Area Forecast Discussion
Issued by NWS Upton, NY

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997 FXUS61 KOKX 240552 AFDOKX Area Forecast Discussion National Weather Service New York NY 152 AM EDT Tue Apr 24 2018 .SYNOPSIS... 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 and Wednesday night, exiting to the north on Thursday. High pressure returns Thursday night with a wave of low pressure passing near the area on Friday and Friday night. A weak frontal system on then moves through on Saturday followed by sprawling high pressure building in early next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Increased clouds in the forecast database to capture the cirrus moving in at mostly broken coverage. Also slightly adjusted temperatures and dewpoints to better match observed trends. 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. Conditions will remain dry and just below seasonable levels for overnight lows. Used a blend of the MOS with slight adjustments outside of the Pine Barrens. 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. Restricted the depiction of patchy fog to those locations where low level RH is maximized within more rural outlying areas, essentially where radiational cooling will be more effective.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... 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. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... 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. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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High pressure will continue to move off the coast into this afternoon. Low pressure approaches from the southwest tonight night. Light and vrb flow this mrng. SE winds increase on today to 10-15 kt. A few gusts 15 to 20 kt are possible in the late morning and afternoon. Winds back towards the E this evening. VFR through 00z Wednesday, with cond lowering to ifr overnight as rain develops. .OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY... .Late tonight...Rain with ifr or lower. E to SE winds may gust to around 20 kt near the coast. .Wednesday...Rain with IFR/LIFR conds. Isolated thunderstorm possible. SE winds 15-20, gusting 25-30 KT. .Thursday...Shower possible with conditions becoming VFR. -Friday-Saturday...Mainly VFR. Chance of showers late Friday into Saturday.
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&& .MARINE...
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The forecast continues to remain on track. A light pressure gradient over the waters will limit winds to 10 kt or less through Tuesday morning. The gradient increases Tuesday afternoon, with winds up to around 15 kt forecast over the waters. A Small Craft Advisory (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... 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. && .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 this evening to 6 PM EDT Wednesday for ANZ350-353-355.
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&& $$ SYNOPSIS...24/DW NEAR TERM...Maloit/JM/DW SHORT TERM...DW LONG TERM...24 AVIATION...JMC/DS MARINE...24/Maloit/DW HYDROLOGY...24/DW EQUIPMENT...

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