South School, NY Hourly Weather Updates

Key Messages

1) Isolated to scattered showers with strong wind gusts possible early this evening.

2) A period of moderate to heavy rain and embedded thunderstorms likely Sunday afternoon into Sunday night, with additional scattered showers and thunderstorms possible Monday.

Discussion

... .KEY MESSAGE 1... Surface trough or weak cold front and a shortwave aloft pass through the area this evening. Lift from the two features will interact with fairly shallow moisture concentrated in the 850-700mb layer. There will be a chance of showers into the evening, but thunderstorm chances appear to be limited with the lack of moisture above 700mb and some capping beneath -10C. Even without thunder, showers could produce strong wind gusts with steep low level lapse rates with a dry sub-cloud layer and a wind profile favoring downward momentum transfer. Highest chances of showers will be east of NYC.

.KEY MESSAGE 2... Developing low pressure center approaches the forecast area before tracking near/over us late Sunday night into Monday morning. Potential flooding and strong/severe wind gust impacts will depend on where the storm center tracks, and at this time, guidance leans toward a track over or just south of us. The primary threat therefore appears to be for a period of moderate to heavy rainfall Sunday afternoon/night with approaching shortwave lift and warm front plus a developing 30-40kt llj lifting high moisture (2-2.5" PWAT). The period when flooding would be most likely is mid- afternoon Sunday until around midnight. East of NYC, flooding threat is overall lower due to current FFG values, but heavy rain with a threat of at least minor nuisance/poor drainage flooding would be possible mainly during Sunday night.

An isolated strong to severe thunderstorm threat still exists Sunday afternoon and evening due to the uncertainty of the exact track of the low center in our vicinity. A low track over or to the north of the region would promote high shear/helicity, albeit with weak instability. Still fairly low predictability on thunderstorm coverage and severity at this time. Did not deviate from NBM regarding thunder chances, but it`s beginning to look like the chance of severe weather is low and more likely to be confined to the southern half of the forecast area if it were to occur.

Additional iso-sct shower and thunderstorm activity is possible on Monday with a trailing slow cold front, but severe wx does not look likely.

Aviation

/00Z SATURDAY THROUGH WEDNESDAY/... A weak cold front or surface trough passes through the area this evening, followed by high pressure building in from the northwest.

Mainly VFR conditions are expected through the TAF period. Exception is east of NYC terminals this evening in any showers where brief MVFR conditions are possible.

Winds will become light and variable this evening before becoming NE at less than 10kt behind the passing front or trough. Winds will then veer to the S/SE at 5-10kt at the coastal terminals.

...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

Wind direction will likely vary considerably this evening as a weak cold front or surface trough passes through the area.

Timing of winds shifts on Saturday, especially at the coastal terminals may vary by 1-3 hours.

.OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY...

Saturday Night: VFR.

Sunday: Mainly VFR in the morning. Increasing potential for MVFR or lower thereafter with showers developing and moving in. Widespread showers, potentially heavy at times at night with potential IFR. Slight chance of thunderstorms. Southerly wind gusts near 15-20 kt afternoon into night.

Monday: MVFR or lower early with showers. Otherwise, improving conditions throughout the day with eventual return to mainly VFR.

Tuesday: VFR.

Wednesday: Mainly VFR. Chance for showers and MVFR at night. Southerly wind gusts 15-20 kt afternoon into night.

Detailed information, including hourly TAF wind component forecasts, can be found at: https:/www.weather.gov/zny/n90

Watches / Warnings / Advisories

/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None.