National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, ME

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-- Discussion containing changed information from previous version are highlighted. --830FXUS61 KGYX 270301AFDGYXArea Forecast DiscussionNational Weather Service Gray ME1101 PM EDT Wed Jun 26 2024.SYNOPSIS...Low pressure will move through the region along a cold fronttonight...bringing showers and thunderstorms to the region. Coolerand drier air will begin to filter in on Thursday with a fewafternoon showers again possible. A cool night is expected Thursdaynight with seasonably cool and dry conditions for the day on Friday.Unsettled weather returns to the region for this weekend withadditional showers and thunderstorms expected as low pressure movesnorth of New England.&&.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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11pm Update...Just some minor refinements to PoPs as the eveningprogresses. Showers have begun to push into north and westernNH. Short term focus has been monitoring strong MCS moving intosouthern New England and how this tracks overnight. Mesoanalysisproves little instability left over from the daytime, andjust some pockets of 200-400 j/kg of MUCAPE elevated. This won`tbe near enough to sustain the ongoing damaging wind event to thesouth as the forcing arrives in southern NH over the next fewhours. Biggest change was to increase rain and thunder chancesfor far SE NH as this activity clips this area on its way out tothe GoME.8pm Update...Not many changes from the day crew. Despite eveningconvection across MA setting up north of 12z HREF guidance,believe this activity pushes east before sfc low pushes acrossNH/ME tonight. RAP soundings in southern NH keep low levels drythrough midnight, but upper level saturation should allowshowers to reach surface. With low but nonzero MUCAPE overnightfor the mountains and then towards the Midcoast, have continuedthunder chances here overnight.Previous Discussion...High Impact Weather Potential: Some low probabilities forexcessive rainfall across southern areas as well as a severethunderstorm risk for far SW New Hampshire.Pattern: A potent shortwave trough can be seen moving through theGreat Lakes region early this afternoon as a surface cold frontdrops toward northern New England. This shortwave will help spawnlow pressure development along the front as it slows while passingoverhead. Thus...forecast concerns will center around shower andthunderstorms associated with this low and more specifically 1)where heavy rainfall may occur and 2) whether there is anysevere threat with the thunderstorm activity.Through this evening: Initial batch of showers is passing eastof the area with a sprinkle or two in it/s wake. While llevelcloud cover will wane through this evening...high cloudinesswill continue to increase as convection develops across NY/PA.8pm temperatures will remain warm...only falling to the 70s toaround 80.Tonight: Overall trend over the past 24 hours has been to lower theQPF in the mesoscale guidance suite...with low pressure riding justsouth of the forecast area overnight as the cold front makes it tothe coast before the surface low arrives. The net result is thatany surface-based instability remains south and east of the forecastarea overnight. There is a small amount of elevated instabilitynorth of the cold front...so a few rumbles can/t be ruled out...butfeel that the severe convective threat will be confined to areassouth of the CWA. With more significant convection south of thearea...the majority of our rainfall overnight will be tied to QGforcing associated with mid level shortwave and the developingsurface low. This favors more light-moderate rainfall rates withthe heaviest amounts potentially towards the midcoast where someweak deformation will have the chance to develop depending on howquickly the surface low spins up. Temperatures will remain generallymild overnight as more significant cold air advection holds offuntil daytime Thursday. Therefore...expect lows in the 50s in themountains and the 60s to the south.
-- End Changed Discussion --&&.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...High Impact Weather Potential: Minimal.Pattern: Shortwave trough over the eastern portion of the forecastarea will move east of the region with a secondary shortwave andassociated trough dropping through the region. Forecast focus willbe on departing morning precipitation...any shower/storm potentialwith the secondary trough...and then cooler temperatures Thursdaynight.Thursday: With low pressure pulling northeast of the forecast areaand initial surface cold front offshore...could see a few residualshowers across the Midcoast to start the day before attention turnstowards a secondary trough that will drop through the region duringthe day with very weak height mid level height falls continuing as asecondary shortwave passes north of New England. While the overallprofile will be drying through the day...some modest moisturepooling ahead of the secondary trough should allow for a few hundredJ/kg of SBCAPE to develop ahead of the trough. Thus...expect someafternoon showers to develop with a few rumbles of thunder possiblethough instability appears too weak to support a severe threat. T8swill have fallen a few degrees C since Wednesday...though downslopeassistance will allow southern NH/southwestern ME to push into thelower 80s again while highs in the 70s with gradually decreasingdewpoints are expected elsewhere.Thursday Night: Canadian high pressure helps drive a continentalpolar airmass into the region Thursday night with PWATs fallingbelow 0.25". Thus...a quieter and much cooler night is in store.Northerly 1000 mb geostrophic winds remain in the 20-30kt rangeovernight which should keep all but the deepest valleys coupled.Some of the statistical guidance drops the northern valleys /BML-HIE/ just below the 40F mark. Given the remaining winds...this maybe a bit too low...but do expect lows in the lower 40s in themountains with lows south of the mountains in the mid 40s to lower50s...warmest in the urban centers.&&.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...A quiet start to the long term before a little more active weatherpattern returns. On Friday high pressure will be centered over NewEngland resulting in mainly clear as seasonable conditions.Friday Night into Saturday the high will drift offshore as lowpressure over the upper Great Lakes pushes east. A warm frontfollowed by a cold front that are associated with this low willcross the area later Saturday Afternoon and Night. This willresult in increasing clouds during the day on Saturday with raindeveloping during the afternoon over NH...reaching westernMaine by late afternoon or early evening. Rain will continueinto the overnight hours of Saturday Night before tapering toshowers by daybreak from west to east. With an upper leveltrough approaching the area on Sunday scattered instabilityshowers and thunder showers will be possible. This upper leveltrough will cross the area on Monday meaning a few showers maylinger on Monday although the bulk of the day should be dry. Asthe upper level trough reaches the Gulf of Maine there areindications that low pressure forms. Right now the models havethis east of the area allowing high pressure over the OhioValley to slowly build east for Tuesday into Wednesday. As longas the low just east of the area does not form further west, wewill see a return of dry and seasonable conditions for Tuesdayinto Wednesday.&&.AVIATION /03Z THURSDAY THROUGH MONDAY/...Short Term...Summary: Low pressure moves through the region tonight along a coldfront with showers and a few thunderstorms. Partial clearing isexpected on Thursday before a few afternoon showers develop. Highpressure builds toward the area Thursday night with clearing skies.Restrictions: VFR ATTM with conditions deteriorating to MVFR/IFRin SHRA and fog after midnight. A few embedded thunderstormswill be possible. Improvement to VFR occurs on Thursday with VFRThursday night.Winds: West southwest winds 10g15kts through this evening willweaken to 5kts or less overnight before strengthening to 8G14ktsfrom the west Thursday. Winds shift to the northwest 5-10ktsThursday night.LLWS: LLWS is not expected through Thursday night.Lightning: There is a low potential for lightning through 19Z atAUG/RKD. Tonight...an isolated thunderstorm is possible...esp forsouthern NH and southwestern ME. Thursday afternoon, an isolatedthunderstorm is again possible.Long Term...VFR conditions Friday into Saturday morning. IFRconditions in developing rain late Saturday over NH overspreadingwestern Maine Saturday evening and continuing Saturday night. MVFRwith areas of IFR in showers on Sunday as a upper level troughcrosses the area. MVFR to VFR conditions return on Monday as Highpressure builds east from the Ohio Valley.&&.MARINE...Short Term...Southerly winds will weaken tonight as a coldfront settles over the waters. Light winds become southwesterlyon Thursday before shifting northwest and strengthening Thursdaynight.Long Term...Wind and waves to remain below SCA conditionsthrough Saturday Afternoon. A frontal system crossing the watersSaturday Night and Sunday will result in SCA Winds and Waves withareas of rain. Conditions to fall below SCA levels Sunday Night andMonday.&&.GYX WATCHES/WARNINGS/ADVISORIES...ME...None.NH...None.MARINE...None.&&$$NEAR TERM...Arnott/CornwellSHORT TERM...ArnottLONG TERM...Lulofs