Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 230019 AAC AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 819 PM EDT Mon May 22 2017 .SYNOPSIS... A weak cold front will push east through the region tonight. High pressure will build over the area on Tuesday and hold over the region through Wednesday. Low pressure will slowly move northeast out of the Ohio Valley Thursday and pass through southern New England on Friday. Low pressure will shift east into the maritimes Friday night. High pressure will build over the area Saturday through Sunday. && .NEAR TERM /THROUGH TUESDAY/... 8pm Update: Forecast largely in good shape this hour...with some adjustments to current temps/dewpoints/winds to match evening observations but not significant changes. Showers continue to march east with very little flow in their wake /occluded front remains well upstream...seen as a fine line over upstate NY/ suggests little in the way of clearing overnight with fog/stratus expected. Have some concerns that fog could become locally dense if the mid/upper levels can dry out fast enough. LAMP guidance is fairly robust with the fog...but does not have great support from the NARRE-TL and experimental HRRR-TLE. Will continue mention of fog through the night...but will not include dense wording at this time based on these trends. 5pm Update: Primary update is to boost PoPs to categorical in areas of rain ahead of arriving occluded front. Otherwise... forecast is in very good shape. At 18z...a 1004 millibar low was centered north of the Great Lakes with an occluded front extending southward through the eastern Great Lakes and mid Atlantic region. NWS Doppler radar mosaic showed several areas of showers along and ahead of this frontal boundary and upstream of the forecast area. For tonight...the frontal boundary will slide eastward and exit the coastline towards dawn on Tuesday. We`ll see a few showers ahead of this boundary with lingering low clouds along with patchy drizzle and fog for the balance of the overnight hours. && .SHORT TERM /TUESDAY NIGHT THROUGH 6 PM TUESDAY/... On Tuesday...the front progresses further offshore with partly to mostly sunny skies under weak ridging. Highs will be mainly in the 70s...with a few 60s along the Maine coast as the light synoptic flow turns onshore by afternoon. The weak ridge will hold Tuesday night with partly cloudy skies as we remain sandwiched between an offshore baroclinic zone and a second over Quebec Province. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Weak southwest flow aloft will be overhead by mid week as one large trough dominates much of the eastern and central CONUS. Over eastern Canada another cyclone will be pushing onshore and causing flow between the two systems to buckle and eventually prompt the eastern low to eject northeast. At the surface a series of weak troughs connected by a baroclinic zone will stretch from the Canadian Maritimes towards southern New England and into the Midwest. On Wednesday a coastal storm will be filling and moving northeast offshore which night will keep the possibility of showers in the forecast along the coast. Elsewhere high pressure will be in control and there will be a break in the precipitation through early Thursday morning before the next batch of precipitation arrives moving from SW to NE. Even with a break in the rain, expect cool and damp conditions with fog and possibly some drizzle at times in onshore flow. Widespread rain moves in Thursday in associated with the eastern upper low mentioned above and a surface warm front. This will prompt heavy showers through Friday with both the EPS and GEFS indicating high PWAT air and plenty of forcing for ascent available to wring out over an inch of QPF. While the weekend will not be a total washout there will be scattered showers Saturday as a cold front moves through. Broad low pressure will remain active into next week but the details get particularly hard to decipher past day 5. However, scattered showers and below normal temperatures are a safe bet. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Short Term /through Tuesday night/... Summary: An occluded front will push east of the region through daybreak Tuesday with overnight fog and stratus giving way to improving flying conditions on Tuesday...continuing through Tuesday night. Restrictions: Conditions will continue to deteriorate to IFR/LIFR both in low CIGS and dropping VSBYS overnight. Quick improvement to VFR is expected Tuesday morning and continuing through Tuesday night. Winds: Light south and southeasterly winds /less than 10kts/ will become light/variable overnight with light /less than 10kts/ northwesterly winds developing for the day on Tuesday /with afternoon local sea breeze development/ before going calm/light and variable Tuesday night. LLWS: No LLWS expected through Tuesday night. Thunder: No thunder expected through Tuesday night. Long Term...Deteriorating conditions develop on Thursday in fog and perhaps drizzle ahead of bona fide RA which arrives later that day. IFR/LIFR ceilings/vsby Thursday night and Friday. && .MARINE... Short Term /through Tuesday night/...Winds and seas are expected to remain below small craft through the period. Long Term...SCAs May be needed Thursday night and Friday as seas increase above 5 ft. && .FIRE WEATHER... Cool and wet conditions are expected tonight with some drying likely Tuesday and Wednesday before the next low pressure system brings rain Thursday and Friday. && .TIDES/COASTAL FLOODING... High astronomical tides Thursday night (11.8 ft MLLW forecast for Portland), will combine with onshore flow possibly resulting in minor coastal flooding. Another high tide on Friday night (12.0 ft MLLW forecast) will likely again result in minor coastal flooding although winds may be offshore by that time. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...Arnott/Schwibs SHORT TERM...Schwibs LONG TERM...Hanes AVIATION...Arnott MARINE... FIRE WEATHER... TIDES/COASTAL FLOODING...

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