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Area Forecast Discussion
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000
FXUS61 KOKX 130752
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
352 AM EDT FRI MAR 13 2015

.SYNOPSIS...
HIGH PRESSURE BUILDS OFFSHORE INTO TONIGHT. AN AREA OF LOW
PRESSURE THEN APPROACHES FROM THE WEST EARLY SATURDAY...THEN
CROSSES THE AREA SATURDAY AFTERNOON. A COLD FRONT WILL MOVE ACROSS
THE REGION SATURDAY NIGHT. HIGH PRESSURE THEN BUILDS IN THROUGH
SUNDAY NIGHT...THEN SLIDES TO THE SOUTH ON MONDAY. A COLD FRONT
MOVES ACROSS THE AREA MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE
THEN BUILDS INTO THE REGION INTO THURSDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
NW FLOW ALOFT TODAY...ALONG WITH WEAK SHORTWAVE RIDGING AT 700
HPA...COUPLED WITH PASSING VORTICITY MINIMUM AT THAT LEVEL AS
WELL...WILL KEEP THINGS DRY TODAY. WILL SEE AN INCREASE IN HIGH
CLOUDS THIS AFTERNOON AS THEY SPILL IN ON THE NW FLOW ALOFT.

FOR HIGHS TODAY...USED A BLEND OF MIXING DOWN FROM 975-925 HPA
WITH NAM 2-METER TEMPERATURES AND A BLEND OF MAV/MET/ECS GUIDANCE.
EXPECT HIGHS TO BE AROUND 5-10 DEGREES BELOW NORMAL.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
TWO MAIN QUESTIONS WITH PRECIPITATION FOR TONIGHT/SATURDAY ARE HOW
FAST DOES THE PRECIPITATION START...AND WILL TEMPERATURES BE BELOW
FREEZING ACROSS MAINLY N INTERIOR ZONES FOR ANY FREEZING RAIN.

MODELS IN GOOD AGREEMENT THAT A SHORTWAVE OF S CENTRAL CANADA
THIS EVENING DIVES SE AND ABSORBS A SHORTWAVE JUST AHEAD OF IT
BY EARLY SATURDAY AFTERNOON OVER SE ONTARIO...DEVELOPING A CLOSED
850-500 HPA LOW THAT TRACKS TO AROUND/N OF LAKE ONTARIO BY 00Z
SUNDAY. MAIN QUESTION ABOUT ASSOCIATED SURFACE REFLECTION IS HOW
QUICKLY DOES THE SURFACE WARM/COASTAL FRONT LIFT TO THE N EARLY
SATURDAY MORNING. THE NAM HAS DONE VERY WELL WITH THIS TYPE OF SET
UP SO FAR THIS YEAR...AND HAVE LEANED TOWARDS IT AS A RESULT. THIS
SUGGESTS COASTAL FRONT DOES NOT LIFT FULLY THOUGH UNTIL SATURDAY
AFTERNOON IN ASSOCIATION WITH SECONDARY LOW DEVELOPMENT TO THE E
OF LONG ISLAND.

LOOKING AT ISENTROPIC SURFACES FOR NAM/GFS/ECMWF THEY ALL SUGGEST
LOW LEVELS DO NOT MOISTEN SUFFICIENTLY TO SUPPORT PRECIPITATION
UNTIL AROUND TO AFTER 6Z...WITH THE GFS THE FASTEST TO MOISTEN THE
285-290K SURFACES...THE NAM THE SLOWEST...AND THE ECMWF IN
BETWEEN. NOTING HOW DRY LOW LEVELS CURRENTLY ARE DO NOT WANT TO GO
AS FAST AS THE GFS AS TI OFTEN IS TOO FAST BRINGING IN
PRECIPITATION WITH VERY DRY LOW LEVELS. HOWEVER...WITH THIS BEING
A FORECAST OF WARM ADVECTION DRIVEN RAIN/FREEZING RAIN - THE NAM
IS OFTEN TOO SLOW IN STARTING RAIN/FREEZING RAIN IN WARM ADVECTION
CASES. SO USED ECMWF AS A COMPROMISE FOR TIMING ON SET OF
PRECIPITATION. 

AS IMPLIED ABOVE - LOW LEVEL THERMAL PROFILES PER BUFKIT SOUNDINGS
HAVE A SUFFICIENTLY DEEP ABOVE FREEZING LEVEL FROM AT LEAST 900-800
HPA...AND IN SOME CASES DOWN TO THE SURFACE AFTER EVAPORATIVE
COOLING IS TAKEN INTO ACCOUNT...THAT ONLY HAVE TWO CHOICE FOR
PRECIPITATION TYPE BASED ON SURFACE TEMPERATURE...RAIN OR FREEZING
RAIN. USED A BLEND OF ECS/MAV/MET GUIDANCE WITH NAM 2-METER
TEMPERATURES AND USED BLEND OF MAV/MET DEW POINTS TO ADJUST TO
WET BULB TEMPERATURE FROM 9Z-21Z SATURDAY. BASED ON THIS...BELIEVE
ITS LIKELY THAT THERE WILL BE A PERIOD OF FREEZING RAIN ACROSS W
PASSAIC COUNTY...MOST OF INTERIOR LOWER HUDSON VALLEY AND MOST OF
S CT. THE PRECIPITATION SHOULD CHANGE TO ALL RAIN IN THESE AREAS
BY 14Z SATURDAY.

HOWEVER GIVEN THE UNCERTAINTY IN PRECIPITATION START TIME...AND
HOW FAST LOW LEVEL COLD AIR SCOURS OUT GIVEN LIGHT SURFACE
WINDS...DO NOT HAVE THE REQUIRED 80 PERCENT CONFIDENCE TO ISSUE A
FREEZING RAIN ADVISORY AT THIS TIME. THIS DECISION WAS
COLLABORATED WITH SURROUNDING WFOS.

ELSEWHERE...INCLUDING ACROSS NYC/LI AND MOST OF NE NJ...EXPECT
PLAIN RAIN WITH THIS SYSTEM. REFER TO THE HYDROLOGY SECTION OF THE
AFD FOR FORECAST AMOUNTS AND POTENTIAL IMPACTS.

RAIN SHOULD BEGIN TO TAPER OFF FROM NW TO SE SATURDAY AFTERNOON.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
LOW PRESSURE CONTINUES TO LIFT TO THE NORTH AND EAST SATURDAY NIGHT. 
AS IT DOES...IT WILL DRAG A COLD FRONT ACROSS THE REGION AND THE 
PRECIPITATION WILL GRADUALLY TAPER OFF. TEMPERATURES SATURDAY NIGHT 
IN THE LOW 30S INLAND AND UPPER 30S ALONG THE COAST. LOWER 40S WILL 
BE POSSIBLE IN AND AROUND THE NYC METRO.  

HIGH PRESSURE STARTS TO BUILD INTO THE REGION ON SUNDAY...THEN SINKS 
SOUTH OF THE REGION DURING THE DAY MONDAY. EXPECT GENERALLY DRY 
CONDITIONS THROUGH THIS PERIOD. TEMPERATURES DURING THE DAY ON 
SUNDAY AND MONDAY WILL BE IN THE 40S WITH NIGHT TIME LOWS IN THE 20S 
AND LOWER 30S.

ANOTHER COLD FRONT MOVES ACROSS THE REGION MONDAY NIGHT AND 
TUESDAY...WHICH COULD RESULT IN SOME RAIN OR SNOW SHOWERS. TUESDAYS 
HIGHS WILL RANGE FROM THE LOWER TO UPPER 40S. HIGH PRESSURE BUILDS 
INTO THE REGION BEHIND THE COLD FRONT ON WEDNESDAY AND THURSDAY WITH 
COOLER TEMPERATURES. EXPECT DRY CONDITIONS WITH HIGHS IN THE UPPER 
30S AND LOWER TO MIDDLE 40S.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
HIGH PRESSURE WILL BUILD OVERHEAD THIS MORNING...THEN SLIDE TO THE
EAST THIS AFTERNOON. A FRONTAL SYSTEM WILL BEGIN TO APPROACH AFTER
MIDNIGHT FRI NIGHT. 

LIGHT N WINDS OVERNIGHT WILL VEER NE THIS MORNING...THEN BECOME
S-SE 5-10 KT THIS AFTERNOON AS THE HIGH PASSES TO THE EAST. 
VFR CONDITIONS EXPECTED FOR NEARLY THE ENTIRE TAF PD...BUT NYC METRO
COULD SEE RAIN WITH MVFR CONDITIONS ARRIVE AFTER 05Z SAT.

.OUTLOOK FOR 06Z SAT THROUGH TUE...
.LATE FRI NIGHT...IFR CONDITIONS EXPECTED...WITH FREEZING RAIN AT OR
VERY NEAR KSWF...AND RAIN ELSEWHERE.
.SAT-SAT NIGHT...IFR CONDITIONS IN RAIN...POSSIBLY IMPROVING TO MVFR
LATE AT NIGHT. 
.SUNDAY...CHANCE OF RAIN WITH MVFR CONDITIONS.
.SUNDAY NIGHT-MON...VFR.
.TUE...CHANCE OF RAIN OR SNOW SHOWERS WITH BRIEF MVFR CONDITIONS.

&&

.MARINE...
A RELAXED PRESSURE GRADIENT WILL KEEP WINDS 10 KT OR LESS ON ALL
WATERS WITH SUB-SCA SEAS AS WELL THROUGH TONIGHT. 

THE PRESSURE GRADIENT INCREASES ON SATURDAY...WITH 25 KT GUSTS
POSSIBLE ON THE COASTAL OCEAN WATERS...WITH SEAS POSSIBLY BUILDING
TO SCA LEVELS THERE AS WELL. SUB-SCA CONDITIONS ARE EXPECTED ON
THE NON-COASTAL OCEAN WATERS ON SATURDAY.

SCA SEAS ARE POSSIBLE ON THE COASTAL OCEAN WATERS SATURDAY
NIGHT...POSSIBLY LINGERING INTO SUNDAY...WITH SUB-SCA CONDITIONS
EXPECTED ON THE NON-COASTAL OCEAN WATERS.

SUB SMALL CRAFT CONDITIONS ARE FORECAST ON ALL WATERS SUNDAY NIGHT
AND MONDAY. SMALL CRAFT ADVISORY LEVEL SEAS MAY BUILD BACK IN MONDAY
NIGHT AND TUESDAY OVER THE COASTAL OCEAN WATERS.

&&

.HYDROLOGY...
DRY INTO AT LEAST THIS EVENING.

FROM AROUND 0.5-1 INCH OF PRECIPITATION IS EXPECTED FROM LATE
FRIDAY NIGHT INTO SATURDAY NIGHT...WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. THIS RAINFALL COMBINED WITH SNOW MELT OVER MAINLY
INTERIOR AREAS COULD RESULT IN MINOR TO MODERATE RISES IN AREA
RIVERS AND STREAMS. RIVER AND STREAMS ARE EXPECTED TO REMAIN
BELOW BANK FULL...BUT ICE WILL BEGIN TO BREAK UP AND MOVE
POSSIBLY CAUSING ICE JAMS AND LOCALIZED FLOODING.

AT THIS TIME WIDESPREAD FLOODING IS NOT ANTICIPATED...SO NO FLOOD
WATCHES HAVE BEEN ISSUED AT THIS TIME. 

ACROSS NYC/LONG ISLAND/URBAN PORTIONS OF NE NJ - THERE IS THE
POSSIBILITY OF MINOR FLOODING OF POOR DRAINAGE AREAS AS WELL FROM
THIS RAINFALL.

NO SIGNIFICANT PRECIPITATION IS EXPECTED FROM SUNDAY THROUGH THE
MIDDLE OF NEXT WEEK.

FOR DETAILS ON SPECIFIC AREA RIVERS AND LAKES...INCLUDING OBSERVED 
AND FORECAST RIVER STAGES AND LAKE ELEVATIONS...PLEASE VISIT THE 
ADVANCED HYDROLOGIC PREDICTION SERVICE /AHPS/ GRAPHS ON OUR WEBSITE.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
NY...NONE.
NJ...NONE.
MARINE...NONE.

&&

$$

SYNOPSIS...BC/MALOIT
NEAR TERM...MALOIT
SHORT TERM...MALOIT
LONG TERM...BC
AVIATION...GOODMAN
MARINE...BC/MALOIT
HYDROLOGY...BC/MALOIT





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