Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201545 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1145 AM EDT Sun Aug 20 2017 .SYNOPSIS... High pressure will build to the south of the region through Monday before sliding to the east on Tuesday. A cold front will move in from the west Tuesday night and cross the region on Wednesday. High pressure and drier air follows the front Wednesday night through Friday. && .NEAR TERM /UNTIL 7 PM THIS EVENING/...
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1145 AM...For this ESTF update...I adjusted near term grids to reflect current radar and satellite trends as well as the latest mesonet. Prev Disc... 845 AM...Minor ESTF update to ingest the current mesonet into near term grids. Prev Disc... 510 AM Update: Going forecast in good shape with some minor adjustments to placement of weak sprinkles/light showers moving east ahead of mid level shortwave. However...regional water vapor imagery shows deep layer drying arriving from the west...which will bring remaining showers to an end in the next 1-2 hours. Fog is also showing some signs of thinning during the past hour along the midcoast...with some new patches showing back up over the CT valley. Rapid improvement is expected around daybreak and shortly thereafter. Temperatures remain mild and bumped up near term temps 1-2 F based upon these observations. Original discussion below... High Impact Weather Potential: Patchy dense fog RKD-AUG-LEW region through daybreak. Current Pattern: Cold front has now exited the forecast area with shortwave trough axis overhead and also about ready to exit east. Blended total precipitable water product shows a pocket of drier air centered over the Great Lakes...poised to move east into New England as heights build behind departing trough. Surface high pressure is centered over WV/VA and is also gradually pulling east. The pattern portends a quiet near term forecast with primary forecast concerns centered around current fog/low stratus and when it will break up. Through Daybreak: Tracking a band of sprinkles and light showers that are now moving into southwestern New Hampshire. These have weakened substantially over the past few hours...but will continue to lift north and east ahead of mid level shortwave through daybreak. By daybreak...any remaining shower activity will become increasingly confined to the upslope areas in the mountains. Further east...have seen occasional dense fog at LEB-AUG-RKD and have issued an SPS for this as improvement will arrive from the west over the next few hours...and certainly no later than daybreak. Temperatures generally remaining in the 60s for overnight lows. Today: For a few hours this morning...expect some lower clouds and perhaps shower/sprinkle activity in the upslope areas of northern NH before better moisture lifts north and east. Otherwise...expect any remaining shallow moisture over eastern areas to quickly mix out today...with skies turning partly to mostly sunny /a few Cu all areas and some mid clouds closer to the international border/ under developing moderate /10 mph gust to 20 mph/ northwesterly winds. Otherwise...T8s have fallen 2-3C from yesterday to around 11-12C...but with more morning sun expect most locations to see high temperatures close to or just shy of what was observed today...with 70s from the mountains north and lower/middle 80s over the coastal plain into the foothills.
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&& .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM MONDAY/... High Impact Weather Potential: None. Pattern Summary: Brisk zonal flow aloft is expected through the short term forecast period between mid level low moving into the Hudson Bay region...with climatological high over the southeastern states. Surface high pressure east of the Mid Atlantic reaches our longitude during the day Monday with ridge axis north of this feature pretty much dominating the surface pattern through the short term forecast period. Driest air through the column will settle overhead tonight...gradually shifting east on Monday with values near climatological norms through the period. Tonight: With high pressure centered just south of the region...llevel gradient relaxes with decoupling expected all areas under clear skies. Afternoon dewpoints suggest a decent place to start for expected overnight lows...and expect a cooler night than the past few with the drier airmass overhead. Lows should reach the 50s for most areas...with southern NH and coastal ME likely remaining at or just above 60. Monday: Deep west southwest flow aloft with surface high pressure gradually pulling off the US east coast with return flow strengthening. Nearest frontal boundary will be draped well north and west of the forecast area...extending from central Quebec south and west into the Great Lakes region. While this won/t be close enough to have any meaningful weather impacts...could see some high cloudiness stream east from any ongoing convection. This bit of cirrus and perhaps a few daytime Cu will be all that will impact viewing of the eclipse over the forecast area. A warm day is in store with T8s around +15C. While the eclipse will likely temper temperatures for 1-2 not expect that this will have much of an influence on the actual highs...which may be pushed an hour later...but still reach the 80s most locations...with MHT-ASH-SFM corridor potentially hitting 90. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... A warm and humid southwest flow will continue Tuesday in advance of an upper trof and associated cold front. By late Tuesday showers and thunderstorms will spread across much of NH and western ME. Tue night into Wed showers and thunderstorms are expected as the upper trof moves across the region. By Wed afternoon the upper trof and cold front moves off the coast allowing clearing to take place in the afternoon. High pressure builds across the region Thu and into the weekend with near seasonal temps and dry conditions. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... Short term /through Monday/... Summary: High pressure will build south of the region through Monday bringing improving flying conditions to the area. Restrictions: LIFR fog/stratus is gradually eroding from the west with RKD/AUG likely to improve to VFR around daybreak. Otherwise...could see some IFR fog develop near LEB around daybreak with upslope cloudiness bringing MVFR restrictions to HIE through the morning. VFR this afternoon through Monday outside of potential fog redevelopment tonight HIE/LEB and potentially RKD. Winds: Light and variable winds overnight will become northwesterly and increase to 10g18kts for the day today before diminishing back to calm tonight. Winds will become westerly 10-15kts for the day on Monday. LLWS: LLWS is not expected through Monday. Lightning: No thunderstorms are expected through Monday. Long Term... VFR Tuesday. Areas of MVFR/IFR conditions in showers and thunderstorms late Tuesday into Wed. Becoming VFR for late Wednesday through Friday. && .MARINE... Short Term /through Sunday Night/... Westerly wind gusts may reach 20-25kts for a time Monday afternoon in the outer waters...but in general winds and waves are expected to remain below SCA levels through the short term forecast period. Ongoing fog over the waters is expected to dissipate this morning. Long Term... SCA`s may be needed late Tuesday into Wednesday over the outer waters. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ ES is the U.S. government's official web portal to all federal, state and local government web resources and services.