Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 150333 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1033 PM EST Tue Feb 14 2017 .SYNOPSIS... Low pressure dropping southeast out of Canada tonight will merge with low pressure tracking northeast off the southern New England coastline tomorrow. This will cause an area of snow to form over over northern New England, with the heaviest snow falling over portions of central and western Maine. Low pressure moves northeast into the Canadian Maritimes on Thursday morning, bringing the snow to an end. Cold high pressure builds in through Saturday. As the high moves east late this weekend, a southwesterly flow will bring warmer air into northern New England through much of the upcoming week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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1015 pm...Pushed back pops a little bit more tonight, and adjusted temps, which have radiated in some spots, and will continue to do so for a few more hours, before clouds roll in. 710 pm...Updates to POPs for this evening and temps overnight. Mostly the POP update was to back off POPs in wrn NH for this evening, keeping this mostly dry with mostly just some flurries possible before midnight in the CT Valley. Temps are radiating a bit better than forecast in clear skies this evening, especially in the ern zones, and have lowered temps and mins in this area tonight by a few degrees. Previously...Temps will be tricky tonight...as dense cirrus shield lifts NEwd. The clearing may allow temps to drop quickly this evening...before WAA causing things to steady out or slowly rise. This will have a big impact on things Wed...as a bust on the colder side tonight could lead to some in situ cold air damming when precip starts in the morning. That could hold off any potential mix until later in the day...if at all. Given that most of the storm will fall in the Wed/Wed night time period that will be discussed in the next section.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Significant winter storm for parts of the forecast area... This forecast revolves around two s/wv trofs...one in the Nrn stream and one in the Srn stream. The Srn stream is forecast to emerge off the Carolinas sparking secondary development of low pressure. It is this low pressure that will interact with the strong Nrn stream trof dropping thru Canada towards Lake Ontario by early Wed. For starters the WAA wing of the Nrn stream s/wv will lift over the forecast area early Wed. This will likely produce a little light snow...but mainly over the mtns. This will be followed by the cold front...where low stability and strong forcing may lead to snow squalls on the leading edge. At the same time strong inflow will develop and transport moisture inland...especially from the NH/ME border NEwd. And this is where the forecast gets tricky. Model forecasts and forecast soundings are favoring a warm boundary layer. In fact forecast soundings are roughly 1000 to 1500 ft deep at the coast...becoming more shallow inland. This is borderline for complete melting of snow before reaching the ground. Additionally...though temps are colder aloft...they are right around 0C or 1C at 950 mb near the coast. Again borderline for all snow. For this reason I have introduced a mix with rain near the coast...and lowered snow ratios to something less than 10 to 1. That being said...these temp forecasts are so borderline that even slight cooling or very heavy precip may be enough to keep ptype all or mostly snow. Either way...between 21z and 00z as the Nrn stream s/wv nears the area and heights begin to fall...temps will rapidly cool back towards the coast. Any rain or mix will likely flash back over to heavy snow. Farther inland cooler temps and elevation will help keep ptype all snow...and upslope against the SE facing slopes will aid in both cooling and QPF enhancement. For that reason I think the higher terrain will likely see the highest snowfall totals. Also inland areas I have a higher confidence in seeing 6 inches or more of snow...so I have upgraded the watch to a winter storm warning for the interior. On the SWrn edge of the strongest moisture transport inland I have put up a winter wx advisory for parts of central NH. On the coast I left the winter storm watch as is...given the high uncertainty regarding temps and ptype. The trend in model guidance has been to edge the mid and upper level low centers SWwd with each new run. This has large implications on the forecast. The farther SW these upper level lows get the less likely it is that we see much dry slot in the forecast area. I feel for at least SW NH at least some dry slot is inevitable...but for the rest of the area this could mean the difference in several inches of snow. Farther SW would also tug the best inflow in the direction of the NH border as well. It would also allow the forecast area to get in on more of the forcing from strong frontogenesis as the mid level lows rapidly develop in the Gulf of ME. There is a higher than normal bust potential with this system. Many small and difficult to resolve details will play a large role in snowfall totals. Suffice it to say...the highest snowfall amounts will be in a more focused area than the last snow storm...not to mention a lower magnitude. The area that ultimately sees a foot or more will be hard to pin down from the general 6 or more inches of accumulation. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Low pressure moves off into the Canadian Maritimes on Thursday, bringing the snow to an end from west to east. There could be some lingering upslope snows in the mountains into Thursday night, but otherwise expect clearing conditions with cold temperatures through Friday. High pressure axis moves into western New England Friday night and could bring the best radiational cooling night. Dewpoints in the teens should set the floor for overnight lows. The high moves east across the area on Saturday with warmer temperatures arriving behind it. A building ridge of high pressure over the center of the continent will provide a warm source of air flowing into New England and block any moisture- laden storm systems from impacting our area. Temperatures in the 40s will be common into next week. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Short Term...VFR conditions expected for the first part of the overnight. WAA and onshore will gradually lower CIGs to MVFR before 12z. HIE and LEB are most likely to see some IFR VSBY in -SN around 12z. Areas of IFR will overspread the rest of the forecast area thru 18z Wed. -RA may mix in at MHT...PSM...PWM...and RKD during the day. Confidence is low on ptype at those terminals. SN to +SN in the evening and overnight...especially at Wrn ME terminals. IFR conditions continue into Thu before gradually improving. HIE will hang onto MVFR thru Thu in upslope SHSN. Long Term...Should see conditions becoming VFR on Thursday outside of the mountains where MVFR ceilings and occasional snow showers persist into Thursday night or Friday. VFR continues through the weekend. && .MARINE... Short Term...Seas continue to diminish across the outer waters. There are some wave heights in excess of 5 ft...though the period is beginning to lengthen quite a bit. Will focus on the winds and seas coming back up Wed into Wed night and issue a SCA for that period. There may be a brief window for near gale force gusts...but confidence was not high enough for a headline at this time. Long Term...Cold offshore winds will likely keep small craft advisory conditions going through Friday, but winds diminish as high pressure moves over the area on Saturday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Warning from 7 AM Wednesday to 10 AM EST Thursday for MEZ012>014-018>022. Winter Storm Warning from 7 AM Wednesday to 7 PM EST Thursday for MEZ007>009. Winter Storm Watch from 6 AM EST Wednesday through Thursday morning for MEZ023>028. NH...Winter Storm Warning from 7 AM Wednesday to 10 AM EST Thursday for NHZ004-006. Winter Weather Advisory from 7 AM Wednesday to 7 AM EST Thursday for NHZ005-007>010. Winter Storm Warning from 7 AM Wednesday to 7 PM EST Thursday for NHZ001>003. MARINE...Small Craft Advisory from 7 AM to 7 PM EST Wednesday for ANZ150>154. && $$ SYNOPSIS... NEAR TERM...Cempa/Legro SHORT TERM...Legro LONG TERM...Kimble AVIATION... MARINE...

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