textproduct: Gray - Portland

WHAT HAS CHANGED

Have lowered precipitation amounts some for today as it appears dry air will further limit amounts, especially nearing central Maine.

KEY MESSAGES

1. Low pressure will bring a period of rain today into tonight.

2. High pressure brings mostly fair weather Monday through Wednesday with temperatures running below normal. Rain chances increase during the Friday to Sunday timeframe as a possible coastal low develops along the Eastern Seaboard.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A short wave trough will approach from the west early today with rapidly increasing clouds. Increasing forcing for ascent will aid in a shield of overrunning rain moving in from the west beginning this morning. The rain will then spread eastward to the rest of the forecast area by early afternoon. There remains uncertainty in amounts at this time as dry high pressure centered just to our northeast should continue to advect low level drier air in from the east. Based on latest CAMs and other sources of deterministic and ensemble guidance, have lowered precipitation amounts pretty much across the board. This has been typical of several rain events this summer, with rainfall amounts ending up lighter than forecast. Drought will continue although a few areas across southern zones may see a beneficial rainfall.

Hourly temperatures may be non-diurnal today as the rain shield impinges on a relatively dry air mass, i.e., temperatures should fall some as the late morning and afternoon progresses through evaporational cooling.

Gradual clearing is expected tonight, especially after midnight.

KEY MESSAGE 2 DESCRIPTION...

Ensemble guidance is in strong agreement that high pressure will move across Canada and arrive in Quebec on Monday. This high to our north will allow for temperatures to run cooler than normal through the week, with highs in the lower 60s and lows in the upper 30s and lower 40s. Frost does appear to be a possibility Tuesday, Wednesday and Thursday nights north of the mountains.

At the end of the week, models show the potential for a coastal low to impact the region. A high degree of storm track uncertainty remains, but the low could allow for some much needed rainfall over the weekend if the low takes a more westerly track. Gusty winds and high surf could be possible as well.

AVIATION /08Z SUNDAY THROUGH THURSDAY/

Through 06z Monday...Mostly clear skies this evening and the introduction of low level moisture has allowed valley fog to develop across the area. More dense cloud decks are on the way from the south and west however, and these should allow fog to dissipate through the early morning hours across NH. SHRA and RA advances across the area this afternoon into the evening, bringing MVFR cigs and occasional MVFR/IFR vis. An eventual trend towards IFR cigs is expected this evening before improvement after midnight local.

Outlook...

Monday: Mainly VFR with breezy N winds 12-15 kts. MVFR cigs may be present through the mountains in the morning.

Tuesday-Thursday: Other than nightly valley FG at LEB and HIE most nights bringing IFR- LIFR restrictions, VFR conditions will prevail through Thursday.

MARINE

Sub-SCA conditions continue through Monday as high pressure slides eastward over the waters. Winds remain generally onshore through early tonight tonight, but will shift around to northerly after midnight as a front crosses the waters.

ENE winds will prevail Monday night through Thursday with gusts between 20-25 kts and seas of 1-3 ft. A coastal low may bring increased winds and seas during the Friday to Sunday timeframe but forecast confidence is low.

GYX WATCHES/WARNINGS/ADVISORIES

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