Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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569 FXUS61 KGYX 161046 AFDGYX Area Forecast Discussion National Weather Service Gray ME 646 AM EDT Tue Jul 16 2024 .SYNOPSIS... Heat and humidity build for the next few days as high pressure strengthens off the Eastern Seaboard, with chances for scattered afternoon or evening showers and thunderstorms each day. A cold front moves through late Wednesday through Thursday, bringing drier and somewhat cooler conditions for the end of the week and going into the weekend with high pressure building in from the west. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 645am Update...Shower activity shifted east overnight, with mainly light showers. The exception was a rather large storm that moved through the western ME mountains dropping around an inch of rain in 45 minutes with plenty of lighting. Still a couple light sprinkles for the morning, but otherwise turning dry. Previous Discussion... An active couple days ahead considering continuing heat and a round or two of potentially strong storms. Mild temps overnight will again allow a quick start to the heat today. Once morning clouds clear out of regions away from the coast, temps again boost into the lower to mid 90s, with heat indices pushing into the mid to upper 90s for many interior and south coastal regions. No changes to the Heat Adv at this time, although some trends are weaker with onshore winds towards the Midcoast today. This could result in a few hours of heat index values into the mid 90s here. Expect a mostly sunny day outside of the mountains after mid morning. Other talking point today will be late day convection. Limited moisture and warm temperatures aloft will keep a lid on rain chances for much of the day. This could change when forcing arrives from the west, perhaps in the way of a mature MCS this evening. These are notoriously hard to track at this range...largely dependent on how the wave of energy evolves over the past 12 hours. Current suite of short range guidance does bring showers/storms towards the NH/VT border this evening. Sfc CAPE remains the most robust across central to southern NH through mid evening amid ample shear. If this line of storms forms and continues to progress east, it should lose some punch as surface inversion will be growing in southern ME. Thus focused gusty wind wording mainly west of the ME Lakes Region. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Complex of showers and storms will be ongoing this evening and into the overnight period. Should see a gradual weakening of thunderstorm intensity and coverage as the night wears on. Kept the mention of thunder for first half of the night as elevated CAPE remains amid the added forcing. Still will have plenty of moisture in the region as the wave passes. PWATs climb above 2in and warm cloud depth exceeds 12kft along with low associated LLJ. Thus expect these storms to contain heavy downpours. As long as storms keep moving amid the strong LLJ and training does not occur, would expect higher amounts to remain at or below a localized inch of QPF. Wednesday will again be hot, but added cloudiness or daytime showers/storms creates some uncertainty on if another day in the 90s will be achieved. NBM and ensemble guidance keeps the hot temps in the region, and went with these for now. Slightly improved lapse rates and earlier moisture could pave the way for additional strong storms Wed. Widespread deep layer shear remains in the region, and still won`t be lacking in the moisture department. Cold front should approach near or just after peak heating for the day, thus decent chance of seeing good instability. While Tuesday`s storms will be fresh on mind, another round may be in store Wednesday packing gusty winds and heavy rain. 00z HREF does have pockets of heavier QPF with this round, perhaps with localized values of 2 to 3 inches in these storms. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Models have been fairly consistent over the last few days for breaking the heat wave come Wed night and Thursday as a more localized -NAO sets up over Greenland and the Atlantic poleward of 50 N. This does help break down the ridge, but there is so much warm over central and western Canada that there really isn`t much of source to cool things down, but itll be more along the lines of less warm, with temps running normal or a little above. However, once we clear the hot air out, it will be mainly dry Friday into early next week, with daytime temps mostly in the 80s, and overnight light in the mid 50s to mid 60s. Thu will also depend on what happens with the passing front, but, as we often see with cold fronts in the summer, if it doesnt get through before dark, it will likely not mix down until nest morning, and because we may rain overnight into Thu morning, may not see the drier air mix down until later in the day, so, while it will not be as hot but itll still be humid. The good news is, we should see the effect of that cold front by Thu night with clearing and lower humidity, with mins in the mid 50s in the mtns to 60 to 65 in the S. Friday through the weekend will be dry and sunny. More comfortable RH are expected Fri with highs 75-80 in the mtns and low to mid 80s in the S and lows Sat morning in the mid 50s to low 60s. Sat and Sunday will be a few degrees warmer, with highs mostly in the 80, but will start to see the RH creep up a bit by Sunday. Monday looks dry and warm as well. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Short Term...Some fog along coastal terminals tonight and early Tue morning. This should retreat to the waters during the day with VFR conditions. A round of showers or storms could affect NH terminals this evening, moving east overnight. Could see some valley fog develop Tues night. Showers and storms again develop Wed afternoon, perhaps a bit more widespread as a cold front approaches. Long Term...Sct TSRA will develop inland during Wed afternoon as a front approaches and move through Wed night. This is the best to see several hours or more of flight restrictions as fog settles in behind any rain that does fall. Flight restrictions could linger into Thu morning, but should see improvement to VFR during the afternoon. Thu night through the weekend will be mainly VFR, the only exception being late night valley fog. && .MARINE... Short Term...Waves and gusts generally below SCA. There will be some shower/storm complexes moving through Tue/Wed afternoon/evening which could bring gusty winds, lightning, and heavy downpours to the waters. Otherwise, marine fog develops tonight and may weaken some Tuesday. A cold front approaches the waters Wed afternoon. Long Term...Generally winds/seas stay below SCA levels through the coming week, but could approach SCA gusts/seas Wed night into early Thu. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Heat Advisory from noon today to 8 PM EDT this evening for MEZ012-018>024-033. NH...Heat Advisory from noon today to 8 PM EDT this evening for NHZ004-006-008>015. MARINE...None. && $$ NEAR TERM...Cornwell SHORT TERM...Cornwell LONG TERM...Cempa