Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 181310 AFDGYX Area Forecast Discussion National Weather Service Gray ME 910 AM EDT Sun Jun 18 2017 .SYNOPSIS... A warm and increasingly humid airmass will remain across the region through Monday. A cold front will approach from the Great Lakes Region on Monday and bring widespread shower and thunderstorm activity to the region. Some of the thunderstorms could produce strong gusty winds, hail, and torrential downpours, especially across inland areas away from the coast. On Tuesday, the cold front will gradually dissipate as it slides offshore. The next cold front will move in on Wednesday and exit the region Wednesday night. High pressure follows this front for Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Update... Have updated the grids based on current surface conditions and radar/satellite trends. Some patchy dense fog will continue along the coast for another hour or so. The dense fog is not widespread and will continue to gradually lift. Therefore, have opted with an SPS to account for slow driving conditions this morning. Most of the observations visibilities are on their way up, however some dense fog likely out near the immediate shoreline. Minor adjustments made to temperatures, dew points and cloud cover for today as well. 600 AM...Minor ESTF update to reflect the current mesonet in near term grids. Prev disc... At 06z...a warm front extended from Quebec through western and central New England. For today...the warm front will advance north and east across the remainder of the area. Clouds will gradually give way to sunshine by afternoon with clouds and patchy fog lingering the longest along the Maine coast east of Casco Bay. There could be a brief pop up shower or thunderstorm across the higher terrain of western and northern New Hampshire as well as in the Maine mountains/foothills. Otherwise...a just a warm and humid day expected across the forecast area today. Highs will range from the upper 70s to lower 80s...with some 70 degree readings along the Maine mid coast in the onshore trajectory.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... For tonight...we`ll continue to see the chance for a passing shower or Thunderstorm from the Connecticut Valley northward along the international border as a cold front inches eastward towards the Saint Lawrence Valley and western New England by morning. Otherwise...a partly cloudy and humid night with patchy fog and haze. Lows will be in the mid 60s to lower 70s. On Monday...temperatures will warm into the upper 70s and lower 80s ahead of the slow-moving cold front. Precipitable water anomalies of plus three to four SD`s across the forecast area and the likelihood that convective cells will train along the boundary support a heavy rain threat and potential for some localized flash flooding from the Connecticut Valley northward through the mountains and foothills of Northern New Hampshire and Western Maine. We`ve issued a flash flood watch for portions of the forecast area for Monday afternoon and Monday night. Forecast temperatures on Monday support capes approaching 1500 j/kg by early afternoon with potential for convection to produce damaging wind gusts and some large hail in the stronger cells. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... The extended starts off fairly active...as slow moving cold front will have yet to clear the forecast area. GEFS...CMC ensembles...and ECMWF are in good agreement that a +2 to 3 standard deviation air mass will remain ahead of the cold front. Coupled with flow parallel to the boundary...training convection in addition to heavy rainfall will continue the flooding threat. At this time it does appear that enough frontal push will be made early Tue that the coast will be spared longer duration rainfall...but it is not out of the question that flash flood watch may need to be expanded E with time. The main upper trof axis will be delayed until Wed. As it swings across we should see numerous showers pop up in the afternoon. It will be a pretty dry environment...so not much in the way of surface based instability. Though forecast soundings do show a little elevated CAPE...so a rumble of thunder is not out of the question. Beyond midweek model guidance wants to keep mean trofing across the Ern CONUS. That would keep the forecast area generally showery with no big heat. With H8 temps generally around 10C that will translate to comfortable temps near normal. The warmest mid level temps are forecast to arrive with some precip...so the warm front may struggle to get N of the area late in the week. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/... Short Term /through 00z Tues/ MVFR and IFR will gradually improve to MVFR with areas of VFR away from the coast this afternoon. Conditions will lwr to MVFR with areas of IFR again tonight in stratus and fog and sct -shra/-tsra. On Monday...MVFR throughout in shra/tsra with strong to severe thunderstorms psb mainly away from the coastal TAF sites. Long Term...There should be areas of IFR ahead of the slow moving cold front early Tue. In addition to the low CIGs...SHRA/TSRA with heavy rain will be moving along the front and restricting VSBYs. The final push of the front looks to move thru mid morning to early afternoon Tue. Upper trof swings overhead Wed and will lead to afternoon SHRA. Local MVFR conditions are possible in any convection. Improvement is expected Thu ahead of the next system approaching from the W. && .MARINE... Short Term /through Monday/...SCA for building winds and seas ahead of a cold front. Long Term...SCA conditions...mainly seas...will linger on the outer waters until the cold front crosses. Winds and seas diminish Wed...but may build again ahead of the next front late in the week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Flash Flood Watch from Monday afternoon through Tuesday morning for MEZ007>009-012>014. NH...Flash Flood Watch from Monday afternoon through Tuesday morning for NHZ001>009-011-015. MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ150>154. && $$ JC

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