Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 191314 AFDGYX Area Forecast Discussion National Weather Service Gray ME 914 AM EDT Sat Aug 19 2017 .SYNOPSIS... A slow moving cold front will approach the region today...crossing the area this evening. High pressure will build in from the west tonight through Monday and will slide offshore on Tuesday. A cold front will move in from the west Tuesday night and will cross the region on Wednesday. High pressure will build in behind the front Wednesday night through Friday. && .NEAR TERM /UNTIL 7 PM THIS EVENING/...
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910 AM...Slow improvement today from west to east as somewhat drier air begins to work in and the low cloud gradually burns off. For this ESTF update...I made minor adjustments to reflect current mesonet as well as satellite trends. Prev disc... 621 AM Update: Minor changes to the forecast this hour to follow morning temperature/dewpoint observations as well as some light shower activity weakening over western Maine. Patchy fog continues...but has been highly variable in space and time. Expect a few more changes once we get a few more visible satellite images to get a better feel for cloud cover above the low stratus and fog. Original discussion below... High Impact Weather Potential: Moderate rip current risk along area beaches. Otherwise...minimal. Current Pattern: Current surface map places low pressure over western Quebec with cold front trailing this feature south through upstate New York and through the Mid Atlantic. East of this cold front...and warm front is draped from west to east across southern New England...responsible for /by far/ the most significant widespread rainfall in well over a month. A weak wave of low pressure formed along this front overnight and has helped push the front back south with northerly flow having overspread much of southern Maine and New Hampshire. Still...southwesterly flow aloft /ahead of Great Lakes shortwave/ over this cool dome continues to spawn a few showers. Southwesterly flow will continue across the forecast area today...with aforementioned warm front moving/mixing northward and forecast concerns centered around shower potential ahead of approaching cold front. Through Daybreak: Generally quiet through daybreak with just a few showers given flow over llevel cool dome. Otherwise...cloudy skies and areas of fog given ample llevel moisture after yesterday/s rainfall. Today: Deep moisture plume moves offshore this morning with PWATs falling back below 1.25" by late morning and through the afternoon. Thus...despite upstream cold front and strengthening mid level flow...instability will be lacking with very poor lapse rates in the 850-500 mb layer. Near term high resolution deterministic and ensemble guidance suggest the best threat of any pop up shower activity will be over northern areas...closest to the coolest temperatures aloft associated with upstream shortwave. Can/t rule out a rumble of thunder...but overall it/s looking like most locations will remain dry today. Given the drying airmass...we should see an increasing amount of sunshine as the day progresses...and with T8s around +15C there is ample room for temperatures to climb well into the 80s over southern NH...with highs tempered a bit further east where morning clouds/fog will be more persistent. Employed MOS for the highs which is a bit above the guidance consensus...with some upper 80s possible in the MHT/ASH corridor.
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&& .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM SUNDAY/... High Impact Weather Potential: None. Pattern Summary: Upstream shortwave pulls through the region tonight associated with surface cold front. Drier air and significant height rises arrive for the day Sunday as a surface ridge of high pressure builds south of New England. Tonight: Surface cold front should pass through the region during the evening hours...but upstream shortwave trough axis will not arrive until closer to 06z...with low level cyclonic flow persisting through the overnight. Thus...could see a few evening showers over the foothills and mountains before any shower coverage becomes increasingly confined to the upslope regime in the mountains. Clouds will persist in this area...with partly cloudy skies to the south and east. With only modest dry advection overnight...lows will again be mild...generally in the upper 50s north to lower/mid 60s south. Sunday: Aforementioned significant height rises spell deep-layer subsidence as PWATs fall back to values around 1 inch...right around normal for this time of year. Could see a few residual showers in the mountains during the early morning...but otherwise a drier and somewhat cooler day will be in store with ample sun and T8s around +12C should allow highs into the 80s south of the mountains /given some downslope assistance/...with 70s elsewhere. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... A ridge of high pressure will be centered south of the area Monday and will move offshore Tuesday as a cold front slowly approaches from the west. This will lead to increasing temperatures and humidity for Monday and Tuesday. High temps Tuesday will mainly range from near 80 in the mountains to near 90 in southeastern New Hampshire and extreme southwestern Maine. Along with the warmer temps and higher humidity, the threat of showers and possible thunderstorms will be on the increase Tuesday afternoon through Wednesday as a cold front approaches and crosses the region. Showers could linger Wednesday night. A Canadian air mass with much cooler and drier air follows moves across the region behind the front for Thursday and Friday as surface high pressure builds into the region. With the colder air moving in aloft and an upper level trough developing over the area Thursday and Friday, an afternoon instability shower can`t be ruled out, especially in mountain areas, but most areas will remain dry. && .AVIATION /13Z SATURDAY THROUGH WEDNESDAY/... Short Term... Summary: Gradual clearing is expected today ahead of an approaching cold front that will move through the forecast area this evening with high pressure and drier air arriving for Sunday. Restrictions: Variable conditions at the moment with many sites LIFR/IFR in low stratus and some fog. There will be gradual improvement from west to east through the morning hours...with a return to VFR expected. Generally VFR for the afternoon with possible isolated to scattered restrictions in showers /and possible a thunderstorm/ LEB-HIE-AUG. This evening...expect VLIFR-LIFR fog/stratus to set in at AUG/RKD with additional fog likely HIE/LEB after 08Z Sunday. All sites will become VFR on Sunday. Winds: Light winds at the moment will generally become southwest 5 to 10kts for the day today before diminishing to light and variable tonight. For the day on Sunday expect winds to shift northwesterly and increase to 10g16kts. LLWS: No LLWS expected through Sunday. Lightning: Very low chance of a thunderstorm this afternoon HIE/LEB/AUG. No thunderstorms expected tonight through Sunday. Long Term...VFR conditions for Monday into Tuesday. MVFR to IFR conditions likely Tuesday night and Wednesday in showers and possible thunderstorms. && .MARINE... Short Term...SCAs /updated to be for hazardous seas only as of 624 am/ continue through this evening over the outer waters with winds now beginning to diminish...but lingering 4-6 foot waves continuing through the day today. Waves diminish this evening...with no flags expected tonight through Sunday. Long Term...No flags into early Tuesday. An increasing southerly flow will increase winds and seas late Tuesday with SCA conditions possible by Tuesday night and into Wednesday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory for hazardous seas until 5 PM EDT this afternoon for ANZ150-152-154. && $$ ES

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