Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 271635 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1235 PM EDT FRI MAY 27 2016 .SYNOPSIS... Warmer air will continue moving into the region through the first part of the weekend...with the hottest temperatures expected for Saturday. Upper level high pressure will be in control...so any showers or thunderstorms are expected to be scattered at best. Moist tropical air will move in Sunday night bringing rain showers. A cold front pulls through Monday night clearing out the rain. Tuesday will be warm with a chance for afternoon thunderstorms. High pressure will move in for the remainder of the week yielding dry and mild weather. && .NEAR TERM /TODAY/...
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1230PM UPDATE... Clouds hanging tough across much of Maine today south of the mountains. This has kept temperatures in the 50s. Should continue to see this erode from west to east through the remainder of the afternoon. As it does so temperatures will finally begin to warm up. Hourly temperatures and high temperatures were updated with this update to account for cooler conditions where the cloud cover will linger the longest. Otherwise no significant changes were needed. 9AM UPDATE... Clouds and isolated showers associated with an initial shortwave trough are moving through central and eastern parts of the area now. Have adjusted cloud cover forecast to better match current trends and to try to paint a picture of decreasing clouds as the morning goes on along the coastal plain while clouds advance into northern areas through the day. Area of showers and storms in Quebec will move eastward and may clip the northern part of western Maine late this morning or early afternoon. Instability generally decreases as these storms move toward our area, so they could lose their punch as they get here. Isolated to scattered convection expected to develop this afternoon over New York, Vermont, and possibly bleeding over into western New Hampshire as well where better heating and instability exist. Further east, an onshore southerly flow will limit instability over Maine. 7AM UPDATE... Coastal fog and stratus is beginning to form...mainly in an arcing band parallel to the coastline. Have adjusted Wx and Sky grids to account for this into mid morning. ORIGINAL DISCUSSION... Warm front is moving into the area this morning. Showers and a couple rumbles of thunder have formed on the leading wing of WAA...captured well by the GFS convergence at 900 mb. GFS transitions focus from ENEwd moving band of showers to more general scattered showers in the background WAA across Nrn zones thru the rest of the morning. Do not think thunder will be widespread...but will keep isolated mention as there have been a few CG and IC flashes detected. Heights aloft rise thru the day...which should continue to keep any shower activity scattered in nature. Onshore flow will limit warming for much of coastal ME...but much of NH will get quite warm again this afternoon. S/WV trof moves thru Quebec this afternoon...shearing out as it does so. The decaying front attendant to it will approach Nrn zones during peak heating. Convection allowing models show the potential for some storms mainly in the mtns during this time. Have removed enhanced wording from the thunder forecast for the afternoon time period based on latest trends in guidance. Strongest forcing remains well N of the area...and lapse rates are rather poor with weak mid level flow across our forecast area. A gusty storm or small hail isn`t out of the question...but organized convection doesn`t appear likely.
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&& .SHORT TERM /TONIGHT AND SATURDAY/... Dominated by upper ridging, tonight looks quiet. Winds look to veer a bit thru the column...which despite a moisture increasing may help to limit coastal stratus development. For now will leave any fog mention out of the forecast. Saturday then looks like the hottest day of the bunch. H9 temps climbing above 20C and westerly low level flow should mean low 90s across much of southern NH. Could see some heat index values creep at or above 95. Given the hot and increasingly humid air mass...at least modest instability should be in place by afternoon. However...we lack a coherent trigger for convection. Modeled QPF is seemingly following terrain features...which makes sense given the lack of other background forcing. For now will keep PoP at chance or slight chance. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... High impact weather: Heavy rain showers Sunday night into Monday bring a chance for flash flood threat. Overview: Summer makes its long awaited return for Memorial Day weekend. A broad upper level ridge builds from Bermuda into the northeastern United States through much of the next week. Tropical moisture will move in for the start of the week before a brief shortwave will yield falling heights on Tuesday only to quickly return to the strong ridge on Wednesday. Saturday night warm air advection continues with ongoing convection from Saturday afternoon. Warm air continues to build in for Sunday as the high crests overhead. On shore flow will keep temperatures at the shore cooler. Sunday night showers will develop ahead of a front pushing through on Monday. Southerly flow around a Bermuda high will push an exceptionally moist airmass into northern New England. The moisture transport will be further enhanced from a weak tropical system moving into South Carolina. Forecast soundings show tropical airmass characteristics with about 4km of above freezing and saturated air by 00Z Sunday. Furthermore, current deterministic guidance suggest PWAT as high as 2 inches is possible...which would put this at the 99th percentile. That moisture will depend largely on how the tropical system is able to develop over the next several days. Even with more modest PWATS /around 1.5 inches/ the storm motion vectors are less than 10kts across much of our area which would bring concerns of flash flooding with any cell training. Have added isolated thunder and heavy rainfall wording for Sunday night and Monday. Monday evening the front pushes through leaving the heavy moisture to our east. While the widespread rain will come to an end thunderstorms remain a possibility for Tuesday afternoon as steep lapse rates combine with upper level support from the right entrance of the jet. Wednesday the upper level ridge returns and remains in place through the end of the week. Highs will be seasonable in the 70s with overnight temperatures in the 50s. Dry and seasonable conditions continue for Thursday with the next rain moving in on Friday. && .AVIATION /13Z FRIDAY THROUGH TUESDAY/... Short Term... 9AM UPDATE... Deck of clouds at about 1000 to 1500 feet persists across the coastal plain from Concord/Manchester eastward to Augusta. This will gradually move east and dissipate through the morning. Could see some afternoon showers/thunderstorms develop over western New Hampshire. Most likely areas impacted will be Whitefield and Lebanon though the chances are quite low. As moisture increases tonight...coastal stratus may again be a problem...though models are forecasting a more offshore wind component. Long Term...Sunday night into Monday will see periods of IFR in rain showers. IFR is most likely along the coast through Sunday night, where fog may develop, but inland areas may also see the rain yield IFR. Conditions will return to VFR by late Monday night. Thunderstorms are possible on Tuesday afternoon. && .MARINE... Short Term...Winds and seas expected to remain below SCA thresholds thru the first half of the weekend. Long Term... Quiet period on the waters as the high pressure keeps winds and seas calm. && .FIRE WEATHER... Very warm and increasingly humid conditions are expected for much of the area through the holiday weekend. Precipitation will be scattered for the first half of the weekend...with showers and storms becoming more widespread Sun into Mon. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM UPDATE...Kimble SHORT TERM...Legro LONG TERM...Curtis

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