textproduct: Gray - Portland

WHAT HAS CHANGED

Minor changes to reflect latest observational trends. The aviation section was updated for the 12Z TAF package.

KEY MESSAGES

1. Upper low continues chances for afternoon and evening showers today, mainly across the interior. Mostly dry weather follows Sunday into Tuesday.

2. Low pressure will bring a frontal passage across the region Wednesday night and into Thursday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Upper low over Nova Scotia will not move much today with a spoke of energy rotating north to south across the area this evening. This spoke of energy will increasing clouds this morning across much of the area as well as chances for showers this afternoon and evening. CAMs are in decent agreement that showers will mostly be confined to the mountains and interior NH while the coastal plain remains mostly dry. There may be enough instability for an isolated thunderstorm across southwest NH. Cloud cover and cooler NE flow will keep highs in the 70s. Shower chances will linger over NH into tonight with trend towards mostly clear skies towards Sunday morning.

High pressure over the Great Lakes will gradually build in Sunday, although with upper low still nearby an isolated shower cannot be ruled out. The incoming high pressure will favor more sunshine than today while highs will be in the 70s. High pressure will be in control Monday for fair weather and highs ranging from the mid 70s north to near 80 degrees across the south. A cold front will cross Monday night into Tuesday, while latest guidance suggest there will be limited moisture leading to mostly fair weather again on Tuesday.

KEY MESSAGE 2 DESCRIPTION...

Early next week, a surface low over Manitoba will deepen and lift northeastward across James Bay into Quebec Wednesday night through Thursday. The surface low will miss the region to the north, but the attendant cold front will approach from the northwest Wednesday. Models suggest deep moisture will advect poleward ahead of the front with ensemble means showing PWATs around 1.50 inches. Will have to monitor timing of the front as models spread timing between Wednesday evening and Thursday morning. Sharp height falls with the approaching front suggests there could be sufficient instability for thunderstorms depending on the timing of the front. Machine learning guidance out of CSU is picking up on the signal for storms both Wednesday and Thursday. Latest NBM brings chance PoPs to much of the area with likely PoPs Wednesday night.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Through 12Z Sunday...Primarily VFR through early this morning with morning FG/low ceilings lifting at LEB and HIE by 14Z. A brief period of MVFR ceilings are possible later this morning into early this afternoon but conditions should return to VFR by mid this afternoon. Scattered showers become possible during the afternoon into the evening that could bring TEMPO MVFR, mainly for the NH terminals. VFR conditions will prevail tonight for most sites, although additional valley FG may bring IFR-LIFR restrictions at LEB and HIE once again. N winds will prevail with daytime gusts up to 25 kts. No LLWS is anticipated through the period.

Outlook:

Sunday: VFR with decreasing clouds, breezy NW winds.

Sunday Night: VFR. Some valley fog possible late for LEB/HIE.

Monday and Tuesday: VFR with no sig wx. Wind shift possible with passing cold front.

Wednesday: Chance of SHRA advancing from the west through the day. This could bring MVFR cigs.

MARINE

Through tonight...Low pressure remains near Nova Scotia through tonight, keeping winds out of the north. Gusts may occasionally approach 25 kts today into tonight over the far outer waters with gusts to 20 kts along the inner coastal waters. Winds relax Sunday and turn northwesterly late Sunday into Sunday night. High pressure builds in late Sunday through Monday with variable winds turning onshore in the afternoon. A weak cold front crosses early Tuesday followed by high pressure with winds and seas below SCA thresholds into Wednesday.

GYX WATCHES/WARNINGS/ADVISORIES

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