Casco Bay Marine Forecast
|Tonight...E Winds 5 To 10 Kt With Gusts Up To 20 Kt, Becoming Ne 10 To 15 Kt With Gusts Up To 20 Kt Late. Seas Around 2 Ft.|
|Sun...E Winds 5 To 10 Kt, Becoming 5 To 15 Kt In The Afternoon. Seas 2 To 3 Ft.|
|Sun Night...E Winds Around 5 Kt, Becoming N After Midnight. Seas Around 2 Ft.|
|Mon...Ne Winds Around 10 Kt, Becoming E In The Afternoon. Seas 2 To 3 Ft.|
|Mon Night...Ne Winds 5 To 10 Kt, Becoming N After Midnight. Seas 2 To 3 Ft.|
|Tue...Ne Winds 5 To 10 Kt. Seas 2 To 3 Ft.|
|Tue Night...Ne Winds 5 To 10 Kt. Seas 1 To 2 Ft.|
|Wed...Ne Winds 5 To 10 Kt. Seas 1 To 2 Ft.|
|Wed Night...N Winds 5 To 10 Kt. Seas 1 To 2 Ft.|
|Thu...Ne Winds Around 10 Kt. Seas 1 To 2 Ft.|
|Thu Night...Ne Winds 5 To 10 Kt. Seas 1 To 2 Ft.|
| Area Forecast Discussion|
National Weather Service Gray ME
307pm EDT Sat April 10 2021
Our warm air mass will be undercut by a backdoor cold front tonight as surface high pressure moves southward from Canada. This will allow for much cooler weather for much of the upcoming week. There is considerable uncertainty in our chances for measurable rainfall as very slow low pressure systems remain mainly west and south of our region. This time, the best chances appear to be late Tuesday into the first part of Wednesday.
Near Term - Through Tonight
Current water vapor imagery shows an active, yet blocked pattern aloft with a series of upper waves and closed lows arcing from the Midwest to Hudson Bay and then through the Canadian Maritimes. Over northern New England there is a narrow ridge of high pressure aloft that will be suppressed south as a spoke of energy rotates south through New Brunswick, Canada late this evening through Sunday morning. At the surface there is a frontal boundary draped from the St. Lawrence Valley through downeast Maine with temperatures well into the 70s across southwest Maine and in the 50s north of the boundary in northern Maine. Through late this afternoon into this evening showers are expected to develop along this frontal boundary as it sags southward with the best chances for showers from Franklin and Somerset Counties through the Mid-Coast. Have also included an isolated chance for thunder here as latest mesoscale guidance show surface based CAPE from 250 to 500 J/kg.
Tonight, as that piece of energy drops south through New Brunswick, the frontal boundary will drop southwest through the area as a backdoor cold front. This will bring continued chances for showers across eastern zones as well as help saturate low levels as winds turn east and then to the northeast. As the boundary layer gathers moisture there will be areas of patchy fog that develop overnight. Lows tonight will range from the upper 30s north to upper 40s south.
Short Term - Sunday Through Sunday Night
By Sunday morning the backdoor cold front will be southwest of the area with mostly cloudy skies and winds out of the east northeast. The front will get hung up to our southwest as the upper low over the Midwest slowly edges eastward. This will keep skies mostly cloudy with cool east to northeast winds for much of the day. Temperatures Sunday will be a good 20F lower than today with highs generally in the 50s.
The upper low to our west will struggle to advance eastward as the overall pattern remains blocked. By Sunday night it will be near the eastern Great lakes bringing low chances for rain showers across southwest New Hampshire. There will be some clearing across the north late Sunday into Sunday night, but overall skies will remain mostly cloudy into Monday morning with overnight lows in the 30s north to low 40s south.
Long Term - Monday Through Saturday
A very blocky pattern continues to be modeled in the latest deterministic and ensemble guidance through much of the upcoming week. This will lead to uncertainty in when and where our best chance for meaningful precipitation will be, if we get any at all. One thing is more certain in that our temperatures in the 60s and 70s are long gone as we head back toward normal.
Based on the latest guidance it looks as though Monday will be mainly dry except for perhaps some isolated showers, mainly across western and southern zones as drier air works in from the north. Across northern zones, developing sunshine is expected on Monday.
On the deterministic side of things, the 12z GFS and ECMWF (European Centre for Medium-Range Weather Forecasts) have come into better agreement for the Tuesday through Wednesday period as upper level low pressure rides eastward near the NY/PA border and eventually to southern New England by Tuesday evening. At this time, this appears to be our best chance at a quarter or more inch of Quantitative Precipitation Forecast, especially across southern NH. In fact, the column appears to be cold enough to support and chance to snow roughly above 1000 feet Tuesday night as long as the precipitation falls at a decent intensity to allow for added cooling. Therefore, as long as the trend on upper level low pressure moving across southern New England holds for Tuesday night, the Monadnocks and portions of the Whites could see a coating of snow. Otherwise, as one heads northward into central and northern NH as well as much of western ME, precipitation chances will be lower.
From late Wednesday onward toward the weekend, the guidance suite is actually in better agreement with the mass fields, yielding drier weather, possibly more sunshine, and warmer temperatures.
Winds will turn from south to the east this evening as a cold front drops in from the northeast. Winds will continue to turn to out of the northeast tonight with seas and gusts remaining below SCA (Small Craft Advisory) through Sunday night.
Long Term...Low-end SCA (Small Craft Advisory) conditions are possible Monday into Tuesday, mainly for 5 foot seas as a long fetch of northeast winds develops. Thereafter, seas should remain 4 ft or lower midweek.
NOAA Gray/Portland ME Office - Watches - Warnings - Advisories
ME...None. NH...None. MARINE...None.