Scientific Forecaster Discussion
fxus61 kgyx 202151
Area forecast discussion
National Weather Service Gray ME
551 PM EDT Fri Oct 20 2017
high pressure will crest over the region tonight and will shift
offshore on Saturday. High pressure will hold off the coast
through Sunday. A slow moving cold front will approach from the
west on Monday and will stall to the west of the region Monday
night and Tuesday as low pressure tracks north through central
New York. Low pressure will continue north into Canada Tuesday
night and will drive a trailing cold front through the area on
Near term /until 6 am Saturday morning/...
550 PM...just made a few minor tweaks, mainly to wind/temps,M
based on current obs. Winds are staying up a bit, and so are
temps, so just kept temps a little warmer through early
evening, before they start dropping off.
Previously...high pressure building in from the west will crest
over the region by Saturday morning. Aside from a few clouds
associated with weak over-running setting up in the
north...should a a clear and calm night with lows ranging from
the mid 30s north to the mid 40s south.
Short term /6 am Saturday morning through Saturday night/...
fair weather will continue on Saturday as high pressure
gradually slides offshore. Return flow will bring warmer air
back into the region along with a few clouds. Once again high
temps will average out well above normal with highs in the north
ranging through the 60s. Developing onshore flow will also cap
temps in the 60s in midcoast and interior central Maine.
Southern New Hampshire and southwest Maine will reach the lower
to mid 70s.
Looking for variable clouds Saturday night with lows from the
mid 30s north to the mid 40s south.
Long term /Sunday through Friday/...
no significant changes to model guidance thru early next week
with the 20.12z suite. An anomalous upper ridge will dominate
the pattern to begin the period. This trof will get flattened by
a S/WV trof traversing the Hudson Bay area...but higher heights
and high pressure will tend to hold over the local area thru at
least Mon. In all likelihood...deep meridional flow will keep
the best rain chances to our west even into Tue. Thru Tue...h9
temps are still forecast to linger around the mid teens...so
70s continue in the forecast. Overnight temps should for the
most part remain mild in return flow...but Sun night surface
ridging should allow for some radiational cooling and I have
adjusted MOS temps slightly to account for typical cool spots.
The main story of the extended however is the deep trof digging
into the central Continental U.S.. ensemble guidance is forecasting a +3
Standard deviation sly flow to develop. This will not only help
to transport the aforementioned warmth nwd...but also deep
moisture. Precipitable water anomalies approaching 2 to 3 Standard deviations
above normal by Wed means that it may soon be time to add heavy
rainfall wording to the forecast. Based on flow generally
parallel to the front...this will be a slow moving event. And
one that may also arrive in two waves...with the lead S/WV trof
and another with the upper low itself. First with the lead
wave...ensemble guidance does indicate a strong 800 mb low level jet will
develop ahead of the front...and deterministic models favor this
extended down below 1000 feet. Given how warm it is in the
boundary layer...the inversion will be marginal at best based on
forecast soundings. Winds could get pretty gusty...especially
along the coast early Wed. Beyond midweek...deep trof will close
off into an upper low center and that should help to slow
everything down. It will also prolong the warmth...and trof axis
does not quite make it thru the northeast.
Aviation /22z Friday through Wednesday/...
short term...VFR tonight through Saturday night.
Long term...widespread VFR conditions into early next week under
high pressure. Over the weekend...high center will be closest
and so LIFR valley fog is more likely at leb and hie. Tue into
Wed...deep moisture and warm air advection over the waters may bring stratus
into coastal terminals. While it is too early to say with
confidence...some areas of IFR cigs are possible.
short term...no flags.
Long term...high pressure in control of the region will keep
winds and seas below Small Craft Advisory thresholds thru early next week.
Developing return flow Mon into Tue will gradually build seas
outside the bays towards 5 ft Tue. Low level winds increase
later Tue and especially overnight into Wed. There may be a
small window for gale force gusts outside the bays...and seas
will build to near 10 ft. Persistent sly flow thru the remainder
of the week will keep seas above 5 ft even as winds begin to
relative humidity values will again drop to around 30 percent in
southern New Hampshire for a brief period Saturday afternoon
but expect winds to be light and variable so fire risk will be
marginal. Expect humidity values to gradually increase on Sunday