Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 161948 AFDOKX Area Forecast Discussion National Weather Service New York NY 348 PM EDT Mon Jul 16 2018 .SYNOPSIS... High pressure remains offshore tonight. A cold front will approach from the west on Tuesday and move through late in the day into Tuesday night. High pressure will build across the region Wednesday through Thursday, then remain over the region through Friday. The high will then move offshore on Saturday with low pressure and its associated warm front approaching for Saturday night into Sunday. The weakening warm front will then linger near the region into Monday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Any showers and storms this evening will be isolated to scattered in nature and primarily inland where sea breezes have not reached. Still can`t rule out additional showers and storms overnight for roughly the same areas as weak shortwave energy passes through with sufficient MUCAPES in place. It`ll be a muggy night with lows in the 70s. There is a moderate risk of rip currents for the ocean beaches into this evening. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... A cold front approaches and is expected to pass through the tri-state area mostly during the late afternoon to evening hours. This will bring showers and thunderstorms to the area. SBCAPEs could range 1500-2500 J/KG, coinciding with unidirectional 0-2 KM shear of 20-30 kt. Strong wind gusts with TSTMs are possible along with a marginal potential for severe gusts. The main limiting factor for severe weather appears to be the high moisture content limiting the potential for steep lapse rates. Another threat with these showers and storms will be flash flooding. Very high moisture content will be in place with PWATs around 2.25, a warm cloud layer depth of 13-14 KFT, and a theta-e ridge shifting through. Best chances for heavy rainfall will be in the afternoon and evening hours when shortwaves and a llj pass through and tap into this deep moisture. Limiting the chances of flash flooding will be the forward speed of the cells as the upper flow will not be aligned with surface cold front, which will also limit the chances of storm cell training. Although models signal higher rain totals over the eastern half of the area, flash flood guidance and antecedent dry conditions don`t support flash flooding there. Any flash flooding would more likely be localized. After collaboration with the surrounding office, have decided to hold off on any flash flood watches. Given the dry pattern we`ve been in and the convective nature of the rainfall, have doubts with some of the guidance that show widespread 1.50 - 2.50 inch accumulations. Will go with the lower side of guidance for total rainfall. The remaining concern will be heat indices and the need for heat advisories. 850mb temps are expected to be similar to today`s however there should be more cloud cover tomorrow in addition to rain-cooled air. Expecting highs in the mid-upper 80s for the locations currently under a heat advisory. Dewpoints should however be higher than today`s. Forecast dewpoints at the top of the mixed layer are progged to be 15-16C and a S-SW wind flow will prevail, so surface dewpoints are not expected to drop much until after the cold front moves through. Expecting dewpoints in the mid 70s, leading to heat indices in the mid 90s for areas within the advisory. This is the only area that`s expected to have 2 consecutive days of 95+ heat indices, so the advisory will not be expanded in area at this time. There is a moderate risk of rip currents for the ocean beaches Tuesday into Tuesday evening. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... An Upper level trough will linger across eastern portions of the region through Wednesday. Have trimmed back any slight chance POPs just a touch from previous forecast, as low level cold and dry advection as depicted by most modeling should keep precip chances near a minimum, even for eastern sections. Upper level ridging will then build Wednesday night through early Friday. Dry conditions with comfortable humidity levels are expected during this timeframe. An upper level trough will then approach out of the Upper Midwest and Southern Canada into the weekend. With high pressure slipping off the east coast early in the weekend, a humid southerly flow will return to the region. With upper and mid level forcing precip chances will increase through the weekend, and peak by Sunday with a warm front just south and southwest of the region along with greatest height falls just NW of the region. The upper level system is then progged to weaken and fill to some degree on Monday. Forcing should still be sufficient to carry chance POPs across the region. Global ensemble mean 500 mb height forecasts still indicate some mean troughing over the eastern CONUS through early next week which would indicate at a minimum diurnal driven convective chances. Ensemble viewer indicates PWs running about 1.5 to 2 standard deviations above normal late in the weekend into early next week as actual PW values should be approaching 1.75 inches during this time. Too early to get into details, but there may be some localized pockets of heavier rainfall during this timeframe with broad deep southerly flow established. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... High Impact Day on Tuesday with Numerous Showers and Thunderstorms in the Afternoon... Offshore high pressure will gradually give way to an approaching frontal system over the Ohio Valley. Largely a VFR forecast outside of any isolated to widely scattered convection through Tuesday morning, which should be mainly north and west of the NYC terminals. A more widespread convective event is forecast for Tuesday afternoon as a cold front approaches the area. Additionally, there could be a period if IFR/MVFR ceilings east of the NYC terminals toward daybreak. The best chance for this would be at KGON. S winds 10-15 KT this afternoon, but a bit weaker across the interior. Seabreeze likely as far north and west as KHPN. KTEB, and KEWR this afternoon. Winds drop off a bit tonight with S-SW 10-15 G20kt on Tuesday. 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: Low chance for a thunderstorm this afternoon. KLGA TAF Comments: Low chance for a thunderstorm this afternoon. KEWR TAF Comments: Timing of afternoon seabreeze could vary by an hour of either side of 19Z. Low chance for a thunderstorm this afternoon. KTEB TAF Comments: Timing of afternoon seabreeze could vary by an hour of either side of 21Z. Low chance for a thunderstorm this afternoon. KHPN TAF Comments: Low chance for a thunderstorm late this afternoon. KISP TAF Comments: No unscheduled amendments expected. .OUTLOOK FOR 18Z TUESDAY THROUGH FRIDAY... .Tuesday Afternoon...Widespread showers/tstms likely with MVFR or lower conditions. S winds G20KT into early evening. .Wednesday-Saturday...VFR. && .MARINE... Sub-SCA conditions prevail tonight with light winds and seas below 5 ft. Winds and seas then increase Tuesday ahead of a cold front. SCA conds expected on the ocean waters by mid-morning and lasting into Tuesday night. Lingering S-SE swell component may result in SCA conditions due to seas for eastern ocean waters during Wednesday afternoon and evening. Otherwise, sub SCA conditions will persist through Friday as high pressure builds across the coastal waters with a light pressure gradient. High pressure will then move east and northeast of the coastal waters on Saturday resulting in an increasing SE swell component. This could result in small craft conditions due to high seas for the ocean waters by Sunday. && .HYDROLOGY... Showers an thunderstorms will be capable of producing locally heavy rain with the potential for primarily minor urban/ poor drainage and small stream flooding. The best overall chances for flooding will be Tuesday afternoon into evening. While not likely to be widespread, localized flash flooding cannot be ruled out. The convective nature of this event will produce a wide range of total accumulated rainfall. Most spots probably end up with around a half inch of rain with amounts ranging up to 1.50 inches less common. Isolated amounts of 2 to 2.50 inches are possible. No hydrologic impacts are expected Wednesday through Monday. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Heat Advisory until 6 PM EDT Tuesday for NYZ072>075-176-178. NJ...Heat Advisory until 6 PM EDT Tuesday for NJZ004-006-103>108. MARINE...Small Craft Advisory from 8 AM Tuesday to midnight EDT Tuesday night for ANZ353-355. Small Craft Advisory from 8 AM Tuesday to 6 AM EDT Wednesday for ANZ350. && $$ SYNOPSIS...JC/JE NEAR TERM...JC SHORT TERM...JC LONG TERM...JE AVIATION...DW MARINE...JC/JE HYDROLOGY...JC/JE EQUIPMENT...//

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