February 8, 2013 Pre Storm Forecast Discussion Boston

000
FXUS61 KBOX 080842
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
342 AM EST FRI FEB 8 2013

.SYNOPSIS…
A HISTORIC WINTER STORM AND BLIZZARD IS ANTICIPATED FOR FRIDAY
INTO SATURDAY…WITH AROUND 2 FEET OF SNOW POSSIBLE. THIS STORM
SHOULD COME TO AN END LATER SATURDAY. DRY WEATHER RETURNS BY
SUNDAY. A GREAT LAKES STORM WILL SWING A COLD FRONT THROUGH NEW
ENGLAND ON MONDAY NIGHT…FOLLOWED BY DRY WEATHER TUESDAY.

&&

.NEAR TERM /UNTIL 12 PM THIS AFTERNOON/…
345 AM UPDATE…FORECAST IS ON TRACK FOR THE MOST PART. CAN SEE
ON THE MOSAIC RADAR A LARGE AREA OF PRECIP ACROSS NEW YORK STATE
AND EDGING INTO NORTHERN NEW ENGLAND AS WELL AS AN AREA OF PRECIP
ACROSS THE MID-ATLANTIC. LOOKING AT SURFACE OBS…THE AREA OVER
NEW YORK STATE IS EVAPORATING BEFORE HITTING THE GROUND WHICH
MAKES SENSE WITH TEMPERATURES IN THE MID 20S AND DEWPOINTS IN THE
LOW TEENS. THE AREA OF PRECIP OVER THE MID-ATLANTIC IS PRODUCING
RAIN AND SNOW. THESE TWO AREAS OF PRECIP WILL BE WHAT WILL
COMPRISE OUR STORM TODAY THROUGH SATURDAY.

MEANWHILE…A 1038 MB HIGH CENTERED OVER QUEBEC AND EXTENDS
ACROSS NEW ENGLAND. THE HIGH WILL SHIFT EAST A LITTLE
OVERNIGHT…EXTENDING ALONG AN ARC FROM QUEBEC TO THE MARITIMES.
THIS WILL KEEP THE COLD AIR IN PLACE OVER SOUTHERN NEW ENGLAND.
SKIES HAVE BECOME OVERCAST…WITH LOW CLOUDS DEVELOPING ON THE
EAST COAST…CAPE…AND ISLANDS. LIGHT SNOW WILL OVERSPREAD THE
AREA THIS MORNING AS WARM ADVECTION CONTINUES AND HIGHER DEWPOINTS
MOVE INTO THE REGION.

&&

.SHORT TERM /12 PM THIS AFTERNOON THROUGH 6 PM SATURDAY/…
* A POTENTIALLY HISTORIC WINTER STORM/BLIZZARD WILL IMPACT
SOUTHERN NEW ENGLAND TODAY INTO SATURDAY.

* BLIZZARD WARNINGS ARE IN EFFECT FOR ALL OF CT…RI…E/SE MA…AND
SE NH. WINTER STORM WARNINGS FOR ALL OTHER LOCATIONS IN
SOUTHERN NEW ENGLAND.

* SNOWFALL TOTALS FOR THE STORM MAY BE IN THE ALL-TIME TOP 10 FOR
VARIOUS CITIES…UP TO AROUND 2 TO 3 FEET POSSIBLE. BLOWING AND
DRIFTING ANTICIPATED RESULTING IN HIGHER DRIFTS.

* TRAVEL CONDITIONS WILL DETERIORATE QUICKLY THROUGH TODAY…
BECOMING NEARLY IMPOSSIBLE BY THIS EVENINGS COMMUTE INTO
SATURDAY.

MODEL CONSENSUS…

THE MODELS ARE IN VERY GOOD AGREEMENT AND IN LINE WITH THE
CONSISTENT ECMWF. GIVEN THIS CONSISTENCY AND CONTINUED
AGREEMENT…HAVE MADE FEW CHANGES TO THE GOING FORECAST LARGELY
BASED ON THE ECMWF.

SYNOPSIS…
LOW PRESSURE IN THE GREAT LAKES AND LOW PRESSURE OFF THE SOUTH
CAROLINA COAST WILL COME TOGETHER EAST OF THE DELMARVA PENINSULA
AND RAPIDLY DEEPEN AS IT MOVES ACROSS THE 40N/70W BENCHMARK. WITH
THE SOUTHERN STREAM COMPONENT…DEEP LAYER MOISTURE WILL BE
BROUGHT UP BY VERY STRONG /HURRICANE FORCE OR GREATER/ LOW LEVEL
WINDS. EXPECT NEAR BLIZZARD TO BLIZZARD CONDITIONS TO AFFECT ALL
OF SOUTHERN NEW ENGLAND TONIGHT INTO SATURDAY.

PRECIPITATION…

LIGHT SNOW THROUGH THE MORNING WILL INCREASE IN INTENSITY INTO
THE AFTERNOON HOURS. WARM AIR INTRUDING AT THE MID LEVELS WILL
BRING A MIX OF RAIN AND SNOW ALONG THE IMMEDIATE SOUTH COAST OF
RHODE ISLAND AND MASSACHUSETTS WITH A COMPLETE CHANGEOVER TO RAIN
LIKELY ON THE OUTER CAPE AND THE ISLANDS FOR A PERIOD TONIGHT.

SNOW WILL INTENSIFY DURING THE EVENING COMMUTE INTO TONIGHT. MODERATE
TO HEAVY SNOW WILL CONTINUE INTO MIDDAY SATURDAY. IT WILL BECOME
LIGHTER DURING THE LATE MORNING HOURS SATURDAY…GRADUALLY
TAPERING WEST TO EAST AS THE SURFACE LOW EXITS OUT INTO THE
ATLANTIC INTO SATURDAY NIGHT.

SNOWFALL AMOUNTS…

MESOSCALE BANDING IS LIKELY TO OCCUR ACROSS THE AREA. WHERE THESE
BANDS SET UP…2 TO 3 INCH/HR SNOWFALL RATES ARE POSSIBLE. IN
ADDITION…A SNOWFALL BAND IS EXPECTED WITH THE MID LEVEL
DEFORMATION ZONE…SETTING UP ALONG THE BOSTON-PROVIDENCE
CORRIDOR. EXPECT THIS IS WHERE THE HIGHEST SNOWFALL AMOUNTS WILL
OCCUR…WITH STORM TOTALS POSSIBLE IN EXCESS OF 24 INCHES.

GENERALLY EXPECT WIDESPREAD 18 TO 24 INCH SNOWFALL TOTALS ACROSS
SOUTHERN NEW ENGLAND. LESSER AMOUNTS ARE EXPECTED OVER THE
OUTER CAPE AND THE ISLANDS WITH THE CHANGEOVER TO RAIN.

WINDS…
EXPECT HIGH WIND CRITERIA /GUSTS GREATER THAN 58 MPH/ THROUGHOUT
THE BLIZZARD WARNING AREA AS WELL AS NANTUCKET TONIGHT AND
SATURDAY. LOW LEVEL WINDS UP TO 90 KTS COMBINED WITH PRECIPITATION
DRAG AND EXCELLENT MIXING WILL RESULT IN VERY GUSTY WINDS. WINDS
WILL GUST FROM AROUND 30 MPH ACROSS WESTERN NEW ENGLAND INCREASING
TO THE COAST TO NEAR HURRICANE FORCE. THIS WILL RESULT IN DOWNED
TREES AND POTENTIAL STRUCTURAL DAMAGE.

THESE WINDY CONDITIONS WILL RESULT IN CONSIDERABLE BLOWING AND
DRIFTING OF SNOW.

PREPAREDNESS…

PLEASE SEE THE SNOW BRIEFING PAGE ON WWW.WEATHER.GOV/BOSTON FOR
PREPAREDNESS ACTIONS.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/…
BIG PICTURE… UPPER LOW OVER THE PACIFIC NORTHWEST DIPS TO THE
DESERT SOUTHWEST BY FRIDAY…THEN TURNS THE CORNER AND LIFTS TO THE
GREAT LAKES MONDAY. PART OF THE UPPER LOW LINGERS OVER THE
SOUTHWEST EARLY IN THE WEEK…BUT THEN SWEEPS NORTHEAST TOWARD NEW
ENGLAND DURING MIDWEEK. GOOD AGREEMENT BETWEEN GFS AND ECMWF UPPER
FLOWS THROUGH TUESDAY FOLLOWED BY SMALL DIVERGENCE MIDWEEK.

THE DAILIES…

SATURDAY NIGHT… MAJOR STORM DEPARTS EAST SATURDAY NIGHT.
LINGERING EVENING SNOW ON THE CAPE BUT SHOULD END QUICKLY.
STRONGEST PRESSURE RISES SHOULD BE OFFSHORE…BUT STILL 2MB/HOUR
RISES ARE EXPECTED EARLY AT NIGHT AND 1 MB/HOUR LATE. SO SUSTAINED
WINDS WILL BE STRONG DURING THE FIRST PART OF THE NIGHT FOLLOWED BY
DIMINISHING SPEEDS OVERNIGHT. SUFFICIENT LOW LEVEL MIXING TO
SUPPORT 50 KNOT/60 MPH GUSTS EARLY…BUT THIS ALSO DIMINISHES
OVERNIGHT. TEMPS ARE A BLEND OF MOS.

THE COMBINATION OF WIND AND COLD AIR WILL BRING WIND CHILLS BELOW
ZERO ALMOST EVERYWHERE…AND BELOW -10F OVER THE NORTHERN HALF OF
OUR AREA. THERE MEANS A POTENTIAL FOR A WIND CHILL ADVISORY IN
PARTS OF THE AREA.

SUNDAY…HIGH PRESSURE BUILDS OVER THE REGION. FAIR WEATHER WITH
DIMINISHING WIND. TEMPS ARE A BLEND OF MOS.

MONDAY… LOW PRESSURE SURFACE AND ALOFT MOVES THROUGH THE GREAT
LAKES. THIS SWINGS A FRONT THROUGH NEW ENGLAND LATE MONDAY OR
MONDAY NIGHT. INCREASING MOISTURE ALOFT…SO EXPECT INCREASING
CLOUDS MONDAY MORNING. GOOD ISENTROPIC LIFT IS FORECAST TO REACH US
LATE MORNING WITH 25-30 MB/HOUR VALUES AT 850 MB MONDAY AFTERNOON.
MODEL CONSENSUS MATCHES WELL THIS THIS…ALL SHOW MEASURABLE PCPN
WEST OF US AT 12Z MONDAY AND OVERSPREADING THIS AREA BY 18Z. OUR
FORECAST FEATURES CHANCE POPS ARRIVING MID TO LATE MORNING WITH
MAXIMUM VALUES TOWARD 00Z. DIMINISHING POPS AFTER MIDNIGHT AS THE
FRONT MOVES OFF TO THE EAST.

TUESDAY-WEDNESDAY… WEAK HIGH PRESSURE BUILDS OVER THE REGION…SO
EXPECT QUIET WEATHER. MIXING POTENTIAL FOR WINDS WOULD FAVOR 25 KNOT
GUSTS TUESDAY.

THURSDAY…UPPER TROUGH MOVES THROUGH. THE ECMWF IS DRY WITH THIS
PASSAGE WHILE THE GFS GENERATES A MAJOR LOW PRESSURE AREA WITH WIND
AND RAIN. MUCH UNCERTAINTY AT THIS STAGE…WE FEATURE CHANCE POPS
FOR WEDNESDAY NIGHT AND PART OF THURSDAY. TEMPERATURES ARE A MAJOR
QUESTION. OUR BLEND OF GUIDANCE YIELDS A CHANCE OF FREEZING
RAIN…BUT WITH NO CONFIDENCE ON THE TRACK OF ANY DEVELOPING LOW
THERE IS NO CONFIDENCE IN ANY RESULTING PRECIP TYPE. AT THIS STAGE
PEOPLE SHOULD TAKE FROM THE FORECAST THAT THERE IS A CHANCE OF SOME
KIND OF PCPN BUT NOT LOCK INTO ANY PCPN TYPES.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/…
FORECASTER CONFIDENCE LEVELS…
LOW…LESS THAN 30 PERCENT.
MODERATE…30 TO 60 PERCENT.
HIGH…GREATER THAN 60 PERCENT.

OVERVIEW…HIGH CONFIDENCE TODAY AND TONIGHT WITH CONDITIONS…
MODERATE CONFIDENCE ON EXACT TIMING.

THROUGH THIS MORNING…EXPECT DRY WEATHER THROUGH 10-12Z WITH VFR
CONDITIONS FOR RHODE ISLAND…SOUTHERN NEW HAMPSHIRE…
MASSACHUSETTS WEST OF WORCESTER AND NORTHERN CONNECTICUT. MVFR
CIGS ALONG THE EAST COAST OF MASSACHUSETTS. CONDITIONS WILL LOWER
ACROSS THE AREA TOWARDS 12Z AND CONTINUE THROUGH MID MORNING AS
LIGHT SNOW MOVES INTO THE AREA.

THIS AFTERNOON…CONDITIONS LOWER TO IFR DURING THE AFTN SNOW
INTENSITY INCREASES. SNOW ALL TERMINALS EXCEPT POSSIBLY MIXING
WITH RAIN AT ACK. NORTHEAST WINDS WILL ALSO INCREASE WITH SURFACE
VALUES REACHING 25-40 KNOTS BY EVENING…EAST WINDS AT 2000 FEET
WILL REACH 60 KNOTS ALONG THE SOUTH COAST BY EVENING…BRINGING
POTENTIAL LOW LEVEL WIND SHEAR.

TONIGHT…IFR ALL TERMINALS AND VERY STRONG WINDS EASTERN MA WITH
NE WINDS G60KT ACROSS CAPE COD AND THE ISLANDS. WINDS AT 2000 FEET
AGL WILL GUST 70-90 KNOTS BOS-PVD-CAPE AND ISLANDS. GUSTS 35-50
KT POSSIBLE FARTHER WEST. SNOWFALL RATES 1-2 IN PER HOUR ALL
TERMINALS.

KBOS TAF…HIGH CONFIDENCE IN TAF

KBDL TAF…HIGH CONFIDENCE IN TAF.

OUTLOOK…SATURDAY THROUGH TUESDAY…

SAT…IFR/LIFR ALL TERMINALS WITH HEAVY RAINFALL RATES OF 1-2 IN
PER HOUR IN THE AM FOR EASTERN MA AND RI. G60KT REMAIN POSSIBLE
CAPE COD AND THE ISLANDS. THEN IMPROVING FROM WEST TO EAST DURING
THE AFTERNOON WITH CONDITIONS POSSIBLY IMPROVING TO MVFR ALONG
WITH WINDS SLOWLY DIMINISHING.

SATURDAY NIGHT…LINGERING STRONG NORTH TO NORTHWEST WINDS EARLY
ESPECIALLY AROUND BOSTON AND THE CAPE/ISLANDS WITH POTENTIAL GUSTS
40-50 KNOTS. WINDS DIMINISH DURING THE NIGHT.

SUNDAY…VFR WITH DIMINISHING WIND.

MONDAY…VFR EARLY BUT WITH LOWERING CIGS THROUGH THE DAY. MVFR
CIGS AND MVFR/IFR VSBYS IN RAIN AND SNOW LATE MONDAY AND MONDAY
NIGHT.

TUESDAY…
VFR WITH WEST WINDS.

&&

.MARINE…
THROUGH SATURDAY…HIGH CONFIDENCE FOR AN EXTREMELY DANGEROUS
STORM FOR MARINERS. WINDS AND SEAS INCREASE THROUGH THIS TIME
PERIOD AS LOW PRESSURE MOVES OVER THE COASTAL WATERS. SEAS WILL
INCREASE TO 30 TO 35 FEET EAST OF MASSACHUSETTS. HURRICANE FORCE
WIND GUSTS ARE EXPECTED IN THIS SAME AREA WITH A 80 TO 90 KT LOW
LEVEL JET. SEAS BEGIN TO SLOWLY SUBSIDE SAT AFTERNOON.

OUTLOOK…SATURDAY NIGHT THROUGH TUESDAY…

SATURDAY NIGHT… DIMINISHING NORTH WINDS. WINDS AT STORM FORCE
EARLY AT NIGHT BUT DIMINISHING TO GALES OR LIGHTER BY SUNRISE.
DIMINISHING SEAS…BUT STILL HAZARDOUS ON THE EASTERN WATERS AND
SOUTHERN OUTER WATERS THROUGH THE NIGHT. THE WIND AND COLD AIR WILL
GENERATE FREEZING SPRAY CONDITIONS OVER THE WATERS THROUGH THE NIGHT.

SUNDAY…
DIMINISHING WINDS AND SEAS AS HIGH PRESSURE MOVES OVER THE
WATERS. LINGERING FREEZING SPRAY DURING THE MORNING.

MONDAY… INCREASING SOUTH TO SOUTHWEST WINDS DURING THE AFTERNOON.
WINDS WILL GUST TO 25 KNOTS IN THE AFTERNOON WITH SEAS NEAR 5 FEET
TOWARD EVENING. SMALL CRAFT ADVISORY CONDITIONS AT NIGHT WITH
SOUTHWEST WINDS EARLY AND WEST WINDS LATE.

TUESDAY…WEST WINDS GUSTING TO 25 KT AND SEAS NEAR 5 FEET MUCH OF
THE DAY.

&&

.TIDES/COASTAL FLOODING…
* COASTAL FLOOD WARNING NOW IN EFFECT FROM SALISBURY MA
SOUTHWARD TO MARTHAS VINEYARD FOR THIS EVENING AND SAT MORNING
HIGH TIDE *

MASSACHUSETTS COASTLINE…

TWO HIGH TIDE CYCLES PRESENT CONCERN…THIS EVENING AND SATURDAY
MORNING. A COASTAL FLOOD WARNING IS NOW IN EFFECT FOR ALL E…NE
AND N FACING SHORELINES ALONG THE MA COAST FOR BOTH THIS EVENING
AND SAT MORNING HIGH TIDES. FOR THIS EVENINGS HIGH TIDE…ONSHORE
WINDS…SURGE AND SEAS WILL BE RAMPING UP. WE THINK THE SURGE WILL
BE GETTING INTO THE 2 TO 3 FT RANGE AND SEAS A LITTLE OFFSHORE IN
THE 15 TO 20 FT RANGE BY THE TIME OF THE HIGH TIDE…GENERALLY
BETWEEN 930 PM AND 10 PM. THIS RESULTS IN A MINOR TO MODERATE
IMPACT.

THE SATURDAY MORNING HIGH TIDE MAY BE THE MORE SERIOUS EVENT AS A
CONSEQUENCE OF IT BEING A HIGH ASTRONOMICAL TIDE AND VERY LARGE
SEAS. WE THINK THE SURFACE WIND ALONG THE IMMEDIATE COAST WILL
HAVE BACKED TO NNE OR N BY THE TIME OF THE HIGH TIDE…BUT STILL
NE WITH A LONG FETCH OVER THE GULF OF ME AND NORTHERN GEORGES
BANK. THE SURGE MAY BE STARTING TO SUBSIDE WITH THE WIND SHIFTING
TO BE MORE FROM THE NORTH VS NORTHEAST BUT STILL IN THE 2 TO 3 FT
RANGE…HIGHEST S OF BOSTON. IN FACT…WE ARE CALLING FOR A 4 TO
4.5 FT SURGE ALONG THE N SIDE OF CAPE COD…INCLUDING THE
SANDWICH/SPRING HILL BEACH AREA WHERE THE WIND WILL BE MORE
DIRECTLY ONSHORE. SEAS ARE EXPECTED TO BE 25 TO 30 FT E AND NE OF
CAPE ANN AND 30 TO 35 FT IN VICINITY OF STELLWAGEN BANK AND JUST
OFF E OF CAPE COD AND NANTUCKET. THUS…WE ARE ANTICIPATING A
MODERATE IMPACT ALONG THE MA E COAST N OF BOSTON AND MODERATE TO
MAJOR S OF BOSTON. WE ARE ESPECIALLY CONCERNED WITH THE IMPACT OF
LARGE BREAKERS ON TOP OF AN ELEVATED TIDE. THERE IS A RISK OF SOME
STRUCTURAL DAMAGE ALONG THE IMMEDIATE COASTLINE SATURDAY
MORNING…ESPECIALLY HULL TO SANDWICH.

RI COAST…

NOT TOO MUCH CONCERN FOR FLOODING GIVEN STORM TRACK YIELDING
NORTHEAST WINDS. HOWEVER WITH TIDES ASTRONOMICALLY HIGH AND GOOD
PRES FALLS ASSOCIATED WITH THE COASTAL STORM…POCKETS OF MINOR
COASTAL FLOODING ARE POSSIBLE FOR THE RI COAST. ALSO FLOOD
THRESHOLD FOR RI COASTLINE IS NOW A BIT LOWER AFTER SANDY ERODED
AWAY MUCH OF THE DUNES ALONG THE COASTLINE.

BEACH EROSION…

THE OTHER ISSUE IS BEACH EROSION. THE BEACH EROSION WILL BEGIN TO
BE NOTED BY THIS EVENINGS HIGH TIDE AND MAY BE SEVERE IN SOME
LOCATIONS FOR THE SATURDAY MORNING HIGH TIDE…INCLUDING THE PLUM
ISLAND AREA…SCITUATE TO PLYMOUTH AND SANDWICH…OUTER CAPE
INCLUDING CHATHAM…AND THE EAST SIDE OF NANTUCKET.

COASTAL FLOOD DEFINITIONS…

MAJOR COASTAL FLOODING…AT LEAST SCATTERED STRUCTURAL DAMAGE ALONG
WITH WIDESPREAD FLOODING OF VULNERABLE SHORE ROADS AND/OR BASEMENTS
EVACUATIONS MAY BE NECESSARY IN SOME AREAS.

MODERATE COASTAL FLOODING…ISOLATED STRUCTURAL DAMAGE POSSIBLE.
NUMEROUS ROAD CLOSURES.

&&

.BOX WATCHES/WARNINGS/ADVISORIES…
CT…BLIZZARD WARNING FROM 6 AM THIS MORNING TO 1 PM EST SATURDAY
FOR CTZ002>004.
MA…WINTER STORM WARNING FROM 6 AM THIS MORNING TO 1 PM EST
SATURDAY FOR MAZ002>004-008>011-026.
BLIZZARD WARNING FROM 6 AM THIS MORNING TO 1 PM EST SATURDAY
FOR MAZ005>007-012>023.
COASTAL FLOOD WARNING FROM 8 PM THIS EVENING TO NOON EST
SATURDAY FOR MAZ007-015-016-019-022>024.
HIGH WIND WARNING FROM 1 PM THIS AFTERNOON TO 7 PM EST
SATURDAY FOR MAZ024.
WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 PM EST
SATURDAY FOR MAZ024.
NH…WINTER STORM WARNING FROM 6 AM THIS MORNING TO 1 PM EST
SATURDAY FOR NHZ011-015.
BLIZZARD WARNING FROM 6 AM THIS MORNING TO 1 PM EST SATURDAY
FOR NHZ012.
RI…BLIZZARD WARNING FROM 6 AM THIS MORNING TO 1 PM EST SATURDAY
FOR RIZ001>008.
MARINE…STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 PM EST SATURDAY
FOR ANZ231>237.
STORM WARNING FROM 4 PM THIS AFTERNOON TO 7 PM EST SATURDAY
FOR ANZ230-251.
HURRICANE FORCE WIND WARNING FROM 1 AM TO 1 PM EST SATURDAY
FOR ANZ250-254.
HURRICANE FORCE WIND WARNING FROM 7 PM THIS EVENING TO 8 AM
EST SATURDAY FOR ANZ255-256.

&&

$$

SYNOPSIS…WTB/RLG
NEAR TERM…RLG
SHORT TERM…RLG
LONG TERM…WTB
AVIATION…WTB/RLG
MARINE…WTB/RLG
TIDES/COASTAL FLOODING…THOMPSON/NOCERA

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