Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 272050 AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 350 PM EST SAT DEC 27 2014 .SYNOPSIS...
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HIGH PRESSURE WILL SLIDE OFF THE MID ATLANTIC COAST THROUGH TONIGHT AS A COLD FRONT APPROACHES FROM THE WEST. THE FRONT WILL MOVE ACROSS ON SUNDAY...AND THEN STALL OFF THE SOUTHERN MID ATLANTIC. A WAVE OF LOW PRESSURE RIDING ALONG THIS FRONT MAY AFFECT THE REGION LATE MONDAY NIGHT THROUGH TUESDAY EVENING. OTHERWISE...HIGH PRESSURE WILL DOMINATE THROUGH FRIDAY...WITH ANOTHER FRONTAL SYSTEM APPROACHING FOR THE START OF NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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EXPECT INCREASING CLOUDS TONIGHT AHEAD OF THE APPROACHING COLD FRONT...AND LIKELY POP WELL NORTH/WEST OF NYC...AND AT LEAST CHANCE OF SHOWERS LATE TONIGHT EXCEPT LONG ISLAND. LOWS TONIGHT SHOULD RANGE FROM THE MID 40S IN MIDTOWN NYC...TO THE MID/UPPER 30S ACROSS ERN LONG ISLAND AND WELL INLAND.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... COLD FRONT SHOULD BE ACCOMPANIED/FOLLOWED BY SOME LIGHT RAIN AS IT MOVES THROUGH IN THE DAYTIME SUNDAY. SHOT OF POSITIVE THETA-E ADVECTION AHEAD OF THE LAGGING H8 COLD FRONT...AND LIFT VIA PASSING MID LEVEL SHORTWAVES AND UPPER DIVERGENCE WITH AN ANTICYCLONIC JET STREAK TO THE NORTH SHOULD RESULT IN A PD OF RAIN FOR MOST PLACES...ESPECIALLY NYC METRO AND LONG ISLAND SUNDAY AFTERNOON AS THESE INGREDIENTS COME TOGETHER. GFS/NAM MOS BLEND ACCEPTED FOR HIGHS...GENERALLY WITHIN A COUPLE DEG EITHER SIDE OF 50. ANY LINGERING LIGHT RAIN MAINLY FOR NYC METRO AND LONG ISLAND EARLY SUNDAY EVENING SHOULD END BY LATE EVENING AS THE H8 COLD FRONT PASSES TO THE SE...BUT SKIES MAY NOT CLEAR VERY MUCH...EVEN NORTH/WEST AS ANOTHER MID LEVEL SHORTWAVE AND THE RIGHT REAR QUADRANT OF THE UPPER JET SWING ACROSS. CAA ON NW-N FLOW ESPECIALLY LATE AT NIGHT SHOULD LOWER TEMPS TO THE 30S...POSSIBLY JUST BELOW FREEZING IN THE INTERIOR VALLEYS. && .LONG TERM /TUESDAY THROUGH SATURDAY/...
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A RETURN TO NEARLY ZONAL FLOW EARLY THROUGH MIDWEEK. PERIODIC SHORTWAVES MOVE ACROSS WITHIN THE QUASI ZONAL FLOW TO GIVE REINFORCEMENT OF COLDER AIR. RELATIVELY STRONGEST ONE WITH SUPPORT OF UPPER LEVEL JET STREAKS INCREASING IS ON TUESDAY. CUTOFF LOW IN THE SOUTHWEST U.S. MOVES EAST SLOWLY MIDWEEK INTO LATE WEEK. THIS PUSHES HEIGHTS UP TO THE EAST OF IT. THIS GIVES MORE OF A RIDGING PATTERN FRIDAY INTO NEXT WEEKEND. BELIEVE THE ECMWF MORE THAN THE GFS WITH THE PROGRESSION OF THE UPPER LEVEL LOW...TAKING A MUCH SLOWER TRACK FOR THIS. FOR MONDAY AT THE SURFACE...A VERY LARGE MAGNITUDE...1050MB AT LEAST...HIGH PRESSURE AREA BUILDS INTO THE NORTHWEST U.S. THIS WILL BE A SOURCE FOR MUCH COLDER AIR. THE HIGH GRADUALLY MOVES SOUTHEAST INTO THE SOUTH CENTRAL U.S. THROUGH MIDWEEK WITH THE LOCAL AREA AIR MASS BECOMING COLDER. WILL HAVE TO MONITOR POTENTIAL FOR SURFACE LOW DEVELOPMENT ALONG A FRONT WELL SOUTH OF THE REGION FOR LATE MONDAY NIGHT THROUGH TUESDAY EVENING. ONLY SREF AND NAM ARE PORTRAYING THIS WETTER SOLUTION FOR THIS TIME FRAME WHILE GFS...PARALLEL GFS...ECMWF...AND CMC ARE DRY AND HAVE ANY PRECIP WELL SOUTH OF THE REGION...GENERALLY SOUTH OF 40 DEGREES NORTH LATITUDE. HOWEVER...WITH A GENERAL CONSENSUS OF THERE BEING A SHORTWAVE AND JET STREAK ENHANCEMENT...EVEN WITH MODELS THAT HAVE DRY QPF FIELDS...WILL KEEP A SLIGHT CHANCE OF PRECIP IN THE FORECAST. WITH THE DRY AND COLD AIR ADVECTION...THE PRECIP TYPE WILL BE MAINLY SNOW DUE TO WET BULB EFFECT WITH PRECIP AMOUNTS BETWEEN NAM AND SREF...SHOWING GENERALLY AROUND THREE TENTHS OF AN INCH OR LESS...OR UP TO 3 INCHES OF SNOW EQUIVALENTLY ACCOUNTING FOR SNOW TO LIQUID RATIO. THIS IS FOR LATE MONDAY NIGHT THROUGH TUESDAY EVENING. AGAIN THOUGH OTHER MODELS ARE COMPLETELY DRY AND THEREFORE THESE PROBABILITIES REMAIN VERY LOW. THE COLD AIR MASS SETTLING IN DOES NOT LAST THAT LONG. MONDAY HAS TEMPERATURES NEAR TO SLIGHTLY ABOVE NORMAL. TUESDAY THROUGH THURSDAY IS WHEN THE BULK OF THE COLD AIR MASS IS IN PLACE WITH HIGHS HOVERING NEAR TO SLIGHTLY ABOVE FREEZING ON AVERAGE. NEAR NORMAL TEMPERATURES RETURN BY LATE WEEK. OUTSIDE OF THE LATE MONDAY NIGHT THROUGH TUESDAY EVENING TIME FRAME...WEATHER IS MAINLY DRY THROUGH FRIDAY. ANOTHER FRONTAL SYSTEM APPROACHES LATE IN THE WEEK WITH NEXT CHANCE FOR PRECIP. MUCH UNCERTAINTY THOUGH SINCE THIS IS DAY 8 OF THE FORECAST. THEREFORE...THESE POPS ARE NO HIGHER THAN 30 PERCENT WITH MODEL RUN FLUCTUATIONS BEING MORE LIKELY AT THIS VERY LATE FORECAST TIME FRAME WITH TIMING AND PLACEMENT DIFFERENCES.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/...
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VFR CONDITIONS THROUGH TONIGHT AS HIGH PRESSURE MOVES OFF THE MID ATLANTIC COAST. LIGHT S/SW WINDS UNDER 10 KT CONTINUE INTO TONIGHT. WINDS VEER TO THE W/SW SUNDAY MORNING. SCT-BKN HIGH CLOUDS THIS EVENING...LOWERING OVERNIGHT AS A COLD FRONT APPROACHES FROM THE WEST. MVFR CIGS IN -SHRA LIKELY TOWARDS DAYBREAK SUNDAY AT KSWF. LOW PROBABILITY OF MVFR CIGS OVER CITY TERMINALS AS -SHRA MOVE EAST SUNDAY MORNING. .OUTLOOK FOR 18Z SUN THROUGH THU... .SUNDAY AFTERNOON...MVFR POSSIBLE IN -SHRA. .SUNDAY NIGHT...VFR .MON-THU...VFR.
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&& .MARINE...
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&& .HYDROLOGY...
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QPF WITH THE FRONTAL PASSAGE ON SUNDAY SHOULD RANGE FROM 1-2 TENTHS OF AN INCH. NO SIGNIFICANT PRECIPITATION OF 1/2 INCH OR MORE EXPECTED.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. NJ...NONE. MARINE...SMALL CRAFT ADVISORY FROM 4 AM TO 10 AM EST SUNDAY FOR ANZ350. && $$ SYNOPSIS...GOODMAN NEAR TERM...GOODMAN SHORT TERM...GOODMAN LONG TERM...JM AVIATION...DS MARINE...GOODMAN/JM HYDROLOGY...GOODMAN/JM

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