Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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775 FXUS61 KGYX 171103 AFDGYX Area Forecast Discussion National Weather Service Gray ME 703 AM EDT Wed Jul 17 2024 .SYNOPSIS... Another day of heat, humidity, and storms today, but change in pattern will bring relief through late week. A cold front passes this afternoon and evening, bringing drier and somewhat cooler conditions for the end of the week into the weekend. High pressure builds in from the west with mostly dry conditions forecast. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7am Update...Not many changes here this morning, most areas start sunny which will aid in meeting Heat Adv criteria once again today as well as adding some instability for storms this afternoon. Bumped up wording to include damaging winds in the SPC SLGT Risk area for this afternoon. Previous Discussion... Another hot and humid start to the day, but dry. This should be the last of our stretch of widespread temps reaching the 90s before cold front arrives later. Trend beginning this afternoon will be increasing shower and strong to severe storm coverage, some containing gusty to damaging winds...and all the potential for very heavy downpours. Despite a late afternoon/evening MCS passing through Tuesday, the hot and humid airmass remains overhead. Temperatures should again quickly rise into the 80s and lower 90s through the late morning and early afternoon. Remaining humidity will make it feel like mid to upper 90s for most interior locations from NH into south central ME. A bit more onshore flow may save the immediate coast from these temps. An approaching cold front this afternoon will be the first step to replacing this airmass, but it won`t happen without consequence. Scattered thunderstorms should be developing along the VT/NH and ME/QC border by early afternoon. For now, CAMs resolve these in multicell clusters roughly oriented along a line as the front moves east. Storm motion is such that cloud layer vectors are quick and from the SW, resulting in potential training along an axis across the interior into mid afternoon. So the greatest chance for precip through much of the afternoon will lie inland from the coast. This should change come the evening as this activity is forced NE. Into these hours, expect the multicellular aspect to shift more stratiform or perhaps a smaller scale bowing segment punching northeast that brings thunder chances to the coast as well as the waters. With wind damage fresh on our minds from storms Tuesday, this will again be a threat this afternoon. The building temps should steepen low level lapse rates, increasing dewpoint depression and building a prominent inverted V signature in area soundings. This is built below a fairly moist sounding with ample DCAPE approaching 1000 j/kg. ThetaE vs. pressure difference between the surface and upper levels is around 20-25, which is another good indicator for storm containing gusty to damaging winds. High freezing level and somewhat limited CAPE should stem severe hail, but can`t rule out smaller sizes in the stronger storms. Expect an interior corridor of these storms with strong winds to be focused from the ME capitol region, down through the ME/NH Lakes region and then southern NH. This was hinted at above, but training storm motion in this very humid and warm environment will also lead to storms containing torrential rainfall. Repetitive storms moving over the same locations will lead to a flash flood threat. A greater chance of this looks to be from SW NH through to the Kennebec Valley of ME. Again, this looks like where a corridor of storms slows before continuing east later in the evening. HREF ens max brings some values of 2 inches in 3 hours across southern NH and the Kennebec Valley, and has been fairly consistent showing this signal. This is closer to flash flood guidance for the ME locations (particularly wet over the past week), but southern NH also received up to 1.5 inch Tues evening with passing storms. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Storm intensity should be waning later in the evening with loss of daytime heating and passing front. Heavy rain threat should wrap up around midnight as long as no remaining clusters of slow moving storms linger. Otherwise skies begin to thin from west to east. A few lingering showers will be possible across central ME Thursday, but instability is largely kept capped with drier air and warm temps aloft relative to sfc. Less humid air will be in the region, but it will still be warm. A start to relief regardless. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... More comfortable lows are on the way for Thursday night thanks to the drier air, mostly clear skies, and light winds behind the cold front. Most should see lows in the 50s with upper 40s even possible across the northern valleys. A period of pretty quiet weather is expected from Friday through the weekend with high pressure largely in control along with a dry airmass. There will be a chance of showers late Saturday as a weak cold front crosses through, but this looks mainly confined to northern areas, and moisture does not look particularly favorable with this system at the moment. While temperatures will be "cooler" than what we have been experiencing lately, highs in the 80s are still forecast each day, possibly close to 90 degrees for southern areas on Saturday ahead of the frontal boundary. The silver lining is that dewpoints will be lower to make the warm temps more manageable, and temperatures will be able to cool off more at night. We`ll probably have some valley fog at night/early morning, too. Mostly dry conditions look to start out Monday of next week, but after that global models are in pretty decent agreement showing a broad low pressure approaching the OH Valley/Great Lakes region. Out ahead of this system, moisture will be on the upswing, and a warm front lifting northward toward New England will increase chances for precipitation toward the end of the forecast period (late Tuesday or even slightly beyond into Wednesday). This is supported by the GFS/ECMWF ensembles, and the NBM showing increasing PoPs on Tuesday looks good. && .AVIATION /11Z WEDNESDAY THROUGH SUNDAY/... Short Term...Spots of MVFR ceilings early, becoming VFR today. Rounds of showers and storms will be possible for the interior terminals, some containing vis reducing rainfall as well as strong winds. Showers linger through midnight, with a cold front passing and expected wind shift. A trend back towards MVFR or even IFR is possible late tonight, with VFR Thursday. Long Term...Mainly VFR Friday through the weekend with the exception of nighttime/early morning valley fog. A weak front approaching from the north late Saturday could bring a few showers to northern areas, but this would be primarily for HIE. && .MARINE... Short Term...A cold front approaches the region today, passing late tonight into Thursday morning. This could bring a round of storms to the waters later, which fog may preempt. These storms may contain gusty winds. Long Term...Winds switch to NW to N into Thursday night, but these will become onshore by Friday afternoon as the seabreeze develops. Another weak front crosses late Saturday and could result in another brief wind shift to the NW. High pressure then settles over the waters Sunday into Monday before low pressure brings increasing precip chances by Tuesday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Heat Advisory from noon today to 6 PM EDT this evening for MEZ012-018>024-033. NH...Heat Advisory from noon today to 6 PM EDT this evening for NHZ004-006-008>010-012>015. MARINE...None. && $$ NEAR TERM...Cornwell SHORT TERM...Cornwell LONG TERM...Combs