Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 181437 AFDGYX Area Forecast Discussion National Weather Service Gray ME 937 AM EST Sat Nov 18 2017 .SYNOPSIS... High pressure will briefly be in control of the region today as we sit in between storm systems. Strong low pressure is forecast to move through New York and into the St. Lawrence tonight into Sunday. Strong southerly flow ahead of it will keep temperatures on the mild side...which should keep the bulk of the precipitation falling as rain. Some frozen precipitation is possible in the higher terrain and northern valleys though at onset. That low pressure will drive a strong cold front through the area Sunday night. Gusty winds are expected right through Monday...along with snow showers in and northwest of the mountains. && .NEAR TERM /TODAY/... 930AM UPDATE... Have updated the forecast primarily to adjust onset time of precipitation. First wave moving through upstate New York currently is expected to bring primarily cloud cover as it arrives in about 3 hours with precip drying up as it arrives. Better shot at rain comes this evening. Have also tweaked high temperatures today based on morning sounding analysis. Steep low level inversion exists this morning, and with cloud cover increasing as the day goes on, it may be difficult to warm out of the mid 40s. 7AM UPDATE ... Minor update. Have dropped temperatures a few degrees in sheltered valleys to reflect the morning observations. ORIGINAL DISCUSSION... Weak high pressure is over the region early this morning, which combined with the clear skies has resulted in temperatures in the teens across much of the area. Low pressure over the Great Lakes will intensify and move up the St Lawrence valley later today into tonight. The first signs of the approaching system are already present as a warm layer begins to nose with observations above 2,000ft reporting temps in the mid 20s and rising. Temperatures will continue to warm today with all but the highest elevations above freezing by later afternoon. Clouds will also move in throughout the day in advance of the next system. && .SHORT TERM /TONIGHT AND SUNDAY/... As the warm frontal precipitation approaches the region this evening it will be a race between the approaching precipitation, radiational cooling and warm air advection to determine the precipitation type. For most of the region from the foothills through the coastal plain temperatures will be above freezing and light rain will begin early in the evening and continue through the night. The forecast is not so clear cut further north. In the mountains, the warm air will begin to come in aloft with the peak of the warm nose expected around 6,000ft. This still leaves a portion of our elevated terrain below freezing with a mix possible through about 2,000ft. In the northern mountain valleys such as Berlin, Rangeley, and Jackman the temperatures may struggle to reach freezing at all during the day, which would result in a brief period of freezing drizzle and light icing as the precipitation approaches. Without any blocking high pressure to hold the cold air in place the warmth is expected to take over and transition everything over to rain by daybreak. With so much uncertainty in the precipitation type for the north have opted to hold off on issuing an winter headlines as the first few hours of sunshine today may largely determine tonight`s precipitation type. Moving into the day on Sunday the core of the system aloft drives a cold front through the region by midday and there will be a quick switch over to snow and temperatures drop rapidly behind the front. The precipitation will end almost as fast as the temperatures drop so little accumulation is expected south of the notches. Along the Canadian border, the front will bring upslope flow which will result in continuing snow into the evening on Sunday. Along with a switch to snow the arrival of the front and cold air will bring gusty winds becoming west to northwest through the afternoon on Sunday. Wind gusts to 40mph are expected through much of the area Sunday afternoon. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Sun night will be a strong CAA regime across the region behind the departing cold front. Steadily dropping temps...gusty winds...and upslope snow showers are expected. Wind direction is not the most favorable for significant snow totals in upslope zones...but a couple inches are possible where WNWly flow can be maximized. Winds should also stay gusty even overnight...though the best chance for strong wind gusts looks to hold off until Mon. Mixing should increase to around H8 during the day Mon...where ensemble forecasts have a 1 to 2 standard deviation wind speed anomaly tracking thru Srn and central New England. Those mixing depths may allow for some 40 kt wind gusts to mix down to the surface...especially across Srn zones closer to the speed max. I increased wind gusts beyond the typically wind gust factor to account for this. The pattern becomes more zonal thru midweek after Mon. Fast moving flow aloft will limit precip chances...though any passing s/wv may increase coverage of upslope snow showers. Deterministic model guidance and ensembles favor Wed night/Thu time period for the next trof to cross the area. There is pretty significant model difference in the depth and impact of this wave. The 18.00z ECMWF favors a stronger phase between Nrn and Srn streams...and so brings larger impacts to the local area. The CMC and GFS favor a passing front with low pressure farther offshore. With lean towards that scenario...with higher PoP in the high terrain. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... Short Term /through Saturday Night/... VFR conditions will erode to MVFR from west to east by afternoon as increasing cloud cover approach and lower in advance of the warm front. Light freezing precipitation is possible across the north tonight before switching over to rain. IFR conditions will continue overnight and into Sunday. An increasing LLJ may result in wind shear for a period of Sunday morning before the winds are able to mix to the surface. Sunday a cold front crosses the region with gusty winds. Long Term...With Wly flow dominating thru midweek...VFR conditions will prevail in downsloping. At HIE upslope flow will keep the clouds around for most of Mon...some local IFR is possible in SHSN...but not likely. Surface wind gusts during the day Mon at all terminals may gust to near 40 kts...with widespread 30 kt gusts expected. && .MARINE... Short Term /through Saturday Night/... High pressure will move east away from our waters as low pressure intensifies over the Great Lakes and passes to our north. Southerly flow in warm advection will move over the waters but is expected to remain below advisory level. A cold front will cross the waters on Sunday with wind gusts to 45mph expecting in cold air advection behind the front and a Gale watch has been issued for Sunday afternoon. Long Term...Strong CAA continues Sun night...with gales likely outside of the bays. Gales may continue on the outer waters thru Mon...before gradually diminishing Mon night into Tue. A transition to zonal...fast moving flow may keep conditions near SCA thresholds for much of the period. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Gale Watch from Sunday morning through Sunday evening for ANZ150>152-154. && $$ NEAR TERM UPDATE...Kimble SHORT TERM...Curtis LONG TERM...Legro

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