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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 191009

Area Forecast Discussion
National Weather Service Caribou ME
609 AM EDT Mon Aug 19 2019

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


600 AM Update: We did reduce fog cvrg for Nrn and Cntrl ptns of
the FA to patchy for the rest of the erly morn with vsbys here 
mostly abv 1 nm attm, but kept areas ovr Downeast areas.
Approx obsvd ovrngt lows were derived from latest obs up to 6 
am with fcst hrly temps/dwpts adjusted into the late morn hrs. 
Otherwise, no chgs were needed to fcst cld cvr, PoPs, and wx
types with sct shwrs moving into Downeast and Wrn ptns of the FA
from the remnants of last ngt's s/wv from Nrn Mid Atlc states. 

Prev Disc: Low ST cld cvr and patchy to areas of fog have moved
into all of the FA xcpt the far NW from NB very erly this morn.
Meanwhile, a left ovr area of shwrs associated with a weak s/wv
from the great lks is about to cross into Downeast and Cntrl 
highlands areas, with most of this activity xpctd to weaken if 
not dissipate before crossing into NB prov. Skies will be slow 
to exhibit much in the way of prtl sunshine this aftn due to the
amt of moisture in the lower wx atmos.

Another s/wv and associated cold front xpctd to arrive from 
Cntrl Can will bring another round of shwrs/tstms to mostly Wrn 
ptns of the FA later this aftn into erly eve. Decent 0-6km bulk
shear vectors alg with max SBCAPEs of 1000 to 1500 J/Kg ovr the
initiation zone near the Ern QB/Wrn ME border could result in a
couple of bowing ln segments as stms enter Wrn ME mid to late 
aftn with brief torrential rnfl rates and strong gusty winds.
Any tstm gaining mid lvl rotation could also produce hail 
despite relatively high fzls. Although rnfl will be lcly hvy,
tstms should cove with the faster forward Corfidi vector motion,
lmtg the potential of prolonged hvy rnfl. Tstms should weaken 
some as the move into Ern and Downeast ptns of the FA toward 
erly eve due to stabilization of the lower atmos due to marine 
or modified marine air ovr these areas. Otherwise, shwrs and 
tstms will end WNW to ESE behind a cold front late this eve into
the ovrngt as a cold front crosses the Rgn with late ngt clrg as
slightly drier air moves into the Rgn on NW winds.


Drier on Tuesday, but warm as high pres settles across the
region. Daytime temps are forecast to reach into the 80s. The
high will remain in control of the region's wx right into early
Wednesday. It will become more humid on Wednesday as a return 
flow of southerly winds will bring in higher dewpoints and 
increasing clouds. Daytime temps will be warmer across the
northern and central areas w/lower 80s, while the south wind
keeps the Bangor region and Downeast a tad cooler. 

The latest set guidance including the GFS,ECMWF and NAM have 
pushed back the timing of the showers/light rain w/the apchg
warm front til Wednesday evening. The Canadian guidance was
faster and wetter showing the potential for some heavy rainfall
into the eastern areas. At first, the thought was that this
could due to some convective feedback, but looking further into
it, there appears to be a nose of warmer that pushes up into 
the region Wednesday night w/the warm front. The GFS does show a
jetstreak of 30 kts at 925-850 mbs w/some elevated CAPE, but it
puts the heavier rainfall over the western areas. The ECMWF has
its jet dynamics well to the east and does line up w/the heavy 
rainfall potential. Tstms were kept in the forecast given the
elevated CAPE and that warm nose, but given the discrepancy on 
the placement and amounts of the rainfall, confidence is low on
adding any enhanced wording for heavy rainfall attm. The 
daycrew will need to assess this further today w/the later 
guidance. Fog was added as well due to the southerly flow and
moist llvls.


The associated cold front is forecast to move across the region
during the day on Thursday. Showers and fog in the morning will
limit instability. There could be a window of opportunity
however by late Thursday morning as a pre-frontal could move 
out ahead of the cold front w/some warming noted by the GFS and 
ECMWF. This will allow for rapid destabilization w/decent CAPE 
potential. There is good shear ahead of the front w/some 
difluence aloft. This should be enough to get some tstms going. 
Another thing to note is the strong upper jet helping enhance 
development. Stayed w/the daycrew's thinking of tstms w/the best
potential attm being across the northern and western areas. It 
will be interesting to see how things move as the new guidance 
comes in.

The cold front is expected to clear the region Thursday night
w/much cooler air on the way for Friday right into the weekend.
The long range guidance including the GFS and ECMWF show the
upper trof remaining across the region into Saturday. This will
allow for clouds to develop during the day. A disturbance 
moving through the trof on Friday has the potential to produce 
some showers mainly across the n and w. Decided to go w/20-30% 
for precip chances. There could be a few showers still around
on Saturday as we remain under the trof. Used a blend apch and
have a slight chance(20%) for a shower or two.


NEAR TERM: Another early morn of VLIFR to LIFR clgs/vsbys in ST
cld cvr and fog across our TAF sites. Clgs and vsbys will again
slowly rise back to MVFR and even low VFR by erly to mid aftn 
as the dwpt depression increases. Clgs and vsbys will briefly 
lower to MVFR or even IFR at TAF sites experiencing tstms 
and/or heavier shwrs later this aftn into erly eve. Otherwise
conditions will become unlmtd VFR by late tngt, after perhaps a
brief pd of low ST and patchy fog ovr Downeast mid to late 
evening before llvl cool advcn behind the cold front drives out 
remaining llvl trop moisture.

Tuesday...VFR all terminals.

Wednesday...Generally VFR w/low clouds moving into BGR and BHB
by the evening. 

Wednesday night...MVFR to IFR w/some showers and fog setting.
Tstms are possible.

Thursday...IFR w/fog and leftover showers/drizzle for all
terminals. Improvement by late morning to MVFR and VFR as the 
cold front apchs from the w. Showers and tstms expected by the
afternoon which could drop conditions briefly to MVFR and
perhaps IFR.

Friday...VFR w/occasional MVFR possible across the northern


NEAR TERM: Locally dense marine fog will continue tdy and a good
ptn of the ngt until offshore winds behind a weak cold front
dries the BL by erly morn Tue. Went with about an 80 percent of
WW3/NWPS guidance blend for fcst wv hts, with recent obsvd buoy
wv hts a little less than guidance. Most sig spectral wv pd 
groups still include a 6 to 7 sec nwrd propagating regional 
short wind fetch group and a 10 sec nwwrd propagating background
swell group from the open N Atlc ocean. 

SHORT TERM: WSW winds around 10 kts will back to the ssw on
Wednesday. Seas will average around 3 ft w/a gradual buildup to
4 ft by Wednesday night. Visibilities will be reduced in fog 
Wednesday night. SW winds will increase to 10-15 kt on Thursday
ahead of the apchg cold front w/wind veering to the W later
Thursday night into Friday. Gusts could apch 20 kts especially
for the outer zones. 





Near Term...VJN
Short Term...Hewitt
Long Term...Hewitt