Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 180132 AFDGYX Area Forecast Discussion National Weather Service Gray ME 932 PM EDT Mon Oct 17 2016 .SYNOPSIS... A warm front will lift northeast through the region tonight. Temperatures will be very warm south of the warm front on Tuesday, but north of the front it will be cooler with showers expected. As low pressure moves through Quebec, it will drag a cold front into New England Tuesday night. This front will linger offshore before lifting back north as a warm front Thursday into Thursday night with more showers possible. Low pressure tracking through the Great Lakes will bring another cold front toward the area Friday into Friday night, more showers possible ahead of it. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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930 PM Update...Have adjusted PoPs a little bit for the overnight hours, mainly across southwestern NH. This due to a dying MCS that should bring some light measurable rain to that region in a few hours. There probably won`t be any thunder in the CWA with this, but cannot rule out an isolated rumble. Otherwise, WAA showers will be possible later on tonight across the rest of the region as the warm frontal boundary above the boundary layer lifts northward. Otherwise, backdoor cold front continues to push southward and has cleared maine and should move southward across southern NH over the next couple of hours. Have adjusted overnight temperatures based on latest trends in observational data, with temperatures already in the lower 40s in the western ME mountains. Temperatures across southern NH on Tuesday will be tricky and will hinge on how stubborn the SFC warm front is when it attempts to return northward. Haven`t changed current forecast temps for Tuesday, but there is considerable bust potential with 20 degree errors possible in some spots. 6 PM Update...Very minor adjustments to the going forecast based on latest trends in radar/satellite and other observational data. The pleasant evening will continue for most...with showers expected to arrive in the western zones around midnight. MCS over Lake Ontario as of 22z will most likely weaken significantly and perhaps fall apart before making it as far east as the CT river valley. A few showers may survive and if they do would affect western NH around midnight give or take an hour. Previously... For tonight will see increasing warm air advection bring mid to high clouds into the region this evening, with potential lower stratus developing closer to the coast as Tds and temps come together. Watching cluster of convection currently moving across Ontario, which is associated with 850mb speed max and tightening thermal gradient. Nam12 keeps bulk of precip N of the CWA, while 18Z HRRR is pushing convection further S into NH and ME, but weakening /although previous runs kept it stronger as it moved into NH. This will be the rain maker as it moves along the front late tonight into early Tuesday...if it holds together northern and western zones could see a quarter to half inch, and some possible thunder, if not, most areas will be limited to a quarter of an inch or less. lows should drop off enough early to bring the mountains down into the mid to upper 40s, and everywhere else into the 50s, but the temp fall will slow a great deal after midnight.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Models have been fairly persistent with keeping the cooler in place in all but srn NH and Ct vly as pseudo cold air damming situation with SE flow holding back the warm air in all but York county ME through most of the day. So highs will vary quite a bit, reaching well into the 70s in the souther tier of NH counties and into the low to mid 70s in the CT valley, perhaps as far north as KHIE. These areas will break into partly to mostly skies in the afternoon. The question is how far on the coastal plain can the warm air make make it before sunset. Will hold the areas to highs around 60, with interior foothill and mountain areas in western ME limited to the mid-upper 50s. Any morning showers should end across all but FRanklin and somerset counties, where some dynamics could persist into the afternoon. Cold front will approach from the west Tue evening and will increase the chance of showers in the N and W, but will likely weaken as they head toward the coast, and should the htreat of any SHRA diminish after midnight. Lows will be balmy for the third week of October, generally in the mid 50s to low 60s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... High pressure builds into the area from the west on Wednesday with another day of warm temperatures expected. Highs for most of the area will be in the 70s, with a few 80s possible in southern New Hampshire. Increased moisture will also keep nighttime lows much above normal. A large upper level trough sharpens over the western Great Lakes and Mississippi Valley on Thursday which will drive cyclogenesis over the eastern Great Lakes. Expect an onshore easterly flow over northern New England on Thursday and an increasing chance of showers as a warm front sharpens to our south. This warm front will lift north into Canada Thursday night into Friday morning while the surface low tracks through the Saint Lawrence Valley or upstate New York. Models disagree on how sharp the upper trough will be and as a result disagree on the resulting track of the surface low, but there is broad agreement that there will be a period of rain beginning on Thursday and lasting through at least Friday night. Both the GFS and ECMWF pull in moisture from a weak tropical low off the east coast as well, which could help produce heavy rain somewhere, but where that may be will depend on the track. The core of the upper trough moves into the Northeast on Saturday and lingers through the weekend. This will bring cooler temperatures and a good deal of cloud cover through the weekend. The GFS maintains a threat of showers through the whole weekend as its upper low drags through while the ECMWF is drier and colder. It is possible that the remaining areas which haven`t frozen yet could see their first freeze late this weekend or early next week. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/...
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Short Term...low clouds develop well after midnight, and IFR conditions expected toward daybreak and lingering through most of Tue morning. KMHT/KLEB/KHIE should improve to VFR in the afternoon, with MVFR lingering elsewhere through the evening. Could see improvement to VFR late Tuesday night after cold front passes. Long Term...Should see mostly VFR conditions Wednesday, but conditions deteriorate Thursday in an onshore flow with increasing clouds and showers. IFR or LIFR conditions are possible Thursday through Friday night. Could see an improvement to VFR this weekend.
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&& .MARINE... Short Term...SCA issued for increasing SW flow ahead of a cold front Tuesday afternoon through Tue evening. Winds seas will diminish late Tue night. Long Term...A frontal boundary which moves into the Gulf of Maine late Tuesday night will linger just outside the Gulf of Maine before pushing back north as a warm front Thursday into Thursday night. It is possible that southerly flow behind the warm front and ahead of the advancing cold front could bring wind gusts to 25 KT over the waters on Friday. Winds behind the cold front may be a bit stronger Friday night into Saturday though the timing is still uncertain. && .TIDES/COASTAL FLOODING... We`re currently in the period of high astronomical tides. High tides of note are referenced to the Portland Harbor tide gage where flood stage is 12 ft mllw. It won`t take much onshore wind or wave action to cause issues along the coast and the situation will be watched closely through late this week. In the strengthening southeasterly flow on Tuesday could bring Portland to just above the 12 ft flood worth watching as some uncertainty exists with the wind forecast. 1251 AM Tue 11.0 ft mllw 108 PM Tue 11.7 ft mllw 200 PM Wed 11.5 ft mllw 256 PM Thu 11.1 ft mllw && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 2 PM Tuesday to 8 AM EDT Wednesday for ANZ150>152-154. && $$ NEAR TERM UPDATE...Ekster is the U.S. government's official web portal to all federal, state and local government web resources and services.