textproduct: Caribou

WHAT HAS CHANGED

-Increased snow showers across the north for Sunday.

-Slowed onset of precipitation on Tuesday, especially across the North.

KEY MESSAGES

1) Unseasonably cold temperatures continue through the weekend.

2) Snow North and a rain/snow mix elsewhere Tuesday morning, transitions to a wintry mix across the North and rain elsewhere Tuesday afternoon. This wintry mix could linger across portions of the North into Wednesday morning, especially across the St John Valley. This will impact the Tuesday afternoon and possibly the Wednesday morning commute across at least portions of the North.

3) Rapidly dropping temperatures could quickly freeze untreated wet surfaces Wednesday afternoon/night, potentially creating slippery travel conditions for the Wednesday evening and Thursday morning commute.

4) There is the possibility for a period of snow across the North and rain/snow elsewhere from Thursday night into Saturday. This could create dangerous travel during at least a portion of this time range.

DISCUSSION

KEY MESSAGE 1...Unseasonably cold temperatures continue through the weekend.

KEY MESSAGE 1 DESCRIPTION... The upper level trof continues to pipe cold air into the region for tonight. The 925mb model temps shows a cold airmass between -8C to -12C across the region tonight. Surface temps will be in the single digits in the north and teens in the south. In addition, a weak vort max will develop to the west and move across the region tonight. Decided to include isolated snow showers. By Sunday, pressure gradients tighten behind the shortwave which will increase winds for the day. This is expected to erode the inversion with a well mixed boundary layer. This will bring surface temps back into the mid 30s in the north and low 40s in the south, though winds will make it feel about 10 degrees cooler.

KEY MESSAGE 2... Snow North and a rain/snow mix elsewhere Tuesday morning, transitions to a wintry mix across the North and rain elsewhere Tuesday afternoon. This wintry mix could linger across portions of the North into Wednesday morning, especially across the St John Valley. This will impact the Tuesday afternoon and possibly the Wednesday morning commute across at least portions of the North.

KEY MESSAGE 2 DESCRIPTION... The guidance still has not converged on a solution for the track of the storm system that will impact the region from Tuesday into Wednesday.

A northern stream shortwave trough moves into Southwestern Ontario Tuesday, tracking to near/just east of James Bay by Wednesday morning, then to eastern Quebec/Labrador by Wednesday evening. The differences in the exact strength, axis orientation, timing and placement of this shortwave trough is causing a lot of variability in the placement of the resultant surface features. There remain three basic scenarios with this system:

SCENARIO A: Surface low tracks near/just north of the northern Maine/Canada boarder. This will result in the least amount of time for a wintry mix and could see the entire region (except for maybe the St John valley) change to all rain. This camp would limit impacts to the Tuesday afternoon commute mainly for the Crown of Maine. A minority of ensemble members follow this scenario.

SCENARIO B: The surface low tracks across Central Maine. This will result in a prolong period of a wintry mix, possibly primarily freezing rain across the North, especially across northern portions of Aroostook, Somerset and Piscatiquis counties. Should see a brief period of snow at the start, change over to a wintry mix Tuesday afternoon, then to mainly freezing rain Tuesday night. Most areas should change to all rain by Wednesday morning, but this wintry mix or freezing rain could linger into Wednesday morning across the St John Valley and portions of the North Woods. Across Downeast Maine and the Bangor/Penobscot region a rain/snow mix Tuesday morning should become all rain Tuesday afternoon and remain rain until tapering off Wednesday. Elsewhere, the transition to all rain should occur during Tuesday night. This scenario could yield a quick 1-3" burst of snow followed by several tenths of an inch of ice across northern portions of Aroostook, Somerset and Piscataquis counties, impacting the Tuesday afternoon and possibly the Wednesday morning commute across at least portions of northern Aroostook. Elsewhere under this scenario: impacts should be limited to mainly the Tuesday afternoon commute across the remainder of the North. This scenario is found in a plurality of ensemble members, and is what is shown in the official forecast.

SCENARIO C: The surface low tracks near or just south of the Maine Coast. This would bring mainly snow across the North, with snow to a wintry mix, possibly changing to rain across the Bangor/Penobscot Region and Interior Downeast, and a wintry mix to rain across coastal Downeast. This scenario would keep most of the impacts with the Tuesday afternoon commute to at most the Bangor/Penobscot Region and interior Downeast Maine (because of an expected later onset time to precipitation across the North in this scenario), but should see more extensive impacts across most of Northern and Eastern Maine for the Wednesday morning commute under this scenario. Impacts could also last into the Wednesday afternoon commute across Interior Downeast as any wintry mix turns into snow before ending. This scenario is only found in a relatively small (about 15%) of all ensemble members. It should be noted, that there are a bit more ensemble members suggesting the storm could go south of the coast of Maine then there were last night.

KEY MESSAGE 3... Rapidly dropping temperatures could quickly freeze wet surfaces late on Wednesday behind a cold front, potentially creating slick travel conditions for the Wednesday evening commute.

KEY MESSAGE 3 DESCRIPTION... There are some model differences in the timing of the arrival of the cold air and on how quickly it moves in. Most solutions bring the cold air into northern Maine Wednesday afternoon and elsewhere Wednesday evening. Some delay it to Wednesday night completely while others, never really have the North exit the cold air at all, and bring the cold air back to all areas by midday Wednesday. For now leaning towards the majority solution. With surface winds forecast to mainly remain below 10 mph, there should not be a lot of evaporation of any surface moisture, so could see widespread freezing of untreated wet surfaces. This could impact the Wednesday afternoon commute mainly across the North and could impact the Thursday morning commute as well elsewhere.

KEY MESSAGE 4... There is the possibility for a period of snow across the North and rain/snow elsewhere from Thursday night into Saturday. This could create dangerous travel during at least a portion of this time range.

KEY MESSAGE 4 DESCRIPTION... The models differ with the track, strength, and timing of a northern stream shortwave trough that should track from the upper Midwest/northern Plains, across the Great Lakes, then into the southern Maritimes some where in the Thursday to Saturday time frame. With the corresponding surface low going from the Plains/Midwest to the Ohio Valley, then likely to a coastal low passing to the south of Maine. Most solutions suggest that this should create a period of snow across the North and rain or snow elsewhere for 12-18 hour period sometime between Thursday afternoon and Saturday afternoon. This could result in a significant snowfall across the North impacting multiple commutes. The uncertainty in track, and strength of this system makes it difficult to specify what impacts are experienced further south. It should be noted that there still are some solutions that take this system completely to the south, with no impacts to the region, though this is a reduced number of solutions compared to previous runs.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Mainly, VFR conditions for all terminals tonight and Sunday. For tonight and Sunday, isolated snow showers are possible for all terminals which will briefly drop conditions to MVFR. Light and variable winds tonight. SW winds 5-15 kts Sunday.

Sun night...VFR, with SCT-BKN MVFR possible at northern terminals. S/SW winds around 5 kts.

Monday: High confidence in VFR at southern terminals. Mainly VFR at northern terminals, with a low chance of MVFR there in the afternoon in any showers. SW winds G15-20KT possible.

Monday night: Mainly VFR with a few hours of MVFR possible in any showers. LLWS possible Monday evening. NW winds G15KT possible late Monday night.

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. N-NE winds G15KT are possible Tuesday morning. LLWS possible Tuesday afternoon.

Tuesday night...IFR or lower likely. Wintry mix at northern terminals, rain at southern terminals.

Wednesday...Becoming VFR.

Wednesday night...VFR.

Thursday...A chance of MVFR or lower in the afternoon, otherwise VFR.

MARINE

A Small Craft Advisory has been issued for Sunday through Sunday night. Gust are expected to reach up to 30 kts. Seas 3-7 ft.

SCA conditions are expected on all waters on Monday, so have extended the SCA through then. SCA conditions are then likely to continue through Monday night and possibly into Tuesday on the coastal ocean waters, with sub-SCA conditions on the intra- coastal waters during this time frame. Gales likely on the coastal ocean waters with SCAs likely on the intra-coastal waters Tuesday night through Wednesday. Gales are possible on the intra-coastal waters during this time period as well.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory from 11 AM Sunday to 6 PM EDT Monday for ANZ050>052.