Area Forecast Discussion
Issued by NWS Portland, ME

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800 FXUS61 KGYX 122244 AFDGYX Area Forecast Discussion National Weather Service Gray ME 644 PM EDT Fri Jul 12 2024 .SYNOPSIS... A mid level disturbance will bring a few showers and thunderstorms to the region tonight and on Saturday with sun breaking through the clouds by Saturday afternoon. Drier air works into the region for Saturday night and Sunday though temperatures will climb. Humidity will increase on Monday and Tuesday before a stronger cold front arrives Wednesday with the potential for some showers and thunderstorms before cooler and drier conditions arrive to end next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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640 PM Update...Not much to update at this hour other than performing a very minor refresh of temps and dewpoints to match observations. Conditions remain sultry out with not much relief overnight with temps still expected to remain in the upper 60s to lower 70s south of the mountains for lows. Another shower or two may develop along a seabreeze/outflow boundary interaction over the next hour or so over toward Skowhegan/Waterville, but otherwise dry conditions will prevail through the remainder of this evening before another wave brings increasing chances for showers/storms after midnight, especially across NH. Previous... High Impact Weather Potential: Isolated heavy rain potential after midnight tonight. Pattern: A deep plume of mid level moisture is evident on early afternoon water vapor imagery...squeezed between a shortwave moving through the Great Lakes region and an upper level low sitting off the Mid Atlantic coast. This upper low...as it spreads north is pushing a stalled frontal boundary back northward allowing a 2" PWAT airmass to nudge back into southern NH and southwestern ME. The offshore upper low will weaken as it moves north tonight... eventually being pushed east by the Great Lakes shortwave as to moves just north of New England overnight. Forecast concerns will center on any shower/thunderstorm potential along the frontal boundary that will be draped across the forecast area. Through this evening: Warm/humid conditions continue this afternoon with a few showers located just north of surface front draped near the mountains. These will wane through early evening. Temperatures will remain rather warm through 8pm...with values still at or above 80 for much of southern NH and SW ME with 70s elsewhere. Tonight: Height falls associated with both the Great Lakes shortwave and the wave to our south move overhead with WSW flow riding over the stalled frontal boundary across the region. PWATs south of the boundary will be over 2" with MUCAPEs over 500 J/kg. The mesoscale guidance indicates that the setup should be sufficient for a few showers and thunderstorms to develop overnight. CAPE plumes are skinny so expect the greatest threat they would pose would be heavy rainfall. Coverage for any shower/storm activity looks to be isolated-scattered. Will mention the localized flood concern in the afternoon hazardous weather outlook.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... High Impact Weather Potential: Localized heavy rain threat through mid morning. Pattern: Upstream shortwave just north of the area to start the day will push east...crossing northern Maine towards evening with the flow aloft turning northwest behind this feature Saturday night. This shortwave will interact with moisture along the coast to produce the potential for showers and thunderstorms before a cold front settles offshore Saturday night drying out conditions. Forecast focus will be on the shower/storm coverage and any potential for heavy rainfall along with the impact of the clouds/precip on temperatures. Saturday: Overall trend in the mesoscale guidance over the past 24 hours has been to decrease the heavy rainfall threat for Saturday morning as we actually sit in a bit of a forcing lull by mid morning as the offshore wave departs...which also acts to shunt deeper moisture plume east of the region in the morning. A weak surface low along the stalled frontal boundary over PA/NJ early Saturday rides ENE during the day which keeps any associated training convection over southern New England and points south. The proximity of the northern stream wave should allow for some scattered convection to develop during the day but the deeper moisture plume will have pushed east and overall MLCAPEs will be rather limited as significant cloud cover should persist through the morning into early afternoon. T8s will be around +15-16C...which would support mid/upper 80s...and given some increasing sun for the second half of the day...expect that we/ll reach these values. Saturday Night: Surface cold front pushes offshore overnight allowing somewhat drier air to filter into the region with clearing skies. This should allow temperatures to fall into the 60s throughout the forecast area which should allow a bit more relief then the previous few nights. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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A persistent period of hot, hazy and humid weather will continue until a potentially significant change in the weather pattern arrives late next week... We begin the long range portion of the forecast on Sunday with operational models and ensemble solutions suggesting a large and significant upper level ridge remaining off the seaboard. This will leave the region with hazy, hot and humid conditions over the region. Temperatures will likely reach 90 degrees across the interior and along the coast from approximately Portland and points south along the shoreline. This may be the start of the first heat wave for portions of the coast, and a continuation of persistent heat waves across the interior. This will also be the first day of the return of hot conditions after one day of clouds and slightly less warm conditions from the start of the weekend. Hot temperatures return to the interior once again on Sunday, in areas where heat indices have been skyrocketing over the last couple weeks. After the short reprieve, this will be a renewed period of heat wave conditions for much of the region. While seabreezes will likely cool off the shoreline slightly during the afternoon, this warm spell will be noted by more of a westerly flow aloft, potentially allowing temperatures to reach 90 degrees in the Forest City as well as much of the southwest coast of Maine and Seacoast of New Hampshire before any onshore winds develop. Surface dew points will be slightly lower than this past week, but nevertheless, hot and humid conditions will lead to a prolonged period of stressful conditions for outdoor activities and areas without proper air conditioning. By Monday, heights aloft will gradually be lowering without any defined short wave in place. This will allow for a primarily afternoon, diurnally driven scattered shower and with sufficient instability, perhaps a thunderstorm or two. Temperatures will be outright hot with lower to mid 90s expected in all portions of the forecast area. The only exceptions will be the higher terrain in the mountains and the Midcoast area of Maine where onshore winds will allow readings to remain in the 80s. It will be humid with dew points continuing in the upper 60s, which is actually a very mild improvement from the lower to mid 70s dew points recorded much of this week. Tuesday will be similar to Monday in terms of the chances for precipitation and hot and humid temperatures across the region. Tuesday may be day 3 of 90 degrees or higher in a row in Portland which would be potentially its first heat wave of the summer, while the interior continues its heat. This all comes with sunshine, good mixing and H8 temperatures near +18C. During the muggy period, expect periods of patchy fog. This will be most likely during the overnight periods along the interior valleys and also potentially near the coastline. More heat on Wednesday with perhaps more scattered showers and storms. Temperatures have the potential to hit 90 or above many areas. However, model ensembles suggest a significant pattern change at this juncture as an upper level trough builds towards the region. Canadian high pressure may build into the region for the later portion of the weak, bringing cooler and much drier air to the forecast area.
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&& .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Short Term... Short Term /18Z Today through Saturday Night/... Summary: A stalled frontal boundary across the area will bring a few showers...thunderstorms and deteriorating conditions overnight with a few additional showers and storms for the day Saturday before drier air brings improving conditions Saturday night. Restrictions: Generally VFR attm and this should prevail through midnight. After midnight...there is the potential for some low clouds and fog along with isolated-scattered showers/thunderstorms south of the mountains. These will continue into the early morning hours Saturday with improvement to VFR for the day. An isolated thunderstorm is possible AUG-RKD Saturday afternoon with additional isolated restrictions. VFR Saturday night. Winds: South and Southwest winds 08G15kts will diminish to 5kts or less tonight before becoming southwest 5-10kts for the day on Saturday. Winds shift to the northwest around 5kts Saturday night. LLWS: No LLWS expected through Saturday night. Lightning: Isolated thunderstorms possible after midnight tonight through the morning hours Saturday with a low potential for an additional thunderstorm Saturday afternoon from AUG to RKD. Long Term...Mainly VFR conditions through much of the period. There will be a chance for IFR conditions in any scattered showers or thunderstorms mainly during the afternoon periods. The exception will be Sunday when conditions will be dry all areas. Patchy fog will continue, mainly at night and mainly over the interior valleys and perhaps the coastline. && .MARINE... Short Term...Residual seas and marginal winds necessitate SCAs for the outer waters from Cape Elizabeth north through tonight. Winds/wave should remain below SCA levels Saturday and Saturday night. Long Term...South to southwest winds will continue through the weekend and into much of next week. Winds and seas should remain just below SCA thresholds each day with sea breeze circulations increasing the gradient and resultant wind fields during the afternoon periods. Patchy fog expected mainly during the nighttime and overnight periods. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ150-152.
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&& $$ NEAR TERM...Arnott/Combs SHORT TERM...Arnott LONG TERM...Cannon