Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 222345 AFDGYX Area Forecast Discussion National Weather Service Gray ME 745 PM EDT Sat Jul 22 2017 .SYNOPSIS... A cold front across the forecast area will exit into southern New England tonight before stalling. High pressure will build by to our north overnight through Sunday and provide some clearing mainly to northern sections of New England. Low pressure will approach from the southwest later Sunday night and for Monday and will deliver cooler temperatures and the likelihood of rain. Conditions will gradually improve by Tuesday night and Wednesday as high pressure moves in. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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730 PM Update... Cold front continues to drop slowly southward early this evening. Band of showers ahead of this boundary has developed across central New Hampshire. HRRR has a pretty good handle on this activity which it gradually drops south into southern New Hampshire by around midnight before shifting out of the forecast area during the early morning hours. Have adjusted pops and wx grids based on current radar trends. Aside from a few tweaks to temps/ other changes planned attm. Previous discussion... At 18z the cold front extended from mid coast Maine westward through central New Hampshire and into upstate New York. This boundary continues to inch southward and will provide a weak focus for widely scattered convection through early evening. The NWS Doppler Radar mosaic has showed some widely scattered echoes over the past few hours and expect that to continue. The boundary will finally settle into southern New england and Long Island Sound by morning before stalling. Clearing should be confined to northern the remainder of the region remains on the northern periphery of the high and mid cloud shield.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... On Sunday...the northeast synoptic flow between the surface high over eastern Canada and the stalled front to our south will gradually become more easterly. Much of the area will remain on the northern periphery of the high cloud shield from the stalled baroclinic zone and those clouds and the onshore flow will limit highs to the mid 70s to lower 80s. It should be a dry day with comfortable humidity levels. Sunday night...thicker clouds will gradually spread north and east in developing warm air advection ahead of approaching shortwave impulse and associated surface reflection. showers should gradually spread north and east in the predawn hours and reach all but our far northern and eastern Maine zones by morning. && .LONG TERM /MONDAY THROUGH SATURDAY/... A temporary pattern shift will occur, with cooler and more raw conditions developing for the beginning of the work week next week. Some much needed rainfall may finally reach the coastline which has missed out on much of the convection during the past month or so do to cooling onshore breezes. Upslope conditions may allow for locally heavy rainfall in the mountains. Temperatures to begin the week well below normal with widespread 60s for daytime highs. Details are below. A significant upper level trough for mid to late July swings east and into New England on Monday. This will trigger cyclogenesis along the south coast of Massachusetts during the day. This will provide a cool and raw northeast flow over the region. Low cloud cover will keep readings in the 60s over many areas, especially near and along the coastline. Showers will break out. The atmosphere will remain fairly stable at the surface, but instability aloft may be sufficient for a few embedded thunderstorms. With high precipitable water values and the likelihood of showers throughout the day, there may be some pockets of locally heavy rainfall. As the showers and isolated storms continue Monday night, the threat of the possibility of localized flooding will be on the increase, mainly in favorable upslope areas where persistent heavy showers are a possibility. By Tuesday, the surface low will begin to exit to the east towards the Canadian Maritimes near Halifax Nova Scotia. With a wind shift, most of the showers will exit the region over southern areas. However, the H7 and H5 low will remain over the region, allowing an easterly upslope flow to continue over the mountains. This will allow for additional showers across the higher terrain during the day. All areas finally begin to have drier air advect into the region Wednesday as the upper level trough shifts to the east and a ridge of high pressure builds into the region. Yet another cold front will approach the region on Thursday, before crossing off the coastline by Friday. This will add a few more scattered showers and perhaps a thunderstorm during the period. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... Short Term /through Sunday Night/...VFR tonight and Sunday with river valley stratus and fog psb late tonight. Areas of MVFR developing aft 05z Mon in -shra. Long Term...Monday will continue to lower into IFR conditions as log pressure develops. There may be an embedded thunderstorm. IFR conditions will likely persist throughout the night especially along the coast Monday night. Conditions will improve on Tuesday with mostly mountain shower activity and increasing ceilings to the south. High pressure builds back in for Wednesday. && .MARINE... Short Term /through Sunday Night/...NE flow will develop behind a cold front tonight and could briefly approach small craft at times in gusts outside the bays overnight into Sunday. Long Term...A low will develop south of New England through Monday. This will bring increasing easterly winds to the waters with small craft conditions potentially during the day on Monday. A strong low level jet may result in a few gusts over SCA thresholds in regions of heavy showers. High pressure will move in for Wednesday with subsiding winds and seas. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.