Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 210555 AFDOKX Area Forecast Discussion National Weather Service New York NY 155 AM EDT Sat Apr 21 2018 .SYNOPSIS... High pressure builds in from the west through tonight, then remains over the region into Monday. A coastal low will likely affect the region the middle of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Forecast is on track with only minor changes made. An upper longwave trough along the eastern Canadian coast and extending into the northeast remains through tonight with a northwest cyclonic flow. Meanwhile surface low pressure along the Canadian coast tracks northeast as high pressure builds to the west. The atmosphere will remain dry and cloud-free tonight. Winds will be diminishing, and likely decouple late tonight. This will allow for good radiational cooling with clear conditions. Inland areas will likely see patchy to areas of frost and included in the weather forecast. However, the Spring frost/freeze program has not begun across these areas. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... The upper trough remains across the northeast through Saturday night as the center of the surface high builds into the northeast. The weather will remain quiet and cloud free. Cyclonic flow and weak cold advection continue through Saturday night, however, the airmass will be modifying under full sun, and highs Saturday will be approaching normal levels. Saturday night will be cloud-free with light winds and again there will be ideal radiational cool conditions. So, expect areas and patchy frost inland. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Upper air pattern will very much resemble early springtime as an upper low over the Mississippi Valley slowly works east on the heels of a departing northern branch trough over the Northeast. Ridging both aloft and at the surface builds across the region to start the week but then gives way to the aforementioned southern branch close low. The system will lift northward in response to a northern branch shortwave trough moving into the upper Midwest and Great Lakes, sending surface low pressure up the eastern seaboard Tuesday into Wednesday. Overrunning rains are forecast to develop across the area Tuesday night and continue into Wednesday night. There are some differences thereafter though with the global models as the ECWMF is more progressive with this system and dries things out for the end of week, while the GFS and GGEM close off the northern branch trough with unsettled conditions lingering until a cold frontal passage Friday night. Thus, will maintain a low chance of showers for the end of the week. The point to be made here there is clearly uncertainty in the guidance for the end of the week as northern branch shortwave energy dives southeast across the Upper Midwest and Great Lakes region. however, all the global models are pointing to amplification of the ridge out west and the trough reestablishing itself across the east by next weekend. As for temperatures, much of the period will feature seasonable temperatures with the exception of Wednesday, where onshore flow will keep highs several degrees below normal. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... High pressure will build in through the TAF period. VFR conditions are expected. Winds will be near 10 kt or less through much of the TAF period mainly from W to NW direction. The winds will initially be NW going into early Saturday and then back to a more westerly direction during the afternoon with some SW flow as a sea breeze for some terminals. Also for this afternoon into early evening, there will be some wind gusts to 15-20 kt. The timing and duration of any sea breezes is uncertain with wind direction possibly varying about 20-40 degrees comparing observed to forecast for Saturday afternoon. The timing of the SW flow could also be 2-3 hours off from forecast. .OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY... .Saturday night through Tuesday...VFR. .Tuesday night through Wednesday...MVFR or lower conditions increasingly likely with rain. && .MARINE... High pressure continues to build into the waters from the west with the pressure gradient force gradually weakening. Seas on the ocean waters have subsided to below SCA levels. Also, winds and gusts were generally below SCA levels, especially across the open ocean waters. However, through early this evening occasional nearshore gusts may reach 25 KT. With frequent gusts and seas below SCA levels the SCA was cancelled. High pressure will be across the forecast waters Saturday and Saturday night with winds and seas remaining below SCA levels. Tranquil conditions are forecast Sunday through Tuesday as high pressure builds across the waters. However, low pressure moving up the eastern seaboard Tuesday into Wednesday will result in increasing winds and building seas with SCA conditions likely to return by Wednesday morning. && .HYDROLOGY... Dry conditions are expected through early next week. A widespread rainfall is expected for the middle of next week with the possibility moderate to heavy rain. Predictability is low on rainfall 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...None. && $$ SYNOPSIS...MET/DW NEAR TERM...JP/MET SHORT TERM...MET LONG TERM...DW AVIATION...JM MARINE...MET/DW HYDROLOGY...MET/DW EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.