textproduct: Caribou

SYNOPSIS

A cold front will move through the area this evening. Weak high pressure builds in through Thursday morning, then slides to the east Thursday night. A low pressure system passes to our northwest Friday, followed by another cold front Friday night. High pressure builds in Saturday with another area of low pressure passing north of the area on Sunday. High pressure builds towards the area again early next week.

NEAR TERM /THROUGH THURSDAY NIGHT/

630 PM Update: Another round of light snow is moving in from the west at this time, however the cold front responsible for this precipitation is weak and lacking the support to maintain precip over the higher terrain. Therefore, any additional snow will be light if any across the north this evening.

430 PM Update: Snow amounts were increased slightly across the forecast area as temperatures are running slightly below previously forecast and the bright band of reflectivity seen on current KCBW radar is indeed all snow, with larger dendrites being the primary flake type... a sign of slightly higher SLRs. Indeed, the 4PM intermediate measurement at KCAR revealed an SLR of around 17:1. Storm total snow is thus increased to a quarter of an inch up to around 1 inch in the north, and up to a quarter of an inch down through the Upper Penobscot valley.

Key message...Possible deteriorating travel conditions this evening with mixed precipitation changing to light snow across the north. Minimal accumulation expected.

Previous Discussion: The cold front passing through this evening will bring a round of precipitation along and just behind it before high pressure moves in tomorrow. Current atmospheric profiles show a warm nose about 3 to 5k feet above the surface, which has been contributed to mixing precipitation all day. The cold front will eliminate this warm nose, but before the front, precip may still be mixed this evening. Precip will not be particularly heavy, so evaporational cooling is not expected to be a factor, we will just have to wait for the colder air to move in aloft. By mid- evening, precipitation should be all snow. QPF values are light, so less than an inch of snow will fall, even without any rain mixing in. The colder temperatures may also contribute to ice forming on roads and other flat surfaces overnight, so caution is advised for travelers. Other wise, Thursday will be quiet with a quick visit from high pressure before a stronger system approaches Thursday night.

SHORT TERM /FRIDAY THROUGH SATURDAY/

*Key Messages: 1) Strong winds are likely with damaging winds possible Friday, particularly along the coast where a High Wind Watch remains in effect. Additional strong winds are likely later Friday night to Saturday morning, particularly across the north.

2) Rain is expected across the entire area Friday along with significant snowmelt. Minor flooding is possible.

3) Temperatures fall below freezing Friday night. Northern areas will see a faster freeze after precipitation ends and more potential for icy surfaces Saturday morning.

*What Changed: 1) Storm Watch issued for all marine zones Friday.

2) Slight increase in winds further inland towards Bangor and Interior Downeast Maine.

Friday: A negatively tilted upper level trough will lead to rapid deepening of the surface low across central and eastern Quebec on Friday. Ahead of its cold front, strong moisture transport will bring PWATs at or around an inch across much of the forecast area. A period of moderate to heavy rain is expected, along with areas of fog from high dew points moving across cold snowpack. Some of the fog may be locally dense. Rainfall amounts of generally three quarters of an inch to an inch and a half are anticipated, with significant snowmelt wiping away a majority of the snowpack for all but far northwestern areas of Maine. The combination of rainfall and snowmelt could cause minor flooding, but significant flooding is not anticipated, due in part to the antecedent drought conditions.

The primary impact is expected to be strong south winds, especially along the coast through the Bangor region and Interior Downeast Maine. A High Wind Watch remains in effect for the coast. Further north, wind advisories will likely be needed for Southern Penobscot County and the remainder of Hancock and Washington Counties. There is a chance (20 to 40 percent) that High Wind Warnings may be required for the Bangor area, depending on the strength of the low level jet. Coastal flooding is not expected due to the current tide cycles being low for the month.

Friday Night to Saturday: A cold front will move through the area after sunset Friday. Timing uncertainty remains, but the consensus is for a quick 10 to 15 degree temperature drop with temperatures remaining above freezing for a period until a secondary front moves through later during the night and drops temperatures below freezing. Downeast areas are expected to have more time between the end of precipitation and sub-freezing temperatures. Depending on the timing, northern areas may see precipitation end as a brief period of snow with temperatures falling below freezing. Icy spots are possible Saturday morning as refreezing occurs. After a few hours of lower winds, winds will increase again late Friday night and Saturday morning as the surface low continues to deepen and the pressure gradient tightens. Winds will be strongest across the north during this period, and Wind Advisories may be needed.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

*Key Messages: 1)A light snow accumulation is likely (60 to 80 percent chance) Saturday night to Sunday for all areas except the coast. 2)Another period of snow is possible (50 to 60 percent chance) Tuesday afternoon into Tuesday night.

Saturday night to Sunday: Zonal flow sets up for Saturday night into Sunday, leading to modest warm advection and a return to near normal temperatures. A warm front crosses the area Saturday night as another weaker area of low pressure passes north of the area, leading to a period of light snow away from the coast. Guidance has decreased QPF with this over the last cycle, so headline level impacts are unlikely.

Monday to Tuesday Morning: High pressure builds towards the area Monday and crests across the area Tuesday morning. An upper level low is forecast to slowly move away across the Canadian Maritimes with little impact aside from some cloud cover and possible flurries Monday. Otherwise, partly to mostly clear skies, dry conditions, and slightly below average temperatures are anticipated.

Tuesday Afternoon to Wednesday/Christmas Eve: There is general agreement that a moderate to strong shortwave and clipper system will move through the area Tuesday night into the morning of Christmas Eve. Snow showers or a period of light snow is possible, along with a reinforcement of colder air and below average temperatures for Christmas Eve. The orientation of the shortwave on most ensemble members suggests limited moisture availability, so a significant storm is unlikely during this period.

AVIATION /00Z THURSDAY THROUGH MONDAY/

NEAR TERM: VFR for southern terminals through the period. MVFR conditions for northern terminals, primarily with ceilings this evening, transitioning to VFR prior to midnight.

SW winds switching to W/NW behind the front. LLWS possible with frontal passage tonight.

VFR conditions continue through the day on Thursday. Winds become southerly and gusts will increase to 20 kts by the evening.

SHORT TERM: Friday: IFR/LIFR with RA and areas of FG. Strong S winds 15 to 25 kt with gusts up to 35 kt, except for BGR and coastal terminals stronger winds 15 to 30 kts with gusts up to 45-50 kts are expected. LLWS likely.

Friday Night to Saturday: Becoming VFR during the evening. WSW winds 10 to 20 kts with gusts up to 30kts in the evening, shifting WNW and increasing to 20 to 30 kts gusting to around 40 kts later Friday night and Saturday morning. Winds decrease to 10 to 20 kts with gusts to 30 kts Saturday afternoon.

Saturday Night to Sunday: MVFR/IFR with light snow, except rain at coastal terminals. S winds 5-10 kts with gusts to 20 kts, shifting WSW Sunday.

Sunday night to Monday: VFR south, MVFR possible north. NW winds 10-15 kts with gusts around 25 kts possible.

MARINE

NEAR TERM: Gale force winds will continue through late tonight, then drop below SCA conditions. Seas will gradually diminish this evening. Conditions, both winds and waves, will drop below small craft levels on Thursday before ramping back up to SCA on Thursday night and eventually gales/possible storms in the short term.

SHORT TERM: Gale force winds are near certain Friday with potential (50 to 70 percent chance) for Storm Force wind gusts Friday afternoon. A Storm Watch has been issued. Winds shift from the west Friday evening, remaining at gale force through early Saturday morning before falling below 25 kts Saturday afternoon. Winds increase again Saturday night, possibly to Gale force, before decreasing again Sunday night into early next week.

Seas continue to increase Friday, possibly reaching around 16 to 19 feet by Friday evening before diminishing to around 10 feet on Saturday and 5 to 9 feet Saturday night through Sunday night. Seas then fall to around 3 to 6 feet early next week before increasing again mid-week.

CAR WATCHES/WARNINGS/ADVISORIES

ME...High Wind Watch from Friday morning through Friday evening for MEZ029-030. MARINE...Gale Warning until midnight EST tonight for ANZ050>052. Storm Watch from Friday morning through Friday evening for ANZ050>052.