Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 230131 AAC AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 931 PM EDT Thu Jun 22 2017 .SYNOPSIS... High pressure will move away from the region tonight. Tropical moisture from the remnants of Cindy...and an approaching frontal system will result in showers and thunderstorms Friday into Friday Night. A series of surface troughs or weak cold fronts will cross the area this weekend into early next week bringing us the chance of showers from time to time...especially over central and northern areas. && .NEAR TERM /THROUGH FRIDAY/... 926 PM Update: Have made minor changes to the forecast this hour...slowing precipitation arrival just a tad...but boosting cloud cover based on evening satellite imagery. Am watching shower activity moving east near KRME/KUCA along the elevated warm front and expect this to make a run at the area after midnight. Still...best forcing waits until well after midnight with best confidence in the north...where PoPs were upped based on latest HRRR simulations which line up well with upstream trends and movement of the warm front. Temperatures nudged up a bit given current observations...increasing cloud cover...and GFS LAMP trends. 552 PM Update: Going forecast in good shape with only minor adjustments needed for temperatures. Expect the evening to remain dry based on upstream radar evolution and recent HRRR simulations with shower and embedded thunder chances arriving from the west after midnight. Previous discussion below... A weak 500 mb ridge moves across the CWA tonight, which should help to keep the evening dry, for the most part. Cannot rule out a shower or sprinkle in the north and west, but this will probably not produce enough to measure if it occurs at all. Clouds will thicken from the west this evening. Very latitudinal stretched trough to our west will bring some WAA across the CWA tonight, with the better chance of showers after midnight and in the nrn and western zones. Some elevated instability as well, so cannot rule out some thunder, but all in all nothing significant overnight, and some places will see nothing at all. Temps will fall this evening, but increasing low level moisture and clouds will likely stall the the temp drop around midnight or so, and lows will range from the mid to upper 50s in the north and east, to the low to mid 60s in southern NH and along the coast. && .SHORT TERM /FRIDAY NIGHT THROUGH 6 PM FRIDAY/... The big question for Friday is whether any part of the sfc CWA can break into the warm sector and get some sun and heating. The warm front should be exiting to the north in the morning, before secondary low forms on the triple point just N of New England, which would allow some southern zones to break out given decent SW flow. This would destabilize the atmosphere enough to produce TSRA, which would open doors for training of cells, producing very heavy rain, and potential for severe storms developing in the afternoon. Since best dynamics will lag a little behind the warm sector, and its questionable how unstable things get given clouds, will not highlight any severe at this time. Heavy rain, however is a better bet, with very moist air, some of it from the remnants of tropical storm Cindy, will produce PWATS of around 2 inches. So, could still see heavy downpours late in the day into the evening, when the better dynamics aloft move through ahead of the front. Highs are a tough forecast, and dependent on if and when any locations see a decent amount of sun, but they will range from the low to mid to 70s in the mid coast area, where onshore flow will hold for most of the day, to the low to mid 80s in srn NH and the CT vly, where the SW flow will be warm and there will be the chance for some sun. The from looks to move through late Friday night, and will follow the best dynamics as well, so while showers will be possible through the night, the threat for torrential downpours should diminish around and after midnight. It is unlikely to see the front at the sfc, until mixing begins Sat morning, so expect humid conditions to linger with lows in the 60s, and mostly in the mid to upper 60s outside the mountains. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Global models in general agreement over this period. A cold front will be located over the coastal plain early Saturday. This could result in a few early morning showers. As the front pushes offshore expect drier air to move in during Saturday. A couple of mountain showers may develop in a developing NW flow. Coastal areas will see a downsloping wind resulting in dry weather. On Sunday the NW flow will continue. A short wave of vorticity will approach which could produce a few showers...again the best chances will be over northern and mountain areas. This pattern will persist on Monday. Late Monday low pressure will develop along the Mid Atlantic Coast. The most recent runs of the models still track this low offshore but hold back some troffiness over New England which would result in a period of rain or widespread showers for Tuesday. As the low continues to move NE the 500 mb trough sharpens and looks to keep the area unstable with the threat of at least a few showers and thunderstorms Wednesday and Thursday. Temperatures will start off normal to slightly above normal Saturday but will become normal to slightly below normal Sunday through Thursday. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... Short Term... Summary: A warm front will lift north across the region tonight with an increasing chance for showers and a few thunderstorms after midnight. A warm and very moist airmass will then yield an increasing risk for showers and thunderstorms by the afternoon hours on Friday under southerly flow. A cold front arrives from the west Friday night with continued chances for showers and thunderstorms. Restrictions: Generally VFR through tonight with some threat for temporary restrictions primarily HIE/LEB after midnight in a shower or embedded thunderstorm. On the day Friday...VFR conditions should dominate all locations through the morning...but by afternoon...expect increasing shower and thunderstorm coverage to result in some occasional MVFR/IFR restrictions...esp at HIE/LEB/AUG. Also...marine layer will likely work into RKD with IFR CIGS/MVFR VSBYS. Shower/thunderstorm coverage will decrease Friday night...but with moist airmass still in place...expect a good amount of haze and fog...with locally dense fog possible depending on how much rain we realize. Winds: Winds less than 5kts overnight before becoming southerly on Friday and increasing to 10g18kts. Southerly winds continue Friday night but diminish to less than 10kts. LLWS: There is some risk of LLWS in the vicinity of RKD after 18Z Friday with low level jet overriding stable air off the ocean. Thunder: Some risk of an isolated thunderstorm through daybreak Friday for LEB/HIE. Thunder threat will increase all areas for the day Friday...particularly afternoon and evening...but remain greatest at HIE/LEB...with thunder threat diminishing with the loss of daytime heating Friday night. Long Term... Mostly MVFR to VFR conditions south of the mountains Saturday though Monday although brief IFR possible in any showers. MVFR to IFR conditions over the mountains in clouds and scattered showers. A better chance of IFR conditions on Tuesday as more widespread showers/rain is expected. && .MARINE... Short Term...SCA issued for SW winds Fri afternoon into early Saturday morning. Winds will likely peak Sat evening. Long Term... Waves and winds to remain below SCA levels. Visibilities may become reduced in rain on Tuesday. && .TIDES/COASTAL FLOODING... Astronomical high tides will continue through the weekend with the possibility of nuisance flooding Saturday night at high tide which will occur at 12:05 am Sunday Morning at Portland and 12:16 am at Portsmouth/Fort Point. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 2 PM Friday to 8 AM EDT Saturday for ANZ150-152-154. && $$ SYNOPSIS... NEAR TERM...Arnott/Cempa SHORT TERM...Cempa LONG TERM...Lulofs AVIATION...Cempa MARINE...Cempa/Lulofs TIDES/COASTAL FLOODING...

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