Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 171851 AFDGYX Area Forecast Discussion National Weather Service Gray ME 151 PM EST Tue Jan 17 2017 .SYNOPSIS... Low pressure moves out of the Great Lakes today then redevelops off the mid Atlantic coast by early Wednesday. This system will bring widespread snow, with highest amounts in the south and some mixed precipitation along the coast. Another weak front will pass by to the north on Thursday. This will be mainly dry with just clouds across the region and a few upslope snow showers along the Canadian border. High pressure will build in for the remainder of the week, with above normal temperatures expected through the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 150 PM Update...Just a few minor adjustments to the going forecast at this time...just more sunshine this afternoon. 950 AM Update...Little change to the overall theme of the forecast and no changes to headlines. Have adjusted PoPs a little bit for late this afternoon and evening, to better line up with current obs and latest mesoscale model guidance. This essentially slows timing by an hour or so due to tightening the gradient on the leading edge. Otherwise, little change to the forecast at this time. Previously... Temps quite variable early this morning, with clouds along the NE zones, this turns out to be the warmest area. Have made some adjustments for the next few hours based on this, but overall forecast remains unchanged for today. PRecip should hold off in all but SW zones until around 6 pm or later. Previously...Our cold air mass that is moving out of the area, will get one more chance to impact our weather, as it gets pulled back west around the poleward side of a low that will be south of the area, bringing snow to the region late today through at least part of Wednesday. However, for the most part the daylight hours will stay dry with increasing clouds, especially this afternoon, and highs climbing to around 30 in the mountains and the mid-upper 30s along the coast and in srn NH. There is a chance that snow /or rain could develop in Cheshire county and along the NH/MA border around the time of the evening commute, but for the most part, precip will hold off until around 00Z or later. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... For tonight, may see precip begin initially as rain especially in Rockingham and eastern Hillsborough as warm boundary layer lingers into early evening. Colder air aloft will push into this areas quickly this evening, so it will change to snow fairly quickly. The only areas it may stay more rain than snow would be in the Hampton/Seabrook/Plaistow area. Otherwise, precip will begin as snow everywhere else, and stay snow through most of the night. Forecast is a little tricky given forecast amounts right around that 6 inch warning criteria. Think that the heaviest will be from south central NH NE thru the Lakes Region and into interior SW ME, as this will be fueled by ESE upslope and potentially good deformation as wedge of 850 mb cold air pushes into warmer air working up from the south. Also this would include inland side of coastal front as well. This is where some banding may be possible overnight and could see some briefly higher snowfall rates. Since system is passing south, amounts will lower as you head nwd and into central ME, with bulk of precip passing offshore E of Casco Bay. Coastal areas were kept a little lower, as warmer air may work in on strong E flow over the waters, and this could lower snow ratios or mix some rain in. But the dam may be strong enough to keep the marine air offshore and may need to push up to warning in coastal Cumberland and York counties. On Wed, the heaviest precip will be moving east during the morning and the afternoon could see some SHSN inland, and maybe some SHRA or DZ near the coast, as weak inverted trough linger thru the afternoon. The departing low should weaken the dam and allow temps to rise, at least a little, above freezing on the coast and in srn NH. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Overview: Blocked and split flow will continue through the weekend. The forecast period starts with a strong ridge built over the eastern Atlantic, blocking the flow. Behind this ridge a trough is dug over Labrador with a series of weak short waves passing through. Over the CONUS the flow remains split. While the northern stream continues to drop south out of Canada across Hudson Bay to our region a 500mb closed low remains over New Mexico with additional waves moving up towards Northern New England. The combination of blocking and split flow yields a very low confidence forecast as blocking is generally slow to move and poorly resolved and the split flow results in difficult timing. By the start of the weekend the deterministic guidance has such a large spread that inferring much beyond climatology and persistence isn`t recommended. Thursday a wave will pass to our north from the northern stream. This air mass is dropping out of northern Canada and is very dry and will mostly result in clouds for the region. In the mountains upslope flow will be enough to squeeze what little moisture there is out. Increased PoPs and accumulations for the far north giving 1-2" of accumulation for Pittsburg, NH through Jackman, ME where upslope is most favored. Friday high pressure will build into the region. The surface high will be accompanied by upper level ridging as the closed low over the southwest tries to break down and is reabsorbed into the main flow. This strong ridge means some above average temperatures for us with highs above freezing across the entire area to start the weekend. Saturday there is a chance for a system to pass to our south bringing a few showers with it. Deterministic models show a major pattern shift for the start of next week. The end of the blocking and split flow allows for another system to move through on Monday into Tuesday bringing the potential for widespread precipitation. However given the uncertainty in the pattern this is a low confidence forecast and have stuck close to what passes for a consensus of models. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... Short Term /through Wednesday/...VFR thru most of today. Conds deteriorate this evening as Sn pushes into the area from the west, with IFR expected to linger into Wed, as low clouds are expected with DZ possible near the coast. Long Term...Thursday will start out as MVFR across the region as clouds move in. The clouds will dissipate to VFR for all but HIE where MVFR conditions will remain through the start of the weekend. Some MVFR may reappear on Saturday in light snow and rain. && .MARINE... Short Term /through Wednesday/... Low pres passing south of the waters will allow increasing E-NE flow tonight into early WED, with SCA winds/seas expected. Long Term... Friday a weak front will pass north of the waters bringing an end to the easterly flow from earlier in the week. Conditions will subside Thursday as high pressure builds into the region and remain calm and below SCA criteria right through the weekend. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Warning from 7 PM this evening to 5 PM EST Wednesday for MEZ012-018>020. Winter Weather Advisory from 7 PM this evening to 5 PM EST Wednesday for MEZ013-021-023>026. NH...Winter Storm Warning from 5 PM this afternoon to 5 PM EST Wednesday for NHZ004-006-008>010-015. Winter Weather Advisory from 5 PM this afternoon to 5 PM EST Wednesday for NHZ002-003-005-007-011>014. MARINE...Small Craft Advisory from 1 AM to 6 PM EST Wednesday for ANZ150>154. && $$ SYNOPSIS... NEAR TERM...Ekster SHORT TERM...Cempa LONG TERM...Curtis AVIATION...Cempa/Curtis MARINE...Cempa/Curtis is the U.S. government's official web portal to all federal, state and local government web resources and services.