Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 212143 AFDGYX Area Forecast Discussion National Weather Service Gray ME 443 PM EST Sat Jan 21 2017 .SYNOPSIS...
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A cold front will drop south across the area overnight. The front will stall to our south Sunday and Sunday night as high pressure builds by to our north over eastern Canada. A storm system tracking up the coast will bring wintry precipitation to the area Monday and Tuesday. A cold upper trough will remain over the area through the latter part of the week with a return to colder temperatures. Scattered snow showers in the mountains and foothills can be expected through the latter part of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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GOES imagery continues to show a few breaks in the overcast. Otherwise...a mainly cloudy and unseasonably mild day for late January. The upper ridge will collapse to our south tonight as a shortwave impulse over eastern Canada rides southeast into Quebec province. The associated surface cold front will drop south across the area overnight with clouds and widely scattered drizzle or flurries across the higher terrain. some spotty light freezing drizzle can`t be entirely ruled out near the international border as well. It`ll be another unseasonably mild night with lows ranging from the mid 20s to lower 30s.
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&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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The cold front will continue to drift a bit further south Sunday before stalling. Any afternoon clearing will be confined to our far eastern Maine zones as surface high pressure noses into the area from Quebec. The northeast flow coupled with the proximity of the stalled boundary to our south may produce a few sprinkles or flurries over far southern New Hampshire. It`ll be noticeably cooler then today...but still quite a bit above normal for the date...with highs ranging from the mid 30s to lower 40s. For Sunday night...colder and drier air will continue to drain southward into the area from the surface high over Quebec. We`ll see clearing over northern and eastern sections while much of New Hampshire and adjacent southwest Maine remains cloudy. The onshore flow may also generate some light mixed precipitation over extreme southern New Hampshire into southern York county Maine. Otherwise...it should remain dry across the forecast area for the balance of Sunday night. Lows should range from around 20 in the mountains to near 30 over far southern New Hampshire.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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Another 24 hours and the crystal ball is no clearer regarding the early week storm. This is mainly because very small details and changes are having large impacts on the forecast outcome. Model guidance has come into a nice consensus on the onset of precip...with things quickly moving into the forecast area from the SW around 00z Tue. Pretty much all guidance also has some very light QPF Sun night and Mon ahead of the system in Ely...onshore flow. Forecast soundings are not saturated in the snow growth zone for most of that time period...which normally points towards drizzle/freezing drizzle. However the low level saturation is quite deep and gets as cold as about -6C. That could be cold enough...especially if any seeding occurs from above...for flurries rather than drizzle in areas below freezing at the surface. Given that the occurrence is a low probability in the first place...and confidence is low on ptype...I think the best bet is to handle with a headline as needed Sun night or Mon for freezing drizzle if it happens at all. Models are still consistent with a -5 standard deviation Ely flow at H8 and H9. It will likely max out S of our area...but remain quite strong as it lifts NEwd. Again that kind of signal is a good one for QPF...and a good one for two areas of higher QPF relative to the rest of the forecast area. One will likely be on the cold side of the coastal front...and the second along the E facing slopes of the mtns. I did my best to reflect this in my QPF grids. That Ely flow will also develop within a pretty deep mixed layer...so at least initially gusty winds are probable over much of the forecast area. Near the coast some gusts could be on the strong side...in excess of 40 kts. The deeper cold inland will start to impeded gusts mixing down as WAA begins aloft and sets up a strong inversion. For that reason I expect the strongest winds to be confined to the coast and coastal waters. The cold air damming signal also remains strong with the 21.12z model suite. Guidance is beginning to pick up on this and I have noticed the different sources tick colder at the surface today. They have started to come in line nicely with the temp grids we have forecast...and so confidence is growing that a good portion of the area will remain at or below freezing for much of the event. The real fly in the ointment for the forecast are mid level temps. All guidance forecasts those temps to climb above freezing at some point...but one question is whether this is before or after the precip comes to an end. Another is just how warm to the mid levels get. As precip is occurring...a difference of just 1C for many locations would mean the difference between warning criteria snowfall...and a lot of sleet. At 12z and with a few of the special raobs across the Gulf Coast...the ECMWF was handling heights better...while the GFS was too deep. So I hedged the mid level temp forecast more towards the ECMWF than the GFS. This did not make significant changes to the forecast however. Warm air will creep in aloft across coastal zones...Srn NH...and the CT River Valley first Mon night. That transition zones will then advance N and E into the interior...with the Wrn ME mtns hanging onto frozen precip the longest. Even with a strong cold air damming influence in my temp forecast...I get plenty of rain from MHT/ASH E and along the ME coast. Rain could be heavy at times...especially near the coastal front. While I do expect some freezing rain in the transition zone...model forecast do have the warmth aloft being quite high...generally above H8...so I expect sleet could be a bigger factor. So I tempered freezing rain amounts some...in addition to snowfall. I do think the swath of heaviest amounts will be from the Monadnocks thru the Lakes Region and into the Mahoosucs/Bigelow Range. 6 inches or more is possible...though confidence in amounts is low because of possible ptype issues. For that reason no watches will be issued at this time. Beyond this system...broad cyclonic flow looks to take hold of the region. No real cold air is in place to work in behind the system...so temps remain above normal for this time of year. NW flow will ensure clouds and upslope snow showers continue for the mtns.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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Short Term /through Sunday night/...Areas of MVFR. Some spotty drizzle/freezing drizzle/snow showers is also possible. Long Term...Ely onshore flow Mon may bring MVFR CIGs into Srn and Wrn areas...especially MHT...PSM...CON...and LEB Mon. Conditions rapidly deteriorate Mon night into Tue. IFR and LIFR will be widespread...except for maybe HIE where downsloping winds keep CIGs higher. Interior terminals will see SN changing to FZRA/PL...and maybe RA...while coastal terminals will see brief SN changing to RA. Winds may also be gusty near the coast...with sfc gusts in excess of 35 kts. IFR or lower conditions linger into Wed. Upslope SHSN look possible for HIE thru the end of the period.
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&& .MARINE...
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Short Term /Through Sunday night/...We continue to observe some swell from the deep storm centered southeast of NewFoundland in the open waters. This swell should diminish as we head into the evening hours. Otherwise...we should see seas and winds below SCA tonight and Sunday as a backdoor cold front drop south across the waters. The northeast flow will strengthen Sunday night and we`ll likely reach SCA outside the bays overnight. Long Term...No major changes to the extended marine forecast. Strong winds are forecast to develop Mon evening and overnight. Winds and seas will build quickly in a well mixed ENE flow. Gales are likely in the bays...with a few gusts to near storm force...and consistent storm force gusts are possible on the outer waters. Gale and storm watches remain in place.
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&& .TIDES/COASTAL FLOODING...
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Despite being in the low portion of our tide cycle...large building waves may product some erosion and splash-over near the times of high tide Monday night and Tuesday. Preliminary storm surge values appear to be around 1.5 to 2 feet with a persistent...strong easterly wind developing.
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&& .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...Gale Watch from Monday afternoon through late Monday night for ANZ151-153. Storm Watch from Monday afternoon through late Monday night for ANZ150-152-154.
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&& $$ NEAR TERM...Schwibs SHORT TERM...Schwibs LONG TERM...Legro

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