textproduct: Caribou

WHAT HAS CHANGED

- Raised high temperatures and lowered dew points Tuesday afternoon - Added key message for potentially significant rainfall Thursday into Friday - Aviation updated

KEY MESSAGES

1) Warmer and dry conditions continue through Tuesday.

2) Significant rainfall is possible Thursday into Friday.

DISCUSSION

KEY MESSAGE 1... 1) Warmer and dry conditions continue through Tuesday.

KEY MESSAGE 1 DESCRIPTION... The axis of the mean northern stream trough over the eastern U.S. slowly passes to the east through tonight. This develops into a closed low off the mid-Atlantic/New England coast on Monday, as deep layered ridging approaches from the west. At the surface, high pressure builds over the region through Monday, as a coastal low tracks well south of Long Island/Cape Cod through tonight, then well south of the Gulf of Maine on Monday.

The result across northern and eastern Maine will be a battle between maritime polar air being brought in the low levels, and drier air coming in from the west above that airmass, working to dry it out from the top down. For now, leaning towards the low level maritime polar airmass winning out, as high clouds coming in from the northwest, should help to limit the amount of mechanical turbulence that is needed to mix down the drier air from aloft. As a result, have continued to increase cloud cover above the NBM, and correspondingly lower highs and raise lows by blending in the NBM50 with the NBM for temperatures today through Monday. Therefore, still expect above normal temperatures away from the coast, where they should run near normal.

The 500mb ridge axis will move directly overhead on Tuesday afternoon with clear skies. 850mb temperatures are forecast to range from 3 to 5 C across the forecast area, which mixed to the surface would yield temperatures in the mid to upper 60s F. A modest south-southeast wind will develop, which will transport cooler maritime air inland and limit high temperatures to the 50s closer to the coast. Forecast soundings also indicate very dry air within and at the top of the mixed layer. Major adjustments were needed to the NBM dew points, especially away from the coast. The combination of preceding dry weather, relative humidity around 20 percent, and a light to modest breeze may lead to elevated fire weather conditions Tuesday afternoon away from the coast.

KEY MESSAGE 2... Significant rainfall is possible Thursday into Friday.

KEY MESSAGE 2 DESCRIPTION... Broad upper level troughing pivots over the Great Lakes into Ontario during the middle of the week. At the same time ridging will erode over Maine Tuesday night into Wednesday and move northeast to just south of Greenland, creating strong blocking which will cause the trough progression to slow and eventually become cut-off. At first some lighter rain is possible Wednesday into early Thursday with weak forcing and onshore flow. However, a stronger shortwave trough arrives later Thursday with ample moisture from the subtropics and precipitable water (PWAT) values around or above 1 inch. A slow moving axis of moderate to locally heavy rainfall is possible. While there is uncertainty in the intensity and location of the band, ensembles show the greatest probabilities for greater than 1 inch of rainfall in excess of 50 percent from Baxter State Park south and west. Some solutions such as the 0z Canadian keep the ridging in tact and most precipitation out of northeast Aroostook County, but this is a small minority of guidance. A soaking beneficial rainfall with little to no flooding issues is most likely, however there is a small chance for hydro issues if higher end solutions showing localized amounts in excess of 3 to 4 inches in 24 hours occur. This will be highly dependent on whether or not the heavier precipitation band stalls over the same area for a longer period, and how much elevated instability develops. Freezing levels are also on the lower end at around 6 to 7kft, which would limit warm cloud processes that generally lead to heavier rainfall rates.

Heavier PWATs move east of the area by the weekend, but unsettled weather will continue with the upper level low likely to remain overhead and cause below normal temperatures and elevated chances for cloudier skies and showers.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

VFR through tonight with light winds.

Monday: VFR at southern terminals with a chance of MVFR at northern terminals.

Monday night to Tuesday: VFR. Light winds Monday night, becoming SSE 10-15 kt Tuesday afternoon.

Tuesday night to Wednesday: VFR, becoming IFR at southern terminals Tuesday night and MVFR at northern terminals Wednesday with -SHRA and -DZ possible. SSE winds 5-15 kt.

Wednesday night: Variable conditions with patches and periods of VFR and MVFR/IFR. SE winds 5-15kt. -SHRA or -DZ remain possible.

Thursday: MVFR/VFR, becoming MVFR/IFR late at southern and western terminals such as BGR and GNR with uncertainty in the onset timing of RA. E winds around 10 kt with gusts to 20 kt. LLWS possible.

MARINE

A relaxed pressure gradient over the waters through Tuesday will limit winds to around 10 kt or less and seas to 2 ft or less.

Winds and seas increase Tuesday night through Friday before decreasing over the weekend. There is some uncertainty in winds and waves, but in general Small Craft Advisory conditions are likely over most waters Thursday through Friday. A period of Gale force winds is possible during this time, especially over the outermost marine zones, ANZ080 and ANZ081 (25 percent chance). However, very stable conditions will limit the gust factor and overall winds. A period of moderate to heavy rainfall and some fog may also lead to visibility reductions during this time.

CAR WATCHES/WARNINGS/ADVISORIES

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