Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Gray ME
514 PM EDT Thursday Jul 30 2015
a cold front will cross the region tonight. A weak ridge of high
pressure will build in from the west on Friday. A broad shallow
trough of low pressure will settle into the northeast Friday night
and will persist through the weekend as high pressure builds south
of New England. A weak cold front will cross the area Saturday.
Another cold front will approach from the west on Monday and will
slowly cross the area on Tuesday. A trough of low pressure will
linger over the region on Wednesday.
Near term /tonight/...
update...a line of showers with embedded stronger storms continues
to advance across New England at this hour. Pockets of at least
marginal instability have allowed for some of these isolated
stronger cells to develop within and ahead of the line.
However...with time the more stable marine environment near the
coast will limit strength of convection. Apart from southern New Hampshire...where
instability will remain elevated the longest...the main threat
appears to be transitioning towards brief heavy rainfall.
Have updated the grids to reflect latest timing based on radar and
mesoscale model trends...as well as adjusted quantitative precipitation forecast grids to isolate
the areas at the greatest risk for heavier precipitation.
Previous discussion...at 18z the surface cold front was entering
western New England. National Weather Service Doppler radar mosaic showed a line of
showers and scattered thunderstorms along and ahead of the
front...with widely scattered convection forming out ahead of the
main line of convection. With the exception of a few middle coast
Maine locations...temperatures have warmed into the 80s and lower
90s ahead of the front with dewpoints ranging from the middle 60s to
lower 70s. While severe weather parameters are not
impressive...can't entirely rule out an isolated cell or two with
strong wind gusts as the convection moves into our area this
afternoon and early evening. Precipitation will end from west to
east this evening as the front sweeps eastward...with any
lingering activity sliding offshore by midnight along with the
front. Lows tonight will range from upper 50s to middle 60s with
patchy fog developing overnight.
Short term /Friday through Friday night/...
on Friday...westerly flow and weak ridging should provide a
partly to mostly sunny day. However...can't entirely rule out a
brief shower in the higher terrain near our international border.
It'll be less humid with highs mainly in the 80s. Partly cloudy
Friday night...with a low chance of a shower after midnight for
far northern and western sections ahead of next disturbance. Lows
will range from the middle 50s to the lower 60s.
Long term /Saturday through Thursday/...
broad shallow surface trough reflecting a large closed low
over east central Canada will settle in for the weekend. A
weak cold front will push in from the west Saturday afternoon
kicking off showers and thunderstorms. Good shear will be in
place so the potential will be there for some severe storms.
High temperatures on Saturday will be from the middle 70s to middle 80s.
The front will push offshore Saturday night as high pressure
builds south of New England. Any lingering showers will end
during the evening. Looking for partly cloudy skies overnight
with lows in the middle 50s to lower 60s.
Closed upper low will bring instability and some showers and
possible thunderstorms to northern zones on Sunday. Convective available potential energy will
be rather marginal but should be enough to produce isolated
convection. Remainder of the region will see a mix of sun and
clouds. Highs once again will range from the middle 70s to middle 80s.
Another weak disturbance rotating around the closed low will
bring a chance of showers Sunday night but these will be brief
and widely scattered and will push east of the region by Monday
A cold front approaching from the west will bring another chance
of showers and thunderstorms to the region Monday. Area most likely
to see convection would be northwest zones. Expect showers and
thunderstorms to continue Monday night as the front slowly pushes
in from the west. Slow moving front will finally cross the area on
Tuesday. Should be enough lingering instability to kick off more
convection before drier and more stable air pushes in from the
west in the afternoon.
Closed upper low will settle into the northeast Tuesday night and
Wednesday bringing much cooler air into the region. Cool and
unstable air will likely result in a lot daytime clouds and
possible showers. High will average out below normal for much of
the remainder of the week.
Aviation /21z Thursday through Tuesday/...
short term /through 11z Sat/...areas of MVFR through 06z in rain showers
and scattered thunderstorms and rain. Local IFR possible in fog and stratus by the way 06 and 12z Friday.
VFR throughout Friday and Friday night.
Long term...VFR Saturday through Tuesday with areas of MVFR/IFR
ceilings and visibility in scattered daytime convection.
short term /through Friday night/...the outer waters briefly approach
20 knots and 5 feet for a few hours tonight with a cold frontal passage
but should remain below small craft threshold.
Long term...no problems noted.