textproduct: Caribou

WHAT HAS CHANGED

- Updated aviation section to reflect latest TAFs

- Southern shift in forecast low track Tuesday night, leading to more mixed precip that could dip into the Upper Penobscot Valley

- Wintry mix possible again with the next low pressure system at the end of the week

KEY MESSAGES

1) Wintry mix expected to develop later Tuesday and Tuesday night for at least the northern half of the forecast area, with a threat for slick surfaces and travel difficulties into the Wednesday morning commute.

2) Rapidly dropping temperatures could quickly freeze wet surfaces late Wednesday, with possible travel hazards for the Wednesday evening commute and impacting cleanup efforts.

3) Increasing chance for more wintry weather late this week.

DISCUSSION

KEY MESSAGE 1... Wintry mix expected to develop later Tuesday and Tuesday night for at least the northern half of the forecast area, with a threat for slick surfaces and travel difficulties into the Wednesday morning commute.

KEY MESSAGE 1 DESCRIPTION... An open wave low pressure system will approach from the west on Tuesday, with a warm front lifting northwards through the forecast area Tuesday night, though the front will begin to slow and stall overnight. The most recent guidance has now shifted to the more southern track solution with the low, bringing the threat of ice further south as surface temperatures remain cooler for longer. As hires guidance begins to cover this storm, QPF has begun to slowly creep upwards as well, with the potential for enhancement on the north side of the low in combination with orographic lift up into the Longfellows.

Though there has been the trend with more models shifting to be better aligned with the Canadian ensembles (seen in Euro ensembles and GFS and Euro deterministic), there remains some guidance which keeps the low closer to the northern border (most GEFS members stick to this solution with this forecast cycle, and the ICON also continues to suggest a northern track). With the continued uncertainty in low track, and low track being paramount to precip type, the exact location of each precip type cannot be determined at this time.

Hazard details:

- Ice: Since the lifting of the warm front will begin to stall across the forecast area, a warm nose inversion will likely remain over the same area for several areas Tuesday night, with large quantities of precipitation moving through at this time. There is increasing confidence that this will lead to the accretion of at least a tenth of an inch of ice, with some areas seeing as much as a quarter inch of ice. Ice amounts will be reduced should the warm nose become less pronounced, leading to the creation of ice pellets instead.

- Snow and Sleet: Snow will likely remain mostly confined to the North Woods through northeastern Aroostook county. Snow character will likely be heavy and wet, especially as precip types begin to change and the snow begins to absorb water from freezing rain. The more sleet mixes in with the snow, the denser the snow will become as well, which could further impair cleanup efforts. It should be noted that NBM sleet probabilities have a notorious low-bias as the blend washes out the finer details of the precise ingredients required for ice pellets, but sleet probabilities from the most recent run of the NBM approach 20 to 25 percent, leading to high confidence that a period of accumulating sleet is likely somewhere across the northern half of the forecast area.

KEY MESSAGE 2... Rapidly dropping temperatures could quickly freeze wet surfaces late Wednesday, with possible travel hazards for the Wednesday evening commute and impacting cleanup efforts.

KEY MESSAGE 2 DESCRIPTION... The cold front behind the mid-week low pressure will lead to a rapid drop in temperatures through Wednesday night. A LLJ will develop ahead of this cold front, which could lead to a brief period of gusty winds Wednesday before the FROPA. Recent forecast soundings have trended stronger with this LLJ, and Downeast areas could see an 850 mb jet approaching 70 to 80 kts in strength. If these winds mix to the surface and surface winds are strong enough for long enough behind the stratiform rain, wet surfaces will have a chance to dry before temperatures crash. However, any surface which remains wet behind the FROPA could rapidly freeze, and this would return the chance for slick surfaces Wednesday evening.

Additionally, with a rapid drop in temperatures, new snow and sleet in the north which will have absorbed some rain during the day on Wednesday will quickly freeze into a more solid mass that could make cleanup efforts more difficult.

KEY MESSAGE 3... Increasing chance for more wintry weather late this week.

KEY MESSAGE 3 DESCRIPTION... Yet another occluding low pressure system will approach from the southwest through the end of the week, with a warm front lifting northwards through the forecast area, again. Though snow remains possible with this low, there is an increasing chance that several hours of widespread mixed precip may occur. The low track remains uncertain at this time range, and solutions exist which bring wintry mix to all areas of the CWA sometime Thursday night through Friday morning, likely impacting the Friday morning commute.

AVIATION /09Z MONDAY THROUGH FRIDAY/

Today...MVFR is possible this morning in scattered snow showers, mainly KHUL N. Otherwise, becoming mainly VFR by afternoon. S to SW wind 10 to 15kt with gusts 20kt. LLWS possible at the terminals, mainly this morning.

Tonight...Mainly VFR expected. NW to N wind 5 to 10 kt.

Tue...MVFR or lower conditions are expected in a wintry mix north and mainly rain for KBGR/KBHB. N to NE wind 5 to 10 kt

Tues night...IFR/LIFR. Rain at southern terminals, FZRA/PL at northern terminals. E winds 5 to 10 kts at northern terminals, SE winds 5 to 10 kts at southern terminals. Gusts to 20 kts.

Wed...IFR/LIFR with rain early, with quick drop in temperature with cold front late and rapid improvement to VFR. Rapid shift in winds to NE with afternoon cold front 10 to 15 kts gusting 20 to 25 kts.

Wed night...VFR across all terminals. NW winds 5 to 10 kts.

Thurs...VFR early, with cigs falling towards MVFR/IFR depending on storm timing. NE winds around 5 kts.

Thurs night - Fri...Decreasing conditions to IFR/LIFR in mixed precip types. Great uncertainty remains in precip type at each individual terminal. Chance for FZRA/PL. E winds 5 to 10 kts with gusts increasing to 20 to 25 kts.

MARINE

A Small Craft Advisory remains in effect through late tonight. Small Craft Advisory conditions may need to be extended into Tuesday.

Conditions will trend upwards towards gales Tuesday night, then winds decrease once more Wednesday night behind a cold front. Seas 3 to 5 ft to increase towards 7 to 12 ft Tuesday night, then gradually improve through the second half of the week.

CAR WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 6 PM Tuesday to 11 AM EDT Wednesday for MEZ001>006-010-011-031-032. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ050>052.