Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 160351 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1051 PM EST Wed Feb 15 2017 .SYNOPSIS...
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Low pressure will rapidly develop in the Gulf of Maine tonight and pulls away Thursday leaving behind upslope snow showers in the mountains. High pressure will build into the region on Friday as the storm departs to the maritimes. A few upslope snow showers will linger in the mountains through Saturday but elsewhere skies will be mainly sunny. Temperatures will warm through the weekend reaching the mid 40s by Sunday.
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1045 pm...Second band of moderate to heavy snow extends from from around KLEW southward through the Portland area, and then offshore of York and Rockingham counties. This band should shift W through around 06Z or so before dissipating. Rates of an inch an hour are likely in this band, and could see them as high as 2" per hours. HRRR has been excellent with these bands today and tonight. Will hold the WSW for now as we will see some synoptic snow developing over the ern zones, but may be a struggle to reach warning criteria here. 8 PM...Intense sfc convergence, along with mid lvl frontogenesis have combines to produce a persistent band of heavy precip from around Casco bay NW through Cumberland and southern Oxford counties. We`ve had reports of 2-3" an hour for a couple hours in this band. Just got reports in the last hour of a changeover along the coast and in Portland, which will limit total snow accums there. Forecasts for this evening lean heavily on meso models, including HRRR, and meso model ensembles. This rotates this band of heaviest precip SSE through York county/ including NH border towns in Carroll county/ and then into Strafford and Rockingham toward midnight. The band will weaken a bit later this evening, so amounts to the south will probably not reach the totals we`ll see in interior SW ME, but should still reach warning criteria. This will also limit the snow to some degree over ern zones, and may not see warning criteria here, but will hold the warning to see how synoptic precip develops this evening. Previously...A dynamic storm is in store for this evening and overnight. Temps have pushed into the mid and upper 30s over parts of Srn NH and coastal Wrn ME. This has allowed precip to start as rain. Farther inland snow has continued in the higher terrain much of the day...with accumulations already around 6 inches. Now things really start to get interesting. As mid level low centers rapidly develop this evening...colder air will be dragged back S thru the forecast area. This will turn any rain back to snow. KGYX 88D dual-pol data is already showing low ZDR and high CC values collapsing back towards the coast as heavier areas of lift and precip move thru. At GYX we flipped from light rain to heavy snow in a matter of minutes as stronger lift moved overhead. I expect this to be the trend thru the evening...with mixed precip transition quickly to heavy snow with rapid accumulations. The coast will be the last place to flip back to snow...but when it does it will be a significant hazard for those on the road. Roads will become slippery in a hurry. The surface trof remains wedged at the NH/ME border back towards the White Mtns. I expect it to hold more or less stationary thru the early evening. For that reason I have focused the higher QPF across extreme SWrn ME into the White Mtns. Later this evening strong low pressure developing in the Gulf of ME will drag this trof Swd. This should be when the heaviest snow occurs for Srn NH. It may not last more than an hour or two...but snow could be very heavy for that short duration. For the rest of the night intensity of snow will taper off but continue into morning. Headlines remain as they were earlier today. Highest snowfall amounts should be near the NH/ME border...especially where SE facing upslope assisted in lift. The lowest confidence in snowfall amounts are just W of the current trof axis...where shorter duration of snowfall may limit totals some. Also to the E over central ME...lower snowfall totals are possible due to mixing and lack of precip. Their best snowfall may come later tonight when low pressure begins to throw moisture back NWrd. The very mesoscale nature of this event will lead to some wildly varying snowfall amounts over short distances.
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&& .SHORT TERM /THURSDAY NIGHT/... Low pressure will gradually pull away from the area Thu. Lingering low level moisture and NW flow will lead to plenty of upslope snow showers in the mtns thru the day. An additional several inches of accumulation is possible. We stay in cyclonic flow Thu night...and that should keep the boundary layer fairly mixed. I stayed close to 2 m temp guidance for lows. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... High impact weather potential: None A rather quiet period of weather as we move into the end of the week and the weekend. The forecast begins with a relatively progressive high amplitude pattern over North American. As of Wednesday morning a large ridge was build up through western North American with above freezing surface temperatures all the way to the Northwest Territories in in Western Canada, and a trough moving through New England and southern Quebec. This ridge will move east over the weekend keeping high pressure in control through the start of next week. Friday the departing low will bring upslope snow showers to the mountains of northern New Hampshire. Have increased QPF and snow amounts slightly compared to guidance as those areas are often able to squeeze quite a bit of snow out of this pattern. Saturday a high builds into the region and temperatures will warm above freezing across most of the area. A weak system passing to the north on Sunday may bring a few scattered flurries to the mountains and increasing clouds however temperatures will again remain warm reaching the mid 40s south to upper 30s north. Those flurries and clouds will stick around into Monday. By Tuesday there is the potential for another storm to bring more widespread precipitation. Confidence is very low at this time and have gone with a consensus blend of guidance. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... Short Term...Widespread IFR or lower is expected tonight in deep onshore flow. -RA along the coast will change to SN...heavy at times. Eventually this may even clip CON and snowfall drops Swd tonight. Conditions improve to MVFR and VFR early Thu...except in the mtns where SHSN will keep occasional IFR. Surface gusts around 20 to 25 kts possible at all terminals Thu. Long Term... VFR will prevail from Friday right through the weekend except in the mountains where HIE will see periods of MVFR in SHSN. && .MARINE... Short Term...Winds and seas will build especially behind rapid strengthening low pressure in the Gulf of ME. Gale warnings for the outer waters and SCAs for the bays remain in effect into Thu. Winds and seas will gradually diminish as low pressure pulls away. Long Term... Very quiet period on the waters with high pressure built overhead. Expect conditions to remain below SCA right through the start of next week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Warning until 10 AM EST Thursday for MEZ012>014- 018>028. Winter Storm Warning until 7 PM EST Thursday for MEZ007>009. NH...Winter Storm Warning until 10 AM EST Thursday for NHZ004>006- 008>010-013-014. Winter Storm Warning until 7 PM EST Thursday for NHZ001>003. Winter Weather Advisory until 7 AM EST Thursday for NHZ007-011- 012-015. MARINE...Small Craft Advisory until 10 AM EST Thursday for ANZ151-153. Gale Warning until 6 PM EST Thursday for ANZ150-152-154. && $$ SYNOPSIS...Curtis NEAR TERM...Cempa/Legro SHORT TERM...Legro LONG TERM...Curtis AVIATION...Curtis/Legro MARINE...Curtis/Legro is the U.S. government's official web portal to all federal, state and local government web resources and services.