Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 181707 AFDGYX Area Forecast Discussion National Weather Service Gray ME 107 PM EDT Tue Apr 18 2017 .SYNOPSIS... High pressure will pass to our north through Wednesday. The circulation around this high will bring a cool onshore flow to the area. Weak low pressure passes to our north on Wednesday and will bring some showers to the region. Another low will bring steadier precipitation late Thursday into Friday. The precipitation could fall as some snow in the mountains. High pressure builds in for the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1 PM Update...Very little in the way of adjustments at this hour. The going forecast remains in good shape. 930 AM Update...Just a few minor adjustments to cloud cover for the rest of the morning into the early afternoon hours. Several large holes in the lower bkn/ovc exist across the CWA so tried to better pin these down in the grids and some places are completely sunny, and others cloudy. Otherwise, still expecting front to drop in from the northeast today which will shift the winds to east this afternoon. ORIGINAL DISCUSSION.... Northerly flow across the area continues to drain in colder air. Temperatures have fallen through the 40s this morning and into the 30s. An area of snow has been noted over eastern and central Maine which is occurring behind yet another front pushing in from the east. It is possible that some of this precipitation could make it into the Kennebec Valley, and yes it could fall as some snowflakes. But overall this should be quite light and not amount to much more than a flurry or sprinkle. Much cooler air in place aloft today means we will start off much cooler. Being nearly a month on the warm side of the equinox means the April sun will do quite a bit to warm things up this afternoon over western New England where temperatures will rebound into the 50s to near 60. But across eastern New England the cold advection continues until winds begin to turn around to the east. This easterly flow will bring cool, maritime air into the area, keeping temperatures in the 40s. Clouds associated with the maritime air may also move in, but dry conditions in the lowest levels should make it difficult for any precipitation to form.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Cool onshore flow continues tonight, but we will not see a good push of higher dewpoints moving in off the water. As a result, we should be able to cool into the 30s or even 20s. Areas that remain free of low clouds will have the best chance of dropping below freezing. This will be across interior Maine and New Hampshire. Flow becomes more southeasterly on Wednesday as a frontal system approaches from the west. Gradually this will bring in some more moist air and a better chance of low clouds and even possibly drizzle. Temperatures stay in the 40s again across Maine but may make the low to mid 50s in New Hampshire. Any more substantial convective showers associated with the approaching front and mid level wave will not arrive until later in the afternoon or evening. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... The 500 mb pattern continues to hold onto large scale omega blocking across the western half of the northern hemisphere, which will keep things active across New England as smaller scale waves moves through in the mid-late week period. This pattern has kept the coldest air locked up in Arctic Canada, and sending waves of the moderately colder air down into the CONUS. However there are signs of the blocking breaking down toward the end of the forecast, which may open the way for the cold core of air to start to spread equatorward next week. Either way, it looks like it will be hard to find any warm spells in the next week to ten days with temps generally running normal or below. Wednesday night will bring some showers to the region as weakening low tracking across Quebec, bringing a quick warm front cold front combo. Models continue to trend northward with best forcing and QPF may not amount to more than one or two tenths of an inch at best, mostly associated with weak WAA Wed night. May see somewhat of a break on Thu in precip, if not clouds, although even some breaks of sun may be possible on Thu as well, as wind develops a bit of westerly component and we see a break in the onshore flow, with temps warming to near normal in the upper 40s north to near 60 in southern NH. This will be short lived as another wave approaches from the west Thu night and crosses the region on Fri. This system is compact, but shows a little negative tilt, so a steadier precip is expected Thu night into Fri as this system moves through, and could produce a half to three quarters inch of QPF. Models are trending a bit warmer with this system, and it looks like mostly rain for all but the higher terrain in the mountains, where it could mix with or change to snow at times, with some accums possible. Otherwise warm, and somewhat moist boundary layer should keep things mainly rain. Best chance for snow outside of the mountains would be Fri night, but this will be as system is exiting, and again will likely be in the form of some flakes mixing in with no accums expected. Saturday looks mainly dry, with some SHRA possible in the mtns, but Sunday into Monday starting to become lower confidence as srn stream closed system allows for a wavy zonal flow in the nrn stream across New England. The Euro would keep us mainly dry with variable clouds and temps running on the cool side of normal, holding back any system associated with the srn stream low until Tuesday. Will continue to lean toward a dry Sunday, with chance pops early next week. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/... Short Term...Mostly VFR conditions expected today, but a maritime air mass moving in from the east could bring some MVFR ceilings with time. The chance of these lower clouds arriving will increase tonight into Wednesday. Long Term...MVFR-IFR Wed night, with worst conditions on the coast. Some improvement to MVFR, or even VFR possible Thu, then a return to IFR or lower Thu night into Fri, with improvement to VFR possible Saturday, although could see some gusty NW winds as well. && .MARINE... Short Term...Relatively light winds and low seas expected today and tonight as high pressure slides by to the north. However, a period of stronger easterly flow is expected this afternoon in the wake of a cold front which could lead to a few gusts up to 25 kt. A developing southeast flow on Wednesday will strengthen to as high as 25 KT and allow waves to build up to around 5 FT by evening. Long Term...Should see winds/seas diminish Wed night and stay below SCA into Thu night, but SCA will likely be needed Fri into Sat. && .FIRE WEATHER... Cool air in place across Maine and eastern New Hampshire will keep relative humidity values higher than recent days. But west of the mountains we will see relative humidity drop below 35 percent again today with light winds expected. The cool, moist onshore flow overspreads the entire area tonight into Wednesday. There will be a chance of showers Wednesday night with more widespread rain expected Thursday night into Friday. && .HYDROLOGY... Flood warnings continue for the Kennebec, Androscoggin, and Connecticut rivers, but colder air should allow snow melt to wane and rivers levels to recede below flood stage today or tonight. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$

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