Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 191103 AFDGYX Area Forecast Discussion National Weather Service Gray ME 703 AM EDT Wed Jul 19 2017 .SYNOPSIS... A weak frontal system will remain near the Maine coastal plain today and Thursday. Very warm temperatures look to be in the cards for Friday and Saturday in a general westerly flow regime. A storm system to our south will lift north and perhaps bring a shot of rainfall and cooler temperatures by late Sunday into early next week. && .NEAR TERM /TODAY/...
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7AM UPDATE... Now that the sun has come up, the first images from the daytime fog product on the GOES 16 satellite are absolutely beautiful. Low level stratus and fog is banked up against the mountains along the coastal plain, with valley fog in the interior valleys as well. Have used this imagery to update sky cover forecast for the next few hours as this is expected to dissipate late this morning. Otherwise no significant changes were needed. ORIGINAL DISCUSSION... Early morning satellite imagery shows clouds and dense fog have overspread the coastal plain of Maine and seeped into eastern New Hampshire beneath a shallow inversion noted on the 00Z sounding from last night. We expect this cloud cover to dissipate during the morning hours, but until then we have issued a Dense Fog Advisory for the areas most likely to see visibility of 1/4 mile or less. Just above the inversion, very warm air has moved into the area. Thus, once clouds break up and low level heating begins, expect a rather quick warm up into the low 80s. Forecast 850 MB temperatures suggest that peak warming today will produce temperatures in the low 90s. However, a rather sharp gradient is expected to exist between the low level southerly flow and a developing well-mixed westerly flow, with the frontal boundary between these two air masses pushing into far western Maine this afternoon. Winds at 850 MB are rather light (10 to 20 KT) out of the west, so this should not be strong enough to force this boundary through Portland today, but it should make it to Portsmouth, Sanford, and Fryeburg. To the west of the boundary, temperatures in the well-mixed environment will peak in the low 90s, while to the east the clouds will hang on longer into the morning and an onshore flow will stunt warming potential to only the low 80s.
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&& .SHORT TERM /TONIGHT AND THURSDAY/... Shortwave trough passing eastward through Quebec and northern Maine will push another weak front through the area tonight. The effect will be felt mainly in the humidity levels, as dewpoints will fall about 5 degrees from what they are today. With winds out of the northwest on Thursday expect another warm day with temperatures in the upper 80s to near 90 degrees. As so often occurs in this region, the temperature in coastal Maine will be warmer behind the front than it was ahead of it due to downsloping northwest winds which should keep the sea breeze influence limited to right along the beaches. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... The extended portion of the forecast starts out with a bit of uncertainty Thursday night as there are considerable differences in the model suite with the strength and speed of a potential short wave trough moving toward the region. The ECMWF is most robust and would bring showers and thunderstorms across roughly the southern half of the CWA late Thursday night. Other members of the 00z suite are much less enthusiastic. This will probably depend on upstream convection across the Great Lakes, so uncertainty will likely remain high through today. However, it`s worth a low chance for showers and thunderstorms as there is some model support for it. If we do get convection Thu night it would likely move offshore early enough Friday to allow for a hot and humid day. Another fair weather day is expected Saturday with warm temperatures once again. More uncertainty is in store for Sunday and early next week as an unsettled/rainy/cool scenario could occur as troughing digs into the northeast. For now, have highest pops Sunday night but will likely have to adjust moving forward as confidence improves. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... Short Term...Areas of dense fog this morning can be expected along the coastal plain of Maine and eastern New Hampshire. Expect visibility to improve shortly after 12Z with cloud cover gradually lifting and dissipating through the morning and from west to east. Should see VFR conditions areawide by the afternoon, though the low clouds could hang toughest at Rockland. With a westerly flow developing tonight and dewpoints falling, do not expect widespread fog and low clouds to redevelop tonight. Long Term...Generally VFR expected Thursday night through Sunday. However, low prob of showers and thunderstorms exists Thursday night across southern ME and southern NH which could lower cigs/vsbys overnight. Otherwise, some morning fog and stratus is possible along the coast and interior valleys during the period. && .MARINE... Short Term...Expect a light southerly flow today, shifting to the west on Thursday and to the northwest on Friday as a series of weak fronts moves through. Pressure gradient remains fairly light so expect winds and seas to be light as well. Long Term...Winds and seas are expected to remain below SCA thresholds through Sunday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Dense Fog Advisory until 10 AM EDT this morning for MEZ012>014- 018>028. NH...Dense Fog Advisory until 10 AM EDT this morning for NHZ004-006- 010-013-014. MARINE...None. && $$ NEAR TERM...Ekster SHORT TERM...Ekster LONG TERM...Kimble

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