Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 192359 AFDGYX Area Forecast Discussion National Weather Service Gray ME 759 PM EDT Wed Jul 19 2017 .SYNOPSIS... A weak cold front will cross the mountains tonight...bringing with it scattered showers. The front is expected to stall over the area Thursday...allowing for another warm day to its south. Temperatures are forecast to climb to near 90 again across much of southern New Hampshire and nearby western Maine. Another round of showers and thunderstorms are possible Thursday 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 weekend as westerly flow takes over. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 750 PM...A few tweaks to Pops/T/Td/SKY/Wind based on current obs. Main issue is what deal with the coastal fog/stratus for the overnight, as it was eroding fairly quickly from the south on the vis sat images before sunset. Models agree with this trend and at some point it should slow with loss of heating. Certainly not expecting the widespread dense fog of last night, but could see some patchy fog late along the coast, as well as the inland valleys. Coastal areas from the eastern end of Casco Bay thru Penobscot are likely to see the most prevalent fog tonight. Also, lowered pops a bit away front the intl border, where precip is light and falling from 10K ft plus deck. Along the intl border, closer to some forcing aloft, could see a few sct convective cells, and maybe even a few rumbles of thunder through around midnight or so. Previously...A weak cold front is approaching the forecast area from the NW...with scattered to isolated showers along it. While an isolated rumble of thunder is not out of the question...decreasing moisture and weak lapse rates aloft will most likely preclude a widespread thunder threat. The front will tend to get strung out along the forecast area tonight...with showers gradually weakening towards morning. Ahead of the front we will also likely see some areas of fog/stratus move back into coastal areas N of PWM. Latest hi-res guidance is less aggressive with inland extent than last night...so I have mainly kept the fog confined to coastal zones. That being said...a delay in the front and drier dew points may allow more widespread fog to develop. So at this time no dense fog advisory is expected...but I will allow later shifts to monitor trends. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... With cold front expected to be strung out across the forecast area...S of it will see another warm day with temps pushing 90 degrees. N of it is expected to be near normal for this time of year. With weak pressure gradient continuing...sea breezes may try to push inland again and keep coastal communities a few degrees cooler. Attention Thu will mainly be on thunderstorm chances in the late afternoon thru the overnight. Model forecasts are consistent in intensifying ongoing convection across MN...and tracking that into the Wrn Great Lakes. This MCS is forecast to continue thru the Lakes overnight...and emerge across NY Thu. Convection is forecast to once again intensify with daytime heating. The question is how far N will this convection make it. Current trends suggest a more ESE track and more glancing blow possibly for Srn zones. I have increased PoP to high chance along the MA border...but it is still carrying a bit more uncertainty than usual. A slight error in modeled placement of convection could mean large changes in forecast across our area Thu/Thu night. It does look like diurnal timing of storms will be unfavorable for strong to severe storms to make it into the forecast area. However an area of thunderstorms and locally heavy rain may be possible across Srn NH if the more Nrn track verifies...like the 19.12z ECMWF shows. What rain does make it into the forecast area will move E of the region by Fri morning. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The models are in decent agreement on the long wave pattern through early next week. Thereafter, big differences emerge regarding the degree of residual troffiness here in New England. Overall, we`re likely to see both heights and temperatures run below average for much of the extended period. We begin the period with a westerly flow and a broad low amplitude trough here in New England. Weak ridging arrives by Sunday in response to digging upstream shortwave energy over the Great Lakes. By the start of the new work week, this energy has carved out a sizable trough across the Great Lakes and northeast CONUS. The trough axis will inch eastward across the region through the remainder of the forecast period. In the dailies...we begin the period with a cold front across southern New England...and a second cold front approaching the international border from the Saint Lawrence Valley. This boundary will drop south across the forecast area on Friday with widely scattered convection. The third and final cold front will drop south across the region Friday night and Saturday with scattered convection. By early Sunday, the boundary will be stalled across southern New England with weak ridging providing a decent day across for Northern New Hampshire into much of Maine. Southern New Hampshire into extreme southwest Maine will be closer to the stalled boundary and associated cloud shield with onshore flow potentially adding some low clouds and fog to the mix. By Sunday night...the frontal zone will ride back north with attendant cloud shield as well as increasing pops and cool unsettled weather in response to evolving upper trough. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... Short Term...Areas of fog are expected to form again tonight N of PWM. Most likely RKD sees IFR or lower conditions for a good portion of the night...though AUG may see some lower CIGs sneak into the area after midnight. Otherwise isolated SHRA are possible tonight from HIE and LEB early this evening through AUG and RKD after midnight. On Thu an area of SHRA/TSRA will move thru the Northeast on an ESE trajectory. The bulk of this looks to miss the forecast area...though it is possible a more Nrn track will bring SHRA/TSRA to MHT/CON/PSM in the evening. Confidence is low in that outcome however. Long Term... Fri...Isold MVFR psb in -shra/-tsra. Sat...Sct MVFR in -shra/-tsra. Sun night - Mon...areas of MVFR in -shra/-tsra with lcl IFR in coastal stratus and fog. && .MARINE... Short Term...Winds and seas are expected to remain below SCA thresholds. Marine fog/stratus are expected to form again tonight N of Cape Elizabeth. The fog is gradually expected to dissipate as a weak cold front approaches early Thu morning. Long Term... Sat PM - Sun AM...Winds and seas could briefly approach small craft outside the bays. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...Cempa/Legro SHORT TERM...Legro LONG TERM...Schwibs AVIATION...Legro/Schwibs MARINE...Legro/Schwibs

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