Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 292022 AFDGYX Area Forecast Discussion National Weather Service Gray ME 422 PM EDT Wed Mar 29 2017 .SYNOPSIS... High pressure will gradually build in from the northwest through Thursday. Expect a mostly sunny day on Thursday with temperatures near normal for this time of year. Low pressure tracking through the Ohio Valley will track off the southern New England coastline Friday night, spreading snow through northern New England which will last into the day on Saturday. There may be some rain near the coast. High pressure follows quickly on the heels of the departing low Sunday into Sunday night. The next low pressure system may impact our area on Tuesday with another chance of rain or wintry precipitation. && .NEAR TERM /TONIGHT/... Clouds should break up a bit more tonight as downsloping northwest winds provide subsidence to the coastal plain. Clouds will linger to the northwest of the mountains in the upslope areas. Temperatures fall into the 20s to near 30 which is near normal for this time of year. && .SHORT TERM /THURSDAY/... High pressure moves into the area during the day on Thursday. Expect a mostly sunny sky with temperatures generally in the 40s to possibly near 50 degrees. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... Confidence continues to grow in a significant late season snowfall for a good portion of the CWA Friday into Saturday. However, there still remains several differences between members in the 12z guidance suite which which lends to continued uncertainty in snowfall amounts and the spatial coverage of heavy snowfall amounts. The ECMWF and the ECMWF ensemble has been the most consistent on a run to run basis. The ensemble has shown a nice steady, orderly uptick in 6" probabilities over the last 4 runs (including the 12z run which now has a large area of 50-60% probs of greater than 12" across southern NH). The NAM is in the euro camp, but at this time I think the onset time of heavy snow is too early and qpf too heavy. The GFS continues to be a southern outlier due to non-existent help from a northern stream short wave trough that most of the rest of the guidance suite has. In essence, what the northernmost guidance members are doing is digging the northern stream short wave trough into northern New England which is helping to bring north the moisture associated with the southern stream trough (sorta like a partial phase). This process is helping to bring April-like PWATS into a winter storm system which is resulting in pretty high QPF in several models. We took a blend of the two camps, but gave a bit of an edge to a ECMWF and GGEM blend. Some concerns with mixing with sleet and rain still exist. On Friday, boundary layer temps may be warm enough, especially in Maine and the Merrimack valley of New Hampshire to the Seacoast. Snow accumulations through mid afternoon Friday may be limited due to melting and a mix with rain. However, when the higher UVVs move in, we expect snow to become dominant over rain. The other issue is that some warmer air may advect in from the south above the boundary layer to the mid levels. This may allow for some sleet across southern NH for a time Friday night which would also limit accums. Therefore we are more conservative in our snowfall accums than what the Euro has. The upshot is that enough confidence exists in a heavy snowfall event that a winter storm watch be issued for central and southern NH at this time. Will hold off on Maine at this time as this would be more of a Friday night - Saturday event there. However, the snowfall may indeed be significant over a good portion of southern/central ME as well; We just have a little more time to look at the uncertainties there. Snowfall consistency should be heavy and wet - especially across southern NH...at least for several hours Friday into Friday evening. This may lead to power outages as many late-season snowfalls do. Otherwise, winds shouldn`t be too much of an issue with this one, but will keep an eye on trends. In a nutshell - confidence is increasing in a significant winter storm for a good portion of the forecast area - especially central and southern zones. However, several uncertainties remain as outlined above. The storm pulls out by later Saturday. Thereafter, there is the potential for something else around Tuesday, but that may remain well south of us. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... Short Term...Expect ceilings above 3000 feet through the remainder of the evening with clouds gradually breaking up to the south and east of the mountains. Winds should diminish this evening and only come back at about half strength tomorrow as high pressure builds in. Long Term...We expect IFR conditions to develop in snow and rain on Friday, first in the morning across southwest NH then spreading eastward through the midday hours. IFR or lower Friday evening through Saturday morning in potentially heavy snow. Improvement is foreseen Saturday late afternoon through Monday. && .MARINE... Short Term...Offshore northwesterly winds will gust to 25 or 30 KT tonight into early Thursday. Should see diminishing winds Thursday afternoon into Friday morning as high pressure moves through. Wave heights will be highest further from shore where the fetch will be enough to possibly generate some 5 FT waves. Long Term...SCA conditions likely Friday night through Saturday night with coastal low pressure. Gales possible for a time Friday night and Saturday. && .TIDES/COASTAL FLOODING... A very high astronomical tide will occur early Friday morning with 11.1` expected in Portland at around 06Z. Onshore winds and seas will just be beginning to develop at this time. Northeast flow will be more pronounced during the Saturday afternoon high tide which is lower at 10.3`. Expect about a 0.5 to 1.0 storm surge at that time which would bring the storm tide to around 11.0 feet or so. With waves running 5 feet or so at the time, splash-over nomograms suggest to only expect little in the way of issues along the coastline. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...Winter Storm Watch from Friday morning through Saturday afternoon for NHZ003>013-015. MARINE...Small Craft Advisory until 8 PM EDT Thursday for ANZ150>154. && $$ LONG TERM...Ekster

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