Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 211313 AFDGYX Area Forecast Discussion National Weather Service Gray ME 913 AM EDT THU JUL 21 2016 .SYNOPSIS... High pressure will remain anchored to our southeast through Friday. The circulation around this high will circulate warm and increasingly humid air into the region ahead of a cold front. The cold front will approach the area on Friday, producing showers and thunderstorms, before sliding offshore Saturday morning. Some of the thunderstorms late Friday and Friday night will produce gusty winds, hail, and frequent lightning. The front stalls over the area Saturday with another round of scattered thunderstorms. Weak high pressure moves through Sunday and Sunday night. Another rounds of showers ands storms is possible late Monday and Monday night as a cold front approaches the region, and the may stall over the area Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 900 AM update...minor tweaks to temps, clouds, and DP based on observations. Prev Disc... At 06z...a 1023 millibar high was anchored southeast of the forecast area. GOES infrared imagery showed clear skies across the region. The clear skies and light winds were allowing patchy fog to develop over interior valleys. For today, little change as the surface high remains in control. Some high clouds will spill into the region from Quebec, courtesy of the convective complex vicinity of the southern tip of Hudson bay, otherwise it`ll be a mostly sunny day. Highs today will be in the 80s and lower 90s, but with comfortable humidity levels for one last day. The westerly flow will turn onshore by late afternoon from Casco Bay and points east allowing some late day relief from the heat. It should be another dry day with any convection over Quebec province remaining to our north. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... For tonight...dewpoints should gradually rise in the southwest flow. Can`t rule out a late night shower or thunderstorm near the international border ahead of a weak surface trough. Otherwise...a partly cloudy night with patchy fog and haze developing. It`ll be milder then this morning with lows mainly in the 60s. On Friday...southwest flow ahead of the approaching surface cold front and a prefrontal trough will allow dewpoints to rise through the 60s while temperatures warm well into the 80s. An approaching shortwave impulse during the afternoon, coupled with peak heating should produce cape values in the 1500 to 2000 j/kg. In response, expect strong to severe convection to develop across the forecast area by afternoon then continue into Friday night. I`ve left enhanced wording in the grids and public products beginning Friday afternoon. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Chance of high impact Wx: Increasing confidence for severe thunderstorms Friday afternoon and evening. There is a chance for more isolated severe storms on Saturday. The strong ridging at 500mb over most of the CONUS and the western Atlantic will hold through the long term forecast period, with the one weakness in the ridge still straddling the intl border from the Great Plains to New England. This should make for a more active period with the threats of showers/storms at least every other day. Moving lower in the atmosphere, it`s hard to much air below normal at 850 mb outside of the Arctic circle thru this period, so expected temps to continue to run mostly above normal. As we get into the low levels, flow becomes fairly stagnant, with only small differences in air masses on either side of sfc fronts, and very little dry air to to tap into to lower humidity levels much. So, in summary, expect very warm and humid conditions over the weekend and into the middle of next week, with frequent potential for scattered showers and storms. The most interesting part of the extended will be Friday night as ongoing convection Friday afternoon to our west has the potential to organize into convective line or MCS and move across the region, especially between 0Z and 6Z. Whether a line forms or not there will be enough instability and presence of elevated mixed layer, along with strong bulk shear to continue the severe threat thru the evening hours. Fri night will be warm and humid with lows mostly in the mid to upper 60s, and maybe not dropping below 70 in urban areas of southern NH. On Saturday, frontal boundary looks to stall or slowly move south across the CWA as the 500 mb trough hangs back a bit. It will be a possible that with presence of frontal boundary and potential NW flow a loft, could see more strong to severe storms on Saturday, but for now, will not mention in zones/grids as confidence is too low. Highs Saturday will be hotter south of the front in southern NH where they will reach into the low 90s, with TDs in the mid to upper 60s, which will produce heat indices in the mid 90s. Elsewhere it will remain on the warm and humid side. It starts clear out later Sunday night as the front finally pushes just south of the CWA and fades out. Some drier air moves in , and will push dew points down to the upper 50s to lower 60s late Saturday night into Sunday. Sunday should be dry with highs back in the 80s to around 90 in southern NH. Sfc humidity increases Sun night and Monday with another threat for showers storms as another front approaches and tries to cross the region Monday night or Tuesday. Temps and humidity may drop off a bit on Wednesday. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... Short Term /through Friday/...Lcl ifr psb through 12z at khie and kleb...otw vfr. Sct mvfr psb aft 08z Fri in mtn -shra/-tsra. Aft 16z Fri...areas of mvfr in shra/tsra with lcl ifr psb in +tsra. Long Term...Friday night will be a busy period with the potential for severs storms, coastal status and fog. Some flight restrictions are expected, but conditions will be changeable. VFr returns on Saturday, but there will be the htreat for another round of TSRA. Mainly VFR Sat night through Monday with night valley fog. && .MARINE... Short Term /through Friday/...Southwest flow will continue with seas gradually building. We may reach marginal small craft conditions during Friday outside the bays. Long Term...SCA possible outside the bays friday evening, but otherwise should remain below SCA through Monday. thunderstorms frinight could produce very strong gusts and frequent lightning. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ UPDATE...TFH

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