Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 152008 CCA AFDGYX Area Forecast Discussion...CORRECTED National Weather Service Gray ME 408 PM EDT Sun Apr 15 2018 .SYNOPSIS... A frontal boundary draped across the area will continue to generate mixed precipitation through the overnight hours. Precipitation is expected to change from a wintry mix to rain from south to north tonight and tomorrow. As the system currently in the Great Lakes region moves through New England tonight and tomorrow, strong gusty winds are expected to develop along with a period of heavy rainfall. A broad area of weakening low pressure will persist over the region Tuesday and will shift east on Wednesday. Another area of low pressure will approach from the west Wednesday night and will move east through the region on Thursday. Low pressure will slowly shift east into the maritimes for the remainder of the period. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Mid level warm front continues to wash out along and N of the LEB to PWM line. Dry air is still lurking just to the NE of the forecast area over The County and Downeast ME...so whatever precip is falling is very light. To the S of the front there is a bit of a break in precip...with the except of far Srn NH where some ocean effect precip continues to fall. With H9 temps forecast to hold around -8 to -10 C...that light ocean effect precip may continue thru the evening in the Ely flow. The next batch of precip to worry about is taking shape across the Chesapeake at this writing. It will continue to move N and expand in area. Surface temps are not expected to move much this evening...meaning the majority...if not all...of the forecast area will be below freezing. Another round of mixed precip is expected...and for that reason I have just extended all winter wx advisories into Mon...and expanded Ewd into central and Midcoast ME. Forecast soundings still show very deep low level cold...so I do expect sleet to be the predominant ptype. That being said...there is plenty of cold air in place and high pressure is expected to remain in a very favorable position for continued cold air damming. In the overnight period any freezing rain that falls should have no problem accumulating. In the mid levels behind the front ESE winds will ramp up tonight. With the strong inversion lowering towards ridge top level...a favorable set up will be in place for downslope wind gusts. The Wrn slopes of the higher terrain will see gusts of 40 to 50 mph...with localized higher gusts in the steeper terrain. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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Early Mon the area of precip from the Mid Atlantic will be lifting thru the forecast area. Parts of the winter wx advisories may be able to drop as precip moves out and temps edge up above freezing. I have gone colder than the coldest model guidance for temps...and even that may be too warm given the propensity for guidance to rush the inversion mixing out. Towards midday the core of the LLJ and strongest forcing for ascent will arrive. PWAT values in excess of 2 standard deviations above normal will support heavy precip...mainly in the form of rain as strengthening SE winds slowly warm the boundary layer. Widespread QPF of 1.5 to 2 inches is expected...and for flooding concerns see the hydrology section below. Ahead of the cold front itself the core of the LLJ will lift across the area. Near the coast...especially N of PWM...SE gusts approaching 50 mph are possible. ECMWF EPS have very high probabilities for 40 kt gusts...and given that added confidence another wind advisory has been issued for this threat...in addition to the downslope winds across Wrn NH tonight into Mon. The coastal wind gusts will continue into late Mon evening before the LLJ moves NEwd. Precip will quickly end from W to E as the cold front sweeps across the forecast area. Upslope showers...changing to snow showers...will linger on the backside of low pressure into Tue morning.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/... Long term begins with a surface low in place over the Great Lakes with an occluded front moving out of northern New England, and a closed upper level low over western New York state. As the upper level low ever so slowly migrates to the east, the cold pool aloft will likely destabilize things enough for scattered afternoon showers through Wednesday night. The possible bigger story begins Wednesday night though. The GFS is indicating low pressure moving out of the midwest and driving east and south across PA. This would place northern New England in a strong baroclinic zone with precipitation being generated during the day on Thursday. Right now it looks like it would be all rain. The 00z ECMWF was taking this system and developing a coastal low out of it, with temperatures cold enough to generate snow. However, the 12z ECMWF now has a more southerly track and takes the system far enough south that it ends up being a miss for us. Will rely more on the GFS as it has at least been stable, but will need to monitor things as they progress. Zonal flow aloft then sets up for the remainder of the extended period with little in the way of weather.&& .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Short Term...Precipitation has come to an end at most TAF sites, with a few exceptions being noted. Sites are primarily IFR, but will likely become IFR/LIFR during the overnight hours as more precipitation moves in. By 06z, western TAF sites will be experiencing LLWS and by 12-18z, most of them should be. In some locations it will be close, but chose to include it as it could have operational impact. Long Term...VFR with areas of MVFR ceilings and vsby in scattered showers Tuesday. VFR with areas of MVFR ceilings Wednesday. IFR/LIFR ceilings developing late Wednesday night and Thursday. && .MARINE... Short Term...NE flow will continue over the coastal waters and slowly veer to Ely thru Mon. Winds will also gradually increase...with gale force gusts expected after midnight. Winds become more SEly late Mon...with some gusts approaching 45 kts outside the bays. LLJ crosses the waters Mon night...with winds becoming Wly behind the cold front and decreasing. Long Term... Will need to watch seas Wednesday night and Thursday as they may approach SCA criteria. && .HYDROLOGY... A very moist air mass will continue to surge northward ahead of a strong low pressure system in the Great Lakes. The heaviest precip is expected Mon afternoon into the evening. A large area of 1.5 to 2 inches QPF is expected...especially along and southeast of the higher terrain. The question is mainly how much snow melt we get in the headwaters...as temps are forecast to remain near freezing for most of those areas. Ensemble river guidance does forecast a couple locations in NH going above flood...but not widespread enough threat for a flood watch at this time. More likely there could be ponding of water in poor drainage areas as well as river flows near flood. && .TIDES/COASTAL FLOODING... Beach erosion and splash over still possible for high tides Mon and Mon night. Current storm surge forecasts keep tide gauges below flood stage Mon...but given the possibility for erosion/splash over a statement may be needed midday Mon. I preferred the ESTOFS guidance thru Mon night...with E flow likely creating a storm surge in excess of 1 ft. That could yield some minor flooding across the Seacoast of NH...possibly into York Co Mon night. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Weather Advisory until 8 AM EDT Monday for MEZ018-023. Winter Weather Advisory until noon EDT Monday for MEZ007>009- 012>014-019>022-024>028. Wind Advisory from 2 PM Monday to 2 AM EDT Tuesday for MEZ025>028. NH...Winter Weather Advisory until 8 AM EDT Monday for NHZ003- 005>015. Winter Weather Advisory until noon EDT Monday for NHZ001-002- 004. Wind Advisory from 2 AM to 8 PM EDT Monday for NHZ001>003-005- 007-011. MARINE...Gale Warning from 8 AM Monday to midnight EDT Monday night for ANZ151-153. Gale Warning from 2 AM Monday to midnight EDT Monday night for ANZ150-152-154. && $$ SYNOPSIS...Pohl NEAR TERM...Legro SHORT TERM...Legro LONG TERM...Pohl AVIATION...Pohl MARINE...Pohl/Legro HYDROLOGY...Legro TIDES/COASTAL FLOODING...Legro

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