Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 221728 AAD AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 128 PM EDT Thu Sep 22 2016 .SYNOPSIS... High pressure centered over Vermont will gradually drift offshore by late today. A cold front over the Saint Lawrence valley will gradually sink southward into the mountains and foothills later today accompanied by a few clouds and widely scattered showers. Low pressure will track east along this front tonight accompanied by more widespread shower activity. The low will exit the coast early Friday and help drive the front and showers to the south of the area by evening. Dry conditions and the coolest air of the season are expected over the weekend, and through much of next week, as a large Canadian high pressure system builds south across the area. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1217 PM Update: Very minor changes this hour primarily to match hourly temperatures and fully clear sky cover over southern NH and southwestern ME. 940 AM Update: Modified temperatures today to better define afternoon seabreeze...but with little change to expected high temperatures. Also adjusted sky cover for current band of altocumulus as a ribbon of mid level moisture /seen in GYX 12Z RAOB/ pushes east. Mostly sunny skies will be the rule outside of this area with deeper moisture not arriving until evening over the north. 622 AM...Minor ESTF update to reflect the 10z mesonet in near term grids. Prev Disc... At 06z...a 1024 millibar high was centered over southern Vermont. A cold front extended from the rooftop of Maine into the Saint Lawrence valley. GOES infrared imagery showed mainly clear skies across the forecast area. The light winds and clear skies were allowing patchy stratus and fog to form across interior valley locations. For today...the surface high will slide east and offshore. The cold front will gradually sink southward into our mountains and foothills by evening. It`ll be accompanied by increasing clouds and a low chance for a late day shower near the international border. Highs today will range from lower and mid 80s over the southern half of New Hampshire and adjacent southwest Maine to the 70s elsewhere. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Low pressure will race east along the slow-moving cold front tonight with the most widespread showers found from the northern third of New Hampshire eastward through the western Maine mountains and foothills. lows will be in the 50s to around 60. The low exits the coast Friday morning and will serve to drive the front to the south of the area by evening. Showers with the frontal boundary will end from north to south during the day as drier air begins to spread in from the north with some late day sunshine for northern areas. Highs will range from the 70s over southern New Hampshire and adjacent southwest Maine to the 60s elsewhere. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... The focus of the extended still is on the cool shot expected for the weekend that will gradually moderate as we head into next week. There remains strong model agreement on both strength and location of ridging...up thru Nunavut. The greater than 3 standard deviation anomaly in the Nrn reaches of Canada will have the tendency to lead to lower than normal heights both W and E of the ridge axis. One such anomaly looks to at least brush New England over the weekend. The real core of the cool air does not look like it will head for the heart of the region...but model forecasts still bring H8 temps below zero for Nrn zones. The CAA accompanying this will bring breezy conditions Sat and Sun...with a chill in the air despite some sun. The pressure gradient Sat night may preclude frost by keeping the boundary layer somewhat mixed. A better chance looks to be Sun night...as surface high tries to nose into New England. If we can decouple...low temps in the low to mid 30s look possible for Nrn zones. The forecast becomes more uncertain beyond the weekend when it comes to how quickly ridging breaks down. The 22.00z ECMWF is a little more progressive and breaks down the ridge in only a couple of days. The GFS on the other hand lingers ridging over the Northeast thru the middle of next week. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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Short Term /Through Friday Night/... Summary: A cold front will slowly settle through the region tonight and on Friday bringing deteriorating flying conditions. High pressure and drier air will arrive from the north Friday night with conditions improving. Restrictions: VFR at the moment all sites. As the front arrives from the north tonight...expect deteriorating conditions /some IFR fog possible LEB ahead of the front overnight/...with shras possible HIE/AUG/LEB/RKD by daybreak Friday...spreading south during the day. This will likely bring a period of MVFR restrictions as early as late tonight HIE...spreading to LEB/AUG through early Friday. Confidence decreases further south...where restrictions may be more brief as shower activity weakens. Improvement to VFR is likely all sites Friday night...with additional restrictions possible HIE/LEB in fog development. Winds: Southerly winds less than 10kts today /with sea breezes developing at all coastal sites/. Winds will go light/variable tonight before gradually shifting northwesterly and increasing to 12g18kts for the day on Friday before decreasing to less than 10kts from the northwest Friday night. LLWS: West/southwesterly winds ahead of the front will strengthen tonight...with 1-2kft winds increasing to around 30kts overnight with a period of LLWS. No LLWS beyond this. Thunder: Very slight chance of a thunderstorm Friday afternoon over far southern NH /MHT/...otherwise no thunder is expected. Long Term...VFR to prevail thru the weekend and into early next week. High pressure will be building in over the weekend...which may bring breezy conditions but dry S of the mtns. Will have to watch for some upslope clouds bringing MVFR CIGs to HIE Sat and Sun before the high center arrives. Sun night could see clear and calm promoting fog in the river valleys...so local IFR or lower is possible...especially at LEB...HIE...CON...and MHT.
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&& .MARINE... Short Term /through Friday/...Quiet on the waters with winds and seas remaining below SCA criteria today. Winds and seas will increase tonight and Friday as a cold front gradually sinks south across the region...but should remain below small craft threshold. Long Term...As front slips S across the waters Fri night into Sat...winds and seas may briefly approach SCA thresholds...especially outside of the bays. Then steady offshore flow should build seas to around 5 ft on the outer waters into early next week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM UPDATE...Arnott SHORT TERM... LONG TERM... AVIATION...Arnott/Legro MARINE...

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