Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201507 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1107 AM EDT Thu Jul 20 2017 .SYNOPSIS... A weak cold front stall over the area today...allowing for another warm day to its south. Temperatures are forecast to climb into the upper 80s to near 90 again across much of southern New Hampshire and nearby western Maine. Another round of showers and thunderstorms are possible this evening and overnight...but the best chances look to be across southern New England and New York State. Temperatures look to warm a few degrees more into the end of the week and early as westerly flow takes over. A low pressure system may bring cooler weather and more potential for rainfall Sunday night into early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Update...Focus for today is mainly on convective chances thru the evening. An approaching jet streak is bringing a broad area of divergence over New England this afternoon. Given warm and humid conditions and associated jet forcing...some scattered thunderstorms are possible as we near peak heating. Forecast soundings suggest around 1000 J/kg MLCAPE...and shear edging towards 50 knots. This should be more than enough for some storm organization...and so I have added gusty winds to the forecast for most areas. Hi-res convection allowing models are focusing the bulk of the afternoon storms over Wrn ME...so I have increased PoP to high chance in those areas. We also have to keep one eye on the developing MCS over Ontario. A SWly H8 LLJ is forcing a complex of storms N of Lake Ontario...and model forecasts and common sense would suggest that with continued heating of a moist environment that storms will maintain or intensify as they move Ewd. Hi-res guidance favors an ESE track...which would correspond to the gradient of highest theta-e air...missing the forecast area to the S. I will keep isolated thunderstorm mention over Srn NH to cover any possible shift N. Previous discussion...Warm and humid conditions expected again today with a sea breeze becoming established along the Maine coastline. Based on sounding analysis, expect maximum heating potential today to be about the same as yesterday, generally right around 90 in areas that are able to realize this potential. With a broader westerly flow today, the sea breeze will be shaped a little differently today, more oriented along the coast and inland of the Midcoast. However, with such a steep low level inversion, early morning warming could warm things up into the mid 80s before the sea breeze becomes established enough to cool things down. With the heat and humidity, there will be instability available for thunderstorms during the afternoon. However, there is not much of a trigger available until a shortwave trough moves in late in the evening. So until then, expect the best chance of convection to be driven by the terrain and perhaps the convergent zone along the sea breeze boundary. Some mesoscale models are showing some development over the Adirondacks drifting east into New Hampshire during the afternoon as well as some development along the sea breeze. But generally speaking this should be fairly isolated if it does occur. Wind shear today will be broadly supportive of more organized thunderstorms, though the shear is unidirectional and very deep. As such, it seems the greatest threat for severe weather will be for damaging winds, and that threat will be fairly small. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Afternoon convection which develops over western New York will begin to push its way east and southeast overnight. It is possible that some of this activity scrapes southern New Hampshire, but the odds are better further to the south. Generally expect mostly cloudy skies from the passing mid level wave and debris from other convection and lows falling into the 60s. Flow becomes a little more northwesterly on Friday, and as such we expect dewpoints to be a bit lower, generally around 60 during the heat of the day. This northwest flow will also squash the sea breeze down to the immediate coastline with temperatures warming into the upper 80s to near 90 in well mixed areas. A front drops in from the north late in the day and could provide a focus for showers and thunderstorms arriving in the late afternoon across northwest Maine. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Warm and relatively quiet weather is expected Friday night through at least the first part of Sunday with offshore flow and little in the way of forcing for ascent. Thereafter, the pattern begins to change as more amplified upper level troughing takes shape. Starting Sunday night, a warm front looks to lift toward the region with the attendant likelihood for rain as agreed upon by several members of the 00z deterministic/ensemble model suite. Preliminary indications are that this trough may stick around for awhile, perhaps providing for an unsettled, showery, and cool pattern into early next week. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... Short Term...Expect VFR conditions today with light winds. There will be a chance of valley fog tonight, but the chances are much lower than previous nights due to expected cloud cover and lower dewpoints. Long Term...Mainly VFR Friday night through Sunday. For Sunday night into early next week it looks like chances for IFR conditions increase in showers, low clouds, and perhaps some fog. && .MARINE... Short Term...Light southerly flow expected today and Friday. Long Term...Conditions are expected to remain below small craft levels through the weekend. There is a chance of SCA conditions early next week in association with a possible low pressure system. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Legro

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