Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 190259 AFDOKX Area Forecast Discussion National Weather Service New York NY 1059 PM EDT Wed Apr 18 2018 .SYNOPSIS... Low pressure tracks across the Ohio Valley this evening and to just south of Long Island on Thursday. The deepening low then quickly exits into the Canadian Maritimes Thursday night through Friday. High pressure builds through the weekend and into early next week. Unsettled weather may return by the middle of next week as low pressure approaches. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Quick updated to adjust short term temperatures and dew points, as dew points continue to fall. HRRR slower with the onset of precipitation and lowered probabilities, especially eastern zones, through 07Z. Dew points have mixed out this evening, and were adjusted down into early this evening. After 00Z dew points will then begin to climb in the warm air advection and moisture advection ahead of an approaching shortwave. With increasing clouds and precipitation onset after 06Z, and continued warm advection, temperatures look to hold nearly steady, and may even rise. Made a minor adjustment upward for overnight lows. Profiles inland saturated and below freezing above the surface. There may be some wet snow mixed with the rain across the higher elevations of Orange and Putnam counties, and added a rain/snow mix. Then mid and upper levels dry after 12Z and precipitation transitions to all rain. On the heels of a departing upper low across eastern Canada, a vigorous shortwave trough at the base of the upper trough will pivot across the area into Thursday. This will send low pressure over the Ohio Valley east tonight and then to the south of the area Thursday morning. Warm advection ahead of the system will result in increasing clouds this evening with light rain developing from west to east after midnight. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Periods of light rain will continue for much of the day Thursday with the highest probability being across the interior where the better thermal forcing will prevail. As low pressure pulls to the east by afternoon, wraparound light rain will continue, tapering off from west to east during the late afternoon/early evening hours. Rainfall totals for the event will range from about a tenth to a quarter inch, with the highest amounts across the interior. As the precipitation winds down, there is the possibility that a few snow flakes could mix in. It will be another unseasonably cold day with temperatures remaining in the 40s, and then dropping into the 30s Thursday night. Gusty NW winds up to 30 mph will develop behind the low late Thursday afternoon/early evening and continue through the overnight. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Generally tranquil weather is expected during this time frame. Departing trough to the northeast makes slow progress, with upper level NW flow continuing across the northeast through the weekend. Ridge builds across the upper midwest and Great Lakes region, to the north of southern stream shortwave that passes from the Rockies through the southern states. The southern stream shortwave, along with northern stream energy will likely make progress toward the east coast Tuesday-Wednesday, potentially resulting in unsettled weather by mid week next week. Otherwise, dry conditions along with slightly below normal temperatures are anticipated. && .AVIATION /03Z THURSDAY THROUGH MONDAY/...
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A wave of low pressure approaches tonight, and passes south of Long Island Thursday morning, then strengthens as it continues out to sea during the afternoon. VFR through at least 06z. Clouds thicken and lower overnight. There is some uncertainty in when conds drop to MVFR, however with guidance indicating pcpn slightly delayed from earlier thinking have sided with the hi-res solutions and delayed MVFR conds as well. Only have conds dropping to IFR at KHPN/KSWF/KBDR/KGON where confidence is a bit higher, although it is a possibility at remaining terminals for at least a couple of hours Thu. Conds improve back to VFR late from W to E. P-type could be an issue at KSWF. Soundings indicate a few hours of SN or RASN until mid levels dry out early Thu morning. Light and vrb winds overnight, pick up out of the E-NE 5-10kt towards morning. As the low passes to the south and strengthens while departing, winds will back to the N then NW and increase to 10-20g20-30kt in the late aftn/eve. .OUTLOOK FOR 00Z FRIDAY THROUGH MONDAY... Thursday night-Friday...VFR. NW winds G20-30KT, mainly Thu eve and after sunrise Fri. .Saturday-Monday...VFR.
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&& .MARINE... Wind and seas will subside tonight as low pressure approaches from the Ohio Valley and passes just south of the waters Thursday morning. As the low deepens heading up into the Canadian Maritimes Thursday night into Friday, near gale force gusts will develop on the waters Thursday evening. A moderate northwest pressure gradient should allow for SCA gusts 25- 30 kt to continue over the waters on Friday, before diminishing Friday night. A small craft advisory has been posted for all the waters beginning Thursday night and continuing into Friday morning, except through Friday afternoon east of Moriches Inlet. The pressure gradient is forecast to relax over the waters this weekend, becoming light by Saturday night. As a result, sub Small Craft Advisory conditions are forecast over the waters around Long Island Saturday-Monday as high pressure builds closer. && .HYDROLOGY... Rain amounts below a half inch are expected tonight through Thursday evening with no hydrologic impacts anticipated. Dry weather follows thereafter. There is the potential for significant rainfall mid week next week. && .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 from 6 PM Thursday to 6 AM EDT Friday for ANZ330-335-338-340-345. Small Craft Advisory from 6 PM Thursday to noon EDT Friday for ANZ353-355. Small Craft Advisory from 6 PM Thursday to 6 PM EDT Friday for ANZ350. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.