Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gray ME
933 PM EDT Thursday Jul 31 2014
high pressure will build in from the east today through Friday.
Afternoon showers and thunderstorms are possible primarily in the
mountains each day through the middle of next week.
Near term /through Friday/...
have updated the grids based on current observations and satellite
imagery. Any remaining precipitation will continue to
weaken...with perhaps a corridor from Wells to psm keeping the
chance of a shower through 03z. Mesoscale models have a good
handle on these showers as they dry up and move off to the east.
Otherwise...just minor tweaks to the winds...dew point and cloud
grids. Have removed any enhanced wording and updated the severe weather potential statement.
main focus is on the thunderstorms in the immediate near term.
Slow heating has occurred today beneath a mostly cloudy sky
across New Hampshire. This has prevented much of the state from reaching
convective temperatures. However...farther east readings climbing
into the middle 70s have triggered scattered thunderstorms across
Maine. For now the storms are struggling to maintain much
height...but with time cooling aloft should support continued
updraft growth. Expect that cape will remain less than 1000 j/kg
for much of the area...but adequate shear will help to keep some
organization to the convection. A few large hail or damaging wind
reports will still be possible. So far the main forcing with
shortwave trough has produced a broken line of
thunderstorms...with gusts around 30 knots and small hail. Though
one cell briefly attained supercell characteristics on the
southern end of the line and managed to produce 1 inch hail. Feel
that this is a fairly good representation of what we can expect
across New Hampshire and then Maine this evening. Will maintain gusty winds
and small hail in the grids until 01 or 02z.
Various convective tools...including Storm Prediction Center sseo and hi-res
models...rapidly weaken storms after sunset. Pop forecast drops off
quickly accordingly. Expecting that fairly widespread valley fog
occurs inland...with coastal fog/stratus reloading from the
midcoast down to kpwm.
Short term /Friday night/...
overall cold pool remains aloft at 500 mb on Friday...which will allow
for another round of afternoon convection. However...middle level
warm advection will result in a larger cap than today. This will
keep a lid on any storms that do form...precluding any severe
threat. Also lightning probably will not be as widespread as today
either...so have adjusted chance of thunderstorms down.
Late Friday night approaching disturbance riding up the East Coast
will begin to spread clouds into the area from the S. Should
remain mostly dry through sunrise...but have some low chance pop
sneaking into southern New Hampshire by 12z.
Long term /Saturday through Thursday/...
story of the long term will be a persistent trough over the Great
Lakes region... with the northeast being on the east side of the
trough axis. Several minor waves will pass through the flow on the
east side of the trough and aid in the development of showers and
storms mostly during peak heating. Cool air aloft also keeps the
atmosphere weakly to moderately unstable as the sun warms the low
levels. The result is that the forecast for this weekend and next
week gets pretty redundant. Showers and storms are possible just
about every afternoon... mainly in the mountains... with
temperatures below normal.
Saturday... shower activity should be primarily confined to the
mountains. Overall instability is weak so thunderstorms will be
A sharper shortwave trough tracks across the area Sunday... with a
possible surface warm front moving north as well. This will bring
a better chance of showers and isolated thunderstorms to the
entire area. The NAM is the most aggressive with the warm frontal
feature... and as such... the NAM wind fields would indicate some
pretty good low level directional wind shear along and north of
the warm front. So any showers or storms which develop along the
warm front could see a weak spin up... but the overall threat will
remain low especially since the other models do not show as
dramatic of a warm front.
Great Lakes trough becomes broader and less amplified Monday...
but will still see the diurnal chance for showers in the
mountains. This trend continues right through the middle of the
week and the end of this forecast period.
Aviation /02z Friday through Tuesday/...
short term...any showers/thunderstorms will quickly end after
sunset...with skies clearing. Any VFR will be short lived
though...as valley fog will be quick to set in with nocturnal
cooling of the boundary layer. In addition...guidance suggests
coastal fog/stratus will redevelop...especially into the midcoast
by 03z. IFR or lower conditions will be possible again...lingering
into middle morning Friday. Mainly VFR is expected Friday
afternoon...with showers or an isolated thunderstorm possible
across New Hampshire. Late Friday night MVFR or lower ceilings may begin to
work northward into the area as a disturbance moves up the East
Long term...generally VFR but there will be a chance for afternoon
showers and storms mainly in the mountains. Nocturnal fog is also
possible at Lebanon and Whitefield.
short term...any thunderstorms that graze the waters will weaken
quickly after sunset. Sub- Small Craft Advisory conditions are expected through
Friday...however areas of dense fog will be present tonight
especially off the middle coast of Maine.
Long term...generally light winds and low seas expected through