Scientific Forecaster Discussion
fxus61 kgyx 201647 aac
Area forecast discussion...updated
National Weather Service Gray ME
1147 am EST Wed Nov 20 2019
a weak mid level disturbance will bring light rain and snow to a
good portion of the region today with minimal accumulations
expected, mainly in the higher terrain. Our active weather
pattern will continue with a strong cold front arriving Friday
bringing a few additional rain and snow showers followed by
cooler temperatures for the coming weekend.
Near term /until 6 PM this evening/...
just a few minor changes to account for more rain than snow
across southern New Hampshire and southwest Maine. To the north snow
showers are ongoing and are spreading east into the western
Maine mountains. Quantitative precipitation forecast is very light everywhere. Expecting highs
to be close to what they are at the moment- mostly in the mid
30s to lower 40s.
940 am update...
weak mid level negatively-tilted trough is bringing some light
precipitation to the forecast this am. Moisture will increase
over the region with some light rain and or snow continuing
through this afternoon across New Hampshire and spreading to portions of
coastal Maine. Not expecting any snow accumulations outside of
the higher terrain which may see up to an inch. Most of the
coastal plain and southern New Hampshire will see more light rain with some
wet snowed mixed in.
Made a few changes to hourly dew points and temperatures as well
as pops to include latest high resolution near term models
along with current observational trends.
645 am update...little change to the going forecast as we're on
track based on latest trends in observations and mesoscale
model data. Did back off on pops for today across a good portion
of ME based on some drying to the northeast and forcing for
ascent remaining a bit further southwest, mainly over
southwestern New Hampshire. Otherwise, very little change other than some
minor adjustments here and there.
An upper level trough and attendant surface convergence zone will
gradually move eastward across the forecast area. This will
allow for enough ascent for light precipitation to fall much of
the day, but especially this afternoon across New Hampshire.
Much of the Maine portion of the forecast area will be drier
during the day today as the area of best surface convergence will
remain across New Hampshire. However, late this afternoon and early this
evening there may be a burst of light precipitation on the
coastal plain of Maine as the departing mid level low aids in
the generation of a brief period of frontogenesis.
Precipitation type today will be mainly rain at lower
elevations with some snowflakes mixed in at times during periods
of briefly stronger ascent. At higher elevations, mainly from
the Monadnocks northward into the White Mountains an inch or two
of snow may fall today, mainly above 800 feet or so. However, a
coating is possible at lower elevations.
Temperatures will be above freezing today in most locations
except hovering around 32 degrees in elevated terrain.
Short term /6 PM this evening through 6 PM Thursday/...
low pressure moves away tonight with any light rain or snow
ending during the evening. Gradual clearing is expected to occur
after midnight. Thursday will finally feature mostly sunny skies
with highs in the 40s.
Long term /Thursday night through Tuesday/...
the extended looks like a busy end to this week followed by a
quiet start to the next.
Fri remains on track for a strong cold frontal passage. Ahead of
the front Thu night I will continue to show a non-diurnal trend
in temps within the sly flow. The low level boundary and upper
level trof are both set to cross the region during the latter
half of the day. Best chances for precip will be in the
mtns...where there will be a combination of frontal precip and
upslope snow showers. Farther S chances for precip will drop off
quickly...and some areas may see little if any precip at all.
The majority of sensible wx will be cold air advection and gusty winds behind
Importantly the front will begin to stall off the coast as the
main shortwave trof lifts towards Newfoundland. This low level
baroclinic zone will be a focus for low pressure amplification
as the next shortwave trof approaches from the central Continental U.S.. it
remains a low confidence track forecast at this range...but
occasional deterministic runs and several ensemble members
support a system close enough to the forecast area to bring
widespread precip. With 925 mb temps forecast to be around 0c
to +1c that brings snow into play for many areas. Given that
ensemble guidance is showing sensitivity towards a shortwave trof
currently S of the Aleutian Islands...we have a couple of days
until we are likely to see some consensus on track and timing.
With that in mind I have stayed close to the multi-model blend.
I did however bump pop up anticipating a bit of a northwest trend/less
progressive bias to forecasts. That also meant that I increased
cloud cover slightly and lowered daytime temps a couple of
degrees with expected precip falling sun.
Aviation /18z Wednesday through Monday/...
mainly IFR conditions expected at most terminals today as light
rain or snow falls (snow in the interior, mainly above 800 ft in
elevation). The low level moisture begins to get scoured out
tonight as low pressure moves away to the east. Therefore,
gradually improving conditions are expected after midnight
tonight. VFR all areas late tonight and Thursday.
Long term...cold front approaches Fri with clouds gradually
lowering thru the day. Overall VFR should prevail until the
frontal boundary is on the doorstep. Some initial shsn will
quickly give way to rain showers and perhaps some mixed precip across
interior areas. Widespread MVFR expected with areas of
IFR...especially in any shsn. The column will gradually cool
again but likely not until after precip has ended at all
terminals but hie. At hie continued upslope shsn will keep the
threat for local IFR or lower conditions into Fri night. VFR
developing low pressure well offshore will cause
northerly winds to strengthen over the waters with Small Craft Advisory conditions
through tonight. Winds and seas gradually subside during the day
Long term...a strong cold front will cross the waters during the
latter half of Fri. Cold air advection will promote strong wind
gusts...especially outside of the bays...beginning Fri evening
and continuing into Sat morning. Gale force gusts are possible
on the outer waters...with strong scas likely in the bays. Winds
and seas will gradually diminish thru Sat...but we will have to
watch for a potential follow up system sun that may prolong Small Craft Advisory
headlines...or possibly even gales if system trends stronger.
surge guidance suggesting that the Wednesday PM tide cycle may
see tidal levels reach action stage. Can't rule out some
splashover...although developing offshore flow will likely
preclude any significant impacts. Will issue a coastal flood
statement for coastal York County to the seacoast for splashover
Marine...Small Craft Advisory until 4 PM EST Thursday for anz150-152-