textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed with this forecast package.

KEY MESSAGES

1. Widely scattered showers and storms may bring gusty winds this afternoon. The better chance for more widespread showers and strong storms comes Thursday.

2. Fair weather returns late week through the weekend, becoming more unsettled early next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Shortwaves rotate through the broader trough today and Thursday bringing chances for showers and thunderstorms, some of which may be capable of producing strong gusty winds. With continued northwesterly flow, moisture will be on the lower end with PWATs just over an inch by the afternoon. This also continues our cooling trend with high temperatures in the upper 70s and low 80s south of the mountains, and in the low to mid-70s to the north. Mostly clear skies may allow for heating to develop a couple hundred joules of instability, and with 25-30 kts of shear storm development is not out of the question. The limiting factor is going to be the lack of moisture which should keep coverage isolated. Still, with dewpoint depressions around 20C a gusty storm is not out of the question.

Thursday looks like the better chance for strong storms as the forcing for ascent is stronger with the trough axis swinging through. Moisture will still be on the lower end so coverage may end up similar if not slightly more than today, but the instability parameters look higher. Again, mostly clear skies should allow CAPE of 500-1500 J/kg to develop with around 30 kts of shear. Halfway decent lapse rates in the mid (6.5-7 C/km) and low levels (7.5-8 C/ km) bring a gusty wind threat again with any stronger storms that develop, but both the CAMs and CSUs machine learning model have been noticeably backing off. The HRRR has been liking a round of early morning showers that makes it harder for later stuff to develop, where as the NAM Nest holds off until the afternoon with a broken line of showers and storms crossing through the evening.

KEY MESSAGE 2 DESCRIPTION... Showers potentially linger through the better part of Friday as the 500 mb trough remains overhead, but models are in good agreement that high pressure begins building into the area by the evening so most areas should see improvement. Friday could see some gusty winds as the pressure gradient tightens with a breeze carrying into Saturday as well. It is a sharp trough axis that moves off to the east so increased northwesterly flow is going to bring us some cool nights with lows in the 40s and low 50s.

Sunday looks to remain mostly dry, but high pressure will be making its exit and the 500 mb flow transitions back to zonal. The pattern becomes unsettled as global models bring low pressure into the region early next week, but unsurprisingly at this time range the track and timing is uncertain. For now the NBM having blanket 30-50% PoPs late Sunday night through Monday seems reasonable

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Through tonight...Valley fog continues to lift and widespread VFR conditions expected today. Sea breeze will likely make a push inland for the coastal terminals by mid afternoon. Isolated showers and thunderstorms are possible this afternoon, most likely in the mtns including the vicinity of HIE. Confidence is currently too low to include in any TAFs. Valley fog tonight will depend somewhat on rainfall, but otherwise a few hours of IFR or lower conditions will be possible again at LEB and HIE.

Outlook:

Thursday-Friday: Periods of MVFR possible due to showers and thunderstorms.

Saturday-Sunday: VFR expected.

MARINE

Winds and seas will largely remain below SCA criteria through the week as a series of generally weak cold fronts cross the waters. Conditions may come close to SCA criteria briefly Friday night and into Saturday.

TIDES/COASTAL FLOODING

Astronomical tides continue to run high, peaking tonight at 11.2 feet at Portland. By this weekend tides will be peaking under 11 feet. Storm surge also continues to run between 0.5 and 1 foot, so water levels may approach flood stage at times with water getting into the most flood prone low spots.

GYX WATCHES/WARNINGS/ADVISORIES

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