Casco Bay Marine Forecast (2024)

Synopsis
A cold front will stall near the coast today as low pressure forms along it. Showers will develop today as the low develops. A few thunderstorms will be possible as well. High pressure then settles in for Tuesday before another cold front moves in for Wednesday night. Best chances for rain and thunderstorms will be late Wednesdays, but this should clear out Thursday as high pressure returns for the end of the week. Temperatures and humidity will swing with the passing of each frontal boundary.

Near Term - Until 6pm This Evening
625 AM

Forecast remains on track with cold front gradually traversing the region with drier air being ushered in behind it. Dewpoint values in the CT River Valley have dropped into the 50s and that trend should continue eastward. Showers and thunderstorms are still expected to develop, especially over central ME, by early afternoon. No changes to the going forecast.

Previously... A cold front currently pushing into our western zones as of 3 AM has pretty much lost all its associated shower and thunderstorm activity. However, with a warm and humid air mass still in place with northward advancing warm front we cannot rule out a few showers or an isolated thunderstorm early this morning. Temperatures on the coastal plain especially north of PWM are warming into the upper 60s to lower 70s at this hour as the warm front finally pushes northward in those areas.

As a relatively deep mid and upper level low moves southeastward from Quebec this morning, low pressure is expected to develop over central ME in the vicinity of triple point. This will once again allow for an increase in shower and thunderstorm coverage by late morning in the mountains, spreading southward as heating increases. The highest concentration of showers today will be in the mountains southward into the foothills of ME, continuing southward to the Midcoast of ME by mid afternoon. This is where the atmosphere will become most unstable and where the best forcing for ascent will occur. A few thunderstorms could produce gusty winds and small hail before the stabilizing effects of rainfall takes over late in the afternoon. With the flow aloft slowing down markedly, a few slow moving downpours will be likely and could produce localized flooding.

Elsewhere in the forecast area, the chances of precipitation will be less, but a few showers or a thunderstorm cannot be ruled out this afternoon.

Highs will be in the 60s in the mountains to the upper 70s and lower 80s at lower elevations where downsloping winds aid in heating.

NW Winds will gust 20 to 25 MPH by late afternoon, especially in the mountains and western zones.

Short Term - 6pm This Evening Through 6pm Tuesday
Showers will dissipate this evening with the loss of heating. Clearing will take place from west to east late tonight as low pressure moves away from the region.

Dry weather with significant warming is expected Tuesday. Highs will be well into the 80s, with some readings around 90 possible in the south. Dew point values will be much lower than they have been lately so heat indices should not be an issue.

Long Term - Tuesday Night Through Sunday
Return flow Tuesday night will usher in warmer and more humid conditions for Wednesday, with highs in the mid to upper 80s for much of the area. A cold front sinking south out of the Great Lakes on Wednesday will support scattered to numerous showers and thunderstorms into Wednesday night. The forcing with the system Wednesday night is concerning, but for now the instability ahead of it could be a limiting factor. Will have to watch for heavy rain producers as well as some concern about strong winds, but these will be conditional and timing dependent so confidence is low at this time. The front will bring a brief cool down for the latter part of the work week. The airmass starts to modify with surface high moving in Friday. Dew points in the 50s will mean very tolerable humidity levels for late June. Another frontal system approaches from the Great Lakes over the weekend, bringing another opportunity for showers.

Marine
Short Term
Low-end SCA (Small Craft Advisory) continues for today for the offshore waters, with seas continuing to provide low-end SCA (Small Craft Advisory) conditions tonight off the Midcoast.

Long Term
- Increased thunderstorm risk Wednesday Night

- Brief elevated winds and seas mid-week

A potent cold front will move through the waters Wednesday Night or early Thursday and will feature an increased risk of thunderstorms. Ahead of the front, elevated winds and seas will linger, with SCA (Small Craft Advisory) conditions possible. Southerly flow then quickly returns by Wednesday and Thursday, with subsiding seas for late week.

NOAA Gray/Portland ME Office - Watches - Warnings - Advisories
ME...None. NH...None.

Marine
Small Craft Advisory until 5am EDT Tuesday for ANZ150-152. Small Craft Advisory until 4pm EDT this afternoon for ANZ154.