Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 231049 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 649 AM EDT Wed May 23 2018 .SYNOPSIS... A cold front across northern Maine this morning will push off the Downeast coast later this afternoon. High pressure will build into the region tonight with frost expected from the Katahdin Region north. A warm front approaching from the west may bring a late day shower Thursday in the Saint John Valley. Much warmer Friday as the warm front lifts north of the region. && .NEAR TERM /THROUGH TONIGHT/...
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6:30am Update... Minor tweaks were made to T/TD and POPs/Wx grids through 12z based on current conditions and trends. Some more substantial changes were made to sky cover by blending in HRRR sky grid to reflect some greater than forecast clearing over southern and central areas, and that this may persist into the mid-morning hours. Day shift may want to consider tweaking high temps up a bit in areas if the sky remains clear in some areas and temps start to outpace the hourly forecast. Original Discussion... A cold front will push into the CWA this morning, and indeed, FVE is already showing a light NW wind. This front will continue to push south through the day, and push off the coast by later this afternoon. Some marginal instability is expected to develop this afternoon ahead of the front - likely too late for any thunder over much of the north, but central and southern parts of the CWA certainly stand a good chance of seeing some thunderstorms. Widespread CAPE of 500-1000 J/kg expected in these areas, and between cold air aloft (-20C around 500mb) and increasing shear, at least some small hail and gusty winds can`t be ruled out. The greatest risk appears to be between noon and 5pm. Model forecasts of the SHERB parameter, geared toward such high shear/low cape situations, approach and locally exceed 1.0 in most models, which is the threshold for considering an increasing possibility of strong to severe storms. However, given the conditional nature of the threat, stronger wording was left out at this time. As the front pushes south, a fairly quick drying is expected behind the front. As high pressure settles over the area this evening and tonight, clearing skies and lower dewpoints will allow temps to quickly drop. Frost Advisory is up for eastern Aroostook and northern Penobscot, with temps dropping into the low to mid 30s. An hour or two of below freezing temps are possible in valley locations in these zones, but confidence wasn`t there for 3 or more hours of sub-freezing temps, so no Freeze Watch or Warning was issued.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY/... Thursday will start clear and in some spots in the north frosty early in the morning. High pressure across the region will move south of New England during the afternoon as a warm front approaches from the west. Clouds will increase during the afternoon with the chance of a late day shower across the western Saint John Valley and North Woods. A band of showers will likely move across northern sections of the cwa Thu night, and perhaps into Fri morning. The warm front is expected to stall out somewhere across or just north of far northern Maine Fri with a very warm air mass across the region. Most of the models have 925H temps into the m/u teens (C) in the Saint John valley with low 20s (C) Downeast. Highs were raised a bit across interior Downeast, and there is the potential that highs could reach the upper 80s to near 90F. A fast moving disturbance may touch off late day showers and possible thunderstorms, with the best chance over the central highlands. Temperatures will be tricky and depend on the final position of the front and the amount of cloud cover; with the potential for a large spread from the far north to interior Downeast. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... A cold front will push south across the area Fri night as low pres over northern Maine Fri eve moves south and east of the region by Sat morning. The models do differ on the placement of the low and where the best chance of showers/rain will be Fri night. Would expect that the best chance will likely shift further south across the cwa with time Fri night, but the details remain uncertain. Sat will be much cooler and drier with some sun in the north, but depending on where the front ends up there could be a continued chance of showers Downeast Saturday; but the latest runs of the GFS, ECMWF, and Canadian push drier air south into the Downeast region and forecast confidence is increasing that it will be mainly dry Downeast. There is more uncertainty during the second half of the weekend. The GFS & Canadian push the front offshore with dry weather, while the ECMWF hangs the front up across the area with the chance of showers. Another wave moving in from the west may bring another chance of showers later Mon into Tue with a cold frontal passage, but details such as any convective potential remain uncertain. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... NEAR TERM: Largely VFR conditions this morning. But as shower coverage increases from north to south through the day, MVFR CIGs and locally MVFR VIS will be possible in and around shower activity. Afternoon thunderstorms possible from KHUL through KBHB, which could create localized increased turbulence and other hazards. A quick return to VFR conditions expected at all sites from north to south later this afternoon into the evening. SHORT TERM: VFR Thu with the chance of MVFR ceilings at KFVE toward 00z Fri as showers move into the area from the west. MVFR ceilings are possible at times Thu night into Fri morning at the northern terminals in showers with VFR expected Downeast. Predominately VFR Fri through Sun, but brief periods of MVFR are possible, especially at the Downeast terminals Fri night into early Sat in showers. The forecast is more uncertain for Sun, but at this time would favor VFR; although can`t rule out MVFR if there are some showers around. && .MARINE... NEAR TERM: Light to moderate S-SW`ly winds continue this morning and early afternoon, with seas generally 2-3 feet in outer waters. As the front pushes offshore later today, winds will shift NW-N`ly and freshen some, with gusts to 20kts possible overnight. Winds will then decrease late Wed night as high pressure pushes toward the coast. SHORT TERM: Light wind and Seas only 1 to 2 feet Thu morning. A west to southwest flow begins to increase late in the day and continues into Fri. The seas will gradually build, and it is likely a small craft advisory will be needed by Thu night and into Friday for seas, although it is more marginal for wind with gusts 20 to 25 knots. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...Frost Advisory from 1 AM to 7 AM EDT Thursday for MEZ002-005- 006. MARINE...None. && $$ Near Term...Kredensor Short Term...CB Long Term...CB Aviation...Kredensor/CB Marine...Kredensor/CB

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