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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 162009

Area Forecast Discussion
National Weather Service Caribou ME
409 PM EDT Tue Jul 16 2019

A warm front will move through the region tonight. A cold front
will move southwards across the area Wednesday into Wednesday 
evening. High pressure follows for Thursday into Friday and will
be followed by another cold front Saturday.

Warm frontal cloudiness will increase tonight. Precip will break
out in northern zones later this evening. These initial showers
will be stable, but as the warm front approaches, instability
will increase later in the night with an H850 thermal ridge. The
warm front introduces much more humid air and a plume of 1.5 to
2.0 inch PWs will stream into the area. Will maintain mention of
isolated thunderstorms after midnight...with the warm frontal
passage. Although no guidance is clearly showing any heavy QPF 
after midnight, do have some concerns with the warm frontal
passage given the instabilty aloft, high PWs, a LLJ and Corfidi
vectors dropping towards zero. At this point, the threat area
would appear to the northwestern portions of the forecast area,
but confidence is not high enough to include mention of heavy
rainfall at this point.  The warm advection will prop up 
tonight's lows towards the mid 60s...except some mid to upper 
50s on the Downeast coast. The arrival of the humid air will 
likely generate some coastal fog later tonight into Wednesday 

For Wednesday, the area will start the day in the warm sector 
with a cold front dropping southward from Quebec. The cold front
will provide a good convection trigger. Dew points over 70F 
ahead of the front and PWs approaching 2 inches...with moisture 
from the remnants of Barry...and a deep warm cloud layer
indicate the potential for locally heavy rainfall. However,
mid and high cloud cover streaming eastward may hinder 
development of SBCAPE and mid-level lapse rates are 
unimpressive. There is some shear towards the coast in the late 
afternoon with the entrance to an upper jet, but timing and 
placement of the shear may not be ideal. Low clouds and fog will
return back along the coast by early evening.

Cold front will be exiting the Downeast coast early Wednesday
night. Rain will taper to showers with slight chance of 
lingering thunder in more convective showers Downeast. Passing 
front will decrease fog amounts along coast, but given humid 
environment some patchy fog may make it inland along coastal 
Downeast beforehand. Strong surface high pressure will then push
over the state for a clear night and dry day Thursday and Thurs
evening with plenty of sunshine. Friday will bring return flow 
from south as high exits and boundary approaches from west. The 
onshore flow element will keep the coast cooler than Thursday, 
but inland areas will see a warmer day, nearing 80 in many 
spots. Additionally, patchy fog over the Gulf of Maine is 
expected to develop Thursday night into Friday morning, with the
chance to work its way inland along coastal Downeast.

Weak boundary will pass Friday assisted by daytime heating and 
convergence. The result will be some showers and a chance of 
thunder in the north. Main front will not have energy or forcing
to pass through region until upper level jet streak advances 
east on Saturday.


Warm air and moisture advection takes place Friday night, with dew
point temperatures climbing into the mid 60s. The warm airmass 
will provide a jump start to expected hot temperatures Saturday 
afternoon. Timing of the cold front passage will be key for 
daily high temps and cloud cover during the day, as well as 
thunder potential. GFS has been relatively consistent in overall
spatial extent and timing, with other long term guidance weaker
but showing convective qualities. Upwards to 2000j/kg of MLCAPE
and 30-40kts of 0-6km shear will be present for storm growth. 
With some mid-level cooling, CAPE in the hail growth zone, and 
some drying in the low levels, highlighting potential hail 
concern. DCAPE values in the 500-1000 range also weigh chance 
of gusty winds. PWATs near 2 inches, so will need to keep track
of Saturday afternoon for chance of heavier rainfall with 
convective storms. Some 90s will break out ahead of the front, 
mainly Downeast and Bangor Region. The north will be warm, but 
with proximity to front, expect cloud cover to restrict too many
highs outside of the 80s. 

Other than quick moving high pressure on Sunday, remainder of
the week wont have much in the way of stronger systems. There
will be the chance for showers for most of the period as
moisture filters back in quickly after the highs departure.
Temperatures will return closer to normal after Saturday, with
many widespread highs in the 80s and lows in the mid to upper


NEAR TERM: All sites will be VFR into the evening. By late
evening, IFR cigs are possible at FVE and will be a threat
through the remainder of the night. After midnight, expect LIFR
to roll into BHB and coastal sites and remain until early 
Wednesday morning. Isolated thunderstorms are possible across
the entire area after midnight. Scattered thunderstorms across
the entire area will occur with a cold front on Wednesday.

Wednesday Night: Cold front will slide off the Downeast coast.
VFR is expected behind in north and towards BGR, but some fog
and showers early evening will start out Downeast with IFR,
especially for BHB. Winds will shift N behind frontal passage.

Thursday and Thursday Night: VFR expected under high pressure.
Light NE winds will shift SSW.

Friday and Friday Night: VFR will continue for most terminals, 
with showers approaching the north. Some thunder is possible 
during afternoon in this area as well with potential reduction 
to MVFR. Winds will be light, between S and SW.

Saturday: MVFR and IFR is possible amid a passing cold front
with showers and thunderstorms during afternoon.


NEAR TERM: Winds will pick up tonight with a few gusts towards
20 kts possible. This will drive a modest increase in seas to 3
feet. Fog is probably the biggest issue...arriving after
midnight and remaining most of Wednesday as a very humid airmass
moves over the cold waters.

SHORT TERM: Conditions expected to be below SCA criteria through
the period. Waves are expected to be between 2 and 3 feet,
building to 4 briefly Saturday.



Near Term...MCW
Short Term...Cornwell
Long Term...Cornwell