Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 180934 AFDOKX Area Forecast Discussion National Weather Service New York NY 434 AM EST Sat Nov 18 2017 .SYNOPSIS... High pressure builds over the region overnight into early Saturday. A warm front will lift to the north later Saturday, then a strong cold front will approach Saturday night, and sweep sweep eastward Sunday morning as strong low pressure passes to the north. A few weather disturbances are possible later next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Ridge axis shifts to the east this morning as a longwave trough advances through the plains and will reach the Midwest/Ohio Valley by evening. Clouds will rapidly increase this morning, and models are in good agreement that overrunning rain associated with an approaching warm front holds off until aftn. Best chances will be N and W of NYC until late. Southerly winds will increase as well, but the strongest winds will hold off until tonight and Sunday. WAA pattern could result in high temperatures occurring late in the day or even right before midnight as some location. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... Neutral upper trough becomes negatively tilted by Sunday morning with a vigorous shortwave moving through New England. At the sfc, low pres in the Ohio Valley this evening will strengthen as it tracks through the eastern Great Lakes and into SE Canada through Sun night. 00z EC has trended a little deeper with the low but not as deep as the GFS/CMC. The NAM is weaker. Warm front should lift through this eve with increasing S winds in the low levels. Cold front then approaches from the west with S-SW winds increasing further and a band of moderate to heavy showers sweeping across with the front overnight. Confidence in any wind-related hazards remains higher across eastern CT and Long Island, where a wind advisory has been issued for tonight into Sunday. Given a significant low-level mass response to the potent upper system, the potential still exists for strong gusts tonight as a jet (50-60kt at 925 mb) strengthens across the coast. NAEFS suggest low-level jet speeds significantly stronger than normal for this time of year - in the 90-98th percentile from 850-700 mb. As previous discussions have mentioned, questions still remain on how much of these winds will be able to mix to the surface. However, given the antecedent dry air mass, saturation may be somewhat slow, and is supported by SREF probabilities showing only a 25% chance of ceilings below 3000 ft by 06Z/Sun. Mixing to 3000 ft would certainly allow gusts perhaps in the range of 50-55kt across eastern Long Island and eastern/coastal Connecticut, especially after the passage of the warm front. There will be another chance to mix stronger winds to the surface with the arrival of any showers/convection as the cold front pushes through the area. There is also very limited elevated instability across the east end of LI so have added in the possibility for a rumble of thunder for a few hours early Sun morning. Otherwise, rain ends from W to E by late morning/early aftn with clearing skies. Could end up with some BKN clouds from lake effect streamers well N/W of the city, but no pcpn is expected to make it into the CWA. There is some uncertainty with the timing of the cold air working in behind the front, but expect falling temperatures during the aftn. Winds may briefly abate Sunday morning following the frontal passage, before strengthening again into the afternoon from the WNW with the passage of a strong mid- level vorticity maximum. Confidence in any wind- advisory level sustained speeds/gusts remains highest across eastern CT/Long Island closer to the departing low. Otherwise, areas farther west will need to be monitored for possible inclusion in the wind advisory for Sunday. Gradient remains tight Sun night with CAA continuing, thus gusty winds continue. && .LONG TERM /MONDAY THROUGH FRIDAY/... A broad area of high pressure will build into the region Monday and Tuesday. This will produce fair weather. SuperBlend was used for temperatures except for Monday night, where MEX was used to better capture radiational cooling. Wednesday remains a bit of a question. A cold front will be approaching from the west. In addition, there remains the suggestion that some semblance of a coastal low will develop. The 12Z GFS is way off the Southeast coast and not a factor. The 12Z ECMWF is trending west and now produces a solid swath of rain across the area. The forecast has been trended towards the ECMWF, with low chances for precipitation included for all areas. The rain would help to suppress high temperatures as well. The cooler SuperBlend was used as a result. The cold front comes through Wednesday night. The ECMWF is much different than the GFS, which pours the cold air into the region. The ECMWF keeps the coldest air locked to the north of the area, most likely due to the dynamics of the strengthening offshore low. A blend of the models was used, however depending on how the pattern ultimately develops, Thanksgiving temperatures could end up being roughly plus or minus 5 degrees from the current forecast for highs. All solutions are dry for the day however, followed by a continuation of the dry weather on Friday. The GFS does spin up a low along the subtropical jet and tracks it east of the area on Friday. The ECMWF spins up something similar on Saturday. This feature will need to be watched for any westward trend. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... High pressure slides east of the region today, with a low pressure system approaching from the West. VFR through this morning, with increasing potential for rain showers and MVFR or lower conds developing late today into tonight. Southerly winds increase this morning into this afternoon. SW winds 15 to 20 kt with gusts 25 to 30 kt likely for coastal terminals late today into this evening. .OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY... .Late Saturday Night...MVFR or lower conditions in -SHRA. LLWS possible for eastern terminals at night due to SW flow 40-50 kt at 2 kft AGL. S-SW winds G25-35KT and occasionally higher for coastal terminals. Low prob for a band of +SHRA and isolated thunder. .Sunday...Conditions gradually improve to VFR with showers ending by afternoon. Strong NW windshift Sunday morning, with NW winds G30- 40KT through the day. Gusts diminish to 25-30 kt Sunday evening. .Monday...VFR. W-NW winds G20-30KT. Gusts diminish gradually at night. .Tuesday...Mainly VFR. MVFR possible late Tuesday night with showers. SW winds G15-20KT. .Wednesday...MVFR possible with showers. W-NW winds G15-20KT. && .MARINE... Tranquil conditions on the seas will be short-lived this morning prior to strengthening southwesterly winds ahead of a cold front. Gale-force winds initially on the ocean waters by afternoon will spread to all other waters as the front nears, with seas building in response. Overnight, a low level jet is expected to strengthen along the coast, with the possibility of storm-force gusts reaching the surface, mainly east of Fire Island on the ocean waters. A Storm Watch remains in effect. The front passes from west to east tomorrow morning, with a brief lull in winds before they strengthen again from the WNW. Gale-force winds will continue into Sunday night, before gradually weakening to SCA-levels. SCA conditions may continue into Tuesday before gradually weakening into Wednesday and Thursday as high pressure builds across the area. && .HYDROLOGY... A band of moderate to locally heavy showers with a strong cold frontal passage late tonight into Sunday morning should cause no more than local nuisance impacts. Total rainfall is expected to range between 1/2 to 1 inch. && .TIDES/COASTAL FLOODING... Water levels will approach minor flood thresholds with this mornings high tide, but are expected to remain just below. Storm surge guidance for Sunday morning high tide may to be on the low side given the strength of southerly winds expected Sat night into Sunday morning ahead of a cold front. But typically, S/SW winds are not conducive to building surge. There is a low probability of a surge of 1-2 ft Sunday morning. If these surge levels develop, minor coastal impacts in a strong SW/W flow would be felt mainly across eastern portions of the Great South Bay into Moriches Bay. Elsewhere any impacts would be brief and localized. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory from 10 PM this evening to 6 PM EST Sunday for CTZ010>012. NY...Wind Advisory from 10 PM this evening to 6 PM EST Sunday for NYZ078>081. NJ...None. MARINE...Gale Warning from 6 PM this evening to 6 AM EST Monday for ANZ330-335-338-340-345. Storm Watch from this evening through Sunday morning for ANZ350-353. Gale Warning from 1 PM this afternoon to 6 PM EST this evening for ANZ350-353. Gale Warning from 1 PM this afternoon to 6 AM EST Monday for ANZ355. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.