Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 250139 AFDGYX Area Forecast Discussion National Weather Service Gray ME 939 PM EDT Wed May 24 2017 .SYNOPSIS... Low pressure over the Ohio Valley will slowly drift east and redevelop along the Mid Atlantic coast Thursday. The system will then move northeast into the Gulf of Maine Friday and into the Canadian Maritimes Saturday. Weak high pressure will build over the region on Saturday. Low pressure will approach from the west on Sunday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Any leftover sprinkles or isolated showers will be ending over the mountains through midnight which were mainly diurnally driven. Clouds will advance into southern sections overnight, however mainly high clouds. This may prevent fog from forming over much of the region. As the CU continues to dissipate over northern/mountain sections, there is the possibility of late night patchy fog further away from the approaching storm. Made minor adjustments to surface temperatures and dew points during the overnight hours based on current trends. Overnight lows will bottom out in the lower 50s in many communities as clouds continue to increase and thicken late tonight into Thursday morning, making for relatively uniform readings. There will be some cooler 40s in the mountains. Prev Disc... Temperatures have peaked in the 60s and 70s with coastal locations already cooling under the influence of a weak sea breeze. An extensive cirrus shield associated with low pressure passing offshore will gradually shift east with time along with a baroclinic zone. Over the Ohio Valley a deepening low pressure system is being fed by tropical moisture and lofting additional cloud cover towards New England. A warm front extending from this system snaked into NY State and was lifting north. Models are still showing some light showers over the mountains along the warm front...but currently we seem to be too dry for anything to reach the ground. There is still a possibility of a light shower late this afternoon and evening over the higher terrain. Expecting a quiet and dry night for most locations with mostly cloudy skies. Overnight lows drop into the 40s and 50s.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Clouds and precipitation chances increase Thursday as the Ohio Valley stacked low nears from the SW. Showers arrive in southern NH late morning and move east during the day. The surface low will rotate offshore near Cape Cod and generally stay well south of the Gulf of Maine as it moves east. This will keep more precipitation on the coast and less inland. Easterly winds will be gusty and keep conditions raw and cool in a marine layer which will extend well inland. This will prevent any chance for thunderstorms. Highs will be capped in the upper 50s and 60s. Thursday night into Friday morning will have widespread rain with some heavy downpours. The majority of the heaviest rains will fall during this time. Once again more precipitation will fall along the coast and just inland than falls towards the north. Expect some fog and drizzle during this time as well. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... An overall very active, cool, and wet pattern for the outlook period. Low pressure will continue to redevelop along the mid atlantic coast and move into the Gulf of Maine Friday. A broad damp onshore flow with cool temps expected. Widespread rains are expected across the region with total QPF amounts from the storm ranging from around a 1/2 inch in the mountains to 1.25 along the coast. Astronomical high tides will continue to be a problem due to the onshore flow (see Tides/Coastal Flooding section). The system exits the region northeast into the maritimes on Saturday with weak high pressure following allowing for some clearing. By late Sunday another approaching upper s/wv rotating northeast toward New England will spread another period of cool damp onshore flow as it allows another weak secondary low to redevelop off the southern New England coast and moves it into the Gulf of Maine Monday. This system quickly exits into the maritimes Monday night followed by another weak area of high pressure for Tuesday. Another upper trof with more wet unsettled weather should arrive for Wednesday. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Short Term...VFR today through tonight. IFR/LIFR ceilings and visibilities will develop on Thursday in showers for southern terminals before spreading north. RA which will become heavy between 00Z-12Z Friday for coastal/southern terminals. Fog and drizzle will be prevalent- especially along the coast further decreasing flight conditions. Areas of MVFR ceilings/ visibilities are more likely for the north. Long Term...IFR conditions Friday. Significant improvement likely will not occur until Sat...when low pressure begins to pull away. Weak ridging Sat into Sun will allow a return to VFR conditions. && .MARINE... Short Term...SCAs have been issued beginning early Tuesday afternoon through Friday afternoon for building seas and gusty winds. Long Term...SCA conditions will continue into Fri night as a coastal storm strengthens in the Gulf of ME. Low pressure will not pull away until Sat...so winds and seas will only gradually diminish into the weekend. && .TIDES/COASTAL FLOODING...
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Minor and isolated coastal flooding is possible this evening from Portland and points south along the coast. However, any high water issues should be minor and with limited wave action, any splash-over will likely be minimal. Higher astronomical tides expected Thursday night with ENE onshore winds increasing and waves gradually building over the region. ESTOFS forecast and Splash-over matrices suggest there should be some areas with minor coastal flooding and splash-over and advisories will likely be needed. In Hampton, water levels approaching 12 feet will be on the high end of the minor category and moderate coastal flooding is possible in that location.
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&& .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 2 PM Thursday to 2 PM EDT Friday for ANZ151-153. Small Craft Advisory from 11 AM Thursday to 2 PM EDT Friday for ANZ150-152-154. && $$ JC

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