textproduct: Caribou

WHAT HAS CHANGED

- Lowered QPF slightly across Northern Maine to follow a trend in Hi-Res guidance.

- Lowered snow to liquid ratios across Northern Maine tonight into Friday AM.

- Increased sleet amounts late Saturday night to Sunday across northern Aroostook County.

KEY MESSAGES

1) Widespread wintry precipitation late tonight through Friday midday, will greatly impact travel tonight into Friday morning.

2) Another period of significant sleet is expected across northern Maine, with some freezing rain and snow also possible Saturday night into Easter Sunday. Difficult travel is possible across northern areas for Easter Sunday morning.

DISCUSSION

KEY MESSAGE 1... Widespread wintry precipitation late tonight through Friday midday, will greatly impact travel tonight into Friday morning.

KEY MESSAGE 1 DESCRIPTION... Setup...A surface low-pressure system, associated with 500mb shortwave energy, will track into the Great Lakes tonight. Meanwhile, surface high pressure north of the Gaspe Peninsula will establish a cold air damming (CAD) pattern at the surface with light east winds tonight. This evening, a warm front will lift north into Maine, riding up and over the cold air as temperatures aloft at 750mb rise above freezing. PWATs will increase to 1.5-2 sigma overnight as moisture advects northeastward. Expect precipitation to break out across the area from southwest to northeast. Surface winds will shift to the S-SE into Friday morning, beginning to erode the boundary layer CAD from south to north, aided by the increasingly warm April sun angle. A cold front will cross the area Friday evening, bringing an end to the precipitation with a brief changeover possible.

PTypes and Timing...As mentioned, PWATs will increase due to warm air advection aloft, reaching 1.5-2 sigma overnight and 2-3 sigma on Friday. Tonight temperatures will be in the mid to upper 20s north, 28-31F for the Central Highlands and Bangor Region, and 30-32F along the Downeast coast. Precipitation will start around midnight across much of the CWA, reaching far Downeast by 2-3AM Friday. Initially, a mix of snow, sleet, and freezing rain is expected along the Downeast coast northward to The Airline (Route 9) and the Bangor Region, which may create slippery travel overnight into the early AM hours. North of there, precipitation will initially develop as snow (with a few inches possible) before mixing.

The 750mb warm nose will rapidly increase over a deep cold pool. Hi-Res CAM soundings are in fairly good agreement regarding the sleet and freezing rain transitions. The initially shallow 750mb warm layer will gradually deepen, leading to a transition from sleet to freezing rain. Toward daybreak, winds will shift to the SE as the CAD erodes. This will change the Downeast coast and Bangor area to plain rain, while freezing rain continues along Route 6 from Greenville to Topsfield. North of there, a prolonged period of sleet is expected from the Baxter Region to the St. John Valley. By mid-morning, continued erosion of the CAD will bring all rain to the Bangor Region, Dover-Foxcroft, and Lincoln, encroaching on Topsfield to Houlton.

The combination of the warm April sun angle and strengthening SE winds (gusting 15-25 mph) will erode the remaining CAD, turning the entire CWA to rain by mid-afternoon. Rain will continue into the evening until a dry slot works north ahead of the cold frontal passage, as the low tracks to our north in Quebec. Precipitation may briefly switch back to snow in the St. John Valley to Caribou area, perhaps leaving an additional dusting. This could lead to a flash freeze across northern zones as temperatures fall quickly back below freezing.

Accumulations...Snow will be mainly confined to the north, with 2-5 inches expected in the St. John Valley, Route 11 north from Oxbow to Portage and the Caribou/Presque Isle areas. The Baxter Region to Houlton and the Moosehead Region can expect 1-2 inches, while areas further south will likely see only a minor dusting. There is potential for significant sleet accumulations 0.5 up to 1.0 inch from the Central Highlands into Northern Maine.

The main uncertainty lies in freezing rain totals, which depend heavily on the strength of the CAD and the increasing sun angle by the time precipitation falls as freezing rain in Northern Maine on Friday. Up to a glaze of ice is possible from just inland of the Downeast shoreline northward to Southern Aroostook County. Up to a tenth of an inch of ice is possible across Northern Maine, with up to a quarter-inch possible in the Greenville area and North Woods.

The greatest chance of heavy mixed precipitation reaching warning criteria exists in Northwest and Northeast Aroostook County, so a Winter Storm Warning remains in effect from 11PM this evening till 5PM Friday. Conditions will rapidly improve during the day so it is possible the warning will be cancelled sooner. For the Central Highlands, Far Eastern, North Woods, and Penobscot Valley Maine a Winter Weather Advisory remains in effect from 11PM this evening to 2PM Friday. Lastly, Coastal Downeast, Interior Downeast and Bangor Region are under a Winter Weather Advisory from 11PM this evening till 10AM Friday.

Impacts...Travel will become slippery nearly areawide late tonight due to snow, sleet, and freezing rain. Untreated surfaces will cool down significantly tonight, leading to slick conditions. As temperatures warm overnight in Downeast areas, travel will gradually improve as surfaces become slushy, and eventually wet. Friday morning, conditions will improve from the Bangor Region northward, reaching Northern Maine by midday. The increasingly warm April sun angle will allow surfaces to heat up and turn wet. The greatest concern for the Friday morning commute will be from the Bangor and Calais regions northward to the St. John Valley. Drivers should anticipate slippery roads, leave extra braking distance, and use caution when walking on untreated surfaces.

KEY MESSAGE 2... Another period of significant sleet is expected across northern Maine, with some freezing rain and snow also possible Saturday night into Easter Sunday. Difficult travel is possible across northern areas for Easter Sunday morning.

KEY MESSAGE 2 DESCRIPTION... In a very similar setup to the system tonight into Friday, another warm front will lift across the area later Saturday night into Sunday as low pressure passes to the northwest. This low is favoring a slightly stronger intensity with a track farther to the northwest, which should lead to slightly warmer temperatures and keep wintry precipitation types away from coastal and Downeast areas. While there is some uncertainty, the general pattern strongly favors significant sleet/ice pellets across far northern areas, with potential for 1 to 3 inches of sleet and perhaps an additional inch or two of snow on top of the sleet, mainly across the Saint John Valley. Freezing rain is also possible, with the greatest ice accretion potential across the Central Highlands into the North Woods, where higher elevations will cause less depth of the refreezing layer. Lighter accumulations of a combination of sleet and freezing rain are likely for central areas east of the Central Highlands. The NBM, likely due to the ECMWF/EPS systematic bias against ice pellets, was too low with sleet probabilities again. Sleet probabilities were increased compared to the NBM, with compensatory decreases to snow and freezing rain probabilities, especially early during the event Saturday night across northern Maine. Any period of snow will likely be brief, with significant reductions in snow ratios made compared to the NBM to 10 to 1 or less due to potential for riming near the warm nose aloft and generally poor conditions for snow growth with strong winds aloft and very little correlation between lift and the DGZ.

Travel impacts are likely north of Bangor for a period Saturday night, with improvement from south to north Sunday morning. By 8AM Sunday morning, the greatest probabilities for sleet and freezing rain will be north of Baxter State Park as temperatures rise or remain above freezing to the south. The greatest impacts to travel Easter morning are expected across this area, especially northern Aroostook County where significant sleet accumulations are expected into the morning. Precipitation is expected to change to rain everywhere around mid-morning as temperatures climb above freezing.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Rest of Today...VFR all terms... Winds generally trending to become VRB winds around 5kt.

Tonight...IFR/LIFR in snow, sleet, and/or freezing rain. Precip transitions to rain at BHB and BGR by 12z Fri AM. SE winds 5-10kt.

Friday...IFR/LIFR early, with mixed precip changing to RA from south to north through the day. Becoming MVFR/IFR in the afternoon. S/SE winds 5-15kt. Gusts to 25kt at northern terminals possible.

Friday night...IFR north becoming MVFR with MVFR becoming VFR south. VCSH/-SHSN possible at northern terms. Wind shift expected between 05-08Z. Winds SW 5-15kt gusting up to 20kt shifting to the N-NNW 10-15kt.

Saturday: MVFR possible early, mainly at northern terminals. Otherwise VFR. NE winds 5-15 kts.

Saturday night to Sunday: VFR early, becoming IFR/LIFR with +PL at northern terminals, mixing with SN at the onset and FZRA Sunday AM before changing to -RA. -PL at central and southern terminals changes to -RA late Saturday night or early Sunday morning. All -RA is expected at coastal terminals such as BHB. SE winds 10 to 15 kts with gusts to 30-35 kts possible. LLWS possible.

Sunday night: MVFR possible at northern terminals, otherwise VFR. WSW winds around 10 kts gusting to 20 to 25 kts.

Monday: Low VFR ceilings, with a chance of MVFR at northern terminals. WNW winds around 15 kts with gusts to 25 to 30 kts.

Monday night to Tuesday: VFR. NW winds 5 to 15 kts.

MARINE

A Small Craft Advisory has been issued for the Coastal Waters out 25nm from 5AM Friday to 2PM Saturday. Southeast winds Friday, shift southwest Friday night then North on Saturday. Winds 15 to 25 kt with gusts up to 30 kt and seas 4 to 7 ft expected. The Small Craft Advisory may need to be extended with later updates.

Small Craft Advisory winds and seas are expected through Sunday evening. Gale force winds are also possible (60 percent chance over outer waters, 40 percent over the intracoastal waters) later Saturday night into Sunday morning. Winds will be first to decrease Sunday night, but seas will remain elevated through much of the night, especially over the outer waters. Winds and seas fall below advisory levels Tuesday into mid-week.

CAR WATCHES/WARNINGS/ADVISORIES

ME...Winter Storm Warning from 11 PM this evening to 5 PM EDT Friday for MEZ001-002. Winter Weather Advisory from 11 PM this evening to 2 PM EDT Friday for MEZ003>006-010-011-031-032. Winter Weather Advisory from 11 PM this evening to 10 AM EDT Friday for MEZ015>017-029-030. MARINE...Small Craft Advisory from 5 AM Friday to 2 PM EDT Saturday for ANZ050-051.