Area Forecast Discussion
Issued by NWS Portland, ME

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327 FXUS61 KGYX 160826 AFDGYX Area Forecast Discussion National Weather Service Gray ME 326 AM EST Mon Jan 16 2017 .SYNOPSIS... High pressure brings fair weather into Tuesday morning. Low pressure moves out of the region Tuesday night into Wednesday night and will bring snow, with some mixed precipitation, to the area. High pressure builds in for the end of the week, with above normal temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Sfc high moves offshore today as weak area of low pressure passes well to the north of the CWA, this will likely produce a round of clouds this afternoon and evening across the nrn zones, and maybe a few flurries or SHSN. Highs today will be several degrees warmer than Sunday, ranging from around 30 in the north, to the mid to upper 30s in the south. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... High pressure will build back in briefly late tonight into Tuesday. Southern areas should be mainly clear, with mountain clouds thinning out after midnight. There will be some potential for rad cooling, with light winds, but overall temps will be warmer than previous nights, ranging from 15-20 in the north, to the mid 20s in the south and along the coast. Tuesday will start off mainly sunny, but clouds will overspread the region from SW- NE in the afternoon ahead of the next system. Could see light rain or snow break out prior to the evening across southern NH, but bulk of precip will hold off until Tue evening. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... High impact weather potential: low confidence of warning level snowfall Tuesday night into Wednesday Overview: The extended forecast is a relatively low confidence forecast due to the uncertain strength and timing of the many shortwaves which will move through the region over the week. To start off the week a strong high amplitude ridge is built into the North Atlantic east of Iceland. This is providing substantial blocking to the hemispheric flow and keeping the coldest of polar air trapped just to our north over Labrador and Baffin island. Across North America we have a split flow with a weak low aloft over the southwestern united states and a weak ridge built on top of it through the northern Rockies. This puts the northeastern CONUS at the junction of two possible storm paths. The first more northern stream is colder and relatively dry consisting of shortwaves originating over Alaska and the Yukon diving southwards across Canada and approaching across northern Ontario. The second path is coming out of Texas and moving up towards the great lakes. This flow is generally weaker but much more juicy due to its ability to tap into moisture from the Gulf of mexico. The two storm tracks is what makes this forecast period so uncertain as the timing of both tracks will impact our weather as the two waves may either reinforce each other or cancel each other out as they approach. /00Z Wednesday to 00Z Thursday/ Our first time period of concern is Tuesday night into Wednesday. Here the southern stream is our primary player with a storm system currently generating widespread freezing rain across the central plains tracks north and east into the great lakes. Precipitation will begin moving into western NH around 00Z on Wednesday and rapidly overspread the region. By 12Z Wednesday a secondary low begins to develop off the Atlantic coast, shifting the precipitation off shore and brining it to an end by 00Z Thursday. Of course all is not quite so straight forward. The main concern here the temperature profile both aloft and at the surface which will determine p-type. Most of the uncertainty in this system is due to the strength of the departing high which will be over the maritimes as evidenced by the ensemble sensitivity. The GFS represents a warmer solution with a weaker high while the Euro is the colder option with a stronger high and the Canadian bridging the difference. My preference is towards the stronger high and colder solution due to the fact that the flow is blocked which generally results in a longer time to move any cold air out. Stronger high pressure will provide colder surface temperatures but also help to force the bulk of the heaviest precipitation amounts to the southern portion of the CWA. This is a double edged sword as the warm air could still infiltrate aloft to the south allowing the southern portions of the CWA /where highest qpf is expected/ to switch over to sleet or wetter snow. The line between snow and rain is very close to the NH/MA border with much of southern NH within 1-2 degrees of switching over. In addition to the temperature profiles there are several other mesoscale effects that may play a significant role in this storm. Provided surface temperatures remain cold enough for snow, there is the potential for a brief period of heavy snow overnight due to excellent updrafts in the snow growth zone. Further a inverted trough may serve to focus the precipitation extending from the newly forming coastal low off Cape Cod northwestward towards Burlington VT across southern NH which could also increase precipitation totals in this region. Finally the high pressure to the north and low forming over Cape Cod sets up a nice scenario for a coastal front as well as upslope snow for southern Maine. All of this combines to yield the highest snow potentials from Lewiston through Fryeburg in Maine and into the Lakes Region of NH and Concord and as far south as the higher terrain of Hillsborough and Eastern Cheshire counties. This region has the potential to see 5+" of snow putting it right on the cusp of a winter storm watch. With all the uncertainty in thermal profiles, and the precipitation still being almost 2 days out have opted not to issue a watch on this forecast package. /Thursday - Friday/ As we move into Wednesday night and Thursday the northern stream pushes another disturbance through the region, this time passing to our north. Here the Canadian is the strongest putting widespread precipitation across much of Maine while the other options are drier and weaker. Again with the blocking have leaned towards a later arrival for this system which would result in just a few inches of upslope snow showers in the mountains for Thursday morning, however the potential for the timing to change and and earlier arrival would result in a reinforcement of the existing system for the midcoast and downeast region. /Friday - weekend/ Friday high pressure builds back into the region leaving us in above normal temperatures. The next potential storm develops to our south off delmarva on Saturday however this is very uncertain at this point. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Short Term...VFR conditions through most of Tuesday. Could see some late day MVFR-IFR at KMHT/KCON/KLEB is SN or RA Tue. Long Term... Tue night - Wed... Snow moving into all terminals with mixing SN/PL/RA for MHT PSM. PWM and RKD will see RA/SN. Widespread IFR on Tuesday night will increase to MVFR by mid day Wednesday. HIE will hold onto MVFR SHSN through through Thursday. && .MARINE... Short Term...HAve issued SCA for outer waters this after and this evening as SW flow surges briefly to around 25 kts and pushes seas up to 5 ft. Long Term...SCA conditions to borderline Gales will result from Tuesday nights easterly flow across the waters. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 1 PM this afternoon to midnight EST tonight for ANZ150-152-154. && $$ NEAR TERM...Cempa SHORT TERM...Cempa LONG TERM...Curtis

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