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FXUS61 KCAR 022109 AFDCAR

Area Forecast Discussion National Weather Service Caribou ME 409 PM EST Sat Dec 2 2023

SYNOPSIS
Weak low pressure will track into the Maritimes tonight. High pressure will be to our north into Sunday. Another low will approach Sunday and track south of the area Sunday night into Monday. A weak upper trough will remain over the area through the middle of the week, with surface high pressure building in Wednesday into Thursday.

NEAR TERM /THROUGH SUNDAY/
Steady precipitation is slowly coming to an end this evening and tapering to snow showers across the area. Temperatures are at to slightly above freezing across northern areas. Across southern areas very moist boundary layer is continuing low clouds, fog and at times drizzle. Weak low pressure that brought the light snow today will continue east into the Maritimes tonight.

Large high pressure to our north will keep the winds NNE-ENE tonight across the area. Moisture will be trapped in the low to mid levels keeping the skies mainly cloudy overnight.
Temperatures will be around 32F for Bangor and the Downeast coast tonight with low 30s in the Central Highlands. Across the north expect low to mid 20s with those light winds. Tomorrow the cold air damming holds temperatures below freezing across the northern 1/3rd of the CWA in the upper 20s to low 30s. In southern areas expect mid 30s. By late afternoon a 500mb shortwave will be negatively tilted working into the Eastern Great Lakes states with nearly vertically stacked surface low beneath. At the same time upper level divergence will setup off the Long Island coast which will give way to secondary cyclogenesis. Precipitation will begin to break out by afternoon closer to sunset from SW to NE across the area.
Precipitation will likely be snow from Bangor to Calais and points northward thanks to the cold air damming with dew points below freezing the wet bulb will be key to watch for snowfall tomorrow. Rain/Snow mix south of the Route 9 corridor with just rain along the Downeast Coast. Roads may become slippery before sunset in places that stay below freezing and north of I-95 in Bangor area. Conditions go downhill into the evening as mentioned below...

SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/
A 500mb shortwave will cross northern New England Sunday night, ahead of a deepening longwave trough turning neutrally tilted through the early week. The shortwave will be fed by the left exit region of a 185kt jet streak, providing plenty of instability for a storm to spread across the forecast area Sunday night into Monday. This jet streak is forecast to be within the top 10% of climatology for wind speed in the northeast region, which will enhance the dynamics of this system. A surface low will be move into southern Quebec prior to occluding, leading to a triple-point low to develop on the coast and tracking up through the Gulf of Maine. This system will be tapped into the Gulf Stream for advecting in mid-level moisture as well.

With northeasterly flow during this storm, cold air will dam up along the higher terrain of western Maine, leading to a cold pool across much of our forecast area near the surface. This cold pool will aid in keeping temperatures below freezing from the surface up, and maintaining an all-snow precip type down through the coast. Some question remains where a heavier band of snow may set up, as well as the exact snow-to-liquid ratios (SLRs) that will be seen. With plentiful cold air through the coast, SLRs could be up to 12:1 near the coast, or if the cold air dam is less intense, SLRs could remain well below 10:1.
Snowfall rates will also affect temperatures, and so more snow and higher SLRs may be seen in any deformation band that sets up, further amplifying storm total potential in that area.

Though uncertainty remains in these finer details, there is fairly high confidence (75%) of 6 to 8 inches of snowfall across the central third of our forecast area. Portions of Downeast closer to the coast will see warmer temperatures at onset and lower SLRs, and may struggle to reach 6 inches of snow. That said, should the heavier snow band shift southwards, they could easily see at least 6 to 8 inches of snow. Across the Crown of Maine, there is moderate confidence (65%) that there will be around 2 to 4 inches of snow, but these totals will be even more reliant on low track, as to whether the northern tier sees a dusting of snow or closer to 4 to 6 inches of snow.

LONG TERM /TUESDAY THROUGH SATURDAY/
An upper level trough will remain overhead through the middle of the week, brining generally unsettled weather to the area. That said, a ridge of surface high pressure is likely to build into the area by Wednesday, and last through much of the rest of the week. This high pressure will reduce the threat for snow showers, though a few flurries cannot be ruled out with the upper level trough in place. Temperatures will be quite cold through the middle of the week as well with persistent cold air advection, as low temperatures will fall into the single digits above zero across the north Tuesday through Thursday nights, with the Downeast region falling into the lower teens for lows into the middle of the week as well.

AVIATION /21Z SATURDAY THROUGH THURSDAY/
NEAR TERM: MVFR/IFR conditions this evening will become MVFR cigs for sites this evening. By tomorrow AM expecting MVFR to become IFR tomorrow. N-NE winds 5-10kt tonight becoming NE 5-15kt tomorrow.

SHORT TERM: Sunday night...MVFR with occasional drops to IFR/LIFR in heavier snow, especially from BGR up through HUL. NE winds 5 to 10 kts.

Monday...MVFR with occasional drops to IFR/LIFR In heavier snow, especially from BGR up through HUL Monday morning. NE winds 5 to 10 kts.

Monday night...MVFR with brief periods of IFR in snowfall. N winds 5 to 10 kts.

Tuesday...MVFR cigs. NW winds 5 to 10 kts.

Tuesday night...Improving towards VFR. Light N to NE winds.

Wednesday - Thursday...Generally VFR with MVFR/IFR possible each morning with lower cigs. Winds light and variable.



MARINE
NEAR TERM: Winds/waves will remain below SCA into Sunday midday.
NE winds will increase later in the day and begin to gust 25-30kt over the coastal waters by sunset. Small Craft Advisory goes into effect at 4pm on Sunday for the Coastal Waters.
Intra-Coastal waters expected to remain below 25kt at this point. Waves 2-3ft this evening becoming 3-4ft tomorrow. Wave period intially 5-6sec tonight becoming 8-9sec tomorrow.

SHORT TERM: An SCA is currently in place Sunday night through the day on Monday, mostly for seas as they sit at 5 to 7 ft, though winds will gust to 30 kts early on. Intra-coastal waters may need to be added to this SCA should gusts increase more pending the track of the storm. Conditions will slowly improve through the middle of the week.

CAR WATCHES/WARNINGS/ADVISORIES
ME...Winter Storm Watch from Sunday afternoon through Monday evening for MEZ003>006-010-011-015>017-031-032.
MARINE...Small Craft Advisory from 4 PM Sunday to 7 PM EST Monday for ANZ050-051.

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