018 FXUS61 KGYX 231636 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1236 PM EDT Wed Aug 23 2023 .SYNOPSIS... High pressure crests Northeast today through tomorrow with continued tranquil weather and seasonably cool weather. Showers return to the fray behind the ridge tomorrow afternoon and evening, then a cold front approaches Friday providing a focus for rounds of showers and embedded thunderstorms until its passage. High pressure returns behind the front by the start of the coming week, with continued below normal temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1230 PM Update... Another round of minor adjustments were made to reflect latest observational trends but otherwise it continues to be a beautiful late August day across the region. Satellite imagery does show some diurnally driven cumulus clouds developing but other than perhaps an isolated shower across northwestern ME by this evening, the vast majority of the area will remain dry. Previously... 1030 AM Update... Minor changes to reflect latest observational trends. It will continue to be a pleasant morning across the region with very little wind to speak of compared to yesterday. Temperatures will climb into the 70s across most locations by early afternoon. Previously... 712 AM Update...Little to update at this hour with valley fog and stratus blanketing the upper Androscoggin and Connecticut River Valleys. Am expecting this to mix out in the coming hour or so as the sun gains elevation. Previously...High pressure builds into New England today, a shortwave appendage extending from a dominant dome of high pressure centered over the central CONUS this week. While the larger high pressure circulation is responsible for a record- breaking heat wave through much of the nation's interior, we in New England continue to be in northwest flow with a seasonably cool airmass overhead. Should be another good day for mixing, although the utter lack of flow under the incoming ridge won't provide much mechanical help. Weak lapse rates above the mixed layer leave some room for observed temperatures to overshoot modeled forecasts, similar to yesterday, so will again lean on warmest guidance bringing temperatures in the 70s... perhaps touching 80 in a couple southern interior locations. Weak flow will allow a sea breeze to cool the immediate coastline, but surface high pressure slips offshore will bolster this effect later in the day for a cooler evening along the coastal plain. The mixing will also produce another cumulus field today, most pronounced across northern zones where mid-level lapse rates and some moisture convergence is best. Convection over the lower Saint Lawrence Valley today may persist long enough to provide a rain shower or two in the Moosehead region late today, but this appears to be an outlier solution with around a 15-20% / slight chance of occurring. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Mid-level pressure and wind charts show a shortwave ridge rotating across New England through tomorrow, coinciding with surface high pressure sliding through southern New England and into the North Atlantic. For tonight, this means another mostly clear and cool night with temperatures again falling toward or past the dew point... into the 40s to near 50 for more sheltered locations, but hanging in the mid-50s elsewhere as southerly flow continues through the mid- levels. Similar to this morning, river valley fog can be expected, especially in the more broad basins with more open water. Southerly flow will be fully in play on Thursday as the mid- level ridge axis crosses east. This brings dew points up, with moisture convergence through the mountains likely producing cloud cover there along with rain shower activity as an axis of weak instability develops. Outside of the mountains, a mix of sun and clouds is forecast as a warm front approaches the region from the west... eventually bringing potential for light rain showers mainly to New Hampshire through the afternoon. I do think there will be enough mixing to warm nicely into the 70s, although places in the north and west are more likely to hang closer to 70. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Overview... A slow moving frontal boundary gradually crosses on Friday and Saturday, with at least one area of low pressure moving along the front and bringing rounds of showers to the area. A stronger front pushes this system offshore, but the upper level low may linger near New England through the remainder of the weekend. High pressure then builds across New England for the early to middle portions of next week. Details... The dry and pleasant stretch comes to an end Thursday night and Friday as rain spreads eastward across the forecast area as a cold front moves our way. A weak area of low pressure along this front will help to enhance some rainfall and shower coverage, but there's still a bit of uncertainty as to whether these higher amounts will set up across southern and coastal areas or across southern New England. This detail will have to be worked out a little closer in time. Regardless, all areas are at least likely to see some rain between Thursday night and Friday night, with eastern areas being the last to see the shower activity arrive and depart. A stronger cold front moves though on Saturday and pushes the bulk of the system offshore, but brings with it another chance of scattered showers on Saturday, especially across northern and western areas. High pressure will eventually press southward into New England, but before it arrives an upper level low behind the front keeps the chance for showers going into Saturday night. The latest models runs are showing a wetter and slower departure of these disturbances, but since this is a recent development the forecast has not changed much for the second half of the weekend until a this proves to be more of a trend than a one off in the models. By early next week high pressure is expected to be centered to the north across southern Canada and flexing its influence across New England. However, strengthening tropical systems in weak steering environments well south of the area add some uncertainty as to how dominant this high will be in our area. With the position of the high to the north, the flow pattern is close to turning more onshore across the Northeast and bringing in more moisture and cloud cover. For the last few days it has looked like the high would bring bright and dry conditions early next week, but the pattern is looking less certain at this point as recent model runs show more moisture trying to enter the equation. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... Short Term...VFR prevails at all terminals today through tomorrow. The only exception is the formation of overnight LIFR valley fog, most likely to occur for KLEB and KHIE between approximately 08Z-12Z. Light westerly winds today veer southwesterly or southerly along the coast with a sea breeze today... then go light and variable or calm tonight. Southerly flow prevails tomorrow, with a chance for gusts around 15 kts. Long Term...Showers bring restrictions at times from Thursday night through Friday night, arriving first across western terminals Thursday evening and spreading to eastern terminals Friday morning. Scattered showers are possible into Saturday, and then gradual improvement to VFR is expected by Sunday. Mainly VFR conditions are expected early next week, with nighttime valley fog being the main exception. && .MARINE... Short Term...Northerly flow this morning is replaced by southerly to southwesterly flow as high pressure sinks through the western Gulf of Maine. Flow wavers westerly tonight, before strengthening out of the south tomorrow... to around 10-20 kts by the afternoon. Long Term...An approaching frontal boundary brings increasing southerly winds and building seas, with SCA conditions likely by late Thursday night and lasting into Saturday. Conditions then improve as the front clears the waters on Saturday, with high pressure building in late in the weekend and early next week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Tubbs SHORT TERM...Casey LONG TERM...Clair