492  
FXUS61 KBOX 231113  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
713 AM EDT MON APR 23 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE REMAINS IN CONTROL THROUGH TUESDAY BRINGING DRY  
WEATHER WITH MILD DAYTIME TEMPERATURES. LOW PRESSURE WILL PASS  
THROUGH NEW ENGLAND LATE WEDNESDAY AND BRING SHOWERS TO THE  
AREA. ANOTHER WEAK LOW PRESSURE CENTER MAY BRING ANOTHER ROUND  
OF SHOWERS TO THE AREA FRIDAY NIGHT.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
7 AM UPDATE...  
 
NOT MUCH TO CHANGE THIS MORNING. SKIES WILL REMAIN CLEAR AND  
WINDS LIGHT. EXPECT SEA BREEZES TO INITIATE MID TO LATE MORNING  
ALONG MOST OF THE COASTLINE. HAVE TWEAKED INTERIOR TEMPERATURES  
UP JUST A DEGREE OR SO GIVEN LATEST GUIDANCE TRENDS. THIS HAS  
THE FURTHER EFFECT OF LOWERING MINIMUM RELATIVE HUMIDITIES A  
LITTLE BELOW 20 PERCENT IN A FEW SPOTS ACROSS INTERIOR MA AND  
THE CT RIVER VALLEY OF NORTHERN CT. FORTUNATELY, WINDS WILL BE  
LIGHT TODAY.  
 
4 AM DISCUSSION...  
 
HIGH PRESSURE REMAINS IN PLACE OVER SOUTHERN NEW ENGLAND. EXPECT  
LOTS OF SUNSHINE AND LIGHT WIND. MIXING AGAIN SHOULD REACH TO AT  
LEAST 850 MB AND POSSIBLY HIGHER THAN 800 MB. NOTE THAT INLAND  
MIXING YESTERDAY REACHED ABOVE 750 MB. TEMPS AT 850 MB SUPPORT  
MAX SFC TEMPS OF 62-64F, WHILE 800 MB TEMPS SUPPORT 65-68F. WE  
TEND TOWARD THE HIGHER VALUES INLAND, ESPECIALLY IN THE  
TRADITIONAL HOT SPOTS... HARTFORD-SPRINGFIELD AND PARTS OF THE  
BOSTON METROWEST.  
 
THE LIGHT FLOW WILL SUPPORT SEA BREEZES ALONG THE COAST, WHICH  
WILL KEEP TEMPS COOLER ALONG THE COAST. WILL MAINTAIN MAX TEMPS  
IN THE 60S INLAND AND 50S COAST.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/
 
 
THE HIGH PRESSURE REMAINS OVERHEAD TONIGHT, THEN SHIFTS OFF TO  
THE EAST TUESDAY. THIS SHOULD MAINTAIN CLEAR SKIES TONIGHT, AND  
SUNSHINE THROUGH HIGH CLOUDS TUESDAY.  
 
RADIATIONAL COOLING TONIGHT SHOULD AGAIN ALLOW TEMPERATURES TO  
FALL INTO THE 30S, WITH THE USUAL COLD SPOTS AROUND FREEZING OR  
A LITTLE BELOW.  
 
WITH THE SURFACE HIGH MOVING OFFSHORE, TUESDAY WILL FEATURE A  
DEVELOPING SOUTH TO SOUTHWEST WIND WHICH WILL ALLOW A SEA BREEZE  
ONLY ALONG THE SOUTH-FACING COASTS. THE RIDGE WILL MAINTAIN DRY  
AIR THROUGH THE DAY. HIGH LEVEL MOISTURE FIELDS DO INDICATE  
INCREASING CLOUDS DURING THE MID TO LATE AFTERNOON, BUT LATE  
ENOUGH TO ALLOW SUNSHINE THROUGH THE DAY. MIXING WILL BE A  
LITTLE SHALLOWER, BUT TEMPS AT ALL LEVELS WILL BE INCREASING. SO  
TEMPERATURES TUESDAY SHOULD AGAIN CLIMB INTO THE 60S EXCEPT 50S  
ALONG THE SOUTH COAST.  
 

 
   
LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/
 
 
HIGHLIGHTS...  
 
* SHOWERS WEDNESDAY INTO WEDNESDAY NIGHT  
* ANOTHER ROUND OF SHOWERS POSSIBLE FRIDAY NIGHT AND LATE SATURDAY  
 
DISCUSSION...  
 
MULTIPLE SHORT WAVE ENERGY SYSTEMS WILL BE AFFECTING OUR AREA DURING  
THIS FORECAST PERIOD. A SOUTHERN STREAM SHORT WAVE TROUGH AND  
SURFACE LOW WILL AFFECT SOUTHERN NEW ENGLAND LATE TUESDAY NIGHT INTO  
WEDNESDAY NIGHT. THIS SYSTEM BEGINS TO PHASE WITH A NORTHERN STREAM  
SHORT WAVE AS IT PASSES THROUGH OUR REGION. STILL ANOTHER SOUTHERN  
STREAM SHORT WAVE AND AN ASSOCIATED WEAK SURFACE LOW PRESSURE CENTER  
MAY AFFECT THE AREA AROUND FRIDAY NIGHT, BUT CONSISTENCY IN HANDLING  
THIS FEATURE AMONG THE MEDIUM RANGE MODELS IS LOW. THIS SYSTEM  
CURRENTLY LOOKS AS THOUGH IT WILL WILL RUN A LITTLE AHEAD OF AN  
APPROACHING NORTHERN STREAM TROUGH WHICH THEN BECOMES A DOMINANT  
FEATURE WITH POSSIBLY COOLER TEMPERATURES FOR THE REST OF THE  
WEEKEND. THERE IS A SIGNAL FOR A LONG WAVE PATTERN CHANGE LEADING TO  
HIGHER HEIGHTS AND WARMER TEMPERATURES ACROSS OUR REGION AFTER THIS  
FORECAST PERIOD.  
 
TUESDAY NIGHT TO WEDNESDAY NIGHT...  
 
THE 00Z OPERATIONAL MODEL RUNS HAVE CONVERGED SOME ON TIMING FOR THE  
SOUTHERN STREAM SHORT WAVE ENERGY DURING THIS TIME PERIOD. AS THE  
MID TROPOSPHERIC SOUTHERN STREAM SHORT WAVE BEGINS TO PHASE WITH THE  
NORTHERN STREAM SHORT WAVE, THE SURFACE WEATHER PATTERN MAY TAKE ON  
THE LOOK OF A SURFACE LOW THAT MOVES NORTH UP THE MID ATLANTIC  
COASTAL PLAIN AND ENDS UP WITH THE LOOK OF A TRIPLE POINT LOW  
PASSING OVER OR NEAR CENTRAL NEW ENGLAND. SUSPECT THAT COOLER AIR  
WILL BE SOMEWHAT RESISTANT TO AN APPROACHING WARM FRONT DUE TO  
ONSHORE MARITIME POLAR AIR BEING FED ON E TO SE WINDS. ANTICIPATE  
RAINFALL WILL BE SHOWERY BUT CONFIDENT THAT ALL AREAS WILL MEASURE.  
PWATS LOOK TO CREST ABOUT 1.2 TO 1.4 INCHES, AND A 50 TO 60+ KNOT  
LOW LEVEL SE JET AT 925 MB WILL HELP FOCUS THAT MOISTURE OVER  
SOUTHERN NEW ENGLAND. THERE ALSO LOOKS TO BE SOME ELEVATED  
INSTABILITY WEDNESDAY EVENING WITH EMBEDDED CONVECTION A  
POSSIBILITY. THIS IS REFLECTED ON THE LATEST GFS RUN WITH MID LEVEL  
LAPSE RATES OF 6.5 TO 7 DEGREES C/KM AS WELL AS OTHER TYPICAL  
INSTABILITY INDICES SUCH AS SHOWALTERS A LITTLE BELOW 0, TOTAL  
TOTALS OF 50+ AND K INDICES ABOVE 30.  
 
AS FAR AS QPF, MAY SEE SOME UPSLOPE ENHANCEMENT GIVEN THE NOSE OF  
THE SE LOW LEVEL JET ACROSS THE WORCESTER HILLS AND/OR EAST SLOPES  
OF THE BERKSHIRES DEPENDING UPON THE EXACT TRACK OF THE LOW LEVEL  
FEATURES. SUSPECT THAT RAINFALL AMOUNTS COULD END UP HIGHER THAN  
MODEL OUTPUT DUE TO SUBTROPICAL MOISTURE SOURCE, STRENGTH OF THE LOW  
LEVEL JET, AND SOME CONVECTIVE ENHANCEMENT BUT VARIABLE DUE TO THE  
SHOWERY NATURE. A PRELIMINARY ESTIMATE WOULD BE A FAIRLY WIDESPREAD  
.5 TO 1 INCH AMOUNTS WITH LOCALLY HIGHER SPOT AMOUNTS OF 1.5 TO  
POSSIBLY 2 INCHES.  
 
THURSDAY THROUGH FRIDAY...  
 
EXCEPT FOR POSSIBLY WIDELY SCATTERED LATE THURSDAY AFTERNOON OR  
EARLY EVENING INSTABILITY SHOWERS OVER THE NW HIGHER TERRAIN, IT  
LOOKS DRY THURSDAY AFTERNOON THROUGH AT LEAST MOST OF FRIDAY.  
CONFIDENCE HAS INCREASED OF AT LEAST MOST OF DAYTIME FRIDAY  
REMAINING DRY.  
 
FRIDAY NIGHT SYSTEM...  
 
THE SECOND SOUTHERN STREAM SHORT WAVE UPPER TROUGH WITH A WEAK  
SURFACE LOW PASSING ALONG OR OFF THE COAST MAY PRODUCE SHOWERS  
ACROSS AT LEAST SOME OF SOUTHERN NEW ENGLAND, BUT CONFIDENCE IS LOW  
DUE TO POOR MODEL CONSENSUS ON THIS FEATURE. THE NEW 00Z ECMWF KEEPS  
THIS SYSTEM FAR OFFSHORE, ALTHOUGH SOME OF ITS ENSEMBLE MEMBERS HAVE  
IT PASSING VERY NEAR SE NEW ENGLAND. THUS, GIVEN THE UNCERTAINTY, WE  
WILL JUST INDICATE LOW CHANCE POPS FOR NOW. THERE IS ALSO SOME  
UNCERTAINTY AS TO HOW MUCH INTERACTION, IF ANY, WITH AN APPROACHING  
NORTHERN SHORT WAVE TROUGH.  
 
REST OF WEEKEND...  
 
A COLD FRONT ASSOCIATED WITH THE NORTHERN STREAM TROUGH MAY RESULT  
IN SCATTERED SHOWERS LATE SATURDAY, BUT THERE'S NO REAL MODEL  
CONSENSUS ON THAT NOW SO CONFIDENCE IS LOW. THAT NORTHERN STREAM  
SHORT WAVE TROUGH BRINGS COOLER TEMPERATURES TO SOUTHERN NEW ENGLAND  
FOR THE LATTER HALF OF THE WEEKEND INTO MONDAY OF NEXT WEEK.  
 

 
   
AVIATION /11Z MONDAY THROUGH FRIDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH TUESDAY/...HIGH CONFIDENCE.  
 
VFR WITH CLEAR SKIES AND UNLIMITED VISIBILITY, EXCEPT SOME  
GUIDANCE STARTS TO HINT AT FOG FORMATION LATE TUESDAY ALONG THE  
SOUTH COAST. AS THE GRADIENT BECOMES ESTABLISHED FROM THE SOUTH  
TUESDAY EVENING, WE MAY START TO SEE FOG PATCHES FORM ALONG THE  
SOUTH COAST AS DEWPOINTS BEGIN TO RISE. WINDS WILL BE LIGHT TODAY  
WITH SEA BREEZES DEVELOPING ALONG THE COASTS BY MIDDAY AND THEN  
DISSIPATING IN THE EVENING. LIGHT SOUTH WINDS TONIGHT AND  
TUESDAY.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /TUESDAY NIGHT THROUGH FRIDAY/...HIGH CONFIDENCE.  
 
TUESDAY NIGHT: BECOMING MAINLY MVFR AFTER MIDNIGHT, WITH LOCAL  
IFR POSSIBLE TOWARD DAYBREAK. SHRA SPREADING INTO THE AREA AFTER  
MIDNIGHT.  
 
WEDNESDAY: MAINLY IFR WITH SHRA AND AREAS BR. AREAS OF MVFR  
CONDITIONS POSSIBLE DURING THE AFTERNOON. POTENTIAL FOR LLWS.  
BECOMING WINDY ALONG THE COAST WITH LOCAL GUSTS TO 30 KT DURING  
THE AFTERNOON. SHRA AND AREAS BR.  
 
WEDNESDAY NIGHT: MAINLY MVFR, WITH LOCAL IFR POSSIBLE. WINDY  
WITH GUSTS TO 30 KT IN THE EVENING. SHRA DIMINISHING OVERNIGHT.  
ISOLATED TSTMS DURING THE EVENING.  
 
THURSDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE OVER HIGHER  
TERRAIN. BREEZY. SLIGHT CHANCE SHRA OVER NW HIGHER TERRAIN.  
 
THURSDAY NIGHT AND FRIDAY: MAINLY VFR.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH TUESDAY/...HIGH CONFIDENCE.  
 
HIGH PRESSURE OVER THE WATERS TODAY WITH LIGHT WINDS, FLAT  
SEAS, AND GOOD VISIBILITY. THE HIGH MOVES OFF TO THE EAST  
TONIGHT AND TUESDAY, WITH WINDS TURNING FROM THE SOUTH BY  
TUESDAY, BUT REMAINING LIGHT.  
 
ONLY CONCERN FOR RECREATIONAL BOATERS IS FOR SEA BREEZES ALONG  
THE COASTLINE TODAY WITH 15-20KT GUSTS AND CHOPPY SEAS NEAR  
SHORE, ESPECIALLY WHEN OPPOSING OUTGOING TIDE.  
 
OUTLOOK /TUESDAY NIGHT THROUGH FRIDAY/...HIGH CONFIDENCE.  
 
TUESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. CHANCE OF RAIN SHOWERS. LOCAL VISIBILITY 1 TO 3 NM.  
 
WEDNESDAY: SMALL CRAFT ADVISORY WINDS POSSIBLE WITH GUSTS UP TO  
30 KT POSSIBLE. LOW RISK OF GALE FORCE GUSTS, ESPECIALLY SOUTH  
AND EAST OF NANTUCKET. AREAS OF ROUGH SEAS ABOVE 5 FEET,  
ESPECIALLY OVER THE EXPOSED SOUTH COASTAL WATERS. RAIN SHOWERS,  
AREAS FOG. VISIBILITY 1 TO 3 NM.  
 
WEDNESDAY NIGHT: SMALL CRAFT ADVISORY WINDS POSSIBLE WITH GUSTS  
UP TO 30 KT. LOW RISK OF GALE FORCE GUSTS EAST OF CAPE COD. ROUGH  
SEAS UP TO 13 FT OVER THE OUTER COASTAL WATERS. RAIN SHOWERS.  
 
THURSDAY: WINDS LESS THAN 25 KT, BUT AREAS OF SEAS AT OR ABOVE 5  
FEET.  
 
THURSDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS AROUND 5  
FEET.  
 
FRIDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FEET  
OVER THE OUTER SOUTH COASTAL WATERS. SLIGHT CHANCE OF RAIN  
SHOWERS LATE.  
 

 
   
EQUIPMENT
 
 
NOAA WEATHER RADIO TRANSMITTERS SERVING PROVIDENCE AND HYANNIS  
ARE OUT OF SERVICE DUE TO PHONE LINE PROBLEMS. THE PHONE  
COMPANY HAS PRIORITIZED THE ISSUES AND IS WORKING TO GET THE  
WEATHER BROADCAST BACK ON THE AIR AS SOON AS POSSIBLE.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...WTB/THOMPSON  
NEAR TERM...WTB/THOMPSON  
SHORT TERM...WTB  
LONG TERM...THOMPSON  
AVIATION...WTB/THOMPSON  
MARINE...WTB/THOMPSON  
EQUIPMENT...  
 
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