Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 141637 AAC AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1237 PM EDT Thu Sep 14 2017 .SYNOPSIS... High pressure now over the region will give way to increasing moisture and a weak low pressure system associated with the remnants of Irma through Friday. This will bring an increase in humidity to the region...with the threat for showers and possibly a thunderstorm. High pressure will build into the region for the coming weekend. Temperatures will remain above normal for September. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1038 AM Update: Primary adjustments late this morning include lowering PoPs through early afternoon based on current radar trends with nearly all activity from this morning coming to an end. Also...temperatures were ahead of inherited diurnal curve...and with T8s around +16C have moved high temperatures upward given a decent amount of sun. Another day of temperatures well above seasonal norms. 845 am Update: Minor adjustments to sky cover...temperatures and dewpoints based on morning observations. Earlier thunder activity along the edge of the H8 moisture gradient has weakened...but 12Z GYX RAOB shows impressive 7.2C/km lapse rates in the H7-5 layer and thus could certainly see a few isolated showers with another thunderstorm as this region lifts north. Will await further destabilization later this morning and through the afternoon for additional shower/storm development...however mid level forcing will really remain centered south and west of the region today...so no more than iso-low chance pops are warranted and inherited forecast has this idea well handled. 645 am Update: Isolated tstorms have developed across west central NH along with a few widely scattered showers. Have made a few minor adjustments to POPs based on these latest trends. Previous Discussion: Today clouds will continue to increase with the scattered showers developing over southern areas as the remnants of IRMA approach from the west. Temps will again be mild today with highs in the mid 70s to near 80. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... The remnants of IRMA moves across the region tonight and Friday with scattered showers and even isolated thunderstorms. Not expecting much qpf with the showers. Totals over southern and central areas generally around a quarter inch or less with very little if any over northern areas. Temps will continue to be mild as dewpoints also rise making for more humid conditions. Stayed close to guidance for temps. Accepted RFC QPF guidance. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... The two branches of the jet stream- the subtropical and polar- will consolidate over the desert SW by Friday night. Strong SW flow will generally be centered across the northern Plains and into southeastern Canada. A strong short wave impulse will become negatively tilted as it ejects ENE late in the weekend, serving to slightly flatten the top of ridging over New England. The northern stream ridge will build a bit more as the short wave moves into northern Canada. By mid week, the impacts of Jose may be impacting the eastern seaboard...but currently confidence in any one scenario is low. Late in the week sharp ridging will dominate the eastern CONUS as Jose moves farther out to sea. We`ll have warm daytime temperatures in the mid to upper 70s for the weekend...giving way to upper 60s to mid 70s for the remainder of the week. Overnight lows will be above normal by a few degrees with periods of cloud cover as well as occasional showers and thunderstorms. The most notable chance for precipitation will be early next week associated with the interaction of an approaching frontal passage and moisture from Jose. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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Short Term... Summary: A mid level disturbance and weak surface wave associated with the remnants of Irma will move through the region through Friday with showers...a possible thunderstorm...as well as increased clouds and fog. Restrictions: Generally VFR at the terminals as of this writing with some MVFR cigs occasionally impacting LEB/MHT over the past few hours. An isolated shower or thunderstorm is possible through this afternoon and evening with a restriction possible...otherwise expect VFR conditions to hold through the evening. Tonight...expect more widespread fog development with LIFR/IFR likely at LEB/HIE/AUG/RKD with lower confidence in fog development elsewhere. A few showers/thunderstorm are possible through the overnight as well...particularly at CON/MHT/PWM. On Friday...the fog will be slow to thin...with stratus likely remaining for at least part of the morning hours. Away from the coast expect improvement to VFR to occur by late morning/early afternoon. Somewhat more widespread shower and isolated thunderstorm activity is expected. Widespread fog likely sets in Friday night with even more widespread IFR/LIFR restrictions. Winds: Very light winds through Friday night...generally less than 5kts outside of 5-10kt southerly sea breezes this afternoon at PWM/RKD. LLWS: No LLWS expected through Thursday night. Lightning: An isolated thunderstorm is possible through this evening over southern/central NH and southwestern ME. On Friday an isolated thunderstorm can/t be ruled out at any of the terminals. Long Term... Expect some fog/stratus into early Saturday morning before VFR conditions become more dominant for the Sunday through Tuesday period /with a daily exception being valley fog at HIE-LEB/.
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&& .MARINE... Short Term... Very quiet conditions with no flags expected through Friday. Long Term... High pressure remains over the waters through the period with light winds expected. There is some threat for marine stratus/fog in the Saturday morning period as low level moisture increases. Beyond this...headline free conditions are expected through the weekend...with some building swell possible early to mid next week depending on the evolution of Jose over the western Atlantic. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM... SHORT TERM... LONG TERM... AVIATION...Arnott MARINE...

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