Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 251518 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1118 AM EDT Mon Sep 25 2017 .SYNOPSIS... High pressure will hold over the region today through Tuesday night with temperatures remaining well above normal. A cold front will approach from the west on Wednesday and will cross the region Wednesday night. Expect a cooler and drier air mass for the rest of the week while Hurricane Maria passes by well to the southeast. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1100 Am Update... Quick update to adjust temp/td/sky and RH grids. Morning valley fog has pretty much lifted across the region with some cu development occurring over the higher terrain in the mountains. Looking for a mostly sunny afternoon with temps once again soaring to near record levels. A developing sea breeze will knock temps back into the upper 70s to lower 80s in coastal areas. May see a sprinkle or shower in the mountains but these should be light and widely scattered. Prev Disc... Update... Have updated the grids based on current conditions. Areas of dense fog continue to expand in western and northern NH as well as portions of the western mountains of Maine. Have raised a dense fog advisory good until 9 am. Otherwise, just a few minor modifications to the morning forecast. Prev Disc... Patchy dense fog expected early this morning. Visibilities locally near a quarter of a mile in fog, but not widespread at this time. Nevertheless, will highlight with a Special Weather Statement for the morning commute. A large ridge of high pressure will remain entrenched over the region today. H8 temperatures near +17C, sunshine and relatively good mixing is expected after the morning fog dissipates. This will allow for another very warm day with readings in the 80s in just about all sections except for the Midcoast region of Maine as winds become onshore near the coast in the afternoon. Moisture will be on the increase today with surface dew points approaching 70 in some areas. This will make it feel even more uncomfortable especially for so late in the season with heat indices climbing into the lower 90s over portions of southern New Hampshire. Sufficient instability and differential heating to possibly trigger a stray shower or isolated thunderstorm near and over the higher terrain today. This is supported by this morning`s mesoscale models. Any convection will likely remain over the higher terrain as wind fields remain very light to spread the shower activity off the hilltops.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Patchy fog once again tonight with visibilities lowering once again. High pressure will remain in control as a warm front remains just north of our region. By Tuesday, expect a repeat performance from Monday. However, temperatures may not be quite as warm as additional cloud cover will drift over the region from an approaching cold front. There may be a slight chance of a shower late in the day over far northern areas as a cold front approaches from the northwest. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... The large ridge which has brought sustained warmth to New England for quite some time will get chipped away at by several progressive troughs this week. The first passes by well to the north on Monday, but in its wake it shoves a cold front southward into northern Maine Tuesday night before stalling. This could be the focus for a shower or two Tuesday night and Wednesday, but otherwise expect the heat and humidity to continue across the area. A southerly low level wind will keep temperatures down a bit across Maine, but humidity remains high. The next trough moves through the lower Saint Lawrence Valley Wednesday into Wednesday night, sending a stronger front southeastward into New England Wednesday night. This will be an air mass changer for our region, with the heat and humidity being swept off to the northeast while cooler and drier air push in from the Canadian prairies. There will be some showers and thunderstorms along the front as it moves toward our area Wednesday night, but the best forcing for precipitation will be sliding off to the northeast, so the best chance of rain will be in the far northwest while coastal locations stand a good chance of remaining dry. Once the front moves offshore it will begin interacting with Hurricane Maria which will have drifted northward to a position south and east of Cape Cod. Expect Maria to be pulled quickly to the east and stay far enough south to avoid any impacts in our area. Meanwhile, the cooler, drier air will bring temperatures back to near normal levels by Friday and Saturday. Another trough swings through New England on Saturday and could provide another chance of showers as it does so. But this trough will be filling as it moves through and does not have a good moisture connection, so precipitation chances will be rather meager. It will, however, send a reinforcing shot of cool, dry air into the region, with high pressure building in for Sunday and Monday. Expect some good radiational cooling conditions at night as high pressure sits over our area for a couple of nights. Although a few spots managed to reach the freezing mark way back on September 2nd, this could be the first freeze of the season for other protected valley locations in the north. This is about two weeks later than normal. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... Short Term...VFR conditions today through Tuesday with high pressure overhead. Patchy fog expected once again tonight over most of the inland valleys. Long Term...A flow off the water on Wednesday could bring in some lower ceilings and visibility late Wednesday into Wednesday night ahead of a cold front. This front will produce some showers and a few thunderstorms in northern areas. Expect VFR conditions to return on Thursday. && .MARINE... Short Term...Winds and seas will remain below SCA thresholds as high pressure remains over the region. Long Term...Although winds remain light over the waters, some larger swells from the tropics may begin arriving Wednesday into Thursday. A cold front will cross the waters early Thursday. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...None.
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