textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes at this time.

KEY MESSAGES

1. A widespread rainfall moves through tonight and Thursday.

2. A gradual drying trend follows for Friday and Labor Day weekend, although there will be chances for scattered showers Saturday afternoon.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A warm front remains stalled to our southwest, with high pressure off to the northeast of Maine. The high gradually moves off to the east tonight, while the warm front lifts north. A wave of low pressure moves along this front tonight, bringing a widespread round or rain, heavy showers, and some thunderstorms.

The front edge of the showers arrives into northern New Hampshire around sunset, and then spreads south and east through the evening hours. A few thunderstorms will be possible as well through the evening across western New Hampshire. Severe storms are expected across Upstate New York today, but by the time they reach New Hampshire the convection is expected to be elevated and not pose a severe threat.

The showers and storms evolve into a steady period of rain overnight with embedded heavier downpours. Rain is expected through the overnight, with the back edge moving from west to east during the morning hours on Thursday. Breaks of sun are likely across New Hampshire during the day tomorrow, bringing the chance for scattered pop up showers during the afternoon hours. Overall rainfall amounts generally look to fall in the 0.75 to 1.25 in range.

The warm front is expected to stall somewhere in western or central Maine. East of the front, low clouds and sprinkles remain through the afternoon hours. It won't be until an occluded front passes through tomorrow night that drier air moves back into the region. Clearing is expected behind this front Thursday night, with nighttime valley fog likely by late in the night.

KEY MESSAGE 2 DESCRIPTION...

An upper low will slowly dumbbell down from central Quebec through northern Maine and over to Nova Scotia Friday into Saturday. While Friday will mainly feature dry conditions, a few showers will be possible in the afternoon over and north of the mountains. A better chance for more widespread showers may evolve Saturday afternoon as a vort lobe rotates down around the upper low to our east. Model soundings suggest that there will be at least some modest instability in place so a few rumbles of thunder may be possible, especially over southern New Hampshire where instability will likely be maximized. Persistent northwest flow will lead to cooler temperatures and dewpoints through the holiday weekend with highs mainly in the mid 60s north to the mid 70s south and some breezier winds out of the north. An approaching ridge may lead to a slight warmup on Labor Day with some low precipitation chances returning to the forecast Monday night into Tuesday.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Conditions lower to IFR and LIFR tonight in rain and lowering ceilings. Conditions improve from west to east late tomorrow morning and into the afternoon. Conditions at AUG and RKD likely take until late in the day to improve. MVFR and VFR then return tomorrow night, but valley fog will be possible at LEB and HIE late in the night.

Outlook...

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

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

Sunday-Monday night: Mainly VFR with valley fog possible at night.

MARINE

A warm front gradually lifts northward across the waters tonight and Thursday. A period of near SCA conditions will be possible Thursday afternoon as a weak wave of low pressure passes north of the waters. A cold front then crosses the waters Thursday night, with improving conditions to follow.

Northerly flow brings fair conditions 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.