328  
FXUS61 KBOX 220830  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
330 AM EST THU FEB 22 2018  
   
SYNOPSIS
 
 
A WAVE OF LOW PRESSURE TRACKING ALONG A STALLED FRONTAL  
BOUNDARY TO THE SOUTH WILL BRING A PERIOD OF SNOW AND SLEET  
ALONG AND NORTH OF THE PIKE WITH RAIN AND SLEET TO THE SOUTH.  
ACTIVE WEATHER PATTERN FRIDAY THROUGH THE WEEKEND AS A SERIES OF  
FRONTAL BOUNDARIES USHER WET WEATHER ACROSS THE REGION WITH THE  
THREAT OF FREEZING RAIN ACROSS THE N/W INTERIOR, HIGH TERRAIN. A  
NEAR-SEASONABLE, QUIET PATTERN FOR EARLY NEXT WEEK.  
 

 
   
NEAR TERM /THROUGH TODAY/
 
 
SCT SHOWERS MOVING EAST ACROSS THE SOUTH COAST REGION WITHIN  
THE DEEP MOISTURE AXIS NEAR AND SOUTH OF THE COAST. THIS SHOWER  
THREAT WILL CONTINUE THROUGH DAYBREAK BEFORE LOW LEVEL DRY AIR  
BEGIN TO PUSH SOUTH TOWARD THE COAST.  
 
OTHERWISE, COLDER AIR HAS BEEN A BIT SLOWER TO ARRIVE ACROSS  
SNE WITH TEMPS STILL IN THE 40S NORTH AND 50S SOUTH, BUT 30S TO  
THE N/W AND GOOD LOW LEVEL DRY ADVECTION WITH DEWPOINTS FALLING  
THROUGH THE 20S. TEMPS WILL FALL INTO THE 30S NORTH AND LOWER  
40S SOUTH AROUND DAYBREAK.  
 
STRONG HIGH PRES TO THE NORTH WITH FLAT WAVE TRACKING ALONG  
STALLED FRONTAL BOUNDARY TO THE SOUTH TODAY AS TEMPS GRADUALLY  
FALL THROUGH THE 30S. LOW LEVEL COLDER AIR UNDERCUTTING  
SOMEWHAT MILDER AIR ALOFT WILL BRING A DECENT SHOT OF MID LEVEL  
OMEGA WITHIN A DEEP MOISTURE PLUME WHICH WILL SPREAD PRECIP  
ACROSS SNE. SOUNDINGS SHOW A RATHER PRONOUNCED LOW DRY LAYER  
WHICH WILL HAVE TO BE OVERCOME AND THIS WILL LIKELY DELAY ONSET  
OF PRECIP UNTIL AROUND MIDDAY AND ESPECIALLY DURING THE  
AFTERNOON.  
 
BIGGEST CHALLENGE REMAINS THE PTYPE FORECAST AS COOLING ALOFT IS  
A BIT SLOWER THAN LOW LEVEL COOLING. PRONOUNCED LOW LEVEL COLD  
AIR WITH 925/950 MB COOLING TO -3 TO -5C THIS AFTERNOON WITH A  
WARM LAYER ABOVE 800 MB WHICH WILL SET UP A ZONE OF SLEET ACROSS  
THE REGION. COLD AIR DEEP ENOUGH FAR NORTH WITH SOUNDINGS  
SUGGESTING MOSTLY SNOW NORTH OF THE PIKE, MIXED WITH SLEET AT  
TIMES, WITH RAIN MIXING WITH OR CHANGING TO SLEET TO THE SOUTH  
PRECIP COULD EVEN CHANGE TO A PERIOD OF SNOW/SLEET ACROSS N CT,  
N RI AND INTERIOR SE MA. PRECIP MAY BEGIN AS A BRIEF PERIOD OF  
RAIN NORTHERN MA BUT WILL QUICKLY CHANGE TO SNOW GIVEN  
EVAPORATIVE COOLING PROCESSES. NOT REALLY EXPECTING ANY  
FREEZING RAIN GIVEN THE DEPTH OF THE LOW LEVEL COLD LAYER, BUT  
THERE IS A LOW RISK NEAR THE MA/CT AND NORTHERN RI BORDER.  
 
DECENT SHOT OF OMEGA THROUGH DGZ NOTED ACROSS NORTHERN MA THIS  
AFTERNOON SO A BRIEF PERIOD OF HEAVIER SNOW IS POSSIBLE.  
EXPECTING AN INCH OR 2 ACCUM NORTH OF THE PIKE, MAINLY ON COLDER  
NON-PAVED SURFACES WITH LOCALLY UP TO 3 INCHES POSSIBLE OVER  
THE BERKSHIRES. LESS THAN AN INCH ELSEWHERE AWAY FROM AREAS  
NEAR THE SOUTH COAST.  
 

 
   
SHORT TERM /TONIGHT/
 
 
PRECIP WILL EXIT THE REGION BY EARLY EVENING WITH DRY CONDITIONS  
MOST OF THE NIGHT AS SURFACE RIDGING BUILDS SOUTH INTO SNE.  
HOWEVER, SUFFICIENT MOISTURE FOR CLOUD COVER TO PERSIST THROUGH  
THE NIGHT, ESPECIALLY SOUTH OF THE PIKE. PARTIAL CLEARING IS  
POSSIBLE ACROSS NE MA LATE. LOWS MOSTLY IN THE 20S TO LOWER 30S.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
*/ HIGHLIGHTS...  
 
- N/W INTERIOR FREEZING RAIN LATE FRIDAY INTO FRIDAY EVENING  
- ONCE AGAIN SATURDAY NIGHT INTO SUNDAY  
- DRY, NEAR SEASONABLE INTO EARLY NEXT WEEK  
 
*/ OVERVIEW...  
 
UPSTREAM PACIFIC FLOW FLATTENING, SE CONUS SUB-TROPICAL H5 RIDGE  
WEAKENING, SW-NE THERMAL WIND AXIS AND STORM TRACK ALONG THE BETTER  
BAROCLINIC ZONE SHIFTS S/E ALONG WHICH MID-LEVEL IMPULSES EJECT OUT  
OF A PREFERRED H5 TROF PATTERN ACROSS THE W CONUS. AN ACTIVE WEATHER  
PATTERN WITH A SERIES OF DISTURBANCES DELIVERING MIXED PRECIPITATION  
EVENTS THRU THE WEEKEND. BUILDING UP OVER THE N ATLANTIC  
SIGNALED BY A STRONGLY -NAO, IN GOING WITH ENSEMBLE MEANS, WE  
FALL WITHIN A NEAR-SEASONABLE, DRY PATTERN W OF FAVORABLE STORM  
DEVELOPMENT OVER SE CANADA. MODEL FORECAST CONSENSUS THROUGH 120  
HOURS (MONDAY) WITH PREFERENCE TOWARDS ENSEMBLE MEANS  
THEREAFTER. HIT ON TARGETS OF OPPORTUNITY BELOW.  
 
*/ DISCUSSION...  
 
LATE FRIDAY INTO FRIDAY EVENING...  
 
OVER-RUNNING PRECIPITATION EVENT. FOCUS ON THERMAL FIELDS BELOW H9,  
ESPECIALLY SURFACE WITH 2M WET-BULB TEMPERATURES, BENEATH THE WARM  
NOSE UP AROUND H8. SURFACE HIGH SITUATED E, LESS N-FUNNELING WINDS  
PER AGEOSTROPHIC MOTIONS. THERE'S THE POTENTIAL FOR A BRIEF PERIOD  
OF FREEZING RAIN. DRY AIR ISSUES, ABOVE AVERAGE HEIGHTS, MID-UPPER  
LEVEL RIDGING, ABSENCE OF DEEP LAYER LIFT, THAT WITH PRECIPITABLE  
WATERS BUILDING TOWARDS 0.75 TO 1.00 INCH, LIGHT TO MODERATE PRECIP  
EVENT IS FORECAST WITH AMOUNTS UPWARDS OF AROUND 0.25 INCHES, NO  
HIGHER THAN 0.50, WITH HIGHEST AMOUNTS ALONG THE W SLOPES OF HIGH  
TERRAIN. A BRIEF PERIOD THOUGH DURING THE HEIGHT OF PRECIP OUTCOMES,  
ICE ACCRETION OF 0.1 TO 0.2 INCHES IS POSSIBLE OVER HIGHER TERRAIN.  
HIGHEST CONFIDENCE TOWARDS N/W MA ESPECIALLY BERKSHIRES, WORCESTER  
HILLS. HIGH-RES GUIDANCE COLDER THAN GLOBAL. WITH THE HIGH SITUATED  
E, RETURN S FLOW, PREFER TO EDGE AWAY FROM COLDEST GUIDANCE AND NOT  
BE PESSIMISTIC. THUS FORECAST ICE ACCRETION AMOUNTS UP AS HIGH AS  
AROUND 0.10 INCHES OVER HIGH TERRAIN, ESPECIALLY BERKSHIRES. LEAN A  
NON-GFS CONSENSUS WITH IMPACTS TO FRIDAY PM COMMUTE.  
 
SATURDAY NIGHT INTO SUNDAY...  
 
ANOTHER OVER-RUNNING PRECIPITATION EVENT ASSOCIATED WITH A CLASSIC  
WARM OCCLUSION INTO S CANADA. STRONGER SYNOPTIC FORCING / LIFT THAT  
INVOKES A SECONDARY SURFACE LOW ALONG OUR COAST WITH A SYNOPTICALLY  
FAVORABLE COLD SURFACE HIGH N/E TOWARDS A FREEZING RAIN EVENT. MORE  
LIKELY OUTCOMES OF COLDER TEMPERATURES FUNNELING S, MAINTAINING OVER  
THE INTERIOR, NOTABLY OCCURRING DURING AN OVERNIGHT PERIOD. PREFER  
EC/NAM/CANADIAN, HIGHER CONFIDENCE OF FREEZING RAIN OVER BERKSHIRES,  
WORCESTER HILLS. ACCRETION AMOUNTS OF 0.1 TO 0.2 GIVEN LESS DRY AIR  
INTRUSIONS, DEEPER LIFT / FORCING. PRECIPITABLE WATERS ONCE AGAIN IN  
THE 0.75 TO 1.00 INCH RANGE.  
 
EARLY NEXT WEEK...  
 
KEEPING WITH ENSEMBLE MEANS, TRAFFIC BUILD UP ACROSS THE N ATLANTIC,  
THE STRONGLY -NAO, THE INITIAL REGION OF FAVORABLE STORM DEVELOPMENT  
OVER SE CANADA, WILL NEED TO CLOSELY MONITOR FOR ANY RETROGRESSION  
AS ENERGY CONTINUES TO EJECT OUT OF A PREFERRED H5 TROF PATTERN OVER  
THE W CONUS. LOOKING DRY AND NEAR-SEASONABLE TILL ROUGHLY THURSDAY  
INTO FRIDAY, BEING W ON THE BACKSIDE OF FAVORABLE STORM DEVELOPMENT.  
NW WINDS PREVAILING. OVERALL, A LOW CONFIDENCE FORECAST.  
 

 
   
AVIATION /07Z THURSDAY THROUGH MONDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH TONIGHT/...MODERATE CONFIDENCE.  
 
TODAY...  
VFR IN THE MORNING, THEN LOWERING TO MVFR/IFR IN THE AFTERNOON  
WITH SNOW/SLEET ALONG AND NORTH OF THE PIKE AND RAIN/SLEET TO  
THE SOUTH.  
 
TONIGHT...  
PRECIP MOVES OFFSHORE BY EARLY EVENING. MVFR/IFR IMPROVING TO  
VFR NORTH OF THE PIKE, BUT MVFR CIGS PERSISTING TO THE SOUTH.  
 
KBOS TERMINAL...MODERATE CONFIDENCE TAF. CONDITIONS LOWERING TO  
MVFR THEN IFR IN THE AFTERNOON WITH A PERIOD OF RAIN, THEN SNOW  
AND SLEET. ANY ACCUM LESS THAN AN INCH.  
 
KBDL TERMINAL...MODERATE CONFIDENCE TAF. CONDITIONS LOWERING TO  
MVFR THEN IFR IN THE AFTERNOON WITH A PERIOD OF RAIN, SLEET AND  
SNOW. ANY ACCUM LESS THAN AN INCH.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...MODERATE CONFIDENCE.  
 
FRIDAY: MAINLY MVFR, WITH AREAS VFR POSSIBLE. RA, FZRA.  
 
FRIDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. RA LIKELY, FZRA  
LIKELY.  
 
SATURDAY: VFR.  
 
SATURDAY NIGHT: MAINLY MVFR, WITH LOCAL IFR POSSIBLE. BREEZY.  
RA LIKELY, FZRA LIKELY.  
 
SUNDAY: MAINLY MVFR, WITH AREAS IFR POSSIBLE. BREEZY. RA, FZRA.  
 
SUNDAY NIGHT THROUGH MONDAY: VFR.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH TONIGHT/...MODERATE CONFIDENCE.  
 
TODAY...  
NORTHERLY WINDS TURNING NE WITH GUSTS TO 20-25 KT AT TIMES. SCA  
ISSUED FOR EASTERN WATERS DUE TO SEAS. VSBYS REDUCED IN RAIN AND  
SNOW THIS AFTERNOON.  
 
TONIGHT...  
MAINLY NE WINDS WITH GUSTS TO 20 KT AT TIMES. SEAS MOSTLY BELOW  
SCA.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...  
 
FRIDAY: WINDS LESS THAN 25 KT. RAIN, SLIGHT CHANCE OF FREEZING  
RAIN.  
 
FRIDAY NIGHT: WINDS LESS THAN 25 KT. RAIN LIKELY.  
 
SATURDAY: WINDS LESS THAN 25 KT.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. CHANCE OF RAIN.  
 
SUNDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS  
UP TO 30 KT. AREAS OF ROUGH SEAS. RAIN.  
 
SUNDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS.  
 
MONDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR ANZ250.  
SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ254.  
 

 
 

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