Scientific Forecaster Discussion
fxus61 kgyx 120849
Area forecast discussion
National Weather Service Gray ME
349 am EST Tue Nov 12 2019
low pressure will exit into the Canadian Maritimes this
afternoon. Behind this system, gusty winds will allow much
very cold air to enter the region tonight and Wednesday. High
pressure will crest over New England Wednesday night, with dry
conditions and very cold air over the region. Dry conditions
will linger into Thursday, with a moderating trend ahead of an
Arctic front on Friday. This strong front will cross the region
Friday evening, followed by a dry, but chilly weekend.
Near term /until 6 PM this evening/...
cold air damming firmly in place as a second wave of
precipitation, this one associated with the cold front,
approaches the area. Low pressure is currently over eastern PA
with height falls of 5mb/3hr over Calais pushing the system up
the coast of Maine. Aloft, most of our area remains in the
classic warm sector with the warm frontal cloud shield located
along the Canadian border and cold front draped down approaching
the Champlain and Hudson valleys. While the warmth has entered
aloft the surface is a different story. Northeasterly flow
is across Maine and extends out into the coastal waters. The
coastal front is located east of the 44007 buoy well out into
the Gulf of Maine and reaching shore south of Boston, Massachusetts. Kgyx
00z sounding showed a fairly deep cold layer,extending up to
850mb, and the kmwn observation of 28f in the last hour
continues to support that.
Cold at the surface and warm aloft sets US up for a classic
freezing rain scenario. In this case the one part missing is the
rain as there is not really any widespread precipitation across
the cold pool at the moment. There is however, plenty of low
level moisture and thus freezing drizzle becomes the ptype of
choice this morning. With that in mind, have expanded the Winter
Weather Advisory to all of southern New Hampshire. While the
cold pool is not as robust as it is across southern Maine we do
see some reports of below freezing temperatures, especially in
the higher elevations of Hillsborough and Cheshire counties and
suspect that elevated surface and colder locations are seeing
freezing drizzle. With the heavier precipitation arriving right
in time for morning travel and dewpoints below freezing expect
the freezing drizzle to transition to a mix of sleet and snow as
the front moves in. While there won't be much accumulations
across southern NH, any amount is enough to be slippery and so
the advisory has been expanded.
The cold front will cross the area later this morning bringing
with it another burst of precipitation. With the cold air expect
this to be mainly in the form of snow, although a brief mix of
sleet at onset is possible further south. Temperatures may
briefly warm to the upper 30s as the front moves through and is
finally able to mix out the cold air but that warmth will be
very short lived as the Arctic air on the backside of the front
comes quickly into the region.
Short term /6 PM this evening through 6 PM Wednesday/...
cold air advection is the theme overnight with temperatures
steadily dropping. The breezy northwesterly flow and cloud cover
will keep the environment well mixed but well mixed cold air
mass will still put temperatures down into the single digits in
the north and teens south. Wednesday the cold air just keeps
coming with temperatures remaining well below freezing across
the region. High pressure will begin to build into the region
allowing for the winds to diminish making way for an even colder
night on Wednesday.
Long term /Wednesday night through Monday/...
high pressure crests over the region Wednesday night with 800 mb
temperatures running in the -12c to -14c range. With clear
skies, light winds and a fresh snowpack in some areas,
temperatures will bottom out rather quickly leading to the
coldest night of the season. Have chosen this night as a target
of opportunity to forecast below most available guidance. Will
forecast near record breaking overnight low temperatures in some
locations with readings dropping down to near zero in the north
to the lower to mid teens in the south. Only fly in the ointment
will be for approaching mid and high level cloudiness from the
west which could potentially shut down the radiational cooling
late at night.
Warm air advection around the periphery of the departing high
pressure system and a weak disturbance aloft will allow for some
cloudiness and possibly some mountain snow showers on Thursday.
We can expect a moderating trend on Friday ahead of an
approaching Arctic front. Daytime temperatures will peak out in
the 35 to 45 degree range in most areas.
Late Friday afternoon and Friday evening, an Arctic front will
cross the region. There will be scattered snow showers and
possibly a snow squall which will mainly be confined to the
mountains and foothills.
Dry and chilly conditions will follow for the weekend.
Aviation /08z Tuesday through Saturday/...
short term...widespread IFR conditions across the region as low
level moisture remains trapped by a surface cold pool. Expect
period of freezing drizzle across the region this morning for
all but the southernmost terminals. A cold front will cross the
region today with temperatures dropping rapidly behind it. As
the temperatures drop, the ceilings improve as we move into
northwesterly flow. VFR returns for Wednesday with much colder
Long term...mainly VFR conditions through the period. However,
the mountains may have a few scattered snow showers and MVFR
conditions at times through the period.
short term...nely flow under cold air damming along the coast
will reverse course midday as a cold front crosses the coastal
waters. Behind the front look for strengthening cold air
advection with winds gusting to gale force. Gale warnings remain
in effect for the outer waters. Winds will begin to diminish on
Wednesday as high pressure starts to build in.
Long term...winds will finally be diminishing over the waters
Wednesday night. Southwesterly winds will be on the increase
Friday ahead of a strong front. Behind this front, wind gusts
may approach gale force by Saturday morning.
ME...Winter Weather Advisory until 7 PM EST this evening for
Winter Storm Warning until 7 PM EST this evening for
New Hampshire...Winter Weather Advisory until 7 PM EST this evening for
Winter Storm Warning until 7 PM EST this evening for nhz001.
Winter Weather Advisory until noon EST today for nhz011>015.
Marine...Small Craft Advisory from 1 PM this afternoon to 6 PM EST
Wednesday for anz151-153.
Gale Warning from 1 PM this afternoon to noon EST Wednesday