Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 241526 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1126 AM EDT Fri Mar 24 2017 .SYNOPSIS... A warm front will cross the region today, and then shift southward as a cold front Saturday. High pressure will build in Saturday night and Sunday. A series of lows will track across the region Sunday night through Wednesday and make for an unsettled period with some bouts of rain or wintry precipitation. High pressure builds in for the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 11AM update... Very dry airmass in place over the region late this morning resulting in hit and miss areas of light to moderate snow and gusty winds. Still expecting some minor accumulations through early afternoon as the airmass saturates and cools in interior sections of Maine and New Hampshire. Temperatures will gradually increase through the afternoon and boundary layer will warm enough in southern zones for precip to mix with rain and eventually go over to plain rain showers. Have update pop/wx grids to relect current radar trends. Aside from a few temp/td tweaks no other changes planned attm. 7AM UPDATE...Will update the forecast based on early morning temperatures. Regional radar imagery shows widespread echoes which have been moving through Vermont and even into New Hampshire and Maine at times. Have yet to see reports of any of this reaching the ground as there remains a very dry layer of air below this. It will moisten up later this morning, though. ORIGINAL DISCUSSION... Surface high pressure over the area early this morning will shift east today, bringing a southerly flow to the region which will help to push out the cold air. Westerly warm advection flow will be ongoing aloft today, bringing increasing clouds and eventually precipitation. Precipitation will become more focused along and ahead of a warm front which will move southwest to east across the area today. Atmospheric profiles indicate that conditions will be cold enough for snow formation ahead of the warm front, with surface temperatures playing the critical role in whether snow or rain reaches the surface. It is likely that temperatures initially warm this morning, but as precipitation arrives and falls into the low level dry air, evaporational cooling will bring surface temperatures down closer to freezing. As a result, expect most of the area to see some snow today, with a possible transition to rain this afternoon and evening as the precipitation comes to an end. There is not a ton of moisture available with this system as it is arriving from the west (off the continent) and does not have a lot of organized lift with it. But total liquid precipitation amounts of 0.1 to 0.25 inches is likely, which could translate to 1 to 3 inches of snow. The ability of snow to accumulate will be impacted by surface temperatures which are expected to be near or possibly above freezing for a good part of the area. Thus if snow does accumulate it may melt quickly afterward. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Any lingering precipitation should depart to the east early this evening as the warm front pushes through. There may be some lingering upslope precipitation in the mountains on the low level westerly flow. Temperatures across most of the area stay in the 30s tonight, in some cases above freezing. But by morning a cold front will be dropping down from the north which will bring colder temperatures and drop northern areas into the 20s. As the front arrives in southern New England during the day Saturday, a weak wave will be moving east along the front. This will spread some precipitation into southern parts of New Hampshire. Precipitation type will again be dependent on surface temperatures, and at this time looks likely to be mostly rain. But there could be some areas of light snow especially on the northern edge. Warmest temperatures on Saturday may well be toward the midcoast of Maine where there could be some sun to bring the temperature into the mid 40s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Overall, 500mb pattern in the extended will lean toward weakly amplified zonal flow, with multiple waves, but nothing becoming very amplified. Should see enough of a trough get carved out of the flow by mid-week as it moves to our east, then we will some ridging at the end of the week. Models tend to be in agreement that cold front will shift far enough south Saturday to allow some ridging to build in through Sunday. So, have backed off pops a little more in this timeframe. But this airmass will be cool with lows Sunday morning back into the teens to mid 20s, and highs on Sunday mostly in the 35 to 40 range, so a few degrees below normal. Sunday night will see WAA return as weakening trough shifts NE thru the Great Lakes as it runs into ridging aloft. The trend is for less QPF Sunday night, given the strong ridging, but if anything falls, many spots will be cold enough for either light snow or freezing rain. This system is slow moving, and light precip will likely linger into Monday, although with a gradual warming trend, so precip should go over to rain in all but far northern zones, with highs mid 30s to low 40s. Secondary wave moves through Tuesday, and will likely see another round of light precip, which could once again show some wintry characteristics Tuesday night before cold front swings through early Wednesday. Digging trough to our N and E should keep us in drier NW flow for the latter part of the week, with temps closer to normal. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... Short Term...VFR conditions this morning become IFR to possibly LIFR in light snow late this morning into the afternoon. Snow may transition to rain through the afternoon especially in southern parts of the area. Could see VFR conditions return to parts of the area overnight tonight. Long Term...Should see mainly VFR Saturday into at least Sunday morning. Then expect deteriorating conditions late Sunday into Sunday night in mixed precip. Expect IFR late Sunday night into Monday, with maybe some improvement to MVFR at times Monday night and Tuesday, but expecting an extended period flight restrictions for Mon- Tue. && .MARINE... Short Term...A southwesterly flow will develop this afternoon behind a warm front. Winds could gust to 30KT at times, and a Small Craft Advisory has been issued. Winds just above the surface will be fairly strong, but the low levels of the atmosphere should remain at least somewhat stable on the warm advection flow, so we should remain below gale force winds today. Long Term...SCAs possible due to wind on Monday, and then potentially for seas Mon night into Tue. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ150>154. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.