Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 070500 AFDOKX Area Forecast Discussion National Weather Service New York NY 1200 AM EST Thu Dec 7 2017 .SYNOPSIS...
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High pressure builds to the south tonight into Thursday, remaining in place through Friday. A series of frontal waves will pass south and east of the area Friday night into Saturday. An upper level disturbance then passes through on Sunday. High pressure briefly follows for Monday followed by a cold frontal passage on Tuesday. Offshore low pressure develops along the front off the Mid Atlantic coast and tracks northeast Tuesday night into Wednesday.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Again, very little to update in the forecast tonight as it largely remains on track. Have adjusted sky coverage upward across portions of NJ, NYC, Long Island and eastern Connecticut to account for thick upper level clouds, as an intense subtropical jet remains just to our south. Deep troughing east of the Rockies, will continue to edge east into the region tonight. At the surface, high pressure with continue to build south of the waters with a relatively tight gradient between it an Ontario low. The result will be continued caa on westerly winds overnight. Mixed low-levels should keep temps near seasonable, 20s interior and 30s coast.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/... Deep longwave troughing will remain entrenched east of the Rockies, with a confluent northern and southern jet stream working over the region. This will keep a subsident pattern over the region during the Thu/Fri time period with high pressure just to the S and SW of the area, but at the same time inducing several waves of low pressure along a stalled offshore frontal system. A pattern which will have to be watched for the weekend. Near seasonable temps expected on Thursday with breezy westerly flow but waning CAA. Jet cirrus will likely continue to filter to obscure sunshine. A reinforcing shot of CAA likely late Thu/Thu Eve in wake of glancing shortwave/trough passage, but potential for late night radiational cooling Thu night as weak high pressure builds in depending on cirrus opacity. Lows have potential to fall to the lower 20s across outlying areas late Thurs night. As polar vortex begins to descend towards the Great Lakes and longwave trough axis begin to neutrally tilt across the Central US, phased jet energy will begin to strengthen and retrograde westward Thu night into Friday. This should begin to retrograde the offshore front closer to the coast into the weekend, but for Friday the main impact will be increased high and mid cloud cover. Cloud cover and reinforced shot of CAA, should result in temps below seasonable on Friday, with highs generally in the upper 30s to lower 40s. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... An amplified upper flow will feature ridging along the west coast and a mean upper trough situated east of the Mississippi River Valley. This will keep the area unseasonably cold through the period and potentially unsettled with offshore low development. A digging shortwave across the upper Great Lakes Friday night will dig into the base of the upper trough across the Tennessee and Ohio Valleys on Saturday. The backing upper flow and jet energy along the east coast will allow for multiple frontal waves to form offshore along a stationary front. There are enough differences in the model suite as well as with their ensemble members to raise concern for a potential snowfall event late Friday night into Saturday. Solutions generally point toward a glancing blow with the 12Z GFS the farthest east with its precipitation, mainly across far eastern Long Island and southeast Connecticut. The ECMWF and NAM are farther west with a potential light snowfall event back as far west as the NYC metro and Lower Hudson Valley. This all hinges on the amplification and progression of the deepening upper trough. Often, in past winters we have seen the models being too far south with the precipitation as strong enough jet dynamics have allowed for some adjustment of the low track to the NW. That being the case, the GGEM appears to be an outlier with a heavy snowfall event across the region. At this time, the forecast calls for a light snowfall event with the potential for 1-2 inches of snowfall across eastern Long Island and southeast Connecticut. However, trends in the guidance the next 24 hours will probably be a good signal to which way we are headed. A clipper low then follows on Sunday with perhaps some instability snow showers and another reinforcing shot of cold air. High pressure briefly follows for Monday with another cold frontal passage on Tuesday. Once again, the global models are pointing toward an amplifying upper trough across the east with offshore low development. It too early at this time to be specific with amounts, but another shot of snow is possible. Temps remain colder than normal through much of this time frame, with a slight warmup expected Monday night into Tuesday ahead of the cold front. Temperatures then drop into the 30s for highs on Wednesday behind the system. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... High pressure builds to the southwest through the TAF period. VFR. W winds around 10 kt or less through the night. For Thursday, continued VFR with W winds increasing 10-15 kt by noon. Afternoon gusts around 20 kt. ...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: No unscheduled amendments expected. KLGA TAF Comments: No unscheduled amendments expected. KEWR TAF Comments: No unscheduled amendments expected. KTEB TAF Comments: No unscheduled amendments expected. KHPN TAF Comments: No unscheduled amendments expected. KISP TAF Comments: No unscheduled amendments expected. .OUTLOOK FOR 00Z FRIDAY THROUGH MONDAY... .THU night...VFR. .FRI-SAT...Possible RASN and MVFR east. .SUN...Mainly VFR. .MON...VFR. && .MARINE...
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The pressure gradient strengthens overnight with continued CAA, allowing for the continuation/redevelopment of marginal SCA gusts on the ocean and central/eastern LI Sound. Winds once again likely fall below SCA on Thursday, with seas following suit. Marginal SCA is possible once again Thu evening in wake of reinforcing cold frontal passage. Westerly flow then diminishes later Thursday night into Friday as weak ridging builds in, with winds and seas falling below SCA. Conditions remain rather tranquil Friday night and Saturday as high pressure builds and waves of weak low pressure pass just to the east. An upper level trough, and surface front pass early Sunday. W/NW winds pickup as the pressure gradient tightens. Seas will build as a result.
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&& .HYDROLOGY... No hydrologic problems are expected through early next week. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. See our headline news on the web at: http:/weather.gov/nyc && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 10 AM EST Thursday for ANZ330-350- 353-355. && $$ SYNOPSIS...NV/DW NEAR TERM...MD/NV/PW SHORT TERM...NV LONG TERM...DW AVIATION...BC MARINE...NV/DW/PW HYDROLOGY...NV/DW EQUIPMENT...

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