Area Forecast Discussion
Issued by NWS Portland, ME

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026 FXUS61 KGYX 280022 AFDGYX Area Forecast Discussion National Weather Service Gray ME 822 PM EDT FRI MAY 27 2016 .SYNOPSIS... Warmer air will continue moving into the region through the first part of the weekend...with the hottest temperatures expected for Saturday. A few scattered showers or thunderstorms may pop up in the afternoon. A cold front will push in from the northeast Saturday night...and likely stall near the Connecticut valley and southwest New Hampshire on Sunday...with onshore flow and cooler temperatures across Maine and part of New Hampshire. Another front approaches from the west Monday and makes for a mainly cloudy and humid day with scattered showers and thunderstorms. High pressure will move in for the remainder of the week yielding dry and seasonable weather. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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815 pm update: Increased pops across northern Somerset and Franklin counties for the next few hours as thunderstorms currently moving through that area. Fog continues to spread south and west...considering high dewpoints over the cold atlantic supersaturation occuring and some visibilities already down to a 1/4 mile in fog so am considering issuing a dense fog advisory along the coast for the rest of the night. Will be monitoring the fog situation along the coast and the adjacent inland areas closely. 645 pm update: Visible satellite loops through the afternoon showed widespread fog just offshore and along the immediate coastal areas of the midcoast moving slowly west. With no mention of fog in forecast...have made a significant update to forecast to include this widespread fog over the waters and the coastal and inland midcoast areas tonight as well as spreading the fog west into southwest coastal Maine by late this evening. The question for the remainder of the night will be how far inland the stratus and fog move. Temperatures were adjusted based on latest obs. previous discussion: Clouds have finally burned off over much of the coastal plain, but visible satellite imagery shows clouds lingering just offshore. The diurnal seabreeze circulation will push these clouds onshore over the next few hours. Meanwhile a warm and moist air mass to the west of the mountains continues to bubble up with cumulus clouds and a few showers and thunderstorms over New York, Vermont, and far western New Hampshire. This activity may affect parts of southern and western New Hampshire at some point this evening but it is not expected to be widespread. Temperatures should drop into the 60s across most of New Hampshire tonight, while 50s will be common across Maine where the cooler maritime air will be felt.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Weak low pressure moving toward the Gulf of Saint Lawrence will send a frontal boundary through New Hampshire and Maine on Saturday. Ahead of the front, winds will be out of the west/northwest. This will allow the building heat and humidity to our west to spill into the rest of New Hampshire and much of western Maine. There is a fair amount of difference between the NAM/GFS on low level temperatures tomorrow with the NAM about 3C warmer than the GFS. As a result, the MOS numbers are pretty far apart with the MET going for a high of 97 at Concord while the MAV says only 88. Tend to favor the NAM in this case as it seems to have a better handle on this air mass so far. Record high at Concord is 94 and this appears to be in jeopardy. Dewpoints in the low to mid 60s will allow heat index values to rise to 95 degrees or higher in parts of southern/urban New Hampshire. Further to the east along the coast a sea breeze will keep things a little cooler. With the synoptic winds expected tomorrow, the sea breeze will be most likely east of Portland. With the heat and humidity building, there is some indication that afternoon instability will be enough to generate showers and thunderstorms. NAM is more aggressive with this, indicating CAPE values above 1200 while the GFS is generally less than half that. There is no obvious forcing mechanism for thunderstorms Saturday, but the terrain and frontal boundary/sea breeze may be enough to force some storms to fire during the afternoon. This activity should diminish during the evening. The cold front finishes its push southward and then westward across the area Saturday night. A cool/moist onshore flow will be in place across the area and cannot rule out some low clouds and drizzle particularly over southeast New Hampshire and southwest Maine. && .LONG TERM /SUNDAY THROUGH FRIDAY/... High impact weather: A few thunderstorms late Sunday night and Monday could produce torrential downpours, and there is a low risk for flash flooding. The overall 500 mb pattern starts out summer-like, with strong western Atlantic ridging in place. Although the ridge starts off extending poleward to Newfoundland, several waves in the flow do knock the ridge gradually back toward the equator. The temps will moderate somewhat but will remain near to above normal thru next week. A chance for showers come mid-late week as a cold front moves thru, but there is no sign for any significant rainfall in the extended forecast. Sunday will start cool with onshore flow persisting behind the back door front. Sunday looks to be mainly dry, but could be fairly cloudy with the onshore flow, although some decent drying above the marine layer could lead to some breaks of sunshine thru the day. The best chance for showers or thunderstorms will be in the north and western zones where the frontal boundary will be sitting on sunday. In fact, CT valley region will likely be on the warm and humid side, while elsewhere temps remain cooler, mainly in the low-mid 60s coast to mid 70s in inland areas on the coastal plain and the foothills. Sunday night will see the marine layer start to erode a bit as warmer pushes in aloft. Clouds will roll in and the threat of showers will increase overnight...as will the humidity from SW to NE. A cold front approaches from the west on Monday, and this will set off showers and storms again in the warm moist air ahead of the front. Even along the coast where marine layer will hold on, should be enough elevated instability that we cannot rule out a thunderstorm here on Monday. The big question is how much, if any, moisture gets picked up from current fledgling tropical system in the Atlantic. Models are in fair agreement that the system moves west too the Carolina coast by Saturday night, but models vary after that. Still could see some of that tropical air mass get shunted northward ahead of the cold front and bring some heavy rain in convective cells late Sunday into Monday, but confidence remains low at this time. Air mass behind the so-called cold front that passes Monday night will remain warm and humid and will need to wait for second surge of cooler air late Tue and Tue night. So Tue will be on the warm and somewhat humid side, although with a fair amount of sun. This secondary cold front moves thru with little fanfare...and may produce a few scattered showers in the mountains on Tuesday. After that temps drop back to near to a little above normal thru the end of the week before another cold front approaches on Friday. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Short Term...Conditions start out VFR this afternoon for most areas, though some low clouds are lurking just offshore. These clouds will likely surge into coastal areas over the next few hours, particularly from Portland eastward. This could bring conditions to IFR or LIFR. Winds become southwesterly by morning which should shift the focus for IFR clouds to eastern parts of the area. This should burn off by mid morning with all areas becoming VFR Saturday. Afternoon showers and storms are possible especially over southern New Hampshire and southwest Maine though the likelihood of affecting any particular TAF site is too low to mention at this point. Long Term...Sunday will start with some IFR, but will see some improvement to MVFR or VFR during the day. A return to IFR expected Sunday night lingering into Monday, with scattered thunderstorms on Monday. VFR returns for Tue/Wed. && .MARINE...
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Short Term...Widespread dense fog over trhe waters tonight. Southwesterly winds become northerly then northeasterly behind a cold front Saturday evening. High pressure slides east into the Atlantic on Sunday with winds becoming southeasterly. Winds through the period should stay below 25 KT with wave heights fairly low as well. Long Term...Winds seas will remain blow SCA conditions Sunday through Wednesday.
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&& .FIRE WEATHER... Warm and humid conditions are expected Saturday. A cold front brings cooler weather Sunday with a moist onshore flow over Maine and eastern New Hampshire. Although showers and storms will be possible Saturday and again early next week, no widespread significant rainfall is forecast. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$

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