textproduct: Gray - Portland

WHAT HAS CHANGED

Widely scattered showers and thunderstorms continue to spread across the forecast area with most of the activity thus far over northern New Hampshire and the western Maine mountains. Another cluster of storms continues in the vicinity of the Midcoast and southern Kennebec Valley that moved through the Lakes Region earlier. Of particular concern is that some of the storms over northern New Hampshire continue to train over the same areas, generally along a broad line from Littleton up through Berlin. These cells will continue to pose a risk for torrential rainfall and isolated instances of flash flooding. Will have to continue to monitor these cells as they move east but we should start seeing them diminish in intensity as we lose daytime heating.

No major changes were needed for this update. Just blended in the latest observations to the going forecast and freshened up the aviation discussion.

KEY MESSAGES

1. Heavy showers and thunderstorms gradually diminish this evening.

2. A very warm day with lingering humidity is expected on Sunday.

3. Heat and humidity continue through Monday, followed by a gradual cool down through the end of the week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

More rounds of showers and storms are expected through the remainder of the afternoon into the early evening. With the moisture rich environment, these storms have been efficient heavy rainfall producers, and a localized flash flooding potential remains a concern. The area of focus for the heavy rainfall and flash flooding potential remains near the foothills and Lakes Regions of Maine and New Hampshire, parts of which also saw some heavy rainfall earlier this morning.

These showers and storms are expected to diminish through the evening hours, with a weak front slipping through during the overnight. This front begins the process of gradually bringing a drier airmass back into New England.

KEY MESSAGE 2 DESCRIPTION...

Sunday looks like another very warm day with highs pushing into the upper 80s to near 90 downwind of the mountains. Dew points look to mainly be in the 60s during the daytime, keeping heat indices mainly in the low 90s to near the mid 90s. So while the coast will flirt with heat indices near 95 degrees tomorrow, a heat advisory doesn't appear warranted at this point.

Some scattered pop up showers and storms will still be possible tomorrow, especially across the north, but do not look as widespread as today's activity.

With the return of some relatively drier air, low temps fall more Sunday night than we've seen for the last few nights. Widespread lows in the low to mid 60s look likely, with upper 50s across the north.

KEY MESSAGE 3 DESCRIPTION...

Monday will remain warm to hot with highs well into the 80s to around 90. However, dew point temperatures will be noticeably lower making for lower heat indices and a drier feel.

Several members of the guidance suite are in agreement that a short wave trough will move across the forecast area during the evening hours along with an accompanying SFC cold front. Chances for showers and thunderstorms will increase during the late afternoon and evening hours with a chance that a few could produce strong winds, with DCAPE approaching 1000 Joules in spots, although SBCAPE seems to be somewhat limited at this time.

A series of additional cold fronts will cross through mid to late week, bringing rounds of scattered showers and possible thunderstorms... although no day currently looks like a washout. Temperatures will also cool towards seasonable averages with highs into the upper 70s to lower 80s. Dew points will lower as well with overnight low temperatures into the 50s.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Through 12z Monday...Showers and storms and storms will continue for much of the area for another few hours, bringing brief restrictions to some terminals. HIE and AUG are the sites most likely to see a thunderstorm over the next hour or two but most other sites could see a passing shower or two. A combination of marine and radiation fog then likely brings IFR to LIFR conditions to AUG and RKD tonight. LEB and HIE see MVFR conditions or lower in valley fog after midnight. Mainly VFR then prevails at most terminals by mid- morning tomorrow, with the fog last to leave RKD. Mainly VFR prevails tomorrow night, but valley fog is likely again at HIE and LEB after midnight.

Outlook:

Monday/Monday Night: VFR conditions during the morning through much of the afternoon. Scattered MVFR or lower conditions in late day and evening thunderstorms.

Tuesday/Tuesday Night: Mainly VFR conditions outside of any possible SHRA/TSRA.

Wednesday/Wednesday Night: Mainly VFR conditions.

MARINE

Mainly fair conditions continue as a weak cold front crosses the waters late tonight and tomorrow. Some marine fog and visibility restrictions continue east of Casco Bay ahead of this front. Clearing and fair conditions follow by late tomorrow and Sunday night.

Winds and seas will largely remain below SCA criteria into early next week as a series of generally weak cold fronts cross the waters.

GYX WATCHES/WARNINGS/ADVISORIES

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