FXUS61 KOKX 230331
AFDOKX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
1031 PM EST TUE DEC 22 2009
.SYNOPSIS...
AN UPPER LEVEL LOW WILL PASS TO THE NORTH TONIGHT INTO WEDNESDAY.
A HIGH PRESSURE RIDGE BUILDING SOUTHEAST FROM CANADA WILL THEN
FOLLOW FOR WEDNESDAY NIGHT INTO THURSDAY NIGHT. ONSHORE FLOW AHEAD
OF AN APPROACHING FRONTAL SYSTEM COULD BRING SOME SPOTTY LIGHT
PRECIPITATION ON FRIDAY...WITH STEADIER PRECIPITATION LIKELY FROM
CHRISTMAS NIGHT INTO SUNDAY MORNING. HIGH PRESSURE WILL THEN
BUILD FROM THE WEST EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
TEMPS FORECAST IS ON TRACK DESPITE GUSTY WINDS HANGING IN.
DEWPOINTS HAVE CRASHED A BIT FASTER THAN FORECAST...SO THESE WERE
ADJUSTED DOWNWARD. IT IS STILL POSSIBLE POSSIBLE THAT THE SFC
LAYER COULD DECOUPLE ENOUGH LATE TONIGHT ACROSS THE INTERIOR AND
LONG ISLAND PINE BARRENS REGION TO ALLOW FOR BRIEF ENHANCED
RADIATIONAL COOLING AND TEMPS DROPPING TO NEAR 10 ABOVE. LOWS
ELSEWHERE SHOULD BE IN THE LOWER 20S NYC...AND 15-20 MOST
ELSEWHERE ALONG THE COAST.
UPDATED GRIDS AND POINT FORECASTS SENT...BUT ZONE FORECASTS REMAIN
ON TRACK.
WILL ALSO CONTINUE TO HIGHLIGHT BLACK ICE IN AN SP'S WITH
WIDESPREAD REFREEZE OF WET ROADWAYS...ESPECIALLY ACROSS LONG
ISLAND AND EASTERN CT.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
CLOUDS SHOULD INCREASE WED MORNING/AFTERNOON AS AN UPPER LOW
PASSING JUST TO THE NORTH CAPTURES MOISTURE AHEAD OF A WARM
FRONT RETROGRADING SW INTO THE CANADIAN MARITIMES.
POSITIVE 500-800 MB DIFFERENTIAL CYCLONIC VORTICITY ADVECTION ON
THE SOUTHERN FLANK OF THE UPPER LOW PER BOTH NAM/GFS SUPPORTS IDEA
OF ENOUGH LIFT TO GENERATE SOME FLURRIES IN SOUTHERN CT AND
PARTS OF THE LOWER HUDSON VALLEY. ONE LAST SURGE OF COLD AIR WILL
FOLLOW PASSAGE OF THE UPPER LOW...WITH GUSTY NW FLOW CONTINUING
AND TEMPS NEARLY AS COLD AS THOSE FORECAST FOR TONIGHT.
SUNNY DAY ON TAP FOR THU AS HIGH PRESSURE RIDGING DOWN FROM
ONTARIO BUILDS INTO THE AREA. SOME MODERATION IN TEMPS EXPECTED AS
MID LEVEL HEIGHTS RISE IN THE WAKE OF THE DEPARTING CLOSED
LOW...WITH HIGHS IN THE MID 30S TO NEAR 40.
THE AXIS OF THE HIGH MOVES EAST OF THE AREA THU NIGHT...WITH LOW
LEVEL MOISTURE QUICKLY RETURNING LATE THU NIGHT INTO FRI WELL
AHEAD OF AN APPROACHING FRONTAL SYSTEM. THIS MOISTURE COULD RESULT
IN FOG IN PLACES LATE THU NIGHT INTO FRI MORNING...WHICH COULD
CAUSE RIMING AND VERY SLIPPERY CONDITIONS CHRISTMAS MORNING...AND
ALSO INCREASING LOW CLOUDS. STEADIER PRECIP WITH THE SYNOPTIC
SCALE SYSTEM OFF TO THE WEST WILL LIKELY HOLD OFF UNTIL FRI
NIGHT...BUT WITH THE ABUNDANT LOW LEVEL MOISTURE AND WEAK LIFT
THERE COULD BE SOME LIGHT RAIN OR DRIZZLE IN THE AFTERNOON.
WILL HAVE TO WATCH TEMPS OVER THE INTERIOR...WHICH VIA CLOUD COVER
AND COLD AIR DAMMING WILL BE AT OR BARELY ABOVE FREEZING...AND
SUPPORTIVE OF LIGHT FREEZING RAIN/DRIZZLE ON COLDER SURFACES.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A HIGHLY AMPLIFIED UPPER AIR PATTERN WILL BE FEATURED AT THE ONSET
OF THE PERIOD WITH A LARGE CLOSED LOW OVER THE UPPER MIDWEST AND A
RIDGE ALONG THE EASTERN SEABOARD. THIS BLOCKING PATTERN WILL ALLOW
FOR SLOW PROGRESSION OF A FRONTAL SYSTEM ACROSS THE EASTERN
SEABOARD FRIDAY NIGHT INTO SUNDAY. THE GLOBAL MODELS HAVE SOME
TIMING ISSUES...BUT OVERALL ARE IN GOOD AGREEMENT WITH THE MASS
FIELDS. THE 12Z ECMWF CONTINUES TO BE A SHADE SLOWER WITH THE
FRONT AND BASED ON THIS PATTERN...SLOWER SEEMS TO BE PRUDENT.
A 1040 MB HIGH BUILDS ACROSS EASTERN CANADA FRI INTO SAT WITH SOME
FREEZING RAIN LIKELY ACROSS INTERIOR VALLEYS. THE EXTENT OF THE
COLD AIR DAMMING WILL BE BEST EVALUATED AS WE GET CLOSER TO THE
EVENT. VERTICAL TEMP PROFILE THOUGH DO NOT SUPPORT FROZEN PCP
(SNOW OR SLEET). THE COLD FRONT ALONG WITH A SFC WAVE OVER THE MID
ATLANTIC WILL BRING RAINS TO THE AREA SAT AFTERNOON AND
NIGHT...WITH CONDITIONS DRYING OUT ON SUNDAY BEHIND THE FRONT.
SIGNIFICANT RAINFALL ON TOP OF THE SNOW PACK WILL LIKELY LEAD TO
SOME FLOODING ISSUES...ESPECIALLY ACROSS CENTRAL AND EASTERN
LONG ISLAND.
A STRONG NW FLOW WILL DEVELOP MON AND TUE...WITH TEMPERATURES
DROPPING BACK INTO THE 30S FOR HIGHS.
&&
.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
VFR. PRESSURE GRADIENT REMAINS TIGHT OVER THE NEXT 24 HOURS...BUT
THE LOSS OF DAYTIME HEATING WILL KEEP GUSTS AT BAY OVERNIGHT. THEY
WILL RETURN ON WED BETWEEN 15Z AND 17Z ACROSS THE AREA. A SCT-BKN
CLOUD DECK WILL ALSO DEVELOP IN THE AFTN...BUT BASES COULD BE
HIGHER THAN WHAT IS CURRENTLY FORECAST. KEWR COULD HAVE SLANT VSBY
PROBLEMS IF DECK REMAINS AOB 4K FT.
WIND DIRECTIONS AT NYC TERMS ARE EXPECTED TO REMAIN MAINLY LEFT
OF 310 THROUGH AT LEAST 18Z THU...THEN POSSIBLY BECOME RIGHT OF
310 BETWEEN 21Z AND 00Z.
OUTLOOK 00Z WEDNESDAY THROUGH SUNDAY...
WED NIGHT-THU...VFR.
THU NIGHT-FRI...SUB-VFR POSSIBLE WITH LOW CLOUDS AND/OR FOG. -FZRA
OR -FZDZ ALSO POSSIBLE INLAND FRI AFTN (KHPN/KSWF).
FRI NIGHT-SAT NIGHT...SUB VFR...FZRA POSSIBLE INTO SAT MORNING
FOR KSWF...OTHERWISE RA. GUSTY SE-S WINDS/LLWS ALSO POSSIBLE.
SUNDAY...RAIN TAPERING OFF W-E...WITH VFR RETURNING AFTN/NIGHT.
&&
.MARINE...
THE SCA FOR THE SOUTH SHORE BAYS...NY HARBOR AND WESTERN LI SOUND HAS
BEEN ALLOWED TO EXPIRE. A FEW GUSTS TO 25 KTS STILL POSSIBLE
PRIMARILY ACROSS THE BAYS...BUT THE TREND ON SURROUNDING OBS HAS
BEEN DOWNWARD.
SCA CONDITIONS ARE LIKELY TO CONTINUE INTO WED NIGHT/THU MORNING
VIA ONE LAST CAA SURGE FOLLOWING PASSAGE OF AN UPPER LOW TO THE
NORTH. THE NEXT STORM SYSTEM WILL THEN IMPACT THE REGION LATE IN
THE WEEK AND THROUGH THE WEEKEND...WITH SCA CONDITIONS ON THE
OCEAN WATERS. MARGINAL SCA CONDITIONS MON-TUE WITH THE NW FLOW
BEHIND THE DEPARTING SYSTEM. UNDERCUT WAVEWATCH BY 1-2 FT ON THE
OCEAN WATERS DURING THIS TIME BASED ON FORECAST WIND SPEEDS.
&&
.HYDROLOGY...
SOME MELTING OF SNOW PACK POSSIBLE THU-FRI AS TEMPS RISE TO NEAR
40 IN NYC METRO AND COASTAL SECTIONS.
POTENTIAL EXISTS FOR ABOUT AN INCH LIQUID EQUIVALENT QPF MAINLY
FRI NIGHT INTO SUN MORNING...ON TOP OF SNOW PACK WITH ABOUT 1-2
INCHES WATER EQUIVALENT IN MOST PLACES...LESSER NORTH/WEST OF
NYC. THIS COULD LEAD TO BOTH URBAN AND SMALL RIVER/STREAM
FLOODING...DEPENDING ON SPEED OF SNOW MELT AND DURATION OF
HEAVIER RAIN.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
NY...NONE.
NJ...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR ANZ350-353-
355.
SMALL CRAFT ADVISORY UNTIL 6 PM EST WEDNESDAY FOR ANZ330-340.
&&
$$
SYNOPSIS...BS
NEAR TERM...BS
SHORT TERM...BG
LONG TERM...DW
AVIATION...AL
MARINE...BS
HYDROLOGY...BG/DW
