090 FXUS61 KGYX 061343 AFDGYX Area Forecast Discussion National Weather Service Gray ME 943 AM EDT Mon Sep 6 2021 .SYNOPSIS... A trough axis will cross the area this afternoon bringing thunderstorms, some of which will be capable of gusty winds and small hail. High pressure and fair weather build in Tuesday, lasting into Wednesday with temperatures warming into the upper 70s and low 80s by Wednesday. A slow moving cold front will approach Wednesday afternoon bringing increasing chances of showers with a chance of thunder late Wednesday through Thursday. Hurricane Larry will pass well offshore this week but building long- period swells are expected, which may result in increased rip currents. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Update... Latest satellite images continues to show plenty of clearing across our forecast area this morning. This will lead to destabilization of the atmosphere as low level lapse rates and wind fields aloft increase. Showers and thunderstorms will cross the region with the latest HRRR showing line segments during the mid to late afternoon hours. Made minor adjustments to the latest near term forecasts of temperatures, dew points and winds. Prev Disc... 710 AM Update... Smoothed out T/Td/sky trends through the morning according to latest observations, plus added patching dense fog this morning. Otherwise just tweaks PoP/Wx for this afternoon/evening using latest CAMs as guidance. Now we wait for convection firing near Niagara and the GTA to track east toward New england. Previously... A weak frontal system slides Downeast this morning after a humid and mild overnight. Looking upstream... clearing is well underway way with dry advection behind the wave, which will help to mix out low clouds with sunrise, allowing surface temperatures to warm into the 70s by the afternoon. The last hold out will be the Midcoast toward Penobscot Bay with onshore flow very slowly exiting with the departing surface wave. Steepening lapse rates from CAA aloft combined with strong mixing will set the stage for convection to fire ahead of sharpening trough axis swinging negatively down the Saint Lawrence River valley today. We're getting to the time of year where more dynamic storms are starting to dip south across the Canadian border... this storm is driven by a 120+ jet in the upper levels, translating to about 60-70 kts of 0-6km bulk shear, providing more than enough upper level support for organized convection in spite of meager instability. Keeping this and very steep LL lapse rates/very high DCAPE in mind... am expecting a couple broken line segments of showers and storms with gusty to locally damaging wind gusts to cross this afternoon and evening. Given freezing levels below 10 kft and ample upper level support... could see some hail in the mix as well. A few discrete cells may pop out ahead of the line as synoptic ascent increases ahead of the wave, but most significant activity should charge right along the leading edge of the trough axis. The northern half of the area... nearest to the strongest forcing, including central and northern NH and western Maine into the Capitol region... have the best chance for experiencing strong to severe storms with dry entrainment and less favorable jet dynamics being limiting factors further south, which aligns well with SPC Sod. For timing... 00Z CAMS and subsequent hourly runs support the main show crossing the Connecticut River around 18Z and exiting into eastern Maine around 00Z. With the dynamics in play, would not be shocked if another line of gusty showers develops behind the line during the daylight hours. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... A fresh northwest flow takes over behind the departing wave tonight into tomorrow. Most clouds will clear out, except over the mountains where upsloping flow and low level moisture will be present, which will keep a few showers going into the morning. Conditions will be much less damp and cooler versus this morning with lows in the 50s over the region... to around 60 right along the shoreline. Upper level flow flattens Tuesday and surface high pressure crests the East Coast off the DELMARVA. Mostly sunny, warm, and dry conditions can be expected area wide. A thermal trough will be dipping down into northern New England so while the southern interior warms to near 80, northern areas may not make it out of the 60s. A light west wind will stunt the sea breeze, but it'll still limit temperatures to the low- to mid-70s along the immediate coast. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... The two main stories in the extended forecast period will be building long period swells the second half of the week into the weekend as Hurricane Larry passes well offshore of New England and the potential for a period of moderate to locally heavy rain with embedded thunder late Wednesday into Thursday with a slow moving frontal passage. The extended forecast period will start with a ridge of high pressure over northern New England Tuesday night while a trough digs into the Great Lakes. This trough will slowly advance eastward Wednesday with a surface low occluding over southeast Canada. The occluding low will drag a cold front through the area Wednesday night into Thursday bringing periods of rain. As the cold front crosses Thursday, Hurricane Larry will be in the vicinity of Bermuda sending increasing swell towards New England. The cold front will eventually help deflect Larry well east of our longitude, although elevated long period swells will last into the weekend. As troughing lingers through Friday expect showery weather before high pressure builds in Saturday. Wednesday will be warm with increasing humidity and breezy southerly winds ahead of an approaching cold front. The 00z model suite is in relatively good agreement that precipitation will hold off for much of the day with mostly sunny skies to start followed by increasing clouds in the afternoon. Chances for rain will increase Wednesday night as the front approaches and will linger through much of Thursday as the front will be slow to cross the area. Will have to watch for the potential of locally heavy rain as PWATs will exceed 1.5 inches and there will be elevated instability Wednesday night leading to the potential for embedded thunder along with fairly unidirectional flow. Global models and their ensembles diverge quite markedly Thursday into Friday with how fast the front clears the area. Some solutions have the front clearing the area by Thursday morning while others as late as Friday morning. With regards to PoPs during this time frame have largely stuck to the NBM that brings a gradual drying trend late Thursday into Friday morning. Although, there is uncertainty with the frontal passage global models agree that Hurricane Larry will track well offshore Thursday night through Friday as the system passes our latitude. Still the system will send long period (15 second) elevated swells into the Gulf of Maine impacting the beaches with potential erosion and increased threat of rip currents. High pressure looks to build in Saturday potentially lasting into Sunday. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... Short Term...Widespread restrictions in low ceilings and patchy fog will lift this morning, by about 13Z, except for KRKD which will hold onto the low clouds another couple hours or so. VFR will prevail thereafter with a westerly wind developing, gusting to 15-20 kts. TSRA with potentially strong winds of 30+ kts approach KLEB/KHIE early this afternoon, then track east toward the other TAF sites through the evening. Brief restrictions are possible with these. Winds take on a northwesterly clip overnight with MVFR possible for KHIE and to a lesser extent KLEB. SKC/VFR prevails Tuesday. Long Term...Mainly VFR Tuesday night through much of Wednesday. Slow moving cold front will bring periods of restrictions in low cigs and SHRA Wednesday night through Thursday along with southerly winds gusting to 20 kts. Conditions expected to improve to VFR Friday into Saturday. && .MARINE... Short Term...Low pressure centered to the north crosses the waters today, pushing a cold front with potentially gusty showers or storms across this evening. Greatest chances for these are along the Midcoast. Conditions are not expected to reach SCA thresholds, however gusts to 25+ kts are possible with showers/storms this evening. Winds turn westerly behind the wave, then southwesterly tomorrow as high pressure crosses the East Coast centered over the DELMARVA. Long Term...Southerly winds increase on Wednesday ahead of an approaching frontal boundary with SCA conditions likely as winds gust up to 25-30 kts and seas build to 4-7 feet. Distant Hurricane Larry will then begin to allow for increasing seas towards the end of the week with seas of 6-12 feet possible across the outer waters and 4-8 feet across the bays. Near shore waves will approach 5 feet as early as Wednesday with increased rip risk near the Mid-Coast. Near shore waves will increase approaching a peak around 10 ft Friday and will remain elevated through Saturday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR/SHORT TERM...Cannon LONG TERM...Cornwell