Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 142024 AFDOKX Area Forecast Discussion National Weather Service New York NY 324 PM EST Thu Dec 14 2017 .SYNOPSIS...
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High pressure builds across the area tonight then quickly shifts offshore on Friday as an area of low pressure develops off the Mid Atlantic Coast. Low pressure quickly departs eastward on Saturday, with high pressure briefly building in again in its wake. A series of weak low pressure and frontal systems will pass through mid week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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The pressure gradient will initially remain tight between the departing low and building high pressure, maintaining breezy conditions and subsequent wind chill values that will fall into the teens and single digits by tonight. Dry advection on the back side of the departing low and the loss of diurnal heating will allow the stratocu to dissipate, leading to mostly clear skies overnight and favorable radiational cooling as the pressure gradient gradually begins to relax with time. The remaining snow pack should aid in cold low temperatures in the single digits to teens, generally about 10 to 15 degrees below climatological normals.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
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The persistent blocking pattern will gradually begin to break down on Friday with a subtle eastward shift to a large scale East Coast upper trough, while upstream low pressure flattens a dominant ridge on the West Coast. Phased vorticity maximums will push eastward, allowing a surface low to intensify off the Carolina coast before ejecting eastward. Across the area, temperatures will remain below normal, largely below freezing, with increasing cloud cover through the day as the phased vorticity maximums approach. Although the heaviest snowfall will remain well south of the area, mid-upper level saturation will gradually increase into the evening, with any developing precipitation aloft subsequently saturating low levels enough to produce at least a dusting of snow along the coast. Cloud cover decreases again Friday night as the system pushes east of the area, while winds gradually increase as the pressure gradient increases ahead of building high pressure. Low temperatures are already forecast to be well below normal, but could drop further depending on the exact timing of clearing skies and increasing winds.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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A progressive pattern in place across the country for the long term period. High pressure builds to the south on Saturday as a coastal low remains well to the southeast of the area. As the low exists, W- NW winds increase, especially across Long Island and Coastal CT where the low level jet moves across. Below normal temperatures, combined with gusty winds, will keep wind chill values in the low 20s during the day. The forecast becomes more uncertain on Sunday night into Monday as a weak warm front moves towards the region. While models are in good agreement regarding upper level energy, there is still disagreement amongst precipitation amounts. However, with winds shifting to the SW expecting a period of rain/mixed precipitation overnight into Monday. Confidence still remains low based on the differences in model guidance. By Monday temperatures return to near seasonal norms for mid December. Thereafter, models in fairly good agreement with a northern stream trough approaching the region on Tuesday, but differences exist in the amount of interaction with southern stream energy/moisture. Primary low pressure system appears to ride through Quebec/Ontario with trailing cold front approaching the region, but precip coverage amounts will be dependent on the aforementioned southern stream interaction. Thermal profile suggests precip would be a wintry mix transitioning to rain, but predictability at this point is low. Upper trough swings through the NE Tue Night into Wed with a glancing shot of modifying arctic air in the wake of the cold front for midweek.
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&& .AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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VFR as high pressure builds in from the west through Friday morning. Low pressure develops off the DelMarVa Friday afternoon. NW wind gusts diminish this evening. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Direction averages 310-320 magnetic this afternoon with +/- 20 degrees of variablity. High confidence forecast. Gusts could extend an hour later than fcst especially on the ITWS. KLGA TAF Comments: Direction averages 320-330 magnetic this afternoon with +/- 20 degrees of variablity. High confidence forecast. Gusts could extend an hour later than fcst. KEWR TAF Comments: Direction averages 310-320 magnetic this afternoon with +/- 20 degrees of variablity. High confidence forecast. Gusts could extend an hour later than fcst. KTEB TAF Comments: No Unscheduled TAF Amendments Expected. KHPN TAF Comments: TAF amendments not scheduled. KISP TAF Comments: High confidence forecast. .OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY... .FRI AFTN/NGT...VFR. CHC flurries in the AFTN and evening. .SAT...VFR. WNW winds G20-25KT daytime. .SUN...VFR. .MON...CHC MVFR -RA, -RASN inland early. .TUE...Becoming MVFR. CHC -RA.
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&& .MARINE...
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Both winds and seas will remain at SCA-levels on the ocean waters through this evening as low pressure departs and high pressure builds across the area. Winds may occasionally gust to near SCA-levels elsewhere, but in general winds and seas will begin to subside overnight on all waters as high pressure builds and the pressure gradient begins to relax. Tranquil conditions will then persist into Friday, before winds and seas increase to SCA-levels again Friday night with the departure of a low pressure system to the south and east. These conditions will persist into Saturday night, followed by a better chance of SCA or possible Gales in the wake of a midweek system.
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&& .HYDROLOGY... No significant hydrologic impacts expected. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until midnight EST tonight for ANZ355. Small Craft Advisory until 6 AM EST Friday for ANZ350-353. && $$ SYNOPSIS...CB/MD/NV NEAR TERM...MD SHORT TERM...MD LONG TERM...CB/NV AVIATION...Tongue MARINE...CB/MD/NV HYDROLOGY...CB/MD/NV EQUIPMENT...

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