Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 121629 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1229 PM EDT Sat Aug 12 2017 .SYNOPSIS... Low pressure over the Great Lakes will move north of the region today...with a cold front moving through New England Sunday morning. This will bring a few rounds of showers and thunderstorms...before drier air works back into the region on Sunday. Quiet and mild weather is expected for Monday and Tuesday of next week with high pressure centered south of the region. A cold front will move through northern New England Wednesday. High pressure will build in Thursday. A warm front will approach the area Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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---1225pm Update--- Update to adjust temperatures a little bit, as well as sky cover and pops. 12z models coming in are showing quite a bit of agreement with chances of thunderstorms this afternoon and evening being primarily limited to western portions of the CWA and the mountains. The HRRR doesn`t get thunderstorms going in our area until this evening. It is clear the atmosphere is beginning to destabilize to our west as echoes are starting to pop up on the Burlington radar. However, it will take some time for the upper level features associated with today`s weather to move eastward into our area. Even so, there should be around 1000j/kg of CAPE to work with later today. Will keep enhanced wording in the forecast for this afternoon, but back off just slightly on pops and timing. ---855am Update--- Quick update this morning to account for current temperature trends. Clearing over New Hampshire this morning is covered pretty well by the current forecast, as is the diminishing precipitation. Temperatures are a bit cooler than forecasted this morning, but with clearing and some sunshine I don`t expect high temperatures to be much different than originally forecast. 615AM UPDATE... Back edge of the showers is moving into western New Hampshire at this hour. Have adjusted precipitation chances going forward to better reflect ending time of precipitation this morning. Have also included mention of patchy fog along the coast of Maine where some observations have begun showing lower visibility in fog. No other significant changes were needed. ORIGINAL DISCUSSION... Northern New England remains in the southwest flow ahead of a trough over the Great Lakes. Within this southwest flow, several smaller troughs are moving through, each bringing a round of showers or thunderstorms. Currently a batch of showers is moving northeast out of southern New England into southern New Hampshire and coastal Maine, while more widely scattered activity is occurring further north. Expect this to continue moving northeast and exit the forecast area by mid morning. This may set the stage for some clearing this afternoon. If the clouds do break up, expect temperatures to warm into the 80s. If we don`t get that sun, then we will be stuck in the 70s. As the trough moves east out of the Great Lakes it will likely trigger some thunderstorms over upstate New York and Vermont, some of which may move into New Hampshire late in the day. Instability will be increasing as low level moisture increases beneath cold/dry advection aloft, while deep layer shear will also be increasing as the day goes on. This could allow some storms to begin organizing and posing a better threat for damaging winds and hail. Still not a ton of confidence on this scenario as the timing and pre-convective cloud cover is still fairly uncertain, but it will not be out of the question to see a severe thunderstorm or two late this afternoon and evening.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Instability will remain over the area tonight in spite of the loss of daytime heating. As a result, any thunderstorms which form and move toward the area in the late afternoon and evening will have a chance of maintaining themselves as they move eastward. There will continue to be a threat for an isolated severe storm or two as wind shear will be on the increase as the more robust upper trough and surface cold front move into the area. Temperatures will remain in the 60s overnight as humidity will be high. Cold front moves through Sunday morning, bringing progressively drier air through the day. The offshore wind will allow temperatures to warm into the 80s all the way to the coast while northern areas will only be in the mid 70s. There could be an isolated shower or thunderstorm in the northern part of the area as the upper trough swings by, but do not expect this to produce any severe weather. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... High pressure noses in from the southwest Sunday night and will be in control until Wednesday when a cold front settles south over the forecast area. Showers and thunderstorms should develop ahead of this front Wednesday afternoon. The highest chance will be in the mountains. High pressure will again build in for Thursday and early Friday. A warm front will approach Friday afternoon spreading showers and possible thunderstorms into the region. The ECMWF is faster with this system and shows showers moving into the mountains as early as Thursday afternoon. Temperatures for the week should mostly be near to somewhat above normal. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Short Term...Expect mostly MVFR conditions in showers early this morning, though there is an area of IFR ceilings which has moved into coastal areas. Expect improving conditions today, though we could hang on to the MVFR conditions most of the day east of Portland. Thunderstorms will be possible late this afternoon and into the evening as a cold front moves through. The best chance of a thunderstorm will be in central and northern New Hampshire. Long Term...Expect mostly VFR conditions. Some valley fog possible at night. && .MARINE... Short Term...A light southerly flow continues today and tonight, with a cold front crossing the Gulf of Maine on Sunday. Long Term...Expect winds and seas to remain below small craft criteria. && .EQUIPMENT... UPDATE: The start date for the downtime for the GYX radar has been adjusted to Sunday, August 13th. The weather radar at Gray (GYX) will be down for maintenance for approximately two to three days, beginning August 13th. During that time technicians will be installing important upgrades. This work has been scheduled to minimize any potential impacts to office operations. During the outage, radar coverage is available from adjacent radar sites including Albany-New York (KENX), Burlington-Vermont (KCXX), Taunton-Massachusetts (KBOX), and Hodgdon-Maine (KCBW). && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ Pohl

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