textproduct: Caribou

WHAT HAS CHANGED

- Reduced thunder chances on Saturday with a less favorable setup expected.

KEY MESSAGES

1) Showers and thunderstorms are expected through early this evening, mainly across central areas. Small hail is possible in any storms, although the strongest storm may produce slightly larger hail.

2) Unsettled weather and a gradual warming trend is expected into early next week with frequent chances of showers and thunderstorms, particularly in the afternoon. A steadier and more widespread rainfall is likely Thursday night into Friday.

DISCUSSION

KEY MESSAGE 1... Showers and thunderstorms are expected through early this evening, mainly across central areas. Small hail is possible in any storms, although the strongest storm may produce slightly larger hail.

KEY MESSAGE 1 DESCRIPTION... A mid to upper level low will rotate across the area this afternoon, while its associated surface low deepens over the Gulf of Saint Lawrence and Canadian Maritimes. NW flow is expected which will advect in a pocket of cooler air aloft and much steeper mid level lapse rates with 500-700mb lapse rates of 6-7 deg C/km expected over much of the area for the peak diurnal heating hours. Surface dew points in the 50s and temperatures in the lower to mid 70s will yield limited instability, generally around 500-1000 j/kg. Light to moderate shear is expected as a jet streak exits to the east, with effective shear generally between 10 and 30 kts. Hail CAPE in the -10 to -30C layer will generally be around 100-300 j/kg. All of these parameters indicate potential for numerous instances of small hail and potential for the strongest storms to approach marginally severe hail.

Earlier stratocumulus across much of Aroostook County, with lesser coverage to the southwest, indicates the most favorable environment for hail will be from approximately Clayton Lake and the Central Highlands through northern Washington County initially, although it may expand northward later as sunshine breaks out and these areas catch up on surface temperatures and instability. Showers and thunderstorms will gradually taper off this evening with loss of daytime heating.

KEY MESSAGE 2... Unsettled weather and a gradual warming trend is expected into early next week with frequent chances of showers and thunderstorms, particularly in the afternoon. A steadier and more widespread rainfall is likely Thursday night into Friday.

KEY MESSAGE 2 DESCRIPTION... The jet stream will remain across the area late this week, this weekend, and into early next week, providing lift in tandem with diurnal heating and summertime moisture to maintain unsettled weather. Mid level lapse rates will remain elevated Thursday afternoon, although hail CAPE appears to be lower due to warmer temperatures above 500mb and rising 500mb heights, which should lead to lesser coverage and intensity compared to today. A shortwave trough and approaching low pressure from the west Thursday night into Friday will lead to widespread showers and steadier rain, with the heaviest totals across northern Maine and the Central Highlands. A few rumbles of thunder are possible, mainly from elevated instability as surface temperatures remain cooler in the 50s and 60s. Additional shower and thunderstorm activity is expected each afternoon through the weekend into early next week, although there may be a slight reprieve on Saturday from drier air, questionable lapse rates, and lack of substantial forcing. Warmer temperatures and increasing dew points will result in more available instability and potential for stronger/more numerous thunderstorms Sunday into early next week, although it is too early to pinpoint any details at this range.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

This Afternoon: VFR with -SHRA and scattered TSRA this afternoon. TSRA may produce small hail and briefly lower flight categories. Less coverage of -SHRA at coastal terminals including KBHB. Variable winds 5 to 10 knots, becoming northwest/west around 10 knots.

Tonight: Mainly VFR with -SHRA early. MVFR/IFR possible in patchy low clouds and fog, especially late. Light northwest/west winds.

Thursday: VFR/MVFR with a chance of afternoon showers. Slight chance of a thunderstorm, but less coverage compared to today. Light and variable winds for the north, S winds 5 to 10 kts for southern terminals.

Thursday night: VFR/MVFR early, then MVFR/IFR with showers becoming more numerous, along with areas of fog and drizzle/mist. Southeast/east winds 5 to 10 knots.

Friday to Friday night: MVFR/IFR with numerous SHRA/-RA. Thunderstorms are possible, mainly for central and southern areas. -SHRA tapers off overnight, but MVFR/IFR persists. SSE winds 5 to 10 kts with gusts to 20 kts, becoming light overnight.

Saturday to Sunday: MVFR early Saturday, otherwise VFR with a chance of showers and thunderstorms in the afternoon. Patchy fog and low clouds overnight may lower flight categories. NNW winds 5 to 10 kts, except with the sea breeze along the coast. Light and variable winds overnight.

Sunday to Monday: Lower flight categories are possible in late night and morning fog/low clouds, otherwise VFR in rain showers and thunderstorms. N/NW winds 5-10 kts during the day, light and variable overnight.

MARINE

Winds and seas below Small Craft Advisory criteria will continue across all of the coastal waters out to 60NM through at least this weekend. Seas of 3 to 4 feet are forecast later today and tonight across most of the waters. Visibility reductions are possible in patchy fog tonight into Thursday morning.

CAR WATCHES/WARNINGS/ADVISORIES

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