Scientific Forecaster Discussion
fxus61 kgyx 180244
Area forecast discussion
National Weather Service Gray ME
1044 PM EDT Tue Sep 17 2019
a reinforcing shot of cooler air invades tonight with patchy
frost across the north. High pressure then moves overhead
Wednesday and remains over the region through Saturday. This
will result in some chilly nights, with the potential for a
frost or freeze Tuesday and Wednesday nights in some areas.
Warmer than normal weather is expected late week through at
Near term /until 6 am Wednesday morning/...
1040 PM...mostly adjusted sky based on the current Sat/obs. The
cluster of stratocu over srn New Hampshire and SW ME as advertised by
models, and this should gradually shift SW overnight and
dissipate around or just after daybreak. Otherwise a few
adjustments to temps, which mainly brought up mins a bit in srn
New Hampshire thanks to the clouds.
650 PM...a few minor changes to the overnight
forecast. Mostly I pulled out the slt chc pops in srn NH, as
latest meso models trending drier, and bets chc for a spkls in
this area would be late this evening and around midnight. I did
add fog to CT Vly area as well.
Previously...widespread scattered to broken cloud cover
continues to blanket the area in cold advection, as a weak wave
aloft crosses north to south down the backside of a departing
trough. Clouds will tend to dissipate approaching sunset,
especially north with very dry air evident in water vapor
satellite imagery at this hour. Scattered clouds are more likely
to hold across southern ME/New Hampshire closer to the forcing wave.
Short term /6 am Wednesday morning through Wednesday night/...
deep northerly flow behind an exiting trough, in increasingly
amplified flow aloft, continues to transport cool air into the
region through tonight. This brings the first widespread frost
chances to the mountains and areas north, especially behind a
shortwave aloft, crossing overnight. While the wave presents
forecast challenges in possible stratus development overnight,
which would abbreviate radiational cooling, it is expected to
clear the northern counties allowing those locations to drop
into the mid-30's. Thus, a frost advisory has been posted for
Coos New Hampshire and the northern tier of ME zones. Otherwise, expect low
level clouds to plague southern New Hampshire late tonight before
scattering out by late morning.
Tomorrow, high pressure builds east into New England with mostly
sunny skies. Am reluctant to go too warm Wednesday with
continued northerly flow, but the column dries dramatically,
leaving little in the way of clouds to limit afternoon highs.
Upper level ridging noses into New England Wednesday night with
another cool, possibly frost night on tap.
Long term /Thursday through Tuesday/...
overview: high pressure is expected to remain over New England
through the upcoming weekend, keeping our region generally dry and
quiet. Our next chance for significant precipitation is not until
Monday when a frontal system is forecast to arrive from the west.
Temperatures will be near normal on Thursday but a warming trend
will push them well above normal on Friday and remain there through
early next week.
Impacts: no significant impacts anticipated.
Details: Thursday begins with surface high pressure nearly overhead
and with an upper level ridge building in from the southwest.
Surface high pressure then remains over New England through the rest
of the work week and through much of the weekend with generally
light winds. The upper level ridge also continues to build over our
region, cresting late Sunday as a large frontal system approaches
from the west. On Sunday, the flow becomes southwesterly ahead of
that system, but the best chances for precipitation will hold off
until Sunday night and Monday. The latest deterministic guidance
continues to have some differences in timing between the faster GFS
and the slower Euro, so kept some chance pops into Monday night to
account for those differences.
As mentioned above, an upper level ridge will begin to build into
New England on Thursday, starting a warming trend that will push
temperatures on Friday up to 10 degrees or higher above normal for
this time of year. Above average temperatures will continue through
the weekend and into early next week, but a cooling trend looks to
begin on Tuesday as upper level troughing moves over New England,
pushing temperatures closer to normal.
Areas of fog will be possible in the northern river and mountain
valleys early each morning, particularly on Thursday night as high
pressure remains centered nearly overhead.
Aviation /03z Wednesday through Sunday/...
short term...VFR conditions prevail through the short term
period with the exception of IFR fog/possible stratus at
leb/hie tonight. A lesser, though non- zero, threat of MVFR
ceiling development exists tonight after 03z across southern New Hampshire.
Nerly winds go variable overnight, calm in sheltered locations,
as a weak wave crosses, before picking up again tomorrow out of
the NE. Dense valley fog is likely to develop Wednesday night
into Thursday morning.
Long term...VFR conditions are generally expected at all terminals
through the period as high pressure dominates the region. Winds
will generally be light and variable Thursday through Saturday
with southwesterly winds increasing on Sunday ahead of the next
frontal system. Hie and leb may see brief periods of MVFR/IFR in
fog in the early/mid morning hours each day.
short term... winds and seas remain below Small Craft Advisory criteria during
the short term with building high pressure.
Long term...surface high pressure is positioned overhead to start
the period, keeping seas and winds below Small Craft Advisory criteria through
Thursday night. Although winds will remain below Small Craft Advisory criteria,
we may see the arrival of long period swell from Hurricane
Humberto on Friday with Small Craft Advisory conditions possible for the outer
waters through Saturday. Could also see wave heights above 5 ft
in portions of Casco Bay Friday afternoon and evening.
ME...frost advisory from 2 am to 8 am EDT Wednesday for mez007>009.
New Hampshire...frost advisory from 2 am to 8 am EDT Wednesday for nhz001-002.