Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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437 FXUS61 KGYX 272356 AFDGYX Area Forecast Discussion National Weather Service Gray ME 756 PM EDT Thu Jun 27 2024 .SYNOPSIS... High pressure builds toward our area overnight bringing cool and quiet weather conditions to region. The high will slide offshore Saturday allowing a warm front to lift north across our region, followed by a cold front Sunday. This will support increasing clouds Saturday followed by numerous showers and locally heavy rain Saturday night into early Sunday. High pressure then arrives for Monday and Tuesday before weakening and sliding offshore Wednesday with seasonable temperatures. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 8pm Update...Interior clearing is proceeding well as daytime heating abates. Still a bit of overcast from showers along the coast, but this too shall clear. With passage of the front, winds do stick around through the night, but gust factor should drop off at the surface as temps cool. No changes to overnight temps at this point. Previous Discussion... High Impact Weather Potential: Isolated thunderstorm possible from the Capitol region to the Midcoast through late afternoon...then minimal. Pattern: Early afternoon GOES 16 water vapor imagery shows this morning/s deep moisture plume now east of the region with a compact shortwave trough diving towards the region out of southern Quebec. Ahead of this feature is a secondary cold front that is crossing the forecast area from northwest to southeast. Much drier air is arriving behind this feature which will focus the near term forecast on cloud trends as well as overnight low temperatures. Through this evening: Shower activity ahead of secondary cold front continues to push east with winds shifting to the northwest in it/s wake. Temperatures begin their fall by 8pm in the mountains with readings in the 50s...with temps across SE NH and the coast of ME still near 70. Tonight: Canadian high pressure settles into New York state overnight with northwesterly cold air advection pushing T8s into the single digits above freezing across the forecast area. A rather substantial low level gradient will remain in place across the forecast area overnight with 1000 mb geostrophic wind values of 20 to 30kts suggesting that most locations outside of the deepest valleys will see a breeze continue through the overnight hours. Arriving PWATs of 0.25" will push into the area as dewpoints fall through the 40s. Thus...expect clearing skies and despite the breeze...it will be a much cooler night than on previous nights with lows generally in the 40s...with a few lower toward the coast /esp over the urban centers/. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... High Impact Weather Potential: None. Pattern: High pressure crests just south of the region on Friday before pulling south and east of New England Friday night with a developing return flow. Thus...a very quiet period of weather is in store to end the week with primary forecast concerns centered on temperatures and cloud cover Friday night as the next system over the Great Lakes begins to approach. Friday: Pretty potent mid level subsidence moves overhead during the day with surface dewpoints in the upper 30s to around 40. This suggests very little in the way of cloud cover and the CU rule agrees...with perhaps a few Cu popping from the mountains north but clear skies elsewhere outside of a few wisps of cirrus from precipitation over the Great Lakes. Northwesterly gradient will keep a breeze from this direction through the day...generally 10-15 mph. T8s around +6C with some downslope assistance under light northwesterly flow should allow temperatures into the low/mid 70s south and east of the mountains...with highs stuck in the upper 60s to around 70 in the north. Friday Night: Mid level flow backs as the next shortwave and associated low pressure system moves into the western Great Lakes with positive temperature and moisture advection developing in the return flow overnight. This will commence the top down saturation process with increasing upper and mid level clouds during the overnight. Thus...temperatures will be warmer than on Thursday night with lows in the upper 40s to mid 50s expected from north to south with no significant weather impact expected overnight. && .LONG TERM /SATURDAY THROUGH THURSDAY/... An unsettled weather pattern returns for the weekend. High pressure on Saturday will drift offshore as an area of low pressure near the upper Great Lakes approaches from the west. This will help push a warm front and an eventual cold front through the area Saturday afternoon and night. Clouds will increase on Saturday with rain developing west to east starting in New Hampshire in the afternoon then reaching Maine by late afternoon/evening. Rain continues overnight before tapering to showers by daybreak on Sunday. There will be plenty of moisture to work with so locally heavy rainfall is possible during this period. Attention will be paid to the position of the frontal boundary and track of the surface low, which could support a swath of heavy rain. WPC has the area in a marginal risk with the window of concern late Saturday night through daybreak Sunday. On Sunday an upper level trough approaches the area which will help to initiate scattered showers and thunderstorms throughout the day. A few showers may linger into Monday as the upper level trough crosses the area although most of the day should be dry. As the upper level trough enters the Gulf of Maine indications are that low pressure will form. However, models continue to show the area of low pressure forming east of the area which will keep any additional showers offshore and allow high pressure to build eastward from the Ohio Valley Tuesday and Wednesday bringing dry and seasonable conditions to the area. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Short Term... Summary: A secondary cold front pushes through the terminals this afternoon with high pressure building overhead tonight and through Friday with quiet weather conditions. Mid and upper level clouds increase Friday night as high pressure passes south of the region. Restrictions: A brief shower at PWM-AUG-RKD in the 18-20Z timeframe may bring a brief MVFR restriction...otherwise expected VFR conditions to dominate through Friday night. Winds: Northwest winds 14g22kts will diminish to 5-10kts for the overnight before strengthening to 10g18kts for the day on Friday. Winds will diminish to calm/light-variable Friday night. LLWS: No LLWS is expected through Friday night. Lightning: Very low potential for an isolated thunderstorm AUG/RKD through 20Z then no additional lightning potential through Friday night. Long Term...Numerous showers and thunderstorms with locally heavy rain Saturday night into Sunday morning will result in sub-VFR conditions. && .MARINE... Short Term...Southwest winds 10G18kts this afternoon will shift to the northwest behind a departing cold front tonight with a few wind gusts 20-25kts overnight through early morning Friday before slowly diminishing through the day turning to the southwest Friday night. Long Term...Small Craft Advisory conditions probable as southerly flow increases ahead of a cold front Saturday night. Showers and thunderstorms may produce locally gusty winds. Monday...The conditions are anticipated to be below Small Craft Advisory criteria as winds subside, however some choppy seas could approach 4 ft on the outer waters. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Arnott/Cornwell SHORT TERM...Arnott LONG TERM...Jamison