Area Forecast Discussion
Issued by NWS Portland, ME

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630 FXUS61 KGYX 181654 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1254 PM EDT Sun Aug 18 2019 .SYNOPSIS... A warm front will approach from the west today and will lift north of the region tonight. Hot and humid weather will return on Monday and Monday night as a weak frontal boundary settles south through the region. Stalled frontal boundary over southern New England will be the focus for showers and thunderstorms late Tuesday and Tuesday night as it lifts back to the north. A stronger cold front will approach from the west on Wednesday and will slowly cross the region Wednesday night and Thursday. High pressure will build in from the west for the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1pm update... Marine layer has finally cleared leaving mostly sunny skies for the area. A look at the morning soundings from both KGYX and KALY shows a fairly strong cap and that is reflected in the lack of cumulus field across the region compared to the last few days. Nevertheless expect the stronger short wave impulse off to the west to provide enough cooling aloft to result in convective showers across southern NH near sunset. 9am update... No major changes to the forecast at this point. Satellite imagery shows fog and low stratus beginning to break up along the coast and expect all but the midcoast to see at least some sunshine today. The next round of convection is already firing out in western NY and expected to move in tonight. While the trend in the models has been towards SW NH seeing the brunt of the convection, will hold off on any significant pop changes for a few hours until we`re able to see what clears out this am. 605 AM...Forecast in good shape, just a refresh to take mention of precip out of the text products and to tweak SKy/temps just abit based on obs. The continued onslaught of weak onshore flow continues this morning, but there`s some gradual changes in store starting today. The strong line of convection that moved through Nh last evening is well into ern ME, and there are a few sct weaker SHRA behind this in central ME but these should move out by 10Z or so as well. Today will start off with the low clouds and fog in place, but in the wake of the wave that moved thru overnight, the weak flow veers a little more S-SW, and this should help most of the CWA se more sun today. Given the weak flow, it;ll happen slowly, and coastal are cloudy until midday to early afternoon, while inland areas should see some sun mid-late morning. 850 temps push up to 15-16 C across the srn half of NH and into SW ME, so inland areas should see highs in the low-mid 80s, as will the CT vly. Coastal areas and central Me will be slower to see clearing and highs will be in the 70s, but still warmer than Sat. Tds will be in the mid-uppr 60s, so it`ll be humid this afternoon as well. Another 500 MB will approach from the W this afternoon, but will weaken as it moves into New England. Cannot rule out a few SHRA/TSRA in the west developing ahead of the wave, but think the better chc of convection will be this evening, as we will subsidence aloft working again any instability thru much of the day. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Should see some convection moving into the CWA from the west this evening. Although instability and thermodynamics look good this afternoon, the dynamic forcing and weakening of the cap look like it will come too late in the day to develop any strong over the CWA. It is possible that strong storms, move into NH from the west this evening, but these look to weaken as they move into CWA, and become slightly elevated convection. They will continue to weaken as they head east overnight though. Look for another round of fog and low stratus as this next wave briefly shifts back onshore just in time for evening.. Lows will be mostly in the mid to upper 60s given the higher tds. Behind the exiting wave and ahead of the next wave which moves thru Mon night will see SW flow increase enuf to allow sun in all areas by mid-late morning. 850 MB temps rise to 16-19C across the CWA, and this will allow for a hot and humid day across much of the CWA, with highs generally 85-90, although it will be cooler in the ME mtns and on the mid-coast, Tds will be in the upper 60s to low 70s, so it will feel worse with apparent temps rising to 90-95 in many spots, and especially in interior srn NH, where a heat advisory may be needed. Instability will be high so cannot rule an isolated airmass TSRA in the afternoon, and the next wave will be approaching form the NW, so there is a better chc for thunder in the mtns late in the day, but again think most of any precip will hold off until evening. Despite high CAPE, vertical shear not all that impressive, and good capping will have to be overcome by the wave which looks like it won`t do much until after max heating again. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Showers and thunderstorms will gradually end Monday evening with loss of heating. Expect clearing overnight as weak frontal boundary settles into southern New England, stalling there by Tuesday morning. Lows overnight will range through the 60s. Modest ridging will build into the region from the west on Tuesday along with lower dew points. Looking for mostly sunny skies across most of the forecast area. May see enough instability and moisture in far southern New Hampshire for a stray afternoon shower or thunderstorm but most of this activity should remain to the south and west. High on Tuesday will range from the upper 70s to mid 80s north and mid 80s to near 90 south. Another in a series of shortwaves will move into southern New England Tuesday night and will spread showers and some thunderstorms into southern New Hampshire and adjacent southern Maine overnight. Models showing some differences in northward extent or precipitation and amounts with the GFS wetter and farther north. With PWAT`s approaching 1.5 to 2 inches in southern New Hampshire and Maine will be leaning toward the wetter GFS solution for pops. Lows overnight will range from the mid 50s north to the mid 60s south. Rain will shift east out of southern Maine Wednesday morning with partial clearing from west to east in the afternoon. At the same time a cold front will approach from the west in the afternoon. Will see some moderate CAPE develop over western zones in the afternoon but narrow band of drier air behind departing shortwave may inhibit convective development. High temperatures will generally range through the 80s. Strong shortwave digging into the northern Great Lakes Wednesday night will drive a potent cold front toward the region. Although timing of the front is not ideal...shear values will rapidly increase Wednesday evening and overnight and any stronger convective cells would certainly have the potential to produce wind damage. Low temperatures overnight will bottom out in the lower to mid 60s. Cold front will push offshore early Thursday with skies clearing briefly during the morning hours. Deep upper trough swinging in from the west will likely produce another round of showers and thunderstorms as heights crash and lapse rates steepen considerably in the afternoon. Strong shear will also create the potential for wind damage with stronger cells... mainly in northern zones. Highs will range through the 70s north and lower to mid 80s south. Much cooler and drier air will stream into the region on a stiff northwest flow Thursday night. Looking for variable clouds in the north and mostly clear skies elsewhere. High pressure will gradually build in from the west Friday through Saturday with seasonable temps and low humidity. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Short Term...Again we deal with low clouds and fog this morning. However, I think inland areas should see VFR by mid morning or so, with coastal terminals breaking out early this afternoon. KRKD may get stuck in the marine lyr all day. We`ll fall back into the murk again tonight, but should see faster improvement to VFR on Monday morning. Long Term...VFR Monday night with areas of IFR/LIFR ceilings and vsby in morning valley fog. VFR Tuesday. Areas of MVFR ceilings Tuesday night into Wednesday morning in showers and Thunderstorms. VFR Wednesday with areas of MVFR ceilings/vsby in afternoon and evening thunderstorms. VFR Thursday. && .MARINE... Short Term...Areas of fog could reduce vis to around mile or lower at times through tonight, but otherwise winds/seas stay blo SCA criteria. Long Term...No problems noted. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...Curtis SHORT TERM...Cempa LONG TERM...Sinsabaugh AVIATION... MARINE... is the U.S. government's official web portal to all federal, state and local government web resources and services.