Area Forecast Discussion
Issued by NWS Portland, ME

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802 FXUS61 KGYX 011308 AAB AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 908 AM EDT Tue Jul 1 2025 .SYNOPSIS... A cold front will approach the region today, with warm and humid conditions ahead of it and a chance of showers and thunderstorms with its passage. A strong storm or two cannot be ruled out but the coverage of storms is low confidence. A brief break on Wednesday will give way to another cold front on Thursday. A similar threat of showers and thunderstorms will accompany that boundary as well. Then drier conditions are expected into the holiday weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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9 AM Update: With improving visibilities across the area of the advisory...will cancel the remainder of the dense fog advisory. No other changes at this time. 8 AM Update...Dense fog advisory for the ME coast, clearing from W to E after sunrise. Midcoast fog could linger through late morning as reinforcing surge of moisture off the cool gulf delays burn off. Showers advancing from the west along with thickening clouds in the north, but generally light to moderate rainfall and no thunder at this time. Can`t rule out a few rumbles of thunder through late morning as this trough feature swings by. The main focus remains on how much daytime heating is inhibited by these morning clouds, and thus the potential for severe weather ahead of the cold front later this afternoon and evening. Forecast appears on track for an isolated strong storm with damaging winds and heavy rainfall. As for precip this morning...guidance is focusing mainly on the northern zones. Convection to the south around NYC is forecast to dissipate as it moves northeast and largely stay south of the forecast area. Warm advection showers to the north are forecast to continue in the mtns. While the southern end of those showers may increase a bit in intensity...the cooling effect of precip and clouds in this area should limit the afternoon severe weather threat across the north. To the south over much of the rest of the forecast area the Storm Prediction Center still has a marginal risk for severe weather. This is driven primarily by the threat for wind gust. Based on forecast soundings I do not disagree with that assessment. Skinny CAPE profiles with an area of drying in the 700 to 500 mb layer would support precip loading and downburst potential. We also should have more than enough shear to organize the updrafts. The limiting factor will be coverage of convection. Current CAMs are fairly scattered thru the day and by the time the front really arrives in the forecast area it is after dark and we are rapidly losing instability. I did remove the severe wording from the grids given the overall uncertainty. It is possible that once we see how morning precip evolves that more targeted areas could be added back to the forecast. I did also add heavy rain wording to thunderstorms for the afternoon. PWATs will be near 2 inches...and HREF max QPF in 6 hours late this afternoon is pushing 3 inches.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... As the front nears the coast this evening showers and storms will be riding northeast along the boundary. Given that the threat for severe weather is expected to be tied mostly to elevated cores...as we increase CIN the threat should decrease pretty quickly. However some torrential rain will remain possible as the near 2 inch PWATs will not be pushed south of the local area until well after midnight. Some marine fog will also be possible...but my current thinking is that southwesterly wind direction and rain outflow will help to keep that in the Gulf of ME vs onshore. Wed will feature a similarly warm day but slightly less humidity and weaker overall forcing. But diurnal heating alone may be enough to pop off some isolated showers or thunderstorms. These would mainly be tied to heating of the higher terrain and will tend to dissipate as they leave that heat source and drift east/southeast. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Key Message: Another front will cross the area Thu with the threat of showers and storms. This will be followed by high pressure and generally dry and pleasant weather thru the weekend. Impacts: Various convection allowing models (CAMs) and ensembles are hinting at a threat for strong to severe storms Thu. This will be highly dependent on timing of the front...as it may already be near the coast at peak heating however. Forecast Details: A reinforcing cold front is forecast to drop out of Quebec and cross New England Thu. CSU machine learning severe probabilities indicate that a marginal to low end slight risk severe threat is possible given the set up. Forecast soundings show both sufficient CAPE and shear to support that thinking. In addition ECMWF EFI also has an elevated CAPE/shear overlap...especially for southeast half of the forecast area. That also means that we have a narrow spatial window for this threat given the current forecasts of frontal timing. If the boundary speeds up it will already be in the Gulf of ME by the time peak heating occurs. After the front high pressure builds in from the west. The ridge axis is not forecast to cross the forecast area until sometime Sat. This will mean largely west to northwest flow Fri and little in the way of moisture advection. That will mean a warm 4th with refreshing dewpoints. Sat into Sun humidity will start to creep back up again with the next frontal passage possible Mon or Tue. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... Short Term...Dense fog LIFR prevalent across the midcoast with improving conditions from west to east. This is impacting AUG/RKD primarily. Elsewhere focus will be on convective development. Showers in the north will expand in coverage, with the potential for thunderstorms this afternoon. Fog conditions likely again overnight. Long Term...Largely VFR conditions expected thru the extended. The exception will be with another frontal passage around the Thu timeframe. Some redeveloping coastal fog will be possible and threaten IFR conditions for coastal terminals. The frontal passage will bring increasing chances for SHRA/TSRA with local MVFR or lower conditions possible. && .MARINE... Short Term...Areas of fog are developing as moisture continues to increase across the coastal waters. Some of this fog may be locally dense thru daybreak. A the frontal boundary nears the waters tonight the southwest winds will increase...and a few gusts near 25 kt are possible. In addition any convection that survives over the trip into the Gulf of ME may also contain gusty winds and torrential rain. Long Term...Winds and seas generally expected to remain below SCA thresholds thru the weekend. Another frontal boundary will cross the waters around Thu. Will have to watch for the redevelopment of coastal fog along with the threat of convection bringing gusty winds to the waters. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...None.
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&& $$ NEAR TERM UPDATE...Arnott