Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 312122 AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 422 PM EST SAT JAN 31 2015 .SYNOPSIS...
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HIGH PRESSURE BRIEFLY BUILDS IN TONIGHT...BEFORE A COLD FRONT APPROACHES AND CROSSES ON SUNDAY. LOW PRESSURE APPROACHES FROM THE OHIO VALLEY AND PASSES JUST SOUTH OF LONG ISLAND MONDAY. THE LOW TRACKS WELL TO THE EAST MONDAY NIGHT WITH HIGH PRESSURE BUILDING IN ITS PLACE. HIGH PRESSURE WILL LARGELY PREVAIL FOR THE REMAINDER OF THE WEEK WITH THE EXCEPTION OF A COLD FRONTAL PASSAGE LATE WEDNESDAY. A DEVELOPING LOW OVER THE GULF COAST STATES LATE IN THE WEEK LOOKS TO TAKE A TRACK WELL SOUTH AND EAST OF THE AREA.
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&& .NEAR TERM /THROUGH SUNDAY/...
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NEAR ZONAL FLOW TONIGHT WITH WEAK HIGH PRESSURE BUILDING IN FROM THE WEST THIS EVENING...AND THEN A POLAR FRONT APPROACHING FROM THE GREAT LAKES. WINDS AND GUSTS GRADUALLY SUBSIDE THROUGH MIDNIGHT...WITH INCREASING HIGH CLOUDS OVERNIGHT. TEMPS WILL NOT BE QUITE AS COLD WITH LOWS GENERALLY IN THE TEENS...EXCEPT 20S NYC/NJ METRO...WITH NEUTRAL TEMPS ADVECTION AND LIMITED OPPORTUNITY FOR RADIATIONAL COOLING. COULD SEE SOME SINGLE DIGITS IN PINE BARRENS AND INTERIOR TRI-STATE WITH DECOUPLING BEFORE CLOUDS MOVE IN. PHASING NORTHERN STREAM AND SW US SHORTWAVE ENERGY BEGINS TO DIG INTO THE CENTRAL US ON SUNDAY WITH GENERALLY WSW UPPER FLOW. A WEAKENING POLAR FRONT APPROACHES THE REGION ON SUNDAY...BUT OTHERWISE INCREASING AND LOWERING CLOUDS AHEAD OF NEXT APPROACHING STORM SYSTEM. A FEW SNOW FLAKES MAY BE OBSERVED OVER NJ VERY LATE IN THE DAY. TEMPS GENERALLY IN THE UPPER 20S TO LOWER 30S.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/...
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MAIN STORY WILL BE NEXT IN A SERIES OF WINTER STORMS AFFECTING THE REGION SUNDAY NIGHT INTO MONDAY. MODELS ARE IN GENERAL AGREEMENT WITH LOW PRESSURE TAKING SHAPE OVER THE CENTRAL PLAIN TONIGHT...TRACKING INTO THE OHIO VALLEY ON SUNDAY AND THEN JUST SOUTH OF THE REGION SUNDAY NIGHT. OVERALL TREND HAS BEEN SLIGHTLY FURTHER NORTH AND WETTER WITH THIS SYSTEM. BASED ON COUPLED JET STRUCTURE...TIGHT LOW /MID- LEVEL THERMAL STRUCTURE...AND GULF MOISTURE FEED OF 2-3 STD PWATS...CONFIDENCE IS HIGH IN AT LEAST A 3/4 TO 1 1/2 INCH QPF EVENT FOR THE ENTIRE AREA. THIS IS BOURNE OUT IN SREF/GEFS/CMCE 1 INCH/24 HR QPF PROBS. SIGNIFICANT UNCERTAINTY LIES IN P-TYPE...PARTICULARLY ALONG THE COAST...WITH A SPREAD OF ABOUT 50 MILES BETWEEN OPERATIONAL SOLUTIONS AND ENSEMBLE MEANS IN HOW CLOSE TO THE COAST THE LOW GETS AND THE POSITION OF THE TIGHT THERMAL GRADIENT ACROSS THE REGION. SBU ENSEMBLE SENSITIVITY SHOWING THIS N/S TRACK UNCERTAINTY IN THE 00Z GEFS/CMCE/ECMWF ENSEMBLES...WITH SENSITIVITY LYING IN DEGREE OF PHASING/INTERACTION BETWEEN NORTHERN STREAM SHORTWAVE ENERGY DROPPING DOWN THROUGH MONTANA AND THE CUTOFF UPPER LOW OVER THE SW US...AND RESULTANT STRENGTH OF TROUGH APPROACHING THE EAST COAST SUNDAY NIGHT/MONDAY AND UPSTREAM RIDGING. A STRONGER TROUGH...MEANING MORE UPSTREAM RIDGING...AND A FURTHER NORTH TRACK. THIS INTERACTION IS NOT COMPLETE FOR ANOTHER 24 HOURS...SO COULD TAKE UNTIL THEN FOR CONFIDENCE IN P-TYPE FORECAST INCREASES. WITH CONFLUENT FLOW ACROSS NORTHERN NEW ENGLAND/SE CANADA...ARCTIC HIGH SHOULD BE LOCKED INTO THAT AREA. PREFER TIGHTER THERMAL STRUCTURE ALOFT OF NAM/ECMWF/CAN VERSUS MORE DIFFUSE THERMAL STRUCTURE OF GFS IN THIS SITUATION...BUT QUESTION IS LOCATION OF THIS BAROCLINIC ZONE. MODEL SOLUTIONS POINTING TO DIFFERING DEGREES OF WARMING IN THE 800-950 LAYER MON MORNING INTO EARLY AFT...BUT TREND IS TOWARDS MORE WARMING. WITH THIS SAID...NORTHWEST TIER OF THE TRI-STATE LOOKS TO BE MAINLY SNOW. BIGGEST FORECAST CHALLENGE IS FOR COAST...ESPECIALLY NYC/NJ/LI...IN AMOUNT OF SLEET/FZRA/RA VERSUS SNOW. 12Z GFS/GEFS ARE FURTHER NORTH WITH LOW TRACK...JUST SOUTH OF LI MONDAY AFTERNOON...WHICH WOULD IMPLY MORE IN THE WAY OF WARMING ALOFT...AND MORE IN WAY MIXING WITH SLEET AND FREEZING RAIN AND EVEN RAIN FOR LI/NYC. 12Z GEM HAS TRENDED IN THAT DIRECTION AS WELL. 12Z NAM...WOULD POINT TO MAINLY SNOW FOR CT AND LOWER HUDSON VALLEY...WITH A MIX OF SIGNIFICANT SNOW/SLEET ACCUM FOR NYC/LI/METRO NJ. 00Z ECMWF...IS SIMILARLY COLDER AND A BIT FARTHER SOUTH AS WITH THE NAM. HAVE TAKEN A MIDDLE OF THE ROAD SOLUTION BASED ON THE UNCERTAINTY...WITH A SLIGHTLY WETTER AND WARMER FORECAST. EVEN WITH CONTINUED NORTHWARD TREND...HIGHEST CONFIDENCE IN SIGNIFICANT SNOW/SLEET/ICE ACROSS INTERIOR NE NJ...AND MOST OF THE LOWER HUDSON VALLEY AND CT. HAVE UPGRADED TO WARNING THERE FOR 5 TO 10 INCHES OF SNOW/SLEET AND UP TO 1/4 INCH OF ICE. INTERIOR PORTIONS OF LOWER HUDSON VALLEY AND SW CT...MORE IN THE 8 TO 14 INCH RANGE WITH LESS ICE/SLEET. EVEN FOR NYC/NJ METRO AND LI...COULD SEE A QUICK 3 TO 5 INCH SNOWFALL ON THE FRONT END WITH SOUTHERN STREAM MOISTURE AND STRONG LIFT LATE SUN NIGHT/EARLY MON MORNING BEFORE ANY MIXING. AFTER CHANGEOVER...A PROLONGED PERIOD OF FZRA/SLEET (1/4 INCH OF ICE) POSSIBLE FOR NORTHERN HALF OF LI/NYC AND NE NJ...WITH COLD AIR DRAINAGE DOWN THE RIVER VALLEYS. HAVE MAINTAINED A WATCH HERE WITH UNCERTAINTY IF WE CHANGEOVER TO MORE RAIN...PARTICULARLY FOR SOUTH COASTAL AREAS. THE ONE ASPECT TO KEEP IN MIND IS IF COASTAL AREAS DO GO OVER TO RAIN...THERE IS POTENTIAL FOR URBAN FLOODING ISSUES. SEE HYDROLOGY SECTION FOR MORE INFO. ANY RAIN/MIXED PRECIP SHOULD GRADUALLY CHANGE BACK TO SNOW FROM NW TO SE MONDAY AFTERNOON/EVE. EVEN SOME SIGNAL OF DEFORMATION BANDING ON THE BACKSIDE...WITH ACCUMULATING SNOW BACK DOWN TO THE COAST. WITH COLD AIR CRASHING BACK DOWN TO THE COAST...POTENTIAL FOR FLASH FREEZE CONDITIONS FOR MONDAY EVENING COMMUTE FOR CITY/COAST IN WAKE OF A WASHING RAIN. SO TO SAY THE LEAST...A COMPLICATED FORECAST FOR THE NYC/NJ METRO AND LONG ISLAND...WHICH COULD STILL SEE SIGNIFICANT IMPACTS EVEN IF IT IS NOT ALL FROZEN.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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A BROAD UPPER TROF WILL REMAIN IN PLACE THROUGH THE UPCOMING WEEK FROM THE CANADIAN PRAIRIE PROVINCES OF WESTERN CANADA SE INTO THE MID ATLANTIC REGION. THIS WILL KEEP A STEADY STREAM OF POLAR AIR MASSES MOVING ACROSS THE REGION WITH GENERALLY UNSEASONABLY COLD CONDITIONS. THIS SEASON HAS BEEN TYPIFIED BY THIS FLOW REGIME WITH NO BLOCK OVER GREENLAND. OCCASIONALLY...A STRONG SHORT WAVE BRIEFLY AMPLIFIES THE FLOW...BUT REMAINS PROGRESSIVE. THE ONLY CHANCE FOR PCPN LOOKS TO BE WITH A POLAR COLD FRONT WED INTO WED NIGHT...WHICH WILL BE IN THE FORM OF SCT SNOW SNOW SHOWERS. MODELS HAVE TRENDED WELL SOUTH AND EAST WITH A LATE WEEK COASTAL LOW MOVING OUT OF THE GULF COAST STATES. THUS...HAVE TRENDED DOWN TO THE POINT WHERE THERE IS NO MENTION OF PCPN LATE IN THE WEEK. INTERESTINGLY ENOUGH THOUGH...MODELS HAVE BEEN WAVERING BACK AND FORTH WITH THESE SYSTEMS...SO PERHAPS NOT COMPLETELY OUT OF THE WOODS. THE ONLY DAY OF THE WEEK THAT LOOKS TO BE NEAR NORMAL WITH RESPECT TO TEMPS IS WED AHEAD OF THE NEXT COLD FRONT.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/...
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**SEE OUTLOOK SECTION FOR HIGH IMPACT PERIOD OF SUN NIGHT-MONDAY** VFR CONDS THROUGH THE TAF PERIOD AS HIGH PRES BUILDS IN FROM THE WEST. WINDS AT OR FAVORING NORTH OF 310 MAG UNTIL AROUND 23Z...THEN FAVORING SOUTH OF 310 THEREAFTER. WINDS MOSTLY WEST TONIGHT. SUSTAINED WINDS AND GUSTS GRADUALLY DIMINISH INTO THIS EVENING. FREQUENT GUSTS END BY MIDNIGHT. VFR FOR MOST OF SUNDAY. A LIGHT SNOW SHOWER POSSIBLE TOWARDS DARK. .OUTLOOK FOR 18Z SUNDAY THROUGH WEDNESDAY... .SUNDAY PM...VFR. .SUNDAY NIGHT-MONDAY...HIGH IMPACT PERIOD. MVFR/IFR LIKELY. SNOW DEVELOPS SUN EVENING AND CONTINUES THROUGH AROUND DAYBREAK. MIXED SLEET AND FREEZING RAIN LIKELY MON MORNING AND EARLY AFTN FOR CITY TERMINALS AND KISP. MIXED PCPN CHANGES BACK TO SNOW LATE MON AFTN. MIXED PCPN COULD AFFECT ALL OTHER TERMINALS AS WELL. E-NE G 25-30KT MON AM BCMG N LATE. .MONDAY NIGHT...BECOMING VFR AS SNOW COMES TO AN END. N-NW G 30KT. .TUE...VFR. .WED...VFR LIKELY. CHC SW G 20KT. .THU...VFR NW G 20KT.
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&& .MARINE...
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NW GALES THIS AFTERNOON...WILL SUBSIDE TO SCA AND THEN BELOW THIS EVENING. THE COMBINATION OF ROUGH SEAS...STRONG WINDS...AND COLD WATER TEMPS WILL ALSO RESULT IN AT LEAST MODERATE FREEZING SPRAY FOR A FEW MORE HOURS...THEN IMPROVING CONDITIONS. 5 TO 9 FT SEAS WILL GRADUALLY SUBSIDE TO LESS THAN 5 FT DURING THE OVERNIGHT HOURS. TRANQUIL CONDS ON THE WATERS SUN AS HIGH PRES BUILDS OVERHEAD AND DEPARTS. CONDS RAMP UP TO SMALL CRAFT ADVISORY LEVELS LATE SUNDAY NIGHT INTO MONDAY MORNING AHEAD OF APPROACHING LOW PRESSURE. A FEW GALE GUSTS MAY BE POSSIBLE ON THE OCEAN. THERE IS THE POTENTIAL FOR A MARGINAL GALE EVENT MON NIGHT ON THE BACKSIDE OF DEEPENING LOW PRESSURE LIFTING UP INTO THE CANADIAN MARITIMES. WINDS AND SEAS ARE THEN FORECAST TO SUBSIDE BELOW SCA LEVELS ON TUE WITH HIGH PRESSURE BUILDING ACROSS THE WATERS. MARGINAL SCA CONDITIONS ARE POSSIBLE ON THE OCEAN WATERS WED IN A PRE-FRONTAL SW FLOW...AND THEN IN THE NW POST-FRONTAL FLOW ON THU.
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&& .HYDROLOGY...
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GENERALLY 1 TO 1 1/2 INCHES OF LIQUID FORECAST WITH THE SYSTEM SUNDAY NIGHT THROUGH MONDAY. MOST OF THIS WILL BE SNOW AND SLEET ACROSS NE NJ...LOWER HUDSON VALLEY AND CT. ACROSS LI/NYC THERE IS A POTENTIAL FOR A PERIOD OF HEAVY RAIN...WITH SOME MODELS SIGNALING UP TO 2 INCHES OF QPF. ALTHOUGH THIS POTENTIAL IS LOW...IF MODEL TRENDS CONTINUE NORTH...THIS POTENTIAL WOULD INCREASE...RESULTING IN URBAN FLOODING ISSUES. NO SIGNIFICANT WIDESPREAD PCPN IS FORECAST FOR THE REMAINDER OF THE PERIOD.
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&& .TIDES/COASTAL FLOODING...
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THERE IS A LOW PROBABILITY OF MINOR COASTAL FLOODING THRESHOLDS BEING REACHED WITH THE MONDAY MORNING HIGH TIDE CYCLE ALONG THE WESTERN SOUTH SHORE BAYS AND WESTERN PORTIONS OF LI SOUND.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON FOR CTZ011-012. WINTER STORM WARNING FROM 7 PM SUNDAY TO 6 PM EST MONDAY FOR CTZ005>010. NY...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON FOR NYZ071>075-078>081-176>179. WINTER STORM WARNING FROM 7 PM SUNDAY TO 6 PM EST MONDAY FOR NYZ067>070. NJ...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON FOR NJZ004-006-104>108. WINTER STORM WARNING FROM 7 PM SUNDAY TO 6 PM EST MONDAY FOR NJZ002-103. MARINE...FREEZING SPRAY ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ330- 335-338-340-345-350-353-355. GALE WARNING UNTIL 6 PM EST THIS EVENING FOR ANZ330-335-338- 340-345-350-353-355.
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&& $$ SYNOPSIS...NV/DW NEAR TERM...NV SHORT TERM...NV LONG TERM...DW AVIATION...JC MARINE...NV/DW HYDROLOGY...NV/DW TIDES/COASTAL FLOODING...NV

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