Marine Weather and Tide Forecast for Old Greenwich, CT

NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
Digging trough and upper low over the Upper Midwest swings east across the Great Lakes region, sending an associated frontal system toward the region. Warm front analyzed to the southwest over the Mid Atlantic begins to approach and lift through tonight.

With multiple spokes of vorticity rounding the trough, there will be a chance of showers and still a chance of a thunderstorm late tonight pushing in from the west. Only other shower activity before this would be any showers popping up offshore to the south as a shortwave passes through and taps into a little bit of elevated instability. Otherwise, likely see areas of fog development once again overnight with light flow and abundant surface moisture. Not thinking the fog will be as widespread or as dense as it was last night since winds near the top of the boundary layer are stronger this time. Still can't completely rule out dense fog in a few hours.

SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/
Upper level low and trough over the Great Lakes pivots east on Saturday, as a vigorous shortwave tracks across the Mid Atlantic.
A warm front lifts thru by the morning, as the associated surface low slides into Quebec. The attendant cold front looks to move through locally in the early to mid evening.

A challenging convective forecast with uncertainty on timing and coverage of any morning activity. The approaching cold front adds more in the way of forcing as the day progresses, and breaks in the clouds should develop by the afternoon. 12z HRRR is progging MLCAPE values as high as 1500 J/kg, along with bulk shear values 30 to 40 kt. That said, cloud cover could limit this instability, and subsidence behind any previous MCS could help to cap the low levels as well. It now appears the core of the shortwave energy passes north and west by mid afternoon, and could help limit any organized severe threat locally. With this, SPC has lowered their threat locally from a slight to a marginal, which seems reasonable based on the above and continued uncertainty.

CAMs aren't overly aggressive in depicting convective development, but should initiation occur, damaging wind gusts would be the primary threat, though large hail and even an isolated tornado cannot be ruled out in the environment.
Coverage looks isolated to scattered, especially across the LoHud Valley and southern CT.

Cold frontal passage progged around 00Z Sun, and behind it winds veer westerly into the overnight, with drying conditions overnight as dew pts fall back into the lower 50s by daybreak.

LONG TERM /SUNDAY THROUGH FRIDAY/
Key Messages:

* Mainly quiet & pleasant weather Sunday through Tuesday.

* A frontal system may will bring rainfall Wednesday, possibly into Thursday and Friday.

A surface low w/ an associated upper-level low will be located over New England Sunday. This low will exit into the Canadian Maritimes by Monday.

This low will bring a second cold front through on Sunday night helping clear out partly to mostly cloud skies and advecting in drier air. This leaves late Sunday night into Monday mostly clear/sunny. A few showers are possible in the northern interior, closer to the periphery of the low Sunday afternoon/evening, but chances look quite low.

A quick moving shortwave will pass over or just to the north of the area Monday afternoon/evening. This may lead to a few clouds, but otherwise, we will remain clear and sunny late Sunday night through most of Tuesday.

An increased pressure gradient from the low to our northeast will lead to breezy W/NW flow Sunday and Monday. As the low exits farther away, the gradient weakens, leaving light winds by Monday night. It remains this way with high pressure at the surface through Tuesday.

12Z guidance still varies in timing and track of a frontal system for the middle of next week. A low over TN/KY late Tuesday will approach the area Tuesday night and pass near or to the south of the area Wednesday into Thursday, pushing more north and/or east of the area on Friday. This will bring a period of wet weather. There is higher confidence in showers on Wednesday, but confidence is lower Thursday and especially Friday and models diverge on a solution.

Sunday and Monday will see highs in the upper-60s to mid-70s, right around the climatological average. Temperatures will be much cooler from a passing frontal system on Wednesday with highs in the low-60s under E/NE flow.

AVIATION /03Z SATURDAY THROUGH WEDNESDAY/
A warm front moves partially through the area tonight then advances further north on Saturday. A cold front follows for Saturday evening.

Conditions lowering to IFR everywhere tonight, improving to MVFR mid-morning Saturday, then VFR in the afternoon. PROB30 for TSRA Saturday afternoon into early evening.

Southerly flow 5-10 kts expected through mid-morning Saturday, then southerly winds pick up to 10-15 kt with some gusts up to 20 kt in the afternoon.

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

Timing of category changes could be off by a couple o hours.
Tempo or prevailing vsbys of 1/4sm possible at KJFK from 08-12z Sat.


OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY

Saturday: Mainly VFR but MVFR possible in the afternoon with chance of showers and thunderstorms with MVFR or lower conditions possible.

Sunday: Mainly VFR. Slight chance of showers inland with MVFR possible. W winds G20-25kt.

Monday - Tuesday: VFR. Monday NW winds G20-25kt day into evening.

Wednesday: MVFR or lower with showers likely, mainly at night. E wind gusts 15-20 kt.

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

MARINE
Areas of fog likely return tonight, potentially becoming dense and persisting into mid Saturday morning. A Dense Fog Advisory may be needed, with the potential for vsbys to fall to less than 1 nm at times overnight into Saturday AM.

Winds and waves remain below Small Craft Advisory (SCA) criteria through at least Saturday night.

Sunday afternoon and evening, wind gusts may marginally reach SCA criteria for the NY Harbor, western Sound and western Ocean.
Otherwise, sub SCA conditions are expected on all waters thereafter through Wednesday. A passing frontal system will lead to ocean seas climbing 5-7 feet Wednesday night through Thursday night.

HYDROLOGY
Locally heavy downpours are possible with any thunderstorms through Saturday aft/eve. While the overall flash flood threat is low, the brief heavy rainfall could lead to minor nuisance flooding in urban and poor drainage areas.

There are no other hydrologic concerns through the end of next week.

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