Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 231651 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1151 AM EST Mon Jan 23 2017 .SYNOPSIS... A storm system tracking up the coast will bring wintry precipitation to the area starting mainly tonight and lasting into Tuesday night. A cold upper trough will remain over the area through the latter part of the week with a return to colder temperatures. Scattered snow showers in the mountains and foothills can be expected through the latter part of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Update...I know it is just the appetizer to the main course...but first thing is first. Ocean effect snow showers continue over the Gulf of ME...and as flow aloft begins to veer more Ely this afternoon these will begin to drift Nwd into parts of Srn NH. Already seeing snow showers in the observation at PSM...and so I increased PoP in a band that will lift Nwd today. Could also see some enhancement in the Ely flow upslope and provides a little extra lift. As for tonight into Tue...high pressure seems to be doing a good job asserting itself over the region. A fresh NE breeze is advecting mid to upper teens dewpoints into the Ern parts of the forecast area...and skies are clearing from NE to SW. Model guidance is starting to get the hint...and most mesoscale guidance now cools temps near the coast as precip is ongoing tonight. That is a concern for model forecasts calling for a lot of coastal rain. Soundings still show a warm layer aloft...but above H8. The NAM continues to be the only model that significantly warms this layer enough for more freezing rain than sleet...before precip comes to an end. The 23.06 GFS remains on the colder side...and the 23.00z ECMWF is coldest of all. I would still like to see the 23.12z GFS and ECWMF before making a final call on winter storm watches. Previous Discussion: High pressure to the north nosing south and currently pushing some colder and drier air in the lower levels south into the area on northeast winds. Widespread clouds are noted over southern and central areas...but further north into the drier air some clearing may try to develop this morning and briefly work south into central areas for a while before the clouds to the south move north. Models fairly close on timing of onset of precipitation spreading north into southern NH this afternoon. Boundary layer temps will be marginal but evaporational cooling at the onset should change any mixed precipitation over to snow with some light accumulations possible over southern NH by the evening commute thus a winter weather advisory was issued for southern areas of NH starting at 4 pm this afternoon. Based on a blend of models adjusted temps just a few degs colder for afternoon highs. Based on the amount of drier air working south slowed the northward progress of precipitation. Feeling is models trying to expand precipitation shield north into central/northern NH and southern Maine too quickly. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... All model trends are further east with the coastal low tracking up the east coast. All models take the vertically stacked system east of the benchmark of 40n/70w. With this more easterly track in mind the low level winds will remain more from the north and northeast allowing some cold air damming to continue longer through Tuesday even along parts of the coast. BUFKIT soundings all show much of the area with a deep warm layer that moves into the area later tonight and Tuesday between 5000-9000 ft with colder temps above and below this area. This will mean snow that develops tonight will eventually change to a broad area of sleet. Some inland areas closer to the coast will also see a band of freezing rain developing as the closer to the coast the deeper the warm layer will be. The northeast cold air low level damming winds will mean that temps will struggle to get above 32 degrees...even near the coast. Before the changeover well inland some significant accumulationsof snow exceeding 6 inches may occur. Snowfall ratios will be low though considering the warm layer aloft. There is not high confidence to forecast over 6 inches of snow at this time based on the above reasoning. With all of the above in mind have decided to keep the winter storm watches in place except over southern NH where we decided to lower it to a winter weather advisory since thresholds should remain below warning criteria. Also have issued winter weather advisories in northern NH and coastal and some interior portions of Maine. The reason for the advisories will be more due to several ptypes including freezing rain with icing amounts of .10-.15 inches. All this mixed bag will continue through much of Tuesday except along coastal areas of Maine and southeast NH where temps finally should reach above 32 degs by later in the morning Tuesday while all other areas remain at or below the 32 degree mark due to the continued north winds as the low passes well to the east. Generally went a little below guidance on temp forecast for tonight and Tuesday due to synoptic situation and trends. Will leave decisions on how to handle the watches to the day shift as trends further develop. Strong winds will develop along the coast later tonight and into Tuesday and a wind advisory for that time frame may need to be considered if trends continue. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Low pressure is expected to be located over the Gulf of Maine at the beginning of the period with upper level low pressure nearly overhead. This will keep at least light mixed precipitation over the region through the first part of Tuesday night before departing. This will include rain at the coast and a mix of snow sleet and freezing rain inland. A trough of low pressure moving in from the northwest Wednesday night and Thursday with a chance of snow and rain showers during this time. Otherwise, a rather innocuous extended period is expected through the weekend with colder temperatures and upslope snow showers expected. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... Short Term /Through Tuesday/...MVFR cigs today will become IFR/LIFR later today across southern NH in developing precipitation and then spreading north and east tonight over the rest of the area. The IFR/LIFR conditions should continue through most if not all of Tuesday. Long Term...Low pressure will be slowly departing Tuesday night. However, IFR conditions in mixed precipitation is expected for at least the first half of the night. Rain is expected at coastal terminals. Otherwise, improvement in conditions is foreseen Wed through the end of the week as the coastal storm departs. && .MARINE... Short Term /through Tuesday/...Storm warnings are in effect for tonight into Tuesday over the outer waters with gales along the bays. Seas should reach near 20 feet by Tuesday morning over the outer waters. By late Tuesday winds and seas will begin to decrease as the strongest gradient winds move to the east of the waters as the system moves slowly east. Long Term...Winds and seas will continue to gradually decrease Tuesday night through the end of the week. However, SCA conditions are likely from time to time through that period. && .TIDES/COASTAL FLOODING... Despite being in the low portion of our astronomical tide cycle, large building waves may produce some erosion and splash-over near the times of high tide Tuesday. Preliminary storm surge values appear to be around 1.5 to 2 feet with a persistent, strong easterly wind developing. A coastal flood advisory may be needed from the impact of the wave action on Tuesday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Watch from 7 PM EST this evening through Tuesday afternoon for MEZ018. Winter Storm Watch from late tonight through Tuesday evening for MEZ007>009-012>014-019>021. Winter Weather Advisory from 10 PM this evening to 9 AM EST Tuesday for MEZ022-024>028. NH...Winter Storm Watch from 7 PM EST this evening through Tuesday afternoon for NHZ005>010. Winter Storm Watch from late tonight through Tuesday evening for NHZ004. Winter Weather Advisory from 1 AM to 7 PM EST Tuesday for NHZ001>003. Winter Weather Advisory from 4 PM this afternoon to 1 PM EST Tuesday for NHZ011>013-015. MARINE...Gale Warning from 3 PM this afternoon to 11 AM EST Tuesday for ANZ151-153. Storm Warning from 6 PM this evening to 11 AM EST Tuesday for ANZ150-152-154. && $$ NEAR TERM...Legro is the U.S. government's official web portal to all federal, state and local government web resources and services.