Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 251133 AFDOKX Area Forecast Discussion National Weather Service New York NY 733 AM EDT Tue Oct 25 2016 .SYNOPSIS... High pressure slowly builds in from southern Canada through Wednesday. The high moves east on Wednesday giving way to a frontal system Thursday into early Friday. Another frontal system impacts the area this weekend, followed by high pressure Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Forecast is mainly on track with minor adjustments made to temperatures, dewpoints, and cloud coverage to better match observed trends. The upper level trough will move east into the Canadian Maritimes today with a shortwave going through the region around the base of the trough. High pressure centered in Ontario builds slowly southeastward. Stratocumulus clouds are moving into the region. Not a widespread cloud cover, just broken coverage over certain parts of the region. Gusts are mainly across immediate coastal sections and over the water, where enough of a vertical temperature gradient exists to allow for more mixing. Strong high pressure remains centered in Ontario while continuing to slowly build southeast closer to the region through the day. A weakening low in the Canadian Maritimes in combination with the strong high in ontario creates a steep pressure gradient. This will allow for gusty northwest flow to continue today. The cold air advection increases as well with a continuous northwest fetch. 850mb temperatures will lower several degrees compared to the previous day so temperatures will be noticeably cooler. There will be cold air advection aloft which should increase the coverage of stratocumulus driven by diurnal instability. Models are even showing some very light QPF extending into the far northwest and southeast sections of the region, which is primarily evident in strong cold air advection scenarios. However, aside from this morning across Orange County NY where there is a slight chance of showers, low levels will be too dry for precip elsewhere and later on today. Used ECS guidance for highs which will be mainly in the 50s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... The center of the high tracks to southeast Ontario and continues to build into the local region tonight. There will be some slight ridging aloft. The winds will become lighter in response to a weaker pressure gradient. The cooler airmass will already be within the region. The closer proximity of the high will result in more subsidence and less clouds. The combination of factors will lead to better efficiency of radiational cooling especially across the interior. Freezing temperatures expected across much of the interior where freeze warning is in effect. Used MAV guidance for lows tonight which will range mainly between 30 and 40. For Wednesday, the high pressure center moves east into Quebec with a continued decrease in pressure gradient across the local region. Winds will be lighter but will still be a little breezy from diurnal heating and inherent mixing. The cold air advection at 850mb decreases as the weather pattern shifts. Cyclonic flow aloft lessens as the upper level low in the Canadian Maritimes shifts east while across the local region, there will be some slight ridging aloft. Model guidance in pretty good agreement with a downward trend in temperatures Wednesday as highs will be a few degrees cooler than the previous day. Used a blend of MET/MAV/ECS guidance for highs Wednesday which will range from the upper 40s to lower 50s. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... A shortwave moving across the Great Lakes region late Wednesday night into Thursday morning, will slowly move east, passing across the local area Thursday night. At the surface, high pressure continues to slide east as a warm front approaches from the west as low pressure tracks across the Great Lakes and across PA/western NY. Warm air advection rain move in late Wednesday night and through the day Thursday. Enough cold air ahead of the WAA, and time of day being early morning could result in some light snow briefly NW zones. Some accumulations are possible across higher elevations before a change to plain rain occurs. Rain is expected through thursday night, before ending during the day on Friday. There is a chance some lingering rain showers could continue into the afternoon across the eastern half of the CWA. High pressure builds to the south as another low moves across the Great Lakes Region Saturday, passing to the north early Sunday. Drier weather returns for the start of next week. Temperatures through the long term will remain slightly below or right around normal. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... VFR as high pressure builds over the region. NW flow with occasional gusts to 20kt possible before 14z. Gusts becoming more frequent thereafter. Winds near 310 magnetic most of the day. See comments below for details. NY Metro Enhanced Aviation Weather Support... Detailed information...including hourly TAF wind component fcsts can be found at: http:/ KJFK TAF Comments: Winds probably prevail mostly at or south of 310 mag through 14z, but chance that winds continue to prevail at or south of 310 mag through 15-16z. Winds could still be south of 310 mag at times thereafter. KLGA TAF Comments: Winds probably prevail at or mostly south of 310 mag through 14z, but chance that winds continue to prevail at or south of 310 mag through 15-16z. Winds could still be south of 310 mag at times thereafter. KEWR TAF Comments: Chance that winds occasionally are north of 310 mag through 15-16z. Thereafter, equal chances of being north or south of 310, but best guess is they will favor south of 310. The afternoon KEWR haze potential forecast is green...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: No unscheduled amendments expected. KHPN TAF Comments: No tactical amendments scheduled and no strategic amendments expected. KISP TAF Comments: No unscheduled amendments expected. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY... .WED...VFR. NW-NNW G20KT possible near the coast. .THU...MVFR conditions likely in rain. IFR conditions possible at night. SE winds 10-20KT. .FRI...VFR. W-NW winds G25-30KT. .SAT...VFR. Chance of rain. SW winds G15-20KT. && .MARINE... SCA conditions once again on all waters today with the steep pressure gradient between a weak low in the Canadian Maritimes and a strong high in Ontario. For tonight, the pressure gradient weakens so gusts will decrease likewise. SCA conditions will keep up across the ocean while non- ocean waters will subside below SCA during the evening after 00Z. For Wednesday, the pressure gradient is weak enough to keep conditions below SCA on all waters. Sub-SCA conditions are expected Wednesday night through much of Thursday. SW flow increases to 15-20 kt Thursday night out ahead of a frontal system which should push ocean seas up to 5-6 ft. As the low passes by Friday, winds shift back around to the west/nw and increase behind the departing low. These winds back yet again to the west/SW ahead of next frontal system Saturday into Sunday. && .HYDROLOGY... Dry weather remains forecast through Wednesday. Low pressure impacts the area Thursday and Thursday night. Forecast QPF is expected to produce anywhere from 1/2 to 3/4 of an inch of rainfall. Local amounts over an inch are possible. No hydrologic impacts expected at this time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Freeze Warning from 2 AM to 9 AM EDT Wednesday for CTZ005>008. NY...Freeze Warning from 2 AM to 9 AM EDT Wednesday for NYZ068>070. NJ...Freeze Warning from 2 AM to 9 AM EDT Wednesday for NJZ002-004- 103-105-107. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ330- 335-338-340-345. Small Craft Advisory until 6 AM EDT Wednesday for ANZ350-353- 355. && $$ SYNOPSIS...BC/JM NEAR TERM...JM SHORT TERM...JM LONG TERM...BC AVIATION...JC MARINE...BC/JM HYDROLOGY...BC/JM is the U.S. government's official web portal to all federal, state and local government web resources and services.