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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 250413

Area Forecast Discussion
National Weather Service Caribou ME
1213 AM EDT Tue Jun 25 2019

High pressure will cross the region tonight. A warm front will 
approach later Tuesday then cross the region Wednesday. A cold
front will approach Thursday.


12:13 AM Update: The combination of a clear sky, light/calm 
wind, and a dry air mass is allowing temperatures to drop into 
the low 40s in the deeper northwest valleys with 50s on the 
hills as strong low level inversions develop. Updated the past 
few hours of observed data and made minor tweaks to the trends, 
but no changes to the forecast lows overnight. 

Orgnl Disc: High pressure will cross the region tonight then 
exit across the Maritimes Tuesday. Clear skies, light winds and 
dry air will allow favorable radiational cooling conditions 
tonight. Low temperatures will generally range from the mid 30s 
to lower 40s across northern areas. However, lower 30s with 
patchy frost is possible across the normally coldest valleys of 
the north woods. Any patchy frost is mostly expected in remote 
non- agricultural valley locations of the north woods. Thus, 
have not issued a frost advisory. Low temperatures across the 
remainder of the region are generally expected to range from the
lower to mid 40s, with local upper 30s in the normally coldest 
locations inland from the coast. A warm front will begin to 
approach later Tuesday. After a mostly sunny morning, expect 
increasing clouds during the afternoon. Showers will then begin 
to expand eastward across the forecast area during the 
afternoon, not reaching eastern areas until toward evening. High
temperatures Tuesday will range from the lower to mid 70s 
across much of the region, with upper 60s to around 70 along the
Downeast coast.


The warm occluded front will cross the forecast area Tuesday
night into early Wednesday morning. The front will be weakening
as it crosses the area. Expect up to a quarter inch of
rainfall, and maybe a bit more towards the coast depending on 
any elevated convection and the evolution of a weak area of low 
pressure in the Gulf of Maine later Tuesday night into 
Wednesday. The weakening front will leave behind a frontal 
inversion for most of the area on Wednesday, as well as a more 
humid air mass. This means clouds will linger much of Wednesday 
except far northwestern zones where highs may break into the 
70s. This could result in a few showers on the western 
international border. Elsewhere, highs will remain in the 
60s, and the immediate coast and outer islands may stay in the 
50s with the low clouds and fog. Another round of low clouds 
and fog is expected Wednesday night. Later Wednesday night, a 
weakening shortwave upper trough will bring the risk of showers 
to northern zones. Elevated convection will be possible, but 
will not include in the forecast at this time. This feature will
also help pump up dew points into the 60s for Thursday. Will 
increase the chances of thunderstorms to the chance category on 
Thursday. Any convection will be delayed until morning low 
clouds and fog burns off and will start in the far northwestern 
zones before propagating eastward. This low level moisture, 
increasing shear and a cool upper trough will produce a decent 
risk of some strong afternoon thunderstorms for the first time 
this year. The best instability will remain in northern and 
western zones with low probability of any convection towards 
the coast on Thursday afternoon.


The humid air mass and shower activity continuing into Thursday
evening makes fog a threat Thursday night. Otherwise, the upper
trough gradually moves east by Friday morning. Have reduced PoPs
on Friday with this forecast package and confidence is not high
enough to include mention of thunderstorms with upper level
ridging. Another vigorous shortwave moves south from Quebec
later Friday night into Saturday and will bring another round of
showers and potential thunderstorms Saturday afternoon and
Saturday night. The chance of stronger thunderstorms is probably
better in the southern half of the forecast area based on the
current timing and evolution. This system evolves into a closed
upper low that crosses the state on Sunday with showers 
continuing, but likely more stable without thunderstorms. The 
entire closed upper low moves south of the area for Monday with 
precip ending, but a lot of low level moisture will ensure 
continuing cloudiness and a few sprinkles.


NEAR TERM: VFR conditions are expected tonight through much of
Tuesday. Occasional MVFR conditions will then begin to develop 
later Tuesday afternoon with developing showers. 

SHORT TERM: Tuesday night will start VFR/MVFR, but cigs will 
deteriorate to MVFR and then IFR by later in the night. Fog 
could affect BGR, GNR and BHB by late night into early Wednesday
morning. For Wednesday, cigs will slowly lift through the day 
but may struggle to exceed MVFR along the eastern border from 
Machias towards CAR and FVE. The low IFR cigs return Wednesday 
night into Thursday morning. Fog will again push inland 
Wednesday night, reaching as far north as GNR, MLT and HUL. Once
the fog and low clouds lift on Thursday, thunderstorms will be 
a threat for Thursday afternoon and evening. The fog risk 
returns Thursday night, but all sites should lift to VFR by 
later Friday morning into Saturday morning. Thunderstorms become
a risk again for Saturday afternoon.


NEAR TERM: Winds/seas will remain below small craft advisory
levels tonight through Tuesday. Visibilities could begin to
lower in developing showers later Tuesday afternoon. 

SHORT TERM: Winds and seas will increase Tuesday night ahead of
a weak low pressure, but due to stable conditions, can't foresee
much more than a few gusts to 20 kts and seas up to 4 feet.
Otherwise, fog dominates the forecast from late Tuesday night
until Friday morning. Thunderstorms will be possible on 





Near Term...CB/VJN
Short Term...MCW
Long Term...MCW