textproduct: Caribou

WHAT HAS CHANGED

Increasing possibilities of a more southern storm track for mid-week system.

Increasing confidence in potential for plowable snow across the North late this week.

KEY MESSAGES

1) A brief period of light snow across the north Monday morning could result in minor travel impacts, then turning unseasonably warm by afternoon.

2) A wintry mix is possible across the North from Tuesday afternoon into Wednesday morning, which could create slick surfaces leading to travel hazards, particularly for the Wednesday morning commute.

3) Rapidly dropping temperatures may quickly freeze wet surfaces late Wednesday, with possible travel hazards for the Wednesday evening commute.

4) Increasing chances for a plowable snow across at least the North late this week.

DISCUSSION

KEY MESSAGE 1... A brief period of light snow across the north Monday morning could result in minor travel impacts, then turning unseasonably warm by afternoon.

KEY MESSAGE 1 DESCRIPTION... The approaching shortwave will bring S flow and increasing clouds tonight. RH models show increase low and mid level moisture that will produce isolated to scattered snow showers in the north. In addition, temps will remain fairly moderate through the night. By Monday, a weak cold front will move through the region with temps reaching well above normal. Showers with the front will bring rain to the north before switch back to snow showers by Monday night. In the north, the Monday morning commute could have some minor travel impacts.

KEY MESSAGE 2... A wintry mix is possible across the North from Tuesday afternoon into Wednesday morning, which could create slick surfaces leading to travel hazards, particularly for the Wednesday morning commute.

KEY MESSAGE 2 DESCRIPTION... A northern stream shortwave trough is forecast to track from the southern Canadian Prairie Provinces Tuesday morning, to far southwestern Ontario by Tuesday evening, to southwestern Quebec by Wednesday morning and into the Canadian Maritime Provinces by Wednesday evening. There is some differences in the exact timing and strength of this shortwave, but the models are fairly consistent in its track. Where they do differ still is on what this means on the surface. There are still 3 scenarios in play with this system.

Scenario A: The surface low tracks to the North - the NAM is the main deterministic model in this camp, and it represents about less than 20 percent of 12Z ensemble solutions. If this scenario plays out, most areas will see at most only a brief period of winter precipitation should be expected late Tuesday before becoming all rain. Across northern Aroostook, there could be several hours of a wintry mix late Tuesday afternoon/evening before changing to all rain. This is viewed as the least likely scenario.

Scenario B: The surface low tracks across central or northern Maine. The deterministic ECMWF is in this camp, but has shifted noticeably southward from previous runs. This represents less than 25% of all 12Z ensemble solutions. This is a significant change from the 00Z ensemble solutions, when it represented over 1/2 of all solutions. Because this is a marked change, leaned towards this solution for the forecast to guard against the forecast returning to this with tonights model runs. This scenario produces 1-3" of snow across the North late Tuesday, then several hours of a wintry mix Tuesday night and possibly into Wednesday morning across the Saint John Valley. This could result in a 1/3-1/2" of freezing rain and around 1/2 to 3/4" of sleet across the North as well. This would result in impacts to the Tuesday afternoon and potentially the Wednesday morning commute across the North. Across the remainder of the forecast area, there would be mainly rain, with around 1/3 to 2/3 of an inch of rainfall. Because most rivers in the southern portions of the area have flushed of ice, and there has been some thawing of the ground, there is expected to be minimal hydrologic impact as a result.

Scenario C: The surface low tracks near the Maine Coast either just inland or offshore across the northern Gulf of Maine. The deterministic GFS, CMC-Regional and CMC-Global are in this camp. It represents almost 60% of the 12Z ensemble solutions. This scenario should result in a plowable snow across at least portions of the North. late Tuesday and Tuesday night, impacting the Tuesday afternoon commute there. The area of wintry mix would shift south across the Bangor/Penobscot Region, interior Downeast Maine, and possibly the southern Central Highlands from late Tuesday possibly into at least early Wednesday morning before changing to rain. This could impact the Tuesday afternoon and Wednesday morning commutes there. Finally along the Downeast Coast, depending on the exact low track will determine how much rain vice a wintry mix this area will see. There should be enough rain mixed in to minimize any wintry impacts. If current trends hold, the forecast will shift to this scenario with future updates. So for now it would be prudent to plan for both Scenarios B and C.

KEY MESSAGE 3... Rapidly dropping temperatures may quickly freeze wet surfaces late Wednesday, with possible travel hazards for the Wednesday evening commute.

KEY MESSAGE 3 DESCRIPTION... Cold air moves in on Wednesday either behind the cold front or the departing surface low depending on which scenario plays out. This should result in the rapid freeze of any untreated wet surfaces, especially elevated ones. The main impact should be for the Wednesday afternoon commute.

KEY MESSAGE 4... Increasing chances for a plowable snow across at least the North late this week.

KEY MESSAGE 4 DESCRIPTION... The models have come closer together with their solutions for the system for late this week.

Deep layered ridging exits to the east late Thursday ahead of an advancing northern stream shortwave trough track across the Great Lakes Thursday night, across southern Quebec Friday, then across New England and into the southern Maritimes Friday night. This should result in a surface low tracking to the southern Great Lakes by Friday morning, to western New England by Friday evening, then transitions to a coastal low which should be south of Nova Scotia by Saturday morning. This storm track should bring snow across the north, possibly mixing with some sleet at times (depending on how fast the coastal low takes over) from Thursday night into Friday night. Across Downeast Maine and the Bangor/Penobscot region there should be a wintry mix mixing with or changing to rain, especially near the coast. Depending on the exact low track, there is a chance for at least accumulating snow across the interior Downeast and the Bangor Penobscot Region as well. This could impact the commutes from as early as Thursday afternoon (low chance), and both commutes on Friday (best chance).

AVIATION /18Z SUNDAY THROUGH FRIDAY/

VFR conditions for all terminals tonight and early Monday morning. For north terminals, MVFR cigs and possible vsby in snow showers through late Monday morning to Monday afternoon. For south terminals, VFR throughout Monday. SW winds 5-10 kts tonight, then increasing to 10-15 kts Monday.

Monday night: VFR with possible MVFR in snow showers. Light WNW winds.

Tuesday: IFR or lower likely, developing from SW to NE. Snow to a wintry mix at northern terminals. A wintry mix to rain at southern terminals. LLWS possible southern terminals and SE winds G15-25kt possible northern terminals Tuesday afternoon.

Tuesday night: IFR or lower likely. A wintry mix to rain at northern terminals. LLWS possible southern terminals.

Wednesday: IFR or lower possible in the morning, then becoming VFR. Snow showers possible ahead of a cold front late morning/early afternoon. NW winds G20-30KT possible in the afternoon.

Wednesday night-Thrusday morning: VFR.

Thursday afternoon-Friday: IFR or lower likely, developing Thursday afternoon/evening. Mainly snow possible at northern terminals with snow and/or rain possible at southern terminals. ENE-NE winds G15-25KT possible.

MARINE

A Small Craft Advisory has been extended tonight through Monday night with guts up to 30 kts and seas 5-9 ft.

SCA conditions are possible on the coastal ocean waters Tuesday, with sub-SCA conditions on the intra-coastal waters. Winds increase Tuesday night with SCA conditions likely on the intra- coastal waters and gales possible on the coastal ocean waters. Conditions should become SCA throughout by Wednesday afternoon. SCA conditions could then continue on the coastal ocean waters Wednesday night and Thursday, with sub-SCA conditions on the intra-coastal waters. SCA conditions are then likely on the coastal ocean waters and possible on the intra-coastal waters from Thursday night into Friday night. Gales are also possible on the coastal ocean waters during this time frame.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ050>052.