Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 220011 AFDOKX Area Forecast Discussion National Weather Service New York NY 811 PM EDT Sun Apr 21 2019 .SYNOPSIS... Low pressure gradually develops off the Middle Atlantic coast tonight. The low then tracks north towards Cape Cod on Monday into Monday night. Weak high pressure briefly builds south of the area on Tuesday. A cold front will move through early on Wednesday. A warm front and its associated low pressure will move into the region Friday, followed by a cold front Friday night into early Saturday. High pressure builds in during next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... For this update have added some patchy fog to the coast, and some interior places in CT especially as there will be a window of areas of clearing, and with still a somewhat moist ground and lightening winds progged during tonight felt that at least patchy fog wording needed to be added. The question will be of course the extent of cloud cover, and high clouds through this evening especially. Perhaps this will play a role in limiting fog. The NAM guidance is hinting at some low stratus as well. Overall decided to decrease cloud cover for the first half of tonight for much of the area, then the clouds increase a bit late tonight. This lead me to lean more towards areas of patchy fog through at least 8z or so. Used a NBM and GLAMP blend for the most part with winds, temps, and dews for this evening as it appeared to match obs well. Broad upper low extending from the Appalachians down to the Carolinas this evening will consolidate along the North Carolina and Virginia coast by Monday morning. Weak surface low to our west will also shift towards the south and off the coast tonight closer to the reorganization of the upper low. Any lingering showers will diminish this evening with the expectation of a dry night. Dew points are progged to fall into the 40s tonight as some drier low level air works across the region. Cloud cover is a bit tricky tonight as there could be lingering stratocumulus and some high clouds. Have gone with a mostly cloudy night. If the stratocumulus is less extensive, then cloud cover may need to be lowered. Lows will generally be in the 40s with some lower 50s in the NYC metro. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... The main focus on Monday will be low pressure associated with the aforementioned upper low. The upper low should pivot to a location just southeast of Long Island by afternoon with a surface low tracking near the 40/70 benchmark. Confidence in the forecast is still not too high given the time frame and this is because there remains a good amount of spread on how far north and west rain bands from the low will reach in the afternoon. Some of the guidance is still differing in the whether or not the surface low remains broad or consolidated. Despite the lower forecast confidence, the highest likelihood for showers in the afternoon and evening lies across Long Island and southern Connecticut. Any showers should hold off until late morning and then spread north in the afternoon. Some high resolution guidance is also hinting at a broken band of showers developing across the higher terrain to our north and shifting south around the low in the evening. Will continue to carry chance PoPs for the rest of the area to account for this potential. Any instability present in the forecast soundings lies below the freezing level, so do not anticipate lightning generation and have left thunder out of the forecast. High temperatures in the 60s are forecast for most locations with readings near 70 possible in the NYC metro. Temperatures are coolest across eastern Long Island and southeast Connecticut where the higher chances of rain exist. The upper low and surface low will gradually shift south and east of Cape Cod Monday night. Showers may continue for the first half of the night across eastern Long Island and southeast Connecticut. Some drier air should work its way in as the system moves away for the second half of the night with some clearing expected. Lows will be in the upper 40s and lower 50s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... By Tuesday morning the upper level system that has been plaguing the region will lift to the northeast with ridging building in, albeit briefly. Tuesday should feature a good deal of sunshine with temperatures getting above normal. Inland locations further west should get well into the 70s, with an afternoon sea breeze cooling down eastern and coastal sections. A good temperature spread should develop during Tuesday afternoon with thermal differential due to sea breeze development. The next shortwave and frontal boundary then approaches for Tuesday night into early Wednesday. Overall system is not overly impressive. There may be a rumble or two of thunder across western sections Tuesday night with the leading edge of showers as SPC has western sections in a general t-storm risk. Not overly impressed with the instability indices, therefore went with slight t-storm chance in far western area Tuesday night, otherwise a light QPF event looks to take shape with amounts probably around a tenth of an inch of so. PWs only around an inch or so based on NAEFS ensemble guidance. The front gets east of the region and washes out a bit by Wednesday afternoon and drier air gets ushered into the region. Decided to keep some POPs in through Wednesday morning as there is not complete deterministic model agreement on the exact timing in which the front completely clears the region. Dry weather then follows as weak high pressure builds in for Wednesday night into Thursday. Clouds should then increase quickly by late in the day Thursday into Thursday night as a warm front and its associated low pressure off to the west and southwest draws closer. This system may have a bit more to work with with respect some lower latitude moisture. This system has the potential to bring a half inch to an inch of rain for late Thursday night into Friday. The global models are then in excellent agreement with respect to the timing of the system exiting to the east Friday night. This should allow high pressure to build in to begin next weekend, with high pressure in control through the entire weekend. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Weak low pressure moves across tonight and then southeast of Long Island on Monday. Mainly VFR conditions are expected during the TAF period. However, there will be potential for IFR stratus and fog late tonight into Monday morning, especially for eastern coastal terminals. The fog may become a higher possibility for those locations that have initially less clouds such as KHPN, KBDR, and KISP. KGON despite initially higher clouds has more low level moisture so fog will be a possibility there as well. Otherwise, more showers are forecast to develop Monday afternoon with a chance for MVFR. The winds will become light and variable near 5kt or less tonight before becoming more northerly on Monday and increasing to around 10 kt in the afternoon with some possible gusts up to 20 kt. .OUTLOOK FOR 18Z MONDAY THROUGH THURSDAY... .Monday night...Possible MVFR in showers early, then VFR. .Tuesday...Mainly VFR. Chance of showers and MVFR at night. Isolated thunderstorms near KSWF Tuesday night. .Wednesday...Morning showers/possible MVFR, then becoming VFR. .Thursday...VFR. && .MARINE... Rough seas will continue on the ocean waters through Monday night due to a south to southeasterly swell. Have extended the SCA for hazardous seas through this time period. Winds on all waters will stay below SCA levels through Monday night as there will be a relatively weak pressure gradient. Low pressure does pass nearby Monday evening, but winds do not look to get above 20 kt. Rough seas will continue on the ocean waters through Tuesday morning due to a southeasterly swell. Seas on the ocean will range from 4 to 6 ft. Seas on the ocean will come down slightly Tuesday afternoon and Tuesday night, with marginal SCA conditions expected into Wednesday with seas generally at 4 to 5 ft. Seas will subside more on the ocean Wednesday night into Thursday as high pressure builds over the coastal waters with sub SCA conditions continuing on the ocean through Friday with seas around 3 ft. Sub SCA conditions will take place across all non-ocean waters through the period. && .HYDROLOGY... No hydrologic impacts are expected through Tuesday afternoon. Any precipitation will be light Tuesday night into early Wednesday, followed by precipitation on the order of a half inch to an inch Thursday night into Friday with no hydrologic impacts expected at this time. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO35 (162.55 MHz) remains off the air. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Tuesday for ANZ350-353-355. && $$ SYNOPSIS...JE/DS NEAR TERM...JE/DS SHORT TERM...DS LONG TERM...JE AVIATION...JM MARINE...JE/DS HYDROLOGY...JE/DS EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.