textproduct: Gray - Portland

WHAT HAS CHANGED

Have increased PoPs south of the mountains early this afternoon as upstream radar trends and hi res guidance suggest some light showers will be possible. Have also bumped up sky cover which has resulted in the high temperature forecast to lower by a couple of degrees. Will continue to monitor for the potential of a few gusty showers/storms across the northern half of the area this afternoon and evening.

KEY MESSAGES

1. A cold front will bring the chance for showers and thunderstorms this afternoon and evening. High pressure will then return Monday.

2. An unsettled pattern brings multiple chances for rain mid to late week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Partly cloudy skies and mainly dry conditions will prevail this morning before a potent H5 s/wv trof and surface cold front brings an increasing chance for showers and thunderstorms this afternoon and evening. Despite limited daytime instability, the combination of sufficient deep layer shear and inverted-V soundings thanks to dry air at the surface will likely allow for gusty to locally damaging winds within any stronger cells. Latest CAM guidance indicates that north-central NH and ME are the most favorable locations for showers and storms, with activity beginning across the north potentially around noon before drifting southeastward through the afternoon and early evening. It will otherwise be a breezy day with WSW wind gusts up to 25 mph with high temperatures into the 70s to middle 80s from north to south.

Showers and storms will wane tonight behind the cold front with overnight low temperatures into the 40s and 50s. Patchy fog is possible, especially across the valleys and in areas that experience earlier rainfall.

High pressure will return on Monday with tranquil weather conditions. Partly to mostly sunny skies will prevail with high temperatures into the 70s to near 80 degrees and lows mainly in the 50s.

KEY MESSAGE 2 DESCRIPTION...

A ridge builds into the Great Lakes through the week, while New England looks to remain on the eastern periphery of the ridge, and closer to a deepening trough across the Canadian Maritimes. This brings a more unsettled and cooler pattern, with multiple systems riding around the edge of the ridge.

The first system likely arrives during the day on Tuesday. Low pressure tracks through southern Canada, while a warm front looks likely to stall across New England and serve to focus more repeated rounds of showers and storms. At least at this point, most of this activity looks to be more focused across southern New England on Tuesday.

A fresh wave of moisture on Wednesday looks to make more progress northward with the front. By this time, what's left of the low pressure system looks to make it's closest pass to northern New England, with both features bringing the best chance for widespread precip.

Then by the Thursday to Friday timeframe the forecast becomes less certain. It's possible that the trough consolidates more south of Nova Scotia, allowing the ridge to begin pushing into New England with warmer and drier conditions. But it's also possible the trough remains more elongated, keeping the unsettled conditions ongoing into the beginning of Labor Day Weekend. On this evening's Euro and AIFS suites a slightly warmer solution was shown over the 12z runs, but it's still too early to know whether or not this is a trend yet. We'll continue to watch this over the coming days.

AVIATION /13Z SUNDAY THROUGH THURSDAY/

Mainly VFR conditions through mid to late afternoon before showers and thunderstorms form ahead of a sagging cold front across the north. Local MVFR or lower conditions are possible in any convection, but most likely this will be confined to a HIE to RKD line and north. Conditions return to widespread VFR tonight, but valley fog is possible especially for any areas that do receive some rainfall. VFR conditions will prevail on Monday with light offshore winds giving way to a sea breeze in the afternoon.

Outlook...

Monday night: Mainly VFR.

Tuesday-Tuesday Night: MVFR and showers possible, with the best chance across southwestern terminals.

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

MARINE

SW winds will prevail today ahead of a cold front with gusts up to 20 kts and seas of 1-3 ft. Winds will veer to the NW tonight behind the cold front before becoming light and variable Monday morning. A sea breeze will then bring SE onshore flow later Monday, although winds and seas are expected to remain below SCA criteria.

Outlook:

High pressure prevails across the waters to start the week with fair conditions. A warm front then stalls across the waters late Tuesday through Thursday, with SCA conditions possible in freshening southeasterly flow.

GYX WATCHES/WARNINGS/ADVISORIES

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