textproduct: Gray - Portland

WHAT HAS CHANGED

The small craft advisory has been cancelled for the waters. Otherwise, the going forecast for this afternoon remains in good shape.

KEY MESSAGES

1. Below normal temperatures continue through the end of the week with below zero wind chills expected most nights through Saturday night/early Sunday morning.

2. A strong coastal low may bring impacts to the coast on Sunday, but most guidance favors a track far enough offshore to keep the impacts minimal.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Ridging over the area has made for a mostly clear day with northwesterly flow bringing the occasional light snow shower to the mountains. Froude numbers this afternoon suggest unblocked flow, so I suppose some flakes are possible downstream, but the showers also aren't that expansive and may resemble flurries more than anything. A shortwave approaches this evening and crosses overnight which trends skies toward mostly cloudy with continued snow showers in the mountains. These added clouds should keep us from radiating as well as last night, but expect very cold temperatures to continue with lows bottoming out in the single digits either side of zero.

Mean troughing continues over the region allowing for cold air to stay locked in place and temperatures to once again not budge much past the upper teens and low 20s in the south, with low to mid teens up north. We see another shortwave rotate through Thursday afternoon over a newly formed upper low over Nova Scotia. This provides upper level forcing for additional showers or flurries, but with no frontal forcing they shouldn't amount to much more. Skies look clearer Thursday night as high pressure begins to build in, but the pressure gradient will be tightening as low pressure deepens over Atlantic Canada which could keep us mixing enough to avoid a true radiational cooling scenario. Regardless, it will be very cold with temperatures bottoming out in the single digits below zero areawide. Factor in the wind chill and we are looking at -10 to -15F south of the mountains and -20 to -25F in the north. Cold Weather Advisories may eventually be needed. This very cold weather with nightly below zero wind chills continues into early Sunday morning.

KEY MESSAGE 2 DESCRIPTION... Global models continue to advertise a strong coastal low lifting to the north-northeast offshore of the eastern seaboard Sunday into Sunday night. This system may ultimately bring some measurable snow and gusty winds to portions of the area, particularly closer to the coast and SE NH, but guidance for the most part currently favors keeping the track of the low far enough to the south and east to keep impacts minimal and the more significant precipitation offshore. We'll see how model trends with the track of this system in the coming days as any shifts to the north and west would bring in higher snow chances/amounts, and there are still some individual members within both the GFS/ECMWF camps holding onto that scenario. In addition, we'll be entering a period of high astronomical tides, so we'll need to watch for the potential for any coastal flooding.

Once this system departs into the Canadian Maritimes Sunday night, drier conditions are expected for the early to middle part of next week with Monday being somewhat breezy. Temperatures look to get back closer to normal with highs in the upper 20s to lower 30s.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...Ceilings thicken and lower a bit this evening, but should stay mostly VFR, with HIE being the exception and riding the MVFR/VFR line. Light snow showers may also pass near or over LEB and HIE tonight, but these have been brief when they do pass overhead and overall the activity is not very expansive so left them with VCSH. Ceilings lift and scatter out after 12Z Thursday.

Outlook:

Thursday Afternoon/Night: Mostly VFR expected with some isolated light snow shower activity expected once again that could bring brief visibility restrictions if they pass over a terminal. Northwesterly wind gusts 15-20 kts are possible through Thursday night.

Friday-Saturday night: A few snow showers and MVFR ceilings at HIE, but otherwise VFR is expected.

Sunday-Sunday night: A coastal storm may bring flight restrictions to portions of the region, but to what degree remains of low confidence as it is dependent on how far offshore the storm system ends up tracking.

Monday: MVFR possible at HIE, but VFR expected elsewhere.

MARINE

Northwesterly winds are expected through Thursday night. Deepening low pressure over atlantic Canada brings wind gusts 25-30 kts to the waters as early as Thursday evening, lasting until at least early Friday morning. Seas are expected to remain below 5ft during this time.

Marginal SCA conditions possible with W/WNW winds gusting to around 25 kt on Friday, but these winds diminish Friday night and Saturday. A strengthening low is then expected to emerge off the southeast US coast Saturday night and then lift N/NNE Sunday into Sunday night. Although the forecast track will still fluctuate in the coming days, gales are increasingly likely over the waters with a possibility of storm force gusts. Northwesterly gales may persist into Monday as the low lifts into the Canadian Maritimes, but then conditions are expected to improve Monday night and Tuesday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.