Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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969 FXUS61 KGYX 201835 AFDGYX Area Forecast Discussion National Weather Service Gray ME 235 PM EDT Sat Jul 20 2024 .SYNOPSIS... A cold front drops south tonight through Sunday, bringing the chance for scattered showers and a stray thunderstorm. Otherwise, mostly dry conditions continue into Monday. Moisture increases Tuesday with daily chances for showers and afternoon thunderstorms into Friday. Cooler conditions are expected for at least Wednesday and Thursday. High pressure looks to return for next weekend with warming temperatures. && .NEAR TERM /TONIGHT/... High Impact Weather Potential: Minimal. Pattern: Quiet weather this afternoon with some high cloudiness across the area. Potent surface cold front sits north of northern New England associated with low pressure across northern Quebec and a strong upper low east of James Bay. While the mid and upper low continue to push east...northwesterly llevel flow at H8 will drive this front towards the international border after midnight and into our the mountains through daybreak. Thus..the forecast focus will be on whether this front can spark and showers and the impacts of associated clouds on overnight lows. Through this evening: Quiet weather is expected through the evening with clouds along the surface cold front nearing the international border by 8pm with mostly clear skies south of this outside of some cirrus esp over the southern half of the area. Temperatures will fall back into the upper 60s in the mountains by 8pm with 70s elsewhere. Tonight: Moisture plume with PWATs to around 1.25" drops into the mountains tonight ahead of the surface cold front with the front beginning to outpace mid level support with instability diminishing through the overnight. The result should be a decaying line of showers reaching the far northern zones overnight with the surface wind shift pushing ahead of the moisture boundary to the coast. Outside of the northern showers...expect partly to mostly cloudy skies...which should keep overnight lows a bit warmer than the previous night...with values in the upper 50s in the mountains and lower to middle 60s to the south. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... High Impact Weather Potential: Minimal. Pattern: Surface front draped across the region Sunday morning will cross the area through the day providing a focus for clouds and some possible showers. Beyond this...drier air drops into the region Sunday night with quiet weather and cooler overnight lows expected. Sunday: Moisture boundary associated with the cold front will continue to drop south through the region...with modest MLCAPE of a few hundred J/kg developing from the foothills to the coast. Mesoscale ensemble guidance indicates the potential for a few showers to form along the advancing boundary /and possibly a rumble of thunder/...but not expecting much in the way of shower coverage. T8s will range widely from north to south...only around +10C in the north to +15C in the south. The result will be highs only around 70 in the mountains... while over southeastern NH...upper 80s will again be possible...with lower/middle 80s elsewhere into the foothills. Sunday Night: PWATs fall to around 0.5" with surface dewpoints in the 40s behind the departing cold front. Given mid level height rises and a surface high pressure axis moving overhead...expect mostly clear skies with temperatures falling into the 40s across the mountains...with lower 50s from the coast into the foothills. && .LONG TERM /MONDAY THROUGH SATURDAY/... Overview... A ridge builds into the Northeast as a near stationary front begins to drift northward through midweek. Increasing moisture from the building ridge brings increasing chances for showers and thunderstorms by Tuesday and Wednesday as the moisture interacts with the front, with shower chances continuing into Thursday and Friday. A stronger cold front pushes through late in the week, with high pressure building into the weekend and bringing drier conditions. Details... Monday looks to be mostly dry as the front makes its farthest south progression, leaving northern New England on the dry side of the front. By Tuesday, the front begins to drift northward as a warm front, likely extending through the forecast area by the afternoon hours. Scattered showers and storms become more frequent by the afternoon hours near the front, but the exact location of the front at this time remains uncertain. Overall, the progression of the weather features have been trending slower on the ensembles as we get closer in time. This continues a trend we have seen over the last few weeks, and is not uncommon in the summertime as forcing and features are not as well defined compared to the cooler season. So currently central and interior areas look to see the most widespread showers and storms on Tuesday, but this will likely still need to be fine tuned over the next couple of days depending on the progress of the front. Scattered showers and cooler conditions are expected for Wednesday as the front lingers and mostly cloudy skies are expected. By Thursday, a weak wave of low pressure likely moves along the front and helps to enhance the shower and storm activity. This looks like the best chance for the threat of some heavier rainfall, especially in any areas that get worked over in the previous couple of days. Friday is where the slowing of the weather pattern since yesterday shows up most, with chances for showers continuing. Should the speed of the low`s progression be slower, Friday could end up even wetter. With it still being almost a week away, it`s too early to sort out any details with this feature, but the trend for now is that it would be slower to depart. Then by next weekend, high pressure begins to build in from the west behind a more well defined cold front that helps clear out the moisture. Temperatures also begin to rise again by next weekend with this increasing sunshine. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Short Term... Summary: A cold front crosses the region from north to south late tonight and Sunday with clouds and a few showers before much drier air moves into the region with clearing skies late Sunday and Sunday night. Restrictions: VFR conditions are expected to dominate the period through Sunday night. Increased cloud cover tonight will likely limit fog development except at LEB where there is potential for fog just before daybreak. Any shower activity is expected to be light and...while some localized restrictions are possible... confidence is not high enough to include mention of them in this afternoon/s TAF package. Winds: Outside of a robust seabreeze for coastal locations... southwest winds around 10kts will gradually diminish with all sites 5kts or less for the overnight. Winds become northwesterly and increase to 8g15kts for the day on Sunday with some potential for a seabreeze again at PSM. Winds go calm/light-variable Sunday night. LLWS: LLWS is not expected through Sunday night. Lightning: There is a very low /20%/ potential for thunder at CON-PWM-AUG Sunday afternoon. Long Term...Mainly VFR conditions are expected on Monday, and then intermittent chances for restrictions with afternoon showers and storms return for Tuesday through Friday. Periods of marine fog and IFR conditions are also possible through coastal terminals during this time period. Conditions likely improve next Saturday as high pressure brings more steady VFR conditions. && .MARINE... Short Term...Winds and waves are expected to remain below SCA levels through Sunday night. Long Term...A front stalls across the Gulf of Maine and lingers for much of the week. Pressure patterns remain weak most of the week, keeping conditions below SCA levels. Areas of dense fog are possible at times Tuesday through Friday as the front lingers. High pressure then clears the fog by next weekend. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Arnott SHORT TERM...Arnott LONG TERM...Clair AVIATION...Arnott/Clair MARINE...Arnott/Clair