Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 161639 AAD AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1239 PM EDT Wed Aug 16 2017 .SYNOPSIS... High pressure will continue to build into New England through Thursday bringing dry conditions and seasonable temperatures. On Friday...a warm front associated with low pressure over the Great Lakes will lift through the region followed by a cold front Friday night. These features will bring the threat of showers throughout the region. High pressure will build back into the region this weekend with warming temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1132 AM Update...Boosted late morning temperatures particularly along the coast based on observations...with a small increase in cloud cover also necessary based on visible satellite imagery. Much drier air is arriving /note quick drop in dewpoint at Rangeley to 45 last hour/ with should help scour out remaining clouds. Expect high temperatures to occur a bit early today along the coast as better cool advection is now arriving and will help slow the rapid rise we/ve seen in the downslope regime late this morning. No other significant changes at this time. 920 AM Update...Quiet weather across the forecast area this morning as high pressure centered north of the western Great Lakes builds south and east towards the region with deep layer subsidence overhead. Have updated near term temperatures to match observations...where values are increasing more rapidly than inherited forecast. 12Z GYX RAOB shows plenty of room for drying and will lower dewpoint some in line with near term mesoscale guidance...with dewpoints falling back into the 40s /see similar values already showing up north of the international border/. Otherwise...only very minor changes to the forecast. Original discussion below... Overnight shower activity has fallen apart as the weak cold front pushes into our area. With moist dewpoints in the 50s expect fog to continue to form through dawn, with some dense fog in the favored valley locations. Today will see valley fog dissipate after sunrise. Increasing northwesterly flow will bring drier air into the region during the day. The pressure gradient will be just strong enough to keep the seabreeze at bay and a few gusts to around 20kts are possible in the coastal plain this afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Overnight high pressure builds over the region. Clear and dry conditions will allow for good radiational cooling as the atmosphere decouples. Widespread overnight lows in the 40s will be the result. With dewpoints preventing the temperatures from falling further, expect patchy fog in the valleys by morning. Thursday will once again be sunny as high pressure remains overhead. The upper low will remain to our northeast once again keeping steady northwesterly flow across the region. Highs will be near 80 south to 70 north. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Surface ridging will be in place to start the period across Nrn New England. Aloft...the ridge axis is not forecast to cross the region until at least midday Fri. So I think precip will have a tough time moving in/developing until that as shifted to our E. On the boundary of the WAA aloft and departing ridge...there may be a band of showers that moves thru. More likely the narrow warm sector will develop into more of an occlusion Fri night with a more strongly forced band of showers and embedded thunder. Models forecast some sharp drying aloft behind this...so rainfall should come to a quick end from W to E into early Sat. The main cold front will not cross the area until later in the day...so the threat of more isolated convective precip will remain in the forecast until then. Main cold pool swings thru aloft on Sun...so it could be a day of destructive sunshine where insolation leads to development of more clouds. Lingering moisture in the cyclonic flow over the terrain should also keep the mtns in the clouds with an isolated shower or two. Early next week high pressure will build to the S of the region. At this time it looks like it will reach far enough N to keep any frontal boundaries N of the forecast area. That high will gradually drift Ewd thru the week...and by midweek SW return flow is expected over the area as the next trof and frontal boundary approach the region from the W. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... Short Term... Summary: High pressure will build into the region through Thursday...before moving east of the area Thursday night. This will allow for generally good flying conditions through the period. Restrictions: VFR conditions will dominate the TAF period outside of overnight fog potential HIE/LEB tonight...with somewhat lesser potential again on Thursday night. Solid agreement from the guidance and climatology for a period of LIFR/VLIFR fog in the 8-13Z timeframe at HIE/LEB early Thursday. Otherwise...expect mostly clear skies to dominate through Thursday before increasing high and mid level cloudiness arrives Thursday night. This cloudiness...if it arrives fast enough...may help preclude additional fog development Thursday night. Winds: Northwest winds 10g18kts will continue through the afternoon before diminishing to 5kts or less tonight. Northwest winds will again strengthen to 10g18kts /strongest AUG-RKD/ for the day on Thursday before likely going calm/light-variable Thursday night. LLWS: No LLWS expected through Thursday night. Lightning: No thunderstorms expected through Thursday night. Long Term...As warm front lifts towards the area and flow becomes onshore...conditions will deteriorate to MVFR or lower across the area. Conditions near the coast will need to be watched...as some coastal fog/stratus is possible. At this time it looks like front will be delayed enough that stratus will have a smaller window to move into coastal Nrn New England. Cold front will sweep across the forecast area Sat...and local IFR conditions are possible in SHRA/TSRA. High pressure will build in Sun with a return to VFR conditions. && .MARINE... Short Term... While the high pressure overhead will keep locally generated hazards to a minimum Hurricane Gert passing off shore will have an effect on the waters in the form of long period swell. Waves of around 5ft with a 12 second period are expected to propagate from Gert as it passes 500 miles south east of the Gulf of Maine. These waves will impact the more south facing aspects of the coast from the midcoast through downeast. A High surf advisory has been issued for the area from tonight through late Thursday for Knox, Lincoln, and Sagadahoc counties, including the offshore islands. A small craft advisory for hazardous seas is also in effect for the adjacent waters during this time period. Within Penobscot bay and Waldo county, as well as further south within Casco bay and Cumberland county, the sheltering effect of the islands and bays, combined with the more east facing aspect will keep surf heights lower. Long Term...As swell from Hurricane Gert diminishes a persistent onshore flow will develop in response to a warm front lifting across the waters. Seas may build above 5 ft again on the outer waters...especially by Sat. Other than this window...winds and seas are expected to remain below SCA thresholds. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...High Surf Advisory from 8 PM this evening to 8 PM EDT Thursday for MEZ025>027. NH...None. MARINE...Small Craft Advisory for hazardous seas from 8 PM this evening to 8 PM EDT Thursday for ANZ150-152. && $$ SYNOPSIS...Arnott NEAR TERM...Arnott/Curtis SHORT TERM...Curtis LONG TERM...Legro AVIATION...Arnott/Legro MARINE...Curtis/Legro

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