Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gray ME
319 PM EDT Friday may 29 2015
high pressure will return today and move off the coast over the
weekend allowing a warm and humid southwest flow to return.
Another cold front crosses the region Sunday morning.
Cool...Canadian high pressure will build back over the region
early next week.
Near term /through tonight/...
main forecast problem will be marine stratus quickly approaching
the coast. Hi-res model guidance actually has a very good handle
on the current depiction based on visible satellite. Leaning
heavily on the narre and hrrr for timing and coverage for the
overnight period. Coastal ME...especially near kpwm will see
stratus soonest...with all coastal areas likely seeing low ceilings by
00z. Through the night this will creep inland...and should roughly
match the current sea breeze front outline. Winds shifting to southwesterly
will keep stratus confined to mainly the Great Bay area and east in
southeastern New Hampshire...while allowing it to push as far inland as kaug and kwvl
in central ME.
While confidence is high in low clouds...confidence is somewhat
lower in fog and drizzle. There are some signs based on forecast
soundings that this could develop overnight. Hrrr is aggressive on
visibilities below 1/2 sm...while narre is a little more up in the air.
Sref visibilities probabilities of greater than 80 percent for less than
1 sm visibility point towards some fog more likely that not. So will
have areas of fog in the grids.
Short term /Saturday through Saturday night/...
gusty SW flow develops ahead of a slowly approaching cold front
Sat. There is sufficient shear for organized storms along the
front...but it will delay in reaching the forecast area. Sref
calibrated severe thunderstorm probabilities peak around 21z across the
far northern zones. Environment looks fair across this area...so will
add gusty winds to these zones...and delay thunderstorms for coast until
overnight. The other threat to watch will be flash flooding. Precipitable water
values will be running higher than normal...and slow frontal
movement coupled with training storms could yield some water
issues. Loss of daytime heating should help any storms to weaken
and become more scattered...but a renewal of development is
possible early sun as the day heats up again.
Long term /Sunday through Friday/...
positively tilted shortwave trough pushes the cold front the
remainder of the way offshore Sunday morning with showers coming
to an end in the early afternoon. Dense high pressure to our north
makes little headway south however as another wave of low pressure
moves along the offshore front. Lingering clouds and cooler
Canadian air moving in will keep the mountains cool (mid 50s)
while much of the coastal plain clears out and warms into the
upper 60s on Sunday. Monday and Tuesday will generally warm into
The proximity of offshore frontal system as well as a steady
stream of short wave energy will keep a chance of showers over
southern and coastal sections of New Hampshire and Maine through Monday.
There is little instability to be had but there may be some
lightning offshore. Following this a Stout cutoff short wave moves
towards the area Tuesday into Wednesday morning on nearly zonal
flow increasing rain chances across the entire area. High pressure
builds in behind this system bringing dry and warm conditions
Thursday and Friday.
Aviation /19z Friday through Wednesday/...
short term...widespread IFR/LIFR is expected tonight for coastal
terminals as marine stratus invades the area. Between 21 and 00z
most sites should be IFR or lower. Kaug may take a couple extra
hours for low ceilings to work inland...but by 03z IFR is expected.
Low ceilings persist into Sat morning before lifting. Gusty SW winds
around 20 kts possible Sat afternoon. Thunderstorms are possible late Sat
into sun for all terminals. Highest confidence for thunderstorms is for
khie Sat evening.
Long term...improving conditions Sunday with periods of MVFR in
showers along the coast continuing through Wednesday.
short term...SW return flow will increase Sat. Cool waters should
limit the amount of mixing of the strongest winds to the
surface...but sustained flow should build seas above 5 feet by late
Sat. Occasional gusts to 25 kts are not out of the question
Long term...waves drop below Small Craft Advisory criteria Sunday morning. High
seas return Monday evening through Tuesday night as a tight
pressure gradient sets up over the waters.
Fire weather...increasing humidity and southwesterly breezes
will lead to late afternoon showers and thunderstorms Saturday
afternoon and night. Wetting rains will be most likely in the
mountains Saturday evening and overnight. The areas near the coast
will be more likely to see wetting rains Sunday.