textproduct: Gray - Portland

WHAT HAS CHANGED

Little change to the going forecast this Sunday evening.

KEY MESSAGES

1. Breezy at times this afternoon as light rain showers taper off. There will be multiple chance for more light precipitation through midweek, mostly in the mountains. High temperatures are forecast to be near normal.

2. There is a growing signal for a system to bring rain and measurable snow to the area late this week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Latest RAP13 analysis depicts the upper low center nearing the Bay of Fundy. This low will lift to the northeast through early this evening, allowing shortwave ridging to briefly build in along with with somewhat drier air. This will bring an end to the lingering light precipitation across western ME a little later this afternoon and some breaks in the clouds, especially into southern and SW ME. For those that do see some thinning of the clouds, it will be a bit breezy this afternoon with gusts up to around 30 mph.

Winds diminish as the sun sets, and even if there is a period of partial clearing this evening, clouds likely fill back in tonight as a 500mb trough swings through. This will bring more upslope precipitation in the mountains with snow and more light accumulations possible in the higher terrain. Overnight lows will be in the 30s and 40s.

The 500mb pattern depicts troughing over the eastern half of Canada and into the Northeastern CONUS through the middle of this week. At the surface, low pressure will be in the vicinity of the Canadian Maritimes, resulting a west to northwest flow. This setup will favor periods of upslope precipitation and mostly cloudy skies in the mountains, which could be further enhanced at times as multiple shortwaves aloft send a couple of fronts through New England. Depending on the time of the waves, it's possible snow could mix in at times in the valleys but is more likely in the terrain, and the higher peaks could pick up additional light snow accumulations.

For areas downwind of the mountains, there is lower potential for showers, but with cyclonic flow/weak instability aloft, my suspicion is that there will probably be periods of mostly cloudy skies each day.

As far as temperatures go, highs will be mostly in the upper 40s to mid 50s south of the mountains Monday-Wednesday. Highs will be limited to the 40s around the mountains with more cloud cover and potential for showers.

KEY MESSAGE 2 DESCRIPTION... A deep trough takes shape over the Great Lakes Region on Thursday generating a surface low over the Ohio Valley. The trough looks to cut off into a closed low and continues to push east along with the surface low Thursday night. On Friday the surface low moves off the coast of the Mid Atlantic and is swung northward by the deepening closed upper low in it's wake, and this is the point where model consensus ends. The track the low takes up the coast is going to determine what impacts we see, if any at all. One of the more clear trends that has been present has been for a more inland track with coastal areas seeing more rain. In fact, as I write this the 12Z deterministic GFS is coming in with very little snow as it has been pushing for a much more amplified trough that directs the center of the low inland right though our area the last couple of runs. This has been an outlier as ensembles have a majority of low centers over the ocean, but spread is also leaning westerly.

At this point I would say the higher peaks, and northern zones have the best chance of seeing measurable snow, with the coast more likely to see wind and rain if trends hold. Inland areas are anyone's guess as precipitation type there is extremely sensitive to track shifts and until we have a clearer consensus on track it will remain low confidence. Global ensemble members continue to be all over the place with rain and snow amounts as a result of this track uncertainty, but the overall trend the last few runs has been an increase in number of members with measurable precipitation. We will continue to monitor trends, but it is going to take more time before we can start breaking down potential impacts.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Through 18Z Monday...Ceilings are expected to range from high-end MVFR or low-end VFR into this evening, and after a period of mainly VFR, MVFR ceilings are again possible overnight into Monday morning, although confidence is not enough to put this in the TAF. The exception as usual is HIE, where MVFR ceilings are expected to continue along with periods of rain showers, possibly mixed with -SN at times, which could bring IFR vis. Northwest winds will gust to around 25 kt this afternoon before diminishing this evening and tonight.

Outlook

Rest of Monday-Monday night: Upslope precipitation and MVFR remain likely at HIE. Elsewhere, ceilings will likely again be in the low- end VFR or high-end MVFR range, and can't completely rule out a a brief shower or two. Northwest wind gusts of 20-25 kt possible late in the day into Monday night.

Tuesday-Thursday: Periods of upslope rain and/or snow showers and MVFR ceilings continue to be likely at HIE. Elsewhere, mostly VFR.

Friday: We are watching the potential for a system that could bring widespread restrictions late this week.

MARINE

SCA conditions remain in place through this evening as northwest winds remain gusty, but these will come down overnight as low pressure lifts into the Canadian Maritimes. The low will remain in the vicinity of the Maritimes through midweek keeping a west to northwest flow over the waters. A couple of cold fronts will also cross the waters during this timeframe, possibly bringing additional periods of SCA level winds/seas.

There's a growing signal in a low pressure emerging off the Mid-Atlantic coast late week. Confidence is low on the eventual track into next weekend, but there will likely be at least some degree of increased winds and seas.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ150- 152-154.