textproduct: Caribou

WHAT HAS CHANGED

- Winter Storm Watch issued for northern Maine where heavy mixed precipitation is possible Wednesday through Thursday morning.

- Increased sleet amounts compared to the NBM across northern Maine.

KEY MESSAGES

1) Heavy mixed precipitation is likely across northern Maine Wednesday into early Thursday. Significant accumulations of snow, sleet, and freezing rain are possible and could result in travel impacts and isolated power outages.

2) Temperatures will remain unseasonably warm through Tuesday resulting in snow melting, and ice rotting on rivers and lakes.

3) Two additional storm systems are likely to bring snow or wintry precipitation to all or most of the forecast area, the first Friday night into Saturday, then the second Sunday afternoon into Monday. Both of these systems have the potential to disrupt travel. The second system has potential for additional impacts from strong south winds depending on its track.

DISCUSSION

KEY MESSAGE 1...Heavy mixed precipitation is likely across northern Maine Wednesday into early Thursday. Significant accumulations of snow, sleet, and freezing rain are possible and could result in travel impacts and isolated power outages.

KEY MESSAGE 1 DESCRIPTION... Significant mixed precipitation is likely Wednesday into early Thursday as high pressure north of the area reinforces cold air across the low levels ahead of an upper level trough over the Great Lakes. The approach of this trough and its surface low will lead to warm air advection aloft across Maine. Strong isentropic lifting is expected with unseasonably high precipitable water values in excess of 1 inch expected to override the cold low level air across the north. 0Z model guidance has come into slightly better agreement regarding precipitation types with a majority of ensemble members and guidance, but not all, favoring a surface low track over the state instead of to the north. While some uncertainty remains regarding the finer details of the sleet, snow, and freezing rain transition zones, there is moderate confidence in the general idea that all or nearly all rain is favored over the southern half of the area, with a zone of at least moderate icing possible around the Katahdin Region into southern Aroostook County. Farther to the north snow will transition to sleet, with the most significant snow accumulations across the Saint John Valley and most significant sleet accumulations favored in between. It is worth noting that while AI models have sided with colder solutions, historically the initial cold air advection prior to the switch in wind direction has been slightly less robust than modeled in similar events, resulting in precipitation type transition zones farther to the north of models. Models also frequently struggle to depict the low level refreezing layer appropriately, underestimating sleet. Some adjustments were made to precipitation types to lower snow and freezing rain probabilities and raise sleet probabilities compared to the NBM.

Regardless of exact precipitation types, guidance favors 1 to 1.5 inches of liquid equivalent wintry precipitation across the north, which meets the threshold for a Winter Storm Watch. Travel impacts are likely, especially for the Wednesday afternoon and Thursday morning commutes. Light snow and sleet may start as early as the Wednesday morning commute also, but greater impacts are expected later in the day into Wednesday night. Ice accumulations locally up to a half inch are possible, but these are currently favored mainly over the North Woods where cold air damming is anticipated and higher elevation will not allow the refreezing layer to be as deep for sleet. However, the zone of greatest icing remains uncertain and may shift to more populated areas, in which case some power outages cannot be ruled out. The forecast will continue to be refined as the low track comes into focus over the next 24 to 36 hours.

KEY MESSAGE 2...Temperatures will remain unseasonably warm through Tuesday resulting in snow melting, and ice rotting on rivers and lakes.

KEY MESSAGE 2 DESCRIPTION... We will remain in a warm air mass today and Tuesday as high pressure along the East Coast continues to funnel warm and relatively humid air north across our region. High temperatures today will top 50 in most inland sites, and on Tuesday will again climb over 50 in all but far northern areas. The warm temperatures combined with some sunshine at times will cause the snow pack to compact and continue to melt. Some ponding in low lying areas may result from the snow melt.

The softening of the river ice combined with some possible rises on the rivers due to snowmelt may result in movement of ice Downeast and in the Lower Penobscot and Kenduskeag Valleys. This could lead to some ice jams early this week. Across the north, the ice will continue to rot but will likely remain in place with little or no significant movement expected.

KEY MESSAGE 3...Two additional storm systems are likely to bring snow or wintry precipitation to all or most of the forecast area, the first Friday night into Saturday, then the second Sunday afternoon into Monday. Both of these systems have the potential to disrupt travel. The second system has potential for additional impacts from strong south winds depending on its track.

KEY MESSAGE 3 DESCRIPTION... An active pattern will set up this weekend into early next week with two additional systems likely to impact travel. The first on Friday night into Saturday is currently favored (roughly 60 percent of members) to track along the coast as a vigorous shortwave trough exits the Great Lakes. This scenario would result in a moderate snowfall across nearly the entire area, with the heaviest amounts across central and Downeast areas. A large minority of guidance tracks the low farther to the northwest, which would result in a large dry slot moving over the area, leading to less precipitation. This solution would also be warmer with some potential for mixing closer to the coast.

A second system is also likely Sunday night into Monday as a longwave trough pivots across the Great Lakes, leading to another surface low moving northeast from the Great Lakes. This system is very likely to be stronger than the early weekend system, but its track varies significantly which will determine impacts. If a stronger low tracks west of the area, which is currently the slightly favored solution, a strong south wind could lead to issues, especially along the coast. Precipitation will likely start frozen regardless of the track, especially away from the coast, so at least some travel impact is looking likely from this system.

AVIATION /06Z MONDAY THROUGH FRIDAY/

Today...VFR conditions are expected at all sites. Some W wind shear at 2K ft expected early this morning followed by SW wind shear at 2K ft this afternoon. Winds SSW around 10 kt.

Tonight...VFR all sites except possibly dropping to MVFR over the far north late. SW wind shear at 2K ft. SW winds around 5 kt.

Tuesday...VFR over southern sites. MVFR across the north. Winds SW around 5 kt across the south and NW around 5 kt over the north.

Tuesday Night...Becoming VFR at northern sites and MVFR at southern sites. N winds 5 to 15 kts.

Wednesday to Wednesday Night...Deteriorating to MVFR/IFR with rain south and mixed precipitation north. E winds 5 to 10 kts with gusts to 20 kts.

Thursday to Thursday Night...Improving to VFR. W winds around 10 kts with gusts to 25 kts.

Friday...Predominantly VFR. W winds 5 to 10 kts with gusts to 20 kts possible.

MARINE

A SCA will be up for the offshore waters this morning, then for both the offshore and intracoastal waters this afternoon through tonight for SW winds gusting up to 30 kt. Winds should drop below SCA early Tuesday. Seas building up to 6 ft today then 7 ft tonight and dropping below 4 ft on Tuesday.

Winds and seas will increase to Small Craft Advisory thresholds on Wednesday before winds likely increase to Gale force Wednesday night through Thursday evening over the outer waters, and possibly over the intracoastal waters as well. Another period of gales is possible Friday night into Saturday and again Sunday night to Monday.

CLIMATE

A record high of 60 degrees was set in Bangor yesterday. Daily high temperatures approaching records are possible again today.

Tuesday, March 10

Caribou: Forecast 43 F; Record 55 F set in 1977 Houlton: Forecast 57 F; Record 58 F set in 1977 Millinocket: Forecast 57 F; Record 54 F set in 2016 Bangor: Forecast 59 F; Record 62 F set in 1977

CAR WATCHES/WARNINGS/ADVISORIES

ME...Winter Storm Watch from Wednesday morning through Thursday morning for MEZ001>006. MARINE...Small Craft Advisory until 8 AM EDT Tuesday for ANZ050-051. Small Craft Advisory from 1 PM this afternoon to 8 AM EDT Tuesday for ANZ052.