Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 041858
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
258 PM EDT TUE AUG 4 2015

.SYNOPSIS...

THUNDERSTORMS CONTINUING INTO THE EVENING HOURS MAINLY PUSHING E.
CONTINUED STRONG TO SEVERE THREATS. DRY...WARM AND LESS HUMID
WEATHER ARRIVES THURSDAY. A PERIOD OF UNSETTLED WEATHER IS
POSSIBLE FRIDAY INTO THIS WEEKEND...BUT CONFIDENCE REMAINS LOW
REGARDING THE TIMING AND COVERAGE OF ANY POTENTIAL WET WEATHER.

&&

.NEAR TERM /THROUGH TONIGHT/...

INTO THIS EVENING...

STRONG TO SEVERE THUNDERSTORMS PERSISTING IN AN AREA OF BETTER
MOISTURE / HIGHER THETA-E FORCED AHEAD OF A MID-LEVEL IMPULSE. A
VERY UNSTABLE ENVIRONMENT WITH DECENT LAPSE RATES THROUGHOUT THE
COLUMN WITH SW-NE UNI-DIRECTIONAL 0-6 KM BULK SHEAR EXCEEDING 50
KTS...WITH SOME TURNING EVIDENT WITHIN THE HIGH-RES GUIDANCE IN
THE 0-1/0-3 KM LAYER. CHECK OUT THE 18Z ALBANY SOUNDINGS WHERE
MUCAPE VALUES ARE NEARLY 3K J/KG AND HIGHLIGHT EXACTLY THE ABOVE
POINTS.

FOCUS MAINLY ACROSS THE N/W REGIONS AWAY FROM WHERE THE DRY-SLOT
IS APPARENT WITHIN THE WATER VAPOR LOOP OVER SE NEW ENGLAND...
THOUGH ACTIVITY IS EXPECTED TO SHIFT S/E INTO THE EVENING HOURS
AHEAD OF A FRONTAL BOUNDARY PUSHED OFFSHORE BY THE MID-LEVEL
IMPULSE.

LIKELY POPS WITH PRIORITIZED THREATS OF THE FOLLOWING: HEAVY RAIN /
FREQUENT LIGHTNING / URBAN AND POOR DRAINAGE FLOODING ISSUES /
STRONG TO DAMAGING WINDS / LARGE HAIL. THERE IS THE POSSIBILITY
OF A TORNADO AS WELL AS WE HAVE ALREADY SEEN A FEW DOPPLER-RADAR
INDICATED.

WATCH NUMBER 469 CONTINUES TILL 8 PM. MAY NEED TO EXPAND INTO N CT
AND RI. CONTINUE TO EVALUATE THE ENVIRONMENT. AT THIS TIME DOWN-
STREAM TRENDS DO NOT FAVOR AN EXPANSION OF THE WATCH. LOOKS LIKE
MOST OF THE ENERGY IS LOCKED ALONG THE LEADING EDGE / PVA OF THE
MID-LEVEL VORTEX DISCERNED FROM HIGH-RES GUIDANCE AND WATER VAPOR
IMAGERY.

TONIGHT...

MID-LEVEL IMPULSE AND ACCOMPANYING TROUGH PUSH E SUBSEQUENTLY EASING
THE SURFACE FRONTAL BOUNDARY OFFSHORE ALONG WITH DEEPER MOISTURE AND
HIGHER THETA-E AIR. WILL SEE SHOWERS / THUNDERSTORMS PUSH OUT TO SEA
WITH SOME OF THE STORMS STRONG TO SEVERE LINGERING LONGEST OVER THE
CAPE AND ISLANDS WITHIN A LOW-LEVEL CONVERGENT ENVIRONMENT OF HIGHER
THETA-E AIR. ANTICIPATED CONCLUSION SHORTLY AFTER MIDNIGHT OF
WET- WEATHER. LIGHT W-WINDS PREVAILING AND DRIER AIR WORKING IN.
EXPECT IT TO CLEAR OUT W TO E ACCORDINGLY. LOWS DROPPING IN AND
AROUND THE LOW-60S WITH SPOTS N/W INTO THE UPPER-50S AS THERE IS
AN OPPORTUNITY FOR RADIATIONAL COOLING TO PROCEED. WITH THAT THERE
IS THE POTENTIAL FOR PATCHY DENSE FOG...ESPECIALLY THOSE AREAS
WHICH OBSERVED RAIN DURING THE DAY.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...

WEDNESDAY...

ANOTHER MID-LEVEL IMPULSE SWEEPS THROUGH THE BROAD CYCLONIC FLOW
FOLLOWED BY THE MID-LEVEL TROUGH. ENOUGH FORCING WITHIN THE LOW- TO
MID-LEVEL ATMOSPHERIC PROFILE TO INVOKE SOME SHOWERY WEATHER...YET
TWO THINGS: ONE IS THAT MOISTURE IS LIMITED WITH DRIER AIR AS THE
SURFACE...INSTABILITY SHOULD BE RATHER WEAK...AND TWO IS THAT A DRY-
SUBSIDENCE INVERSION WILL BE WORKING DOWN THROUGH THE ATMOSPHERIC
PROFILE ACROSS THE AREA PUTTING A SQUASH ON ACTIVITY. WHILE CAN
NOT DISAGREE WITH PRIOR FORECASTER OF THE COOLER TEMPERATURES
ALOFT YIELDING SMALL HAIL...FEEL THAT DRY AIR AND SUBSIDENCE
ACROSS THE REGION MAY LIMIT THE LIFT. REMOVED FROM PREVAILING IN
THE FORECAST.

SO WITH THE FORCING APPARENT WILL GO WITH CHANCE POPS FOR SCATTERED
SHOWERS AND MAYBE A THUNDERSTORM FOCUSING ON THE EARLY-HALF OF
THE DAY. FROM THEN ON DRIER WEATHER WITH BREEZY W-WINDS. A TAD
COOLER AS THE AIR-MASS ALOFT COOLS. HIGHS AROUND THE LOW 80S.
SEASONABLE.

WEDNESDAY NIGHT...

BEHIND THE TROUGH IT LOOKS TO REMAIN A BIT BREEZY W. CAN NOT RULE
OUT A FEW LOCALES EXPERIENCING LIGHT WINDS OVERNIGHT. SHOULD SEE
QUIET WEATHER AND CLEAR CONDITIONS. ALL FACTORS COMBINED...THERE IS
SOME POTENTIAL FOR RADIATIONAL COOLING AND HIGHEST CONFIDENCE IS TO
THE N/W WITHIN SHELTERED VALLEY REGIMES. LOWS DOWN INTO THE MID- TO
UPPER-50S WHILE LOW-60S ALONG THE COAST. DEWPOINTS IN THE LOW-50S.
AN END TO THE HEAT AND HUMIDITY AND QUITE REFRESHING.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...

HIGHLIGHTS...

* UNSETTLED WEATHER REMAINS POSSIBLE FRIDAY INTO THE WEEKEND
* TEMPERATURES TRENDING BELOW NORMAL THROUGH MOST IF NOT THE ENTIRE
  PERIOD

OVERVIEW AND MODEL PREFERENCES...

NOTING FAIRLY GOOD AGREEMENT WITH 12Z OPERATIONAL MODELS RUNS INTO
FRIDAY...THEN EACH GOES ON THEIR MERRY OWN WAY WHICH LENDS TO LOW
CONFIDENCE BEYOND FRIDAY. ONE BIG QUESTION WILL BE HOW THE H5 CUTOFF
LOW ACROSS QUEBEC AND MARITIMES FLATTENS OUT...WHICH ALSO FLATTENS
OUT THE FLOW ACROSS MOST OF THE NORTHERN STREAM. DEPENDING UPON
WHETHER THIS UPPER LEVEL SYSTEM FLATTENS OUT WILL DETERMINE HOW FAR
S THE LARGE HIGH PRES RIDGE BUILDS OUT OF CENTRAL CANADA. ALSO
NOTING A STALLED FRONT S OF THE REGION WHICH HAS A SHORT WAVE MOVING
ALONG IT...WHICH COULD PUSH SOME MOISTURE INTO PORTIONS OF SOUTHERN
NEW ENGLAND. ANOTHER FLY IN THE OINTMENT IS THE POSSIBLE
AMPLIFICATION OF LONG WAVE TROUGH ACROSS THE MID ATLC REGION THIS
WEEKEND.

NEEDLESS TO SAY...LOW CONFIDENCE FORECAST BEYOND FRIDAY DUE TO THE
WIDE VARIANCE OF OP MODEL RUN SOLUTIONS. WENT ALONG WITH MOST
AVAILABLE GUIDANCE /EXCEPT GFS/ THROUGH FRIDAY...THEN TRANSITIONED
OVER TO AN ENSEMBLE MODEL BLEND SIMILAR TO WPC GUIDANCE FROM
SATURDAY ONWARD.

DETAILS...

THURSDAY...HIGH PRESSURE BUILDS OUT OF CENTRAL CANADA INTO UPSTATE
NY. WEAK SHORT WAVE MOVES ACROSS NORTHERN NEW ENGLAND AND...WITH
LACK OF AVAILABLE MOISTURE IN THE GENERAL W-NW FLOW...EXPECT DRY
CONDITIONS. HIGHS LOOK TO RUN AROUND 80 DEGREES...SLIGHTLY BELOW
SEASONAL NORMS.

THURSDAY NIGHT THROUGH SATURDAY...SHORT WAVE MOVING ALONG STALLED
FRONT FROM THE OHIO VALLEY. COULD START TO SEE SOME MOISTURE MOVING
NE INTO N CT/RI/SE MA OVERNIGHT THU NIGHT THEN PUSH FURTHER N DURING
FRI. STILL A LOT OF QUESTION ON HOW FAR THIS RAIN WILL PUSH INTO THE
REGION...IF AT ALL. FOR NOW...KEPT CONTINUITY GOING FROM THE
PREVIOUS FORECAST WITH MAINLY CHANCE POPS...THOUGH LOW LIKELY IN
PLACE ACROSS S COASTAL AREAS FRI INTO FRI NIGHT.

HAVE LOWERED POPS TO CHANCE FOR EARLY SATURDAY THEN SHOULD PUSH E
DURING THE AFTERNOON INTO SAT EVENING.

SUNDAY THROUGH WEDNESDAY...MUCH OF THIS FORECAST CONTINUES TO
DEPEND UPON THE FRI-SAT PATTERN SETS UP. AT THIS POINT...LOOKS LIKE
IT SHOULD BE MAINLY DRY BUT COOL ON SUNDAY. MODELS SIGNALING ANOTHER
H5 LONG WAVE TROUGH DIGGING ACROSS EASTERN GREAT LAKES AS H5 LOW
TRYING TO CUT OFF AGAIN ACROSS HUDSON BAY. MAY SEE PERIODS OF WIDELY
SCT SHOWERS FROM TIME TO TIME DURING THIS TIMEFRAME...BUT LOW
CONFIDENCE ON TIMING AND PLACEMENT.


&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...

FORECASTER CONFIDENCE LEVELS...

LOW...LESS THAN 30 PERCENT.
MODERATE...30 TO 60 PERCENT.
HIGH...GREATER THAN 60 PERCENT.

SHORT-TERM /THROUGH WEDNESDAY NIGHT/...

INTO THIS EVENING...MODERATE CONFIDENCE.
STRONG TO SEVERE TSRA WITH POTENTIAL THREATS: LARGE HAIL / STRONG
TO DAMAGING WINDS MAINLY OUT OF THE W / HEAVY RAIN WITH MVFR-IFR
VSBYS. MVFR TO LOW-END VFR CIGS. LOW RISK TORNADO. ACTIVITY
SWEEPING ENE AT 25-30 KTS.

TODAY...MODERATE CONFIDENCE.
SHRA/TSRA DEVELOPING TOWARDS MIDDAY GOING W TO E INTO THE EVENING
HRS. STRONG TO SEVERE POTENTIAL. +RA WITH GUSTY WINDS AND POSSIBLE
HAIL. BRIEF MVFR / IFR CONDITIONS WITH TSRA.

TONIGHT...MODERATE CONFIDENCE.
SHRA/TSRA LINGER OVER THE SE TERMINALS TILL AROUND 6-9Z. TEMPO
MVFR- IFR CONDITIONS. OTHERWISE LIGHT W-WINDS AND VFR...THOUGH
TERMINALS WHICH EXPERIENCED RAIN DURING THE DAY LIKELY TO SEE
MVFR-LIFR PATCHY DENSE FOG.

WEDNESDAY...HIGH CONFIDENCE.
SCT SHRA WITH LOWER POSSIBILITY OF TSRA. LOW RISK OF SMALL HAIL.
BREEZY W-WINDS WITH GUSTS UPWARDS OF 20 KTS. SCT-BKN LOW-END VFR
CIGS.

WEDNESDAY NIGHT...HIGH CONFIDENCE.
W-WINDS DIMINISHING. VFR. SKC. LOW CONFIDENCE PATCHY DENSE FOG.

KBOS TERMINAL...MODERATE CONFIDENCE. ENOUGH CONFIDENCE THAT STORMS
WILL IMPACT THE TERMINAL WITH SIGNIFICANT IMPACT...BUT UNCERTAIN
ON THE EXACT TIMING.

KBDL TERMINAL...MODERATE CONFIDENCE. WATCHING CLOSELY FOR STORM
IMPACT. STORMS COULD POTENTIALLY HOLD OFF TO THE N.

OUTLOOK /THURSDAY THROUGH SUNDAY/...

THURSDAY...HIGH CONFIDENCE. VFR.

THURSDAY NIGHT THROUGH SATURDAY...LOW CONFIDENCE ON TIMING...HIGHER
CONFIDENCE ON TRENDS. MVFR-IFR CONDITIONS IN AREAS OF RAIN SOMETIME
DURING THIS PERIOD. VFR BEFORE AND AFTER PERIODS OF RAIN.

SUNDAY...LOW CONFIDENCE MAINLY FOR TIMING. MAY SEE LEFTOVER SHOWERS
WITH BRIEF MVFR CONDITIONS EARLY...THEN VFR.

&&

.MARINE...

FORECASTER CONFIDENCE LEVELS...

LOW...LESS THAN 30 PERCENT.
MODERATE...30 TO 60 PERCENT.
HIGH...GREATER THAN 60 PERCENT.

SHORT-TERM /THROUGH TUESDAY NIGHT/...

TONIGHT...MODERATE CONFIDENCE.
SHOWERS AND THUNDERSTORMS LINGER OVER THE SE WATERS ALONG WITH
BREEZY SW-WINDS. SUBSEQUENT 5-6 FOOT SEAS BEGINNING TO DIMINISH
INTO MORNING AS THE WET-WEATHER AHEAD OF A FRONTAL BOUNDARY PUSHES
OUT TO SEA BEHIND WHICH WINDS BACK W.

WEDNESDAY...HIGH CONFIDENCE.
W-WINDS CONTINUING PERHAPS BREEZY WITH GUSTS UPWARDS OF 20 KTS.
SEAS WILL GRADUALLY DIMINISH THROUGH THE PERIOD. THERE IS THE
POSSIBILITY OF SOME RENEWED SHOWER ACTIVITY THOUGH LIKELY CLOSER
TO THE SHORE.

WEDNESDAY NIGHT...HIGH CONFIDENCE.
W-WINDS DIMINISHING ALLOWING SEAS TO RELAX. SHOULD SEE QUIET
BOATING WEATHER.

OUTLOOK /THURSDAY THROUGH SUNDAY/...

THURSDAY-THURSDAY NIGHT...HIGH CONFIDENCE. WINDS AND SEAS BELOW
SMALL CRAFT CRITERIA. LOCALLY REDUCED VSBYS IN LIGHT RAIN THU NIGHT.

FRIDAY THROUGH SUNDAY...MODERATE CONFIDENCE. EASTERLY WINDS GUSTING
UP TO 20 KT. WITH ONSHORE WINDS...SEAS LOOK TO BUILD UP TO 5-6 FT
HIGHEST ACROSS THE EASTERN OUTER WATERS. RAIN LIKELY FRIDAY NIGHT
THROUGH SATURDAY NIGHT...LIMITING VISIBILITIES AT TIMES...THEN
SHOULD IMPROVE DURING SUNDAY.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR
     ANZ230>234-236-250-251.
     SMALL CRAFT ADVISORY UNTIL 8 AM EDT WEDNESDAY FOR ANZ235-237-
     254>256.

&&

$$

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



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