Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 111556 AAC AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1156 AM EDT Fri Aug 11 2017 .SYNOPSIS... A warm, moist air mass will remain across northern New England today, with temperatures above normal and a few showers and thunderstorms. Low pressure over the Great Lakes will move east into Quebec on Saturday, with a few rounds of showers and thunderstorms possible until a cold front moves through early Sunday. Drier air moves in behind the cold front for early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1140 AM UPDATE... Going forecast generally in good shape with largest changes to sky cover /reduce it/ and some adjustment to PoPs for the afternoon with temperatures looking good. High resolution mesoscale guidance trends show best threat for afternoon convection being tied to terrain in NH and western Maine...along southern edge of remnant cool pool caused by morning round of convection. GOES visible imagery shows some growing convection in this area already...so have focused PoPs /still in the chance category/ in this region for the afternoon. Instability parameters look even less impressive than yesterday with H7-5 lapse rates not much above 5-5.5C...so while thunder is certainly likely with any cells that develop...severe convection is rather unlikely...with a marginal llevel wind gust potential given decent 1000-850 mb lapse rates. 815 AM UPDATE... Have adjusted shower/storm coverage based on morning observations...with this activity exiting the area in the next 2 hours. Very minor changes to temperatures to match 12Z observational data. 515AM UPDATE... Area of showers with embedded thunderstorms has expanded in coverage as it moves north. Have adjusted precipitation chances for these areas and downstream to reflect increased confidence in precipitation there. No other changes were needed. ORIGINAL DISCUSSION... A shortwave trough is moving north northeast through the area early this morning, triggering a few showers and an isolated thunderstorm. This will continue to push to the north northeast and will likely be near the Canadian border by 8AM. With this feature moving into Canada and northern Maine, expect shower and thunderstorm chances behind it across our area to be a bit lower, though cannot rule out a pop up shower inland. Temperatures will warm into the upper 70s to mid 80s with a little more humidity than we`ve seen in recent weeks.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Upper trough over the Great Lakes will begin to swing eastward into Ontario and Quebec tonight into Saturday with an embedded shortwave trough tracking through northern New England. This will bring another chance of showers tonight mainly in the northern and western portion of the area. Temperatures fall into the upper 50s to low 60s, a few degrees above normal for this time of year, buoyed by the cloud cover and high low level moisture. Models are still a little chaotic in the finer details of how the precipitation patterns will develop as the upper trough moves into the area on Saturday. The trend seems to favor a break in the showers behind the initial shortwave trough early Saturday, with another round of showers and thunderstorms forming as the main trough axis moves through New York State and into western New England late on Saturday. Cloud cover is currently expected to hold temperatures in the 70s on Saturday, but if we get breaks in the clouds we could see another day of 80s as temperatures aloft remain just as warm as the last few days. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... A weak cold front with an associated upper level trough will gradually cross the region Saturday night. This will bring scattered showers to Maine and New Hampshire with the deepest moisture supply and heavier precipitation remaining well south of the region. Marginal instability may trigger thunderstorms overnight as CAPE values increase. Patchy fog may develop early in the night, followed by some drier air with cold air advection by morning. On Sunday, the upper level trough may trigger an additional shower or possibly a stray thunderstorm over eastern areas. The best dynamics will be limited to northern areas however. As drier air filters into the region on Monday, the chance for any precipitation diminishes as we return to a dry period, particularly for southern areas. Note that portions of south coastal Maine has already been placed in drought status. A very week upper level trough will cross the region late Tuesday. Any widely scattered showers will mainly be limited to northern areas. A stronger upper level low pressure system will pass by well to our north on Wednesday, bringing a slight chance of showers which will once again be primarily confined to northern areas. The next chance for precipitation for all areas, including the coastal drought region will be on Friday. At that time, a large scale upper level trough will approach New England from the west. A slow moving surface trough will approach from the west as well, allowing moisture to feed northward ahead and along the system for Friday night and Saturday. && .AVIATION /16Z FRIDAY THROUGH TUESDAY/... Short Term...Low level stratus will plague the Rockland area early this morning. Generally expect this low level cloud cover to dissipate around mid morning, but it is possible that this continues deeper into the day. Elsewhere, scattered showers and a few embedded thunderstorms will lift into northern New Hampshire and northwest Maine this morning. Another round of showers is expected to move in tonight, possibly bringing some MVFR or IFR conditions mainly to Lebanon and Whitefield. Otherwise, VFR conditions are expected to prevail. Long Term...Low clouds and coastal stratus may move northward off the Gulf of Maine Saturday night ahead of a slow moving cold front. This will lead to IFR conditions with patchy fog during the overnight hours and into early Sunday. Mainly VFR conditions are expected thereafter. Conditions do deteriorate once again late next week as a large, broad scale trough approaches the region and a southerly flow brings low clouds and visibilities from the Atlantic. && .MARINE... Short Term...Expect a light onshore southerly flow through Saturday. Long Term...Winds and seas are expected to remain below SCA thresholds thru this weekend and into next week. && .EQUIPMENT... The weather radar at Gray (GYX) will be down for maintenance for approximately four days, beginning August 12th. During that time technicians will be installing important upgrades. This work has been scheduled to minimize any potential impacts to office operations. During the outage, radar coverage is available from adjacent radar sites including Albany-New York (KENX), Burlington-Vermont (KCXX), Taunton-Massachusetts (KBOX), and Hodgdon-Maine (KCBW). && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Arnott

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