Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 262011 AFDOKX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 411 PM EDT SUN APR 26 2015 .SYNOPSIS...
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LOW PRESSURE OVER THE CANADIAN MARITIMES AND ANOTHER LOW MOVING OFF THE MID ATLANTIC COAST TODAY WILL CONSOLIDATE INTO A BROAD AREA OF LOW PRESSURE OVER THE WESTERN ATLANTIC MONDAY INTO TUESDAY. THIS SYSTEM WILL MEANDER SOUTH OF NOVA SCOTIA ON TUESDAY THEN DEPART TO THE EAST AS HIGH PRESSURE BUILDS IN FROM THE WEST. MEANWHILE...LOW PRESSURE OVER THE GULF COAST STATES WILL TRACK TO THE MID ATLANTIC COAST BY THURSDAY AND CONTINUE NORTHEAST INTO THE ATLANTIC THROUGH THE END OF THE WEEK. A FEW UPPER LEVEL DISTURBANCES MAY IMPACT THE AREA NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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GOING INTO TONIGHT...THERE COULD BE AN ISOLATED SHOWER IN RESPONSE TO POSITIVE VORTICITY ADVECTION ASSOCIATED WITH THE MID LEVEL TROUGH AXIS MOVING ACROSS. THE MAIN UPPER LEVEL JET STREAM STAYS SOUTH OF THE REGION. AT THE SURFACE...A TROUGH AXIS WILL BE MOVING ACROSS THIS EVENING...WITH WINDS BECOMING MORE NW BEHIND IT. THE CHANCES WILL BE VERY LOW FOR THIS SHOWER ACTIVITY DUE TO THE DRY AIR NEAR THE SURFACE. TEMP AND DEWPOINT SPREADS WILL BE AROUND 20 DEGREES GOING INTO THE EARLY EVENING SO THE SHOWERS MAY JUST DISSIPATE UPON TRACKING FARTHER SOUTHWARD. OTHERWISE...MAINLY A DRY FORECAST WITH DECREASING CLOUDS LATE BEHIND THE TROUGH AXIS. WINDS DO NOT BECOME ALL THAT LIGHT AS A PRESSURE GRADIENT REMAINS BETWEEN THE WEAKENING LOW ACROSS THE CANADIAN MARITIMES AND HIGH PRESSURE MOVING INTO THE NORTHWEST PART OF THE GREAT LAKES. THIS WILL MITIGATE RADIATIONAL COOLING IN ADDITION TO THE CLOUDS. LOWS WERE A BLEND OF MAV/MET/GMOS YIELDING A RANGE FROM THE MID 30S TO MID 40S.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
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FOR MONDAY AND MONDAY NIGHT...THE MID LEVELS STILL CONVEY PERIODIC SHORTWAVES AS DIAGNOSED BY POSITIVE VORTICITY ADVECTION WHICH ROTATE AROUND AN UPPER LEVEL LOW. THE UPPER LEVEL LOW PUSHES SOUTH OF NOVA SCOTIA THROUGH THE PERIOD. THE MAIN UPPER LEVEL JET STREAM CONTINUES TO STAY SOUTH OF THE REGION. AT THE SURFACE...A TROUGH APPROACHES MONDAY AND MOVES ACROSS MONDAY NIGHT. A FEW LOWS OFFSHORE...ONE OF WHICH IS ASSOCIATED WITH THE TROUGH WILL MERGE...WITH THE MODELS SHOWING A STRONGER DEEPER LOW WELL OFFSHORE BY EARLY TUESDAY. IN TERMS OF WEATHER...SCATTERED SHOWERS WILL BE IN STORE DURING THE DAY AND EVENING HOURS...SLOWLY DECREASING MONDAY NIGHT FROM WEST TO EAST. THE SHOWERS WILL BE PERIODIC AND BY THE OUTPUT OF MESOSCALE MODEL REFLECTIVITY FIELDS...COVERAGE AT TIMES COULD BE MORE SPARSE. THEREFORE...DID NOT LOWER TEMPERATURES TOO MUCH AND KEPT USING A BLEND OF GMOS/MET/MAV GUIDANCE. MAX TEMPERATURES MONDAY ARE FORECAST TO RANGE MAINLY IN THE LOWER 60S. ALSO...MODELS SHOW SOME WEAK INSTABILITY MONDAY AFTERNOON INTO EARLY EVENING...SO THERE COULD BE A THUNDERSTORM. FOR THE FORECAST...KEPT THE THUNDERSTORMS TO SLIGHT CHANCE POPS. THERE WILL BE A PERSISTENT SOUTHEAST TO NORTHWEST PRESSURE GRADIENT REMAINING...AS WINDS WILL STAY UP AND INCREASE IN THE 950-800MB LAYER MONDAY NIGHT. THE COMBINATION OF THIS AND ABUNDANT CLOUDS WILL KEEP LOW FORECAST ON THE WARMER SIDE MONDAY NIGHT...IN THE LOWER 40S.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
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A BLOCKY UPPER LEVEL PATTERN WILL PERSIST INTO THE SECOND HALF OF THE WEEK WITH THE FLOW FLATTENING ACROSS THE WESTERN AND CENTRAL US BY NEXT WEEKEND. THE LARGE PERSISTENT CUTOFF LOW PRESSURE SYSTEM OVER THE NORTHEAST AND SOUTHERN CANADIAN MARITIMES WILL REMAIN S OF NOVA SCOTIA ON TUE AS SPOKES OF VORTICITY MOVE AROUND IT. THERE IS UNCERTAINTY IN THE TIMING OF THESE SHORTWAVES TRACKING WITHIN THE CYCLONIC FLOW...AND HAVE KEPT SCHC POPS OVER EXTREME EASTERN LONG ISLAND AND SE CT EARLY TUE MORNING AS MOST OF THE MODEL GUIDANCE INDICATES THAT THE VORT MAX MOVES THROUGH LATE MON NIGHT/TUE MORNING. THE GFS BRINGS IT THROUGH DURING THE AFTN...BUT IT IS ALONE IN THIS SOLN. THE CUTOFF FINALLY MOVES FAR ENOUGH AWAY ON WED TO PRECLUDE ANY ADDITIONAL PCPN CHANCES AS UPPER LEVEL RIDGING BUILDS IN. DRY CONDS AND PARTLY CLOUDY SKIES ARE EXPECTED. THERE IS BETTER AGREEMENT WITH THE UPPER LEVEL PATTERN WED INTO THU AS A NRN STREAM SHORTWAVE MERGES WITH A SRN STREAM CUTOFF LOW PRES SYSTEM. HOWEVER...THE GFS REMAINS FASTER MOVING THE UPPER RIDGE AXIS E OF THE AREA...DESPITE THE BLOCKING FROM THE AFOREMENTIONED DEPARTING CUTOFF LOW. THINK THIS IS TOO QUICK AND LIKE THE EC`S SOLN BETTER WHICH HAS ALSO HAD MORE RUN TO RUN CONTINUITY OVER THE PAST FEW DAYS THAN THE GFS. SINCE 00Z LAST NIGHT...THE GFS HAS BEEN HINTING AT ANOTHER CUTOFF LOW DIVING OUT OF SE CANADA AND PHASING WITH SOUTHERN STREAM ENERGY WITH COASTAL LOW PRES TRACKING UP THE EASTERN SEABOARD. THE EC HAS CONSISTENTLY HELD OFF ON CUTTING THE H5 FLOW OFF...KEEPING THE FLOW MORE PROGRESSIVE AND ALLOWING THE SOUTHERN STREAM ENERGY TO PASS WELL S OF THE AREA. HAVE ADDED LOW CHC POPS TO THE FORECAST THU NIGHT THROUGH FRI NIGHT TO ACCOUNT FOR THE GFS TRENDS...BUT THIS IS A LOW CONFIDENCE FORECAST. A FEW UPPER LEVEL SHORTWAVES MAY MOVE ACROSS THE REGION NEXT WEEKEND...ALTHOUGH IT LOOKS LIKE ONLY LIGHT QPF WOULD IMPACT THE REGION. TEMPERATURES WILL BE NEAR NORMAL LEVELS THROUGH THE PERIOD.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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A WEAK TROF ACROSS THE NYC TERMINALS THIS AFT/EVE WILL GRADUALLY WEAKEN THIS EVENING. HIGH PRESSURE THEN RE-ESTABLISHES ITSELF TONIGHT. ANOTHER TROUGH SWINGS THROUGH THE REGION ON MONDAY. BKN INSTABILITY THIS AFT/EVE. ISOLATED SHRA ACTIVITY EARLY THIS EVE...MAINLY CT TERMINALS. SEABREEZE ALONG THE CT/NYC/LI COAST WILL SLOWLY WORK N THROUGH THE REST OF THE AFT INTO EARLY EVE. WITH GUSTY NW FLOW TO N AND W OF SURFACE TROUGH...SEABREEZE HAVING TROUBLE APPROACHING KLGA/KEWR. SEABREEZE MAY WAVER ALONG THE SE PERIPHERY OF KEWR INTO EARLY EVENING...AND MAKE A LATE PUSH AT KLGA. HAVE ADJUSTED TAFS ACCORDINGLY. WINDS WEAKEN AND BECOME NW THIS EVENING AS HIGH PRESSURE STRENGTHENS...WITH STRATO-CU GRADUALLY SCATTERING OVERNIGHT. BKN 040-060 STRATO-CU DEVELOPMENT EXPECTED MONDAY WITH SCATTERED SHOWER DEVELOPMENT IN THE AFT/EVE. BRIEF MVFR POSSIBLE WITH SHRA IN THE AFTERNOON. LOW PROB FOR ISOLATED TSRA...MAINLY KGON. NW WINDS 10 TO 15 KT WITH GUSTS TO 20 KT MON AFTERNOON. WINDS GENERALLY RIGHT OF 310 TRUE. .OUTLOOK FOR 18Z MONDAY THROUGH FRI... .LATE MON-MON NIGHT...POSSIBLE MVFR WITH SHOWERS. .TUE-WED NIGHT...VFR. ISOLATED SHRA POSSIBLE TUE. .THU...VFR. LOW PROB FOR -SHRA. .FRI...LOW PROB FOR COASTAL STORM.
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&& .MARINE...
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FOR THE NEAR AND SHORT TERM THROUGH MONDAY NIGHT...THERE WILL BE A PERSISTENT...REINFORCING PRESSURE GRADIENT FROM THE SOUTHEAST TO NORTHWEST. THE GRADIENT IS WEAK TONIGHT BUT INCREASES MONDAY AND ESPECIALLY MONDAY NIGHT WITH A DEEPER LOW FORMING WELL OFFSHORE AND HIGH PRESSURE GRADUALLY SLIDING SOUTHEAST INTO THE GREAT LAKES. SUB SCA CONDITIONS ARE FORECAST THROUGH MONDAY BUT SCA WILL BECOME LIKELY MONDAY NIGHT ACROSS THE OCEAN. THIS IS FROM THE PRESENCE OF SHOWERS TO HELP BRING DOWN MOMENTUM IN THE EVENING AND THEN THE WINDS FURTHER INCREASE LATE IN THE 950-800MB LAYER. THE MOS GUIDANCE ALSO HAS AN INCREASING TREND WITH SUSTAINED WINDS FROM THE PREVIOUS RUN. FOR OTHER WATERS...THERE COULD BE A 25 KT GUST MONDAY NIGHT BUT CONFIDENCE WAS NOT AS HIGH IN THESE LOCATIONS AND OCCURRENCES FOR THESE HIGHER GUSTS WILL PROBABLY BE QUITE BRIEF. SCA GUSTS MAY LINGER INTO TUE MORNING...HOWEVER THERE ARE DIFFERENCES BETWEEN THE GUIDANCE ON WHEN THE WINDS ALOFT SUBSIDE...SO DON`T HAVE THE CONFIDENCE TO CONTINUE THE ADVSY INTO THE 4TH PERIOD. SUB-ADVSY CONDS THEN PERSIST THROUGH THU. DEPENDING ON THE TRACK OF A COASTAL STORM AT THE END OF THE WEEK....SCA FLAGS MAY BE NEEDED ONCE AGAIN.
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&& .HYDROLOGY...
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NO SIGNIFICANT PRECIPITATION IS NOT EXPECTED THROUGH WEDNESDAY.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. NY...NONE. NJ...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 PM MONDAY TO 6 AM EDT TUESDAY FOR ANZ350-353-355.
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&& $$ SYNOPSIS...JM NEAR TERM...JM SHORT TERM...JM LONG TERM...24 AVIATION...NV MARINE...24/JM HYDROLOGY...24/JM

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