FXUS61 KBOX 051759
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
100 PM EST SAT DEC 5 2009
.SYNOPSIS...
LOW PRESSURE DEVELOPING OFF THE MID ATLANTIC COAST THIS AFTERNOON
WILL MOVE RAPIDLY NORTHEAST TODAY AND INTENSIFY DRAMATICALLY AS IT
PASSES SOUTHEAST OF NANTUCKET TONIGHT. A GOOD PORTION OF SOUTHERN
NEW ENGLAND WILL RECEIVE IT/S FIRST SIGNIFICANT SNOWFALL OF THE
SEASON. THIS LOW WILL QUICKLY MOVE AWAY ON SUNDAY AND BE REPLACED BY
HIGH PRESSURE THROUGH MONDAY. WEAK LOW PRESSURE MAY AFFECT SOUTHERN
NEW ENGLAND MONDAY NIGHT. ANOTHER FAST MOVING LARGE LOW PRESSURE
SYSTEM WILL IMPACT THE REGION MIDWEEK WITH A MIXTURE OF
PRECIPITATION AND WIND.
&&
.NEAR TERM /UNTIL 9 PM THIS EVENING/...
NOON UPDATE: RAISED AMOUNTS SLIGHTLY IN THE MONADS SWD INTO THE HIGH
TERRAIN ORH HILLS AND N CT HIGH TERRAIN. ADVY EXPANDED SE NH.
BLENDED 12Z RGEM/NAM/GFS QPF WITH PREV FCST AND FELT THIS WAS BEST
FIT FOR THE MOMENT. ISO AMTS IN ORH COUNTY MAY NEAR 8 INCHES BUT FOR
NOW...ADVY CONTS AS PREV ISSUED REMAINDER SNE.
WILL NEED TO CONSIDER UPPER CAPE COD SNOW ISSUES TONIGHT IN THE 4PM
FCST.
BL WARMTH CONTINUES TO BE A PROBLEM FOR R TO SNOW THRU 19Z...AND
THEREAFTER WE HAVE TRANSITIONED SLIGHTLY FASTER...ESP HIGH TERRAIN
AND LARGEST PRES FALLS E OF DELMARVA... ABOUT 5 MB IN 3 HRS.
&&
.SHORT TERM /9 PM THIS EVENING THROUGH 6 PM SUNDAY/...
A WINTER WEATHER ADVISORY IS IN EFFECT FOR MUCH OF SOUTHERN NEW
ENGLAND FOR TONIGHT...EXCEPT FOR SOUTHERN NH AND IMMEDIATE COASTAL
LOCATIONS OF SE MASS AND RI. UPWARD VERTICAL MOTION SHOULD BE
CRANKING PRETTY GOOD BETWEEN 00Z AND 06Z. THIS WILL RESULT IN A
TRANSITION FROM RAIN TO SNOW FROM WEST TO EAST...AND IT MAY OCCUR
VERY QUICKLY BETWEEN 00Z AND 03Z ON THE COASTAL PLAIN AS LONG AS
STRONG OMEGA DEVELOPS. THE EXACT AMOUNT OF SNOWFALL WILL DEPEND ON
QPF...WHERE THE BEST OMEGA ENDS UP BEING...AND THE TEMPERATURE
PROFILES.
SOME OF THE GUIDANCE IS TRYING TO CLOSE OFF THE MID LEVEL LOW FOR A
TIME THIS EVENING...AND THIS MAY INCREASE SNOWFALL RATES QUITE
STOUTLY AS MESOSCALE BANDING TRIES TO TAKE SHAPE...ESPECIALLY ACROSS
EASTERN ZONES. THIS COULD ADD A BIT MORE TO SNOWFALL TOTALS THERE.
FOR NOW...WE THINK THE HIGHER ELEVATIONS OF CENTRAL MASS AND CT WILL
DO BEST IN TERMS OF SNOW...BUT THIS IS THE TYPE OF SYSTEM THAT COULD
THROW A FEW CURVEBALLS. AT THIS TIME...WE ARE FORECASTING A GENERAL
2 TO 5 INCHES OF SNOWFALL...WITH 3 TO 6 IN THE HIGHER ELEVATIONS. IF
MESOSCALE BANDING WERE TO GET GOING THIS EVENING...THEN HIGHER
SNOWFALL TOTALS COULD BE EXPECTED...EVEN ON THE COASTAL PLAIN.
EASTERN MASS/INTERIOR SE MASS/RHODE ISLAND LOOK PARTICULARLY
INTRIGUING WITH RESPECT TO THE POTENTIAL FOR MESOSCALE BANDING AND
WE/LL HAVE TO KEEP AN EYE OUT FOR THAT THIS EVENING. COASTAL FRONT
ENHANCEMENT MAY BE ANOTHER FACTOR TO CONSIDER AS WELL. THERE/S A LOW
PROB THAT SOMEONE SEES LOW-END WINTER STORM WARNING CRITERIA
SNOWFALL OUT OF THIS...BUT THOSE AREAS ARE TOO DIFFICULT TO PINPOINT
AT THIS TIME. IN ADDITION...SOUTHERN NEW HAMPSHIRE ISN/T COMPLETELY
OUT OF THE WOODS. THEIR ADVISORY CRITERIA IS A BIT HIGHER THAN THE
REST OF SNE SO DIDN/T ISSUE ONE AT THIS TIME...BUT THEY MAY NEED TO
BE UPGRADED LATER IF IT LOOKS FOR CERTAIN THAT HIGHER QPF VALUES
WILL MAKE IT UP THERE.
SNOW MAY FALL HEAVY AT TIMES THIS EVENING. SINCE THE BOUNDARY LAYER
TEMPERATURES WILL BE NEAR FREEZING...SNOW MAY ACCUMULATE ON TREES AND
WIRES CAUSING BRANCH BREAKAGE AND THE POTENTIAL FOR SCT POWER
OUTAGES.
NORTHERLY WINDS WILL BECOME AN ISSUE ON THE CAPE AND ISLANDS WITH
GUSTS UP TO 50-55 MPH POSSIBLE AS THE STORM CONTINUES TO INTENSIFY.
SUNDAY...QUIETS DOWN WITH A NICE LOOK TO THE LANDSCAPE WITH FRESH
SNOW COVER. A BIT CHILLER THAN TODAY.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
ACTIVE PATTERN CONTINUES INTO NEXT WEEK. LEFT OVER SNOW SHOWERS MAY
LINGER UNTIL 13Z OR 14Z OVER THE CAPE AND NANTUCKET. OTHERWISE...
BECOMING MOSTLY SUNNY AND BLUSTERY ON SUN. EXPECT MON TO START OUT
DRY BUT THEN BECOME MOSTLY CLOUDY WITH CHANCE SNOW SHOWERS ACROSS
NORTHERN ZONES AS SHORT WAVE TROF RAPIDLY APPROACHES IN FAST ZONAL
FLOW. THERE MAY BE A WEAK SURFACE LOW OR TROUGH REFLECTION MON
EVENING.
LOOKS LIKE ENOUGH MOISTURE AND DYNAMICS TO WARRANT A LOW CHANCE OF
SNOW SHOWERS IN NORTHERN ZONES FOR MON EVE. THIS APPROACH SUPPORTED
BY SREF .01 PROB.
CONSIDERABLE COLD AIR IN PLACE AHEAD OF NEXT SIGNIFICANT EVENT WED
AND WED NIGHT WHEN EXPECT STRONG OVERRUNNING AND START OF
PRECIPITATION AS SNOW MOST LOCATIONS. MOST MEDIUM RANGE MODEL OUTPUT
BRINGS PRIMARY SURFACE LOW ACROSS EASTERN GREAT LAKES WITH
DEVELOPING TRIPLE POINT LOW THAT TRACKS RIGHT ACROSS SOUTHERN NEW
ENGLAND. LOW LEVEL JET OF 60+ KT FROM SE ACROSS TIGHT TEMPERATURE
GRADIENT ACCOMPANIED BY SUBTROPICAL SOURCE OF MOISTURE WILL LIKELY
PRODUCE COPIOUS AMOUNTS OF PRECIPITATION. ATTM...THINKING THERE WILL
BE A BURST OF SNOW...PERHAPS A FEW INCHES ON THE FRONT END AND THEN
A CHANGE TO SLEET/FREEZING RAIN AND THEN MOSTLY RAIN. MAY HAVE A
MORE SIGNIFICANT SNOW ACCUMULATION ACROSS SW NH...AND IF TRIPLE LOW
FAR ENOUGH EAST...THEN LOW LEVEL COLD AIR COULD HANG IN AND CAUSE A
SNOW TO SLEET TO FREEZING RAIN SCENARIO ACROSS SW NH AND NW MA. HAVE
CAPPED POPS AT LIKELY CATEGORY DUE TO LENGTH OF TIME BEFORE MID WEEK
EVENT AND INHERENT UNCERTAINTY WITH SUCH LEAD TIMES. ALSO HELD BACK
THE ONSET A LITTLE SINCE EXPECT A LOT OF LOW LEVEL DRY AIR THAT WILL
NEED TO BE OVERCOME AT THE OUTSET.
THERE IS A CHANCE THAT SOUTH WINDS MAY REACH WIND ADVISORY CRITERIA
OVER THE CAPE AND ISLANDS SOMETIME WED NIGHT...BUT THIS DEPENDS ON
DETAILS THAT ARE HARD TO RESOLVE THIS FAR OUT.
A SHIFT IN THE TRACK AND TIMING OF TRANSFER OF ENERGY TO SECONDARY
LOW COULD RESULT IN FAIRLY DRAMATIC CHANGES TO THE FORECAST...
ESPECIALLY WITH REGARD TO PTYPE AND WIND THREATS.
WE TURN COLD AGAIN AFTER THE MID WEEK EVENT. KEPT CHANCE POPS GOING
IN NORTHERN ZONES ON THU UNTIL THE PASSAGE OF THE UPPER TROF.
&&
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
THROUGH THIS EVENING...CIGS LOWERING TO IFR FROM S-N DURING THE
AFTERNOON. -SN OVER THE CT VALLEY INTO SW NH AND THE HIGHER TERRAIN
OF CENTRAL MA/S NH WILL PUSH S AFTER 21Z...REACHING KBOS BY AROUND
02Z THEN BRIEFLY ON THE CAPE AND ISLANDS AFTER 06Z. VSBYS BETWEEN
MVFR AND IFR MAINLY AFTER 23Z.
N-NE WIND GUSTS AOA 35KT ACROSS CAPE COD AND THE ISLANDS AFTER 23Z.
TONIGHT...IFR-LIFR CIGS AND MVFR-IFR VSBYS. CONDITIONS START TO
IMPROVE TO VFR ACROSS CT VALLEY/SW NH AROUND OR AFTER 06Z...THEN
PUSH E POSSIBLY REACHING KBOS BY 10Z.
N-NE WIND GUSTS AOA 40KT ACROSS CAPE COD AND THE ISLANDS.
OUTLOOK /SUNDAY THROUGH THURSDAY/...
SUNDAY...MVFR-IFR CIGS POSSIBLE EARLY KBOS-KHYA-KACK...THEN VFR ALL
AREAS. SFC WIND GUSTS 20 TO 25 KT MAY CAUSE MECHANICAL TURBULENCE.
MON...VFR...EXCEPT AREAS OF MVFR POSSIBLE DURING MON EVENING IN SCTD
-SHRA/-SHSN.
TUE...VFR.
WED...POTENTIAL FOR IFR AND STRONG WINDS.
THU...BECOMING MOSTLY VFR BUT STRONG WINDS.
&&
.MARINE...
GALE WARNINGS HAVE BEEN POSTED FOR ALL WATERS EXCEPT FOR BOSTON
HARBOR AND NARRAGANSETT BAY...BUT IT/S POSSIBLE THAT THOSE TWO
LOCATIONS MAY BE ADDED LATER. OVERALL...COASTAL STORM PASSES
SOUTHEAST OF NANTUCKET TONIGHT. WINDS AND SEAS INCREASE TO GALE AS
THE AFTERNOON PROGRESSES...WITH THE STRONGEST GUSTS...POSSIBLY 45
KT...OVERNIGHT TONIGHT. SEAS WILL BECOME VERY ROUGH.
OUTLOOK /SUNDAY THROUGH THURSDAY/...
EXPECT LEFTOVER HAZARDOUS SEAS ON SUN AND GALE FORCE WINDS EARLY.
WIND DIMINISHES LATE IN DAY AND SEAS SUBSIDING SUN NIGHT. INCREASING
SE WIND WILL REQUIRE AT LEAST SMALL CRAFT ADVISORY HEADLINE IF NOT
GALE WARNING FOR SOUTH COASTAL WATERS ON WED. NW GALE LIKELY ON
BACKSIDE OF SURFACE LOW FOR THU.
&&
.TIDES/COASTAL FLOODING...
NE TO N WIND COULD BRING A 1 TO 1.5 SURGE TO SANDWICH AND OTHER
NORTH AND NE FACING CAPE COD BAY SHORELINES LATE TONIGHT BUT EXPECT
ONLY SPLASHOVER AT WORST AS THE NIGHTTIME ASTRO TIDE IS NOT
ESPECIALLY HIGH. SHOULD BE LOSING ONSHORE FLOW COMPONENT OF WIND BY
THE TIME OF THE HIGHER SUN AFTERNOON ASTRO TIDE.
&&
.EQUIPMENT...
GLOUCESTER AND PROVIDENCE-JOHNSTON NWR TRANSMITTERS ARE OFF THE
AIR. RTS UNKNOWN. WE ARE WORKING ON THE PROBLEMS.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...WINTER WEATHER ADVISORY UNTIL 7 AM EST SUNDAY FOR CTZ002>004.
MA...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
SUNDAY FOR MAZ005>007-013>018.
WINTER WEATHER ADVISORY UNTIL 7 AM EST SUNDAY FOR MAZ002>004-
008>012-026.
WIND ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST SUNDAY FOR
MAZ022>024.
NH...WINTER WEATHER ADVISORY UNTIL 7 AM EST SUNDAY FOR NHZ012-015.
RI...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
SUNDAY FOR RIZ001>004-006.
MARINE...GALE WARNING FROM 5 PM THIS AFTERNOON TO 7 AM EST SUNDAY
FOR ANZ231>235-237-250-251-254>256.
SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 7 AM EST
SUNDAY FOR ANZ230-236.
&&
$$
SYNOPSIS...DRAG/EKSTER
NEAR TERM...DRAG/EKSTER
SHORT TERM...EKSTER
LONG TERM...THOMPSON
AVIATION...DRAG/EVT/THOMPSON
MARINE...DRAG/EKSTER/THOMPSON
TIDES/COASTAL FLOODING...THOMPSON
EQUIPMENT...DRAG
