Area Forecast Discussion
Issued by NWS Caribou, ME

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FXUS61 KCAR 210110

Area Forecast Discussion
National Weather Service Caribou ME
910 PM EDT Tue Aug 20 2019

High pressure will cross the region tonight. A warm front will
cross the region Wednesday. A cold front will cross the region
Thursday. Another cold front will cross the region Friday. High
pressure will build across the region later Saturday through


9:10 PM Update: Clear from the Saint John Valley to the coast
this evening. High pressure will settle to the south of the FA
overnight with a clear sky to continue. The nights are getting a
little longer now and some river valley fog is possible for a
couple of hours around dawn. Updated with the most recent
observations, but no significant changes are planned at this

Previous discussion:
High pressure will cross the region tonight through early
Wednesday with mostly clear skies. Low pressure will begin to
intensify across Quebec province Wednesday, drawing a warm
front toward the region late. Shower/thunderstorm chances will
increase, from west to east, Wednesday afternoon. Based on
forecast soundings, helicity and shear values indicate the
potential for rotating storms later in the afternoon and
evening. A low level jet also begins to strengthen in advance
of the warm front. Have included enhanced wording for gusty
winds and hail across western portions of the forecast area from
late Wednesday afternoon into the evening where severe
thunderstorms are possible. Low temperatures tonight will range
from around 50 to the mid 50s north, to the mid to upper 50s
Downeast. High temperatures Wednesday will range from around 80
to the lower 80s across much of the region, with mid to upper
70s along the Downeast coast with onshore winds.


Shortwave or area of remnant convection will track across New
England Wednesday evening and overnight. This will bring chance
of thunderstorms with small hail or gusty winds early, and
heavy rain throughout.

Anticipate a swath of rain and showers to accompany this as exit
region of upper level jet approaching from the west adds
support to plenty of moisture in lower levels. Thunderstorms
will potentially be embedded, and in the highly sheared
environment, would pose a gusty wind threat. At the evening
timing, these storms will mostly rely on mixed layer instability
with close to nil surface based CAPE. Some of the convective
composites or parameters (such as STP or SCP) may be giving
erroneously high numbers due to large amounts of helicity or
shear vs. comparatively low instability within the complex.

How guidance handles the system as it tracks east on Wednesday
will vary the region of best forcing and thus wind/hail threat.
This expands to heavy rain threat as well, but more confidence
here with lifting warm front. Know much of the FA will be in
warm sector with moisture values like PWAT surging into 1.5-2
range during evening and overnight hours. Precipitation
Potential Placement highlights Downeast as greatest chance for
heavy rain as well as converging and nearly balanced Corfidi/sfc
wind vectors. These vectors become more uniform in direction as
cold front begins to slide through the north early Thursday
morning. Downeast would be under threat of more thunderstorms
Thursday afternoon if cold front is slow enough, allowing
surface instability to gain strength once again during day.
Potent 40-50kts of 0-6km shear will also be in place for chance
of a isolated stronger storm over interior Washington/Hancock Co
if some clearing occurs. Front will track to clear Downeast
Thursday night with dry conditions expected for much of the area
Friday. Some remaining moisture could bring a isolated shower
or two in the Crown of Maine during afternoon. High temperatures
will be cooler on the way into the weekend.


Upr lvl trof wl be exiting into the Canadian Maritimes at the start
of the long term with just an isold shower possible Fri evng. Med
range guidance differs on upr air pattern beginning 00z Sun with 12Z
GFS indicating the base of a H5 trof ovr Long Island vs CMC/EC H5
low in vicinity of New England. Latest GFS appears to be more
realistic for the extndd portion of the fcst with ridging at the sfc
and aloft vs the latest EC. GEFS ensemble indicates high pressure
both at the sfc and aloft with EC also hinting at high pressure at
the sfc along with wk low aloft. Hv sided twd GFS for the long term
with temps blo normal throughout the weekend. Temps begin to
moderate on Mon as return flow commences with high nosing ewrd into
Canada ahd of next system mvg in fm the Great Lks by the middle of
next week.


NEAR TERM: VFR conditions are expected tonight through early
Wednesday. Variable conditions are possible later Wednesday with
a chance of showers/thunderstorms. Some of the thunderstorms
could produce gusty winds and hail later Wednesday afternoon
and evening, particularly across western areas.

Wednesday Night-Thursday Morning...MVFR to IFR still likely
with periods of heavy rain and a chance of thunderstorms. Fog
could hinder operations as well lowering visibilities.

Thursday...IFR in morning with fog, improving to VFR across the
north. MVFR is possible Downeast with remaining clouds and
chance of thunder in afternoon. S winds 10 kts veering to SW.

Thursday Night through Sunday...VFR with some MVFR possible
Friday and Sat afternoon. Winds WNW 10-15 kts with some higher


NEAR TERM: Winds/seas will remain below small craft advisory
levels tonight through Wednesday. Shower/thunderstorm chances
will increase later Wednesday afternoon and evening.

SHORT TERM: Below SCA conditions expected. A few gusts of wind
may approach 25 kts Wednesday night/Thurs morning with patchy
fog, but expected to remain around 20 kts through Thurs night
again with patchy fog moving in. Waves of 2-4 ft through
Thursday night will increase Fri afternoon, but remain below
5ft. Waves decrease 2-3 ft Sat and Sun.





Near Term...CB/Norcross
Short Term...Cornwell
Long Term...Farrar
Marine...CB/Norcross/Cornwell is the U.S. government's official web portal to all federal, state and local government web resources and services.