textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed for this forecast package.

KEY MESSAGES

1. Expect seasonable temperatures and breezy northwest winds today with dry and pleasant weather on Monday.

2. Several rounds of downpours/thunderstorms Tuesday-Wednesday evening. Pleasant, seasonable temperatures through the end of the period.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Winds will shift to out of the northwest behind a cold front this morning, becoming breezy through the afternoon. Gusts up to 35 mph will be possible. Any early morning showers should move out to sea fairly quickly, but we could see a few lingering showers and clouds over the mountains. Any remaining wildfire smoke should also move out this morning and the pattern should give us a break from it's return for at least a couple of days. Highs will be around seasonable averages for this time of year, ranging from the mid 60s to lower 70s north, to the mid to upper 70s most elsewhere. A few lower 80s are likely over southeast New Hampshire and coastal Maine. Tonight's lows will mainly range from the upper 40s to the upper 50s.

High pressure moves in on Monday, leading to lighter winds, dry weather, and slightly warmer temperatures. Highs will mainly range from the low to mid 70s north, to the low to mid 80s south.

KEY MESSAGE 2 DESCRIPTION...

A slow moving, but deep trough, digs into the Northeast. Deep southwest flow aloft will really transport in a juicy environment. This will set the stage for scattered downpours as early as Tuesday afternoon, but more likely from Tuesday night- Wednesday night. With hi-res guidance just beginning to come into range, can see a bit of a convective augmentation to this rainfall event. Therefore, will likely have a few waves of heavy precipitation across the forecast area, with some drier periods too.

Mean guidance shows PWATs surging to 1.50-1.90", which is AOA the 90th percentile of climatology. In addition, some deterministic output is suggesting robust IVT transport from the Gulf Coast states. All this is to say there will be a moist environment favoring efficient rainfall in place. Have seen QPF lower on NBM since yesterday, but it is still advertising a healthy inch region- wide. This slight drop is likely due to a more scattered nature to the rain.

Overall not a strong signal for robust/organized convection, given weak low-level shear, CAPE, and general slow/pulsy storm motions. Do see a modest severe signal emerging on Wednesday. Will likely need some morning destabilization to realize the 1000 J/Kg MUCAPE that some guidance is indicating, so as is typically the case with convective setups around here, "stay tuned".

Should generally have near seasonable temperatures this upcoming week. Tuesday-Wednesday will have a small diurnal range given the moisture and clouds in place. By Thursday-Friday, current expectations are a strong kick of dry westerly flow behind the trough. This looks to really dry things out, with dew points potentially dropping into the 40s. Combined with 850 mb temperatures dropping to 10-12C, dare we say a taste of early fall? The only fly in the ointment will be upstream wildfire smoke.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Through tonight...VFR has returned to most of the area except for along and north of the mtns where an upslope MVFR deck lingers. That will continue into midday when it begins to scatter out. The only restrictions will be at HIE however. Otherwise it will remain gust thru the day with west to northwest gusts up to 25 kt. Winds will relax at sunset, and depending on how calm it gets some valley fog may be possible at HIE and LEB.

Outlook...

Monday: VFR expected.

Tuesday-Wednesday: MVFR to IFR possible with increasing chances for SHRA and a few TSRA.

Thursday: Becoming VFR after some morning showers.

Friday: VFR expected.

MARINE

A cold front passes the waters early this morning. The passage of this front will lead to increasing southerly to southwesterly winds of 25 to 30 kts.

Winds shift more offshore later this morning, remaining gusty but mostly falling below SCA levels. While wave heights will have built 5 to 8 ft, the NW winds should knock these down to 3 to 4 ft by mid morning.

High pressure builds in Monday, keeping conditions under SCA levels, and then the next front brings another chance at SCA conditions toward the middle of next week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ150- 152-154.