Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 250318 AAD AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1118 PM EDT Mon Jul 24 2017 .SYNOPSIS... Low pressure tracking through the Gulf of Maine tonight will keep rain in the forecast through the evening with lingering showers tapering off Tuesday morning. High pressure builds in from the west on Tuesday and shifts offshore on Wednesday. Some warmer air moves in on Wednesday, bringing temperatures back up to near normal. But a cold front pushes toward the area on Thursday, with low pressure possibly forming along the front bringing another chance of rain and cooler temperatures. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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1117 PM Update... Minor changes to account for current observational trends. Rain has transitioned to heavy drizzle along the coast with any bona fide showers relegated to the mountains and foothills. Shower activity may pick up again as upper level support arrives shortly. 959 PM Update... Shower activity still ongoing across the region as both the 700 and 500 mb lows have yet to cross New England. Expect weak showery activity overnight as this occurs. Euro and GFS20 are more bullish with precip overnight with the HRRR and RAP models much more spotty. The latter models have a better handle on the situation attm and have kept only slight chance or chance PoPs in where warranted. Regardless plenty of low level moisture is still lingering and stratus will continue to be an issue as well as patchy fog and drizzle over southern sections. Temperatures are not going to change much through daybreak with overnight lows just a few degrees lower than they are now. Adjusted the forecast for these broad points. 605 PM Update... PoPs were adjusted as well as stratiform vs. shower wording as rain shield moves to the east and is slowly replaced by lighter and more showery activity. This will also be the case overnight. Also added drizzle over southern portions of NH and SW Maine near the coast where ceilings are around 200-800 ft and not expected to lift for a while. Previous discussion... The large area of steady, moderate rains will continue to exit to the east this evening. This will leave the region with pockets of mainly light rainfall and patchy fog. The latest HRRR continues to show most of the precipitation exiting eastern areas during the 03Z to 06Z range. With the cloud cover and a northeasterly gradient, temperatures will not move all that much from their current readings.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Much of the precipitation will be east of the region on Tuesday. Low level winds will back to the north during the day, allowing for limited drying. However, the upper level low pressure system will remain overhead during this period. Scattered showers will develop as lapse rates increase and surface temperatures reach milder conditions than today, about 70 degrees for many locations. This precipitation will be mainly away from the coastline. The scattered showers will diminish around sunset on Tuesday evening as high pressure builds over northern New England. This will leave the remainder of Tuesday night rainfree. However, plenty of low level moisture will linger over the region, allowing patchy fog to form once again. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... High pressure crosses the area Tuesday night, bringing decent radiational cooling conditions with a dry air mass in place. Temperatures will fall into the 40s and 50s overnight, rather cool for this time of year. High pressure shifts offshore on Wednesday with a return southerly flow developing. This will bring warmer and more humid conditions back into the area, though we will still see temperatures near normal for late July. Models diverge a bit on the handling of the next trough. The GFS sends most of the energy with this trough eastward in progressive fashion to our north, sliding a cold front through our area on Thursday. This would bring a chance of showers and thunderstorms as the front moves through, with less humid but still seasonable temperatures behind the front for Friday. The ECMWF and CMC models, however, are in agreement that the better energy will linger near the base of the upper trough, spinning up a rather strong surface low which tracks across southern New England on Friday. This would send a good chunk of rain headed our way, with temperatures staying quite cool on Friday. Given the newly upgraded GFS is the outlier, it would seem that the ECMWF/CMC might be on to something here. Have tilted the forecast in favor of this scenario for Friday, though uncertainty remains. High pressure builds in behind the departed front/low for the weekend, bringing fair weather and temperatures near seasonal normals but with only moderate humidity. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Short Term...Pockets of light rain and fog will continue overnight, bringing some areas of IFR and LIFR conditions. Ceilings will be lowest along the coast. A gradual lifting of the clouds will occur on Tuesday, but there will still be scattered showers. Long Term...There will be a chance of thunderstorms on Thursday and a chance of more widespread IFR to LIFR conditions in rain on Friday. && .MARINE... Short Term...Prolonged northeasterly flow over the waters will allow waves to build into the 4 to 7 foot range. Increased gradient will allow for wind gusts to 25 to 30 knots along the outer waters. Seas will be slow to subside on Tuesday. Long Term...Winds and seas remain fairly calm over the waters for the next several days as high pressure crosses the Gulf of Maine. A return southerly flow begins on Thursday, with a cold front or low pressure passing through on Friday. Depending on the track of this low, it is possible that advisory level conditions could occur. && .TIDES/COASTAL FLOODING... The astronomical high tide in Portland Harbor is 11.5 feet tonight. Northeasterly winds will allow for a half foot or more storm surge overnight, bringing the storm tide to between 12 and 12.5 feet. Flood stage is 12 feet. Minor flooding is expected along the wharfs and wharf side streets in Portland, Granite Point Road in Biddeford and the Backbay area of Hampton. Nearshore waves building to 4 to 7 feet may allow for some splash-over in Saco tonight. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Coastal Flood Advisory until 3 AM EDT Tuesday for MEZ023-024. NH...Coastal Flood Advisory until 3 AM EDT Tuesday for NHZ014. MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ150-152-154. && $$ NEAR TERM...Hanes SHORT TERM...Cannon LONG TERM...Kimble is the U.S. government's official web portal to all federal, state and local government web resources and services.