804  
FXUS61 KBOX 221804  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
204 PM EDT WED MAY 22 2019  
   
SYNOPSIS
 
 
SEASONABLE AND DRY BENEATH HIGH PRESSURE TODAY, DIMINISHING WINDS.  
A FEW SHOWERS ARE POSSIBLE LATE TONIGHT INTO EARLY THURSDAY AS A  
WARM FRONT APPROACHES. SHOWERS AND SCATTERED THUNDERSTORMS LATE  
THURSDAY INTO EARLY FRIDAY MORNING AHEAD OF A SWEEPING COLD FRONT.  
DRY FRIDAY NIGHT INTO SATURDAY MORNING. ON AND OFF SHOWER CHANCES  
BEGINNING LATE SATURDAY THROUGH MEMORIAL DAY. COOLER WEATHER RETURNS  
NEXT TUESDAY BEHIND A COLD FRONT.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
2 PM UPDATE ...  
 
SEASONABLE, DRY CONDITIONS CONTINUE. HIGHS BUILDING INTO THE LOW 70S  
AT THIS HOUR WHICH IS ALLOWING FOR DEEP BOUNDARY LAYER MIXING UP TO  
H8 (4-5 KFT). STILL A GOOD PRESSURE GRADIENT ALOFT AS A STORM SYSTEM  
EXITS OFF SE CANADA AND HUDSON BAY HIGH PRESSURE BUILDS S. DECENT  
N WINDS PERSIST WITH VARIABLE GUSTS 10 TO 15 MPH. HOWEVER, THE  
INTERIOR WARMTH AND THE FACT THAT WINDS HAVE DIMINISHED SINCE THIS  
MORNING HAS ALLOWED FOR ONSHORE SEA-BREEZES ALONG THE COAST. SOME  
STRUGGLE TO PROGRESS INTO THE INTERIOR GIVEN N WINDS, NEVERTHELESS  
WILL BE COOLER ALONG THE COAST AS WE GO INTO THIS EVENING. MID TO  
HIGH CLOUDS ON THE INCREASE OUT OF THE W WITH ISENTROPIC ASCENT  
ALONG A LIFTING WARM FRONT ONGOING OVER THE E GREAT LAKES.  
 
TONIGHT ...  
 
MOSTLY DRY AND MILD. A CHANCE OF SCATTERED LIGHT SHOWERS INTO THE  
W CT RIVER VALLEY TOWARDS THURSDAY MORNING. MID-HIGH LEVEL CLOUDS  
THICKENING AND LOWERING TOWARDS MORNING WITH ENHANCING ISENTROPIC  
UPSLOPE ALONG THE W-PERIPHERY OF DEPARTING HIGH PRESSURE RIDGE SE  
OF NEW ENGLAND. STILL A MEASURE OF LINGERING DRY AIR AND SUBSIDENCE  
INFERRED FROM FORECAST MODEL SOUNDINGS. WILL KEEP CHANCE POPS IN  
FAR W MA AND CT AS THERE IS SOME CONFIDENCE OF UPSLOPE PRECIPITATION  
ALONG THE LIFTING WARM FRONT FROM THE OH RIVER VALLEY TO REACH THE  
SURFACE, ALBEIT LIGHT, JUST A TRACE TO A HUNDREDTH OF OUTCOMES BY  
DAYBREAK THURSDAY.  
 

 
   
SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/
 
 
2 PM UPDATE (FURTHER UPDATES POSSIBLE AT 4 PM) ...  
 
THURSDAY INTO THURSDAY NIGHT ...  
 
LATE AFTERNOON INTO EVENING WIDESPREAD SHOWERS WITH EMBEDDED HEAVIER  
SHOWERS, POSSIBLE THUNDERSTORMS. CONFIDENT HEAVY RAIN, HOWEVER LOWER  
CONFIDENCE WITH REGARDS TO STRONG TO SEVERE WEATHER, PARTICULARLY  
STRONG TO DAMAGING WINDS AND THE POSSIBILITY OF A TORNADO, ALBEIT A  
LOW RISK.  
 
SYNOPTICALLY, N-CONUS LOW OCCLUSION EJECTING E WITH ATTENDANT H3 JET  
STREAK. PRECEDING WARM FRONT, BROADSCALE 295-300K SURFACE ISENTROPIC  
ASCENT, EXPECT SCATTERED MORNING SHOWERS ALONG A CONVERGENT NOSE OF  
A H8-9 LOW-LEVEL JET WITH INCREASING THETAE. CLOUDS LINGER WITH HIGH  
PRESSURE SE, SUBSEQUENT SURFACE ONSHORE S FLOW BENEATH A H9-8 WARM  
NOSE WITH H85 TEMPERATURES +14C PRIOR TO A SWEEPING COLD FRONT OVER  
S NEW ENGLAND AROUND MIDNIGHT OVERNIGHT. BIG QUESTION IS WHETHER WE  
CAN DESTABILIZE OVER S NEW ENGLAND BEFOREHAND. SURFACE LOW EJECTING  
OVER N NEW ENGLAND AROUND EVENING BENEATH THE LEFT FRONT QUADRANT OF  
A PARENT H3 JET STREAK. POTENT H5 VORTMAX DIGS ACROSS NEW ENGLAND AS  
A W JET THROUGHOUT THE COLUMN RACES E WITH DRIER AIR ON THE BACKSIDE  
OF THE AFOREMENTIONED TRAILING COLD FRONT.  
 
MESOSCALE, AGAIN, BIG QUESTION IS WHETHER WE CAN DESTABILIZE, MORE  
SO IF TEMPERATURES WARM INTO THE 70S. CLOUDS, CAPPED BY A WARM-NOSE  
AROUND H9, AND MARITIME ONSHORE S-FLOW WILL LIMIT THE ENVIRONMENTAL  
POTENTIAL ALONG WITH THE LATE-DAY INTO EVENING EVENT. NOTING STRONG  
W SHEAR AND LOW-LEVEL HELICITY, HOWEVER WEAK INSTABILITY IN AN OVER-  
ALL SATURATED MOIST-ADIABATIC, CONVECTIVELY UNSTABLE ENVIRONMENT ON  
THE ORDER OF 500 J/KG AS THE COLD FRONT SWEEPS THROUGH. CONVECTIVE  
INDICES MET OR EXCEEDED IN TANDEM. AND WITH THE STRONG, DRY W JET  
THAT LOOKS TO IMPINGE REARWARD OF THE COLD FRONT, ITS A QUESTION AS  
TO WHETHER SYNOPTIC INFLUENCES WILL ERODE STORM-TOP DEVELOPMENT OR  
ENHANCEMENT.  
 
AGREE WITH SPC OUTLOOK IN LIMITING THE STRONG TO SEVERE POTENTIAL TO  
THE E. CONFIDENCE ON WIDESPREAD SHOWERS WITH EMBEDDED HEAVIER RAIN,  
SOME RUMBLES OF THUNDER. NOT RULING OUT THE POTENTIAL FOR A STRONG,  
PERHAPS EVEN A SEVERE THUNDERSTORM. NOTING THE ENVIRONMENT ABOVE,  
ANY SEVERE WEATHER THREATS WOULD MAINLY BE STRONG TO DAMAGING WINDS  
WITH THE VERY LOW RISK OF A TORNADO. FREEZING LEVELS TO 10 KFT AND  
PRECIPITABLE WATERS TO 1.5 INCHES WITH BOTH SYNOPTIC AND CONVECTIVE  
SUPPORT, WILL ALSO HAVE TO WATCH FOR HEAVY RAINERS AND LOCALIZED  
FLOODING.  
 
FINAL NOTE, STORM ATTRIBUTES FROM HREF ALONG WITH SEVERE PARAMETERS  
AND PROBABILITIES FROM SREF AS WELL AS CIPS ANALOGS NOT ONLY ARE  
PUSHING THE SYSTEM THROUGH FASTER PER DPROG/DT BUT ALSO PUT THE  
HIGHEST CONFIDENCE ON OUTCOMES SW OF OUR AREA. SPC HAS SHIFTED THEIR  
D2 OUTLOOK ACCORDINGLY. IF ANYWHERE IN S NEW ENGLAND WHERE THERE IS  
THE POTENTIAL FOR STRONG TO SEVERE WEATHER, SEEMINGLY IT WOULD BE  
ACROSS W NEW ENGLAND INTO THE CT RIVER VALLEY.  
 
CLEARING OUT AND DRYING OUT OVERNIGHT WITH BREEZY W/NW WINDS THAT'LL  
FOLLOW. GIVEN THE MIDNIGHT TIMING, NOT EXPECTING LOWS TO DROP DOWN  
SIGNIFICANTLY, WILL HOLD IN THE 50S.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
HIGHLIGHTS...  
 
* COLD FRONT PUSHES ACROSS WITH SHOWERS AND SCATTERED  
THUNDERSTORMS THURSDAY NIGHT INTO EARLY FRIDAY  
* SHOULD BE DRY AND SEASONABLE LATE FRIDAY INTO FRIDAY NIGHT  
* FAST MOVING SYSTEMS MAY BRING SCATTERED SHOWERS FROM TIME TO  
TIME THROUGH THE HOLIDAY WEEKEND  
* DRY AND SEASONABLE CONDITIONS MAY RETURN BY TUESDAY  
 
OVERVIEW...  
 
CONTINUE TO SEE ACTIVE WEATHER PATTERN ACROSS THE LOWER 48,  
ALONG WITH A FAST MOVING MID LEVEL STEERING FLOW ACROSS THE  
NORTHERN TIER STATES, ESPECIALLY FROM THE GREAT LAKES TO THE  
NORTHEAST. LOOKS LIKE H5 SHORT WAVES IN THIS FAST FLOW WILL  
SHIFT EASTWARD, BRINGING BATCHES OF SHOWERS FROM TIME TO TIME  
THROUGH THE HOLIDAY WEEKEND. CAN NOT RULE OUT A FEW THUNDERSTORMS  
WITH ONE OR TWO MORE ENERGETIC H5 SHORT WAVES INTO THE HOLIDAY  
WEEKEND.  
 
RATHER GOOD MODEL AGREEMENT AMONGST THE 00Z MEMBERS INTO  
SATURDAY, THEN SOLUTIONS DIVERGE WITH THE FAST MID LEVEL  
STEERING FLOW IN PLACE. ABOVE AVERAGE CONFIDENCE EARLY IN THE  
FORECAST PERIOD, THEN DECREASES FROM THE WEEKEND ONWARD.  
 
DETAILS...  
 
FRIDAY THROUGH SATURDAY...  
 
BACK EDGE OF PRECIP SHOULD PUSH E AS THE COLD FRONT MOVES  
ACROSS EARLY FRIDAY MORNING. SHOULD SEE GENERALLY DRY CONDITIONS  
FRIDAY INTO SATURDAY AS HIGH PRESSURE RIDGE BUILDS ACROSS.  
MIGHT SEE A FEW SPOTTY SHOWERS LINGER INTO MIDDAY FRIDAY ACROSS  
N MASS AS THE LOW SHIFTS OFF THE MAINE COAST. ANOTHER QUESTION  
ABOUT THE TIMING OF THE NEXT SYSTEM THAT BRING SCATTERED SHOWERS  
INTO AREAS NEAR AND N OF THE MASS PIKE DURING SATURDAY  
AFTERNOON.  
 
NOTE INCREASING LOW LEVEL NORTHERLY JET MOVES ACROSS ALONG WITH  
VERY GOOD LOW LEVEL MIXING ON FRIDAY. SO, MAY SEE N-NE WIND  
GUSTS UP TO 25-35 MPH, POSSIBLY A BIT HIGHER THROUGH EARLY  
AFTERNOON. WINDS SHOULD DIMINISH AS THE HIGH MOVES IN.  
 
TEMPERATURES ON FRIDAY WILL BE CLOSE TO SEASONAL LEVELS WITH HIGHS  
IN THE MID 60S ACROSS THE HIGHER TERRAIN AND ALONG THE COAST,  
RANGING TO THE LOWER-MID 70S. READINGS MAY BE A FEW DEGREES COOLER  
AS CLOUDS MOVE IN DURING SATURDAY. WINDS SHIFT TO S-SW SATURDAY  
AFTERNOON AND BECOME GUSTY ALONG THE IMMEDIATE S COAST.  
 
SATURDAY NIGHT THROUGH TUESDAY...  
 
ANOTHER ENERGETIC SHORT WAVE MOVES ACROSS SATURDAY NIGHT, SO  
COULD SEE SCATTERED SHOWERS WITH A FEW THUNDERSTORMS DURING THE  
NIGHT. PRECIP SHOULD SHIFT E BY MIDDAY SUNDAY, WITH ANOTHER  
QUICK PERIOD OF DRY CONDITIONS. MILD TEMPS MOVE IN AS WELL, WITH  
FORECASTED HIGHS IN THE 70S WITH A FEW SPOTS POSSIBLY REACHING  
80.  
 
MAY SEE ANOTHER ROUND OF SHOWERS MOVE ACROSS WITH YET ANOTHER  
SYSTEM LATE SUNDAY NIGHT THROUGH MEMORIAL DAY. FOR NOW, SHOULD  
SEE DRY, SEASONABLE CONDITIONS ON TUESDAY, BUT RATHER LOW  
CONFIDENCE FOR THIS TIMEFRAME DUE TO WIDE MODEL SOLUTION SPREAD.  
 

 
   
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY NIGHT/...HIGH CONFIDENCE.  
 
18Z UPDATE (NO CHANGES) ...  
 
REST OF TODAY ...  
VFR. N WINDS AROUND 10 KTS, GUSTING AT TIMES. SEA-BREEZES ONGOING  
WILL PUSH INLAND TOWARDS EVENING RESULTING IN A PREVAILING S/SE  
WIND.  
 
TONIGHT ...  
CIGS LOWERING TO LOW-END VFR. POSSIBLY MVFR ALONG THE BERKSHIRES  
BY MORNING. SCT -SHRA MAINLY OVER THE W CT RIVER VALLEY 9Z-12Z.  
NOT EXPECTING ANY VSBY ISSUES. S WINDS STRONGEST ALONG THE S-COAST.  
 
THURSDAY INTO THURSDAY NIGHT ...  
LOW-END VFR CIGS BECOMING MVFR WITH HIGH TERRAIN IFR AROUND 21Z-3Z.  
FORECAST WIDESPREAD -SHRA WITH EMBEDDED +RA AND POSSIBLE TSRA. TSRA  
COULD INCLUDE GUSTY W WINDS. VSBY ISSUES WITH +RA DOWN TO IFR. OTHER-  
WISE, 15-20 KT SW WINDS PREVAIL, GUSTS UP TO 25 KTS ESPECIALLY ALONG  
THE S-COAST WILL BACK W REMAINING BRISK AROUND 6-9Z WITH CONDITIONS  
IMPROVING.  
 
KBOS TERMINAL...  
SEA BREEZE ONGOING. WILL REMAIN AROUND 12-14 KTS AT 090-120 THROUGH  
EVENING.  
 
KBDL TERMINAL...  
HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...  
 
FRIDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. WINDY WITH AREAS  
OF GUSTS UP TO 30 KT. SLIGHT CHANCE SHRA.  
 
FRIDAY NIGHT: VFR. WINDY WITH LOCAL GUSTS UP TO 30 KT.  
 
SATURDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. CHANCE SHRA.  
 
SATURDAY NIGHT: MAINLY MVFR, WITH LOCAL IFR POSSIBLE. BREEZY.  
CHANCE SHRA, ISOLATED TSRA, PATCHY BR.  
 
SUNDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY. SLIGHT  
CHANCE SHRA.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY NIGHT/...HIGH CONFIDENCE.  
 
2 PM UPDATE ...  
 
REST OF TODAY ...  
N WINDS RELAXING AS HIGH PRESSURE BUILDS INTO THE WATERS. SMALL  
CRAFT ADVISORIES HAVE BEEN ALLOWED TO DROP. NEAR-SHORE SEA-BREEZES  
HAVE DEVELOPED AROUND 10 KTS. WILL SEE A S/SE WIND TREND EMERGE  
OVER ALL WATERS INTO THIS EVENING.  
 
TONIGHT ...  
HIGH PRESSURE SE AS A WARM FRONT APPROACHES FROM THE W. WINDS WILL  
STILL BE A BIT BRISK ALONG THE NEAR-SHORE WATERS OVERNIGHT WITH  
AROUND 10 TO 15 KTS SUSTAINED. SEAS REMAINING BELOW 5 FEET.  
 
THURSDAY INTO THURSDAY NIGHT ...  
COLD FRONT SWEEPING THE WATERS AFTER MIDNIGHT INTO FRIDAY MORNING  
AHEAD OF WHICH WIDESPREAD RAIN SHOWERS ARE TO BE ANTICIPATED, SOME  
OF WHICH WILL BE HEAVY AT TIMES AND THERE'S THE POSSIBILITY OF  
LIGHTNING. S/SW WINDS INCREASING AHEAD OF THE FRONT, AROUND 20 KTS  
SUSTAINED WITH GUSTS UP TO 30 KTS ... WILL BACK OUT OF THE W WITH  
FRONTAL PASSAGE REMAINING BREEZY AROUND 15 KTS WITH GUSTS AROUND  
20 KTS. WAVES BUILDING UP TO 6 TO 8 FEET ON THE OUTER WATERS.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...  
 
FRIDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS  
UP TO 30 KT. SEAS UP TO 5 FT. SLIGHT CHANCE OF RAIN SHOWERS.  
 
FRIDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
LOCAL GUSTS UP TO 30 KT. LOCAL ROUGH SEAS.  
 
SATURDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
SLIGHT CHANCE OF RAIN SHOWERS.  
 
SATURDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 25 KT. AREAS OF SEAS APPROACHING 5 FT. RAIN SHOWERS  
LIKELY.  
 
SUNDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
SLIGHT CHANCE OF RAIN SHOWERS.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR ANZ254.  
 

 
 

 
 
SYNOPSIS...SIPPRELL/EVT  
NEAR TERM...SIPPRELL  
SHORT TERM...SIPPRELL  
LONG TERM...EVT  
AVIATION...SIPPRELL/EVT  
MARINE...SIPPRELL/EVT  
 
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