textproduct: Gray - Portland

WHAT HAS CHANGED

Few changes needed for this quiet Monday evening update. Just blended in the latest observations to the going forecast.

KEY MESSAGES

1. Low pressure tracking along a stationary front will provide a focus for clouds and rain Tuesday, mainly across south-central NH and SW Maine.

2. An unsettled pattern brings the best chance for widespread rainfall late Wednesday and Thursday.

3. A gradual drying trend follows for Friday and Labor Day weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Latest surface analysis places a stationary front from the northern Great Lakes ESE through Long Island, NY with high pressure over SE Canada into northern New England. High pressure will keep much of the area mostly dry tonight as a wave of low pressure starts to form along the stationary front. Valley fog will be likely for portions of the CT Valley as well as northern valleys where radiational cooling will be more efficient.

Clouds will advance northeastward across NH late tonight as the wave of low pressure nudges the stationary front northward. Rain will become likely across southern NH by day break with rain spreading northward Tuesday morning. Models are in reasonable agreement that high pressure will hold firm over SE Canada and will limit rain chances north of a line from the White Mountains to KLEW to KRKD. Rainfall will generally be light, while some elevated instability combined with PWATs greater than 1.5 inches could lead to some localized heavier rates over NH. Chances for rain will diminish Tuesday evening into Tuesday night from NE to SW as the wave of low pressure tracks SE offshore of Cape Cod. Total rainfall will approach 0.75 inches across SW NH and will diminish to the northeast. Otherwise it will be cooler Tuesday with highs in the low 70s while northern areas that see more sun could push into the mid 70s.

KEY MESSAGE 2 DESCRIPTION...

A more widespread and robust round of showers and storms approach the area from the west on Wednesday. Most of the day on Wednesday itself looks mainly dry, with the best chance for some scattered showers across the higher terrain. By late in the day, the more widespread round of showers begins to push into western New Hampshire.

A weak low pressure center gradually organizes as it moves through New England Wednesday night and Thursday. This likely brings a round of steady rain and heavier showers to all of the forecast area, with the potential for a widespread 0.75 to 1.5 inches of rain, the most a lot of towns have seen in a while. The steadiest rain looks to fall during the overnight hours Wednesday and the first half of the day on Thursday. The chance for showers persists through the afternoon on Thursday.

KEY MESSAGE 3 DESCRIPTION...

Overnight Thursday night and Friday, a trough deepens across Nova Scotia while the surface low pressure deepens as well. This consolidates most of the unsettled conditions to the east of New England by Friday, and leaves us on the western edge of the trough. This results in a drier and cooler pattern with northerly flow. The bulk of the heat under a large ridge affecting much of the eastern 2/3 of the country remains west of New England. So while we won't break into the warmth, being on the western edge of the trough brings a drier outlook for the weekend than previous model runs were suggesting from the last few days.

Highs in the 70s look to prevail for most of the area from Friday through at least Sunday, with nighttime lows in the 40s to low 50s. Being under the influence of the trough, mornings will be the sunniest part of the day, with pop up clouds and scattered showers likely a feature each afternoon from Friday through Sunday. The chances for showers progressively lower each day, and are most likely across the higher terrain.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Through Tuesday night...Mainly VFR through 06Z tonight. Thereafter, valley fog likely brings IFR/LIFR to LEB and HIE. MVFR cigs and -RA move into southern NH by 12Z and expand north and east to LEB, CON, and PWM through Tuesday morning. Cigs may lower to IFR thresholds at times into Tuesday afternoon. HIE, AUG, and RKD likely stay VFR through the day Tuesday. Onshore flow may allow for a period of IFR cigs across much of the area Tuesday evening into the first half of Tuesday night with some improvement to MVFR/VFR towards Wednesday morning.

Outlook...

Wednesday-Thursday: MVFR more likely by late Wednesday at most terminals with showers.

Thursday night-Friday: Improving conditions, with MVFR still possible in brief showers. Valley fog is possible at LEB and HIE.

Friday night - Sunday: Mainly VFR during the daytime, but brief MVFR ceilings remain possible in afternoon showers. Nighttime valley fog is likely at HIE, LEB, and CON, and still possible at all other terminals.

MARINE

Winds and seas remain below SCA thresholds through Tuesday night. Low pressure will track along a front south of the waters Tuesday bringing steady SE to E flow and periods of rain. Chances for rain diminish Tuesday night as the low tracks southeast of Cape Cod.

A broad developing low pressure system approaches from the west Wednesday night, crossing the waters on Thursday. A period of SCA conditions are possible in southerly flow ahead of this system on Thursday. Northerly flow brings a return to fair conditions Thursday night and Friday. Marginal SCA conditions are then possible across the outer waters this weekend in northerly flow as low pressure deepens across Atlantic Canada.

GYX WATCHES/WARNINGS/ADVISORIES

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