Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201040 AFDGYX Area Forecast Discussion National Weather Service Gray ME 640 AM EDT SAT AUG 20 2016 .SYNOPSIS... High pressure will shift offshore this morning then remain anchored off the coast through early Sunday. A cold front will approach from the west late Sunday and slowly cross the region Sunday night and early Monday. High pressure and drier air follows the front late Monday through Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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638 AM...minor ESTF update to reflect current satellite trends and to ingest the 10z mesonet into near term grids. Prev Disc... At 06z...a 1018 millibar surface ridge was draped across the forecast area. A 1005 millibar low was over northern Quebec province with a weak and diffuse warm/stationary front extending southward through the eastern Great Lakes and mid Atlantic region and a trailing cold front through the western Great Lakes. GOES infrared imagery showed mainly clear skies across the forecast area under the cresting surface ridge. However, the light winds and clear skies were allowing patchy stratus and fog to develop across our area most notably over interior valleys. For today, any early morning stratus and fog will burn off quickly with a mainly sunny start as the surface ridge retreats offshore. By afternoon, a few clouds associated with the weak surface boundary should spread northward into mainly southern and western New Hampshire with a low chance for a late day shower/isolated thundershower there. Highs today will be within a few degrees either side of 80F , with the exception of the immediate mid coast of Maine which will be a few degrees cooler in developing onshore flow.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Little change tonight with the surface ridge parked offshore and the weak surface boundary remaining to our south and west. There will continue to be a few clouds across southern and western New Hampshire along with the chance for an isolated shower. Otherwise, a dry and partly cloudy night with more widespread stratus and fog developing in the onshore flow. Lows tonight will range from the mid 50s to the lower 60s. On Sunday, low clouds and fog should gradually lift with partly sunny skies for much of our Maine zones while we`ll see more clouds over New Hampshire ahead of the approaching cold/occluded front. We`ll see an increasing chance for showers and a few thunderstorms as we head through the day...with areas vicinity of Penobscot Bay and the Kennebec valley staying dry for the balance of the day. Sunday will be cooler then today given the expected cloud cover and the persistent onshore flow. Highs should range from the mid 70s to the lower 80s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... All models remain in good agreement with the timing and evolution of approaching surface cold front. As upper trough approaches New England Sunday evening, surface cold front advects into eastern New York. Ahead of the front, high precipitable water values will surge northward from the mid Atlantic Region. Showers will cross Maine and New Hampshire during the night. The atmosphere only becomes modestly unstable with surface based CAPE values briefly in the 200-300 J/KG range, bringing a minimal risk of thunderstorms. Nevertheless, a brief period of locally heavy rainfall remains a possibility through the daybreak hours on Monday. Thereafter, cooler and drier air begins to filter into northern New England as high pressure builds east from the Ohio River Valley. There will still be a chance for a shower during the day however as the upper level trough finally crosses our forecast area by mid/late afternoon. There will be a chill in the air by Tuesday morning as readings fall into the mid 40s to lower 50s. Thereafter, dry and cool conditions continue on Wednesday with patchy fog during the overnight hours over the inland valleys. A southwest flow (both at the surface and aloft) will advect warmer temperatures into the region by late in the week as high pressure slips off the Eastern Seaboard. The next chance for precipitation will be Friday as a weakening cold front passes through New England. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Short Term /through Sunday/...Some IFR/LIFR conditions in areas of valley stratus and fog through 13z...otw vfr today. Areas of ifr/lifr developing tonight aft 04z Sunday in stratus, fog and isolated -shra. Bcmg vfr aft 14z Sunday...with areas of mvfr developing by afternoon over the Connecticut valley in -shra/-tsra and gradually spreading eastward. Long Term...VFR looks to prevail for much of the extended outside of passing front Sun night. Along the front, SHRA/TSRA may create local IFR or LIFR conditions. If coastal fog/stratus were to develop...more widespread IFR conditions could occur from PSM thru PWM...AUG...and RKD. By midweek high pres will bring VFR during the day...but valley fog will be possible with LIFR conditions for LEB and HIE especially. && .MARINE... Short Term /through Sunday/...quiet on the waters as a surface ridge traverses the waters through tonight. On Sunday...increasing southeast flow may brings winds and seas close to small craft threshold outside the bays by evening. Long Term...Ahead of approaching cold front late Sun seas may build to near 5 ft on the outer waters. Will have to watch for areas of coastal fog developing as a warm and moist air mass briefly tries to work back into the area ahead of the front. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ ES

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