Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 180450 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1250 AM EDT Thu May 18 2017 .SYNOPSIS... Much warmer air is spilling into New England from the west as a ridge of high pressure moves over the Northeast. Expect hot conditions on Thursday with many areas reaching 90 degrees. A cold front will drop through the area on Friday with some gusty northwest winds and cooler temperatures in the afternoon. A shower or thunderstorm is possible as the front arrives. High pressure builds across the region on Saturday with cooler weather. Low pressure arrives from the west on Monday bringing the next chance of widespread significant rainfall. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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1240 AM Update... Have updated the forecast based on current conditions. A mild night in some areas continue with temperatures remain in the 70s over southernmost sections. A southwest gradient and high cloud cover will keep readings on the mild side overnight, leading to hot conditions tomorrow. The air quality alert has been updated and resent. 940 PM Update...SYNOPSIS... No major changes to the forecast for this update. Have adjusted temperatures, winds, and dew points based on current trends. We are seeing good radiational cooling as winds decrease and especially outside areas with more cloud cover. 705 PM Update... Still very warm out there in parts of the region with much of NH in the 80s and even 90 or above at 6 PM. Most of western Maine is in the 70s. Increased overnight temperatures a bit with readings still so warm. Dew points are in the 40s and low 50s. Some echoes showing up on radar are moving into northern sections in association with a short wave disturbance, but the lower levels are quite dry so not adding PoPs at this time. Cloud cover is increasing however and this will also keep temperatures a bit warmer overnight, mainly over northern NH. Previous discussion... The hot weather has arrived. Afternoon temperatures have already hit 90 across interior western New England. Westerly winds have added a downsloping component which has aided in mixing from the Connecticut River Valley region eastward leading to the hot temperatures. Further to the east, an onshore southerly flow has kept conditions in the 70s through much of Maine. Will see some cooling tonight with the loss of daytime heating, but with dewpoints in the 50s in place and a moderate wind continuing expect lows to only be in the 50s and 60s.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... It will be another hot day on Thursday, but this time the whole area will get in on the heat. Westerly flow should keep the coastal cooling confined mainly to the immediate coastline to the east of Portland, and even there temperatures will warm into the 70s and 80s. In the well mixed areas of southeast New Hampshire and southwest Maine expect peak temperatures as warm as the mid 90s. This will likely break daily records at Portland, Concord, and Augusta. Westerly winds may gust to around 20 to 30 MPH at times tomorrow in the well mixed environment. The heat combined with low level moisture (dewpoints in the 60s) will lead to some instability across the region on Thursday. However, expect the ridge to be solidly in place across our area with a capping inversion at about 700MB which will prevent thunderstorms from developing. Further to the northwest near the approaching front there will be better forcing to help erode or overcome this cap. Expect some of this remnant thunderstorm activity to move into northern parts of the area late Thursday evening into Thursday night. Any storms that do form will have plenty of shear to work with, so supercells with a threat for large hail and damaging winds will be a possibility. But again, current thinking is that these storms will be unable to form in our area and thus will not arrive until later, limiting the severe weather threat. With the warm start to the evening and dewpoints in the 60s, expect much of the area to remain in the 60s overnight Thursday night. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... A s/wv trof digging thru New England will drive a cold front across the region Fri. There are pretty significant timing differences between the 17.12z GFS and ECMWF...with the ECMWF being the slower of the two. That definitely brings some bust potential into play with high temps Fri. A slower front will allow parts of the forecast area to get very warm again. At this time...ECMWF forecasts of H8 temps around +15 to 16C would likely mean some mid 80s possible. I hedged more in this direction than the faster GFS. Some showers and thunderstorms are likely with the frontal passage...but given the time of day I do not think thunder will be all that widespread. Strong high pressure moves in Fri night thru the weekend. In addition to breezy CAA behind it...temps will be noticeably cooler over the weekend. Ensemble forecasts show the fresh Canadian air mass to be about normal for this time of year...so I do not expect high temps to be too far from average. It will just feel much cooler after some 90 or near 90 degree days for most people. But a well placed high pressure and H8 temps in the single digits mean that some areas may end up frosty in the morning...so we will have to watch zones S of the mtns for frost headlines. The next chance for rain will be Mon...as an upper low across the central CONUS lifts into Canada. The 17.12z GFS is more robust will trailing s/wv trof and thus has more QPF and a stronger front crossing New England. The ECMWF tends to shear the s/wv out instead...with a weaker front and less QPF. Given that convection across the Plains will play a large role in evolution of this system...I will stick to the multi-model consensus for PoP. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... Short Term...Gusty winds should diminish a bit tonight. Expect a west southwest wind on Thursday with VFR conditions continuing. There could be a few thunderstorms in the northern part of the area Thursday evening into Thursday night as a cold front drops toward the area. Long Term...Cold front crosses the area Fri. SREF probabilities for low CIGs are low ahead of it...but it is possible some marine stratus could form if moisture return is better than forecast tomorrow. Otherwise some MVFR SHRA are possible as the front moves thru. TSRA are possible as well...but timing of the front suggests that threat is less likely. High pressure will bring widespread VFR conditions thru Sun. Another front is forecast to cross the region Mon...which could bring another round of MVFR conditions. && .MARINE... Short Term...Expect a light to moderate southwesterly wind over the waters through Thursday. There could be a few gusts up near 25 KTS at times. Long Term...Persistent SW flow ahead of the cold front may bring seas to around 5 ft Fri outside of the bays. Behind the front CAA may allow for some 25 kt gusts...again most likely outside the bays. High pressure moves in for the weekend allowing winds and seas to diminish. && .FIRE WEATHER... Hot weather spreads across the rest of the area on Thursday. Although dewpoints will be in the 60s, the heat will allow relative humidity to fall to as low as 30 percent during the afternoon with gusty west southwest winds. Expect cooler weather Friday through the weekend resulting in higher humidity levels. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ JC

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