Area Forecast Discussion

WHAT HAS CHANGED

Slowed end of categorical pops based on timing of high resolution guidance.

Increased pops on Monday based on a blend of the high resolution models.

KEY MESSAGES

1) Rain, changing to snow across the North before ending into tonight, with black ice possible overnight/early Monday morning. Isolated to scattered snow showers Monday, then black ice possible again Monday night.

2) Unseasonably cool temperatures to start the week, with no big storm systems expected through the week.

DISCUSSION

KEY MESSAGE 1... Rain, changing to snow across the North before ending into tonight, with black ice possible overnight/early Monday morning. Isolated to scattered snow showers Monday, then black ice possible again Monday night.

KEY MESSAGE 1 DESCRIPTION... Have left in a slight chance for thunder for this afternoon across portions of Downeast Maine with Thunder observed over coastal SE Maine already.

A full latitude trough slowly approaches from the west through Monday, with its axis crossing the area Monday night. The region remains under diffluent flow aloft into this evening. Allowing for continued light to moderate rainfall. As the associated surface cold front pushes through this afternoon/early this evening from NW to SE, the rain will mix with, and across the North change to snow from NW to SE before ending by around midnight. Across the North up to around 1" of snow is possible for elevations up to around 1000 ft, with accumulations mainly on grassy surfaces. At elevations above 1000 ft accumulations of 1-3" are possible across the North, with up to 4-5" possible up above 3000 ft.

There should be a lull in the precipitation overnight, with even possibly some clearing. This should allow for the possible formation of black ice, as winds should be generally less than 10kt. Low level instability increases Monday due to strong cold air advection on NW flow aloft should bring isolated to scattered showers. Initially over the Northwoods and Central Highlands, then during the afternoon, possibly down into Interior Downeast Maine. While for the most part, little or no accumulation is expected, with around 100 J/kg of CAPE and low level lapse rates of around 7.5-8.5 C/km - cannot rule some isolated strong snow showers. These could produce locally heavy snowfall, reducing visibilities to under 1 mile, and potentially bringing a quick accumulation (most likely 1" or less) of snow, even on roadways. Any areas where there was snowmelt after experiencing a snow shower, could experience black ice Monday night, with lows well into the teens across the North and 20s elsewhere.

KEY MESSAGE 2...Unseasonably cool temperatures to start the week, with no big storm systems expected through the week.

KEY MESSAGE 2 DESCRIPTION... An upper level trough of unseasonably cool air will dominate through mid week. Afternoon high temperatures will be a few degrees below normal for this time of year. Nighttime temperatures will get below freezing for most areas except Downeast. Although a few showers are possible at times mid week, no big storm systems are expected to affect the region. Minimum afternoon relative humidity values are expected to be the lowest on Tuesday, generally ranging from 25 to 30 percent. Fortunately, winds are expected to be on the light side to help mitigate any fire weather concerns. Minimum relative humidity values return to above 40 percent the rest of the week.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Mainly IFR or lower to get started, with a few pockets of MVFR, with all areas becoming IFR or lower again this afternoon. Rain changes to snow across northern terminals this evening before the precipitation comes to an end. Its possible for a couple of hours of moderate to maybe even heavy snow at northern terminals this evening, however only confident enough to place this in a PROB30 group at this time. Southern terminals might mix with snow before ending, but currently not confident enough to reflect in the TAF. All terminals become VFR late tonight/early Monday morning. Monday should mainly be VFR, but cannot rule out an isolated snow shower at northern terminals in the late morning/early afternoon with a very low chance of MVFR conditions.

Winds have gone light and variable KHUL/KBGR/KBHB and should probably remain so until this evening at southern terminals and around mid afternoon at KHUL. Then winds become NW throughout this evening at around 10KT with possibly some gusts to 15-20KT at the southern terminals and KFVE. NW winds at under 10KT at all terminals overnight, with southern terminals probably becoming light and variable again. NW winds Monday G15-20KT likely for all but KBHB, where currently do not have the confidence to reflect in the TAFs.

Late Monday afternoon: MVFR or lower possible in any snow showers, otherwise VFR. NW winds G15KT possible.

Monday night: VFR. NW-N winds G15-20KT possible in the evening.

Tuesday-Tuesday night: VFR. Winds light and variable.

Wednesday-Wednesday night: MVFR possible in sct showers, otherwise VFR. S winds shifting to NW around 5 kt.

Thursday: MVFR possible in sct showers, otherwise VFR. NW winds 5 to 10 kt.

Thursday night-Friday: VFR. N winds around 5 kt.

MARINE

Gusts to 25 kt now expected on the intra-coastal waters tonight, so have expanded the SCA in effect for tonight for the coastal ocean waters for tonight to include there. The coastal and intra-coastal waters should then experience sub-SCA conditions Monday. SCA conditions are then possible again on the coastal ocean waters Monday night. The waters from 25-60nm should experience sub-Gale conditions tonight-Monday night.

Winds and seas are expected to remain below SCA criteria Tuesday through Friday.

CAR WATCHES / WARNINGS / ADVISORIES

ME...None. MARINE...Small Craft Advisory from 7 PM this evening to 6 AM EDT Monday for ANZ050>052.