Area Forecast Discussion
Issued by NWS Portland, ME

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947 FXUS61 KGYX 222223 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 623 PM EDT Sat Apr 22 2017 .SYNOPSIS... High pressure and drier air will finally build into the region on Sunday. A cold front will drop south into northern New England Sunday night into Monday and stall. Low pressure will slowly move up the Eastern Seaboard Tuesday and Wednesday with drizzle and periods of rain. A cold front will approach from the west Thursday into Friday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 625 PM Update... Areas of light drizzle and fog continue across the area this evening. An isolated shower may be possible over the higher terrain. Adjusted drizzle to just cover the coastal locations and lightened the intensity as few stations are reporting it. At the moment ceilings are increasing, but dew point depressions will decrease after dark, and BUFKIT soundings show many areas with a mixture of lower stratus and fog once again overnight. Adjusted QPF accordingly. No other changes at this time other than hourly temperatures/dew points. Previous discussion... A short wave trough will cross the region tonight. The result will be better mixing and drying as it passes, which will aid in getting rid of the murky low clouds and drizzle. This will first occur in the west, then finally make it to the coastal plain by dawn. We will have to watch for locally dense fog overnight however. This may occur on the coastal plain as stratus builds down. In addition, some dense fog may also form over the interior if skies go clear for several hours. Otherwise, not much in the way of measurable precipitation is expected overnight. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... High pressure builds across the region on Sunday and this will result in a much nicer day than what we have seen the last few days. During the afternoon, southwest flow will develop which will help boost temperatures into the 60s in many places under plentiful sunshine. A cold front will cross the region from the NW Sunday night. This front will be moisture starved and no bring anything except a period of clouds and perhaps a brief rain or snow shower to the far northern mountains. && .LONG TERM /MONDAY THROUGH SATURDAY/... Taking a look across the Northern Hemisphere we see a pool of lurking cold Arctic air over central and northern Canada while warm air continues to build and spread across most of the Lower 48 states. Polar front separating the two air masses stays primarily to our north, with most of the cold air surges heading more east than south. The closest our area comes to seeing this cold air will be on Monday when northern areas will be brushed by this cold as it heads to the east. On Monday the cold front which dropped south into the northern half of the area during the overnight will lose its forward momentum and get washed out during the heating of the day. Should see temperatures warming from the bottom up over the interior especially across central and western New England on Monday, with temperatures peaking in the mid to upper 60s. 850 MB temperatures of around +4C in southern areas translates to about 67-68F with good heating and mixing. But the light wind flow will quickly develop an onshore component as the warming land generates a sea breeze circulation and helps to reinforce high pressure offshore. This should be a fairly early sea breeze along coastal Maine and even into coastal New Hampshire, so temperatures there will peak in the upper 50s to near 60 before stalling or cooling in the afternoon. Further to the north temperatures peak out in the 40s to near 50 in the western Maine mountains where colder air remains behind the dissolving front. Onshore flow developing Monday afternoon will strengthen Monday night into Tuesday as a cut off low over the Southeast US slowly pulls northward up the East Coast. This will promote increasing clouds and rain chances on Tuesday with a maritime air mass in place keeping temperatures in the 40s, with some low 50s to the west and north of the mountains. This onshore flow persists into Wednesday as well, but with low level dewpoints on the increase. Model forecast mid 50s dewpoints being advected in off the ocean suggests widespread fog and drizzle are likely considering the cold ocean surface temperatures. Weak surface low tracks near Cape Cod and into the Gulf of Maine late Wednesday with the fog and drizzle lasting through Wednesday night as there is not a good clearing flow behind the low. Should see a deeper south to southwesterly flow on Thursday as the weakening cut off low moves east and we begin to be affected by the next approaching wave moving through southern Canada. Models diverge a bit on timing of this wave, with the ECMWF surging this wave further north while the GFS shoves it further east. Either way it should be a warm day Sunday with temperatures warming into the 70s to possibly near 80 in the southern New Hampshire warm spots while southerly winds keep coastal Maine a little cooler due to the better onshore wind component. Under the GFS scenario, a cold front will move into western New England Thursday afternoon, sparking thunderstorms. However, the ECMWF solution keeps the front much further west and ridging over our area would keep things dry for another day. At this point the best that can be said is that a cold front will move through Thursday or Friday with a chance of showers as it does so. If it moves through during the daytime there will be a better chance of thunderstorms, but if it goes through at night it may not produce much in the way of precipitation at all. The front lingers near the area into the weekend which will keep a chance of showers in the forecast as minor waves track along the stalled front. && .AVIATION /22Z SATURDAY THROUGH THURSDAY/... Short Term...IFR or lower conditions are expected much of tonight on the coastal plain. Further west, improving conditions are expected as the night wears on as high pressure builds in. However, if skies clear out for a time, radiation fog and stratus may form for a few hours before sunrise. VFR conditions are expected area-wide Sunday and much of Sunday night. Long Term...Should see VFR conditions on Monday, but an onshore flow will bring increasing clouds Monday night into Tuesday, with lowering ceilings to MVFR or IFR during the day Tuesday as rain begins. Rain and drizzle will be widespread through Wednesday night with IFR or worse conditions likely. Should see improvement to VFR on Thursday as the onshore flow finally ends. && .MARINE... Short Term...A SCA for seas has been issued for the ocean waters through 5 AM for 5-6 ft seas, which will decrease from east to west. Otherwise, tranquil conditions are expected Sunday. Low- end SCA conditions are possible Sunday night in advance of a cold front. Long Term...Flow becomes onshore on Monday as a sea breeze circulation begins. The onshore flow gets reinforced Monday night into Tuesday as low pressure slowly moves up the East Coast. East to northeast winds increase to as high as 25KT on Tuesday with the onshore fetch promoting increasing wave heights with time. Weakening low pressure moves through the Gulf of Maine Wednesday night with winds becoming light as it does so. Waves will take a while to subside and could stay above 5 FT through Friday. .FIRE WEATHER... Drying conditions are expected Sunday and Monday with min RH values dropping back into the 30s and 40s under mainly light winds. && .TIDES/COASTAL FLOODING... We will be entering a period of high astronomical tides toward the middle of the week. At Portland the astronomical tide is forecast at 11 FT Tuesday night and 11.5 FT Wednesday night. With a prolonged period of onshore flow expected, there will likely be a minor storm surge of about 1 FT especially on Tuesday evening when wind flow will be strongest. Minor coastal flooding is possible during the Tuesday evening high tide. Winds will be much lighter Wednesday night as low pressure moves through the Gulf of Maine, but in the absence of a strong clearing offshore flow there will likely be a lingering surge which will maintain a threat for minor coastal flooding around high tide. The highest tides will be 11.7 FT early Friday morning and again early Saturday morning with a light southerly flow unlikely to cause a significant surge. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory for hazardous seas until 5 AM EDT Sunday for ANZ150-152-154. && $$ NEAR TERM...Hanes SHORT TERM...Ekster LONG TERM...Kimble

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