Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 241746 AFDOKX Area Forecast Discussion National Weather Service New York NY 146 PM EDT Wed May 24 2017 .SYNOPSIS... A low pressure system tracks southeast of Long Island this morning with high pressure briefly building in this afternoon and evening. A slow moving low pressure system affects the area Thursday into Friday before weak high pressure returns again for Saturday. Another frontal system will then impact the area for the latter half of the holiday weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Clouds have thinned and broken up across the area. This should last until 22z or 6 pm. Weak sea breezes will continue to develop with day time aftn heating. Winds blowing from the Atlantic Ocean will place a hold on day time maxes, with the highest temps west and north of NYC.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Continued cloud cover ahead of the broad upper low to the west will keep temperatures overnight closer to normal. Rainfall will increase from southwest to northeast by morning as the upper low and a slowly deepening surface low move into the area. An extended period of southwest flow will continue to advect Gulf moisture northward, leading to possibly moderate rain at times through the day. As the warm front lifts through the area by afternoon, elevated instability may support a slight chance of thunderstorms, though no severe weather is expected at this time. As the surface low deepens, the tightening pressure gradient will lead to strengthening onshore flow, which will keep temperatures well below normal and also lead to coastal impacts with above normal tides. See TIDES/COASTAL FLOODING for associated impacts. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... An unsettled weather pattern continues through this period as an upper low lifts out of the Northeast on Friday, while another another drops into the Midwest and Great Lakes states over the weekend. Upper level ridging between the two systems briefly builds across the area for the first half of the weekend. Models are in good overall agreement in taking surface low pressure over the Mid Atlantic states Thursday night south and east of the area and then into the Gulf of Maine on Friday. Showers and isolated thunderstorms Thursday night will taper off on Friday with lingering clouds and showers through much of the day as deep-layered cyclonic flow remains across the region behind the departing low. Conditions will then briefly dry out Friday night into Saturday as both ridging aloft and at the surface translates east across the area. Things get a little more tricky heading in Sunday as another frontal system approaches the area. There are differences amongst the global models, in particular with the ECMWF and GGEM, as both more aggressive with a frontal wave ejecting east out ahead of the main frontal system. However, the 00Z ECMWF has trended toward the GFS, with a late day warm frontal passage on Sunday, followed by a weak cold frontal passage late Monday. There remains some uncertainty with the timing of warm advection rainfall Sunday into Sunday night. It could possibly hold off until late in the day. Scattered convection is then forecast for Memorial Day along and ahead of the cold front. Conditions briefly dry out Monday night into Tuesday before the upper trough and another cold front approach Tuesday night. Temperatures during the period will be near seasonable levels. && .AVIATION /18Z WEDNESDAY THROUGH SUNDAY/...
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Weak high pressure this afternoon will be followed by the approach of another low pressure system late tonight into Thursday NE-E winds this afternoon around 10-15 kt, strongest near the coast. ESE flow has already developed along the CT coast and could also develop across city terminals and Long Island this afternoon and evening. Flow briefly weakens overnight before increasing out of the E-NE early Thursday morning. Gusts 20-25 kt expected Thursday morning. VFR conditions through this evening with conditions gradually lowering to MVFR late tonight and then IFR Thursday morning as rain develops. IFR continues Thursday morning with potential for LIFR as well. An isolated thunderstorm is also possible Thursday morning. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Uncertainty with timing of wind veering to the ESE. NE flow may hang on a few hours longer than indicated in TAF. There is a chance wind veers to the SE this evening. KLGA TAF Comments: NE flow may hang on a few hours longer than indicated in TAF. There is a chance wind veers to the SE this evening. KEWR TAF Comments: NE flow may hang on a few hours longer than indicated in TAF. KTEB TAF Comments: NE flow may hang on a few hours longer than indicated in TAF. KHPN TAF Comments: No unscheduled amendments expected. KISP TAF Comments: Patches of MVFR possible through 19z. Winds could veer more to the SE this afternoon/evening than indicated in TAF. .OUTLOOK FOR 18Z THURSDAY THROUGH MONDAY... .Thursday-Thursday night...LIFR/IFR in rain through Thursday night. Chance of thunderstorms Thursday afternoon. ENE Gusts up to 20 kt possible Thursday afternoon. .Friday...MVFR/IFR possible. Chance of showers. .Saturday...VFR. .Sunday-Monday...MVFR/IFR possible in showers.
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&& .MARINE... Cancelled the Small Craft Advisory through today for the Atlantic Ocean coastal waters based on observations and near term forecast trends. Otherwise...the pressure gradient will gradually increase this afternoon as an area of low pressure moves offshore. Marginal NW SCA winds and seas will develop by 6 pm. A second area of developing low pressure to the southwest will maintain an easterly flow and allow seas to remain elevated on the ocean through Thursday. Low pressure passes off the New England coast Friday. Ocean seas of 5 to 7 ft remain through Friday, then diminish to less than 5 ft for Saturday and the remainder of the weekend. && .HYDROLOGY...
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0.50" to 1.50" of rain is forecast from afternoon midnight through the day on Friday. Higher amounts are possible in any thunderstorms that develop on Thursday. Minor urban and small stream flooding is possible Thursday due to antecedent wet conditions. Another round of light to moderate rainfall is possible for Sunday into Monday.
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&& .TIDES/COASTAL FLOODING...
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There is an increasing threat for successive rounds of minor coastal flooding tonight through Thursday night, with the greatest threat for widespread minor and potentially moderate coastal flooding during the Thursday night high tide cycle. This is due to a slow moving low pressure system approaching the region, and with less than 1/2 ft of surge needed in many places to reach minor flood thresholds and 1 to 2 ft for moderate.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for NYZ075-178-179. NJ...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EDT Thursday for ANZ350-353-355. && $$ SYNOPSIS...MD NEAR TERM...GC/MD/DW SHORT TERM...MD LONG TERM...DW AVIATION...DS MARINE...MD/DW HYDROLOGY...MD/DW TIDES/COASTAL FLOODING...

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