textproduct: Gray - Portland

WHAT HAS CHANGED

No meaningful changes have been made to the ongoing forecast.

KEY MESSAGES

1. Morning fog dissipates, with showers and thunderstorms redeveloping into the afternoon. These will be more focused in southern Maine and eastern New Hampshire today, with a similar gusty wind threat for any stronger storms.

2. High pressure brings fair weather with lower humidity over the weekend.

3. Rain chances return from Sunday night through mid week as a stationary front sets up.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Fog and low stratus from the overnight should erode through early morning. Breaks in stratocu develop late morning and early afternoon, and this will aid in destabilization from the foothills to the coast. Morning stratus may be more resilient towards the Midcoast and around Penobscot Bay into the Lower Kennebec Valley, resulting in some differential heating through the morning hours.

Slow moving cold front will bisect the CWA through the afternoon, and this will be the primary lifting agent along with diurnal heating. CAPE, moisture, and low/mid level lapse rates all indicate an environment conducive to thunderstorm development in the afternoon. Hodographs are elongated, but overall shear is on the lower side where thunderstorms are expected to develop.

Given this imbalance, storms that rapidly deepen with a marginal updrafts could collapse resulting in gusty outflow winds. CAMs favor southern ME for shower/storm coverage, but an area from the foothills to the coast in both ME and NH stands the best chance for storms today. If onshore flow is strong enough, storms may weaken in a marine airmass before reaching the immediate coast, particularly up the southern ME coast.

Shower and thunderstorm coverage decreases in the evening with instability. The cold front will then push along and then off the coast with clearing skies across the interior. CAA follows, with a cool night forecast. Overnight lows fall into the lower 50s across the interior, with 40s across the northern mountains and valleys. Temps linger around the upper 50s along the immediate coast.

KEY MESSAGE 2 DESCRIPTION...

The cold front clears our region by early Saturday morning, setting us up for a fairly pleasant final weekend of meteorological Summer. Drying westerly flow out of Canada combined with a weak high pressure cresting over the region will usher in much drier airmass. Plenty of dry air aloft to mix down, and with clear skies and deep mixing, expect dew points to fall to the 40s/50s. It will be a great time to open up the windows with refreshing, cool nights Friday and Saturday night. Overnight/early morning fog will be possible both nights in typical fog prone areas.

Sunday will be a bit of a transition day, with some model outcomes ushering in showers late in the day while others keep it mostly dry. The greatest rain chances appear to be across Coos County NH into northwest Maine. However dew points will remain in the "comfortable zone", and expect the day to still feature a good amount of sunshine in our southern zones.

KEY MESSAGE 3 DESCRIPTION...

Looking towards next week, the high pressure will shift south towards the Southeast U.S. coast. Combined with a deepening trough over Canada, this puts us back into an active storm track with likely a few disturbances riding on strong WNW upper-level flow between these two features. These embedded shortwaves can be notoriously tricky to time out in a quasi-zonal type of pattern, but guidance is beginning to hone in on one opportunity for precipitation Tuesday, then another Wednesday night- Thursday. It is likely there will be some concentrated opportunities for rain.

Should see a strong temperature gradient emerge, with New England trending towards the cooler side of things. In any case, this is a low confidence forecast as frontal position and the influence of clouds/precipitation will bear watching. For now it looks like highs in the 60s/70s to start the week, but with rising dew points and mild nights. Some guidance suggests we may break into the "warm sector" deeper into next week with winds turning to the southwest.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Through 12Z Saturday...Patchy fog this morning will keep restrictions down to IFR/LIFR for the next couple hours. VFR is expected in most places, though low stratus is likely to blanket the Midcoast, affecting KRKD. Scattered showers and thunderstorms could allow for a brief period of restrictions in the afternoon. More valley fog is possible late tonight and could impact KLEB and KHIE, as well as KRKD. Otherwise most other sites should remain VFR tonight.

Outlook:

Friday night: Mainly VFR outside of valley fog.

Saturday-Sunday: Mainly VFR, no sig wx.

Sunday night-Tuesday: CIGs and periods of SHRA will likely bring at least MVFR conditions at times.

MARINE

S winds will prevail at 5-12 kts with seas of 2-4 ft, highest outside of the bays. An uptick in wind speeds is likely Friday evening and overnight as a cold front passes over the waters. Marine fog is possible tonight through Fri morning.

High pressure builds in from the west Saturday and sinks south of the waters Sunday. A cold front crosses the waters Sunday night and Monday and stalls south of the waters into Tuesday. Winds and seas will likely remain below SCA thresholds through the period.

GYX WATCHES/WARNINGS/ADVISORIES

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