Area Forecast Discussion
Issued by NWS Portland, ME

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954 FXUS61 KGYX 221300 AFDGYX Area Forecast Discussion National Weather Service Gray ME 900 AM EDT Tue May 22 2018 .SYNOPSIS... High pressure lingers over the area today as a low pressure system approaches from the southwest. A warm front will lift into the region in the late afternoon and this evening bringing widespread rain showers. A cold front will cross the region Wednesday. High pressure will build into the region Thursday. The next weather maker nears the northeast for the weekend. && .NEAR TERM /UNTIL 8 PM THIS EVENING/...
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900 AM...At 12z a 1014 millibar low was over the lower Great Lakes with a warm front extending eastward through southern New England. GOES imagery showed an extensive area of high and middle cloud had overspread the area in advance of the surface low and frontal boundary. NWS Doppler Radar mosaic showed a large areas of showers upstream and just entering western New England at the moment. The 12z KGYX raob was dry in the lower levels...so I expect it will be at least a few more hours before the rain reaches the ground across much of the forecast area. Prev Disc... 645 AM Update... Minor changes to push back cloud cover and PoP timing. No other significant alterations to the forecast at this time. Previous discussion... Shortwave energy will arrive a stream over the region throughout the day and evening. Accompanying this will be a weak surface low which should develop over the eastern Great Lakes around midday. As the associated warm front lifts into the area, a cloud deck will move into the region from the south and west. Issues with a substantial rain event include a lack of deep moisture. As far west as Massena and Binghamton NY are still reporting clear skies as of 0730Z. The latest KGYX 00Z sounding shows a dry adiabatic layer from the surface to 10k ft, with a moist layer at 10k ft, followed by another extremely dry layer thereafter. So it will take time for top-down saturation to occur, and longer for measurable precipitation. Have pushed back categorical PoPs several hours for most spots and lowered QPF overall. Seeing a quarter inch over the highest mountain ranges is likely, however, a tenth or two (or less) is more reasonable for the coastal plain through tonight. Highs today should warm quickly in the dry airmass, even for the CT River Valley, where again clouds/PoPs should be later than expected. In fact much of ME may have to wait until evening for a steady light rain. Highs will be in the 60s and 70s.
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&& .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Precipitation will diminish overnight with additional light QPF for the higher terrain. NW winds will develop and allow for another cool night in the upper 40s north to low to mid 50s south. Residual, paper-thin moisture in the boundary layer may provide enough substance for patchy fog, especially where rain was measurable. On Wednesday the attendant cold front will march slowly across the area, taking all day to reach the coast. Again most QPF will be squeezed out over the mountains with additional orographic lift, with an isolated shower possible but not likely over the coastal plain. Highs will be variable, with 60s over the north and lower to mid 70s inland. Southern NH will make a run at 80 degrees. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... The end of the week will be mainly characterized by sunny skies and warm temperatures. Aloft the trough which had been in place over eastern Quebec will move eastwards allowing a ridge to build in through the end of the week. 850mb temps climb to 13C by late Friday night with surface temperatures steadily increasing. With weak surface pressure fields expect an afternoon seabreeze to be the only limiting factor for high temperatures. As we move into the weekend the forecast transitions from the high confidence low impact of the end of week high pressure to low confidence and slightly higher impact by Sunday and into Monday. From Saturday morning the flow aloft begins to split which introduces more uncertainty. To our south a cut off low with potential tropical moisture is over the Gulf of Mexico, while the northern stream of the split offers a low moving out of Saskatchewan. With two bodies we get twice the uncertainty plus phasing. For the moment have leaned towards the northern stream dominating which is reflected in the ensemble sensitivity. This northern stream feature would push a warm front out ahead of it with WAA and rainfall moving in for Saturday night. Both the front and the moisture try to hang around through Memorial Day with some deterministic models trying to pull the tropical connection northwards. While some precipitation seems confident for the end of the weekend the uncertainty makes pinning down any timing or amounts at this time range unlikely have have opted to keep high chance PoPs through most of the end of the weekend. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... Short Term /through Tuesday Night/...VFR conditions in a very dry airmass with light and variable winds this morning. This afternoon southerly flow develops with winds around 10 kts. Showers will take longer to develop in this airmass, so expected no precipitation at terminals until after 18Z. Showers will be most likely over mountain terminals and southern NH terminals. Long Term... VFR with high pressure dominating through Saturday. A seabreeze will impact coastal locations in the afternoon. Late Saturday showers will develop with periods of MVFR or even brief IFR in rain through Monday. && .MARINE... Short Term /through Tonight/...Winds and seas will remain on the calm side today and tonight. Long Term... Increasing southerly flow will result in winds and waves near SCA on the outer waters by late in the day Friday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ ES

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