Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 291611 AAC AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1111 AM EST Tue Nov 29 2016 .SYNOPSIS... An area of low pressure moving through southern New England will spread wintry precipitation into northern New England this morning before transitioning to rain for much of the area by this afternoon. Precipitation ends from west to east this evening, but another area of low pressure will bring more rain possibly changing to snow in northern areas Wednesday night into Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1110 AM Update... Have extended parts of the winter weather advisory where temperatures are reluctant to rise above freezing. Most areas are seeing freezing rain or drizzle at this time but snow may be mixing in at times. Removed coastal NH as readings have come up in this area. Concord...Laconia...and nearby locations as well as coastal Cumberland County are slowly warming and may be able to drop advisories before noon. Another...more robust area of precipitation is moving NE from NY state and Massachusetts so we are not out of the woods yet. 825 AM Update... Areas of freezing rain...freezing fog...and rain are moving through NH and portions of Maine this morning. Temperatures are warming up gradually every hour although dew points are low which is a concern. Will be watching closely the next couple hours and have added Rockingham and Cumberland to the Winter Weather Advisory. 7AM UPDATE... The first substantial radar echoes have made it into New Hampshire, though so far only traces of precipitation have been observed. Several observing sites have reported "UP" or unknown precipitation, while some have actually reported freezing rain. Heavier band of precipitation will arrive in New Hampshire within the hour. Temperatures this morning have been on the rise over southwest New Hampshire and much of the area in general, though temperatures remain at or below freezing with dewpoints even lower suggesting that evaporational cooling could keep temperatures near freezing a little longer. Near the coast Portsmouth and Portland have risen to 31 and 30 degrees respectively with precipitation still a ways off. These areas will likely rise above freezing before precipitation arrives. As a result will continue current advisory structure. Have made some adjustments to temperature, POP, and weather grids based on latest observations and expected trends. Otherwise no substantial changes to the forecast were needed. ORIGINAL DISCUSSION... Today will feature a complex precipitation type forecast resulting from very cold temperatures this morning and cold air damming across interior western Maine. A shortwave trough ejecting out of the base of a large Midwestern upper low will track through New England today. Weak surface low pressure will track through southern New England, which will help to keep the low level winds out of the east, piling up cold air against the higher terrain. Regional radar already shows stronger echoes moving through New York state and into Massachusetts, but surface observations reveal that most of this is not reaching the ground until you get to western New York. This is a result of very dry air in the mid to low levels of the atmosphere as evidenced by the 00Z sounding from GYX last night. This dry air could allow the first bouts of precipitation to start as light snow as it moves into New Hampshire near sunrise. But strong warm advection aloft (in the 850 to 700 MB layer) should change precipitation to rain as it falls. However, surface temperatures in many areas may remain below freezing creating a period of freezing rain which could cause icy conditions on roadways. Across southern New Hampshire, temperatures are already beginning to warm up a bit from their early morning lows, but dry air at the surface indicates that temperatures may stay below freezing as precipitation begins to fall. As a result, the Freezing Rain Advisory will continue and has been expanded to include the Manchester and Nashua corridor. It is possible that freezing rain may arrive even further east into Rockingham County as well, but there is still a good deal of uncertainty regarding when that will arrive and what temperatures will be when it does so. Will need to monitor this and might need to expand the advisory again depending on how conditions evolve. Northern New Hampshire may begin as snow and transition to sleet and freezing rain during the mid morning. It is expected that south to southeasterly low level winds will allow warm air to mix down in the Connecticut River Valley today which will allow temperatures to warm above freezing. However, there is still some uncertainty on when that will occur. There could be up to a tenth of an inch of ice accumulation before temperatures warm up. Across interior western Maine and east central New Hampshire there should be a pretty decent cold air damming setup today which will allow low level temperatures to stay in the 20s to low 30s even into the afternoon. This will provide the opportunity for a longer period of freezing rain and ice accumulations of a tenth of an inch or slightly more before temperatures eventually warm. Currently the winter weather advisory ends at 4PM, but cold air damming situations are notoriously long lived and it is possible that this might need to be extended in time if temperatures fail to warm as forecast. Along the Maine coastline an easterly wind should allow warmer air to move in from the ocean and keep most of the precipitation as rain. In the western Maine mountains, temperatures at all levels may remain cold enough for snow for a majority of the day, allowing snow to accumulate to 3 to 6 inches. However, warm air aloft should move in eventually even up to the Canadian border so there may be a change over to freezing rain in this region as well later this afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Precipitation should come to an end from west to east tonight as low pressure moves east. Low level winds shift to the west allowing the cold air damming to break and warmer temperatures to arrive especially over the coastal plain and southern parts of the area. In fact, daily high temperatures may occur in the evening or even up to around midnight. But eventually as the low moves further away there should be an opportunity for at least some cooling with temperatures bottoming out generally in the 30s. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... At 500 mb models continue to trend toward a less amplified and less blocky pattern through the weekend and into early next week. For the most part the troughs will be fast moving, but this will not preclude a significant event, given the thermal gradients this time of year. Temps will bounce around a bit through the period but generally should be near to above normal. Starting Wednesday the second of the almost back to back systems will move in as fairly impressive chunk of energy rotates around base of trough to our west and begins to form a coastal surface low. Should see a strong surge of mid-level warm advection Wednesday afternoon and evening, which will lead to moderate to maybe heavy rain. And, it will be mainly rain at the start, with the possible exception of a period of snow in the far NE zones, as highs climb to into the 40s to around 50 in the south. By Wednesday evening, should see cold air starting to move down from the N and may turn the precip back to snow in the far NE. Should see the rain end across southern NH and SW ME Thursday morning, with precip winding down from SW-NE during the rest of the day. Cold air will continue to move in from the N, with snow creeping a little bit southward and lowering in elevation a bit across the mountains. There is the possibility that areas from Coburn Gore and Jackman northward could see six inches or more of snow. Friday will see a bit of a break, as ridging builds in briefly, and temperatures will stay above normal but not quite as warm as previous days. The upper level low finally tracks to our north and drags a cold front through area Friday night into Saturday. Temperatures return to normal over the weekend, but other than a few rain/snow showers it should stay dry. Next chance of precipitation will be centered around Monday, with the Euro showing a deepening coastal storm while the GFS advertises a ridge, so forecast confidence is low for early next week. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/... Short Term...Should see conditions worsening to IFR this morning from west to east. Precipitation may start out as light snow before transitioning to freezing rain and then rain as the temperature warms. When this transition occurs is a difficult thing to pinpoint even this late in the game. The longest period of freezing rain may be at Augusta or Whitefield where freezing rain could last into the early afternoon. By this evening stronger winds moving in just above the surface will lead to low level wind shear at all TAF sites through tonight. Long Term...Conditions improve to VFR briefly on Wednesday morning, but flight restrictions return from SW-NE Wednesday afternoon with IFR or lower expected Wednesday night. Gradual improvement to VFR on Thursday. Mainly VFR expected Friday and Saturday, with the exception KHIE, which will likely be stuck at MVFR in upslope clouds and SHSN. && .MARINE... Short Term...Southeast winds ahead of the developing low tracking near the coastline will strengthen and likely gust to gale force over the outer waters this evening into tonight. Winds should diminish a bit after the low moves by. Long Term...SCA may be needed Wednesday night into Thursday in SE flow ahead of low pressure and then in NW flow behind the departing low. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Weather Advisory until 1 PM EST this afternoon for MEZ018-019-023-024. Winter Weather Advisory until 4 PM EST this afternoon for MEZ012>014-020-021. Winter Weather Advisory until 10 PM EST this evening for MEZ007>009. NH...Winter Weather Advisory until 1 PM EST this afternoon for NHZ003-005-006-008>010-013. Winter Weather Advisory until 4 PM EST this afternoon for NHZ001-002-004. MARINE...Small Craft Advisory until 4 AM EST Wednesday for ANZ151-153. Gale Warning until 1 AM EST Wednesday for ANZ150-152-154.
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&& $$ NEAR TERM...Hanes SHORT TERM...Kimble LONG TERM...Cempa is the U.S. government's official web portal to all federal, state and local government web resources and services.