Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 290812 AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 412 AM EDT WED OCT 29 2014 .SYNOPSIS...
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A COLD FRONT CONTINUES TO APPROACH TODAY...EVENTUALLY MOVING THROUGH THE WHOLE REGION THIS EVENING. HIGH PRESSURE THEN BUILDS INTO THE REGION THURSDAY. WEAK HIGH PRESSURE BUILDS OVER THE AREA THURSDAY NIGHT. A FRONTAL SYSTEM CROSSES THE AREA FRIDAY...THEN MERGES WITH AN EXISTING STATIONARY FRONT OFFSHORE...TO PRODUCE AN AREA OF LOW PRESSURE OFF THE MID ATLANTIC COAST BY SATURDAY MORNING. THIS LOW THEN TRACKS NORTHEAST TO THE GULF OF MAINE BY SUNDAY MORNING. CANADIAN HIGH PRESSURE THEN BUILDS IN TO THE WEST INTO MONDAY...THEN TO THE SOUTH INTO TUESDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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AN UPPER LEVEL LOW DEEPENS AS IT BECOMES MORE OF AN OPEN WAVE TRAVELING THROUGH QUEBEC. AT THE SURFACE...A COLD FRONT APPROACHES THE REGION...WITH A PRE FRONTAL TROUGH MOVING ACROSS THIS AFTERNOON WITH THE COLD FRONT MOVING THROUGH IN THE EVENING. THE PARENT LOW ATTACHED TO THE FRONT SLOWLY DEEPENS THROUGH THE DAY WHILE MOVING IN MORE OF A NORTHWARD DIRECTION. INITIALLY THIS MORNING...MOIST LOW LEVELS AND PATCHY FOG WILL DISSIPATE WITH DIURNAL WARMING...AND WITH A SOUTHWEST FLOW INCREASING TODAY...A VERY MILD DAY IS ANTICIPATED. A BLEND OF MOS GUIDANCE OF ECS...MAV...AND GMOS WAS USED WITH GREATER WEIGHT OF THE WARMER ECS. WITH THE SOUTHWEST AND THEN WEST FLOW BY THIS AFTERNOON AFTER THE PRE FRONTAL TROUGH MOVES ACROSS...LESS MARINE INFLUENCE WILL ALLOW FOR A WARMER DAY. IN ADDITION...MODELS HAVE DELAYED THE ONSET OF SHOWERS AND KEEP INDICATING SHOWERS BREAKING UP WITH EASTWARD MOVEMENT...LENDING TO A DRIER FORECAST OVERALL. HENCE...JUST HAVE ISOLATED TO SCATTERED COVERAGE...LATER WITH GREATER EASTWARD DISTANCE.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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THE UPPER LEVEL TROUGH SLOWLY DEEPENS AND BECOMES LESS AMPLIFIED AS THE PARENT LOW NEARLY MAINTAINS THE SAME STRENGTH. SHOWERS WILL HAVE GREATEST PROBABILITY EARLY THIS EVENING FOR MUCH OF THE REGION NEAR AND RIGHT BEHIND THE ASSOCIATED COLD FRONT. THE SHOWERS EVENTUALLY DECREASE FROM NORTHWEST TO SOUTHEAST AS THE COLD FRONT PUSHES SOUTHEAST OF LONG ISLAND BY LATE THIS EVENING. THE NORTHWEST FLOW DOES NOT INITIATE UNTIL LATE TONIGHT...HELPING USHER IN COLDER AIR. USED MAV GUIDANCE FOR LOWS AS THEY HAVE BEEN RELATIVELY CLOSER TO PREVIOUS OBSERVED MIN TEMPS. FOR THURSDAY...HIGH PRESSURE BUILDS IN FROM THE WEST WITH SOME SLIGHT RIDGING ALOFT. NORTHWEST FLOW PREVAILS THROUGH THE DAY...MAKING FOR DOWNSLOPE FLOW. THEREFORE...EXPECTING COASTAL LOCATIONS TO BE WARMER THAN INTERIOR LOCATIONS. A COMBINATION OF MAV AND ECS GUIDANCE WAS USED FOR HIGH TEMPS.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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A WEAK SHORTWAVE RIDGE CROSSES THE AREA THURSDAY NIGHT...WITH ASSOCIATED SUBSIDENCE KEEPING THINGS DRY. A WEAK 700-500 HPA SHORTWAVE APPROACHES FAR SE ZONES FRIDAY...WARRANTING SLIGHT CHANCE POPS THERE BY AFTERNOON. NOTE THIS IS CONSISTENT WITH ECMWF/NAM/GFS/SREF/CMC ALL SHOWING LIGHT QPF DEVELOPING NEAR/OVER THE TWIN FORKS OF LONG ISLAND FRIDAY AFTERNOON. MODELS IN FAIRLY GOOD AGREEMENT THAT A DEVELOPING 850-500 HPA CLOSED LOW DIVES SE FROM THE UPPER OHIO RIVER VALLEY FRIDAY NIGHT...WITH ASSOCIATED SURFACE SYSTEM PASSING TO THE SE OF THE AREA. APPEARS WILL SEE SUFFICIENT WEAK DYNAMICAL FORCING TO PRODUCE ISOLD-SCT -SHRA OVER THE AREA AS A RESULT. THIS CLOSED LOW BECOMES A CUTOFF LOW OFF THE MID ATLANTIC COAST SATURDAY...THAT TRACKS TO THE SOUTHEAST OF THE 40N/70W BENCHMARK SATURDAY NIGHT. NOTE THE GFS FOR NOW APPEARS TO BE AN OUTLIER IN HOW FAR E IT KEEPS ITS PRECIPITATION SHIELD...SO LEANED TOWARDS A NON-GFS SOLUTION FOR POPS WITH THIS SYSTEM. BASED ON THIS HAVE LIKELY POPS OVER ROUGHLY THE SE 1/2 OF THE CWA AND HAVE CHANCE POPS ELSEWHERE. THERE IS SOME INDICATIONS THAT NW PORTIONS OF THE CWA COULD ULTIMATELY END UP DRY FROM THIS SYSTEM - HOWEVER DO NOT HAVE CONFIDENCE TO GO BELOW CHANCE POPS AT THIS TIME. APPEARS SOLUTION FOR THIS SYSTEM IS CONVERGING TO ONE WHERE FOR THE MOST PART THE COLD AIR DOES NOT ARRIVE IN ENOUGH TIME TO PRODUCE ANY WIDESPREAD SNOW OVER THE AREA...HOWEVER DO HAVE THE POTENTIAL FOR A RAIN/SNOW MIX SATURDAY NIGHT FOR AREAS N OF LONG ISLAND SOUND...AND POSSIBLY OVER WESTERN PORTIONS OF THE LOWER HUDSON VALLEY AND WESTERN NE NJ...IF THE COLD AIR MOVES IN FAST ENOUGH BEFORE THE PRECIPITATION COMES TO AN END THERE. FOR NOW...CANNOT RULE OUT THE POSSIBILITY THAT...IN PARTICULAR HIGHER ELEVATIONS - SAY THOSE ABOVE 1000-1500 FT - COULD HAVE A PERIOD OF ALL SNOW SATURDAY NIGHT DEPENDING ON THE EXACT INTENSITY OF THE PRECIPITATION. AS IS USUAL IN THESE RAIN/SNOW CASES...THE HEAVIER THE RATE OF PRECIPITATION FALL THE GREATER THE LIKELIHOOD FOR ALL SNOW...AND THE LIGHTER THE RATE OF PRECIPITATION THE GREATER THE LIKELIHOOD FOR ALL RAIN. ACROSS NYC/LONG ISLAND AND EASTERN PORTIONS OF NE NJ IT APPEARS THAT THERMAL PROFILES SUPPORT MAINLY IF NOT ALL RAIN...SO HAVE FORECASTED ACCORDINGLY. ON THE WHOLE CURRENT INDICATIONS SUPPORT THE IDEA OF MOST AREAS THAT DO SEE ANY SNOWFALL RECEIVING LITTLE TO NO ACCUMULATION...WITH THE BEST CHANCE FOR ANY LIGHT ACCUMULATION - AND THEN MAINLY ON GRASSY SURFACES IF AT ALL - BEING AT ELEVATIONS MAINLY ABOVE 1000-1500 FT. GUSTY NE WINDS ARE POSSIBLE ACROSS MAINLY E ZONES SATURDAY NIGHT...WITH GUSTS UP TO 30 TO MAYBE 40 MPH POSSIBLE....WITH GUSTS OF 20 TO MAYBE 30 MPH POSSIBLE OVER W ZONES. THE STORM EXITS FAIRLY QUICKLY TO THE NE SUNDAY...FOR NOW HAVE SLIGHT CHANCE POPS FOR -SHRA/-SHSN OVER FAR EASTERN ZONES SUNDAY MORNING...BUT WOULD NOT BE SURPRISED IF SUNDAY ENDED UP BEING DRY THROUGHOUT. SUNDAY WILL BE QUITE GUSTY WITH NW WINDS GUSTING UP TO 30-40 MPH QUITE POSSIBLE. DEEP LAYERED RIDGING BUILDS IN FROM THE WEST SUNDAY NIGHT/MONDAY...THEN OVER THE AREA MONDAY NIGHT...THEN EXISTS TO THE EAST ON TUESDAY. SO HAVE GONE WITH A DRY FORECAST IN THIS TIME FRAME FOR NOW. DEPENDING ON EXACTLY HOW FAST THE RIDGE EXITS TO THE EAST...COULD END UP NEEDING POPS BY LATE TUESDAY AHEAD OF A NORTHERN STREAM SHORTWAVE...BUT CONFIDENCE IN THIS IS TOO LOW AT THIS TIME TO WARRANT MAKING THAT CHANGE NOW. FOR TEMPERATURES IN THE LONG RANGE: FOR LOWS THURSDAY NIGHT - NOTING SOME POTENTIAL FOR RADIATIONAL COOLING - USED THE MINIMUM OF MAV/MET GUIDANCE AND NAM W-METER TEMPERATURES...EXCEPT OVER THE NYC METRO WHERE A BLEND OF THE THREE WAS USED. EXPECT VALUES TO BE A FEW DEGREES BELOW NORMAL. ON FRIDAY A BLEND OF MAV AND MET GUIDANCE WITH NAM 2-METER TEMPERATURES AND MIXING DOWN FROM 900 HPA PER BUFKIT SOUNDINGS WAS USED FOR HIGHS. READINGS SHOULD BE A FEW DEGREES BELOW NORMAL. FOR LOWS FRIDAY NIGHT A BLEND OF MEX/MEN/EKD/ECE/ECM/WPC GUIDANCE WITH NAM 2-METER TEMPERATURES WAS USED...WITH VALUES FORECAST TO BE AROUND NORMAL IN THE IMMEDIATE NYC METRO...AND SLIGHTLY ABOVE NORMAL ELSEWHERE. FROM SATURDAY-TUESDAY A BLEND OF MEX/MEN/EKD/ECE/ECM/WPC GUIDANCE WAS USED...WITH ECMWF 2-METER TEMPERATURES BLENDED IN SATURDAY AND SATURDAY NIGHT TO BETTER REFLECT IMPACT OF PRECIPITATION. HIGHS WILL RUN AROUND 10 DEGREES BELOW NORMAL SATURDAY AND SUNDAY...AND LOWS SATURDAY NIGHT AND SUNDAY NIGHT AROUND 5 DEGREES BELOW NORMAL. HIGHS MONDAY WILL RUN WELL BELOW NORMAL...LOWS MONDAY NIGHT SLIGHTLY BELOW NORMAL...AND HIGHS ON TUESDAY NEAR NORMAL.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... A COLD FRONT WILL SLOWLY PASS THRU THE REGION TODAY. A FEW SHRA OR SPRINKLES INVOF THE FRONT TODAY. ALTHOUGH A BRIEF MVFR SHRA IS POSSIBLE...IT WILL BE MAINLY VFR THRU THE TAF PERIOD. SWLY WINDS VEER TO THE W WITH THE FRONT. A SECOND FEATURE BRINGS WINDS TO THE NW TNGT AFT 2Z. OCNL GUSTS POSSIBLE AFT 12Z...THEN BECOME MORE FREQUENT IN THE AFTN AND ARE INCLUDED IN THE TAFS AS A RESULT. WINDS AT 2K FT AROUND 35-40KT TIL 10-12Z. .OUTLOOK FOR 06Z THURSDAY THROUGH SUNDAY... .WED NIGHT-FRI...VFR. .FRI NIGHT-SAT...MVFR OR LOWER CONDS LIKELY...MAINLY VIA RAIN SHOWERS BUT RAIN/SNOW SHOWERS AT KSWF DURING THE LATE NIGHT AND MORNING. NE-N WINDS G20-25KT. .SAT NIGHT...MVFR OR LOWER CONDS LIKELY WITH CHANCE OF RAIN AND SNOW. N WINDS G25-30KT. .SUNDAY...BECOMING VFR WITH PRECIPITATION ENDING. NW WINDS G25-30KT. && .MARINE...
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SEAS HAVE BEEN RIGHT NEAR THE THRESHOLD OF SCA OF 5 FT MUCH OF THE NIGHT. EXPECTING THIS TO CONTINUE WITH INCREASED SOUTHWESTERLY FETCH THROUGH THIS MORNING AND THEN THIS AFTERNOON WILL HAVE SOUTH TO SOUTHEAST SWELL KEEPING SEAS RELATIVELY HIGHER. WIND GUSTS TO 25 KT MAY BE MORE LIMITED BUT CANNOT RULE OUT SOME GUSTS TO THAT MAGNITUDE...PARTICULARLY LATE THIS MORNING THROUGH THE AFTERNOON WHEN THE PRESSURE GRADIENT INCREASES. BY TONIGHT...SCA CONDITIONS WILL LIKELY JUST BE CONFINED TO THE OCEAN ZONE OF MORICHES INLET TO MONTAUK INLET OUT 20 NM AND THEN BY AFTER MIDNIGHT...SUB SCA CONDITIONS WILL BE IN PLACE AS HIGH PRESSURE TAKES OVER. THESE SUB SCA CONDITIONS WILL CONTINUE THROUGH THURSDAY. A RELATIVELY RELAXED PRESSURE GRADIENT OVER THE WATERS WILL PRODUCE WINDS OF 10KT OR LESS OVER THE WATERS AROUND LONG ISLAND FROM THURSDAY NIGHT INTO FRIDAY EVENING. WINDS INCREASE TO 10-20KT AFTER MIDNIGHT FRIDAY NIGHT...WITH A CHANCE OF SMALL CRAFT GUSTS...MAINLY OVER THE COASTAL OCEAN WATERS. WINDS CONTINUE TO INCREASE INTO THE WEEKEND DUE TO THE PASSING OF A STRENGTHENING COASTAL LOW TO THE SE. THERE IS THE POTENTIAL FOR GUSTS TO GALE FORCE ON ALL WATERS FROM SATURDAY AFTERNOON INTO SUNDAY. THIS THREAT WILL BE HIGHLIGHTED IN THE HWO.
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&& .HYDROLOGY...
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AROUND A TENTH OF AN INCH OR LESS OF RAINFALL IS EXPECTED WITH THE SHOWERS THROUGH THIS EVENING. THERE IS THE POTENTIAL FOR UP TO A HALF AN INCH OR SO OF QPF TO FALL FROM FRIDAY NIGHT THROUGH SATURDAY NIGHT. NO SIGNIFICANT HYDROLOGIC IMPACT IS ANTICIPATED AT THIS TIME.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. NY...NONE. NJ...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ353- 355. SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ350.
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&& $$ SYNOPSIS...MALOIT/JM NEAR TERM...JM SHORT TERM...JM LONG TERM...MALOIT AVIATION...JMC MARINE...MALOIT/JM HYDROLOGY...MALOIT/JM

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