textproduct: Gray - Portland

WHAT HAS CHANGED

No changes needed this morning as the forecast remains on track for a dry and breezy day. Just updated the aviation discussion for the 12Z TAFs.

KEY MESSAGES

1. Expect a seasonable and breezy day today with plenty of sunshine. Widespread chances for showers and storms return Saturday.

2. Seasonable summertime conditions expected into next week, with another chance for widespread showers and storms Tuesday and Wednesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure builds into the region through the day, but the pressure gradient will be a bit slower to relax on the eastern and northern portions of the forecast area. This will lead to plenty of sunshine and some breezier northwest winds this afternoon with some gusts up to 25 mph or so.

Temperatures will be a bit cooler today with highs expected to be closer to seasonal averages for this time of year. Highs will range from the mid 60s to lower 70s north, to the upper 70s and lower 80s south and along the coast.

Winds will calm down tonight and if clear skies can hang around, we may see some valley fog settle in overnight into Saturday morning. Lows will mainly fall into the upper 40s to upper 50s.

We will transition back to southwest flow aloft on Saturday as the next shortwave trough approaches and brings the next chance of widespread showers and storms. We will be a little bit warmer with highs in the lower 70s north, to the upper 70s and lower 80s across most of the Maine coast, to the mid/upper 80s over southern New Hampshire. Combine these with widespread dewpoints in the 60s and we will see some instability on the order of 500 to 1000 J/kg of MUCAPE by the afternoon/evening hours. Many of the regional models and in range CAMs suggest that we could see multiple rounds of showers and storms through the day on Saturday. Strong low level and deep layer shear will mean that a few of these storms could become strong with gusty winds and small hail. The NAEFS suggests PWATs will be in the 90th percentile or greater for this time of year by late Saturday so some heavy downpours will also be possible. Showers and storms gradually start to diminish and move out overnight.

As a final note, the HRRR continues to bring some smoke aloft back into portions of New Hampshire tonight, spreading to the rest of the forecast area on Saturday. The HRRR also suggests that some of this smoke could make it down to the surface so we will have to watch those trends. Smoke could also impact temperatures on Saturday.

KEY MESSAGE 2 DESCRIPTION...

It will dry out Sunday morning with another push of northwest surface winds. Possibly some CAA terrain-induced showers across the high terrain in the north, but generally looks like the more enjoyable day of the weekend. A high pressure crests overhead on Monday bringing more pleasant conditions and continued seasonable temperatures.

Eyes then turn to Tuesday-Wednesday, as a slow moving, but deep trough, digs into the Northeast. With some downstream ridging, this may amplify the longwave trough while also slowing its forward propagation. The result will be an extended period of deep SW flow aloft. This will really transport in a juicy environment. EPS and GEPS ensembles both show PWATs surging to 1.8-2.0 inches, which is quite a strong signal for this range on ensemble guidance. In addition, some deterministic output is suggesting robust IVT transport of up to 1000 kg/m/s. NBM mean guidance is also indicating 1.0-1.5" of QPF across the region, which some individual ensemble members that feature significantly higher totals. All this is to say there will be the potential for locally heavy rainfall in the Tuesday- Wednesday timeframe, which may evolve in a few separate waves of downpours.

Finally, still monitoring how much wildfire smoke will affect the region into next week, as those Canadian wildfires are expected to continue burning for the foreseeable future. It seems plausible a stronger burst of northwest flow on Sunday will push the smoke plume south of New England, but there is a potential it could return north/overhead sometime next week with periods of decreased air quality.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Through 12Z Saturday...Expect VFR conditions to generally continue through tonight. However, nighttime valley fog will also be possible, potentially leading to scattered MVFR or lower visibilities in the vicinity of LEB and HIE. Any fog should lift quickly on Saturday morning.

Outlook...

Saturday-Saturday night: Saturday begins VFR, but then chances for MVFR to IFR restrictions increases later in the day along with SHRA and possible TSRA. The higher chances for IFR (and possibly lower) arrive Saturday evening into Saturday night.

Sunday: Conditions expected to return to VFR in the morning, except lingering MVFR ceilings and SHRA possible at HIE.

Monday: VFR expected.

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

MARINE

Expect fair conditions to continue through tonight as broad high pressure builds in.

Saturday-Thursday...Winds and seas will be on the increase on Saturday with gales possible Saturday night ahead of a cold front. The front crosses early Sunday morning, shifting winds to W and NW. These will likely subside below gale and SCA levels, but seas could stay above 5 ft much of the day. High pressure builds in for Monday, keeping conditions under SCA levels, and then the next front brings another chance at SCA conditions toward the middle of next week (be Tues-Weds or Weds- Thurs).

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Watch from Saturday afternoon through late Saturday night for ANZ180-182.