textproduct: Gray - Portland

WHAT HAS CHANGED

Tonight should feature a fairly steady breeze at least through midnight. After, a few locations across the interior and foothills may rapidly cool should clear skies prevail.

Continued to mention isolated snow showers in the forecast for late Saturday.

KEY MESSAGES

1. Temperatures fall well below normal tonight through Saturday night as cool, continental air arrives from Canada.

2. Wintry weather remains possible late next week, as the weather pattern is expected to stay active.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... The trend to full sun today has been deceptively cool given the breezy conditions and stagnant to falling temperatures. Temps will continue to cool into the teens and lower 20s for much of the area overnight. Even cooler temps in the single digits are likely across the northern valleys.

Cold air advection amid a much cooler airmass will be the primary driver, but may see a narrow window of radiational cooling tonight. Low level winds should maintain some level of mixing through the evening and early overnight hours, with another round of clouds arriving right as they slacken. This could leave pockets of good cooling conditions with values outside of the mountains falling into the lower teens or upper single digits.

Breeze ticks up again Saturday as a wave approaches from the west. Could see some isolated snow showers as this moves through later in the afternoon/evening, but mtns to the west and weakening daytime heating (amid an otherwise cool day in the upper 20s and 30s) could make these sparse.

Saturday night stands the chance for running a few degrees below current forecast depending on the sky forecast. If clouds abate, radiational cooling seems more likely as winds will be lighter as high passes just to the south. With a couple rounds of low level moisture riding around the top of the ridge, it will again be a tricky overnight temp forecast.

KEY MESSAGE 2 DESCRIPTION...

Warm front is forecast to lift into the forecast area Mon night. I expect that low clouds will begin to develop prior to showers moving in from the west. The set up looks fairly favorable for prolonged period of dreary weather. At this time range the details are tough to pin down, but showers, fog, drizzle are all possible. This first event looks to be on the warmer side with low pressure tracking thru southern Canada. I could see temps coming in colder than NBM guidance with high pressure lurking just north of the border. Ensembles show very little threat of wintry precip over the southern half of the forecast area, but northern zones are likely to see at least some light accumulation before any changeover occurs. A cold front crosses the region around Wed but a follow up wave will be right on its heels to end the work week. This second wave has a much better potential to be wintry. A strong high pressure is currently forecast to migrate across Quebec and will be in a good position set up a cold air dam. Ensemble guidance even has a snow threat as far south as southern NH. This is really the one to watch.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18z Saturday...VFR under SKC this afternoon and evening with gusts to 20 kt. Winds slacken overnight, but a NW breeze should continue. Will see some MVFR ceilings make their way into the mountains this evening for HIE. Winds tick up again Saturday morning, but not as gusty as today.

Outlook:

Saturday night: May see a brief line of SHSN move across NH and southern ME terminals late Saturday. Otherwise, VFR prevails.

Sunday and Sunday night: VFR. Some MVFR cigs are possible towards the US/CAN border.

Monday: VFR, no sig wx.

Monday Night: IFR conditions possible with low CIGs developing as warm front moves into the area.

Tuesday: Areas of IFR possible.

Tuesday Night: Areas of IFR possible.

Wednesday: Cold front forecast to cross the region and conditions will improve to VFR behind the front.

MARINE

SCA conditions continue this evening and overnight in the wake of exiting cold front. Wave heights will slowly fall below criteria Saturday. Below SCA conditions are forecast through Saturday night as high pressure passes south of the waters.

A prolonged period of southerly to southwesterly winds are forecast to develop early to midweek. The sustained direction should allow seas to build above 5 feet outside of the bays rather quickly, with gusty winds continuing thru the end of the week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 AM EDT Saturday for ANZ150-152. Small Craft Advisory until 8 PM EDT this evening for ANZ154.