Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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863 FXUS61 KGYX 080247 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1047 PM EDT Sun Jul 7 2024 .SYNOPSIS... High pressure will maintain mostly dry conditions through Monday with very warm and humid conditions continuing for much of the week. A stationary front wavering over the Northeast will provide a focus for showers and storms Tuesday into Wednesday. A trough will approach from the west during the second half of the week transporting deep moisture into the region as well as bringing more widespread showers and thunderstorms Thursday and Friday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 1045 PM Update... Minor changes to reflect latest observational trends. The marine fog bank is beginning to move towards the islands of the Mid-Coast and this inland trajectory is expected to continue through the night. Valley fog is also likely to develop as temperatures radiate some. Previously... 645 PM Update... The inherited forecast remains in good shape with only minor adjustments made based on latest observational trends. It will continue to be a dry evening for most with gradually cooling temperatures. Previously... A stalled front continues to sit just offshore this afternoon, and will remain nearly stationary through the overnight. This keeps dew points higher closer to the coast, while western and northern areas see more mixing and dew points dropping into the low to mid 60s. Some isolated pop up showers are showing up across the higher terrain, but these are expected to quickly tapper off around sunset. Closer to the coastline, fog is likely to move onshore again through the evening hours across the MidCoast, and may also do so along the southern coastline after midnight. Radiation and valley fog is expected to develop again tonight across interior locations as skies remain mostly clear. && .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/... Tomorrow looks quite similar to today overall, except for a slightly stronger sea breeze along the coastline. A ridge axis crests the area in the early morning, allow for the sea breeze to more easily develop by the late morning hours, keeping highs confined to the 70s to low 80s near the coast. Away from the coast and outside of the higher terrain, temperatures warm back into the upper 80s to low 90s again under mostly sunny skies. A weak mid level trough swings through during the afternoon hours, and is likely to kick off some isolated showers across the higher terrain and parts of Central Maine tomorrow. Otherwise, conditions look fairly quiet for tomorrow. Clouds and some leftover shower activity begin to drift into southwestern NH late tomorrow night as moisture begins to increase across the area. Lows bottom out near 70 across southern NH, while most other locations dip into the 60s. Patchy fog is likely to develop again tomorrow night as our pattern remains fairly consistent && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The 500 mb pattern across North America will feature a pronounced ridge along and west of the Rockies, a downstream trough, and a ridge in the western Atlantic to start the long term period. A warm and humid airmass will be in place Tuesday with a stationary front wavering over the area providing a focus for showers and storms into Wednesday. The main story in the long term period will be the poleward transport of deep tropical moisture from Beryl within the aforementioned trough over the central US. Global models and ensembles are in decent agreement that the ridge in the western Atlantic will hold firm while the trough over the central US gradually moves east through the end of the week. The eastward migration of this trough will start to transport some of this deep moisture into the Northeast with increasing forcing for ascent Thursday and Friday. The pattern de-amplifies next weekend suggesting a drying trend while disturbances aloft will maintain low PoP in the forecast through the end of the period. Tuesday will be very warm and humid with highs into the upper 80s to low 90s with dewpoints near 70 degrees south of the mountains. This will bring heat index values into the mid 90s for portions of southern NH and interior SW Maine. The forecast challenge for Tuesday is the amount of cloud cover as there is a large spread in both global models and CAMs with some showing mostly cloudy skies for much of the day and others showing mostly sunny skies through Tuesday morning. This cloud cover will have implications for both high temperatures as well as instability for thunderstorms. Most model solutions suggest there will be scattered afternoon thunderstorms, while those with less in the way of cloud cover suggest a few strong to severe storms cannot be ruled out with ample SB CAPE and decent deep layer shear. A short wave rotating through Quebec will act to shift the stationary front offshore for a drying trend Tuesday night into Wednesday morning. The trough over the central US will lift northeastward towards the Great Lakes Wednesday. By this time Beryl will be a post tropical low with the trough advecting a plume of anomalous PWATs towards the Northeast. This moisture will lead to mostly cloudy skies Wednesday with PoPs increasing Wednesday afternoon. Global models are in decent agreement that the plume of highest PWATs will be on the order of 2 to 2.5 inches while the northward extent of this plume remains somewhat in question. Nevertheless, ensembles suggest that PWATs will likely exceed the 90th percentile across much of the area Wednesday night through Thursday night. All the while forcing for ascent will increase with the approaching trough and the right entrance region of a jet streak sliding overhead. While much will need to be ironed out over the coming days, there is a growing signal for heavy rain impacting the region centered on Thursday. The trough will linger west of the region Friday maintaining chances for for showers and storms. This trough eventually weakens and lifts northeast of the area going into Saturday with PoPs decreasing through the weekend. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... Short Term...VFR conditions likely give way to IFR and LIFR in fog at RKD and AUG again tonight, with valley fog bringing LIFR to LEB and HIE again tonight. PWM and PSM likely see restrictions from fog as well, but this is lower confidence and may be more intermittent. VFR returns tomorrow morning for the day, and then fog likely returns again tomorrow night to the same terminals. Long Term...There will be chances for showers and storms most days Tuesday through Friday with restrictions likely in this activity. Thursday will likely have the most widespread activity and resultant flight restrictions. A humid airmass in place will also bring the threat for fog most nights. && .MARINE... Short Term...A stalled front keeps locally dense fog ongoing across the waters, especially toward the MidCoast and farther east. Intermittent fog likely continues into tomorrow night as moisture increases again on southerly flow as a weak area of high pressure moves east of the waters. Long Term...High pressure in the western Atlantic will maintain southerly flow over the waters for much of the week while gusts look to remain at or below 20 kts. Seas also look to remain below SCA thresholds through the period. A humid airmass will remain over the Northeast bring the threat of marine fog over the waters most nights. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Tubbs