Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 240906 AFDGYX Area Forecast Discussion National Weather Service Gray ME 506 AM EDT Tue Oct 24 2017 .SYNOPSIS... A slow moving cold front will approach from the west today. The front will slowly cross the region from west to east late tonight through Wednesday with the attendant threat for heavy rain. Low pressure may form along the front on Thursday prolonging the rainfall. A ridge of high pressure will build over the region on Friday and will shift offshore on Saturday before the next low pressure system approaches from the southwest late in the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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5 AM Update...Have updated the forecast for a few items. 1) Cancel the dense fog advisory as increasing low level jet is aided in scouring out the fog. 2) Increase temperatures a degree or two for today, and 3) Add higher PoPs across southeast zones for early this morning based on latest radar trends. Previously... After weeks of warm and benign October weather, things are going to change for the wetter here today through midweek. A strong upper level trough and attendant cold front will approach from the west today and only slowly move eastward across northern New England through Thursday. Forcing for ascent will be fairly minimal for much of today as the dynamics of the system hang back to the west. However, moistening southerly flow in the midst of a gradually strengthening low level jet will allow for periods of showers/rain today. This will especially be the case along south and southeast facing slopes of the mountains where moist upslope flow will wring out of the moisture. In the meantime (early this morning) locally dense fog will continue for the morning commute, especially coastal and central Maine. As mentioned above, the low level jet will increase today as the pressure gradient tightens between the approaching front to the west and strong sfc high pressure departing to our east. We may be able to realize some SFC-based mixing this afternoon with a little heating, and this may allow some gusts between 30-40 MPH. However, widespread wind advisory-criteria winds/gusts are not expected at this time. Even still, a few downed trees and scattered power outages are expected given our past history with sub-advisory winds.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Cold front knocks on our western doorstep early this evening. A relatively narrow band of convective rainfall with some embedded thunder should should move into the CT River valley zones between 00z and 03z. With high PWAT air mass streaming northward ahead of the front, heavy downpours will be likely. In addition, with the aforementioned low level jet in place, convection may be able to mix down widely scattered damaging wind gusts. The SPC still has NH in a marginal risk for severe - and we concur. The threat for heavy rainfall and attendant threat for strong wind gusts will move eastward overnight, getting into Maine around or shortly after midnight. Minor urban and small stream flooding will be possible, but the very dry weather the last few months will likely cap the potential for anything more significant. Low pressure is expected to develop along the front to our south on Wednesday which will prolong the threat for rain throughout the day. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... A progressive pattern develops through the next week with a series of deep troughs moving in to out west over the great lakes. Wednesday night the slow moving cold front will just be starting to exit the area to the east as the upper level trough begins to moderate and move eastwards. By Wednesday night the eastern portion of the forecast area will continue to see some heavy rain while to the west the showers will cut off fairly abruptly as the cold air cuts off the moisture supply. Good consensus on the timing of the heavy rain departure. A bit more uncertainty in the rest of the day on Thursday. A wave develops along the front holding the moisture and rain showers in the region through Thursday... this may result in rain pushing back westwards into the northern white mountains for a portion of the day. Eventually the front and associated low pressure will depart to our east. Behind the front winds will come around to northwest. With the departure of the low level jet wind speeds will be light but the flow will be enough to keep showers around in the mountains. Cold air advection will set up as the core of the upper level low moves over us Thursday night. Temperatures will be cold enough for snow at the higher elevations, and we may see snow levels descend as low as 2000ft. Overall the air mass is borderline for snow so no significant accumulations are expected. Friday into Saturday a ridge builds back into the area as temperatures return to a bit above normal with highs reaching into the 60s. The ridge will be short lived as the next system begins to take form for the start of next week. Another deep trough will dig southwards to our west setting us up for a repeat of the rain and cold frontal passage for the start of next week. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/...
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Short Term...IFR or lower conditions this morning will briefly lift to VFR early morning. They may oscillate between VFR and MVFR today based on winds and rain coverage. They should lower to IFR this evening though. A southerly low level jet will strengthen today which will allow for LLWS at several terminals by afternoon. The threat for LLWS will continue through Wednesday morning. A few thunderstorms will be possible tonight as a cold front moves into the region with the attendant threat for locally strong SFC wind gusts. Long Term...Heavy rain with a departing cold front will leave the eastern portion of the area in IFR conditions for Wednesday night. Through the day on Thursday lingering MVFR showers will hold over the entire region. With all the moisture Valley fog is likely overnight on Thursday into Friday in the CT river valley as the winds decrease and the surface is able to decouple. Conditions finally improve to VFR for Friday through the weekend before the next system impacts the region on Sunday into Monday.
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&& .MARINE... Short Term...Gales have been posted for the ocean waters as well as Penobscot Bay. Will hold with a SCA for Casco bay for the time being. Southerly winds will gradually increase today and peak tonight into Wednesday morning - with gales expected most zones during that time. Long Term... With the departure of the front to the east comes an end to the low level jet and gale conditions. Winds will be back below small craft by late wedensday although the seas may take a few more hours to subside. Winds again will again increase to small craft criteria again as northwesterly cold advection sets up behind the front on Thursday night into Friday. && .HYDROLOGY... Overall, we are looking at 2-3" of rain across the area between Today and Thu. Southeastern slopes of the White Mountains could see local amounts around 4 inches.This should be enough to end the abnormally dry conditions present across the interior of the region. Along the coast in the region of moderate drought approx 3-6" is needed to return the Palmer drought index to near normal, so while this storm will certainly help it will likely not completely erase our water deficit through the midcoast. Still, with river levels running very low, mainstream flooding is not expected, but a few flashier basins may reach near flood stage. In New Hampshire, the Pemigewasset River at Woodstock is forecast to approach flood stage. Flashier tributaries in the White mountains may also see sharp rises with the passage of the front. However, could see a lot of rain in a short period time as a line of heavy showers and/or thunderstorms moves through late Tonight and Wed morning, and this could lead to some poor drainage and minor urban flooding due to clogged storm drains or higher rainfall rates in embedded thunderstorms. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...Small Craft Advisory from 10 AM this morning to 5 PM EDT Wednesday for ANZ153. Gale Warning from 5 PM this afternoon to 9 AM EDT Wednesday for ANZ152-154. Gale Warning from midnight tonight to 2 PM EDT Wednesday for ANZ150-151.
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&& $$ NEAR TERM...Ekster SHORT TERM...Ekster LONG TERM...Curtis

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