIER WEATHER FOR FRIDAY AND SATURDAY. AN APPROACHING WARM FRONT SUNDAY WILL BRING MORE HUMID UNSETTLED WEATHER FOR THE EARLY PART OF NEXT WEEK. && .NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
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* A FEW STRONG TO SEVERE STORMS POSSIBLE LATE THIS AFTERNOON INTO THE EVENING HOURS * CONTINUE TO MONITOR FOR THE POTENTIAL FOR STRONG TO SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO THE LATE EVENING HOURS. CURRENTLY THE COLD FRONT HAS JUST PUSHED THROUGH SYRACUSE NY AND WILL CONTINUE ITS EASTWARD PROGRESSION TOWARDS SOUTHERN NEW ENGLAND THROUGH THE AFTERNOON. AS IT APPROACHES ANTICIPATE ISOLATED SHOWERS AND THUNDERSTORMS TO POP-UP AT FIRST BUT THEN A MORE BROKEN LINE SEGMENT TO MOVE THROUGH BY THE EVENING HOURS. LOOKING AT SPC MESO ANALYSIS...SB CAPE VALUES HAVE REACHED TO 2500 J/KG WITH NOT MUCH IN THE TERMS OF EFFECTIVE SHEAR FOR SOUTHERN NEW ENGLAND. RAP 0-6KM BULK SHEAR VALUES ARE WEAK AS WELL...WITH ONLY 10-15 KTS. AS OF 18Z...THE STRONGER WIND SHEAR AND UPPER LEVEL JET DYNAMICS ARE STILL SITUATED UP NEAR THE COLD FRONT WHICH IS ALSO WHERE THE DEEP LAYER MOISTURE IS LOCATED PER THE K-INDEX. HENCE WHY THE STORMS ARE STARTING TO FIRE ACROSS UPSTATE NEW YORK. AS THE FRONT MOVES EASTWARD DURING THE AFTERNOON...SOME OF THESE PARAMETERS WILL ALSO SHIFT EASTWARD. THE BIGGEST LIMITING FACTOR FOR US RIGHT NOW IS THE LACK OF DEEP LAYER MOISTURE AND SHEAR...WHICH IS NOT PROJECTED TO MOVE INTO THE REGION UNTIL CLOSER TO 00Z. THEREFORE BELIEVE THAT JUST A FEW ISOLATED LOW TOP SHOWERS WILL DEVELOP OVER THE NEXT FEW HOURS. AFTER 00Z THE FRONT WOULD HAVE MOVED CLOSER TO THE REGION WITH BETTER SHEAR AND MOISTURE. THE ONE THING TO BE CONCERN IS THE AMOUNT OF INSTABILITY. WITH THE ATMOSPHERE NOT BEING WORKED OVER AND THE WARM...MOIST ATMOSPHERE BOILING OVER THE REGION TODAY BELIEVE ONCE THE STORMS MOVE INTO THE REGION THEY WILL EAT UP ANY INSTABILITY AND DEVELOP INTO STRONG STORMS. STILL CANNOT RULE OUT THE POTENTIAL FOR SEVERE WEATHER BUT HAVE INCREASING CONFIDENCE THAT AT LEAST STRONG STORMS WILL DEVELOP. AFTER DISCUSSING WITH SPC DECIDED TO ISSUE A WATCH FOR THE LOCATIONS THAT ARE PROGGED TO HAVE THE BEST MOISTURE/INSTABILITY AND SHEAR FOR WHEN/IF THUNDERSTORMS MOVE OVER THOSE LOCATIONS. MAIN THREATS ARE DAMAGING WINDS AND LOCALIZED FLOODING AS PWATS CONTINUE TO INCREASE ABOVE 1.8 INCHES.
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&& .SHORT TERM /MIDNIGHT THROUGH 6 PM THURSDAY/...
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* SHOWERS WILL LIKELY LINGER ACROSS THE CAPE...ISLANDS AND ADJACENT SE MASSACHUSETTS DURING MUCH OF THURSDAY THURSDAY... THE FRONT DEACCELERATES AS IT APPROACHES SOUTHEAST NEW ENGLAND AND THEN A WAVE MOVES ALONG THE FRONT DURING THE DAY THURSDAY. THUS...EXPECT SHOWERS TO LINGER THURSDAY MORNING ACROSS THE SOUTHEAST HALF OF THE AREA AND FOR MOST OF THE DAY ACROSS CAPE COD...THE ISLANDS AND ADJACENT SOUTHEAST MA. WILL BE MUCH COOLER THURSDAY BEHIND THE FRONT...AND SOUTHEAST OF THE BOSTON TO PROVIDENCE CORRIDOR CLOUDS WILL ALSO ACT TO CAP THE TEMPERATURE. FOR MOST LOCATION...EXPECT HIGHS IN THE 70S ON THURSDAY. THE ATMOSPHERE MAY BE MARGINALLY UNSTABLE ENOUGH TO SUPPORT A FEW EMBEDDED THUNDERSTORMS OVER THE CAPE AND ISLANDS AS WELL AS SOUTHEAST COASTAL WATERS ON THURSDAY.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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BIG PICTURE... FOUR FEATURES IN THE LARGE SCALE FLOW. TROUGH ALONG THE PACIFIC NORTHWEST COAST...RIDGE EXTENDING FROM THE ROCKIES AND PLAINS TO NORTHERN CANADA...CLOSED LOW OVER NORTHERN QUEBEC WITH TROUGH AXIS ACROSS THE GREAT LAKES...BUILDING RIDGE OVER THE WESTERN ATLANTIC. THE QUEBEC TROUGH HANGS OVER NORTHEAST NORTH AMERICA...THE TROUGH AXIS AND COLDEST TEMPS ALOFT SWING ACROSS NEW ENGLAND THURSDAY NIGHT/FRIDAY. THE PACIFIC NORTHWEST TROUGH RUNS OVER THE TOP OF THE ROCKIES RIDGE...THEN MERGES WITH THE QUEBEC LOW OVER THE WEEKEND. THIS DRAWS THE CLOSED LOW SOUTH OVER THE GREAT LAKES/NORTHEAST EARLY NEXT WEEK. THE ATLANTIC HIGH PRESSURE MEANWHILE BLOCKS OFF THE EASTWARD EXIT OF THIS MERGER. THE COMBINATION OF UPPER LOW PRESSURE OVER THE LAKES AND HIGH PRESSURE OVER THE ATLANTIC CREATES A SOUTHWEST FLOW UP THE EAST COAST FROM THE DEEP SOUTH FOR THE FIRST HALF OF NEXT WEEK. MODELS HAVE BEEN SHOWING CONSISTENCY BOTH RUN TO RUN AND WITH EACH OTHER. THIS INCREASES CONFIDENCE IN THE OVERALL SOLUTION...BUT WITH THE USUAL UNCERTAINTY IN TIMING SHORTWAVES MOVING THROUGH THE FLOW. THIS IS ESPECIALLY TRUE FOR MONDAY AND TUESDAY. THE DAILIES... THURSDAY NIGHT...COLD FRONT LINGERS OFFSHORE WHILE THE UPPER JET RIGHT ENTRANCE REGION MOVES OVERHEAD. THIS MAY SUPPORT A WAVE ALONG THE FRONT DURING THE FIRST PART OF THE NIGHT...BUT THE JET SHIFTS EAST AFTER MIDNIGHT AS SHOULD THE SUPPORTING DYNAMICS. WE WILL KEEP CHANCE POPS ON THE CAPE AND ISLANDS EARLY IN THE NIGHT. IF THE JET POSITION AT 00Z IS AS ADVERTISED...WE MAY BE A LITTLE CONSERVATIVE ON EVENING POPS. OTHERWISE THE MOVEMENT OF THE UPPER JET SHOULD TREND SOUTHERN NEW ENGLAND TO END ANY REMAINING PCPN AND BRING CLEARING SKIES. FRIDAY-SATURDAY... SURFACE HIGH PRESSURE BUILDS OVER THE REGION WITH DRY WEATHER AND DEWPOINTS IN THE 50S. TEMPS AT THE TOP OF THE MIXED LAYER WILL SUPPORT UPPER 70S TO MID 80S BOTH DAYS...A LITTLE WARMER SATURDAY. ONE CONCERN WILL BE SEA BREEZE DEVELOPMENT ON FRIDAY WHICH MAY HOLD DOWN AFTERNOON TEMPS ON THE EASTERN COAST. OTHER CONCERN WOULD BE THE PASSAGE OF THE UPPER TROUGH AND COLDER TEMPS ALOFT. THIS LATTER CONCERN COULD DESTABILIZE THE AIRMASS AND PROMOTE CUMULUS DEVELOPMENT. BUT MODEL RH FIELDS SHOW A DRY AIRMASS WITH RH VALUES BELOW 700 MB BELOW 50 PERCENT. WILL KEEP SKY COVER LOW FRIDAY...THEN INCREASING CIRRUS ON SATURDAY AFTERNOON. SUNDAY... PACIFIC NORTHWEST SHORTWAVE DIGS AS IT APPROACHES THE GREAT LAKES AND GENERATES A SURFACE LOW. STRONG LOW LEVEL JET IS EXPECTED TO DEVELOP IN THE OHIO VALLEY SATURDAY WITH 35-40 KNOT WINDS AT 850 AND 900 MB. AS THIS MOVES EAST IT WILL BRING DEEPER MOISTURE TO NEW ENGLAND WITH PRECIP WATER VALUES CLIMBING TO 1.5 INCHES BY SUNDAY. THE LIFTING OF THIS AIR OVER THE DEPARTING SURFACE LAYER WOULD GENERATE SOME SHOWERS/SCT TSTMS. WE WILL MENTION CHANCE POPS LATER SATURDAY NIGHT INTO SUNDAY. MONDAY-TUESDAY...THE MERGING LOW OVER THE GREAT LAKES SURFACE AND ALOFT WILL SWING A FRONT THROUGH NEW ENGLAND. TIMING IS IN QUESTION AT THIS POINT WITH THE GFS SHOWING FROPA MONDAY NIGHT WHILE THE ECMWF STALLS THE FRONT OVER US. WITH NO CLEAR TREND ON A DAY 7 FORECAST...WE WILL STAY CLOSE TO BLENDED GUIDANCE SOLUTION OF DIMINISHING POPS TUESDAY. BUT WITH LOW CONFIDENCE.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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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 THURSDAY/... GENERALLY MODERATE CONFIDENCE ON FORECAST. THROUGH 22Z...GENERALLY VFR. AFTER 22Z INTO TONIGHT...MVFR CIGS AND VSBYS IN VICINITY OF SCT TSTMS AHEAD OF A COLD FRONT. A FEW TSTMS MAY BRIEFLY LOWER CIGS/VSBYS TO IFR LEVELS. ALSO...A FEW TSRA MAY PRODUCE STRONG WIND GUSTS. THERE IS ALSO A MODERATE POTENTIAL FOR IFR CIGS FORMING TONIGHT ACROSS THE CAPE AND ISLANDS. THURSDAY...GENERALLY MVFR CIGS AND VSBYS TO START IN ANTICIPATED RAIN OR SHOWERS. CONDITIONS WILL BE IMPROVING FROM NW TO SE THROUGH MUCH OF THE DAY. EXCEPT ALONG AND SE OF A PYM-UUU LINE WHICH MAY STAY IN LOWER CLOUDS THROUGH MUCH OF THURSDAY...IMPROVING LATE. KBOS TAF...HIGH CONFIDENCE. VFR THROUGH MOST OF THE DAY. TSTMS POSSIBLE AFT 00Z TO THE N AND W OF BOS AND CLOSER TO THE AIRFIELD ITSELF AFT 03Z. KBDL TAF...HIGH CONFIDENCE IN TAF. TSTMS POSSIBLE AFT 22Z. ANY TSTMS COULD CONTAIN STRONG WIND GUSTS. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY...MODERATE CONFIDENCE. THURSDAY NIGHT THROUGH SATURDAY...VFR. LOCAL IFR POSSIBLE IN EARLY MORNING FOG/LOW CLOUDS. POTENTIAL SEA BREEZE FRIDAY AFTERNOON. SUNDAY... VFR BUT WITH AREAS OF MVFR IN SHOWERS/TSTMS/FOG.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY/...MODERATE CONFIDENCE. THE SW FLOW WILL STRENGTHEN AHEAD OF A COLD FRONT TO PRODUCE GUSTS APPROACHING 25 KT ACROSS MANY OF THE WATERS. SEAS MAY APPROACH 5 FEET EAST OF CAPE ANN...ACROSS THE E PORTION OF STELLWAGEN BANK...AND E OF CAPE COD THIS AFTERNOON. ALTHOUGH THE WIND WAVE WILL BE FORMED FROM THE SW FLOW...THERE IS ALSO A SWELL THAT IS ENCROACHING THE COASTAL WATERS FROM THE EAST. ALTHOUGH OF FAIRLY LOW AMPLITUDE OF LESS THAN 3 FEET...THE SWELL APPEARS TO BE ENOUGH TO TRIGGER A MODERATE RIP CURRENT RISK ALONG PORTIONS OF THE EAST FACING COAST. AREAS OF FOG MAY DEVELOP ALONG THE SOUTH COASTAL WATERS TONIGHT. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY...MODERATE CONFIDENCE. THURSDAY NIGHT-FRIDAY-SATURDAY... NORTH TO NORTHEAST WIND THURSDAY NIGHT BECOMES LIGHT FRIDAY WITH AFTERNOON SEA BREEZES DEVELOPING. WINDS BECOME SOUTHWEST SATURDAY BUT REMAIN BELOW 25 KNOTS. SEAS 4 FEET OR LESS THROUGH THE PERIOD. SUNDAY...A WARM FRONT APPROACHES THE WATERS WITH WARMER MORE HUMID AIR AND WITH CLOUDS/SHOWERS/TSTMS. INCREASING SOUTH-SOUTHWEST WINDS WITH GUSTS 20-22 KNOTS...APPROACHING SMALL CRAFT THRESHOLD. THESE WINDS WILL ALSO BUILD SEAS ON THE EXPOSED WATERS TO 5 OR 6 FEET. A SMALL CRAFT ADVISORY MAY BE NEEDED. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ230>237-251. SMALL CRAFT ADVISORY UNTIL 3 AM EDT THURSDAY FOR ANZ250-254. && $$ SYNOPSIS...WTB/THOMPSON NEAR TERM...DUNTEN SHORT TERM...THOMPSON LONG TERM...WTB AVIATION...WTB/DUNTEN MARINE...WTB/THOMPSON

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