Area Forecast Discussion
Issued by NWS Portland, ME

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453 FXUS61 KGYX 211519 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1019 AM EST Thu Feb 21 2019 .SYNOPSIS... Snow winds down this morning as a warm front lifts northeast across the region. It will warm up into the 30s and 40s today before a cold front drops in from the north tonight. High pressure slides in from the west through Saturday. The next storm system will develop in the southern plains and track into the Great Lakes spreading more precipitation into the New England on Sunday. Snow may transition to freezing rain before coming to an end Sunday evening. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1000 AM Update... Quick update to drop expired winter weather headlines in New Hampshire. Areas of light snow continue in western Maine but expect this activity to end over the next couple of hours. Have also adjusted pops and weather based on latest radar trends. No other changes planned attm. Prev Disc... 800 AM Update.... Quick update to adjust pops and wx across the region. Fairly large area of freezing drizzle left in the wake of last nights precipitation. Should see this light freezing precip through mid morning before mixing gets going and starts drying out the low levels. Aside from a few temp/td tweaks...no other changes planned attm. Prev Disc... Precip is winding down early this AM, and have adjusted POPs for a speedier end to precip this morning with it ending across most of the CWA between 12Z and 14Z. Going to hold the advisories as they are because there is some FZDZ in spots where there are no radar echoes, and it is the morning commute. Overall total snow amounts will likely fall closer to 2-4" across much of the area. Previously...Our weak but double barrelled low pressure system will track east this morning, and precip will end quickly from W-E during the early to mid morning. In fact, back edge of precip is into SW NH at 0830Z, as there is very little dynamic forcing, and the precip is being driven by WAA, which will shut off once the sfc low to our S passes by. There could be a short period of FZRA/FZDZ in srn zones as it ends, but it should all be done with by 12-14Z in most places. After that once the wind shifts to W around midday, skies will begin to clear and temps will warm into the upper 30s to low 40s S of the mtns. In the mtns, upslope flow will allow clouds to linger with snow showers and some additional accumulations. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... A secondary cold front will push thru early this evening and this will shift winds a bit more NW, and allow some colder air to filter in, but all in all should mainly be clear with lows around 20 in the mtns, where clouds/SHSN will linger, to the mid 20s in the south. Friday looks mostly sunny and on the mild side, as sfc high builds over the CWA, with highs 30-35 in the N to around 40 in the south. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... High pressure moves directly across the area Friday night allowing for good radiational cooling conditions. Low level dewpoints suggest the floor for low temperatures will be in the low teens, with only the coldest valleys dropping into the single digits. As the high moves east on Saturday we will warm back up into the 30s to low 40s. The next precipitation maker is currently dropping south along the California coast rotating around the broad upper low over the inter-mountain West. It will emerge over the southern plains Saturday morning with low pressure forming over the Texas Panhandle and tracking northeast into the Great Lakes. With yet another storm tracking to our west, this means another messy precipitation type forecast for our area. However, unlike most of the previous warm frontal precipitation makers this season, this time the warm front lifts in from the south bringing a better easterly pressure gradient to the north of it. Such a flow is a more pronounced cold air damming signal than has been seen yet this season. Thus we expect that precipitation likely starts as snow around midnight Saturday night but transitions to freezing rain on Sunday where warmer air is able to advance northward aloft. There remain a few areas of uncertainty regarding the Sunday forecast. The first involves the formation of secondary low pressure as the trough axis nears the coast. The ECMWF closes off the new surface low to our south which aids in keeping deeper cold air over our area and limiting the advance of warm air aloft. This means more snow than freezing rain. Meanwhile other models still allow for a further northward advance of warm air aloft bringing a more widespread threat of freezing rain on Sunday. In addition, temperatures do not start off all that cold Saturday night so the strength of the low level inversion is a bit unclear. If this inversion does not set up properly, then the cap to the cold air dam won`t form and the easterly flow will pull in warmer air and change precipitation to rain for the southern half of the area. But if it does set up, this wind flow regime would suggest that the cold air dam would hold in place across most of the area even including southern New Hampshire. Current forecast represents a bit of a blend of all these possibilities, allowing for a moderate advance of warm air aloft while holding the cold air dam at the surface for interior western Maine and central New Hampshire but bringing warmer air in for southern New Hampshire and coastal Maine. Precipitation will be increasing in intensity as it moves across the area on Sunday, aided in part by the development of that secondary low pressure over the Gulf of Maine. Current forecast calls for moderate to heavy snow accumulation over interior western Maine while lighter snow amounts are expected for western and southern New Hampshire where a precipitation type transition to freezing rain is more likely. Total icing is expected to be light and the preceding coating of snowfall will likely limit the impacts of it a bit. As the broader trough axis crosses the area Sunday evening winds will shift to the west allowing better mixing of the low levels. This means areas that were in the cold air dam will see a brief warm up before cold advection takes over. Pressure gradient is pretty tight and the low level jet is strong enough to suggest that with the mixing Sunday night and Monday we will see some stronger wind gusts. Gusts to 35 to 45 mph are possible. High pressure builds in from the west Monday and Tuesday. Good low level mixing on Monday means temperatures will make it into the 30s, but it will be almost 10 degrees colder on Tuesday. The next wave to move through our region is most likely to arrive on Wednesday, however there is still considerable disagreement among the models on where this will track and how it will evolve. The GFS tracks this wave to our north while the ECMWF tracks it to the south and much colder. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... Short Term...Look for improvement to VFR around midday, except KHIE which will see lingering MVFR cigs and SHSN into this evening. VFR will persist thru Friday. Long Term... VFR through Saturday, but then ceilings lower Saturday night as the next frontal system approaches. Expect IFR or worse conditions as snow spreads across the area early Sunday morning with a transition to freezing rain likely in southern New Hampshire and possible into southwest Maine. Winds shift to the west Sunday evening behind a cold front with conditions improving to VFR but with strong west winds. && .MARINE... Short Term...Not sure we`ll see SCA winds until late this afternoon when cold front pushes through and winds shift to west. These west winds will continue thru tonight, but should subside on Friday. Long Term...High pressure moves across the area Saturday morning with light winds shifting to the south and then to the east Saturday night. Low pressure forms along a frontal boundary as it moves into the Gulf of Maine Sunday evening. Expect an east to southeast wind gusting to 30 KT or so ahead of the low Sunday morning but shifting to the west behind it Sunday evening. The west winds will have better low level mixing and will allow for wind gusts of 35 to 45 KT on Monday and diminishing a bit into Tuesday. && .TIDES/COASTAL FLOODING... Storm surge of around a half foot will combine with high astronomical tides today to produce minor coastal flooding and splash over at high tide which occurs around noon. A Coastal Flood Advisory is in effect from 10 AM to 2 PM Thursday for coastal New Hampshire and southwest Maine. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Weather Advisory until noon EST today for MEZ007>009- 012>014-018>028. Coastal Flood Advisory until 2 PM EST this afternoon for MEZ023-024. NH...Coastal Flood Advisory until 2 PM EST this afternoon for NHZ014. MARINE...Small Craft Advisory until 7 AM EST Friday for ANZ150-152-154. && $$

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