Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 221959 AFDOKX Area Forecast Discussion National Weather Service New York NY 359 PM EDT Thu Sep 22 2016 .SYNOPSIS...
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High pressure over the region gradually gives way to a cold front over the Great Lakes, which passes through Friday evening. Canadian high pressure will build in this weekend, then pass east on Monday. A frontal system may approach from the west some time from Tuesday into Thursday.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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Another mild night is on tap across the region as high pressure retreats offshore with a cold front approaching from the Great Lakes. Outside of a few mid level clouds, mostly clear conditions will prevail with light and variable winds. 12Z NAM appears to be too aggressive with its low-level moisture with stratus/fog development. Airmass in place is very dry noted with dew points in the upper 40s to lower 50s this afternoon. In addition, moisture advection is weak at best with a light SE flow. For overnight lows, used a MOS/Model consensus blend with readings ranging from the mid 50s to lower 60s. There is a moderate risk of rip current development at Atlantic Beaches through this evening.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
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Cold front approaches area from NW on Friday with an amplifying upper trough across eastern Canada. Cold frontal passage looks to be during the early evening hours, passing south of LI/NYC metro by 10 PM. There is decent low-level lift with the front and marginal instability with CAPES around 500 J/KG across the interior, otherwise best upper forcing remains north of the region. Thus, looking for a low chance of showers and possibly a thunderstorm from late afternoon in the interior, through the early morning hours far eastern sections. Much of the cloud cover and precipitation will be post-frontal, with the 85h-70h front. Ahead of the front Friday, unseasonably warm conditions will continue with a SW flow and warm heights aloft. Highs will range from the lower 80s at the coast, to the mid and upper 80s NYC metro and interior. A gusty northerly flow will develop behind the front Friday night with gusts up to 20 mph. Clearing will be gradual from the NW during the morning hours. Lows Friday night will be a few degrees cooler than the previous night, but still a few degrees above normal. There is a moderate risk of rip current development at Atlantic Beaches on Friday.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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Forecast early on is relatively straightforward, as a cooler and much drier Canadian air mass arrives for Sat through Mon. Morning clouds should give way to afternoon sunshine on a gusty NE-N flow. High temps should be 10-15 degrees cooler on Sat than those fcst for Fri, in the lower and mid 70s, then a little cooler for Sunday and Monday, with upper 60s and lower 70s. Lows both Sat night and Sunday night should have a wide range due to ideal radiational cooling conditions under clear skies, with diminishing winds toward daybreak Sunday and light winds Sunday night, from 50-55 in NYC metro, to the 40s most elsewhere, to the mid/upper 30s in outlying areas. Per current forecast frost advisories could be needed for interior portions of the Lower Hudson Valley and SW CT for Sunday night. Meanwhile, a complicated flow regime will be setting up across North America this weekend into the middle of next week, with decreasing forecast certainty after Monday. Medium range guidance has been forecasting an omega block to develop over the eastern two-thirds of the continent, but the details remain sketchy. Earlier runs of the ECMWF and today`s 12Z GFS have advertised a stronger block, which would keep a weak frontal system to our west through the middle of next week, with reinforcing shots of cooler air for us as mid level shortwaves rotate around the eastern leg of the block over the Canadian maritimes, while today`s 12Z ECMWF, by cutting off part of the energy of the western leg of the block over the Southwest this weekend, is allowing a more progressive pattern and frontal passage Mon night into Tue. As a result the forecast trends to near average temps and mainly slight chance PoP from late Monday night onward.
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&& .AVIATION /19Z THURSDAY THROUGH TUESDAY/... High pressure remains over the region into early Friday. A cold front approaches friday afternoon and evening. East to southeast winds will remain around 10 kt or less through the afternoon. Winds become light and variable again tonight, before becoming southwest during the mid to late morning on Friday. VFR through the TAF period. Some of the forecast guidance is hinting at some low stratus tonight, this will need to be monitored. Confidence of any stratus development is low. 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: Winds may stay to the right of 150 this afternoon. Wind speeds may stay less than 10 kt. KLGA TAF Comments: No unscheduled amendments are expected. KEWR TAF Comments: Winds may stay to the right of 140 this afternoon. Wind speeds may stay less than 10 kt. KTEB TAF Comments: No unscheduled amendments are expected. KHPN TAF Comments: No unscheduled amendments are expected. KISP TAF Comments: No unscheduled amendments are expected. .Outlook for 18Z Friday through Tuesday... .Friday afternoon...VFR with southwesterly flow. .Friday Night...Winds will shift to the north after a cold frontal passage. A few showers are possible, but conditions will remain mainly VFR. .Saturday-Tuesday...VFR. && .MARINE...
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A weak pressure gradient remains across the waters through Friday ahead of an approaching cold front. Gusty north winds behind the cold front Friday night and SE/E swells may bring seas to around SCA criteria on the ocean waters. Confidence is too low to issue at this time. The combination of wind waves in post-frontal northerly flow and incoming swells from distant Karl should lead to SCA conditions on the ocean mainly from late Fri night into Sat night. An afternoon buoy ob near Karl currently shows 11-ft seas with a 10-second period, which per swell decay algorithm would arrive Sat afternoon as long period 4-ft swells, which in combination with N flow around 15 kt should likely lead to at least 5-ft seas Sat night even if Karl does not strengthen. Quiet thereafter with high pressure in control Sunday through Mon night, then possibly a weak frontal passage late Mon night into Tue.
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&& .HYDROLOGY... No significant widespread rainfall is expected through Friday night. It should be dry from Saturday through at least early next week. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...Goodman/DW NEAR TERM...DW SHORT TERM...DW LONG TERM...Goodman AVIATION...BC MARINE...Goodman/DW HYDROLOGY...Goodman/DW

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