textproduct: Caribou

WHAT HAS CHANGED

-Added fog within warm sector of approaching low pressure this weekend, particularly across the Downeast region. -Increased sleet in forecast due to forecast sounding profiles being conducive for ice pellets in addition to freezing rain Saturday morning

KEY MESSAGES

1) Light wintry mix Friday night into Saturday, which could create slick travel conditions by early Saturday morning. Areas of fog could also limit visibility through this time.

2) Warming trend with above normal temperatures, leading to melting snow pack and river/lake ice rot into the middle of next week.

DISCUSSION

KEY MESSAGE 1... Light wintry mix Friday night into Saturday, which could create slick travel conditions by early Saturday morning. Areas of fog could also limit visibility through this time.

KEY MESSAGE 1 DESCRIPTION... A low pressure system will approach from the west Friday night into this weekend. Leading the way will be a warm front, lifting north through the CWA Friday night into Saturday morning. The forecast area will likely spend Saturday afternoon in the warm sector of the approaching low pressure system. A cold front will then cross the region through Saturday night.

Forecast soundings continue to increase confidence in a cold air damming setup, with a warm nose around 900mb that will lead to a wintry mix developing along the leading edge of precipitation. Mid level dry air will need to saturate before precipitation makes it to the surface, and there is still some uncertainty in how quickly this will happen through Friday night. Guidance has a bias of saturating dry air aloft more quickly than ends up happening, and based on this previous bias, precip chances have been reduced over the first 6 hours Friday night to slow the onset of precipitation. That said, this may not have been trimmed enough, and there is the potential that precip may not begin until after sunrise Saturday morning, particularly across the Rt 11 and US-1 corridors.

The type of wintry precip that falls will highly depend on the timing that precip begins as well as how quickly CAD erodes and the surface warms. If the dry air aloft holds on until after sunrise, there could be little to no wintry mix, as increased warm air advection aided by the return of diurnal heating will quickly overcome weak to moderate CAD and precip may begin as warm rain. However, if the dry air aloft saturates more quickly and the CAD holds on a little stronger, freezing rain and/or sleet may fall through the second half of the night. The most likely areas for this wintry mix will be the Central Highlands up through the north: wherever cold air may dam, though the Bangor area through the Downeast region could see a brief period of freezing rain and/or sleet before temperatures quickly rise above freezing.

At this time range, it is difficult to differentiate between sleet and freezing rain chances, so in this forecast these chances have been set to equal to each other. With such a defined warm nose such as seen on GFS forecast soundings and a clear CAD setup, sleet is definitely in the realm of possibility, though the chances of sleet are often very washed out in the NBM, which is why chances were increased with this forecast.

QPF amounts are overall light with this system, particularly during the time in which wintry precip types are possible. Therefore, not anticipating any large ice accretions or sleet accumulation, but just enough icing is possible to create slick travel conditions Saturday morning.

Finally, the rush of warm air and moisture over frozen and snow covered ground will likely generate advection fog, with areas of fog likely Downeast to limit visibility through the day on Saturday before loss of snow pack, warming surface, and increased winds erode the fog.

KEY MESSAGE 2... Warming trend with above normal temperatures, leading to melting snow pack and river/lake ice rot into the middle of next week.

KEY MESSAGE 2 DESCRIPTION... A split stream flow may develop into the next work week, with the subtropical jet to our south and polar jet to our north, ushering future low pressure systems south and north of our CWA respectively through the first half of the next week. With a more mild air mass in place and no change in air mass through the beginning of the week, temperatures may gradually climb each day, with daily high temperatures lifting into the upper 40s to mid 50s through the forecast area each day. For lows, temperatures could fall into the mid 20s to low to mid 30s each night.

There is a chance for another low pressure system through the middle of next week, with lots of unknowns at this time. Given the more mild temperature pattern, precip types could be colorful once more, and it is not out of the question that another warm nose (such as seen on forecast profiles) could lead to another round of wintry mix. Should the orientation or speed of this system change however, this system could be all rain, or a mix of rain and snow, or precip chances could trend down and the system end up not being as impactful. This system will continue to be closely monitored over the next several days.

AVIATION /06Z THURSDAY THROUGH MONDAY/

VFR conditions are expected through tonight. VFR at the Aroostook terminals Friday with MVFR ceilings possible KBGR/KBHB. N to NE wind around 10 kt today, then 5 to 10 kt tonight. E wind around 5 kt Friday.

Fri night - Sat...MVFR/IFR. Wintry mix possible overnight through early Saturday morning, becoming rain through the day on Saturday. SSE winds 5 to 10 kts overnight becoming S at 10 to 15 kts gusting 25 to 30 kts on Sat.

Sat night - Sun...Improvement to VFR. Winds shift W winds 5 to 10 kts.

Sun night - Mon...VFR across all terminals. SW winds 5 to 10 kts with gusts to 20 kts.

MARINE

A Small Craft Advisory remains in effect through Friday morning for the outer waters.

Wave heights are likely to remain around 4 to 6 ft Friday night despite wind gusts diminishing below 25 kts, and small craft advisory criteria will likely continue to be met Friday night through Saturday. Winds will begin to increase on Saturday with the passage of a low pressure system, and there is increasing confidence gusts will increase to gales by Saturday night, then taper once more into the day on Sunday. SCA criteria may then continue into the early part of next week. Mild air temperatures will limit any chance of freezing spray development.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory from 7 AM this morning to 7 AM EST Friday for ANZ050-051.