textproduct: Caribou

WHAT HAS CHANGED

- Snow and ice amounts have decreased and sleet amounts have increased across the north as more precipitation is now forecast to fall as sleet.

-(640 AM Update) Cancelled the existing Small Craft Advisory and replaced it with a new one on Wednesday. Also updated the aviation section for the 12z TAFs.

KEY MESSAGES

1) Heavy mixed precipitation is likely across northern Maine Wednesday into early Thursday. A significant accumulation of sleet, along with some snow and freezing rain is possible and will result in travel impacts and difficult snow removal.

2) A fast moving storm system may bring snow late Friday night into Saturday morning. This could impact travel with slushy and slippery roads Saturday morning.

3) A large storm system approaching late in the weekend may bring snow north and a mix Downeast Sunday night, changing to rain across the area early Monday. Strong south winds may accompany the storm. This could bring some messy travel across the north early Monday, and the chance for isolated power outages.

DISCUSSION

KEY MESSAGE 1...Heavy mixed precipitation is likely across northern Maine Wednesday into early Thursday. A significant accumulation of sleet, along with some snow and freezing rain is possible and will result in travel impacts and difficult snow removal.

KEY MESSAGE 1 DESCRIPTION... A cold front will cross the area today into tonight as high pressure passes north of Maine over central and northern Quebec. This will set the stage for significant mixed precipitation as warm, moist air ahead of an incoming shortwave trough lifts over the low level cold air. Gulf moisture with precipitable water values in excess of 1 inch will build across Maine by Wednesday evening. Most guidance has a double barreled surface low with one center passing northwest of the are and one over the area. This should keep cold air locked in place near the ground for most of the event across far northern Maine, with forecast soundings showing a sufficiently deep refreezing layer for predominantly sleet Wednesday into Wednesday night after precipitation starts as a brief period of snow for the far north. Snow ratios were capped around 10 to 12 to 1 due to the expectation of riming from a warm nose aloft, and general poor conditions for dendritic growth. Low level cold air may erode late in the event, decreasing the refreezing area in the low levels and leading to a transition to some freezing rain. This zone appears to most likely be transient rather than static, which should reduce ice accretion at any one location.

Farther south, uncertainty remains regarding how far south heavier precipitation will be on Wednesday morning, along with uncertainty in how far south subfreezing temperatures will make it, particularly after a very warm day today. Historically models overdo cold air advection in these scenarios, and the NBM appeared to be bias correcting temperatures downward on top of this, so temperatures near the consensus of guidance with no bias correction were preferred, which increased lows above freezing in the Bangor area and towards the coast, thus causing the forecast to be all rain compared to freezing rain on the NBM. Close attention will need to be paid to the temperatures today and progress of the front to determine whether or not the cold front is behind guidance projections, which could shift the southern extent of freezing precipitation even farther to the north.

There is additional uncertainty in the timing of a surge of low level warm air northward late Wednesday night into Thursday morning. The surface low pressure track has generally trended slightly NW, which could cause some QPF to fall as rain at the end of the event. There is high confidence in meeting locally defined mixed precipitation winter storm warning criteria for northern Aroostook zones, which is either 1 inch of QPF falling as any combination of snow, sleet, and freezing rain, or 1 inch of sleet. However, there is not 80 percent confidence yet for zones on the south end of the watch due to uncertainty in QPF and the transition timing to rain. For simplicity, the entire watch was kept for now and will be reevaluated today. Winter Weather Advisories will likely be needed for at least one tier of zones south of the current watch. Regardless of exact amounts and headlines, travel conditions will deteriorate on Wednesday and remain poor Wednesday night. Significant accumulations of sleet are expected with 1 to 3 inches, locally up to 4 inches of all sleet within the watch area, with the highest sleet amounts across the far north. This amount of sleet can be very difficult and strenuous to remove. Above freezing temperatures are expected on Thursday, allowing any freezing rain to melt off elevated surfaces as west winds increase. With more precipitation expected to fall as sleet and above freezing temperatures now expected at the end of the event, the power outage risk has decreased, but a few outages still cannot be ruled out.

KEY MESSAGE 2...A fast moving storm system may bring snow late Friday night into Saturday morning. This could impact travel with slushy and slippery roads Saturday morning.

KEY MESSAGE 2 DESCRIPTION... A fast moving clipper type storm will cross the Great lakes on Friday and approach Friday evening bringing a chance for snow across most of the area Friday night. Forecast models disagree on the track of this system with the ECMWF carrying the low to our north and the GFS bringing the low to the central part of area. However, the models agree that cold air will be well enough entrenched for snow everywhere except possibly the coast. The snow inland and mix or rain along the coast will taper off on Saturday. The ECMWF is quicker to end the precip with the low tracking to our north allowing for a dry intrusion to quickly sweep in and end the precipitation early saturday morning. The GFS, with a more southern track of the low, carries a continuation of snow into Saturday afternoon across the north which then tapers off late in the day.

Impacts from this system will involve snow covered and slippery roads late Friday night into early Saturday morning. Some messy travel may continue into midday Saturday across the north. Road surfaces across central and southern areas will likely just become wet by midday Saturday.

KEY MESSAGE 3...A large storm system approaching late in the weekend may bring snow north and a mix Downeast Sunday night, changing to rain across the area early Monday. Strong south winds may accompany the storm. This could bring some messy travel across the north early Monday, and the chance for isolated power outages.

KEY MESSAGE 3 DESCRIPTION... Models are in agreement on a strong, deep and cold trough digging into the Plains late in the weekend and supporting a large storm system developing in the Upper Midwest. This will impact our area. However, there is disagreement on the timing. The GFS has an overrunning warm frontal boundary extending east across the northern part of our area late Sunday while the ECMWF still has high pressure across our area on Sunday. Snow will move into the north late Sunday if the GFS solution is right but not until late Sunday night if the ECMWF is right. As the storm continues to approach on Monday, a tight gradient between the large system and high pressure off to the east will bring an increasing south wind across the area with indications that a strong low level just may impact at least the Downeast region. Warm air surging north will change precipitation to all rain on Monday. As the storm lifts north into Eastern Canada, a Cold front will come through late Monday or Monday night, possibly accompanied by strong gusty winds as it increases mixing and pulls down some strong winds from aloft. Moderately cooler air will return Monday night into Tuesday.

Potential impacts form this storm include snow covered and slippery roads late Sunday or Sunday night into early Monday, mainly north, and strong winds on Monday possibly causing scattered power outages.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

VFR through 10z tonight. Light winds today, increasing out of the north at 5 to 10 kts with gusts to 15 to 20 kts possible this evening.

Wednesday to Wednesday night: MVFR ceilings build first at southern and western terminals just before daybreak/10z, then lift northward through the morning. IFR ceilings will build in shortly after. Mixed precipitation develops north of BGR around or just after 12z Wednesday with moderate to heavy sleet/ice pellets expected for northern Maine terminals by Wednesday afternoon into the night. East winds 5 to 10 kts with gusts to 20 kts, shifting southeast Wednesday night.

Thursday...IFR, improving to MVFR and possibly VFR downeast late. SW to W wind 10 to 15 kt with gusts to 25 kt. SW wind shear at 2K ft.

Thursday night...Thursday night...VFR except possibly occasionally MVFR over the far north. W wind around 10 kt.

Friday...VFR. W to SW wind 5 to 10 kt.

Friday night...VFR possibly dropping to IFR. SE wind 5 to 10 kt.

Saturday...IFR north and MVFR south. N wind around 10 kt across the north and W wind 10 to 15 kt over the south.

MARINE

Winds and seas will remain below advisory levels through this evening before wind gusts increase to 25 to 30 kts again early Wednesday morning. A few gusts may approach gale force later Wednesday night, but confidence in frequent gusts to gale force is not sufficient for a gale headline at this time. Wave heights over the outer waters may approach 10 feet Wednesday night. A wave period around 5 to 8 seconds is expected. Rain will develop Wednesday afternoon into Wednesday evening, leading to reduced visibility at times.

A gale may be needed Thursday into Thursday night for NW winds gusting up to 35 kt across the offshore waters. A gale will likely be needed again Friday through Saturday for W winds gusting up to 40 kt. A strong gale and possibly storm will be needed Sunday night into Monday for strong S winds gusting up to 45-50 kt. Seas will be around 10 ft Thursday, subsiding to around 5 ft Friday, and building back to to 10 ft Friday, down to 8 ft Saturday and 3 to 4 ft Sunday then back up to 12 ft Monday.

CLIMATE

Record high temperatures were set at Caribou, Millinocket, and Houlton on Monday. Bangor tied their record. Daily high temperatures approaching records are possible again today.

Tuesday, March 10

Caribou: Forecast 46 F; Record 55 F set in 1977 Houlton: Forecast 59 F; Record 58 F set in 1977 Millinocket: Forecast 59 F; Record 54 F set in 2016 Bangor: Forecast 67 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 from 6 AM Wednesday to 6 AM EDT Thursday for ANZ050>052.