Scientific Forecaster Discussion
fxus61 kgyx 202102
Area forecast discussion
National Weather Service Gray ME
402 PM EST Sat Jan 20 2018
a weak cold front will drop south from Canada tonight and will
stall over southern New England Sunday and Sunday night. The
front will lift north on Monday and Monday night as a warm
front. Low pressure will track northeast through the St Lawrence
Valley on Tuesday and will drive a cold front through the region
in the afternoon. A trough of low pressure will linger over the
region Tuesday night and Wednesday. High pressure will gradually
build in from the west Wednesday through Friday.
Near term /through tonight/...
weak cold front will gradually sag south from Canada tonight.
This boundary already re-enforcing cloud cover in northern zones
and may produce a few snow showers later this evening in the
usual upslope areas in the mountains. Expect any accumulations
to be light and spotty. Remainder of the region will see
variable high and mid level clouds. Lows overnight will
generally range through the 20s from north to south.
Short term /Sunday through Sunday night/...
cold front will gradually stall over southern New England on
Sunday. Will see varying amounts of cloud cover through the day
but temperatures will still top out above normal as cooler air
remains north of the region. Highs will range through the 30s
north and lower to mid 40s south.
Clouds will thicken Sunday night as the front begins to lift
north as a warm front. Aside from a few snow showers in the
mountains most of the forecast area will see a dry night. Lows
will range through the teens in the north and 20s south.
Long term /Monday through Saturday/...
focus in the extended continues to be on Mon night/Tue system.
Not much significant change in available guidance today...with a
wave moving into California today amplifying into the MS River Valley by
Mon. High pressure build build out ahead of it to the north...while
warm air advection surface and aloft drives a warm front towards New England.
The devil is in the details of where that warm front hangs up at
the surface...because it appears that the mid level front should
make appreciable progress thru the forecast area.
Given the high pressure positioning...I have stayed below
guidance temps and near the previous forecast. Gefs and European model (ecmwf)
eps guidance continues to show mean surface primary low headed
for the the ern Great Lakes...with a secondary redeveloping
across New England. My feeling is that this mean secondary is
too far inland...and will likely end up developing closer to the
coast. That being said...it will likely be farther north than is
necessary to keep really cold air in place. But it will delay
the warm up a bit.
An examination of all ensemble guidance clustered together shows
that with the 20.00z suite stronger high pressure located to our
NE...or colder scenarios...were favored when there were higher
heights ahead of the developing wave across the intermountain
west. This is possibly a result of maximum primary intensity
occurring earlier...and strongest conveyor belts maturing and
weakening before arriving across the northeast. The 20.12z GFS
and European model (ecmwf) so far have initialized too low with heights ahead of
the wave...and we will have to see if those trends continue. The
important window will really be tonight into early sun to see
how features are developing.
The resulting forecast for our area will be a light snow or mix
at onset...turning into a break in precip as the dry slot moves
into the area. There could be a period of drizzle or freezing
drizzle...but I did not want to complicate the forecast more
than it already is. Steadier precip moves in Tue...and it will
likely bring a mixed bag of some snow in the mtns...with
sleet...freezing rain...and eventually rain for more srn and
central locations. Snow amounts will be light...especially
outside the mtns...with freezing rain amounts looking like less
than a quarter inch as well.
Beyond this system...after cold air advection midweek...a gradual moderating
trend to milder than normal will develop.
Aviation /19z Saturday through Thursday/...
short term...VFR tonight and Sunday with areas of MVFR ceilings
in the mountains. Areas of MVFR ceilings develop Sunday night as
onshore flow sets up.
Long term...VFR begins the period. Heading into the
afternoon...some weak forcing may allow for some light precip
to develop. It appears a dry slot moves in Mon night...but
gradually warming and moistening air mass will lead to
widespread IFR conditions developing. Downsloping winds may keep
hie MVFR or VFR into Tue. Steadier precip moves in Tue...which
may begin as a pl/freezing rain mix at all terminals before changing to
rain...especially near the coast and across srn New Hampshire. IFR or lower
conditions linger into Tue evening before wly flow scatters out
short term...continuing sca's through tonight for the outer
Long term...sly winds will begin to increase Mon...and
especially into Tue as low pressure moves thru New England. A
period of gale force winds gusts is possible outside the bays as
the core of the low level jet moves overhead Tue. Small Craft Advisory conditions
will likely linger thru the end of the week...as cold air advection follows the
system and winds and seas slowly diminish.
Marine...Small Craft Advisory until 6 PM EST this evening for anz151-
Small Craft Advisory until 6 am EST Sunday for anz150-152-154.