Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 261526 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1126 AM EDT Sun May 26 2019 .SYNOPSIS... A cold front will move through the region today with a chance of thunderstorms, mainly across northern and eastern portions of the forecast area. A secondary cold front will drop south through the region on Monday. High pressure will build in from the west Monday night. A warm front will approach from the southwest Tuesday night and will move north into the region on Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1100 AM Update... Showers beginning to redevelop across southern Quebec and these will become more widespread in coverage as they move into the mountains over the next several hours. 1KM HRRR Intensifies this activity as it heads southeast through the afternoon with some thunderstorms forecast for our eastern zones where better instability is lingering. One inhibiting factor will be the persistence of stratus over midcoast and central interior Maine through late morning which has held down heating. So any stronger convection in doubt at this point but with the strong shear over the area would still expect gusty winds and perhaps some small hail in any storms which do develop. Have adjusted pops/wx grids based on latest radar trends and tweaked area temps/tds. Will also be dropping SCA`s for the outer waters and bays. No other changes planned attm. Prev Disc... 710 AM Update...Didn`t change much with this forecast update. Just a few minor adjustments to temperatures, PoPs, and winds for the next few hours. Have seen a couple of thunderstorms develop west of BTV VT as of 11z. This activity is likely on the very leading edge of the ascent associated with an approaching short wave trough. There is also likely some WAA induced by the advection of the leading edge of the steep lapse rates aloft. Near-term CAM output haven`t really handled this well thus far. However, the thinking is that the current activity near BTV will weaken over the next hour or so and not likely make it to western NH. However, there is a low prob of this happening so added slt chance to low chance PoPs in the CT River Valley this morning. The development of additional storms (possibly strong) in the mountains southeastward to the Midcoast southward to perhaps Cumberland County will be tied to the degree of surface-based instability that develops due to insolation. The other factor is short wave trough timing which currently seems to be a bit faster than previously modeled. This could cross the area before peak heating and may limit convective coverage. Will watch this over the course of the AM, but will keep gusty winds and small hail wording in the forecast for central Maine and Midcoast zones for this afternoon (mainly between 1 and 4 PM). Previously... Plenty of rain and showers present across the forecast area early this morning, mainly across central and northern zones. Much of this activity will move offshore by 12z this morning allowing for at least some partial clearing except perhaps the Midcoast region of Maine. A prefrontal trough will move from west to east across much of the forecast area by midday today allowing for westerly winds and warming temperatures. Highs are likely to be in the 80s across southern NH, with 70s most elsewhere. A short wave trough will approach from the northwest today. The leading edge of this short wave trough is located near the southern Quebec/Ontario line as of 07z this morning and is already associated with thunderstorms as per latest lightning imagery. As this short wave trough continues to move toward New England, convective showers and isolated thunderstorms will likely develop over northern VT and southernmost Quebec. Convection-allowing mesoscale models are in good agreement that upscale growth of the area of showers and thunderstorms will occur as they move southeastward from northernmost NH and the western ME mountains, peaking in intensity across central and Midcoast ME between 1 and 4 pm before moving offshore. This region will have the best surface convergence, deeper low level moisture, and best mid and upper level support for thunderstorms. If ample sunshine can develop across central and Midcoast ME before storms approach, then one or two storms may become strong to marginally severe as deep layer shear will be strengthening in the presence of several hundred J/KG SBCAPE. Remnant elevated mixed layer will provide for somewhat steeper than normal mid-level lapse rates which may aid in stronger upward parcel accelerations. Main threat would be strong gusty winds. More isolated activity is possible further south to Cumberland County ME. If a storm or two can develop that far south it could be strong with strong gusty winds being the main threat. Can`t rule out an isolated storm or a couple of showers elsewhere today, but with prefrontal trough expected to have moved all the way to the coast across southern zones early on, surface convergence will be unfavorable for development. A dry or mostly dry day is expected across southern zones as a result. A cold water beach hazards statement has been issued for coastal zones.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Fair weather is expected tonight before a secondary cold front moves into the region Monday afternoon. The air mass will be quite dry in advance of this front, so only widely scattered showers are expected at best. The vast majority of the day will be dry. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... High pressure rolls into the area from the northwest Monday night. This will bring a clear and calm night with good radiational cooling conditions. Low level dewpoints in the upper 30s to low 40s suggest that lows will be mostly in the 40s with some 30s likely in the sheltered valleys. Could even make a run at the freezing mark in the coldest spots up north, but for now it looks like a good frost potential in northern valleys. The Tuesday through Thursday period will see several waves tracking east through the westerly flow aloft each bringing another chance of showers as warm, moist air tries to push its way northward into New England. With an onshore low level flow expected it may be difficult for this warm air to make much progress at ground level. The first wave arrives Tuesday afternoon as high pressure shifts into the Gulf of Maine and clouds increase from the west. Temperatures will be a bit cooler than normal with highs only in the 60s, coolest in the south where clouds will arrive earlier. There`s still a fair amount of disagreement among the models on when and where this wave tracks, but there seems to be an emerging consensus that weak low pressure tracks by to our south with the frontal zone remaining to our south as well. The best chance of rain will be in southern areas Tuesday afternoon and Tuesday night. Wednesday looks like we will be mostly in between waves, so we may squeeze out a mostly dry day in the midst of an otherwise wet period. The warm front aloft may push all the way into northern Maine, but southerly low level winds will keep cooler air in place at ground level. Western Maine stays in the 50s while southern New Hampshire warms into the 60s to perhaps 70 degrees with plenty of clouds. The next wave tracks quickly eastward along the mid level frontal zone Wednesday night spreading another round of warm advection showers through the area. Cannot rule out some rumbles of thunder as well as the warm/moist advection may generate a bit of elevated instability. The third wave will send a cold front through the area late Thursday or Thursday night. Before it does so, expect the low level inversion to break and the warmer air will be felt area wide on Thursday. Expect widespread temperatures in the 70s with some near 80 in southern areas. Although there are still a lot of moving pieces still yet to find their place, the warm and humid air mass should be enough to generate a few thunderstorms as the cold front arrives. This would be particularly true if it crosses through the area during the day on Thursday. High pressure builds in behind the front for Friday finally bringing a dry day. Temperatures warm into the upper 60s to mid 70s in a northwest flow. The high shifts east on Saturday with a southerly flow developing and a cold front dropping south out of Canada. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... Short Term...Cigs and vsbys will improve to VFR this morning except perhaps the Midcoast of ME where MVFR may last through late morning. Local MVFR to IFR in sct showers and thunderstorms from 1-5 pm across central and Midcoast ME. VFR tonight and Monday. West winds gust around 20 kt today. Long Term...VFR through Tuesday morning. Expect increasing clouds and lowering ceilings from southwest to northeast during the day Tuesday. Showers are likely in southern parts of the area with IFR conditions possible. Although we may get a break from the showers on Wednesday MVFR to IFR conditions may persist especially across western Maine. More rain moves through Wednesday night. There could be some improvement to VFR at times on Thursday with a chance of showers and thunderstorms as a cold front arrives. && .MARINE... Short Term...SCA conditions this morning will subside this afternoon. Conditions will remain below SCA thresholds tonight and Monday. Thunderstorms may move off the Maine Midcoast (possibly as far south as Cumberland County ME coast) between 1 and 5 PM and may contain gusty surface winds to 35 kt. Long Term...High pressure builds into the Gulf of Maine Tuesday and then shifts eastward. A warm front tries to lift north Tuesday night but will likely stall through Wednesday before finally shifting north early Thursday. A cold front moves in from the northwest Thursday night. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Beach Hazards Statement until 8 PM EDT this evening for MEZ023>028. NH...Beach Hazards Statement until 8 PM EDT this evening for NHZ014. MARINE...None.
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