Severe Thunderstorm Warning 128, NWS Boston/Norton, MA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
219 PM EDT MON AUG 16 2010

.SYNOPSIS...
COLD FRONT WILL CROSS SOUTHERN NEW ENGLAND THIS EVENING AND THEN STALL
OR DISSIPATE NEAR THE SOUTH COAST ON TUESDAY. WEAK HIGH PRESSURE
MOVES IN FOR WEDNESDAY...THEN A COASTAL LOW PRESSURE MAY AFFECT
SOUTHERN NEW ENGLAND THURSDAY WITH MORE SHOWERS AND THUNDERSTORMS.
MAINLY DRY WEATHER IS EXPECTED FOR THE END OF THIS WEEK INTO THE
EARLY PART OF THIS WEEKEND. ANOTHER LOW PRESSURE SYSTEM MAY BEGIN
TO AFFECT SOUTHERN NEW ENGLAND FROM THE WEST SUNDAY INTO EARLY
NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
MAIN FORECAST CHALLENGE FOR TODAY REVOLVES AROUND THE COVERAGE OF
THUNDERSTORMS AND THEIR INTENSITY.

STRONG/SVR TSTM CLUSTER MOVING INTO BERKSHIRE COUNTY AT 18Z. CT
RIVER VALLEY REMAINS UNDER STRATUS AND SO SUSPECT WILL SEE
WEAKENING AS TSTMS MOVE E OF BERKSHIRES.

FROM THIS MORNING...THERE ARE SEVERAL FACTORS THAT MAKE STRONG CONVECTION
POTENTIAL A TOUGH CALL. AS NOTED IN THE PRIOR AFD...LOOKS LIKE
BEST SHORT WAVE FORCING FOR CURRENT ACTIVITY WILL BE A LITTLE
NORTH OF AREA BUT WARY THAT WE WILL BE CLIPPED AT LEAST ACROSS SW
NH. SNE IS RATHER SOLIDLY PACKED WITH LOW CLOUDS AT 14Z WITH NO
SUBSTANTIAL BREAKS SHOWING UP YET...AND MORE OF A S VERSUS SW WIND
ATTM. STILL THINK WE WILL GRADUALLY BEGIN BREAKING AT LEAST
PARTIALLY OPEN INTERIOR SECTIONS AFTER ABOUT 18Z. IF WE DO BREAK
OUT...SBCAPES WOULD PROBABLY QUICKLY INCREASE TO AROUND 2000 J/KG
GIVEN EXPECTED DEWPOINTS IN UPPER 60S/LOWER 70S.

LOOKS AS THOUGH MID LEVEL LAPSE RATES SHOULD STEEPEN SOME LATE
THIS AFTERNOON AND EVENING BETWEEN WARM ADVECTION AT LOWER LEVELS
AND SLIGHT COOLING WITH PASSING SHORT WAVE ENERGY ALOFT. THERE
SEEMS TO BE SOME HINT IN MOST MODELS OF AN AREA OF GREATER
INSTABILITY OVER NE MA THIS EVENING.

WIND FIELD ARE RELATIVELY STRONG WITH HINT OF SNE BEING IN RIGHT
REAR QUAD OF AN EXITING JET AND A STRONGER JET NOSING INTO
SOUTHEAST NY. THE CURRENT CONVECTION OVER UPSTATE NY APPEARS
SITUATED AT LEADING EDGE OF MID LEVEL JET. THE MID LEVEL JET IS
SHOWN BY ALL MODELS TO CONTINUE INTO OUR COUNTY WARNING AREA BUT
WEAKEN AS IT CROSSES THE AREA. FOR NOW...THINK NW MA AND SW NH
PROBABLY BEST SITUATED FOR STRONG/SEVERE CONVECTION THIS AFTERNOON

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
SHOWER AND THUNDERSTORM ACTIVITY COULD PERSIST WELL INTO THE NIGHT
AS THE COLD FRONT SLOWS DOWN AND WEAKENS AND ANOTHER SHORT WAVE
TROF APPROACHES. WOULDN/T BE SURPRISED TO SEE SOMEWHAT OF A
REGENERATION OF CONVECTION ACROSS SOUTHEAST ZONES LATER AT NIGHT.
THEREFORE...WILL CONTINUE WITH CHANCE POPS IN THE SOUTH WHILE
CLEARING THINGS OUT IN THE WEST/NORTHWEST.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH WEDNESDAY...THEN DIVERGE
INTO SEVERAL SOLUTIONS HEADING INTO THIS WEEKEND. TIMING DIFFERENCES
ALSO COMPLICATE THE FORECAST. THE GREATEST DIFFERENCES ARE IN THE
WEEKEND FORECAST WHEN THERE ARE FAIRLY MAJOR DIFFERENCES FROM RUN
TO RUN AS WELL AS AMONGST THE MODELS. DECIDED TO MINIMIZE THESE
DIFFERENCES BY USING A BLEND OF VARIOUS MODELS. USED A 00Z GFS/NAM
BLEND FROM TUESDAY INTO WEDNESDAY...THEN SWITCHED TO A BLEND OF
THE 00Z GFS/12Z ECMWF WEDNESDAY NIGHT INTO SUNDAY.

DID TAKE A QUICK LOOK AT THE 00Z ECMWF...WHICH ARRIVES ABOUT 3 AM
IN OUR SYSTEM...AND IT MORE CLOSELY RESEMBLES THE 00Z GFS INTO
THURSDAY. THAT SAID...STILL SOME TRACK AND TIMING DIFFERENCES TO
IRON OUR OVER THE NEXT COUPLE OF DAYS.

EXPECTING A COLD FRONT TO LINGER JUST SOUTH OF NEW ENGLAND
TUESDAY, THERE MAY BE SCATTERED SHOWERS LINGERING AROUND CAPE COD
AND THE ISLANDS EARLY IN THE DAY...BUT MOST OF SOUTHERN NEW
ENGLAND SHOULD BE DRY. SEASONABLE TEMPERATURES EXPECTED.

MODELS TRY TO NUDGE A WEAK HIGH PRESSURE EAST WEDNESDAY...BUT NOT
THINKING THERE WILL BE MUCH SUCCESS. JUST ABOUT ALL 00Z MODEL
SOLUTIONS DEVELOP A REX BLOCK OVER THE DAVIS STRAIGHT BY MONDAY
NIGHT...THEN TRANSITIONS INTO AN OMEGA BLOCK BY WEDNESDAY. THIS
PLACES SOUTHERN NEW ENGLAND BENEATH THE BROAD WESTERN MID LEVEL
TROUGH INTO THIS WEEKEND. THIS MEANS AT LEAST A SLIGHT CHANCE OF
SHOWERS AT JUST ABOUT ANY TIME FOR THE END OF THIS WEEK INTO THIS
WEEKEND. THERE ARE A COUPLE OF PERIOD WITH A GREATER RISK OF THESE
SHOWERS THAN OTHERS.

THE FIRST IS ASSOCIATED WITH A LOW PRESSURE OFF THE MID-ATLANTIC
COAST. THIS LOW PRESSURE IS FORECAST TO APPROACH SOUTHERN NEW
ENGLAND LATE WEDNESDAY INTO THURSDAY. GIVEN THE SLOW-MOVING MID
LEVEL FLOW...COULD SEE SOME RAINFALL LINGER INTO THURSDAY NIGHT.
THE AREAS MOST LIKELY TO SEE RAINFALL FROM THIS SYSTEM WILL BE THE
SOUTH COAST OF MA..RI AND NORTHERN CT. A HIGH PRESSURE ACROSS
EASTERN CANADA TRIES TO NUDGE IN FRIDAY...WHICH COULD TURN OUT TO
BE A DRY DAY.

THE NEXT SYSTEM COULD IMPACT SOUTHERN NEW ENGLAND THIS WEEKEND.
THE 00Z GFS IS MUCH QUICKER BRINGING THIS LOW PRESSURE EAST THAN
THE 00Z ECMWF. USED THE CONSENSUS TIMING FOR NOW...BUT THE SLOWER
ECMWF TIMING MIGHT WORK OUT BETTER DEPENDING ON IF THE DOWNSTREAM MID
LEVEL BLOCK BREAKS DOWN. FOR NOW...WILL MENTION A CHANCE OF
SHOWERS SATURDAY NIGHT INTO SUNDAY.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
REST OF THIS AFTERNOON...WIDESPREAD MVFR CIGS 1 THSD TO 2 THSD
FEET PERSISTING ACROSS MUCH OF CWA WITH PATCHES IFR CONDITIONS.
SCT SHOWERS AND TSTMS AHEAD OF A COLD FRONT THIS AFTERNOON AND
EVENING. THE TSTMS MAY BRIEFLY PRODUCE MVFR...EVEN IFR CONDITIONS
IN HEAVY RAIN...ALONG WITH THE POTENTIAL FOR STRONG SURFACE WIND
GUSTS...ESPECIALLY ACROSS WESTERN/NORTHERN MA AND SW NH. CURRENT
THINKING IS THAT MOST OF THE TSTMS SHOULD WEAKEN E OF BERKSHIRES
DUE TO LACK OF OR AT LEAST DELAYED SFC HEATING.

TONIGHT...MEDIUM CONFIDENCE IN WIDESPREAD MVFR CIGS/FOG DEVELOPING
WITH SCT AREAS OF IFR STATUS/FOG DEVELOPING. ELEVATED CONVECTION
MAY HOLD TOGETHER TO COAST BUT THINK ANY SVR THREAT SHOULD BE
MINIMAL.

KBOS TERMINAL...CIGS EVER SO GRADUALLY LIFTING ABOVE 3 THSD FT BY
19 OR 20Z. SCT SHOWERS AND TSTMS AFT 22Z MAY BRIEFLY LOWER CIGS
AND VSBYS TO MVFR LEVELS. SVR UNLIKELY DUE TO LACK OF SFC HEATING.

TUESDAY...HIGH CONFIDENCE OF CONDITIONS BECOMING VFR THROUGHOUT
REGION...ALTHOUGH LINGERING MVFR/IFR UNTIL 13 OR 14Z POSSIBLE IN
SHOWERS...STRATUS AND FOG ACROSS CAPE AND ISLANDS.

OUTLOOK...WEDNESDAY THROUGH FRIDAY...

WEDNESDAY...MODERATE CONFIDENCE.  MAINLY VFR.  MVFR/IFR CONDITIONS
POSSIBLE IN SCT SHRA/TSRA DURING THE AFTERNOON TOWARD THE SOUTH
COAST...AND IN PATCHY FOG OVERNIGHT.

THURSDAY...MODERATE CONFIDENCE.  MVFR/IFR CONDITIONS POSSIBLE IN SCT
SHRA/TSRA THROUGH THE PERIOD AND PATCHY FOG OVERNIGHT.

FRIDAY...MODERATE CONFIDENCE.  MAINLY VFR.

&&

.MARINE...
5 FT EASTERLY SWELL JUST OFFSHORE CONTINUES...AND WILL CONTINUE
SCA FOR THE OUTER WATERS. DO NOT EXPECT SWELL TO CLIMB MUCH ABOVE
5 FEET...ALTHOUGH WIND CHOP COMBINED WITH THE SWELL COULD BRING
SEAS TO 6 FEET IN SPOTS S AND E OF NANTUCKET.

SEAS WILL GRADUALLY DIMINISH TONIGHT.

OUTLOOK...TUESDAY THROUGH FRIDAY...

WINDS AND SEAS EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
CRITERIA...BUT SHOULD BUILD THURSDAY AS A COASTAL LOW PRESSURE
APPROACHES FROM NEAR DELAWARE.  SHOWERS AND THUNDERSTORMS ARE
POSSIBLE TUESDAY MORNING ALONG WITH PATCHY FOG. MORE SHOWERS
EXPECTED TO ARRIVE LATE WEDNESDAY INTO THURSDAY.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
NH...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 AM EDT TUESDAY
     FOR ANZ250-254>256.

&&

SYNOPSIS...EKSTER
NEAR TERM...BELK/EKSTER/THOMPSON
SHORT TERM...EKSTER
LONG TERM...BELK
AVIATION...BELK/THOMPSON
MARINE...BELK/EKSTER/THOMPSON

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE TAUNTON MA
1126 AM EDT MON AUG 16 2010

NHZ011-015-161630-
CHESHIRE NH-WESTERN AND CENTRAL HILLSBOROUGH NH-
1126 AM EDT MON AUG 16 2010

...STRONG THUNDERSTORM IN NORTHWEST CHESHIRE COUNTY...

AT 1125 AM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM CAPABLE OF PRODUCING WIND GUSTS TO 40 MPH NEAR
WALPOLE...MOVING EAST AT 35 MPH.

* SOME LOCATIONS AFFECTED INCLUDE...SURRY...GILSUM...MARLOW...
  STODDARD...WINDSOR...ANTRIM...HILLSBOROUGH...DEERING AND WEARE.

FOR YOUR SAFETY...GET INSIDE WHEN THIS STORM APPROACHES. WINDS MAY BE
STRONG ENOUGH TO BRING DOWN SMALL BRANCHES. MINOR STREET FLOODING AND
PONDING OF WATER IN POOR DRAINAGE AREAS IS ALSO POSSIBLE.

&&

LAT...LON 4312 7185 4315 7167 4314 7165 4307 7164
      4306 7162 4304 7162 4301 7244 4308 7245
      4314 7214 4313 7213 4313 7204 4316 7203
      4319 7189

JWD

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