Area Forecast Discussion
Issued by NWS Portland, ME
FXUS61 KGYX 270441
Area Forecast Discussion
National Weather Service Gray ME
1241 AM EDT Mon Mar 27 2017
A warm front will approach from the southwest tonight, before a
weak wave of low pressure forms and passes through the Gulf of
Maine Monday. This will provide a round of mixed wintry
precipitation Sunday night into Monday. Low pressure moves north
of the region on Tuesday and drags a cold front through on
Wednesday. High pressure will build in from Canada for the end
of the week.
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1230 AM...Some spotty light precip associated with mid lvl
WAA is tracking NE through ME now....mostly PL with some SN
interior and just RA on the coast. Will see a little bit of a
break for the rest of the overnight before we get another round
of WAA precip from developing low along the NH/MA border. This
should arrive in srn NH by the morning a commute and will move
into ME during the commute. Interior areas of coastal counties
could see some FZRA/PL at the start.
850 pm update: Made wholesale changes to forecast for tonight. Have
dropped the advisories along the southwest coast of ME and the
seacoast of NH since little to no pcpn expected til late tonight
(lowered pops) due to very dry air mass in place in lower
levels, and also southeast winds to keep temps along southwest
coast above freezing by the time pcpn begins. Also have pushed
back timing of onset of advisories that are in place since the
main band of pcpn not expected to arrive until late tonight and
mainly for Monday. Based on latest mesonet data adjusted temps.
Also, lowered snowfall totals and also ice accum totals for
inland areas where the freezing rain and winter weather
advisories still in place.
6 pm update: A few areas of very light precipitation upstream
will continue to move northeast this evening with most, if not
all, of it drying up as it moves into the forecast area due to
a very dry air mass over the area in the lower levels. Surface
temps are running 35-42 degs attm based on latest mesonet data
so increased temps into this evening. Also made adjustments to
ptype into the early evening. Based on the warm boundary layer
temps and developing low level southeast flow any very light
pcpn that does reach the ground could fall as rain.
Will be watching to see how surface temps/dewpts react this
evening to the low level southeast flow becoming established.
Dewpoints already rising and temps may struggle to fall below
freezing over southern and coastal areas before they rise later
tonight. Any evaporational cooling over southern areas may not
offset the waa due to the sely flow. It appears we may need to
drop some advisories on a later update over some areas across
southern NH and parts of coastal ME.
Two batches of precipitation will cross our forecast area. First
batch over western New England this afternoon will attempt this
passage the rest of this afternoon and evening. However,
extremely dry Canadian air remains in place in the lower levels
of the atmosphere. Much of the echoes shown on radar will
dissipate before any precipitation reaches the ground.
Nevertheless, latest model suite projecting light precipitation
overnight in a warm air advection, cyclonic flow. With such cold
and dry air in place, this precipitation will mainly be in the
form of light sleet or snow. The most likely area to have
freezing rain accretion still appears to be southern New
Used a non-diurnal curve for the overnight lows. Temperatures
will likely drop with some light precipitation due to
evaporation cooling with the first batch. Thereafter,
temperatures warm through the night.
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
Mixed precipitation gradually changes to rain over southern and
central areas during the day Monday with mixed precipitation
continuing in the north. A weak wave of low pressure will
likely form in the Gulf of Maine during the day. This will
prevent significant warming as winds become northwest for a
period of time.
Areas of mixed precipitation likely to continue over the north
Monday night. However, much of the dynamics associated with the
system will have shifted to the east of the region. Any
precipitation should be light.
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
The models remain in decent agreement on the longwave pattern
through late in the work week. Thereafter, timing and strength of
individual impulses embedded in fast flow across the northern
tier of the CONUS becomes problematic. There is a corresponding
decrease in forecaster confidence in sensible weather details
after day five. We begin the period with a digging shortwave
impulse near the southern tip of Hudson Bay and a weakening
impulse over the midwest. By late Wednesday...we`re left with
shortwave energy centered over eastern New England. At the
surface...low pressure will track from the lower Great Lakes to
southern New England by Tuesday night with an area of overrunning
rain...and some light wintry mix near the international
border...ahead of this disturbance. By early Wednesday...the low
and associated frontal system will exit the coast with a brisk
northwest flow in its wake along with some upslope clouds and snow
showers for the higher terrain. Rising heights arrive for Thursday
with a building ridge of high pressure providing a dry but brisk
day as gusty northwest winds continue. The ridge will crest
overhead Thursday night before retreating offshore on Friday. The
next impulse and associated surface low should approach from the
midwest by early Saturday. However...models offer a plethora of
solutions with this system lending considerable uncertainty to
sensible weather details for next weekend.
.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Short Term...Very dry air in place initially in the lower
levels. However, moisture will eventually brings ceiling and
visibilities down into the IFR category later tonight through
Monday. Possible LLWS away from the coast tonight if winds aloft
Some modest improvement in ceilings/visibilities Monday night.
Tue...MVFR with areas of IFR in ceilings...-ra and fog.
Wed - Thu...Sct MVFR in mtn -shra/-shsn.
NW sfc wind gusting to 25 kt.
Short Term...Have raised flags for small craft. Winds increase
out of the southeast on Monday. Seas will remain above 5 feet
for the outer waters, so SCAs will continue into Monday night.
Wed - Thu...Small Craft conditions are likely.
ME...Winter Weather Advisory until 5 PM EDT this afternoon for
Winter Weather Advisory from 5 AM to 10 AM EDT this morning
NH...Winter Weather Advisory until 5 PM EDT this afternoon for
Freezing Rain Advisory until 10 AM EDT this morning for NHZ005-
MARINE...Small Craft Advisory from 8 AM this morning to 6 PM EDT this
evening for ANZ153.
Small Craft Advisory from 8 AM this morning to 6 AM EDT
Tuesday for ANZ150>152-154.