textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes at this time.

KEY MESSAGES

1. A warm front remains stalled across southern New England, while high pressure remains across northern Maine into Wednesday.

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...

The stalled front that served to focus rounds of showers across New Hampshire earlier today remains in place. While the steadiest precip has moved out at this point, scattered showers and occasional drizzle will linger and increase in coverage south of the mountains overnight tonight as the airmass continues to moisten. Some patchy fog will also be possible tonight as well.

The high pressure across Maine strengthens through tomorrow, keeping northeastern areas brighter and drier for another day. Further west, clouds increase through the daytime as the next wave of low pressure approaches from the west. Some scattered showers and sprinkles remain possible through the day tomorrow, but the bulk of the next round of precip holds off until tomorrow night.

KEY MESSAGE 2 DESCRIPTION...

An upper-level ridge axis will continue to move east of the forecast area late Wednesday as a closed low moves into central Quebec. A surface low will also deepen over west central Quebec with a cold front extending to the south southwest and a warm front extending to the southeast. Widespread precipitation chances will increase from west to east Wednesday night in warm air advection as mid-level heights fall. A secondary low may then form along the cold front over southern Quebec and propagate southeast across northern New Hampshire and central Maine on Thursday, eventually moving out to sea by Friday morning. Another batch of widespread showers and a few thunderstorms will accompany this low/frontal passage. While most locations should at least see some measurable rain, activity on Thursday may be a bit more convective and hit or miss at times. Still, the NBM is advertising widespread medium to high probabilities (50 to 80 percent) for 24-hour QPF of an inch or greater by the time the low moves out to sea Thursday night. Thus, a good soaking rain appears likely for most locations across New Hampshire and western Maine with some locally higher amounts due to the convective nature on Thursday and seasonably high PWATS in the forecast. As we move into the range of some long range CAMs, it is apparent that we may see a lull or two in activity Wednesday night through Thursday.

A few stronger thunderstorms also can't be ruled out on Thursday with some NAM forecast soundings over southern New Hampshire advertising some modest instability and decent shear. The degree of destabilization remains highly uncertain considering widespread cloud cover and rain/showers through the day.

KEY MESSAGE 3 DESCRIPTION...

The upper low moves across Nova Scotia late Friday into Saturday, leaving some unsettled conditions in place over the mountains with some isolated to scattered diurnal showers possible Friday and Saturday afternoon. Persistent northwest flow will lead to cooler temperatures and dewpoints through the holiday weekend. Saturday and Sunday will feel a little bit like early autumn with highs mainly forecast 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 TUESDAY THROUGH SUNDAY/

IFR becomes more likely at most terminals with lowering ceilings. LIFR is more likely at LEB late tonight with valley fog. Improvement back to MVFR and VFR is expected for the daytime tomorrow, before ceilings lower again Wednesday evening.

Outlook...

Wednesday-Thursday: MVFR or lower possible by late Wednesday at most terminals with showers. A few thunderstorms are possible over southern New Hampshire terminals.

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

High pressure remains centered northeast of the waters through the day on Wednesday. A stalled front southwest of the waters moves into the waters late on Wednesday and Wednesday night. 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.