textproduct: Gray - Portland

WHAT HAS CHANGED

Loaded in the latest surface observations and adjusted the aviation section for the 12Z TAF package.

KEY MESSAGES

1. Dry and very warm conditions will persist through Friday with highs in the 80s to near 90 degrees. Humidity will be low limiting excessive heat impacts.

2. Remaining very warm on Saturday with a cold front bringing increasing chances for showers and storms this weekend.

3. Drier weather for the first half of next week with temperatures near normal on Monday and climbing to above normal toward the middle of next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Deep layer ridging extending from the Ohio Valley into New England will allow for warming temperatures aloft today. Temperatures at 850 mb will push +15C both this afternoon and again on Friday. BUFKIT profiles show mixing up to 800 mb which will allow for highs into the 80s with interior warm spots climbing to around 90 degrees. A dry air mass in place along with deep mixing will keep dewpoints in the 40s and 50s so apparent temperatures will be the same as ambient air temperatures. Surface high pressure centered south of New England will promote WSW winds across the area that may keep the sea breeze from making much progress inland with relief mainly confined to the beaches. Regardless, temperatures along the coast are forecast to push into the 80s before the sea breeze gets going. Mostly clear skies and light winds tonight will allow for some radiational cooling with most locations dropping into the 50s for lows.

Friday will be similar to today temperature wise with some increase in clouds as a short wave tracks into the Great Lakes Region. Steady WSW winds will again battle against the sea breeze with coastal areas pushing into the mid to upper 80s for highs. Much of the area will see highs into the upper 80s with interior warm spots making a run into the low 90s. Increasing moisture will keep Friday night lows in the upper 50s to low 60s.

KEY MESSAGE 2 DESCRIPTION...

Low pressure tracks just north of the Great Lakes Friday night with a boundary lingering across the International Border. Models have continued to trend drier for Friday night, so any showers that move into the area should be confined to northern NH and the western ME mountains. Overnight lows will be mild and in the upper 50s to low 60s.

Saturday will be another very warm day, especially south of the mountains, while low pressure tracks across the area and southwest winds continue ahead of a cold front. Highs should be mostly in the 80s, but there may be an area that stays in the 70s stretching from the Midcoast to near Augusta with winds more onshore. Northern areas should see most of the showers in the morning with a few storms also possible, but southern areas will see these chances increase in the afternoon and evening as better lift arrives and daytime instability builds. There does appear to be some potential for a couple of strong storms somewhere across the region with more CAPE across southern NH, although the more favorable shear may be more across northern areas.

Showers remain likely Saturday night and into Sunday as the primary shortwave trough approaches and sends the cold front through sometime during the first half of the day. There could be a couple of storms on Sunday, but looks like it would be a pretty brief window. Precipitation should taper off later in the day from north to south as drier air works its way southward.

One more thing about this system: Not expecting any hydro issues, but PWATs are forecast to climb to around 1.50", which is above the 90th percentile for this time of year. So there could be some hefty rain rates within showers and storms.

KEY MESSAGE 3 DESCRIPTION...

Drier conditions settle in for Monday behind Sunday's front with most available guidance bringing highs into the 70s. After that, ensembles favor upper-level riding building toward the Northeast, offering a warming trend to bring temperatures back above normal while also keeping things mostly dry through midweek.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Through 12Z Friday...VFR. Dry airmass should prevent widespread valley fog development again tonight. Light and variable winds will become steady out of the WSW today. Winds turn more onshore for coastal terminals this afternoon followed by slackening winds tonight.

Outlook:

Friday: VFR expected.

Friday night: HIE could see showers and MVFR to IFR restrictions Friday night. Other terminals should remain dry but can't rule out MVFR ceilings. RKD could see IFR stratus or marine fog.

Saturday-Sunday: MVFR to IFR restrictions possible as a cold front brings increasing chances for showers and thunderstorms.

Sunday night: Any lingering precipitation comes to an end as the front pushes south, but patchy fog could bring additional IFR restrictions.

Monday-Tuesday: VFR expected.

MARINE

High pressure centered south of the waters will keep winds and seas below SCA thresholds today through Friday. Winds will generally be out of the south during the day and light offshore winds at night.

Friday night-Thursday...Marine fog/stratus is possible Friday night into Sunday morning as a cold front approaches from the north. The front will also bring increasing chances for showers Saturday afternoon through Sunday and possibly a couple of storms. Ahead of the front, southwesterly flow is expected to stay below SCA criteria, but once the front crosses the first half of Sunday, north to northwest winds could reach SCA levels Sunday into Sunday night. Winds and seas likely stay below SCA levels for the first half of next week as high pressure builds across the waters.

GYX WATCHES/WARNINGS/ADVISORIES

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