textproduct: Gray - Portland

WHAT HAS CHANGED

A freeze warning and frost advisories have been issued across parts of the interior for tonight.

KEY MESSAGES

1. Summer comes to an end today, with temperatures returning to normal during the day and chilly readings tonight. Areas of frost are likely across parts of the interior, and sub freezing temperatures across the northern valleys.

2. High pressure will dominate the remainder of the forecast. Some rain will push into the area to end the weekend, but the question is how far northeast does the rain make it before sliding out to sea.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Cold frontal passage has been largely dry across the forecast area, but is really noticeable with the change in dewpoints across parts of the area. Dewpoints are tumbling into the 30s across northern parts of the forecast area and will continuing working south thru sunrise. High pressure will settle over the region by tonight and that combination of surface high and dry air mass will allow for strong radiational cooling. NBM guidance is looking rather warm given the set up, so my preference is to blend in a little MOS and NBM 10th percentile to capture the colder readings. Resulting temp forecast and the fact that recent rainfall and green up will provide some low level moisture, areas of frost are likely. Because of this, a freeze warning has been issued for the northern valleys, with frost advisories for the surrounding areas across the interior and through the Connecticut River Valley.

KEY MESSAGE 2 DESCRIPTION...

Much of the extended looks like it will feature large scale eastern CONUS ridging aloft. While this does not rule out rainfall, it tends to be a drier pattern overall. First up will be a warm front lifting towards the forecast area this weekend. Ridging/surface high pressure hold strong thru the first half of the weekend it looks like, so any rain will be holding off until later Sun or even into Mon. Ensemble guidance is fairly insistent that some light precip occurs across much of the forecast area, but it is clear that measurable rainfall is more likely across the southwestern portions of the forecast area vs northeast. NBM guidance is giving categorical PoP across southwest NH and low likely creeping thru the remainder of the forecast area. At this time I do not see a compelling reason to deviate from that. Otherwise once this system passes thru the region a return to warmer than normal temps is more likely given the upper ridging.

AVIATION /02Z THURSDAY THROUGH MONDAY/

Through Thursday...VFR conditions expected thru Thu. Steady breeze continues overnight as cooler and drier air pushes into the region. With high pressure building in today there will be a better chance for sea breezes to develop and push inland during the afternoon, shifting wind direction to onshore. Winds will go light and variable after sunset.

Outlook...

Friday: VFR conditions expected.

Saturday and Saturday night: VFR conditions expected to prevail much of the time, though some MVFR CIGs may begin to creep in late Sat night.

Sunday and Monday: Periods of MVFR or lower as CIGs lower and areas of rain move thru the region.

Tuesday: Gradual improvement to VFR expected.

MARINE

With high pressure building over the waters beginning today, conditions are largely expected to remain below SCA thresholds. The weaker pressure gradient should allow for sea breezes to develop during the afternoons and lead to breezy onshore winds at times.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Freeze Warning from 11 PM this evening to 8 AM EDT Friday for MEZ007-008. Frost Advisory from 11 PM this evening to 8 AM EDT Friday for MEZ009-012-013-033. NH...Freeze Warning from 11 PM this evening to 8 AM EDT Friday for NHZ001-002. Frost Advisory from 11 PM this evening to 8 AM EDT Friday for NHZ003>007-011. MARINE...None.