textproduct: Caribou

WHAT HAS CHANGED

- Continue to increase confidence in snow showers late Friday night through Saturday night, including that some could be locally heavy. - Confidence is increasing in a winter storm from Wednesday through Thursday, with mainly snow across the North and a wintry mix elsewhere.

KEY MESSAGES

1) Breezy NW winds leading to reduced visibility and slippery travel from blowing and drifting snow tonight across Northern Maine.

2) Snow showers probable from late Friday night through Saturday night, some of which could be locally heavy. Areas experiencing heavy snow showers should expect reduced visibilities making driving difficult at times.

3) A winter storm should bring mainly snow across the North and a wintry mix elsewhere from Wednesday through Thursday. This could make travel potentially hazardous, especially across the North.

DISCUSSION

KEY MESSAGE 1... Breezy NW winds leading to reduced visibility and slippery travel from blowing and drifting snow tonight across Northern Maine.

KEY MESSAGE 1 DESCRIPTION... Surface low pressure continues to deepen across the Maritimes this evening as surface high pressure works into the Great Lakes. A relatively tight pressure gradient remains with the atmosphere mixed up to 1.5-2.5kft and winds aloft are 25-30kt so expecting to mix these down for several hours tonight. NW winds 10-15mph with gusts 20-35mph through the late evening into early overnight hours. Expecting areas of blowing snow across the CWA wide ponds/lakes given the frozen lake/pond conditions and wide open area which will impact visibility for recreation activities. Patchy to some areas of blowing snow in the agricultural areas of Aroostook and Northern Penobscot Counties. Expect blowing snow to mainly end tonight but cannot rule out ground level drifting snow to continue to impact some roadways into the AM hours and once again tomorrow. Winds relax to generally less than 15mph on Friday.

KEY MESSAGE 2... Snow showers probable from late Friday night through Saturday night, some of which could be locally heavy. Areas experiencing heavy snow showers should expect reduced visibilities making driving difficult at times.

KEY MESSAGE 2 DESCRIPTION... Models have come into solid agreement that the 850-500mb closed lows will track from southwestern Quebec Saturday morning, to near the western boarder with Quebec by Saturday evening to the general vicinity of the Bay of Fundy by Sunday morning.

This will result not only strong differential positive vorticity but strong frontogenetic forcing at first in the 850-700mb layer late Friday night/Saturday morning and then by Saturday afternoon in the 700-500mb layer as well. The frontogenetic forcing diminishes in the 850-700mb layer after midnight Saturday night and in the 700-500mb layer Sunday morning. In addition low-mid level lapse rates increase to 7.7-8.5C/km Saturday afternoon/evening across most of the region as well. Based on this should have sufficient forcing to support locally heavy snow showers. However, with precipitable waters peaking out around 0.2-0.25 inches there will be limited moisture to work with. In addition, winds should be less than 30kt at the top of the mixed layer, so snow squalls appear to be unlikely.

With all that, most areas should on average receive less than an inch of snowfall, with the potential for 1-2" on average across portions of the North from 12z Sat to 12z Sun. However, in areas that do experience locally heavy snow showers, especially more than one, it would not be surprising if there were some localized reports of 2-4" of snow, with the best chance for this across the St John's Valley and Eastern Aroostook, where the best forcing is currently forecast to be.

In addition, any area that does experience a heavy snow shower should see visibilities go down to under 1/4 mile for at least part of its duration. This will make travel locally difficult if/where this occurs. Once again, relative light winds in the boundary layer should preclude any snow squalls.

KEY MESSAGE 3...A winter storm should bring mainly snow across the North and a wintry mix elsewhere from Wednesday through Thursday. This could make travel potentially hazardous.

KEY MESSAGE 3 DESCRIPTION... A surface to 850mb warm front approaches from the south Wednesday and Wednesday night, then stalls to the south Thursday, with waves of low pressure ridging along it. Aloft a series of shortwaves crosses the area during this time frame.

This will provide a prolong period of precipitation across the region. It appears that the precipitation should transition to a wintry mix or rain as far north as Eastern Aroostook by Wednesday afternoon, then become all snow from N to S Wednesday evening. The precipitation should again become a wintry mix across the Bangor/Penobscot Region and most of Downeast Maine on Thursday. There is some concern about where the northern extent of the precipitation shield will be with the northern edge with this system somewhere around the northern border with Canada. While it is to soon to specify amounts there is the potential for a few to possibly several inches of snow across Northern and portions of Central Maine, with lesser amounts across Downeast Maine, where there will be the most mixed precipitation and plain rain with this system. At this time, there does not appear to be an appreciable wind threat with this system through the day on Thursday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Before sunset...SCT/BKN MVFR cigs. NW winds 10-15kt with gusts 20-30kt. VCSH possible at northern terms.

Tonight...FEW VFR cigs becoming SKC. NW winds 5-15kt with gusts 20-25kt. LLWS likely all terms generally WS020/33040KT.

Friday...VFR. NW winds 5-15kt with gusts up to 25kt.

Friday Night...VFR. Light and variable winds.

Late Friday night-Saturday night: MVFR or lower possible, with the best chance at northern terminals. Best chance for VFR is at southern terminals. WNW-NW winds G15-20KT possible Saturday night.

Sunday-Monday: Becoming VFR throughout Sunday morning. NW winds G15KT possible Sunday.

Monday night-Tuesday: MVFR or lower possible, with the best chance of this at Northern terminals.

MARINE

Small Craft Advisory now in effect until 10AM EST Friday for the Coastal Waters our 25nm. Northwest winds 15 to 25 kt with gusts up to 30 kt and seas 3 to 5 ft. For the Intra-Coastal Waters the Small Craft Advisory remains in effect until 7AM EST Friday. Northwest winds 15 to 20 kt with gusts up to 25 kt and seas 2 to 3 ft. Rest of Friday afternoon into the evening expect winds/seas below SCA criteria.

Saturday should see conditions below SCA levels, though just below on the coastal ocean waters. SCA conditions are possible on all waters Saturday night, and possibly continue into Sunday. The waters should then see sub-SCA conditions Sunday night- Tuesday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory until 10 AM EST Friday for ANZ050-051. Small Craft Advisory until 7 AM EST Friday for ANZ052.