Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 151618 AAD AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1218 PM EDT Tue Aug 15 2017 .SYNOPSIS... A cold front will move south out of Canada today triggering scattered showers and thunderstorms, especially this afternoon. High pressure builds in Wednesday before another low pressure system affects the region Friday with the potential for a period of beneficial rain. Drier conditions develop Saturday with fair weather continuing into early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Noon Update... Cumulus clouds have developed as heating has ensued this morning...especially over northern and central areas of NH and ME. Temperatures have warmed into the 70s areawide. Dew points have increased a few degrees. All these components will contribute to thunderstorm development this afternoon. Some echoes are showing up in southern Quebec with lightning noted near and west of the St. Lawrence River Valley along a pre- frontal trough and slow moving cold front. We should see storms reaching our northern border shortly. SPC has expanded the area of marginal risk to include almost all of NH and ME save for coastal NH, coastal York county, and portions of the Mid Coast of ME. 935 AM Update...Cloud cover and showers are affecting portions of the coastline as well as southern sections of the forecast area. Skies are clear across much of the central and northern sections with some fog still being reported in mountain valleys and the Mid Coast of Maine. This will come into play later as storms fire along a southward moving cold front in areas which have received ample surface heating. Temperatures as well as PoPs were adjusted slightly. 650 AM Update...No significant changes to the going forecast this morning. Showers/light rain moving across southern zones as expected - just tweaked pops here and there. Otherwise, things are in good shape. Previously... A short wave trough will approach from the west today, likely delivering a bout of scattered showers and thunderstorms this afternoon. However, before then, WAA ahead of the approaching trough is allowing for a batch of showers across southern New England as of 07z. Some of these will move northeastward affecting southern NH and portions of coastal ME through mid morning. The HRRR seems to have a decent handle on this, so blended in a healthy dose of it for the morning hours. In addition, there will likely be some early morning fog and low clouds. For this afternoon, some SBCAPE should develop given moistening low levels along with breaks of sun. However, it should remain on the weak side mainly owing to weak mid level lapse rates. Nevertheless, as the short wave trough approaches, scattered showers and thunderstorms are expected to develop, with the greatest coverage expected across northern and central zones. Moderate deep layer shear should allow for some storm organization which may allow for a couple of strong to severe storms, with damaging winds being the main threat. Again, central and northern zones seem to be the main target as best forcing for ascent will ride northeastward into that region this afternoon. However, areas further south may see a few as well. Took a blend of available guidance for high temperatures today, which puts most locations in the upper 70s. However, if clouds and showers linger longer than expected this morning then highs may end up being a little bit lower than forecast.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Short wave trough pushes off to the east this evening bringing an end to the threat for thunderstorms early on. A few showers may linger over the mountains overnight, but most of the region should be dry. However, some fog may once again develop and become locally dense, especially where it rains this afternoon. Cooler and drier for Wednesday as high pressure moves in. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... The end of the week will start off with high pressure overhead but by the end of the week and upper level blocking pattern breaks down allowing low pressure to move in from the Great Lakes by Saturday. The upper level trough remains overhead through the end of the weekend before long wave ridging finally returns to the area for the start of the week. Wednesday night will see high pressure in place overhead with relatively modest 500mb heights as the strong low which had been forming the eastern end of the omega block begins to move into Labrador. With dry conditions throughout the atmosphere this will be a nice night for radiational cooling and as a result the low temperatures have been pushed downwards towards the lower end of guidance. 1000-500 thickness values are forecast to drop to near 550 dm through the north. The last time we saw similar values (July 23) low temperatures in the 30s were reported across interior northern Maine. Dewpoints will be the key factor in determining the low temperature and have opted to keep lows in the mid 40s across the north for now. Moving into the day on Thursday we see brief ridging make an appearance with sunny skies and a sea breeze. By Thursday night low pressure developing over the Great Lakes will begin to approach the area bringing southerly flow and increasing clouds. The arrival of the rain has shifted later in time when compared to last nights model runs, however this is consistent with the climatology of blocks being slow to break down. While there is now much better agreement amongst deterministic guidance on rain starting to reach the CT valley by Friday morning I would not be surprised to see this consensus drift further in time with rain starting late morning or afternoon. No matter the start time by Friday night and Saturday look for widespread rain showers to move into the region. Some of the rain showers could be heavy at times, due to the high precipitable water values and southerly flow bringing tropical moisture into the region, however a bit leery of any of the higher amounts shown in models as the trend recently has been dry and convection is by nature hard to pin down. Most of the rain will move out of the area on Saturday, however Sunday may again see some showers or even thunder in the mountains as the upper level trough pulls through. By Monday high pressure will move in, keeping most areas of Northern New England under clear to mostly clear skies for the eclipse. Areas where clouds could become a concern include the northern mountains where upslope flow and afternoon destabilization may generate some scattered cumulus and the midcoast and Penobscot bay where onshore flow could generate some local stratus along the coast. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/... Short Term...Low clouds and stratus should lift by early to mid morning most terminals although some MVFR conditions may linger through the morning across southern NH and coastal ME. VFR conditions are expected this afternoon, but a few showers and thunderstorms will bring briefly lower ceilings and vsbys. VFR other than some fog overnight. VFR Wednesday. Long Term... VFR conditions for Wednesday through Friday morning. Friday will see rain move in from west to east dropping conditions to MVFR with patches of IFR possible during the day. Overnight Friday into Saturday look for rain and IFR fog at all terminals. A return to VFR will happen on Saturday afternoon for all but the northern mountains where MVFR ceilings will linger. && .MARINE... Short Term...Conditions are expected to remain below small craft thresholds through Wednesday. Long Term... High pressure builds over the waters Wednesday and Thursday before a low pressure system and cold front brings rain across the region on Friday night. Winds and seas will increase modestly with this system but should remain below small craft criteria. High pressure builds in for the end of the weekend. && .EQUIPMENT... The weather radar at Gray (GYX) is up and running as of early this Tuesday morning and should be available for this afternoon`s showers and thunderstorms. However, techs are still testing the new parts so it still could go down from time to time today. During any outages, radar coverage is available from adjacent radar sites including Burlington-Vermont (KCXX), Taunton- Massachusetts (KBOX), and Hodgdon-Maine (KCBW). Also, the radar at Albany (KENX) suffered a failure that has been attributed to azimuthal motor/gear issues. It is expected to be down for several days. See FTMENX for updates. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Hanes SHORT TERM...Ekster LONG TERM...Curtis

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