Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 201758 AFDOKX Area Forecast Discussion National Weather Service New York NY 158 PM EDT Fri Apr 20 2018 .SYNOPSIS... Deepening low pressure lifts north through the Canadian Maritimes today, while high pressure builds in gradually from the midwest through early next week. A coastal low will likely affect the region the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Forecast on track, with only minor updates to temperatures, dew points and winds. Closed upper low and associated coastal low lift north through the Canadian Maritimes today, with trough axis moving through by early afternoon. Cyclonic flow remains with a gusty NW flow. Despite deep mixing, 850 hpa temps of around -5 c will keep temps 7-10 degrees below seasonal normals. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Deep closed low continues to lift north along the Eastern Canadian seaboard, with mean troughing continuing over the NE US in its wake. At the surface, high pressure builds into the region from the west. Although a weak backside shortwave will have a surface trough moving through the region in the afternoon. Clear and chilly conditions tonight, with areas of frost across outlying areas where temps radiatively cool to the upper 20s to lower 30s. Elsewhere lows generally in the mid 30s. Continued W/NW flow on Saturday, but weaker than today. A gradual moderation in airmass and deep mixing should allow temps to rise into the mid to upper 50s. Mostly sunny skies expected, with just few-sct afternoon CU with shortwave/trough passage. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... The northern branch of the upper level jet will be near to just south of the region late this weekend and then will be moving north of the region for Monday. The southern branch of the upper level jet getting enhanced by an upper level trough near the Gulf early next week will be approaching the region towards midweek along with the upper level trough. The southern branch shows some phasing northeast of the region going into next Thursday with the rest of the southern branch staying south and west of the region. At the surface, a large area of high pressure and its subsidence will keep minimal clouds late this weekend. The high will move offshore late Monday through Tuesday. During this timeframe, the airmass will moderate as winds will be lighter due to a weak pressure gradient. Towards the middle of next week, particularly starting Tuesday night is when rain chances return to the forecast. This will be as a low pressure system approaches from the Southeast coast. The low center itself, appearing in the models as a triple point, moves across late Wednesday or Wednesday night. Then this low will move north to northeast of the region Thursday. Its magnitude remains rather weak so not much of an increase in pressure gradient is expected. Winds will not increase that much as a result. One feature to note though will be the significant precipitable water. There is some model indication that this parameter will reach 1 to 1.25 inch Wednesday. This happens to be when most model precipitation is forecast as well, coinciding with the most vertical lift. There is a chance there could be some heavy rain at times as the precipitable water value will be approaching or even exceeding the 90th percentile for that time of year according to OKX precipitable water sounding climatology. The rain will be likely Wednesday into Wednesday evening, with chances of rain remaining into Thursday as well with the upper level trough to the west of the region. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... A weak trough of low pressure crosses the area this afternoon. High pressure then builds in from the west into Saturday morning. VFR through the TAF period. Wind gusts around 25 kts are expected through the afternoon. Winds will then abate this evening, with speeds decreasing to around 10kt. City and coastal terminals will lose their gusts after 0z, with inland terminals a few hours sooner. Winds will range around 10 kts late Saturday morning and afternoon. Wind direction will start off NW on Saturday, before becoming more westerly towards the early afternoon for the city terminals. 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: Moderate-high confidence in winds to the right of 300 True/310 Magnetic into this evening. Timing in gusts ending may be off by +/- 1 to 2 hours this evening. KLGA TAF Comments: Moderate-high confidence in winds to the right of 300 True/310 Magnetic into this evening. Timing in gusts ending may be off by +/- 1 to 2 hours this evening. KEWR TAF Comments: Moderate-high confidence in winds to the right of 300 True/310 Magnetic into this evening. Timing in gusts ending may be off by +/- 1 to 2 hours this evening. KTEB TAF Comments: Timing in gusts ending may be off by +/- 1 to 2 hours this evening. KHPN TAF Comments: Timing in gusts ending may be off by +/- 1 to 2 hours this evening. KISP TAF Comments: Timing in gusts ending may be off by +/- 1 to 2 hours this evening. .OUTLOOK FOR 12Z SATURDAY THROUGH WEDNESDAY... .Saturday...VFR. NW-W winds. .Sunday through Tuesday...VFR. .Tuesday night through Wednesday...Sub VFR conditions increasingly likely Tuesday night and into Wednesday. && .MARINE... Seas across the outer ocean waters were running about a foot below forecast levels. Gusty NW flow around SCA levels will persist into mid afternoon and ocean seas are expected to also remain around 5 feet on the outer waters. Marginal NW SCA gusts possible to re-develop on the ocean waters this evening in wake of weak frontal passage. Thereafter, winds diminish below SCA tonight as high pressure builds towards the waters. Expecting a quiet period with sub-SCA conditions this weekend through next Tuesday with high pressure in control and a weak pressure gradient. Next Tuesday night is when there is expected to be a return to SCA conditions for the ocean with southeasterly fetch building ocean seas to 3 to 5 feet as the high moves farther offshore and low pressure along the Southeast coast approaches. && .FIRE WEATHER... The combination of gusty NW winds of 20 to 30 mph, and min rh values falling to around 30 percent, may create an enhanced threat of brush fire spread amidst fine fuels (upright grasses and reeds) today. The limiting factor will be 1 to 2 tenths of an inch of rain yesterday. && .HYDROLOGY... Dry conditions are expected through early next week, with water levels for area rivers and streams gradually falling. A widespread rainfall is expected for the middle of next week with the possibility of occasional heavy rain. Predictability is low on rain amounts and hydrologic impacts at this time. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ330- 335-338-340-345-350-353-355. && $$ SYNOPSIS...JM/NV NEAR TERM...MET/NV SHORT TERM...NV LONG TERM...JM AVIATION...JE MARINE...JM/MET/NV FIRE WEATHER... HYDROLOGY...JM/NV EQUIPMENT...

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