Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 200843 AFDOKX Area Forecast Discussion National Weather Service New York NY 343 AM EST Sat Jan 20 2018 .SYNOPSIS...
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A strong low pressure system tracks across Eastern Canada today, while southern US high pressure slowly slides offshore through the weekend. A weak cold front will pass through the area tonight, returning north as a warm front Monday Night. A strong frontal system will cross the region on Tuesday, with high pressure returning for the remainder of the week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Unseasonably mild conditions today, with confluent PAC/polar jet to the north of the region. At the surface, a strong low pressure system moves east through southeastern Canada, while high pressure remains across the southern US. A breezy WSW flow (gusts 30 to 35 mph) and fair skies with a PAC airmass will provide an unseasonably mild day with highs in the upper 40s to lower 50s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/...
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Zonal upper flow continues, with confluence of Pacific and polar jet to the north of the region, and southern stream energy tracking through the deep south. A weak cold front, associated with the strong low pressure moving through SE Canada today, will press through the region tonight. This will bring in a glancing shot of Canadian air for Sunday, as polar high pressure noses towards Northern New England. High temps will fall several degrees from today, but still a few degrees above seasonable levels (lower to mid 40s). NAM is indicating stratus development under a strengthening subsidence inversion on Sunday, but seems higher prob for this across PA and points west. If stratus does develop this far east, temps would likely run several degrees cooler than forecast. Better potential for stratus and light precip/drizzle development appears to be Sunday Night into Monday morning, with strong theta-e advection over a warm front to the south of the region. Potential for an icy mix across Lower Hudson Valley and Southern CT in this pattern, which would result in a hazardous Monday Morning commute for these areas.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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Models in good agreement with PAC shortwave energy digging through the SW states, and eventually phasing with subtropical jet energy tonight into Sunday. The resultant deep closed upper low is then expected to track NE across the Central Plains and Mid Mississippi valley Sun into Mon, before beginning to phase with northern stream energy as it swings into the NE US on Tuesday. Timing/phasing differences have decreased with these energies, with increasing confidence in track of primary low pressure through the Great Lakes Monday Night into Tuesday, and secondary low pressure developing in vicinity of the region Tuesday and lifting into New England Tuesday Night. Model-to-model and run-to-run consistency continues for a quick moving moderate to heavy rain event for Monday night into Tuesday, in response to strong deep layer lift (region under of nose of 65-75 kt LLJ and left front quad of a 125+ kt jet streak in difluent upper flow) of a subtropical moisture plume with PW +2 to + 3 standard deviations above normal over the region, focused ahead of the cold front and a surface wave. Cant rule out some embedded thunder as well with the strong forcing and weak elevated instability. Despite a low level inversion, a period of 30 to 40 mph gusts appears likely for LI/SE CT Tue ahead of cold front as a 60-70 kt 950mb llj works over this region, with a low prob for a few gusts to around 50 mph being mixed down with any convection/heavy rain. Before that, on Monday, the warm front will likely be unable to move north through the region until llj works into the region Monday Night. This based on cold air damming signal from high pressure nosing down the coastal plain from SE Canada. This will likely spell chilly conditions with stratus, drizzle, and light rain showers continuing Mon into Mon eve. Icy conditions may linger into the afternoon for interior locales, particularly in the CT River Valley due to cold air drainage. The frontal system pushes through Tuesday afternoon, with breezy conditions and CAA in its wake, returning dry and more seasonable temps for mid to late week.
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&& .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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High pressure remains centered to the southwest of the region today. A weak frontal passage occurs tonight. VFR through the TAF period. SW winds today veer to the WNW tonight behind the frontal passage. Gusts to around 25 kt are possible at times after 14Z til around 22Z or later. Sustained winds may be stronger at JFK and ISP. .OUTLOOK FOR 12Z SUNDAY THROUGH WEDNESDAY... .Sunday...VFR. .Monday...Chance of MVFR or lower in -SHRA. S winds G20KT late day. .Tuesday...IFR in rain. LLWS. S winds G25KT morning, W winds G30- 35KT aftn. .Wednesday...VFR. W winds 15-25KT with G25-30KT.
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&& .MARINE...
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An initially weak pressure gradient will increase over the forecast waters through the day as a cold front approaches. Seas are expected to increase once again in response, while SCA-level gusts will be possible on all waters by afternoon. A few gusts to near gale-force will be possible on the eastern waters. The front passes east this evening, with winds and seas gradually decreasing thereafter as high pressure builds across the area once again. Apart from the possibility of some lingering 5-ft seas into Saturday night, the remainder of Sunday into Monday should be somewhat tranquil as the high passes east. Conditions will then become increasingly hazardous into Monday night as a potent low pressure system approaches the area. As a warm front passes to the north Monday night, winds will rapidly strengthen, with gale-force winds possible particularly on the eastern waters into Tuesday afternoon. Seas will rapidly build in response to the strengthened flow. As the cold front follows and pushes east Tuesday evening into Wednesday, seas will remain elevated, while gusts to gale-force may be possible into Tuesday night. Expect at least SCA- level conditions to continue on all waters into Thursday as the pressure gradient remains strong between the departing low pressure and a building high.
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&& .HYDROLOGY...
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A frontal system passing through late Monday night into Tuesday has the potential to bring 1/2 to 1 1/2 inches of rain. No significant hydrologic issues are anticipated at this time.
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&& .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...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ330- 335-338-340-345. Small Craft Advisory until midnight EST tonight for ANZ350-353. Small Craft Advisory until 6 PM EST this evening for ANZ355.
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&& $$ SYNOPSIS...NV NEAR TERM...NV SHORT TERM...NV LONG TERM...NV AVIATION...MD MARINE...MD HYDROLOGY...NV EQUIPMENT...

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