textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes since the previous forecast cycle.

KEY MESSAGES

1. Unsettled weather is expected through Sunday night, but no widespread significant rainfall amounts are anticipated.

2. Isolated rain chances Monday and Tuesday under a lingering upper level low. Tranquil conditions by midweek, and loose signals for increasing humidity late week ahead of another system.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Mainly cloudy skies will persist through the remainder of today with an increasing chance for a few scattered showers, especially across western ME. Temperatures will remain nearly steady into the lower to middle 70s in most locations.

Latest forecast guidance and upstream observations continue to indicate that marine fog/stratus will push inland overnight, especially across western ME south of the foothills as well as the NH Seacoast. It will otherwise remain cloudy with a few scattered showers possible at times with overnight low temperatures into the 50s to near 60 degrees in most locations.

Closed low pressure will trek across southern Quebec on Sunday, sending a series of fronts across New England. Our region will be within a weak warm sector with partial clearing allowing high temperatures to warm into the middle to upper 70s with dew points into the upper 60s to near 70 degrees. A negatively tilted H5 trof axis will arrive during the afternoon into the early evening, acting as a catalyst for stronger flow aloft and upward vertical motion. Latest CAMs continue to indicate that MU/MLCAPE will increase into the 500-1000 J/KG range with 0-6km bulk shear of generally 35-40 kts. Cool temperatures aloft will support marginally conducive mid-lvl lapse rates, thus supporting the potential for a few strong to marginally severe thunderstorms. The primary threat will be strong to locally damaging winds but hail cannot be ruled out within an stronger updrafts. The greatest threat window looks to be between 2-8PM with eastern portions of the CWA the least at play given SE sfc flow.

Sunday night will feature a continued chance for a few widely scattered showers along with fog as overnight low temperatures fall to within a few degrees either side of 60 in most locations.

KEY MESSAGE 2 DESCRIPTION...

A closed upper low will continue to meander from southwest to northeast Quebec Monday through Tuesday night. This feature will lead to plenty of clouds to start the work week as we remain in persistent cyclonic flow aloft. While widespread significant rainfall is not expected, there should be some isolated to scattered showers (hit or miss) at times and a locally heavy downpour is possible. There may also be enough breaks in the clouds for at least some instability to develop Monday and Tuesday afternoons so a few thunderstorms are possible. Shear would be sufficient for a few stronger storms if updrafts can become strong enough. Gusty winds would be the primary threat.

The cutoff low then kicks out in the Wednesday/Thursday timeframe as upper level ridging approaches from the west, promoting dry weather and warming temperatures. The ridge then passes overhead quickly and the next system approaches late in the work week and possibly into the weekend.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Through tonight: Marine FG/stratus will move inland tonight, bringing IFR-LIFR restrictions to most TAF sites. Valley FG is also likely. Scattered SHRA are possible. Winds will be light out of the ENE.

Outlook:

Sunday: Fog scatters out as rain showers lift across the area. Some improvement to MVFR and VFR is possible by evening. TSRA is possible between 2-8PM, mainly across inland terminals and any storms will be capable of locally strong winds and possible GR.

Sunday night: Continued improvement in conditions, except local LIFR in valley fog.

Monday: Local MVFR or lower possible in showers.

Monday night: VFR conditions expected.

Tuesday: Local MVFR or lower possible in showers.

Tuesday night and Wednesday: VFR conditions expected.

Thursday: Mainly VFR but local MVFR or lower in showers late in the day.

MARINE

Winds and seas are expected to remain below SCA thresholds thru the period. Will have to watch the overnight period, when areas of fog and low stratus may develop ahead of an approaching warm front. Those foggy conditions are expected to lift out by late Sun.

GYX WATCHES/WARNINGS/ADVISORIES

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