textproduct: Caribou

WHAT HAS CHANGED

-Issued new frost advisory for tonight

-Lowered low temperatures more for tonight. Another widespread frost/freeze is expected across northern Maine.

-Confidence increasing in frost potential across portions of the North Saturday night.

KEY MESSAGES

1) Near to below freezing temperatures are expected over the north again tonight, leading to widespread frost, especially in colder valleys. Additional frost is possible Saturday night. This may lead to damage to sensitive vegetation.

2) Widespread soaking rain likely From Sunday night into Memorial Day. This could help aid in mitigating on going drought conditions across portions of the region.

DISCUSSION

KEY MESSAGE 1... Near to below freezing temperatures are expected over the north again tonight, leading to widespread frost, especially in colder valleys. Additional frost is possible Saturday night. This may lead to damage to sensitive vegetation.

KEY MESSAGE 1 DESCRIPTION... Another round of frost and freeze conditions is expected across northern Maine tonight as high pressure sets up just north of the area. After slight warming today, weak cold air advection will resume from the northeast, with sub-540dam 1000-500mb thicknesses lingering across much of northern and eastern Maine. The combination of a cold air mass and favorable radiational cooling conditions will likely cause temperatures to fall below most guidance again. The NBM 10th percentile was preferred for most points, but valleys and areas that typically see cooler temperatures in clear skies and light winds could be even colder similar to this morning. Another frost advisory will be necessary over nearly the same areas once the advisory this morning ends. The frost/freeze program is not active across portions of northwestern Maine, and many of these areas are expected to see sub-freezing temperatures again tonight.

Models continue to slow down progression of the axis of deep layered ridging to the east this weekend. The result is high clouds ahead of the next system should be slower to arrive than previously expected. This coupled with light winds with the center of surface high pressure transiting the region, should allow for decent radiational cooling conditions Saturday night. Given NBM warm bias when there is strong radiational cooling, used a blend of NBM10/NBM/ConsMOS for lows Saturday night. This should allow for widespread frost across Northern Aroostook overnight, with patchy frost just to the south. The frost is a threat to sensitive vegetation.

KEY MESSAGE 2...Widespread soaking rain likely From Sunday night into Memorial Day. This could help aid in mitigating on going drought conditions across portions of the region.

KEY MESSAGE 2 DESCRIPTION... The exiting of the deep layered ridge axis to the east late Sunday, allows for strong low level warm advection to set up Sunday night and to continue into Memorial Day. At the surface, high pressure slowly exits to the east, with a cold air damming signature over the region, that is reinforced by a surface low tracking across the Gulf of Maine on Memorial Day.

As a result, rain develops from SW to NE Sunday night. Then tapers off from SW to NE Monday afternoon as the coastal low exits to the southeast.

This system should bring widespread wetting rain to the region from Sunday night into Memorial Day, with the potential for up to 2/3 inch of rainfall area wide. The rainfall coupled with the cold air damming should result in Monday being cooler than Sunday, with highs mainly in the mid to upper 50s.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Through Saturday... VFR. NW winds around 10 kts today, gusting to 20-25 kts. Light and variable winds are expected tonight and Saturday, with a modest south sea breeze around 5-10 kts developing Saturday afternoon across Downeast terminals.

Saturday night-Sunday...VFR. S-SE winds G15-20KT possible Sunday afternoon.

Sunday night-Monday...IFR or lower conditions likely develop by late Sunday night. LLWS possible Sunday night.

Monday night-Tuesday...VFR, except for a brief period of MVFR possible Tuesday afternoon in any stronger showers at northern terminals Tuesday afternoon. W winds G15KT possible Tuesday afternoon.

MARINE

Winds and seas below advisory thresholds continue through Saturday. Sea surface temperatures remain in the mid 40s.

A fairly relaxed pressure gradient over the waters Saturday night and Sunday should limit winds to 10 kt or less and seas to 2 ft or less. SCA conditions are possible over the coastal ocean waters Sunday night into Monday night, with sub-SCA conditions over the intra-coastal waters. On the outer waters Sunday night and Monday, there should be wind gusts up to 25-30KT and seas up to 8 ft. While winds subside Monday night on the outer waters, seas should remain up to 7 ft. A relaxed pressure gradient returns to the waters on Tuesday, with winds 15 kt or less and seas 4 ft or less on the coastal ocean waters and 5 ft or less on the outer waters.

CAR WATCHES/WARNINGS/ADVISORIES

ME...Frost Advisory until 7 AM EDT this morning for MEZ002-005-006- 010-011-031-032. Frost Advisory from midnight tonight to 7 AM EDT Saturday for MEZ002-005-006-010. MARINE...None.