Boston Discussion --> Comma Head Impact
Posted by JAC on 12/24/2010, 8:11 am
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
646 AM EST FRI DEC 24 2010

* POTENTIAL WINTER STORM SUNDAY THROUGH MONDAY

CHRISTMAS NIGHT...WILL NOTE INCREASING HIGH CLOUDS OVERNIGHT AS
THE UPPER LEVEL TROUGH APPROACHES. MEANWHILE SURFACE LOW PRESSURE
WILL DEVELOP ACROSS THE DEEP SOUTH. LIGHT ONSHORE FLOW WILL
DEVELOP WITH LOW LEVEL MOISTURE INCREASING OVERNIGHT PARTICULARLY
ALONG THE SOUTH COAST. THERE COULD BE A TOUCH OF LIGHT SNOW OR
FLURRIES OVERNIGHT BUT NOTHING SIGNIFICANT IS EXPECTED.

SUNDAY THROUGH MONDAY...
LOW PRESSURE TRACK AND TIMING ISSUES CONTINUE TO PERSIST AMONGST
THE OPERATIONAL MODELS AND ENSEMBLE DATA BUT WITH SLIGHTLY BETTER
AGREEMENT IN RECENT RUNS OF A MORE PROGRESSIVE SOLUTION.

THERE REMAINS THE POTENTIAL FOR A SIGNIFICANT WINTER STORM OVER A
PORTION OF THE AREA AS A LONG WAVE TROUGH AMPLIFIES ACROSS THE
EASTERN CONUS...AND RIDGING OVER A PORTION OF THE WESTERN CONUS.

LATEST WATER VAPOR LOOP EARLY THIS MORNING INDICATED A SOUTHERN
STREAM SHORT WAVE LOCATED ACROSS EASTERN NEW MEXICO...WITH A
NORTHERN STREAM SHORT WAVE ACROSS THE DAKOTAS. THESE TWO SHORT
WAVE DISTURBANCES ARE EXPECTED TO PHASE ALONG THE EASTERN SEABOARD
LATE SATURDAY NIGHT AND EARLY SUNDAY. INITIALIZATION LOOKED FAIRLY
GOOD EXCEPT THE 00Z GFS HANDLING OF SOUTHERN STREAM SHORT WAVE ENERGY.

UNCERTAINTY CONTINUES REGARDING THE TRACK AND INTENSITY OF COASTAL
LOW PRESSURE SUNDAY. THE 00Z GFS IS NOW LESS PROGRESSIVE AND ON THE
WESTERN ENVELOPE OF ITS ENSEMBLE MEAN. THE 00Z GLOBAL ENSEMBLES
HAVE TRENDED SLIGHTLY FURTHER WEST. THE 00Z UKMET AND CANADIAN GGEM
CONTINUE TO TRACK LOW PRESSURE SE OF THE BENCHMARK LATE SUNDAY. THE
00Z AND 06Z NAM CONTINUES TO FLUCTUATE OFFSHORE. THE 00Z ECMWF HAS
BECOME MUCH MORE PROGRESSIVE...TRACKING JUST SE OF THE BENCHMARK
AROUND 00Z MONDAY. IT IS FAIRLY WELL REPRESENTED BY THE GFS
ENSEMBLES AND THE GLOBAL ENSEMBLE MEAN. THE 00Z ECMWF IS NOW ABOUT
6 TO 12 HOURS FASTER THAN THE LATEST 00Z GFS SOLUTION.

THE OPERATIONAL MODELS ARE CONTINUING TO HAVE DIFFICULTY RESOLVING
PHASING ISSUES BETWEEN THE NORTHERN AND SOUTHERN BRANCHES OF THE JET
STREAM. OVERALL DECIDED TO USE A 50/50 BLEND OF 18Z HPC/00Z GFS
AND THE MORE PROGRESSIVE 00Z ECMWF. THIS BRINGS LOW PRESSURE CENTER
CLOSE TO THE BENCHMARK POSITION APPROACHING 00Z MONDAY...THEN QUICKLY
INTO THE CANADIAN MARITIMES AFTER 12Z MONDAY.

IF THIS DOES OCCUR...THE POTENTIAL FOR A SIGNIFICANT SNOWSTORM WOULD
INCREASE ACROSS A PORTION OF THE AREA. ATTM THIS APPEARS TO PRIMARILY
BE FOCUSED ACROSS SE NEW ENGLAND FOR THE SUNDAY THROUGH MONDAY
TIMEFRAME. IT APPEARS THAT EVEN WITH AN OFFSHORE LOW TRACK...THE
RAPID DEEPENING OF THE SURFACE LOW...AND THE NEARBY COMMA HEAD
PRECIPITATION/DEFORMATION ZONE BANDING WILL LIKELY REACH A PORTION
OF EASTERN MASSACHUSETTS AND RHODE ISLAND. THEREFORE HAVE MAINTAINED
LIKELY POPS PRIMARILY ALONG AND SE OF THE INTERSTATE 95 CORRIDOR
SUNDAY AFTERNOON THROUGH EARLY MONDAY...WITH CHANCE POPS INLAND.
USED A BLEND OF THE LATEST SREF AND MOS GUIDANCE TO DERIVE POPS.

AS MENTIONED STRONG WIND MAY ACCOMPANY PRECIPITATION ALONG
THE COAST AS THE DEVELOPING OCEAN STORM DEEPENS. DID CAP WIND
SPEEDS GIVEN THE UNCERTAINTY OF STORM TRACK...BUT AT LEAST WIND
ADVISORY CRITERIA IS A POSSIBILITY ACROSS THE CAPE AND ISLANDS.

CAUTION IS ADVISED IN LITERAL MODEL INTERPRETATION AT THIS
POINT...AS WE ARE STILL A COUPLE OF DAYS AWAY FROM THIS POTENTIAL
EVENT. A LOW TRACK FURTHER SOUTHEAST WOULD CONFINE THE SIGNIFICANT
SNOW THREAT TO THE CAPE AND ISLANDS...AND A LOW TRACK FURTHER WEST
WOULD BRING THIS THREAT TO MUCH OF THE AREA.

THE DETAILS REMAIN UNCERTAIN REGARDING SNOW AMOUNTS AND WIND IMPACT...
BUT SOME POSSIBILITY EXISTS FOR WINTER STORM WATCHES AND/OR WIND
ADVISORIES/HIGH WIND WATCHES BEING HOISTED THE NEXT DAY OR SO FOR
A PORTION OF THE REGION LATE SUNDAY INTO MONDAY. GIVEN THE
UNCERTAINTY ON POTENTIAL AREAL IMPACT...STILL HAVE SOME TIME TO
MULL OVER FUTURE MODEL DATA TO REFINE THE FORECAST...STAY TUNED TO
THE LATEST FORECASTS.

$$
SYNOPSIS...BELK/STRAUSS
NEAR TERM...BELK
SHORT TERM...BELK
LONG TERM...STRAUSS
AVIATION...BELK/STRAUSS
MARINE...BELK/STRAUSS
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" Possible" Major Eastcoast Blizzard - Fred, 12/22/2010, 9:47 am
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