Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 181521 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1121 AM EDT Tue Jul 18 2017 .SYNOPSIS... Bermuda high pressure will bring a southerly wind flow to New England today through Thursday, transporting warm and humid conditions into the region. A series of cold fronts will begin moving in from the northwest later this week, cutting back on the heat and humidity. The strongest of these fronts will move through on Friday, with this front stalling near southern New England this weekend. Several areas of low pressure are expected to track along this stalled front this weekend, bringing several rain chances late in the weekend through early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1100 AM Update... Ocean stratus and fog continue to lift and clear late this morning across the forecast area although mid coast areas of Maine will likely remain in the clouds through early afternoon. Remainder of the area should see the clearing trend continue. Have backed off on afternoon showers and thunderstorms with the most likely areas to see convection in the far north and far eastern zones. Forecast K indexes drop off dramatically through 18z especially in southern New Hampshire and southwest Maine. PWAT`s showing a similar trend as upper trough heads east. Have adjusted pop and wx grids to reflect current thinking and radar trends. Aside from a fewtemp/td/sky grid tweaks...no other changes planned attm. Prev disc... Update... Have updated the grids and issued a dense fog advisory earlier this morning based on current observations and trends. Much of the Maine coastline will continue to have visibilities a quarter mile or lower. This will slow down travel and make for a difficult commute this morning. Have also included thunderstorms for eastern areas where a few lightning strikes have develop along a line north of Augusta. More showers and scattered thunderstorms, some with locally heavy rainfall, will develop later this morning and through the afternoon. Prev Disc...The proximity of the upper level trough will be sufficiently close enough to our forecast area as it departs to produce more scattered showers today. The instability increases once again today with high values of CAPE and relatively steep lapse rates mainly over southern areas away from the coastline. A few of the storms may contain locally very heavy rainfall. There will be areas of fog early that will need to mix out. Eventually, partial mid July sunshine will yield max temperatures in the lower to mid 80s over much of New Hampshire and adjacent portions of interior western Maine. Less sunshine and the influence of a maritime layer will keep areas outside interior western Maine in the 70s, with the coolest location once again the Midcoast region.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/ ...
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Fog redevelops tonight, however perhaps not as widespread or dense as the low level flow attempts to become more westerly with time. Dew point values will remain sufficiently high to keep most areas in the 60s for overnight lows. On Wednesday, this developing westerly flow aloft allows H8 temperatures to peak out at +16C. With sunshine across the region, expect very warm temperatures with readings topping out at 90 degrees over portions of southern interior New Hampshire. 80s can be expected most elsewhere, with the Midcoast region cooler, in the lower 70s near the shoreline. Dew points will remain in the mid to upper 60s as well, making it feel a few degrees warmer.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... Broad scale flow pattern this week features a large ridge of high pressure over the Great Plains where building heat will warm temperatures into the low 100s. Another ridge covers much of the Atlantic with a rather persistent high center near Bermuda. In the weakness between these two ridges, a weak trough persists over the East Coast of the US which has brought a few rounds of showers and storms the past few days. The core of the jet stream remains near or just north of the Canadian border, with the warm and muggy conditions spilling northward into New England. Meanwhile, to the north of the Westerlies up in the Arctic a series of large upper lows will meander around the northern latitudes, with the northern Canada low eventually making progress southward across Hudson Bay and into Quebec late in the week. As this low moves south it will send a series of cold fronts through New England, with the jet stream shifting south over New England. This will put us within or to the north of the storm track late this weekend and into early next week, leading to cool temperatures and frequent rain chances. Trying to time the various fronts which move through our region later this week is particularly difficult as the waves which drive these fronts through the Westerlies are not very well resolved by the various models. The impact on the forecast comes into play if one or more of these fronts were to move through during the daytime, providing greater support for showers and thunderstorms. The greatest air mass change does not come until Friday or Friday night when the heat and humidity finally gets shoved out of here, being replaced by cooler and less humid weather for Saturday. The front stalls somewhere near southern New England this weekend, with several areas of low pressure tracking along this meandering front through early next week. With the storm track generally to our south, expect temperatures to trend below normal with several chances for rain late this weekend and into early next week. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Short Term...IFR/LIFR ceilings/vsby early this morning...then becoming VFR. Area of MVFR conditions tonight. Long Term...Generally expecting VFR conditions but cannot rule out afternoon showers and thunderstorms. The best chance may be on Friday afternoon. && .MARINE... Short Term...Winds and seas will remain below Small Craft Advisory thresholds. Have added areas of dense fog to the coastal waters forecast for this morning and added this in the Hazardous Weather Outlook product. Long Term...Expect a light southerly flow over the Gulf of Maine through most of the week. A cold front moves through on Friday with high pressure building in behind it. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...None.
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&& $$

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