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FXUS61 KCAR 182229

Area Forecast Discussion
National Weather Service Caribou ME
629 PM EDT Sun Aug 18 2019

High pressure ridges over the area tonight. A warm front will
lift northward across the area Monday. A cold front will cross
the region Monday night. High pressure will cross the 
region Tuesday. A cold front will approach later Wednesday then
cross the region Thursday. Another cold front is possible


6:30 PM Update: There are isolated showers, mainly to the north
of the Katahdin Region early this evening, but no electrical 
activity. These showers should die off this evening. A strong 
shortwave moving out of NY State may produce a few more showers 
and isolated thunderstorms very late tonight toward morning, 
mainly across the southern half of the FA. Otherwise, expect low
clouds and fog to move in along the coast early this evening 
and advance north overnight. Made some minor tweaks based on the
latest observations, satellite, radar, and near term models. 

Previous discussion:
The southerly onshore flow and elevated dew points will make 
another round of fog and low clouds for tonight. It will start 
near the coast where fog has remained all day and advect inland.
Fog and stratus will spread northward through the night, 
covering the entire area after midnight. The denser fog will be 
towards the coast and in higher upslope terrain. By late night 
into the morning, a weak shortwave currently in upstate NY and 
PA will propagate into the forecast area. This feature will 
bring some morning showers and even higher dew points. Can't
rule out embedded thunder around Hancock County near dawn. The 
warm front will also prolong the duration of the low clouds 
through the morning into the early afternoon and reduce 
instability. The pre-frontal trough ahead of the cold front 
will arrive in the afternoon. By that time, some clearing will 
be possible along the western border of the forecast area. Bulk 
shear will be increasing from the north during the afternoon and
will be favorable. Expect afternoon thunderstorms to develop 
near the western border of the forecast area and move eastward 
into a more stable environment towards the eastern border and 
Downeast during the late afternoon into the evening. The threats
with storms will be heavy precip and winds. PWs will be 
approaching 2 inches in the afternoon ahead of the front. With 
good surface heating bringing highs around 80F and dew points 
near 70F, the best SBCAPE in the forecast area will likely be in
the southern half of Piscataquis County, maybe spreading into 
SW Penobscot. In this area, a number of parameters such as 0-1km 
shear and EHI, low LCLs, sig TOR and supercell composite 
approach interesting values in some guidance, but the window of
opportunity is fairly narrow late in the day. SPC maintains the
forecast area in general risk for thunderstorms.


A weak cold front will cross the region Monday night, with high
pressure building toward the region late. Expect a chance of
showers/thunderstorms with the cold front early Monday night.
Clouds then decrease overnight with building high pressure. High
pressure crosses the region Tuesday with mostly sunny skies.
High pressure moves to the east Tuesday night through Wednesday,
with a developing return flow across the region. Uncertainty
exists regarding a possible disturbance approaching the region
from the southwest Tuesday night. Expect partly cloudy skies
Downeast Tuesday night, with mostly clear skies north. A cold 
front crossing Quebec province will approach the Saint Lawrence 
River Valley late Wednesday. The approaching cold front, 
possible upper disturbance and diurnal instability will support 
a chance of morning showers with a chance of afternoon 
showers/thunderstorms. Temperatures will be at near normal, to 
slightly above normal, levels Tuesday/Wednesday.


The cold front approaches northern Maine Wednesday night, then
crosses the region Thursday. Expect a chance of
showers/thunderstorms in advance of the front. An upper low
moves northeast of Maine Friday into Saturday, though the exact
track is uncertain. A disturbance moving around the low and a 
surface cold front/trof crossing the region could support a 
chance of showers across mostly the north and mountains Friday. 
Dependent on the proximity of the upper low, a slight chance of
showers could persist Saturday. High pressure will cross the 
region later Saturday then begin to exit across the Maritimes 
Sunday with generally partly cloudy/mostly clear skies. Expect 
near normal level temperatures Thursday/Sunday, with below 
normal level temperatures Friday/Saturday.


NEAR TERM: Conditions will again deteriorate overnight with fog
returning to coastal sites such as BHB this evening. Fog and 
IFR cigs will move into BGR later this evening and overspread 
all sites after midnight. Conditions will slowly lift Monday 
morning, but will likely be slower to rise than today with the 
warm front lifting north and some rain/drizzle. BHB could be IFR
all day. In the afternoon, concerns turn to thunderstorms 
moving across the area ahead of cold front. Some of these storms
could be quite strong.

Monday night...Occasional MVFR early with a chance of 
showers/thunderstorms. VFR late.


Wednesday...Generally VFR. Chance of a shower/thunderstorm.

Wednesday night through Thursday...Variable conditions with 

Friday...Generally VFR. Occasional MVFR possible across the
north and mountains.


NEAR TERM: Fog continues as the predominant issue over the
waters through Monday. Long period south swell continues near 3
to 4 feet. Winds will pick up towards 15 kts Monday afternoon.
There's a chance of thunderstorms arriving from the north by

SHORT TERM: Winds/seas will remain below small craft advisory
levels Monday night through Wednesday. Visibilities will be 
reduced in fog Monday night. Could also have the chance of a 
shower/thunderstorm Monday evening, with another chance of
showers/thunderstorms Wednesday.





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