textproduct: Caribou

WHAT HAS CHANGED

- Winter Weather Advisories have been extending north to include portions of the Central Maine Highlands and Upper Penobscot Valley region.

- Southern shift in vort max for Saturday leading to an increased chance for convective snow showers across the entire CWA

KEY MESSAGES

1) Snow will overspread the region tonight with impacts to the Wednesday morning and evening commutes expected.

2) Snow showers possible Saturday across the north could create sudden drops in visibility, and temperatures will warm, lifting to at or above freezing through the end of the weekend.

DISCUSSION

KEY MESSAGE 1... Snow will overspread the region tonight with impacts to the Wednesday morning and evening commute expected.

KEY MESSAGE 1 DESCRIPTION... Low pressure will dive southeast out of Ontario province today and then off the Maine coast during Wednesday. The warm advection pattern aloft in advance of the system will result in snow developing from west to east this evening, then spreading east across the entire forecast area after midnight. The snow is expected to reach the Bangor region between 10 PM and midnight, and much of Downeast Maine by around midnight. The snow is expected to reach the Houlton/Presque Isle/Caribou areas between 1 AM and 3 AM early Wednesday morning. Thus, impacts to the Wednesday morning commute are expected in the form of potentially slippery travel conditions. With generally light winds expected, we are not expecting blowing snow to be a factor overnight.

By Wednesday morning, the low will exit the Maine coast and then pass east to the south of Nova Scotia Wednesday afternoon. An inverted trough extending westward from the departing low will serve as the focus for additional snowfall during the day Wednesday. As is the case much of the time with these systems, exact placement of the trough axis will be critical as to who receives the most snow with this system. Although confidence is high that it will snow, it is somewhat lower as to where the axis of heavier snow will fall on Wednesday.

Some guidance is indicating the axis may set up across coastal and central portions of Washington county. But if it sets up farther to the west, then the Hancock county coast could receive heavier snowfall. Although the latest forecast maintains the previous Winter Weather Advisories, it should be noted that localized heavier snowfall is possible somewhere along the Downeast coast, which would tip the scales toward warning level snowfall criteria (widespread 6 or more inches for the Downeast region). Needless to say, the greater impacts will be realized where the heaviest snow fall occurs.

KEY MESSAGE 2... Snow showers possible Saturday across the north could create sudden drops in visibility, and temperatures will warm, lifting to at or above freezing through the end of the weekend.

KEY MESSAGE 2 DESCRIPTION... A very strong 500 mb vorticity max originating over Newfoundland through the middle of the week may retrograde through the end of the week and dive back south over the forecast area Friday into Saturday. This pattern could lead to enough instability for convectively supported snow showers. Current model trends have shifted south with this feature, both in the global GFS and global ECMWF, and so the area which could be impacted by these convective snow showers has now expanded to the majority of the forecast area. The limiting factor for this system will be moisture availability: This low pressure system will have arctic connections instead of tapping into the Gulf Stream, leading to a lack of QPF. That said, steep low level lapse rates continue to be found on forecast soundings and could combine with a tighter pressure gradient aloft to generate convective snow showers that may limit visibility or impact travel during the day on Saturday. A warming trend is in store for behind this low, with temperatures lifting above normal, and potentially above freezing, across the entire forecast area.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

VFR is expected at all the terminals through this afternoon. Conditions are expected to deteriorate to IFR in developing snow, mainly after midnight. IFR conditions are expected at the airfields on Wednesday in snow. Light and variable wind today, becoming light east around 5 kt tonight. E to NE wind 5 to 10 kt Wednesday.

Wednesday night - Thursday night: Gradual improvement to VFR/MVFR during the day on Thursday across all terminals. NW winds 10 to 15 kts with a gusts 20 to 25 kts Thursday.

Friday - Friday night: VFR across all terminals. NW winds 5 to 10 kts.

Saturday: VFR with possible trend to MVFR in snow showers, with deteriorating conditions most likely across northern terminals. NW winds 5 to 10 kts.

MARINE

A small craft advisory remains in effect for the outer coastal waters through 7 AM EST. Winds should then decrease below SCA levels this afternoon and tonight, although a few gusts to 25 kt are possible into tonight. Winds/seas should generally remain below SCA levels on Wednesday.

Wind gusts will increase towards 25 kts on the intracoastals and 30 to 35 kts on the coastal waters Wednesday night into the day on Thursday. These strong small craft advisory conditions will likely continue through the end of the week, with conditions improving into the weekend. Seas will generally remain at or below 4 ft through this time, with light freezing spray possible each morning.

CAR WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 7 PM this evening to 7 PM EST Wednesday for MEZ010-011-015>017-029>032. MARINE...Small Craft Advisory until 7 AM EST this morning for ANZ050- 051.