Area Forecast Discussion
Issued by NWS Upton, NY

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221 FXUS61 KOKX 232015 AFDOKX Area Forecast Discussion National Weather Service New York NY 415 PM EDT Mon Apr 23 2018 .SYNOPSIS...
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High pressure track east across the western Atlantic, while low pressure over the southern states works northward through the middle of the week. The low will lift across the area on Wednesday. High pressure returns on Thursday with a wave of low pressure passing near the area on Friday. A weak frontal system on then moves through on Saturday followed by sprawling high pressure builds in thereafter.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Upper air pattern features a southern branch closed low working slowly east across the Tennessee Valley, and an upper ridge moving off the eastern seaboard. At the surface, high pressure continues to work away from the area but there will be enough low-level ridging overnight for a weak E/SE flow. Low pressure over the Tennessee Valley will lift slowly north. Conditions will remain dry and just below seasonable levels for overnight lows. Used a blend of the MOS with slight adjustments. High level cloudiness ahead of the low will very slowly work northeast. Depending on how fast the clouds and low level moisture come in could result in some locations cooling more quickly than others with some patchy fog as well.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/...
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Models are in good overall agreement in taking low pressure over the Tennessee Valley northeast through Wednesday, taking the low near or just west of NYC late Wednesday. The ECMWf is on the slower side of the guidance. Clouds will overspread the area from the SW during the day with light overrunning rains developing from west to east in the evening and becoming steadier overnight. A strong low-level jet will enhance warm advection rains toward daybreak, with the possibility of a thunderstorm during the morning and afternoon hours. The coverage will diminish in the afternoon and may become more convective in nature. Instability aloft though is marginal and not surface-based. Rainfall totals will be highest from NYC and points north and west due to orographic enhancement with a modest SE flow. Gusts up to 30 mph will be possible along the coast. Amounts will range form 0.75 inches far eastern areas to 1.25 in the hills north and west of NYC. Should the upper trough become more negatively tilted than forecast, these amounts will likely need to be increased due to more offshore convection and warm conveyor belts rains working into the region Highs on Tuesday will be a bit cooler due to the cloud cover and onshore flow, but will be milder Tuesday night for the same reason. Highs on Wednesday will be similar.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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There are some differences in the upper pattern right out of the long term gate Wed night that continue through the remainder of the period. The general H5 flow consists of troughing over eastern North America giving way to western ridging during the second half of the weekend or early next week. Models begin with differences in location of the upper low, EC/CMC the slowest moving with the NAM/GFS the fastest. Given the scenario, have sided with the slower moving, and thus have PoPs continuing bust decreasing Wed night. A wave of low pres tracks through or near the NYC metro area Wed night with a temporary lull in winds during the eve. This combined with a S-SE flow could keep areas of fog around into the eve, but since winds will be shifting to the S-SW, have only gone patchy attm. Elevated instability also appears to be present during the eve, although its marginal so have included SCHC thunder. A few areas of rain may linger into Thu, especially across northern zones, otherwise dry weather returns into Fri with weak sfc ridging building in. A shortwave trough tracking through the Plains midweek tracks through the SE states Thu and up the east coast on Fri. All NWP, except the GFS keeps pcpn offshore, although 12z CMC and EC have trended westward. Pcpn remains east of the area, but is closer, thus have SCHC-CHC PoPs in the forecast to account for this. High uncertainty with a potential frontal system impacting the area on Sat. GFS is less amplified aloft, keeping energy associated with trough axis well to the N while CMC/EC are sharper/cut off at H5. Have gone with consensus for the time being with a SCHC-CHC PoPs. Deep layered ridging then builds in behind this resulting in dry and warm weather into next week. Near to slightly above normal temps are expected through the period.
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&& .AVIATION /20Z MONDAY THROUGH SATURDAY/...
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High pressure continues to drift off the southern New England coast into Tuesday afternoon. Low pressure approaches from the southwest late in the forecast period. VFR. Winds SE around 10 kt. There is a low chance of a sea breeze developing late this afternoon, with winds becoming SSE. Early this evening, after 01Z, winds diminish to under 10 KT, and at the outlying terminals winds become light and variable. Tuesday winds will again be SE to S and increase to 10-15 KT. Occasional gusts 15-20 KT are possible toward 18Z. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Amendments possible for sea breeze. KLGA TAF Comments: Amendments possible for changes in wind direction. KEWR TAF Comments: Amendments possible for changes in wind direction. KTEB TAF Comments: Amendments possible for changes in wind direction. KHPN TAF Comments: No unscheduled amendments. KISP TAF Comments: Amendments possible for changes in wind direction. .OUTLOOK FOR 18Z TUESDAY THROUGH SATURDAY... .Tuesday afternoon...VFR. E to SE winds, gusts 15-20KT possibly near the coast by mid to late afternoon. .Tuesday Night...Rain with MVFR conds developing in the evening, then IFR conds likely after midnight. E to SE winds, gusting to around 20KT at times. .Wednesday...Rain with IFR conds, and ISOLD TSTM possible. SE winds 15-20, gusting 25-30 KT. .Thursday...Showers ending with conditions becoming VFR. -Friday-Saturday...Chance of showers late Friday into Saturday with VFR to MVFR.
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&& .MARINE...
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SCA has been issued for the ocean waters Tuesday night into Wednesday and will likely need to be extended into Wednesday night for lingering high seas. Conditions are marginal for the bays, harbor, and sound. Low pressure moving up the eastern seaboard Tuesday into Wednesday will result in strengthening easterly winds and building seas Tuesday Night. Winds likely subside below SCA Wednesday evening as low pressure moves to the north. An inversion over the waters is expected to keep higher winds aloft Wed night. However, SCA seas will likely linger on the ocean waters into Fri before subsiding. Sub advsy conds are then expected on all waters for the rest of the forecast period.
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&& .HYDROLOGY...
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A widespread 3/4 to 1 1/4 inches of rain is likely Tuesday Night into Wednesday, with heaviest amounts favored across NYC metro, NE NJ, Lower Hudson Valley, and SW CT. Minor urban and poor drainage flooding is possible if high end of rainfall ranges are realized.
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&& .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 8 PM Tuesday to 6 PM EDT Wednesday for ANZ350-353-355.
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&& $$ SYNOPSIS...24/DW NEAR TERM...DW SHORT TERM...DW LONG TERM...24 AVIATION...MET MARINE...24/DW HYDROLOGY...24/DW EQUIPMENT...//

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