Area Forecast Discussion
Issued by NWS Portland, ME

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019 FXUS61 KGYX 132259 AFDGYX Area Forecast Discussion National Weather Service Gray ME 659 PM EDT Mon May 13 2024 .SYNOPSIS... A warm front will push towards the region tonight with a few showers before much warmer air arrives across southern NH and far southwestern ME for the day on Tuesday. A cold front will drop towards the region bring the chance for showers and thunderstorms Tuesday afternoon and evening. A stalled frontal boundary will result in unsettled weather for the middle and latter portions of the week with temperatures remaining seasonable for mid May. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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655 PM...Updates mostly based on current obs, but did try to better time POPs through the evening at least. Current radar trends show that showers moving into drier air and dissipating, although whatever is falling at cloud level is probably not reaching the ground, given the dry low levels. Most of hi res models suggest nothing but a few sprinkles in NH this evening with better organized SHRA moving in after midnight. Previously... High Impact Weather Potential: Minimal. Pattern: A brief period of shortwave ridging has moved overhead today ahead of low pressure and associated mid level trough centered over James Bay. This low will continue to press eastward through the near term forecast period...flattening the mid level ridging overhead with warm advection/isentropic ascent increasing across the area. Thus...forecast challenges will be on cloud and shower trends as the column moistens in the presence of modest support for ascent. Through this Evening: Expect diurnal Cu field to diminish from the coast into the foothills...but clouds advancing from the west will keep skies at least partly cloudy through the evening with 7pm temperatures falling back into the upper 50s to lower 60s. Tonight: Isentropic ascent at the leading edge of a modest 850 LLJ will push across the region tonight with PWATs increasing to around 1". All of the current run HREF members include some shower activity in this region of ascent with the strongest signal for rainfall towards the Canadian border which will be closer to the best mid level forcing. Will draw likely PoPs in this area with lower values to the south. There will be some diminishing mid level instability...so a rumble of thunder can/t completely be ruled out overnight. Lows will fall into the 40s for much of the area in line with consensus guidance and consistent with southerly flow off the cool Gulf of Maine waters.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... High Impact Weather Potential: An isolated strong to severe thunderstorm is possible across New Hampshire Tuesday afternoon. Pattern: Low pressure north of our region will continue to push east through the short term forecast period with a warm front crossing the forecast area Tuesday with the trailing cold front sagging into the region from the north Tuesday night. Forecast challenges center around convective potential ahead of the surface cold front and locally heavy rain within this convection as mid level flow looks to line parallel to the front. Tuesday: Warm front...draped across the forecast area at 12Z will push north and east with T8s building above 10C and PWATs moving towards 1.25" through the day. Upstream cold front doesn`t make much progress towards the region during the day with best llevel convergence focused to the north...but modest instability across the southern half of New Hampshire is likely as summer-like warmth moves into the region. Short term ensembles based probabilities suggest that the greatest threat for afternoon convection will be in the foothills and mountains given both forcing location as well as cool onshore flow developing towards the coast. While forcing well south of the cold front looks rather weak...any convection that does fire has the potential to be robust with 30- 35kts of deep shear and the potential for MLCAPEs to push 750-1000 J/kg. Thus...there/s a chance for an isolated severe storm over NH...with southerly flow trajectory greatly limiting convective potential as you move east into Maine. T8s pushing above 10C should allow temperatures across southern NH and far SW ME /away from the immediate coast/ to rise into the upper 70s to around 80...with more cloud cover to the north and more marine influence to the east holding highs back in the 60s. Tuesday Night: Any instability wanes as surface cold front sags into the region overnight. Thus...weakening shower activity is likely with a few rumbles of thunder through the evening. Overnight lows will be warmer given our location in the warm sector...with 50s throughout the CWA. Given elevated dewpoints and some shower activity expect patchy fog as well. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Overview... A slow moving front stalls and washes out over the area on Wednesday. At the same time, a slow moving cut off low pressure system tracks through the Mid Atlantic and offshore from Wednesday through Saturday before dissipating. Another slow moving low pressure system will take a similar track south of New England this weekend. Details... Overall the forecast over the last couple of days has trended toward warmer and a longer duration of unsettled conditions. So Wednesday and Thursday don`t look quite as wet as they had, but Friday and Saturday now look to continue the chances for showers. Cut off low pressure systems are notoriously tricky for both the models and forecasters to discern. With these being the main drivers of our forecast this week, it`s worth noting that further changes are likely as well in the coming days. The cold front approaching from the north looks to be trending a little slower, and not making as much southward progress. This allows warmer temperatures for at least Wednesday and Thursday as the marine air is delayed by at least a couple of days. At the same time, the cut off low looks to be tracking more slowly. This lessens the rainfall expected on Wednesday, but causes the forecast to be quite similar for Wednesday through at least Saturday with times of showers. POPs are higher for Wednesday because it`s closer in time, but at least scattered showers are expected Thursday through Saturday as well. POPs on these days are likely to increase in some spots as we get closer in time and certain areas become more highlighted as seeing a better chance for rain. Overall, the best chance for seeing the most frequent showers looks to be across interior areas and the higher terrain. As for temperatures, highs looks to generally warm into the 60s and 70s each day, with the warmest readings found across western locations, and generally cooler toward the coastline. As we get into next weekend, the next system will be following closely behind the first one. This likely increases chances for showers further during the day on Saturday and Sunday. It also looks to bring cooler temperatures, as easterly flow brings in cooler and damp maritime air. As mentioned, this forecast has been volatile over the last couple of days as the cut off low regime continues. This weekend`s forecast is subject to change, but that`s the way it looks to be trending at this point. Over the last week or so, the trend has generally been toward warmer and less wet conditions as we get closer in time, but it`s too early to know at this point if that trend will continue this weekend. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Short Term... Summary: A warm front crossing the region tonight through early Tuesday followed by a cold front Tuesday night will bring increased chances for showers and possibly a thunderstorm with fog chances increasing by Tuesday night. Restrictions: Restrictions in showers...some fog and developing low clouds are likely after midnight tonight outside of southern NH...with MVFR/IFR possible before improving conditions for Tuesday with AUG/RKD the slowest to improve during the day...though showers and a few thunderstorms during the afternoon may bring additional restrictions...again most likely at LEB/HIE. Deteriorating conditions in low clouds and fog with LIFR/IFR is likely Tuesday night. Winds: Southeast winds 5-10kts /stronger along the shoreline/ are will spread inland through the afternoon before diminishing overnight. Southerly winds will strengthen to 10-15kts for the day on Tuesday before diminishing to 5kts or less Tuesday night. LLWS: LLWS is not expected through Tuesday night. Lightning: There is a very low potential for an isolated thunderstorm overnight tonight with a greater chance for a thunderstorm Tuesday afternoon and evening...particularly over New Hampshire. Long Term...Generally VFR conditions are expected more often than not from Wednesday through Saturday, but periods of MVFR conditions with showers are likely during this time period. By next weekend, longer periods of MVFR to possibly IFR look likely with more showers and some marine fog possible. && .MARINE... Short Term...Light winds are expected through early Tuesday before strengthening southerly flow will bring building waves with marginal SCA conditions possible by late Tuesday and Tuesday night. Long Term...A cold front stalls and dissipates across the waters on Wednesday. A slow moving low pressure system tracks south of the waters from Wednesday through Saturday. Seas begin to build by Friday, with SCA conditions possible by late in the week and this weekend. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS...Arnott NEAR TERM...Arnott SHORT TERM...Arnott/Cempa LONG TERM...Clair AVIATION...Arnott/Clair MARINE...Arnott/Clair