Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 230439 AFDOKX Area Forecast Discussion National Weather Service New York NY 1139 PM EST Mon Jan 22 2018 .SYNOPSIS... A warm front lifts north through the region overnight and early Tuesday morning. A cold front then crosses the Tri-State Tuesday afternoon and early evening, followed by a trough of low pressure pushing through the remainder of Tuesday night. High pressure then builds in for the rest of the work week, followed by a frontal system over the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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SW flow aloft overnight, coupled with E-SE flow at the surface, and dry mid levels, will produce areas of drizzle and fog. Visibilities across Long Island have reduced to generally 1/4 mile or less, so have issued a Dense Fog Advisory there through 9Z. Less than one mile at times. There is some potential this may need to be extended in time, depending on exactly how fast the warm front lifts to the north. Elsewhere visibilities range from 0 to 5 miles at ASOS/AWOS sites across the CWA. There is the potential for the Dense Fog Advisory to be expanded to other portions of the CWA. Will continue to closely monitor overnight. As low to mid level isentropic lift and saturation increases overnight expect rain to develop from SW to NE after midnight. Should see some improvement in visibilities late tonight as you get increased low level lift and some rain, both of which should create enough mixing to raise visibilities. Lows tonight should occur this evening, then temperatures should slowly rise overnight in response to low level warm advection. Lows should be from the mid 30s to around 40, except lower 40s in the immediate NYC Metro.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... As a warm front continues to push north tonight and into Tuesday a deep moisture airmass along with precipitable water values of 1 to 1.25" will set the stage for periods of moderate to locally heavy rainfall, as a cold front approaches late tonight and moves across the area Tuesday morning. The front is forecast to move through fast, so the heavy rainfall at this time doesn`t seem to be a significant threat. There will be some good instability ahead of the approaching cold front. Will continue the mention for an isolated thunderstorms as the cold front makes its way across the area. There is also the potential for strong winds above the surface to mix down in any thunderstorms. Regardless, a tight pressure gradient will lead to strong winds across the area through the day but at the moment it appears winds will be brief and sporadic enough to preclude a Wind Advisory for now. The front will pull offshore by Tuesday evening. Northwest winds behind the front will usher in more seasonable temperatures. Tuesday nights low will be in the low to mid 30s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Not much change in the 12Z data regarding the long term. High pres builds in from the w on Wed, with wnw winds ushering in a colder airmass. Deep mixing provides a high confidence in temps, so a blend of the data was used. There could be a period of bkn-ovc aftn cu which the model data is not picking up on attm, so an upgrade in cloud cover is possible with subsequent updates. With deep unidirectional flow, winds should keep the lowest lvls mixed Wed ngt. Temps therefore not as cold as a pure mos blend. Still breezy on Thu but deep subsidence will produce a sunny day. The superblend was used for temps. Still in the cool regime Fri as return flow does not commence til late in the day. The superblend again used for temps. Some mid clouds may infiltrate the skies if the waa aloft develops fast enough. A warming trend on Sat as a frontal sys approaches. The GFS and ECMWF have diverged on timing however, with the ECMWF now about 24 hrs slower than the GFS, bringing the cdfnt and bulk of the rain in on Mon. The fcst remains close to the more consistent timing of the GFS, with pops focused on Sun and Sun ngt. Lower pops remain in place for Mon, but again this could change if the ECMWF becomes a trend. The superblend was used for temps. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... A warm front just S of Long Island will push through late tonight followed by a cold front Tue aftn. Difficult forecast continues, especially for NYC and Long Island terminals. IFR/LIFR with locally VLIFR conds prevail at all terminals. Although the depth of the low cloud deck is all of around 500 ft, am starting to have doubts that conds improve for a couple of hours NYC/LI overnight. Not completely out of the question though with winds aloft increasing and dry air just above this low cloud deck. Have moved the potential into a tempo group since the improvement may not be for very long if it occurs at all. Otherwise, rain forecast to move in 09-13z. Any improvement on Tue is forecast to be gradual and current forecast may even be improving conds too early, especially in the morning. Moderate to heavy rain showers and isolated thunderstorms will impact the area from daybreak through the afternoon with the approach of a cold front. E/NE 5-10kt become light and vrb away from the coast overnight. Winds veer to the SE then S late tonight into Tue morning as warm front pushes north of the region. LLWS/Compression likely Tue with gusts up to 35 kt possible, strongest for KISP/KGON. Cold frontal passage with wind shift to west will occur from mid to late afternoon. .OUTLOOK FOR 00Z TUESDAY THROUGH SATURDAY... .Tuesday Night into Wednesday...VFR. WNW G20-25KT possible. .Thursday-Friday...VFR. .Saturday...Showers possible with S-SW G20KT. && .MARINE...
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Minor changes were made with this update to reflect the latest trends in observations and guidance. The forecast appears on track. With visibilities at ASOS/AWOS close to the coast generally less than 1 mile, have issued a Marine Dense Fog Advisory through 9Z. There is some potential this may need to be extended in time, depending on exactly how fast the warm front lifts to the north. South to southwest flow will rapidly strengthen across the area waters overnight, with at least Small Craft Advisory (SCA) level winds developing by morning. There probably will be some occasional gusts to 25 kt on the coastal ocean waters late overnight as well. Depending on the strength of the inversion, there is potential for strong low- level jet winds to mix to the surface, with at least occasional gale- force winds on Tuesday. Occasional gale force winds will also be possible in any thunderstorms that can develop. Seas will rapidly build in response to the strengthened flow, remaining elevated even as the cold front moves through Tuesday evening. Winds may briefly drop off as the front moves through, before rapidly strengthening again following its passage. SCA level winds in the 25 to 30 kt range are expected Tuesday and Tuesday night on all waters, so have an SCA up accordingly. A SCA will be needed on the ocean Wednesday and Wednesday night. Winds will be marginal elsewhere. Winds and seas will then creep up towards sca levels again on Thursday as low pressure deepens over the Atlantic. Winds and seas should be below SCA levels on Friday, then sw flow increases over the weekend ahead of a frontal system.
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&& .HYDROLOGY... Total rainfall through Tuesday is expected to range from around 1/2 to 1 inch, with locally up to 2 inches possible in any stronger convection. There is a small chance for localized ponding of water in any areas receiving locally heavy rainfall due to convection, but no significant hydrologic issues are anticipated at this time. No significant hydrologic impacts are anticipated from Tuesday night through early next weekend. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...Dense Fog Advisory until 4 AM EST Tuesday for NYZ078>081-177- 179. NJ...None. MARINE...Dense Fog Advisory until 4 AM EST Tuesday for ANZ330-335-338- 340-345-350-353-355. Small Craft Advisory from 6 AM Tuesday to 6 AM EST Wednesday for ANZ330-335-338-340-345-350-353-355.
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&& $$ SYNOPSIS...JMC/Fig/Maloit NEAR TERM...Maloit SHORT TERM...Fig LONG TERM...JMC AVIATION...24 MARINE...JMC/Fig/Maloit HYDROLOGY...JMC/Fig/Maloit EQUIPMENT...

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