Area Forecast Discussion
Issued by NWS Upton, NY

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597 FXUS61 KOKX 231154 AFDOKX Area Forecast Discussion National Weather Service New York NY 754 AM EDT Mon Apr 23 2018 .SYNOPSIS... High pressure centered over the Northeast will drift offshore today, and further over the Atlantic on Tuesday. Low pressure will affect the region Tuesday Night into Wednesday Night. Another low pressure or frontal system may affect the region Friday or Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure, centered over the Northeast, will drift off the coast today. This will maintain another sunny, dry and seasonably mild Spring day. Light NE winds will become onshore this afternoon, with sea breeze along the entire coastal plain this afternoon. A blend of the MET/MAV was used, which takes areas w of the Hudson River close to 70, and lower to mid 70s elsewhere.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... The high will continue to slide ewd thru the period, allowing low pres over the Southeast to draw closer to the cwa. The models have been consistent in holding off on pcpn until Tue eve, so pops have been scaled back during the day on Tue. Main challenge will be clouds, as the modeling suggests a dense cirrus developing as early as tngt. Water vapor imagery supports the supply of moisture, so clouds have been ramped up late tngt and all of Tue. Tue looks mainly ovc attm. This cloud shield should keep temps from bottoming out like they did this mrng, so the fcst has been warmed abv guidance. Of course, if clouds don`t increase as expected tngt, temps will verify lower than fcst. With a lgt onshore flow, there could be some patchy fog. The Superblend was used for Tue, with the increasing sely flow limiting temps. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Models continue in good agreement with a large southern closed upper low over the Tennessee River Valley Tuesday, opening and lifting into the NE US through Wednesday in response to northern stream shortwave energy moving into the upper Midwest/Great Lakes. At the surface, resultant low pressure lifts towards the region Tuesday Night into Wednesday, and then to the north Wed Night/Thu. One interesting feature to be watched, that is being picked up by the operational models (very clearly in the NAM), is development of a sub-tropical wave within WCB convection off the SE coast Tuesday. This features then rides north up the coast in the WCB and either merges or swings around the primary low as it approaches the region Wed. Overall, a soaking rain with breezy E/SE winds is expected to develop across the area late Tuesday night and continue into Wednesday afternoon. Timing differences still exist on timing of heaviest rain, during the late Tuesday Night into Wed afternoon time period. Can`t rule out an isolated thunderstorm Wed morning into afternoon along/ahead of approaching warm front with weak elevated instability and forcing from approaching shortwave energy and 55-65 kt SE llj. Most operational solutions are muted with the development of a sub-tropical wave, keeping rainfall to a 1/2 to 1 inch event. Meanwhile the NAM is denoting potential for a heavier rainfall with a stronger wave and sub-tropical Atlantic moisture inflow, resulting in a 1 to 2 inch rainfall. This interaction will have to be monitored over the next 24 to 36 hrs, as the NAM may be resolving a convectively induced wave better than other operational guidance. In any case, have increased QPF to 3/4 to 1 1/2 inches based on upward trend in GEFS and SREF mean and mode, and to capture potential for the stronger sub-tropical connection noted in the NAM. Interestingly, the operational GFS is a the bottom of the envelope of QPF spread of GEFS members. Highest QPF amounts are favored across NYC metro, NE NJ, Lower Hudson Valley and SW CT with orographic lift of moist SE inflow. Otherwise, models in general agreement with best forcing/moisture move NE Wed afternoon into Wed Eve, with lingering showers Wed NIght, a slower trend than 24 hrs ago. Thereafter, models still have notable spread in the evolution of the above mentioned Upper Midwest/Great Lakes trough, as its energy splits N/S during the mid to late week period. Differences exist in the strength of the southern energy that splits off, and with the amplification of the northern energy over the Eastern Great Lakes and Northeast Wed Night/Thu as it phases with the initial southern wave moving up the coast. This is further complicated by differences in evolution of the next northern stream shortwave diving into the Central US for late week, that does a similar split. It appears the evolution of the northern portion of this energy, and the interaction (if any), with the southern energy that got left behind, will be a key determinant in sensible weather for Fri/Sat. So a complex forecast to say the least. At this point, it appears there is potential for a progressive low pressure or frontal system to affect the region during the Friday or Saturday time period, but predictability on details remains low. Will continue with low chance of showers in the forecast during this time to denote the potential. Temperatures during this time period will be seasonable, except a few degrees below seasonable Wednesday with low pressure affecting the region. In fact, if the more progressive/less amplified solutions are correct, Thursday into Saturday could be slightly above seasonable, pushing 70 for NYC/NJ metro and solidly in the 60s elsewhere. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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High pressure moves across the terminals through midday and then moves offshore for the remainder of the TAF period. Mainly VFR conditions are expected through the TAF period with mostly clear conditions through this evening. Cirrus increases late tonight into Tuesday. For places such as KGON where cirrus increase will be later than for other terminals, could have some patchy fog developing late tonight into early Tuesday with a low chance for MVFR/IFR visibilities. Winds will be generally NE-E near 5 kt this morning and then will become S-SE 5-10 kt late this morning into this afternoon. Expect some variance of 1-3 hours at individual terminals with the timing of the wind direction shifts with the first shifts for KJFK and CT terminals. Winds become lighter and more southerly tonight near the coast and away from the coast just light and variable in direction. 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: Amendments possible with wind shift timing from NE to SE, which could vary 1-3 hours from forecast. The afternoon KJFK haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KLGA TAF Comments: Amendments possible with wind shift timing from NE to SE, which could vary 1-3 hours from forecast. The afternoon KLGA haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KEWR TAF Comments: Amendments possible with wind shift timing from NE to SE, which could vary 1-3 hours from forecast. The afternoon KEWR haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KTEB TAF Comments: Amendments possible with wind shift timing to SE, which could vary 1-3 hours from forecast. KHPN TAF Comments: Amendments possible with wind shift timing to SE, which could vary 1-3 hours from forecast. KISP TAF Comments: Amendments possible with wind shift timing from E to S, which could vary 1-3 hours from forecast. .OUTLOOK FOR 12Z TUESDAY THROUGH FRIDAY... .Tuesday...Lowering VFR cigs in afternoon. SE winds G15-20KT especially near the coast by mid to late afternoon. .Tuesday Night...Rain with MVFR conds developing in the evening, then IFR conds likely after midnight. SE winds G20KT at times. .Wednesday...Rain with IFR conds. E-SE winds G20-25KT. .Thursday-Friday...Mainly VFR.
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&& .MARINE... Winds and seas will remain blw sca lvls thru Tue. Low pressure moving up the eastern seaboard Tuesday into Wednesday will result in strengthening easterly winds and building seas Tuesday Night, with SCA conditions likely to returning Tuesday Night and continuing into Wednesday afternoon. Winds likely subside below SCA late Wed into Wed Eve as low pressure moves over and then NE of the region, and could remain sub-SCA into the weekend. Ocean seas will likely be slower to subside, likely remain elevated at SCA levels into Friday from residual SE swells. One caveat, there is low potential for another low to affect the region Friday with more widespread SCA conds. && .HYDROLOGY... Dry conditions are expected through Tuesday. A widespread 3/4 to 1 1/2 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. There is a low potential for up to 2 inches of rain in the above mentioned areas, which would increase the threat for urban/poor drainage flooding, and potentially cause some localized minor small stream flood impacts. && .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...JMC/NV NEAR TERM...JMC SHORT TERM...JMC LONG TERM...NV AVIATION...JM MARINE...JMC/NV HYDROLOGY...NV EQUIPMENT...

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