Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 252141 AFDGYX Area Forecast Discussion National Weather Service Gray ME 541 PM EDT Thu May 25 2017 .SYNOPSIS... A broad area of low pressure from the Ohio Valley through the mid Atlantic coast will slowly lift northeast tonight...reaching Cape Cod by Friday morning. Low pressure will continue northeast into the maritimes through Friday night. Weak high pressure will build over the area on Saturday and will shift offshore on Sunday. Weak low pressure over the eastern Great Lakes will lift north into western Quebec Sunday night and will drive a cold front toward the region on Monday. The front will slowly cross the area Late Monday night and Tuesday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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Update... Have updated the forecast based on current conditions and latest set of mesoscale models. Rain continues to spread north and east, however it remains fairly light and fragmented in most areas. Heaviest precipitation remains over Upstate New York well to our west. However, satellite imagery continues to show a large plume of moisture forming off the Mid Atlantic coastline and moving quickly to the north. Mesoscale models have this heavier precipitation arriving from south to north within the 06Z and 12Z time frame. Have made minor adjustments to pops and temperatures for the next 6 hours. Areas of light rain will continue with downsloping over the northern Connecticut River Valley. Prev Disc... Higher pressure and easterly winds have kept much rain from intruding into northern New England by retarding the advancement of precipitation into Maine and northern and central NH until the last couple of hours. The flow has intensified along the coast as the pressure gradient increases/low pressure nears. Temperatures have been kept down in this marine airmass while northern sections were able to break out into the 60s. CAM models have been correct in showing a weakness this afternoon in precipitation fields over NH and especially Maine as energy diverges both towards northern NY State as well as offshore. We`ll see a break in most shower activity more or less this afternoon and evening...however there will be widely scattered showers still around...mainly over the mountains. Around midnight a stronger short wave associated with this system will pivot into the area and precipitation will increase both in intensity and areal coverage. This is when we will see the bulk of the 1-2 inches with this event. We`ll see some heavy downpours for the overnight period into Friday morning. Winds are picking up as mixing deepens today and expect ESE winds to gust to 25 kt through the night. Continued with drizzle tonight mainly in between the two systems as the onshore flow intensifies. Lows will be in the upper 40s to around 50.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... After the heavier rain expected during the morning hours...precipitation tapers off to showers by Friday afternoon. Again the heavier rain will be along the coast with some enhancement over terrain. The long duration of this event should preclude any flooding issues but poor drainage areas may see some brief issues in heavier rainfall that occurs through tomorrow. Expect temperatures to warm only about 5-10 degrees from overnight lows tonight to highs Friday. Tomorrow night clouds will begin to decrease across the region. The upper low will be engulfed in another circulation south of Greenland while the surface cyclone fills. Overnight lows Friday night will drop farther in a drier airmass with lows in the 40s most locations and perhaps up to 50 degrees in warm spots. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Mean long wave trof position will remain over the Great Lakes, this will mean a general cool wet pattern can be expect for the outlook period with a few dry periods between systems. Starting with Saturday, the system that exits into the maritimes allows weak high pres over the area and a drier north to northwest flow to develop for Saturday into Sunday with cool temps. By late Sunday into Monday, the next short wave that rotates around the base of the Great Lakes trof then moves northeast bringing another period of wet weather with a developing onshore flow that keeps temps cool. With the mean upper trof remaining over the Great Lakes through mid week a continue unstable southwest flow with embedded short waves with keep unsettled conditions through Wednesday. It appears we may finally get rid of the onshore flow by midweek so temps may actually get back to near normal high temps reaching into the 70s. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... Short Term...IFR/LIFR ceilings developing today and persisting through tomorrow. ESE winds will gust to 25 kts most terminals through tomorrow. Early on LLWS will affect HIE and LEB tonight. Drizzle and fog will affect most TAF sites outside of HIE and LEB tonight before the moderate to heavy rain arrives. Long Term...Winds and seas generally light. No flags. && .MARINE... Short Term...Continuing SCAs through Friday afternoon. At that point we may need a SCA just for high seas for the outer waters. Long Term...Conditions become VFR Sat into Sun before returning to MVFR conditions for Sun night and Monday and possibly through midweek in scattered showers. && .TIDES/COASTAL FLOODING...
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Highest astronomical tides of the year on tap for tonight and Friday night. A Coastal Flood Advisory remains in place for all coastal zones for around the time of high tide tonight. The astronomical tide in Portland is 11.8 feet near midnight tonight. Expect about a half a foot to locally as much as a foot of storm surge overnight. Flood stage in Portland is 12 feet. Localized minor flooding is expected with possibly pockets of moderate flooding, mainly in the Backbay area of Hampton New Hampshire. Will update the Coastal Flood Statement to increase the storm tide values.
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&& .GYX WATCHES/WARNINGS/ADVISORIES... ME...Coastal Flood Advisory from 10 PM this evening to 1 AM EDT Friday for MEZ023>028. NH...Coastal Flood Advisory from 10 PM this evening to 1 AM EDT Friday for NHZ014. MARINE...Small Craft Advisory until 8 PM EDT Friday for ANZ150>154. && $$ Cannon is the U.S. government's official web portal to all federal, state and local government web resources and services.