Lebanon, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

615
FXUS61 KGYX 302211
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
611 PM EDT Fri May 30 2025

.SYNOPSIS...
Showers will gradually diminish tonight with the loss of daytime
heating. However fog and low clouds will begin moving in from
the Gulf of Maine overnight ahead of a strong late spring storm.
A widespread, soaking rainfall will move through the region
during the first half of Saturday. Rain could be heavy at times,
but overall it looks like a steady light to moderate rainfall.
The storm will wind down to showers Saturday night and showers
may linger into Monday before beginning to clear out.
Temperatures will also be much cooler Sunday into Monday. After
that we become warmer and drier as high pressure builds across
the Northeast for much of next week.

&&

.NEAR TERM /THROUGH SATURDAY/...

6 PM UPDATE...Forecast remains on track. A few edits were made
to cloud cover and temperatures to reflect most recent
observations.

Previously... Diurnal showers have popped up mainly across two
parts of the forecast area. One in the mtns...where elevated
heat source is the primary driver of convection. The second is
over southeastern NH where a little convergence band has
developed and is forcing showers northeast along it. Not seeing
much evidence of ice in the cloud tops just yet...but I would
not rule out a rumble of thunder from any of these.

Otherwise most of tonight should be dry and mild for this time of
year. There is a fog bank lurking off the tip of Cape Cod...and hi-
res guidance brings it onshore around or just after midnight. This
seems reasonable to me...so I have used the HRRR for timing of fog
and low clouds in the forecast.

&&

.SHORT TERM /SATURDAY NIGHT/...
Most of the precip will arrive after sunrise Sat...so I will include
that in this portion of the discussion. A well defined S/WV trof
crossing the Appalachians today will lead to cyclogenesis early Sat
along the Mid Atlantic coast and crossing southern New England.
Model guidance is converging on a track that cuts across ME...so it
looks increasingly like we will experience the WAA precip but
largely miss out on the deformation banding. With the dry slot
moving over much of the southeastern part of the forecast area I
suspect that model QPF may be slightly high once WAA precip shuts
down. So I lowered QPF after 18z Sat for those areas...and storm
total precip is now just below 1 inch. In the mtns where southeast
upsloping and more of the wrap around precip occurs totals remain 1
to 1.5 inches. Still do not anticipate any flood threat out of this
event...but the risk if there was any is shifting west.

Sat night will remain unsettled and showery. The focus will
primarily be in the higher terrain...where northwesterly upslope
helps to drive the lift. With clouds and showers around the temps
should remain mild.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Overview...

The upper level low associated with the Saturday system slowly
exits through New England on Sunday. High pressure begins to
build in on Monday. The high continues to build on Tuesday,
along with a moderating trend. The highs moves offshore by
Wednesday, with a building warm airmass and moisture for
Wednesday and Thursday. A cold front then approaches late in the
week from the west.

Details...

Sunday sees relatively drier conditions as the upper level low
moves through New England. More breaks of sun allow temps to
warm into the mid 60s south of the mountains, with 50s across
the higher terrain. With the cold air aloft, pop up clouds and
showers likely develop by the early afternoon after some morning
sun and heating, especially across the higher terrain. These
dissipate late in the day, with a drying trend Sunday night.

High pressure builds in from the south on Monday, marking the
start of a multi day warming trend for next week. With WSW flow,
warmer temperatures likely reach the coast on Monday, before a
shift to a sea breeze late in the day. Highs are generally
expected to reach the 70s downwind of the mountains, with 60s
across the higher terrain. Some clouds are possible through the
first half of the day as the last of the trough exits, with more
sun by late in the day.

The warming trend continues through the week as the high
builds, and then shifts offshore Wednesday, setting up a more
synoptic southwesterly flow. Widespread 70s look likely for
Tuesday, and widespread 80s for Wednesday and Thursday. With the
high offshore, a stronger sea breeze would be expected along
the coast each day after a quick morning warm up. Humidity also
begins to increase by Thursday, with dew points in the 60s
looking increasing likely.

By late in the week, a cold front likely approaches from the
west. The progression of this front is still quite uncertain,
and still a week away. A strong ridge builds across the
Northeast by late in the week, and is unlikely to break down too
quickly with the approaching front. This leads to some spread
amongst the models on just how quickly it will move, or if it
even ends up arriving at all. Regardless of whether it arrives
or not, chances for showers and storms increase late in the week
in the moistening airmass, and warmer conditions are likely to
continue until the front passes. The one other feature to watch
by the end of the week and into the weekend would be high
pressure building from the north with the potential for a back
door cold front in the late week to weekend time frame.

&&

.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
Short Term...VFR conditions this evening will give way to an
expanding marine stratus layer around midnight. Areas of IFR or
lower are expected from PSM to all western ME terminals. Near
the coast fog may become dense at times. Rain will move in near
daybreak and may act to mix out the fog a bit. Low CIGs will
remain until winds shift to a west of north direction. Despite
that there may be lingering MVFR CIGs into Sat night.

Long Term...Some MVFR conditions with showers are possible on
Sunday, especially at HIE. Mainly VFR prevails early next week,
but nighttime valley fog will be more likely mid to late in the
week. Some marine fog will also be possible at RKD by Thursday.

&&

.MARINE...
Short Term...South winds will continue to turn onshore thru
overnight. Areas of fog are expected to develop across all
waters and fog may be dense at times. With low track now
forecast more inland that will to a longer and stronger duration
of onshore winds before shifting to southwest. I increased wind
speeds Sat slightly to go along with building seas...so a
period of SCA conditions is looking more likely Sat.

Long Term...Marginal SCA conditions linger into Sunday with
southwesterly flow behind the departing low, and lingering seas.
High pressure then slowly builds across the waters early next
week, and shifts offshore by midweek. SCA conditions will be
possible in increasing southwesterly flow from Wednesday through
the end of the week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$


UPDATE...Palmer
NEAR & SHORT TERM...Legro
LONG TERM...Clair
AVIATION & MARINE...Clair/Legro