Area Forecast Discussion
Issued by NWS Portland, ME

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KGYX 122340 AFDGYX Area Forecast Discussion National Weather Service Gray ME 740 PM EDT Mon Mar 12 2018 .SYNOPSIS... Low pressure will develop off the Carolina coast and rapidly intensify as it tracks up the eastern seaboard on Tuesday. Expect widespread accumulating snowfall across the region from Tuesday into Wednesday. The low will move into the Canadian maritimes with snow showers lingering in the mountains through the end of the week. High pressure builds in for the weekend. A cold front will cross the region early next week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 720 pm Update: At 22z low pres continued to deepen rapidly off the Carolina coast. Clouds now overspreading Maine and New Hampshire from the south as well as developing stratocu moving west from over the waters. A few light sprinkles occurring over the seacoast and southwest coastal areas of Maine but is of no significance. Only minor tweaks needed to afternoon package for this ESTF. Previous Discussion: At 18z...a 1021 millibar ridge was retreating offshore. A 995 millibar low was situated off the Carolina coast. Onshore flow and daytime heating has produced widespread clouds across the area. A second deck of thicker clouds was advancing northward ahead of the developing surface low and a potent shortwave impulse over the southeast CONUS. NWS Doppler radar showed some light return offshore...and we will see a few light rain or snow showers over southern and coastal sections tonight ahead of the main precipitation shield that arrives in the predawn hours of Tuesday then spreads rapidly north and east. For this package no significant timing differences were made to start time as ocean effect precipitation will blend with synoptic snow shield overnight. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/... Coastal low rapidly deepens during the day Tuesday as it moves north-northeast as potent upper impulse goes negative tilt. There remains that slight jog to the east but the available envelope of 12z guidance continues to bring the surface low close to the 40N/70w benchmark before it takes a more northerly turn towards Nova Scotia late tomorrow. The heaviest snow will fall during the day Tuesday with 1 inch per hour rates for much of New Hampshire and 1 to 3 inch per hour rates for coastal and central Maine. The snow will lighten up tomorrow night...although closer to the storm center...namely the capital district and mid coast Maine will see the heavy snow lingering into the evening hours. Steadier snow will gradually taper to snow showers from southwest to northeast on Wednesday...with the exception of the mountains and foothills where cyclonic upslope flow will keep accumulating snows in place. Gusty north to northeast winds will produce sharply reduced visibilities during the day Tuesday with strongest gusts along the coastal plain. Compared to the early morning forecast package...a blend of available model QPF results in similar snowfall amounts for this system. However...I did extend the snowfall graphic through late Wednesday to capture some additional synoptic and upslope snows that will fall during the day on Wednesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Our coastal storm will retrograde north and west during the midweek period as it slowly weakens with time. The system will fill to 981 mb by the time it reaches northern Maine on Thursday. Most of the moisture will be shunted well to the east of New England by that time. However, the mountains will still receive snow showers as the upper level low remains over the region. This same upper level low will be just north of Maine on Friday, allowing more mountain snow showers from time to time. By early Saturday, another disturbance will cross the region in a fast northwest flow aloft. This will allow for more mountain snow showers as well as a reinforcing shot of cold air. Temperatures will only top out in the 20s north to the 30s south which is below normal for this time of the year. Yet another reinforcing shot of cold air will arrive late Sunday and Sunday night. H8 temperatures below -20C will enter much of central and northern Maine and New Hampshire. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Short Term /through Wednesday/...MVFR cigs lowering to IFR from southwest to northeast in developing -sn and cigs. LIFR with areas of LIFR Tuesday in SN and SN+ with N to NE wind gusting to 30 KT. IFR and areas of LIFR continue Tuesday night in -SN and areas of SN with N wind gusting to 25 KT. IFR improving to MVFR by afternoon over southern NH and southwest Maine with lingering IFR elsewhere in -SN. Long Term...Mainly VFR conditions for the long term portion of the forecast. However, the mountains may fall to MVFR (HIE) in scattered mountain snow showers for the middle and end of the work week. && .MARINE... Short Term /through Wednesday/...Quiet beginning, but winds/seas quickly ramp up tonight with gale conditions expected after midnight and storm force gusts by daybreak. Seas quickly build Tuesday approaching 20 ft at the peak of the wind. Winds should drop off to Gale tomorrow night into the day Wednesday. Long Term...SCAs will likely be needed during the middle and end of the work week due to persistently strong west to northwest winds. There is a small window when gale force winds will be possible with the passage of a cold front Friday night into early Saturday. && .TIDES/COASTAL FLOODING... A coastal low will develop near the Carolinas and move northwards just southeast of the Gulf of Maine on Tuesday and Tuesday evening. Expect storm force east to northeasterly winds to allow seas to build up to around 20 ft in the nearshore waters. The onshore flow will allow for a storm surge of at least two feet. These conditions will result in beach erosion and splashover at the time of high tide on Tuesday morning and again Tuesday evening. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Warning from midnight tonight to 8 AM EDT Wednesday for MEZ012-018>020-023>025. Winter Storm Warning from 4 AM Tuesday to 2 PM EDT Wednesday for MEZ007>009-013-014-021-022-026>028. Coastal Flood Advisory from 8 AM Tuesday to midnight EDT Tuesday night for MEZ023. NH...Winter Storm Warning from midnight tonight to 8 AM EDT Wednesday for NHZ003>015. Winter Storm Warning from 4 AM Tuesday to 2 PM EDT Wednesday for NHZ001-002. Coastal Flood Advisory from 8 AM Tuesday to midnight EDT Tuesday night for NHZ014. MARINE...Gale Warning from 2 AM Tuesday to 2 AM EDT Wednesday for ANZ151-153. Storm Warning from 6 AM to 8 PM EDT Tuesday for ANZ150-152-154. && $$ NEAR TERM...Marine is the U.S. government's official web portal to all federal, state and local government web resources and services.