Area Forecast Discussion
Issued by NWS Caribou, ME
FXUS61 KCAR 250156
Area Forecast Discussion
National Weather Service Caribou ME
956 PM EDT Sat Sep 24 2016
Surface high pressure will slowly build toward the region from the
west through Monday as an upper level low across the Maritimes
continues to move east. Low pressure and an occluded front will
approach the area Tuesday.
.NEAR TERM /THROUGH SUNDAY/...
935 PM Update: Again, msly minor chgs to fcst hrly temps, dwpts,
and cld cvr based on trends from latest sfc obs and sat imagery.
Otherwise, no chgs to fcst lows attm with hrly temps not xpctd to
fall rapidly compared to last ngt given more xpctd with wind and
cld cvr from the NNW.
Orgnl Disc: The coldest air mass of the season is advecting into
the area through the period. High pressure will remain to the west
and the pressure gradient will tighten overnight between the high
and low pressure near Labrador. This means mixing will continue
through the night and reduce the risk of frost except in the
normally colder/sheltered locations. Will go with patchy frost in
all of the northern zones tonight but will continue to hold off on
the advisory. Also expect clouds to increase towards the Crown of
Maine late in the night as a shortwave pushes south from Quebec.
The trough may set off a few sprinkles Sunday morning...mostly
towards the Saint John Valley. This trough will cause mostly
cloudy skies for northern Aroostook on Sunday morning. Elsewhere,
cumulus fields will cause partly sunny skies. Expect slightly
cooler highs on Sunday with lower 50s north and mid to upper 50s
for Bangor and the Down East region. Strong low level mixing will
generate another windy day as gusts again reach the 20-30 mph
range by late Sunday morning.
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
High pressure sliding in from the northwest will likely allow for
some clearing skies and calming winds Sun night, which may very
well be the coldest night of the fall so far for many spots. Will
likely need at least a Frost Advisory for the northern zones. Some
patchy fog also possible in the clear and calm conditions. Monday
will be clear and dry as the center of the sfc High passes over
the CWA. Dry conditions will persist into the start of Mon night
as the upper ridge crests over the region. However, S`ly winds
that are forecast to develop Mon evening will likely keep most
spots warm and/or breezy enough overnight to preclude frost.
An occlusion racing out ahead of low pressure over the Great
Lakes will approach early Tue. Some areas, especially the western
CWA, may see rain by sunrise, and rain will spread over the entire
state by midday Tue. There remains some disagreement between
available guidance on the speed of the rain advance, with the
ECMWF and NAM generally about 6 hours ahead of the GFS and CMC.
This disagreement precluded putting categorical POPs in at 12z,
but felt confident enough to bring them in by late morning. Rain
chances persist across the CWA through most of the day, but will
begin winding down from west to east later Tue afternoon.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
An occluding front will be pushing east of the area Tuesday night. Some
rain may linger in eastern areas early in the night. Otherwise,
dry air circulating in from the southwest ahead of low pressure in
the great lakes should bring partial clearing later at night. Wednesday
will then be partly sunny and mild as a corridor of dry air between
the low to the west and the occlusion off to the east remains over our
area. Dry weather will likely last through Thursday. However, we will
have to keep watch for a possible secondary low developing off the Mid-
Atlantic coast as the upper trough moves east from the Great
Lakes. Right now most of the guidance is keeping moisture from
this secondary low to our southeast, but if the trough backs the
moisture more than is currently indicated it could bring wet
weather to parts of the region at the end of the week. A very
large and strong ridge of high pressure will then build into the
east as the weekend approaches. This will bring dry weather Friday
into the weekend. A weak back door cold front may push into the
area on Sunday cooling the north off a bit. Ridging should then
rebound early next week bringing dry weather and a warming trend.
.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
NEAR TERM: VFR conditions are expected throughout the period with
the possible exception of MVFR cigs at FVE early Sunday morning.
The only other concern is the gusty NW winds that will be as
strong...or stronger than today.
SHORT TERM: Patchy fog, especially in valleys, may cause localized
IFR or LIFR conditions Sun night into early Mon morn, especially
for KHUL north thru KFVE. Otherwise, no aviation concerns thru Mon
evening. As the next system approaches, mid-level cloud deck
appears likely to move in between 06z and 12z Tue, with MVFR/IFR
CIGs possible in any early areas of rain. As rain spreads over
more of the CWA during the day Tue, expect MVFR/IFR CIGs and at
least MVFR vsbys to impact all TAF sites thru Tue eve. Improving
conditions expected after 06z Wed. Currently expecting good
conditions Wed into Thu, but can`t entirely rule out lingering
rain and psbl lower CIGS if the previous system does not depart as
quickly as expected.
NEAR TERM: 935 PM Update: It appears SWAN wv guidance is to high
compared to obsvd buoy wv hts this eve ovr the N Gulf of ME, so
we went with lower WW3 wv guidance, and even this intially is
about a foot to high. Thinking is that once the wind increases to
10 to 15 kt with gusts to 20 kt Sun morn, wv hts will increase
WW3 guidance values, which is what we merge to attm.
Orgnl Disc...Right on the cusp of an SCA with gusts to
25 kts late tonight into Sunday morning accompanied by 4-6 seas.
Winds and seas will subside later Sunday.
SHORT TERM: At this time, SCA conditions are not expected Sun
night thru most of Tue. Wind gusts and seas may be close Sun
night before conditions die down, so this will bear watching.
Onshore winds developing Mon night into Tue will gradually build
seas, and an SCA may be needed by Tue eve, mainly for possible
seas of 6ft or more.