Area Forecast Discussion
Issued by NWS Portland, ME

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074 FXUS61 KGYX 212133 AFDGYX Area Forecast Discussion National Weather Service Gray ME 533 PM EDT Fri Oct 21 2016 .SYNOPSIS... A slow moving frontal boundary and a developing low pressure center will bring wet weather and a cool onshore flow to the region into Saturday. Later Saturday and Saturday night...the low will gradually lift north into Quebec. On the backside of this system...colder air will arrive on gusty northwest winds for the latter part of the weekend and early next week. Some accumulating snow will be possible in the mountains Saturday night into Sunday night. A large Canadian high pressure system will then dominate the region through midweek next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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530pm update... Main update at this time was to the PoP to more closely reflect the radar returns showing rain pushing into western new hampshire and keeping eastern sections lower. Region of stronger convection /as seen by -60C IR cloud tops/ now moving over the 70W/40N benchmark. Satellite trends and high res guidance continues to point to it moving northwards into our area around midnight. Heaviest rainfall would be from portland eastwards to penobscot bay. While the rain looks to move through relatively quickly, there is a slight chance for it to get hung up along the coast which will need to be monitored. Previous Discussion: There are two main wx concerns for tonight...rnfl and fog. For starters marine fog is already creeping back SWwd along the ME coastline. Inland vsbys have improved slightly...but will trend back down after dark and likely stay that way as low pressure moves overhead. NARRE-TL hints at dense fog moving towards the forecast area from the S after at this point will keep fog in the forecast and monitor for a potential dense fog advisory. Regarding the rnfl...the area to watch is developing S of Cape Cod at this hour. A large area of convection continues to peel off of the sub-tropical low pressure off the Carolinas...heading towards New England. The low level moisture has already arrive across Srn New England...with showers moving N thru the area. I have increased PoP across Srn NH in the next couple of hours for these showers. Satellite cloud patterns already suggest low pressure circulation is developing within this convection...and model guidance pivots this into Wrn ME this evening. Global guidance of the GFS and ECMWF have finally come around to the idea of potentially heavy rnfl along and E of the low pressure track. This matches hi-res guidance like the HRRR and NCAR ensembles. Most favorable area will be the border of NH and ME...and on Ewd thru the night. Best period for potential heavy rnfl will be 00z to 06z this the low level jet pivots NEwd.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Band of rnfl exits the forecast area early Sat...but with surface trough overhead I do not expect much clearing. Stratus should linger...and there may be drizzle in the early part of the day with weak lift continuing in the dry slot. Upper trof swings thru the region in the afternoon. An area of showers is likely to be forced out ahead of this feature...sweeping SW to NE across the forecast area in the afternoon. It is near and after this time that winds will begin to increase...especially as colder air filters into the area. Behind the upper trof strong pressure rises may help to bring some gusty winds...though that potential looks best across Srn New England. As cold air deepens Sat night it is more likely that is when winds begin to pick up across our forecast area. At this time it looks to be a slow and gradual build up...before CAA really kicks in on Sun. Snow levels will also be dropping Sat night...and some accumulations are possible at the highest elevations late Sat. The best shot is above 3000 feet...but elevations down to around 2000 feet may see some flakes as well. Winds and poor trajectory for cold air delivery most likely keep the valleys well mixed enough to preclude any snwfl. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Upcoming Potential Hazard: Strong, gusty winds on Sunday. Winds align through a deep layer as a strong surface low (~980 mb) exits into the Canadian Maritimes. The upper low shifts east of New England as well, allowing for a deep, well mixed layer. Models have shifted into agreement for the passage of the upper level features. This passage, in combination with a strong gradient and cold air advection will allow for very gusty winds Sunday. Wind advisories may be needed as we continue to monitor the situation. Wind gust over 45 mph would lead to scattered power outages. Expect upslope rain showers to develop. Cold air advection and the wet bulb affect will allow the rain showers to mix with and change to snow showers at the higher elevations where a light coating of snow is expected. A short wave quickly races through the region Sunday evening, bringing a reinforcing shot of cold air and continued very gusty conditions along with moisture to the region. The upper level low will remain over the Canadian Maritimes for much of this upcoming work week. This will keep cool and breezy conditions over the region as high pressure remains in control of the Northeast. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... Short Term...Widespread LIFR conditions will continue thru tonight. Some brief improvement to VFR and MVFR over parts of NH will deteriorate again tonight as well. The low level jet lifting over the region late this afternoon and evening will also yield some marginal LLWS at the TAF sites. LIFR and IFR remains widespread until late Sat when CAA will start to mix out the wedged in low level air mass. Long Term...Conditions will improve to VFR by Sunday morning outside of the mountains, which will linger in MVFR to IFR briefly in SHRA at KHIE through Sunday. Also look for NW winds of above 30+ kts on Sunday. VFR is expected at all terminals much of next week. && .MARINE... Short Term...SCA conditions will continue into Sat...with brief breaks in wind as low pressure center moves overhead. Eventually CAA developing on the backside will increase winds to near gale force on the outer waters late Sat. Long Term...A period of gales is possible Sat night into Sunday with winds diminishing a bit Sunday night into Monday morning. Gale watches have been issued for the outer waters with borderline gale conditions possible over the bays. && .TIDES/COASTAL FLOODING... && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ150>154. Gale Watch from Saturday evening through Sunday afternoon for ANZ150-152-154. && $$ SYNOPSIS... NEAR TERM...Curtis SHORT TERM... LONG TERM...Cannon AVIATION... MARINE... TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.