Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 161401 AFDGYX Area Forecast Discussion National Weather Service Gray ME 901 AM EST Thu Nov 16 2017 .SYNOPSIS...
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Low pressure will develop over southern New England then track through the Gulf of Maine this evening. Coastal rain and some accumulating interior snows are expected. Gusty northwest winds follow this system late tonight and Friday. High pressure builds in again for Friday before the next storm system arrives late Saturday and Sunday with another mixed bag of precipitation. High pressure then returns for early next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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900 AM...The current forecast is largely on track. For this ESTF update...I adjusted the near term grids to reflect radar trends as well as the latest mesonet. Prev disc... 645 AM Update...Little change to the going forecast early this morning as light precipitation is arriving on time across western zones. The precip is taking the form of light snow and rain depending on location. The same is expected as the leading edge moves into ME later this morning. A few locations, especially those with decent elevation, may see a coating of snow this morning before going over to rain. The higher elevations of the Whites and western ME mountains are still expected to be the only ones with several inches of snowfall through this evening. Previously... A short wave trough approaching from the west will allow light precipitation to overspread the forecast area from west to east this morning. Much of this precipitation will be in the form of rain, but higher elevations will likely see light snow. Lower elevations may start as snow or a mix of snow, sleet, and rain. However, SFC temperatures are already rising so little if any accumulations are expected at lower elevations. Elevations above 2,000 ft may pick up 2 to 5 inches of snow today. Secondary low pressure develops and deepens in the Gulf of Maine later this afternoon and continues to make the forecast for late this afternoon and evening a bit tricky. As the secondary low develops, mid level frontogenetical forcing will become quite strong on the coastal plain up through central Maine. This will likely result in a relatively short period of moderate to heavy precipitation moving from south to north. Much of this will be in the form of rain despite the strong upward vertical motion as the column below 850 mb will be just a bit too warm. However, there will be a window of opportunity centered a few hours either side of 00z where the dynamics may be strong enough to cool the column sufficiently for a period of heavy snow in a potential comma head. This would mainly be along/near the I-95 corridor north of Lewiston. Have forecasted a relatively small area of 1-3" centered around Kennebec County to account for this possibility. However, if the forcing for ascent is weaker or mainly offshore, then the precipitation will fall in the form of rain outside of the higher elevations. In any event, it will be interesting to see how things unfold late this afternoon and early evening. But for now, winter weather advisories are not necessary as any areas of >4" snowfall should be confined to the higher elevations. Other than that, there could be some minor urban/poor drainage flooding This afternoon on the coastal plain in the period of locally heavy rainfall. In addition, areas of fog are expected to develop by early afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... The low pressure system quickly moves away this evening, ending the precipitation from south to north. In fact southern and western zones will likely see an end to the precip late this afternoon. Northwesterly winds will kick in behind the strengthening low later tonight and become gusty. These winds will continue through Friday with gusts up to 40 MPH not out of the question. Upslope snow showers in the mountains will add to the snow totals in the higher elevations. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... The weekend starts off with a brief ridge of high pressure before a potent storm system dives southwards and crosses the region Saturday night into Sunday. The cold air lingers for the start of next week. Friday night will see temperatures fall to the low teens north to low 20s south as weak high pressure moves over the region. The next system will move out of the Great Lakes and up the St. Lawrence Valley on Saturday. As it does a warm front will lift north through our area on Saturday afternoon. With the later in the day onset for precipitation expect all but the far northern portions of the forecast area to rise above freezing before precipitation begins resulting in a mostly rain event. In the north, and above 1500ft rain will mix with and change over to snow. Overnight Saturday into Sunday the warm sector pushes well into the region, at least aloft, as the 850hPa passes to our northwest. There will likely be a few areas in the north which change over to freezing rain, especially any sheltered valleys where the warm air is unable to mix out. The freezing rain will rapidly change back over to snow as a strong cold front pushes through early Sunday morning. This front has a lot of upper level support with tropopause falling to around 500mb behind the front. This will create a burst of strong winds on Sunday morning as the front passes. Additionally the strong front may touch off some snow squalls as it moves through northern New Hampshire and western Maine. Soundings show a well mixed lower layer which will result in wind gusts to 40 mph possible across the area. The warm temperatures, reaching as high as almost 50F in the south will go hand in hand with the stronger wind gusts as both are the result of a well mixed atmosphere. Again in the northern mountain valley a few areas may struggle to rise above freezing at all with the result being calmer winds and a changeover from freezing rain directly to snow on the backside of the front. Looking at the system as a whole, a mix of snow, sleet, and freezing rain will likely require Winter Weather Advisories for Saturday night into Sunday for the northern portion of the area. Winds will approach wind advisory criteria on land, and gust in excess of Gale force over the ocean water. The cold are advection and breezy conditions will continue through the day on Sunday and into Sunday night. Upslope snow showers will persist through Sunday night along with the northwesterly winds. As we head into the busy travel week of Thanksgiving the pattern remains fairly progressive with a chance for more snow by mid week. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... Short Term /through Thursday Night/...Conditions will become IFR today as rain and snow overspreads the region along with fog. The snow will be confined mainly to the mountains. However, a period of snow will be possible around KAUG early this evening. Conditions improve tonight with VFR returning which will last through Friday except in the mountains. Westerly winds gust around 30 kt Friday. Long Term...Expect IFR in fog and then drizzle to develop along the coast as a warm front lifts northwards on Saturday. The conditions will then improve to MVFR until the cold front comes through on Sunday. Wind gusts to 40mph possible as the front moves through. Conditions will improve to VFR by Sunday afternoon for all but the northern mountains where MVFR snow showers will persist. && .MARINE... Short Term /Through Friday/...Gale warnings continue for Friday as wind gusts of 35-40 kt are expected. Long Term... Warm front will lift north of the waters on Saturday before a strong cold front passes on Sunday morning. During Fropa and behind the front will see wind gusts to gale force expected across the waters. Winds will remain strong through the afternoon Sunday before the pressure gradient finally relaxes. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Gale Warning from 4 AM to 8 PM EST Friday for ANZ150>154. && $$ ES

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