Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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655 FXUS61 KGYX 081440 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1040 AM EDT Mon Jul 8 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 afternoon into Wednesday. A trough will approach from the west Wednesday transporting remnant moisture from Beryl into the region Wednesday into Thursday. Thunderstorms are again possible Friday as a stalled remains over the region. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1040 AM Update...Going forecast is in good shape and have mostly made minor tweaks to PoPs this afternoon and T/Tds to align with observed trends. Latest satellite has shown CU developing over the higher terrain and surface obs show winds have started to turn onshore along the immediate coast. The incoming 12Z guidance does suggest the will be chances for isolated showers this afternoon along the sea breeze boundary focused along and just south of the foothills. 635 AM...Just a few tweaks to temps/sky based on current conds, but overall should be mainly sunny and very warm day, with some relief along the coast from the sea breeze. Previously...Any morning fog along the mid coast or in the sheltered valleys should diminish by 8 AM again this morning. Weak sfc high moves across the CWA between zonal flow aloft, with a slight anticyclonic bend to it, and this should keep things generally sunny and dry today. It will be another very warm day, but the W flow slackens and shifts a little more to the S. This should allow the sea breeze to show earlier in the day and move a little more inland as flow will be more onshore than along shore. Still it wont prevent all but the immediate coastline to get into the 80s but should see highs limited to 80-85 in the coastal zones. While the rest of the CWA will make it to 85-90 again, with low 90s in srn NH. The W flow should keep Tds in the low to mid 60s where temps are the highest, which will prevent apparent temps form reaching advisory levels. Given the sfc instability can;t rule out a shower or two this afternoon in ME, probably along the sea breeze boundary, but strong capping at ~700 MB should prevent any convective showers from producing lightning. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Skies are mainly clear tonight with just some cirrus, but will have to watch for coastal stratus/fog moving in this evening. Given the more direct onshore flow today, theres a better chance fog approaches the shore late in the day and moves onshore once heating diminishes. The best chance for this is mainly from somewhere in York county NE through the mid-coast and this where mins are generally in the low to mid 60s, along with the mtns which should see lows in the lower 60s in many spots. In central and southern NH low will be limited to the upper 60s to around 70 in many areas. Fog may linger a little longer into the morning along the mid coast on Tuesday, but an increasing SW flow should clear it out and also limit the sea breeze somewhat along the entire coast in the afternoon. Increasing low level moisture and very warm temps aloft will push temps across much of the area into the upper to lower 80s. This along with high Tds may require a heat advisory, especially over parts of S NH on Tuesday. The cooler will be the mtns where more clouds are possible and the immediate coast where highs will likely be limited to around 80. Some uncertainty remains for the tempos though as a weak 500 MB trough wave moves through and pulls a very weak cold front into the far nrn zone by Tuesday evening. This could set off some SHRA/TSRA across the CWA, mainly in the afternoon into Tuesday evening. If storms fire up earlier could produce anvil cirrus which will limit max temps to some degree. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... 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 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 /15Z MONDAY THROUGH FRIDAY/... Short Term...Early morning valley and coastal fog fog should burn off by around 8 am again today with VFR expected though about sunset everywhere. A better chance for coastal fog/stratus tonight especially at KPWM/KRKD coming in early in the evening, and may see stratus spread inland to KAUG. Valley fog at KHIE/KLEB expected after midnight. The coastal fog may take longer to burn off Tue morning, but should see VFR by mid morning. TSRA will be possible mid to late afternoon and evening. Long Term...There will be chances for showers and storms most days Wed 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...Fog builds back over the waters today as light becomes onshore, and should thicken late today and overnight. Flow becomes more SW on Tuesday, so fog may become more patch during the day but should return Tue evening. Winds/seas stay below SCA levels through Tuesday. 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...Cempa/Schroeter SHORT TERM...Cempa LONG TERM...Schroeter