National Weather Service Forecast Discussion

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KOKX 121205
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
705 AM EST FRI MAR 12 2010

.SYNOPSIS...
HIGH PRESSURE SLOWLY RETREATS TO THE NORTHEAST OVER SOUTHEAST
CANADA THROUGH THE WEEKEND...AS LOW PRESSURE APPROACHES FROM THE
WEST THROUGH SATURDAY NIGHT. THIS LOW PASSES JUST SOUTH OF LONG
ISLAND SUNDAY AND SUNDAY NIGHT...THEN SLOWLY PULLS AWAY TO THE
EAST EARLY NEXT WEEK. A DRY COLD FRONT WILL CROSS THE TRI-STATE
TUESDAY...FOLLOWED BY HIGH PRESSURE BUILDING IN THROUGH THE
MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --AN AREA OF LIGHT TO MODERATE RAIN CURRENTLY STRETCHING FROM NORTH
CENTRAL PA...SOUTHEAST TO THE DELMARVA PENINSULA WILL SLOWLY LIFT
NORTHEAST TODAY...AS THE LOW TO MID LEVEL RIDGE AXIS SLOWLY LIFTS
TO OUR NORTHEAST. BEFORE THE RIDGE AXIS PASSES BY...MOIST LOW
LEVELS WITH DRY AIR ABOVE WILL PROMOTE MAINLY PATCHY DRIZZLE
ACROSS THE TRI-STATE. ALSO ACTING TO LIMIT THE SPREAD OF THE RAIN
TO THE NORTHEAST...IS RELATIVELY LOW DEWPOINT AIR (LOW TO MID 30S
COMING IN FROM THE EAST-NORTHEAST ON LOW LEVEL EAST-NORTHEAST
FLOW WHICH WILL KEEP LOW LEVEL TEMPERATURE-DEWPOINT SPREADS
FAIRLY LARGE. ALSO A VORTICITY MINIMUM AT BOTH 700 AND 500 HPA
WILL APPROACH AHEAD OF THE AREA OF RAIN...ADDING TO LOW TO MID
LEVEL SUBSIDENCE AND DRYING.

AS A RESULT HAVE LIMITED POPS THIS MORNING TO SLIGHT CHANCE EAST
AND CHANCE WEST (WITH A SMALL SLIVER OF LIKLIES FAR SW)...THAT
INCREASE TO CATEGORICAL WEST TO SLIGHT CHANCE FAR NORTHEAST BY
LATE AFTERNOON (RIDGE AXIS STILL OVER FAR NE AREAS LATE THIS
AFTERNOON).

WITH LIGHT PRECIPITATION (MUCH OF IT EVAPORATING IN LOW LEVELS
CAUSING EVAPORATIVE COOLING)...OVERCAST SKY CONDITIONS...AND
STRENGTHENING ONSHORE FLOW...BLENDED COOLER MET GUIDANCE WITH NAM
2-METER TEMPERATURES FOR HIGHS TODAY - MAINLY MID 40S.-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
GFS REMAINS A FAST AND DEEP OUTLIER WITH THE CUTOFF LOW...MAINLY
DUE TO CONVECTIVE FEEDBACK ISSUES ULTIMATELY LEADING TO IT
ERODING THE RIDGE AHEAD OF THE CUTOFF LOW TO QUICKLY. THE NAM AND
ECMWF WERE FAIRLY SIMILAR SO FOLLOWED A BLEND THROUGH THE SHORT
TERM.

EXPECT PRECIPITATION TO GRADUALLY BECOME STEADIER FRIDAY
NIGHT...AND THEN GRADUALLY INCREASE IN INTENSITY
SATURDAY...BECOMING HEAVY AT TIMES SATURDAY AFTERNOON IN RESPONSE
TO AN EASTERLY LOW LEVEL JET INCREASING TO 50-60KT...INCREASING
LOW TO MID LEVEL FRONTOGENETIC FORCING...INCREASING QUASI-
GEOSTROPHIC FORCING (AS INDICATED BY Q-VECTOR CONVERGENCE)...AND
INCREASING DIVERGENCE ALOFT IN RESPONSE TO THE REGION BECOMING IN
THE LEFT FRONT QUADRANT OF A 85 KT JET 250 HPA STREAK. THE RAIN
WILL CONTINUE TO BE HEAVY AT TIMES SATURDAY NIGHT...WITH THE LOW
LEVEL EASTERLY JET INCREASING IN STRENGTH TO 70-80KT. BASED ON
THIS...HAVE CONTINUED THE FLOOD WATCH FOR THE ENTIRE CWA SATURDAY
AND SATURDAY NIGHT - SEE THE HYDROLOGY SECTION OF THE AFD FOR
DETAILS ON QPF AMOUNTS AND FLOOD THREAT.

AS THE LOW TRACKS TO THE SOUTH SUNDAY/SUNDAY NIGHT...THE PRESSURE
GRADIENT RELAXES DUE TO THE PROXIMITY OF THE LOW...AND THE LOW
LEVEL JET WEAKENS TO 30-40 KT BY SUNDAY EVENING. THE LOW LEVEL
FLOW BECOMES SHEARED SUNDAY NIGHT WITH FLOW AT 850 HPA REMAINING
EAST NORTHEAST...WHILE FROM 950 HPA TO THE SURFACE THE FLOW BACKS
TO THE NORTH-NORTHEAST...REDUCING THE LOW LEVEL MOISTURE FEED
EVEN FURTHER. AS A RESULT TAPER POPS DOWN FROM CATEGORICAL SUNDAY
MORNING...TO CHANCE FAR WEST AND LIKELY REMAINDER BY LATE SUNDAY
NIGHT. IN ADDITION WITH THE CUT OFF LOW TRACKING JUST TO THE
SOUTH SUNDAY NIGHT...WILL HAVE ENOUGH OF THE COLD POOL OVER NW
AREAS...THAT THERE SHOULD BE SOME SNOW MIXING IN WITH THE RAIN
ACROSS THE NORTHERN INTERIOR LATE SUNDAY NIGHT/MONDAY
MORNING...ESPECIALLY ACROSS HIGHER ELEVATIONS.

IN ADDITION TO THE PRECIPITATION...THE STORM WILL PRODUCE GUSTY
EASTERLY WINDS ACROSS THE REGION FROM SATURDAY INTO SUNDAY NIGHT.
THE STRONGEST WINDS WILL LIKELY BE FROM SATURDAY AFTERNOON INTO
SUNDAY MORNING CORRESPONDING WITH THE PERIOD OF THE STRONGEST LOW
LEVEL JET. WITH THE JET BEING 70-80 KT FROM 950-850 HPA SATURDAY
NIGHT...THERE IS A SOLID POTENTIAL FOR WIND ADVISORY SUSTAINED
WINDS...ESPECIALLY OVER COASTAL AREAS AND HIGHER ELEVATIONS. IN
ADDITION...DEPENDING ON HOW STRONG THE LOW LEVEL INVERSION ENDS
UP BEING...AND HOW MUCH STRONGER WIND MIX DOWN WITH HEAVIER
RAINFALL...THERE IS SOME POTENTIAL FOR GUSTS TO HIGH WIND WARNING
STRENGTH (AT LEAST 58 MPH). WILL MENTION THIS THREAT IN THE
HWO...BUT WITH CONFIDENCE IN THIS AT LESS THAN 50 PERCENT...DID
NOT GO WITH A HIGH WIND WATCH AT THIS TIME. MOST LIKELY A WIND
ADVISORY WILL END UP BEING ISSUED FOR AT LEAST COASTAL PORTIONS
OF THE TRI-STATE FOR SOME IF NOT ALL OF THE TIME FRAME FROM
SATURDAY AFTERNOON INTO SUNDAY MORNING.

WITH THE LOW CLOUD COVER AND PRECIPITATION THERE WILL BE LITTLE
IN THE WAY OF DIURNAL RANGE THROUGH THE SHORT TERM...UNTIL THE
AREA GETS ON THE BACKSIDE OF THE CUTOFF LOW SUNDAY NIGHT AND
COLDER AIR COMES IN FROM THE NORTH AND IS ALSO MIXED DOWN FROM
ALOFT.

FOLLOWED A BLEND OF MET/MAV TEMPERATURES FOR LOWS TONIGHT...A
BLEND OF COOLER MAV AND NAM-2 METER TEMPERATURES ON SATURDAY...A
BLEND OF MAV/MET/NAM 2-METER TEMPERATURES SATURDAY NIGHT AND
SUNDAY AND A BLEND OF MEX/MEX ENSEMBLE MEAN AND NAM 2-METER
TEMPERATURES SUNDAY NIGHT. BASICALLY LOWS FROM THE MID 30S TO
AROUND 40 AND HIGHS IN THE LOWER TO MID 40S..EXCEPT ACROSS THE
NORTHERN INTERIOR AREAS SUNDAY NIGHT WHERE LOWS IN THE LOWER 30S
ARE CURRENTLY FORECAST.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
USED THE MORE CONSISTENT ECMWF FOR THE FIRST PART OF THE
EXTENDED...AND CONTINUED CHANCE OF RAIN (RAIN/SNOW NORTHERN
INTERIOR MONDAY MORNING) - WITH LIKELY POPS EAST MONDAY
MORNING...TAPERING DOWN TO CHANCE POPS MONDAY AFTERNOON THEN TO
DRY WEATHER BY LATE MONDAY NIGHT.

A DRY COLD FRONT SHOULD PASS THROUGH TUESDAY...FOLLOWED BY HIGH
PRESSURE BUILDING INTO THE MIDDLE OF THE WEEK AS SPLIT FLOW SETS
UP OVER THE EASTERN UNITED STATES...WITH THE A RESULTANT DRY
NORTHWEST FLOW ALOFT OVER THE REGION.

FOLLOWED A BLEND OF MEX/MEX ENSEMBLE MEAN/LOW MEX ENSEMBLE MEMBER
FOR HIGHS MONDAY (REFLECTING IMPACT OF WETTER SOLUTION THAN GFS
BASED MEX IS BASED ON)...THEN A MEX/MEX ENSEMBLE MEAN BLEND FOR
THE REMAINDER OF THE EXTENDED. AFTER ANOTHER BELOW NORMAL DAY ON
MONDAY...EXPECT TEMPERATURES FOR THE REMAINDER OF THE EXTENDED TO
RUN SLIGHTLY ABOVE NORMAL.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --MVFR CEILINGS AND VFR VISIBILITIES THIS MORNING. CEILINGS AND
VISIBILITIES LOWER TO IFR AS LIGHT RAIN DEVELOPS AFTER 16Z...THEN
REMAINS THROUGH THE END OF THE FORECAST. SOME UNCERTAINTY WITH
THE TIMING OF THE LOWERING CEILINGS. IN THE METRO AREA CEILINGS
COULD FALL TO HIGH END IFR FOR A SHORT PERIOD EARLY THIS MORNING.

EASTERLY WINDS FROM 060 TO 090 AT AROUND 10 KT INCREASE AND BECOME
GUSTY THIS AFTERNOON...WITH GUSTS 20 TO 25 KT. LATE TONIGHT WINDS
BECOME SUSTAINED AT 20 TO 25 KT WITH GUSTS AROUND 30. A DEVELOPING
LOW LEVEL JET WILL INCREASE CHANCES OF LOW LEVEL WIND SHEAR AFTER
05Z WITH WINDS BETWEEN 1000 AND 2000 FT RUNNING 40 KT TO 50 KT.

KJFK AFTERNOON HOURLY WIND FORECAST IN SUPPORT OF RUNWAY
CONSTRUCTION ALL WIND DIRECTIONS ARE TRUE...ADD 13 DEGREES FOR
MAGNETIC
     12/19Z 07015G24KT
     12/20Z 07015G26KT
     12/21Z 07016G27KT
     12/22Z 07017G28KT
     12/23Z 08017G28KT
     13/00Z 08018G28KT
     13/01Z 08018G28KT
     13/02Z 07018G28KT
     13/03Z 07018G29KT

OUTLOOK 12Z SATURDAY THROUGH TUESDAY...
SATURDAY AND SATURDAY NIGHT...IFR IN RAIN AND FOG. STRONG GUSTY
WINDS. LLWS LIKELY.
SUNDAY THROUGH MONDAY...IFR LIKELY INTO SUNDAY NIGHT...IMPROVING TO VFR BY
MONDAY MORNING.
TUESDAY...VFR.-- End Changed Discussion --

&&

.MARINE...
WITH THE TIGHTENING PRESSURE GRADIENT BETWEEN LOW PRESSURE OVER
THE CENTRAL UNITED STATES TO THE SOUTHEAST COAST...AND HIGH
PRESSURE OVER SOUTHEASTERN CANADA EXPECTED TO INCREASE TODAY AND
INTO SATURDAY WILL CONTINUE WITH THE SMALL CRAFT ADVISORY AND
UPGRADE THE GALE WATCH TO A WARNING. WINDS ALOFT WILL BE IN THE
40 TO 50 KT RANGE BUT NOT SURE HOW MUCH OF THIS WILL MIX TO THE
WATER SURFACE. WINDS ALOFT INCREASE SATURDAY INTO SATURDAY
NIGHT...70 TO 80 KT FOR A TIME SATURDAY NIGHT. SO WILL EXTEND THE
GALE WARNING INTO SATURDAY NIGHT. WILL HAVE TO CONSIDER IF THESE
HIGHER WINDS DO MIX DOWN TO POST A STORM WATCH FOR SATURDAY
NIGHT.

WINDS ARE EXPECTED TO DIMINISH SUNDAY AS SFC LOW PRESSURE PASSES
SOUTH OF THE WATERS AND MOVES SLOWLY EAST INTO MONDAY.

WITH THE POWERFUL LOW APPROACHING THIS WEEKEND...SEAS OF 14 TO 18
FEET QUITE POSSIBLE OVER THE OPEN OCEAN WATERS SATURDAY.

SCA CONDITIONS SHOULD CONTINUE ON MOST WATERS INTO SUNDAY NIGHT-
MON AS THE COASTAL STORM SLOWLY PULLS AWAY FROM THE AREA. OCEAN
SEAS WILL BE RATHER SLOW TO SUBSIDE THEREAFTER...WITH LONG PERIOD
SWELLS OVER 5 FT LINGERING THROUGH AT LEAST TUE MORNING AND
POSSIBLY THROUGH WED MORNING.

&&

.HYDROLOGY...
SPOTTY LIGHT RAIN/PATCHY DRIZZLE TODAY...WILL GRADUALLY GIVE WAY
TO A STEADY RAIN DURING TONIGHT ACROSS THE ENTIRE TRI-STATE. THE
RAIN WILL THEN CONTINUE THROUGH THE WEEKEND...WITH THE HEAVIEST
RAINFALL OCCURRING SATURDAY AFTERNOON AND NIGHT...AND THEN TO COME
TO AN END BY LATE MONDAY NIGHT. CURRENTLY EXPECT 2.5-4 INCHES OVER
THE LOWER HUDSON VALLEY/NE NJ/NYC...AND 2.5 TO 3 INCHES FURTHER
EAST WITH LOCALLY HIGHER AMOUNTS. WITH PRECIPITABLE WATERS AROUND
1 INCH SATURDAY AFTERNOON AND NIGHT...THERE IS THE POTENTIAL FOR
RAINFALL RATES OF 1/2 TO 1 INCH PER HOUR AT TIMES (THOUGH VERY
LIKELY NOT FOR AN ENTIRE HOUR). WITH THIS PROLONGED PERIOD OF
HEAVY RAINFALL...WITH OCCASIONALLY STRONG RAINFALL RATES...THERE
IS A HIGH POTENTIAL FOR URBAN/POOR DRAINAGE AND RIVER/STREAM
FLOODING THROUGHOUT THE AREA SATURDAY AND SATURDAY NIGHT. RESIDUAL
RIVER FLOODING COULD LINGER SUNDAY IF HEAVY RAINFALL MATERIALIZES
AS ANTICIPATED. IF AS SUGGESTED BY SOME GUIDANCE...THE HEAVIER
RAINFALL LINGERS INTO SUNDAY MORNING...THE FLOOD WATCH COULD END
UP BEING EXTENDED BY LATER SHIFTS.

FOR NE NJ AND THE LOWER HUDSON VALLEY...FLASH FLOOD GUIDANCE IS
LOWER (ESPECIALLY FOR NE NJ)...WITH WET ANTECEDENT CONDITIONS. IN
ADDITION HIGHER ELEVATIONS IN THESE REGIONS STILL HAVE SOME SNOW
PACK. FURTHER EAST...SATURATED GROUNDS ACROSS LONG ISLAND AND
SOUTHERN CT HAVE RESULTED IN HIGH WATER TABLES. THESE SATURATED
GROUNDS WILL BE UNABLE TO ABSORB THE RAINFALL...AND POOR
DRAINAGE IS QUITE LIKELY/AND SIGNIFICANT BASEMENT FLOODING IS
ALSO POSSIBLE.

&&

.TIDES/COASTAL FLOODING...
A PERSISTENT EASTERLY FLOW...STEADILY INCREASING THROUGH
SATURDAY...AND INCREASING ASTRONOMICAL TIDES DUE TO AN
APPROACHING NEW MOON...MAY RESULT IN WIDESPREAD MINOR COASTAL
FLOODING SATURDAY DURING THE TIMES OF HIGH TIDE WITH DEPARTURES
OF 2 TO 3 FEET. THEN SATURDAY NIGHT WIDESPREAD MINOR COASTAL
FLOODING DURING THE HIGH TIDE CYCLES IS LIKELY WITH LOCALLY
MODERATE POSSIBLE IN THE SOUND. DEPARTURES OF 3 TO 4 FEET ARE
POSSIBLE. THESE LEVELS WILL PUT PARTS OF WESTERN LI SOUND OVER
MODERATE BENCHMARKS. THIS AREA WILL NEED TO BE MONITORED CLOSELY
FOR A POTENTIAL COASTAL FLOOD WATCH. ON THE ATLANTIC SIDE...ANY
MODERATE COASTAL FLOODING WILL LIKELY BE CONFINED TO THE SOUTH
SHORE BACK BAYS OF WESTERN LI. AGAIN...DURING THE SUNDAY MORNING
HIGH TIDE CYCLE MODERATE FLOODING WILL BE POSSIBLE IN THE WESTERN
LI SOUND WITH WIDESPREAD MINOR ALONG THE SOUTH SHORE. LOCALLY
MODERATE FLOODING WILL AGAIN BE POSSIBLY ESPECIALLY IN THE SOUTH
SHORE BACK BAYS.

IN ADDITION...BEACH EROSION IS LIKELY FOR THE SOUTH SHORE BEACHES
WITH HIGH SURF FROM EASTERLY SWELLS. SEAS ON THE OCEAN ARE
FORECAST TO RANGE FROM 15 TO 18 FEET SATURDAY NIGHT INTO SUNDAY.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...FLOOD WATCH FROM SATURDAY MORNING THROUGH SUNDAY MORNING FOR
     CTZ005>012.
NY...FLOOD WATCH FROM SATURDAY MORNING THROUGH SUNDAY MORNING FOR
     NYZ067>081.
NJ...FLOOD WATCH FROM SATURDAY MORNING THROUGH SUNDAY MORNING FOR
     NJZ002>006-011.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ330-
     335-338-340-345-350-353-355.
     GALE WARNING FROM 6 PM EST THIS EVENING TO 6 AM EDT SUNDAY FOR
     ANZ330-335-338-340-345-350-353-355.

&&

$$
SYNOPSIS...PFM
NEAR TERM...PFM
SHORT TERM...PFM
LONG TERM...PFM
AVIATION...MET
MARINE...MET
HYDROLOGY...PFM
TIDES/COASTAL FLOODING...MET

NWS OKX Office Area Forecast Discussion