Area Forecast Discussion
Issued by NWS Portland, ME

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518 FXUS61 KGYX 190739 AFDGYX Area Forecast Discussion National Weather Service Gray ME 339 AM EDT Wed Jun 19 2024 .SYNOPSIS...
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High pressure will remain east of New England through much of this week, continuing our period of hot and humid conditions through Thursday. Record high temperatures and potentially dangerous heat index values are likely. A cold front will slowly cross through the region on Thursday and Friday with an increasing chance for scattered strong thunderstorms and cooler temperatures starting on Friday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Nighttime microphysics satellite imagery early this morning shows some passing cirrus overhead along with some valley and coastal marine fog that is beginning to develop. Current temperatures are into the 60s and 70s and they will likely drop another degree or so prior to sunrise. It will otherwise continue to be a warm and humid morning. Surface high pressure will remain anchored east of New England today, allowing for southwesterly flow over our region. Warm temperatures aloft combined with afternoon mixing will result in high temperatures into the middle 90s across most interior locations with 70s/80s along the coast and in the mtns. Surface dew points will be into the upper 60s and lower 70s, which will push heat indices into the middle 90s across areas covered under the heat advisory with readings up to around 105F within the excessive heat warning. Latest CAMS continue to show the potential for a few afternoon and evening thunderstorms to develop as a s/wv crosses southern Quebec. Forecast soundings indicate a high CAPE and low shear environment with bulk shear of only around 15 kts. Despite this, inverted-v soundings combined with precip loading and high DCAPE introduces a locally strong wind threat within any stronger storms. Coverage is expected to be spotty though due to fairly weak forcing and a mid-level CAP. The Storm Prediction Center has placed much of our area under a MRGL risk for severe storms this afternoon. Any remaining showers and thunderstorms will diminish this evening, leaving behind another warm and muggy night. Lows will primarily be into the 70s. Fog may develop overnight, especially across the valleys.
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&& .SHORT TERM /THURSDAY/...
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Clouds will increase from north to south on Thursday ahead of a sfc cold front that will cross during the afternoon and evening hours. Ahead of this front, it will be another hot and humid day with high temperatures into the lower to middle 90s away from the coast with 80s in the mtns and the coast. Heat indices will climb up to around 100 degrees for a few hours, which will likely necessitate additional heat advisories. This strong sfc heating will allow for steep low-level lapse rates with MLCAPE increasing to around 2000 J/KG. This combined with 20-30 kts of 0-6km bulk shear and PWATs nearing 2.00" once again introduces the potential for scattered strong to severe thunderstorms. The primary hazard will be locally damaging winds with precip loading but the added shear could also allow for some hail as well. Coverage is likely to be greater than today due to the additional forcing from the passing cold front. The storm Prediction Center has placed much of the CWA into a MRGL risk with a SLGT risk in southwestern NH.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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The cold front will clear the coast Thursday night, bringing an end to the showers and thunderstorms. Lows will range from around 60 across the north to the 70s south. It will be still be warm on Friday, especially over southern NH, but will be much more manageable than the temps today- Thursday with the post-frontal air coming in. Highs are forecast to be in the mid- upper 80s for southern NH and the low-mid 80s for the rest of the area. There will also be a tight moisture gradient with the higher moisture across NH and this area has 30-50% chances for showers while chances decrease to the north and east. Although still running above normal for this time of year, temperatures will follow a cooling trend over the upcoming weekend as heights lower, flow aloft becomes more zonal, and more in the way of clouds are expected. In addition to this, dewpoints will also come down into the 50s for most of the area on Saturday (except lower 60s in southern NH) before creeping back upward into the 60s on Sunday. Highs on Saturday are forecast to be in the upper 70s to lower 80s, and these may increase by another couple of degrees by Sunday as southerly flow starts increasing ahead of a cold front. This is certainly good news after the hot weather this week. There is another chance for shower late Saturday into Saturday night as energy aloft moves overhead, but due to confidence have stuck with NBM of 40-50% at this time. A better chance for more widespread precip and possibly a few storms arrives late Sunday and into Monday as a more potent upper trough pushes a cold front through New England. Assuming the front pushes through as advertised (decent agreement in the models this far), we should see drying conditions by next Tuesday or so.
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&& .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
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Short Term...Patchy FG and low ceilings will continue to result in the potential for IFR to LIFR restrictions through around 12Z, mainly at KLEB. Otherwise, VFR conditions will prevail today with southwesterly winds at 10-15 kts. Scattered TSRA are possible this afternoon and any storm may contain locally strong winds and restrictions. Patchy FG will once again be possible tonight, which will result in IFR to LIFR restrictions through early Thursday morning. VFR conditions early Thursday will be followed by a greater chance for scattered TSRA in the afternoon and evening. Some LLWS is possible late tonight into early Thursday. Long Term...For Friday and Saturday, precip chances look lower overall, but the better chances will be across the NH terminals. A cold front approaches Sunday into Monday with chances for widespread precip and restrictions.
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&& .MARINE...
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Short Term...Southwesterly winds will prevail today through Thursday with gusts between 15-20 kts. A few gusts to around 25 kts are possible across the outer waters. Seas will be at 3-4 ft and marine fog will be possible, especially at night. Long Term...Broad high pressure remains over the waters Friday and Saturday before southerly flow potentially exceeds SCA levels Sunday into Monday as a cold front approaches.
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&& .CLIMATE...
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RECORD HIGHS FOR JUNE 19: Concord-98 in 1995; Augusta-98 in 1995 Portland-94 in 1995 RECORD WARM LOWS FOR JUNE 19: Concord-69 in 2017,1876; Augusta-72 in 1995; Portland: 72 in 1995 RECORD HIGHS FOR JUNE 20: Concord-98, 1993 Augusta-95, 1953 Portland- 93, 2020 RECORD WARM LOWS FOR June 20: Concord-73 in 1931; Augusta-67 in 1974; Portland-69 in 2020
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&& .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Heat Advisory from noon today to 8 PM EDT this evening for MEZ007>009-022>028. Excessive Heat Warning from noon today to 8 PM EDT this evening for MEZ012>014-018>021-033. NH...Heat Advisory from noon today to 8 PM EDT this evening for NHZ001>003-005-007-011-014. Excessive Heat Warning from noon today to 8 PM EDT this evening for NHZ004-006-008>010-012-013-015. MARINE...None.
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&& $$ NEAR TERM...Tubbs SHORT TERM...Tubbs LONG TERM...Combs