textproduct: Gray - Portland

WHAT HAS CHANGED

A new Severe Thunderstorm Watch has been issued for portions of southern New Hampshire, in effect until 7am. Scattered showers and thunderstorms continue through early morning, ending as a cold front presses towards the coastal waters. Will be monitoring storm ingredients once again this afternoon as isolated to scattered quantities develop.

KEY MESSAGES

1. Overnight instability and shear still support occasional instances of strong to severe thunderstorms through early this morning. These should be focused across far southern Maine and central to southern New Hampshire.

2. Additional cold fronts will approach today and again Thursday, bringing chances for showers and storms and a slight cooling trend into the weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Overnight instability remains in place, albeit mostly elevated, through early morning. A 500mb jet exit region will nose into northern New England over the next few hours, providing lift and kinematic support for strong to severe thunderstorms.

Storm lifecycles have been fairly routine through last evening and into the overnight hours, but coverage has been very difficult to forecast and message. 00z GYX RAOB displayed a very stout cap aloft, but with an EML above. This setup is rare for the region, and while significant widespread severe has not come to fruition, it bears watching given the parameter space should a storm take advantage of it.

The approaching jet may provide that extra lift needed to bypass the cap's ability to wilt compromised updrafts. Thus think the ongoing Severe Thunderstorm Watch(es) is warranted considering upstream activity now passing through Upstate NY.

KEY MESSAGE 2 DESCRIPTION...

Troughing will deepen over the eastern U.S. today through the end of the week. Northwesterly winds behind a cold front will usher in a drier airmass later today despite warm high temperatures. One thing to watch will be lingering Canadian wildfire smoke, which had a significant impact on high temperatures yesterday. Should this remain, then high temperatures today will likely fall a couple degrees cooler. There is the potential a few showers and thunderstorms both this afternoon and again Thursday afternoon with perhaps some severe potential, although on a localized scale.

High pressure builds in Friday for fair weather. A short wave moving within the long wave trough over eastern North America will approach over the weekend. This will bring increasing chances for showers late Saturday into Sunday morning.

AVIATION /02Z WEDNESDAY THROUGH SUNDAY/

Through 06z Thursday...Mostly VFR expected. Periods of showers and convection will continue in the region through early morning. Direct hit by TS would bring IFR vis during passage. At this time, this seems possible for LEB given upstream radar imagery. Elsewhere confidence in timing and probability is low enough to not mention TS. Cold front crossing this morning will bring an end to thunderstorm chances, but increase NW winds, gusting to 25 kt. Additional SHRA/TS chance this afternoon, but isolated. VFR continues into this evening and tonight with precip coverage decreasing.

Outlook:

Thursday-Saturday: Mainly VFR conditions with WNW flow prevailing. SHRA/TSRA Thursday afternoon/evening may bring TEMPO restrictions.

Saturday night-Sunday: Chances for rain may bring a period of at least MVFR.

MARINE

Another cold front crosses Thursday with SW winds increasing ahead of the front and then shifting offshore Friday morning. Winds and seas likely remain below SCA thresholds into the weekend.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ150>152.