Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 241942 AFDGYX Area Forecast Discussion National Weather Service Gray ME 342 PM EDT Sat Sep 24 2016 .SYNOPSIS...
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High pressure moving out of Canada will bring cooler temperatures and drier air to the region through Sunday night. Many towns in the area may see their first frost or freezing temperatures tonight or Sunday night. Gradually moderating temperatures are expected Monday before another approaching cold front brings the threat for showers for Monday night and Tuesday. Cool weather will return for Wednesday.
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&& .NEAR TERM /TONIGHT/...
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Only issue for tonight will be frost/freeze potential, mainly in the northern zones. Any clouds this afternoon will diminish with loss of daylight, and winds will slacken some on the coastal plain, but will become light in sheltered areas. This will allow for good radiational cooling and the development of fog or frost in the mountain valleys. The question remains as to weather fog of frost forms first, and indications are that fog would be favored over frost, but some uncertainty remains. Either way there`s a good chance that even with fog temps fall below freezing in the far north, and so the freeze warning remains in place here as well. Overall lows will range from around 30 in the far north to the low 40s along the coast and in urban southern NH.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
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Sunday morning will see the passage of a weak 500mb wave which will help intensify surface low over the maritimes and tighten up the pressure gradient making for a cool and breezy day...with gusts of around 25 mph at times. Should see more clouds in the first part of the day with sunnier skies in the afternoon as drier air works in and highs in the mid to upper 50s north...the low 60s south. Sunday night will bring good radiational cooling conditions with cold air aloft, and will see a better possibility of frost in all areas but the immediate coast with lows ranging from the upper 30s in the north to around 40 in the south.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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High amplitude ridge moves into New England from the west on Monday with surface high pressure shifting offshore. Temperatures warm into the 60s with increasing high clouds arriving from the west later in the day as the next upper trough approaches. This trough will begin spreading showers into the area along its cold front late Monday night into Tuesday with the front and showers pushing offshore Tuesday evening. Models continue to diverge in how to handle the upper trough from Wednesday onward as is typical with cut off lows. As a result, there is a high degree of forecast uncertainty. The GFS sends the trough eastward rather quickly, evolving it more as a sharp open wave which crosses the area by early Friday and is replaced by ridging through the weekend. The ECMWF however maintains a cut off low which dives southward into the southern Appalachians before drifting northward toward the eastern Great Lakes early next week. Such dramatic differences lead to low forecaster confidence this weekend. Much of the current forecast involves a blend of the available forecast models with neither solution particularly favored over another. Wednesday and Thursday look dry no matter which model is preferred as high pressure shifts toward the region. Have decided to include a low chance for showers beginning on Friday to account for the possibility of energy rotating around the cut off low envisioned by the ECMWF. This chance of showers lingers into next weekend. Daytime temperatures seem likely to be in the 60s through the period, though it could be a little cooler if the low lingers and brings showers. Nighttime temperatures mainly in the 40s to low 50s, though it could be cooler if the drier GFS is correct.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/...
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Short Term...Mainly VFR conditions expected. Winds will gust to 25 mph on Sunday at many of the airports. Valley fog likely tonight at KHIE/KLEB. Long Term...Increasing cloud cover expected from west to east late Monday, with conditions becoming MVFR or IFR in showers late Monday night through Tuesday. A cold front will push through on Tuesday, ending the showers but it could take a little while for the low level moisture to clear out and conditions to go VFR again. Morning fog is a possibility at LEB and HIE Wednesday and Thursday morning as is typical this time of year.
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&& .MARINE...
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Short Term...Winds and seas will continue near SCA criteria, but should remain below those levels through Sunday night. Long Term...Increasing southerly flow ahead of the cold front on Tuesday could approach 25 KT. The prolonged fetch will allow wave heights to build from 5 to 8 FT Tuesday night. Should see conditions calm down again on Wednesday with high pressure moving toward the area. There is a high degree of uncertainty in the forecast from Thursday onward with winds generally from the NNE at 10 to 15 KT the most likely result. It is possible that low pressure could form off the mid Atlantic coast bringing more of an easterly component to the winds and perhaps some stronger wind speeds and higher wave heights.
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&& .GYX WATCHES/WARNINGS/ADVISORIES... ME...Freeze Warning from 2 AM to 8 AM EDT Sunday for MEZ007-008. Frost Advisory from 2 AM to 8 AM EDT Sunday for MEZ009-012-013. NH...Freeze Warning from 2 AM to 8 AM EDT Sunday for NHZ001-002. Frost Advisory from 2 AM to 8 AM EDT Sunday for NHZ003-004. MARINE...None. && $$ NEAR TERM...Cempa SHORT TERM...Cempa LONG TERM...Kimble

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