Groton, Connecticut 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

336
FXUS61 KOKX 152140
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
540 PM EDT Thu May 15 2025

.SYNOPSIS...
A warm frontal boundary moves in from the south this evening and
stalls within the area. Associated weak low pressure moves
across late tonight into early Friday. Thereafter a surface
trough moves across Friday and another one moves across
Saturday. A low to the north sends a cold front through
Saturday night. This low lingers in New England and into the
Canadian Maritimes through Monday as high pressure pushes in.
High pressure remains in control Tuesday into Tuesday night.
Another frontal system impacts the area Wednesday into Thursday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Hourly temperatures were running just a tad cooler than forecast
thin evening and have been adjusted accordingly. Otherwise, the
foecast remains on track.

For tonight, with any instability decreasing with the loss of
diurnal heating, shower and thunderstorm coverage is expected to
considerably decrease with the absence of any significant
synoptic lift. Upper level trough will be shifting east of the
area, taking the highest positive vorticity advection farther
east of the region.

Winds become light and variable direction. Another night of low
clouds and fog is expected across the area. A relatively warmer
guidance for low temperatures tonight using MET/NBM ranging from
the mid 50s to lower 60s.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/...
A subtle mid level shortwave moves across Friday with some
associated positive vorticity advection. At the surface, the
frontal boundary across the area dissipates, leaving a general
weak pressure gradient between low pressure well to the north
and west and high pressure well to the south and east.

Light southerly flow at the surface is expected. A warmer day is
expected. NBM/NBM 50th percentile combination used for daytime
high temperatures, well into the 70s for most locations and some
locations reaching 80. More instability will be generated at the
surface as a result, making for a higher chance of showers and
thunderstorms. Marginal risk for damaging winds with these
thunderstorms, particularly for areas that have more
instability.

The convection trends downward Friday night with the loss of
diurnal heating. Winds in lower levels increase. This will keep
warmer min temperatures Friday night. Again used combination of
NBM and NBM 50th percentile, with lows ranging from upper 50s to
lower 60s. Fog will be possible but was not put in forecast due
to uncertainty with how well mixed boundary layer could be.

Upper level low approaches the region Saturday with greater
height falls. At the surface, a cold front approaches from the
north and west. There is a likely a pre-frontal trough that
develops that will be the focus for convective initiation.
Chances for showers and thunderstorms increase during the day
with highest chances mid afternoon through early evening.

The southerly flow increases Saturday and with further increase
in winds in 5-10 kft, bulk shear increases. Warmer temperatures
are forecast also using NBM and NBM 50th percentile. Outside of
Twin Forks and SE Connecticut which have highs more in the lower
70s, rest of area is in mid 70s to near 80 with NYC Metro and
parts of NE NJ getting more into the lower 80s. With more low
level instability and more bulk shear, there is more of a risk
for damaging winds with thunderstorms. SPC has western parts of
the region with a slight risk for severe thunderstorms.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Messages:

 * A cold front cuts off precip Saturday night.

 * Becoming mostly sunny on Sunday with only slight chances for
   showers.

 * Dry & quiet Monday into Tuesday.

 * Another frontal system may bring a return to rainfall Wednesday
   into Thursday.

A surface low in southern Canada/northern New York sends a cold
front through Saturday night. Showers and/or any remaining
thunderstorms diminish with the passage of the cold front with drier
air getting advected in.

Mostly sunny skies take over as high pressure gradually builds in
from the northwest. To our northeast, low pressure will continue to
exit into New England and into the Canadian Maritimes through
Monday. This will lead to breezy W/WNW winds from an increased
pressure gradient through Monday.

An upper-level trough to our west on Saturday passes east SUnday
night. As it moves farther away, it takes the surface low with it
farther out to sea Monday night and thereafter. This allows a ridge
to our west with high pressure at the surface to fully take hold, if
briefly, Tuesday into Tuesday night. Dry conditions continue with
winds becoming light under a weak pressure gradient.

A frontal system from the Great Plains then moves into the Ohio or
Tennessee River Valleys on Tuesday, moving through or in the
vicinity of our region Wednesday into Thursday. Expecting showers
during this timeframe. Too soon to call chances for thunderstorms.
MOdel guidance still varies with timing, magnitude, and track of
this frontal system. Have gone with chance POPs Wednesday into
Thursday, as a result.

Temperatures look to cool each day in the long-term period. Highs on
Sunday will be in the low/mid 70s with all highs in the mid/upper-
60s by Wednesday. Nightly lows will range from the mid-50s to the
mid-40s.

&&

.AVIATION /22Z THURSDAY THROUGH TUESDAY/...
Low pressure weakens and passes near or just south of Long Island
tonight. Another weak low approaches late Friday morning.

Conditions vary significantly across the region from LIFR to VFR as
breaks in the overcast have developed along the south coast of Long
Island. Periods of VFR are possible along the coast into early this
evening. Toward sunset conditions lower again to LIFR and IFR, and
at times late tonight VLIFR. Conditions will be improving to MVFR
Friday morning. There will be a chance of showers with thunderstorms
Friday afternoon. Low confidence forecast with timing and conditions
for tonight.

Winds light E/SE to light and variable become light and variable
throughout during this evening. A light south flow develops Friday
morning.


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

Amendments expected for changing flight categories throughout the
TAF period.

.OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY...

Friday afternoon: MVFR with showers and a slight chance of tstms.

Saturday: MVFR. possibly IFR in the morning, becoming VFR in the
afternoon with showers likely, and a chance of thunderstorms with
MVFR.

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

Monday - Tuesday: VFR. Monday NW winds G20-25kt.

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

&&

.MARINE...
Generally weak pressure gradient in place in the short term
through Saturday with conditions remaining below small craft
advisory thresholds.

Winds and waves are currently expected to fall below SCA criteria
Saturday night through Tuesday. However, wind gusts may near SCA
criteria on all waters Sunday under an increased pressure
gradient.

&&

.HYDROLOGY...
Basin averaged amounts with showers and thunderstorms is
expected to be near quarter to a half inch with locally higher
amounts through Saturday. Thunderstorms could result in areas
experiencing minor flooding, especially within urban, low lying
and poor drainage areas. With increasing translational speed to
thunderstorms, flash flooding is not expected.

There are currently no hydrologic concerns Saturday night through
the middle of next week.

&&

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

&&

$$

SYNOPSIS...JM/BR
NEAR TERM...JM/BR
SHORT TERM...JM
LONG TERM...BR
AVIATION...MET
MARINE...JM/BR
HYDROLOGY...JM/BR