Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 231124 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 724 AM EDT Sat Mar 23 2024 .SYNOPSIS... A low pressure system crosses the area today through tonight, then exits into the Maritimes Sunday. High pressure returns Monday through Tuesday. A warm front enters the region Wednesday. && .NEAR TERM /THROUGH TONIGHT/...
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724 AM Update: Moderate snowfall has begun in the greater Bangor area, stretching east into Washington County. Snow will continue to quickly spread northwards through the rest of the forecast area over the next several hours. The previous forecast remains on track with no major changes needed. Previous Discussion: SIGNIFICANT WINTER STORM TODAY THROUGH TONIGHT Synoptic: A strengthening jet streak will lift just north of the state today, placing our CWA in the right entrance region of a jet streak containing winds approaching 170 kts. This divergence aloft will aid in pulling a trough of low pressure at the surface up and through the forecast area. This trough will remain connected to tropical moisture in the Gulf of Mexico, advecting substantial moisture into the region as well. Hazards: With cold air already established across the forecast area, precip will begin as snow. As the low crosses the area, and temperatures warm slightly through the day, a transition towards rain will occur along the coast. The rain/snow line is likely to make it as far north as central Penobscot and northern Washington counties. The warm air will advect in along southerly winds at around 850 mb, but across the Interior Downeast region, winds will remain out of a more northerly direction at the surface, which will maintain some near-surface cold air advection. All together, this will lead to the development of a warm nose aloft along the rain/snow line through the Interior Downeast region where a period of sleet and freezing rain will occur. The timing of this mixed precip is this evening into tonight. Despite several hours of freezing rain, the heavy rainfall rates expected due to strong forcing will limit how much ice buildup will occur, especially on power lines and tree branches, where heavy rain may runoff before it has a chance to freeze. This complicating factor limits confidence on forecast ice amounts, however the impact of ice on untreated flat surfaces remains the same, in that untreated surfaces will quickly become slick. Heavy rain, freezing or otherwise, may cause ponding in areas with poor drainage, or where drains become blocked due to earlier snow and sleet. Across the north, precip will remain all snow. With strong forcing dynamics at play and a large plume of moisture, heavy snowfall will be supported through the evening and into the overnight hours, with rates approaching 1 to 2 inches per hour through an extended period of time. Winds will pick up through the night tonight, gusting to 35 mph at times in the higher terrain and along the coast. Some blowing snow is possible, especially in areas which do not receive mixed precip and as temperatures drop through the night.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... Behind the low on Sunday, northwesterly flow and cold air advection will continue through the day.The tightening gradient behind the trough and the increased instability with the cold air advection will increase surface winds through the day, and with plenty of snow available from the most recent storm, blowing and drifting snow will be an issue, particularly across the north where snow will be drier and more transportable. Temperatures will also continue to drop across the region as the Arctic air mass infiltrates the area. High temperatures will be just below freezing on Sunday, but Sunday night temps will drop into the single digits in the north and into the 20s for the Downeast coast as a surface high moves in and the atmosphere decouples. On Monday, the surface high will begin to slide eastward and the cold air will retreat a little bit. This will moderate highs during the day on Monday to the mid to upper 30s across the region. However, Monday night will continue to be cold with clear skies aloft allowing the atmosphere to decouple overnight again. Night time lows will be slightly warmer, in the teens in the north and the 20s to the south, but still below freezing across the region. This will refreeze any water on the roads from earlier in the day and surfaces could be quite slippery Tuesday morning. && .LONG TERM /TUESDAY THROUGH FRIDAY/... On Tuesday, a surface low will develop offshore and move east of the forecast area, while another low develops over the Ohio Valley. This will place Maine under a longwave ridge, with southerly flow continuing to bring warm air overhead. At the surface, a shortwave ridge will keep the pattern dry for a short period, but will also bring northerly flow, mitigating the warming aloft. This will slow the warming trend midweek. Wednesday, the surface ridge will retreat northward as the longwave ridge weakens and shifts eastward. This will allow two potential shortwaves to approach the forecast area: a backdoor shortwave from the east, as a front also approaches from the west. With a shortwave trough moving through the upper level pattern overhead, this will provide the necessary instability to bring precipitation over the area. With the prior warm air advection, this is likely to start out as a snow event, but transition over to rain primarily during the day on Thursday and Friday. Some model uncertainty remains with this event at the end of the week, as the first precip band moves off to the east and a second low develops to the south and moves northward. Timing details are blurry on the development of this low across the southern tier of the U.S. and how far northward the inverted trough extends the next band of precip. Given this, the long term forecast was painted with a bit of a broad brush, however it is likely that there will be a break between the first and second round of precip that will become more evident as we get closer in time. && .AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
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NEAR TERM: VFR conditions will continue across northern terminals this morning, MVFR to IFR cigs are beginning to build in to GNR/BGR/BHB terminals as snow begins to move into the area. All terminals through the region will trend towards IFR to LIFR as snow moves in, then becomes heavy Saturday afternoon into the evening hours with visibilities a quarter mile or less. BGR down through the coast will likely see a transition away from snow towards +FZRA at BGR and +RA at BHB Saturday evening through the night. For most terminals, NE winds 5 to 10 kts will begin to shift N to NW through Saturday night, becoming 10 to 20 kts with gusts 25 to 30 kts. BHB and along the immediate coast will begin SE at 5 to 15 kts before also shifting NW along with the other terminals for Saturday night. SHORT TERM: Sunday...Variable conditions with any blowing snow. Otherwise, VFR to MVFR early with a slight chance/chance of snow showers. VFR late. North/northwest winds 10 to 20 knots with gusts up to around 25 knots, diminishing to 10 to 15 knots late. Sunday night...VFR. North/northwest winds 5 to 10 knots. Monday through Tuesday night...VFR. North/northeast winds around 10 knots. Wednesday...VFR/MVFR. A chance of snow and rain. East/northeast winds 5 to 10 knots, becoming variable.
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&& .MARINE... NEAR TERM: A gale warning is now in place for the waters beginning at 4pm this afternoon as winds continue to increase to 35 to 40 kts. Seas will gradually increase as well, becoming 8 to 10 ft on the coastal waters through tonight. Wind directions will be primarily SE, but will sharply shift NW late tonight behind the passing low pressure system. Snow early this morning will transition to moderate to heavy rainfall this evening, with vis dropping to one mile or less at times tonight. SHORT TERM: A prolonged period of gale force winds exists through the period. A brief return to SCA conditions will occur Sunday afternoon, but gales will generally persist through Tuesday morning. Winds will finally drop below 25 kts Wednesday morning. Seas will also remain high during this timeframe, ranging around 8 to 10 feet before dropping to 5 to 7 feet on Tuesday and then gradually subsiding on Wednesday. && .CAR WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Storm Warning until 8 AM EDT Sunday for MEZ001>006-010- 011-015>017-031-032. Winter Weather Advisory until 5 AM EDT Sunday for MEZ029-030. Flood Watch from 5 PM EDT this afternoon through late tonight for MEZ029-030. MARINE...Gale Warning from 4 PM this afternoon to 8 PM EDT Sunday for ANZ050>052.
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&& $$ Near Term...AStrauser Short Term...LF Long Term...LF Aviation...AStrauser/LF Marine...AStrauser/LF

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